Poster session 1

Present contribution will illustrate the importance of understanding the relationship: technology-structure–properties in explanation of specific feature of electrospun nanofiber membranes. Polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) membranes have been prepared using needleless electrospinning with wire electrode.

The effect of technological parameters like spinning conditions and properties of polymer solution on fiber morphology are well known. Present work showed the significant effect of crystal structure and charge distribution on polymer chains on forming nanofiber morphology during electrospinning. PAN and PVDF are good candidates to demonstrate this effect due to their non-centrosymmetric crystal structures.

Molecular modeling in combination with X-ray diffraction and high resolution scanning electron microscopy revealed the tendency to formation of strip-shaped electrospun PAN and PVDF fibers. These flat fibers, due to their flexibility are rolling up longitudinally forming hollow fibers with large surfaces, which are very desirable for subsequent chemical modification and practical use in filtration media.

Tunable affinity separation enables ultrafast solvent permeation through layered double hydroxide membranes

Membranes are playing increasingly important roles in purification and separation processes due to inherent advantages like facile, low-cost and green compared to the traditional thermal-driven processes. To enhance permeability to further augment the feasibility of membrane-filtration, emerging two-dimensional (2D) materials are promising as building blocks for making organic solvent nanofiltration (OSN) membranes. The key novelty of this study is the demonstration that, by simply altering the divalent cation type in the layered double hydroxide (LDH) crystal structure, the physicochemical activities of the membranes can be significantly enhanced to allow for the permeation of solvent at an ultrafast rate. Results show that the micrometer-thick LDH laminate supported on a nylon substrate not only provided superb solutes rejection, but also enabled nanofiltration permeances in aqueous and organic solvents (namely, acetone) as high as 298 and 651 l m^-2 h^-1 bar^-1, respectively. Both experiments and simulations suggest that the superior performance originates from the interfacial interactions between the solvent and LDH, as shown in the Figure below.

Introduction: Traditional protective garments loaded with activated carbons to remove toxic gases are very bulky. Novel graphene oxide (GO) flake-based composite lamellar membrane structure is being developed as a potential component of a garment for protection against chemical warfare agents (CWAs) represented here by simulants, dimethyl methyl phosphonate (DMMP) (a sarin-simulant) and 2-chloroethyl ethyl sulfide (CEES) (a simulant for sulfur mustard), yet allowing a high moisture transmission rate.

Methods: GO flakes of dimensions 300-800 nm, 0.7-1.2 nm thickness and dispersed in water were formed into a membrane by vacuum filtration on a selected porous polymeric support membrane undergoing noncovalent π-π interactions with GO flakes. The GO flakes underwent crosslinking later with a diamine introduced during the vacuum filtration followed by physical compression and heating followed by a further spray-coating of a selected polyurethane (PU).

Results: Membranes without crosslinking and PU coating blocked toluene for 3-4 days and DMMP for 5 days while exhibiting excellent water vapor permeation. Further, they display very low permeances for small molecule gases/vapors (XRD-based interlayer-gaps shown in Figs.1, 2). The cross-linked membranes with a PU-coating could be bent without losing barrier properties vis-à-vis the CWA simulant DMMP for 5 days; a membrane not subjected to bending blocked DMMP for 15 days (Fig.3). For the crosslinked and PU-coated compressed membranes after bending, the separation factors of H₂O over various other species for low gas flow rates in the dynamic moisture permeation cell (DMPC) were: α_H2O-_He, 42.3; α_H2O-_N2, 110; α_H2O-_ethane, 1800. At higher gas flow rates, moisture transmission rate went up considerably due to reduction in the boundary layer resistances and exceeds the threshold water vapor flux of 2000 g/m²-day for a breathable fabric. Such a membrane displayed considerable resistance to permeation by CEES as well.

Discussion: Significant progress was made toward a usable barrier for toxic vapors.

Fig.1. XRD scans of a 4 mg and a 2 mg GO-based membrane on a porous substrate without compression (Cheng et al., ACS Applied Materials & Interfaces, Accepted, 2020).

Fig. 2. XRD of an 8 mg GO membrane compressed and crosslinked on a porous substrate without any PU coating (Cheng et al., ACS Applied Materials & Interfaces, Accepted, 2020).

Fig.3. Upright Cup method plots of mass loss vs. time for 15 days for water vapor and

DMMP for crosslinked and PU-coated GO membranes (Cheng et al., ACS Applied

Materials & Interfaces, Accepted, 2020).

Two-dimensional (2D) laminar membranes with controllable mass transporting features are promising separation units in fields of the environment, resources and energy. The nanoscale channels formed between neighbouring layers, owing to adjustable size and surface chemistry, are always considered the major transport regulator. Besides these parallel channels, wrinkled structures have been observed in 2D membranes yet not received intensive attention. In this study, we elucidate the morphology of intrinsic nanowrinkles in graphene-based membranes and their role in mediating trans-membrane water and ion transport. With characterization and simulation results, these wrinkles are found naturally formed into an arc-like shape with 2-3 high centre and two narrow wedge corners. By altering preparation process with hexane or ethanol, resultant membranes show smoother or more crumpled structure correspondingly. Such change in wrinkle density leads to varied water permeation but stable salt passage in reduced graphene oxide (rGO) membranes, proving the crucial role of wrinkles in controlling transport. While they serve as fast channels for water, their connection with narrow interlayer channels may form a selective network to mediate ion transport. These new results are expected to deepen the understanding of mass transport mechanisms through graphene-based membranes, and to provide new perspective to develop future 2D membranes via wrinkle engineering.

Membrane-based technologies offer a versatile alternative to absorption and adsorption systems for CO₂ separation due to their simplicity, low-cost, low energy consumption & environmental impact. Recently, progress in nanotechnology has enabled development and use of tailored nanoparticles that enhance CO₂ separation properties when fabricated as inorganic membranes or used as fillers to fabricate mixed matrix membranes (MMMs). The morphology and chemical properties of nanofillers are tuned to facilitate enhanced CO₂ transport while reducing permeation of other gases like N₂, CH₄ and H₂.

In this work, novel Graphene Oxide-based 2D scaffolds with Metal-Organic Frameworks (MOF) nanoparticles grafted to the basal plane (termed as MOF@GO) have been developed for application in CO₂ separation. GO nanosheets are renowned for their gas barrier property due to their high aspect ratio creates high tortuosity to gas transport both in inorganic membranes and MMMs. Differently, the decorated MOFs increase surface sorption of CO₂ creating a unique pathway for its transport. Two MOFs (UiO-66-NH₂ and MIL-101) were successfully grafted on the surface of size-sieved GO-nanoflakes. The resulting MOF@GO nanofillers were predominantly crystalline (Figure 2) with exceptionally high surface area of ~505 m² g^-1 for UiO-66-NH₂ and ~2540 m² g^-1 for MIL-101.

The synthesized nanofillers with new architectures serve as viable starting material for inorganic membranes consisting of few-layered GO deposited on porous support. The CO₂-philic MOFs locked between interlayers act as binders, tuning interlayer spacing and provide enhanced CO₂ permeation by surface sorption and diffusion. On the other hand, when dispersed in polymeric matrices to form MMMs, the surface grafted MOFs help in reducing the barrier effect of GO to CO₂ permeation while the GO basal planes still offer tortuous resistance to permeation for other gases that do not interact with the MOFs like N₂, CH₄ and H₂. Membranes of both these configurations are currently being investigated.

Figure 1: S(T)EM image of UiO-66-NH₂@GO (left); MIL-101@GO (right)

Figure 2: XRD patterns of of UiO-66-NH₂@GO and MIL-101@GO

Although the existing membrane nanofiltration technologies offer practical solutions for the removal of heavy metal ions from wastewater, the realization of a membrane with excellent selectivity, a high permeability, and an antifouling capability remains of a great need. Due to the superior properties of carbon nanotubes (CNTs) for many applications, there has been a substantial interest over the last decade to develop various types of filtration membranes composed of CNTs, including buckypapers (BPs). In this regard, BP membranes for nanofiltration applications were fabricated using multi-walled carbon nanotubes (MWCNTs) via vacuum filtration process. To facilitate the formation of aqueous dispersions of MWCNTs, two biopolymers (i.e., chitosan and carrageenan) of 0.1% (w/v) were used. In this study, we investigate the effects of these two biopolymers on the membrane’s mechanical and surface properties. The measurements of the contact angles of the BP membranes show that the MWCNT/ carrageenan membrane exhibits more hydrophilic surfaces compare to the MWCNT/ chitosan membrane. The MWCNT/chitosan membrane was found to be mechanically robust with tensile strength and young’s modulus of 35.48±1.47 MPa and 0.486 GPa, respectively, whereas MWCNT/carrageenan showed modest mechanical properties. Water permeability and heavy metals removal were evaluated using a dead-end (ED) filtration system of the two types of membranes. The MWCNT/chitosan BP membrane showed more permeability compared to the MWCNT/carrageenan membrane, while the MWCNT/carrageenan membrane showed better heavy metals removal which can reach up to 99% for lead ions at a pressure of ~ 1 bar. Other characterization techniques including morphological properties and surface area using scanning electron microscopic (SEM) images and Brunauer, Emmett, and Teller (BET) were also investigated. 

Large-scale application of membrane in post-combustion carbon capture has been limited by the trade-off between CO₂ permeance and CO₂/N₂ selectivity of most polymeric membrane materials. In order to overcome this limitation, research efforts on facilitated transport membrane (FTM) have been devised with the objectives of (1) developing carriers with high CO₂ loading capacity and reactive diffusivity, and (2) validating the outstanding CO₂ selectivity at actual flue gas conditions. In this presentation, novel FTM was synthesized in a composite membrane configuration with a 170-nm selective layer coated on a polyethersulfone nanoporous substrate. In the selective layer, polyvinylamine with amine-sites covalently bound to the polymer backbone was used as the fixed-site carrier and an amino acid salt, synthesized by deprotonating sarcosine with 2-(1-piperazinyl)ethylamine, was blended as the mobile carrier. The membrane exhibited a CO₂ permeance of 1450 GPU (1 GPU = 10^–6 cm³(STP) cm^–2 s^–1 cmHg^–1) and a CO₂/N₂ selectivity >140 at 67°C.

Using a roll-to-roll continuous membrane coating machine, the FTM was successfully scaled up to a width of 14 inches and a total length of > 1200 feet. The scale-up membrane was used to fabricate spiral-wound (SW) modules in a multi-leaf configuration with a membrane area up to 3 m². Three prototype SW modules each with a membrane area of 1.4 m² were tested at the National Carbon Capture Center (NCCC) in Wilsonville, AL, USA. With the actual flue gas, the membrane modules showed ca. 1450 GPU CO₂ permeance and 185 CO₂/N₂ selectivity at 67°C with feed and permeate pressures of 4 and 0.3 atm, respectively. The module performance was essentially identical to that obtained from the flat-sheet membrane and from the module using the simulated flue gas. A 500-h stability was demonstrated despite the interference of low flue gas flow rates and flue gas outages at NCCC. During the field trial, carbon capture rates of better than 40% were achieved by a single SW module. Except for a few flue gas upsets, the CO₂ purities in the captured stream were 94.5% or better on dry basis. In addition, a short transient time of the membrane system was observed, which benefits the dynamic integration of the carbon capture technology into the power plant. Further analysis of the tested membrane revealed that no detectable amounts of Cr, As, Se, and Hg were deposited onto the membrane. The data obtained from this project validate the membrane material and provide basis for the design and fabrication of full-scale SW module with a membrane area larger than 50 m².

The current environmental situation motivates the development of feasible carbon dioxide separation techniques for diverse processes, such as biogas upgrading and flue gas treatment. Beneath this background, the development of mixed matrix membranes (MMMs) has raised as a versatile option due their potential advantages. Novel MMMs synthesis routes evaluated the employment of metal-organic frameworks (MOFs) supporting ionic liquids (IL@MOFs), showing improvements on membrane selectivity and mechanical properties 1.

However, the influence of the IL location incorporated in IL@MOF-MMMs on the gas transport properties is still unknown. This work focuses on the atomistic study of the ionic liquid influence in terms of location and loading in IL@MOF-MMMs aiming to achieve a better understanding of the interactions and mechanisms that determine selectivity and flux.

Ultrason S6010 (polysulfone-PSf) (BASF), Basolite®Z1200 (ZIF-8) (Sigma-Aldrich), and 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [EMIM][Tf2N] (Io-li-tec GmbH), were selected for the preparation of [EMIM][Tf2N]@ZIF-8-PSf MMMs. Direct impregnation and solvent evaporation methods were utilized for the preparation of the composite IL@ZIF-8 and flat MMMs, respectively.

The as-synthesized materials were characterized by scanning electron microscope coupled with energy-dispersive x-ray analysis (SEM-EDS), Fourier transform infrared spectroscopy (FT-IR), pure gas adsorption isotherms, and gas permeation studies. Monte Carlo molecular simulations using the software Materials Studio were carried out.

Preliminary simulation results successfully agreed with the solubility coefficients obtained experimentally (Figure 1). Figure 2 gathers three encapsulation scenarios of IL inside the MOF and their simulated solubility coefficients. The MOF partial coverage scenario (case 1) provided the highest solubility coefficient for CO2. Finally, the competitive adsorption study of CO2/N2 and CO2/CH4 shows an enhancement of the membrane selectivity in every scenario, agreeing with binary gas mixtures experimental observations.

The location of the IL proved to be a key factor in the MMMs preparation and CO2 separation performance. IL@MOF-MMMs present an appealing approach for CO2-selective processes.

Figure 1. Experimental and simulated CO2 permeation parameters for synthesized membranes.

Figure 2. a) Schemes of scenarios of MMMs considered, depending on IL location (1-coverage, 2-semi-encapsylated, 3-total encapsulation); b) Solubility coefficient for carbon dioxide, methane and nitrogen from molecular simulations for polysulfone, 10wt.%ZIF-8 in polysulfone and 10wt.%[EMIM][Tf₂N]@ZIF-8 in polysulfone, considering different IL locations.

1. Ban, Y. et al. Confinement of Ionic Liquids in Nanocages: Tailoring the Molecular Sieving Properties of ZIF-8 for Membrane-Based CO2 Capture. Angew. Chemie Int. Ed. 54, 15483–15487 (2015).

CO₂ emission of the power plants is one of the main contributor to the global warming. [1]. The most extended post combustion CO₂ capture technologies rely on absorption columns, which includes a variety of operational problems such as fouling, channelling, high capital costs, etc. Membrane technology has been introduced as an alternative to the conventional technology [2], [3]. However, amine-based systems have high energy requirements for solvent regeneration and large solvent losses due to amine vaporization[4],[5]. For this reason, the use of novel absorption solvents has been proposed in membrane contactors. For example, solvents with similar functionality as amines, such as amino acid salts (AAS) [7] [8] are positively characterized by their high surface tension and non-volatility, and their kinetics is defined by zwitterion reaction [8],[10]

In this work, five different amino acids have been studied for CO₂ capture. The feasibility of CO₂ capture is studied in the membrane contactor using the amino acid salts solutions as the solvent, activated with NaOH. The process performance using the amino acids was compared to that using only NaOH in solution.

Results and discussion:

The overall mass transfer coefficient (K_ov) and process performance using amino acids and amino acid salts were studied. All amino acids saturated shortly after the start of experiments except arginine. The results could be explained since acid dissociation constant (pKa) for some amino acids is low. However, similar performance of arginine to NaOH is related to their comparable high pKa values.

The amino acid absorption improves after the activation with a base. As all amino acids have a primary amine group, it is expected to observe a similar performance when they are activated. However, not all amino acids showed same absorption rate for CO₂ capture, which is related to the difference in their structure. In addition, the absorption rate is higher when an amino acid is activated with a base that has higher pKa. A stronger base has higher capability of activation of amino acids.

References

[1] A. S. Brierley and M. J. Kingsford, “Impacts of Climate Change on Marine Organisms and Ecosystems,” Current Biology. 2009.

[2] D. Bhattacharyya and D. C. Miller, “Post-combustion CO2 capture technologies — a review of processes for solvent-based and sorbent-based CO2 capture,” Curr. Opin. Chem. Eng., vol. 17, pp. 78–92, 2017.

[3] H. Karlsson and H. Svensson, “Rate of Absorption for CO2 Absorption Systems Using a Wetted Wall Column,” in Energy Procedia, 2017.

[4] V. Sang Sefidi and P. Luis, “Advanced Amino Acid-Based Technologies for CO2 Capture: A Review,” Industrial and Engineering Chemistry Research. 2019.

[5] P. Luis and B. Van Der Bruggen, “The role of membranes in post-combustion CO2 capture,” Greenhouse Gases: Science and Technology. 2013.

[6] F. Weisler, “Membrane Contactors : an Introduction To the Technology,” Ultrapure Water, no. June, pp. 27–31, 1996.

[7] J. Van Holst, J. P. M. Niederer, G. F. Versteeg, and F. Science, CO 2 capture from flue gas using amino acid salt solution, vol. 31, no. 5. 2012.

[8] S. Shen, X. Feng, R. Zhao, U. K. Ghosh, and A. Chen, “Kinetic study of carbon dioxide absorption with aqueous potassium carbonate promoted by arginine,” Chem. Eng. J., vol. 222, pp. 478–487, 2013.

The enormous amount of greenhouse gas emission by the combustion of fossil fuels since 19^th centuries causes the human-made global warming with the current atmospheric CO₂ concentration over 400 ppm. The substitution of fossil fuels (e.g. coal, petroleum, natural gas, etc.) for renewable energy sources will take the next few decades for the technical development, while one of the substantial alternatives is carbon capture, utilization and storage (CCUS) technology.

CCUS can not only reduce the emission of greenhouse gas into the atmosphere but also promote the production of the additional beneficial products such as microalgae or mineral carbonation. Whereas CO₂ storage essentially requires CO₂ capture technologies, CO₂ utilization might needs CO₂ separation or not. Membrane-based gas separation process is one of the most feasible CO₂ separation processes for CCUS among the state-of-the-art technologies including amine-based wet-scrubbing and sorbent-based capture. Membrane technology has the advantages of i) low energy consumption without a phase change during the separation, ii) small footprint and easy scale-up of membrane modules, and iii) clean process without any additional emission of harmful by-products.

Here, we demonstrate the strategies to apply our membrane process for an integrated CCUS pilot plant at a LNG-fired power plant in Pangyo just 5 km south from Seoul. The integrated plant includes a microalgae cultivation, CO₂ separation and mineral carbonation, where the membrane process plays an important role of enriching CO₂ up to 75 vol%. CO₂ separation at power plants located between cities is unlikely to apply separation techniques other than membranes. The membrane process has been designed and installed as three stages of membrane cascade to treat 400 Nm³/hr, and the separation performance with the long-term operation will be discussed.

Carbonic anhydrase (CA) has been extensively studied as CO₂ hydration kinetics enhancer in CO₂ absorption. The main driver is that the hydration reaction is the rate limiting step when applying aqueous benign solvents to capture CO₂. To protect the enzyme from the harsh conditions in the stripper, CA is usually immobilized. However, depending on the immobilization method, this procedure can lead to reduction of enzyme activity or increase of mass transfer limitations. Room temperature ionic liquids (ILs) have been proven as potential solvents in biochemical reactions, increasing in many cases the enzyme activity and stability with respect to organic solvents. Furthermore, polymerized ILs (PIL) present high CO₂ solubility. Therefore, there has been numerous studies focused on the application of PIL to gas permeation. However, research on enzyme immobilization in PIL based materials is limited. The present study focus on the elaboration, characterization and testing of CA immobilized in poly(ionic liquid) based materials for the development of membranes. Different materials are studied such as hydrophobic and hydrophilic PILs with different cross-linker amounts. They are characterized by delta pH method, pPNA hydrolysis, Bradford assay, FT-IR, SEM, DSC etc. Concerning enzyme activity, changes on T_optimum and pH_optimum are addressed. Additionally, leaching and stability are analysed. Changes in enzyme activity/stability are discussed in terms of interactions with the PIL.

The development of materials with improved transport properties, and chemical and thermal stability, is necessary to further enable membrane technologies for emerging industrial applications. In this work, a new polymer family is discussed for its application as high-performance gas separation membranes. The synthetic strategy adopted is based on ring-opening metathesis polymerization (ROMP).¹ The high-molecular-weight polymers prepared via this route are alternatives to traditional single-stranded polymers and offer great synthetic tunability. Here, ROMPs are synthesized into bottlebrush polymers that feature flexible backbones connecting pre-designed, rigid, ladder side chains that form tunable ultramicropores. Figure 1 illustrates the morphology of a ROMP structure obtained through molecular mechanics simulations.

Interestingly, these ROMPs are the first family of materials synthesized with a method different than step-growth polymerization that exhibit separation performance resembling that of state-of-the-art PIMs.² Additionally, ROMPs manifest additional stability, shown by their resistance to CO₂-induced plasticization, which was among the highest reported for uncrosslinked polymers to date.² Moreover, because functional groups on the side-chains (i.e., -OCH₃ instead of -CF₃, Figure 1) face each with this bottlebrush design, subtle changes to the substituents were demonstrated to have a remarkable impact on transport properties. Additionally, the length of the side chains connected through the norbornene backbone can be controlled, furthering the tunability of transport properties. The CO₂ permeability of CF₃-ROMP was measured to be >21,000 Barrer, making this polymer one of the most permeable in literature along with PIMs^3,4 and PTMSP⁵. Physical aging investigated through diffusion experiments and wide-angle X-ray spectroscopy showed promising results for CF₃-ROMP, especially for small gases such as He and H₂.

The structural diversity explored in this work enables the rational design of an entirely new class of microporous polymers with enhanced transport properties and remarkable stability, potentially addressing some of the fundamental limitations in current design strategies for polymer membranes.

Figure 1. Schematic representation of the morphology of CF₃-ROMP

[1]Y. Zhao, Y. He, T. M. Swager, ACS Macro Lett. 2018, 7, 300.

[2]Y. He, F. M. Benedetti, S. Lin, C. Liu, Y. Zhao, H. Ye, T. Van Voorhis, M. G. De Angelis, T. M. Swager, Z. P. Smith, Adv. Mater. 2019, 31, 1807871.

[3]I. Rose, C. G. Bezzu, M. Carta, B. Comesanã-Gándara, E. Lasseuguette, M. C. Ferrari, P. Bernardo, G. Clarizia, A. Fuoco, J. C. Jansen, K. E. Hart, T. P. Liyana-Arachchi, C. M. Colina, N. B. McKeown, Nat. Mater. 2017, 16, 932.

[4]B. Comesaña-Gándara, J. Chen, C. G. Bezzu, M. Carta, I. Rose, M.-C. Ferrari, E. Esposito, A. Fuoco, J. C. Jansen, N. B. McKeown, Energy Environ. Sci. 2019, 12, 2733.

[5]Y. Hu, M. Shiotsuki, F. Sanda, B. D. Freeman, T. Masuda, Macromolecules 2008, 41, 8525.

Membrane contactors are well known to intensify gas-liquid absorption processes and offer stable mass transfer, across the membrane, over long time scales for CO₂ capture application. However, most of the studies are focused on the use of amines solutions, i.e. monoethanolamine aqueous solution, which are quite expensive to regenerate. Thus, the used these amines solutions are not recommended for high CO₂ concentration in the gas as reported for cement industry.

This communication intends to investigate the use of membrane crystallization for CO₂ capture in the cement industry. The aim is to produce a carbonate salt that can be industrially reused. The study focuses on BaCO₃ which also is a model compound.

From the choice of the polymer material to the experiments on membrane modules, results obtained regarding the influences of the operating and geometrical conditions on the process performances will be presented and discussed in order to specifically address the following questions:

1. What are the key parameters governing the crystallization location?
2. How to select the membrane material and the module design?
3. What are the process performances and stability? What are the parameters to follow to control the crystallization?

Acknowledgments: This research was funded by the Agence Nationale de la Recherche, France (ANR), through the Project Grant ICARE.

Aiming at reducing greenhouse gas emissions and average global temperature, mainly by lowering CO2 releases and ultimately its concentration in the atmosphere, innovative post-combustion technologies for CO2 capture are indispensable on the vision of a clean energy production. Gas-liquid membrane contactors appear as a mature technology in which high specific surface area, independent gas and liquid flow rates, a compact and energy efficient separation units and easy scale-up design allows envisioning its implementation for the carbon dioxide capture and separation. Nonetheless, the feasibility of a gas-liquid membrane contactor on such low partial pressure systems relies on the correct selection of the solvent, envision to present advantageous thermophysical properties, like low vapor pressure and viscosity, while being capable of chemically react with CO2. Researches have proposed several approaches for enhancing the CO2 chemical absorption, ranging from the optimization of acetate-based ILs to the ILs functionalization. Recently, amino-acid-based ILs appear as a class of solvents with a huge potential for gas separation, but the number of experimental studies on gas solubility is still limited to a few families. This work proposes a separation process, based on a gas-liquid membrane contactor coupled with a non-volatile solvent based on amino-acids (aiming at enhancing the solvent chemical reactivity while optimizing its transport properties). Thermophysical properties such as viscosity and density, thermal stability, gas solubility measurements, and permeation studies were measured, aiming at identifying the most promising solvents for the intended application.

Introduction : CO₂ capture is a major challenge fitting with several priority objectives of the 2030 Agenda for Sustainable Development for preventing dramatic climatic changes. For CO₂ post-combustion capture, polyethylene oxide (PEO)-containing multi-block copolymers are good candidates because of their strong affinity for CO₂ but PEO crystallization and weak mechanical properties are two important limitations to be overcome for high PEO contents.

Methods : New poly(urea-imide) (PUI) multi-block copolymers were obtained in high yields from Jeffamine (mixed PPO/PEO/PPO) oligomers of molecular weights 600, 900 and 2000 g/mol. Varying the Jeffamine soft block content led to very different PUI physical properties, morphology and CO₂ permeation properties. Their investigation by DSC, DMTA, TEM, Synchrotron WAXS/SAXS and “time-lag” pure gas experiments followed a multi-scale approach from molecular scale to macroscopic membrane properties.

Figure 1. Synthesis of new PUI multi-block copolymers for CO₂ capture

Results : The crystallization of the Jeffamine soft blocks was avoided and a main limitation of PEO-based multi-block copolymers was overcome even for high PEO contents up to 70 wt%. The smallest soft block content led to a rigid copolymer with very poor phase separation and large interpenetrated domains, resulting in low CO₂ permeability (2 Barrer) and extremely high selectivity (207) for CO₂/N₂ separation (Figure 2). The highest soft block content corresponded to a very soft copolymer with soft blocks forming well-separated highly permeable nano-domains. Consequently, CO₂ permeability was enhanced 28 times up to 57 Barrer while ideal selectivity (50) was maintained in the high range for CO₂ capture.

Figure 2. Structure-morphology-membrane property relationships for CO₂ capture

Discussion : The best PUI ranked among the best PEO-based multi-block copolymers reported for CO₂/N₂ separation. Its high selectivity, film-forming ability, and excellent adhesion on a wide range of supports makes it a promising candidate for TFC membranes or mixed matrix membranes.

Heat stable salts (HSS) formed and continuously accumulated in the amine-based solvents due to solvent degradation/feed gas impurities can dramatically change the efficiency of the amine scrubbing process. HSS can be removed by using different methods including membrane separation such as electrodialysis (ED). We studied the effect of carbon dioxide loading of the lean 30 wt% monoethanolamine (MEA) solution on the efficiency of HSS ED removal and MEA loss. In the model MEA solvent containing 48 meq/L of HSS, the CO₂ loading was varied from 0.2 down to 0 moles (CO₂)/mole (MEA). The reclaiming of model MEA solvent was carried out using lab-scale two-stage ED unit where the brine stream after the first stage was additionally treated using second ED stage that allowed reducing MEA loss. It was shown that the decrease of CO₂ loading from 0.2 down to 0 moles (CO₂)/mole (MEA) resulted in a substantial reduction of the MEA loss and the specific power consumption with respect to HSS removed (from 140 down 37 kJ per 1 g of removed HSS anions). This was explained by the drop in the total concentration of ions formed by the interaction of the MEA solution with carbon dioxide. The change of CO₂ loading was associated with additional power consumption towards further solvent regeneration in the column. Based on the preliminary estimations of power consumption required for additional CO₂ stripping with the respect to the power consumption of the ED stage, the lean solvent CO₂ loading of 0.1 mole/mole was shown to provide an optimum for the power input at 25.9 MJ/kg (solvent) [1].

This work was carried out within the State Program of TIPS RAS.

[1]. E.Grushevenko et al. Membranes, 9 (2019) 152.

The photocatalytic reduction of CO₂ into added-value chemicals using sunlight is a promising approach to promote energy bearing products, mitigating the adverse effects of anthropogenic CO₂ emissions.

In this work, we investigated the photocatalytic reduction of CO₂ coupling, for the first time in literature, the assets offered by the continuous operating mode with the use of C₃N₄-TiO₂ photo-catalyst directly embedded in a dense Nafion matrix [1,2].

Overall, alcohols production, most of which is MeOH, was promoted by a low contact time and high H₂O/CO₂ feed molar ratio as a result of the fast removal of the reaction mixture from the reaction volume exposed to UV light. On the contrary, the slow removal as well as the water defect caused a partial oxidation of MeOH and EtOH, favouring HCHO production. At 5 bar, MeOH and HCHO resulted the unique products, with a lower amount of MeOH and a greater amount of HCHO with respect to the results obtained at 3 bar. This behaviour could be attributed to a hindered desorption induced by the higher reaction pressure, which leads to partial oxidation reactions and, thus, to the formation of HCHO to the detriment of MeOH.

The comparison with other photocatalytic membrane reactors showed that MeOH production increases with the TiO₂ content in the catalytic membrane, passing from 17.9 when only C₃N₄ was embedded into Nafion membrane to 45 for 100% of TiO₂. Membrane reactor with C₃N₄-TiO₂ photocatalyst, resulted more performant than the other systems in terms of carbon converted, even though less selective toward MeOH.

1. Pomilla F. R.; Brunetti A.; Marcì G.; García-López E. I.; Fontananova E.; Palmisano L.; Barbieri G.; ACS Sus. Chem. Eng., 2018, 6, 8743

2. Brunetti A.; Pomilla F.R.; Marcì, G.; García-López, E. I; Fontananova, E.; Palmisano, L.; Barbieri, G.; App. Cat. B: Env. 255 (2019) 117779

Global warming and climate change has become more and more the problem of the present, not of the future. Therefore, governments has increased greenhouse gas emission regulations all over the world. The regulations to control CO₂ emission affect not only the power generation industry, but also the traditional smokestack industries (e.g. petrochemicals, steel and cement industries, etc) where greenhouse gas emissions are high. Compared to the well-known CO₂ capture projects at power plants, the traditional smokestack industries, despite their high CO₂ emissions, are not commonly organized because of the complex processes and emissions of various compositions.

Membrane-based gas separation process has the advantage of a very compact and simple process which makes it the best option for a retrofit CO₂ capture against amine-based solvent-scrubbing and sorbent-based capture. Based on the preliminary lab-scale and bench-scale studies of polyimide membrane CO₂ capture, we have demonstrated a CO₂ capture membrane pilot inside a cement manufacturing factory. From the pipeline at a stack to the multistage membrane cascade, the whole membrane process including dust removal, cooling, gas compressing has been performed in six containers of 3×12 m² which are stacked in two floors. It was operated in response to two different feed gas composition when the raw material at raw mill was supplied or not. Over the several months, the performance of the membrane process has been traced in terms of CO₂ purity, CO₂ recovery, and the amount of CO₂ captured, etc.

Sol-gel derived organosiloxane membranes make up one of the important categories of membrane separation due to the superior thermal stability at elevated temperatures compared with conventional polymeric membranes. Amine-functionalized silica-based membranes, synthesized via co-condensation, impregnation, and post-grafting techniques, have been widely reported and show great potential for CO₂ separations. Thus far, however, very few amine-functionalized silica-based membranes have offered appealing CO₂ separation performance with both high CO₂ permeance and CO₂/gas permselectivity. Generally, for amine-containing membranes, the CO₂ permeation performance is decided by the combination of adsorption/sorption and diffusivity of CO₂ in the membrane matrix. Hence, the membrane affinity to CO₂ and the ultramicroporosity should be rationally designed to promote the fabrication of high-efficiency CO₂ separation membranes. In this study, we first developed a series of molecule-scale hybrid amine-silica membranes synthesized from organoalkoxysilane precursors with unhindered amines (simple primary and secondary amines) and sterically hindered amines (tertiary and pyrimidine amines) as illustrated in Fig.1a. A systematical comparison of membrane performance implied that amine-silica based membranes with mild affinity (sterically hindered amines) demonstrated greater potential for CO₂ separation due to the good balance between CO₂ adsorption/reaction and diffusion/desorption across the membrane thickness (Fig.1b). Consequently, the CO₂ separation performance was further optimized by tuning the ultramicroporosity of amine-silica membranes with sterically hindered amines via (i) thermally-induced liberation effect of small molecules (case of TA-Si) or (ii) incorporation of microporous silica-based networks. The modified membranes/materials presented a slightly improved ultramicroporosity with limited increases in gas adsorption (CO₂ and N₂). However, a surprising increase in CO₂ permeance (>2000 GPU in the case of modified BTPP membranes), with moderate CO₂/N₂ selectivity (~20), was observed in the resultant modified membranes. Therefore, the rationally designed amine-silica membranes with high-flux would hold great potential for use in industrial post-combustion CO₂ capture.

Fig. 1. (a) Chemical structure of amine-silica precursors used in this study; (b) Trade-off of CO₂ permeance and CO₂/N₂ selectivity for amine-silica membranes prepared in this study. The Robeson upper bound (2008) was also shown for comparison by assuming a membrane thickness of 500 nm.

Natural gas is composed mainly of methane gas (CH₄) and carbon dioxide (CO₂). The CO₂ reduce the calorific value of the mixture, limiting its application in industrial activities and combustion processes. The use of membranes for separation of gases is a technology that has aroused industrial and scientific interest due to its efficiency and lower energy consumption compared to other technologies currently employed. The major issues regarding the application of large-scale membranes equipment for CO₂/CH₄ separation are the membranes, since the currently CO₂ capture by gas-separation membranes is not as effective as other CO₂ recovery methods because of the low permeability and selectivity of commercially available membranes – most of it polymeric. The aim of this work is the development of dual layer hollow fiber ceramic composite membranes, using low-cost materials as a support material, by co-extrusion, for the separation of CO₂ and CH₄. The study materials for the support are: two different alumina and Kaolin. In the active layer the zeolite is use. The manufacture involves the production of suspensions of the ceramic powders in polymer solutions (Polyethersulfone (PES)/N-methyl-2-pyrrolidone (NMP)/Additive) to form hollow fibers by simultaneous double extrusion, phase inversion by immersion and calcination. Double layer membranes will be produced and their physical properties will be evaluated: viscosity of the ceramic solution, internal structure and surface (SEM), surface area and porosity, mechanical strength (three point flexural test), as well their performance with permeability test. The membranes are expected to be stable and durable in the long term, and thus they can be employed at industrial scale.

Biohydrogen production is an attractive alternative to hydrogen (H₂) production from fossil fuels, since it requires low energy consumption and it is a more environmentally friendly process.¹ Considering the potential of H₂ as a clean energy carrier, the implementation of high performance and cost-effective biohydrogen purification techniques is of vital importance to enable its application in fuel cell.

The CO₂/H₂ separation performance through the most promising poly(ionic liquid) (PIL)–ionic liquid (IL) composite membranes, bearing pyrrolidinium-based PILs with [NTf₂]^– and [C(CN)₃]^– anions and different weight percentages of the corresponding ILs, was evaluated in our previous work at biohydrogen production conditions (T=35°C and p_feed=1bar).² Single gas permeation experiments were conducted and the prepared membranes revealed CO₂/H₂ separation performances above the upper bound.²

In this communication, multicomponent gas permeation tests using a ternary mixture of H₂, CO₂ and N₂ and different feed pressures ranging from 1 to 4 bar and temperatures from 20 to 80°C will be presented. For all membranes, mixed CO₂, H₂ and N₂ permeabilities increase with increasing of temperature. Moreover, no significant changes in both mixed gas permeabilities and CO₂/H₂ selectivities were observed with increasing feed pressure from 1 to 4 bar, meaning that the prepared composites did not lose their separation efficiency up to p=4 bar. Overall, the studied PIL–IL membranes showed mixed CO₂/H₂ separation performances above the upper bound even at the highest temperature and feed pressure tested thus showing their potential for the envisaged application.

Acknowledgements

Andreia S. L. Gouveia is grateful to FCT (Fundação para a Ciência e a Tecnologia) for her Doctoral (SFRH/BD/116600/2016) research grant. Liliana C. Tomé has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 745734. This work was supported by FCT through R&D unit UID/QUI/00100/2013 (CQE).

References

1. Das, D.; Veziroǧlu, T. N., Int. J. Hydrogen Energy 26 (2001),13-28.

2. Gouveia A. S. L., Ventaja L., Tomé L.C., Marrucho I. M., Membranes 8(4) (2018), 124.

The refrigeration industry is undergoing critical changes for the reduction of the Global Warming Potential (GWP) of commercial refrigerant gas blends. In this sense, the Kigali Amendment to the Montreal’s Protocol (2016) and EU Directive 517/2014 stablished a road map towards a substantial decrease on the use and placing in the market of hydrofluorocarbons (HFCs). Nevertheless, some HFCs will continue to be used in the formulation of novel refrigerant blends that meet the new requirements of lowering the overall GWP. In this context, membrane technology is called to play a relevant role to boost the recovery of low GWP HFCs from end-of-life equipment for their reuse in a circular economy approach.

In this work, we assess for the first time the separation performance of composite polymer ionic liquid membranes (CPILMs) towards the selective recovery of difluoromethane (R32) from mixtures with other high GWP refrigerants, e.g., tetrafluoroethane (R134a) and pentafluoroethane (R125). Both single and mixed gas permeation experiments were performed. Permeability measurements were performed in continuous operation and the permeate gas was analysed by gas chromatography. The effect of operating conditions (feed pressure, temperature and composition) on gas permeability and selectivity was studied through several CPILMs prepared with poly-ether-b-amide polymer and different types and content of ILs. In addition, the mid-term stability of the CPILMs was evaluated.

Results showed that the CPILMs outperformed the functionality of neat polymer films, both in permeability and selectivity factor, which were doubled. Overall it has been demonstrated that membrane technology can recover the refrigerant R32 from waste refrigerant mixtures, in appropriate conditions to be reused in the formulation of new refrigerant blends. In addition, the CPILMs were stable over wide pressure and temperature ranges and operation time of several weeks.

Research supported by Project KET4F-Gas – SOE2/P1/P0823, co-financed by the ERDF within Interreg Sudoe programme.

Thin flexible films with good barrier properties are important for food preservation. Common packaging materials are laminated multilayers with Al_xO_y as the gas barrier layer, however, metalized packaging generally lacks transparency, flexibility and recyclability.¹ A fully polymer-based system polyethylenimine (PEI) and polyacrylic acid (PAA) was reported to have excellent oxygen barrier properties.² PAA is polar that limits the solubility of non-polar oxygen and the complexation of these two polyelectrolytes creates a dense structure. Here we present a new method to prepare PEI-PAA films by evaporation induced complexation. Ammonia was added into PAA solution to adjust the pH which prevented direct complexation with PEI. In the previous studies, coacervates were prepared for the film formation which left the exact film compositions unknown. With our method, different molar ratios of PEI: PAA high concentration solutions were successfully prepared. Thin films were deposited on biaxially orientated polypropylene (BOPP) sheets using a wire bar. During drying, the evaporation of ammonia triggered the complexation and the ratios remained the same. SEM images indicate dense films were formed. From initial observations, films prepared with equal/ excess PAA all showed a brittle nature, which led to cracks. 20 µm thick films prepared with ratio PEI: PAA 3:1 were tested, they successfully reduced the oxygen permeation to 0.02 barrer, while BOPP oxygen permeation was around 0.6 barrer. To further understand the relationship between the microstructure and gas barrier properties, characterizations such as IR and DSC will be conducted in the future.

[1] R. J. Smith, C. T. Long and J. C. Grunlan, Transparent Polyelectrolyte Complex Thin Films with Ultralow Oxygen Transmission Rate. Langmuir 34, 11086-11091 (2018).

[2] M. Haile, O. Sarwar, R. Henderson, R. Smith and J. C. Grunlan, Polyelectrolyte Coacervates Deposited as High Gas Barrier Thin Films. Macromolecular Rapid Communications 38, 1600594 (2017).

In this work, we present the successful development of asymmetric hollow fiber membranes using a temperature resistant polymer (polybenzimidazole - PBI) for pre combustion applications. The influence of polymer properties (different suppliers), solvents (DMAc and NMP) and additives (LiCl, PVP K30) on the morphology and gas permeation properties of the developed membranes have been studied. Comparing with intrinsic polymer permeation properties (20 Barrer for H₂ and a H₂/CO₂ ideal selectivity of 20), after several spinning trials, for each studied system, the optimal performance was achieved (see Table 1, bottom line).

In DMAc, at similar concentration, polymer dope solutions containing PBI from Fumatech have much higher viscosity than from PBI Performance products. Therefore, the necessary PBI concentration for manufacturing best performance fibers was lower when using PBI from Fumatech than from Performance Products (Table 1 column 2 and 3).

In NMP, there is a stronger interaction between PBI polymer chain than with DMAc given that

the necessary LiCl concentration, in order to prevent gelation, was higher than when using DMAc.

The addition of PVP K30 allowed spinning at take up rates up to 50 m/min.

Table 1: Optimum main spinning parameters, fiber dimensions and permeation properties for pure PBI hollow fiber membrane fabrication.

¹at 25 °C and 10 s⁻¹ shear rate, ² at 150 ºC, 7 bar, H₂/CO₂mixed gas (50/50 vol%)

The research leading to these results has received funding from the European Union under grant agreement n° 608490 project M⁴CO₂ under grant agreement n° 760944 project MEMBER.

One of the biggest challenges for the next decades is to stop the process of global warming. A possible approach to decrease the CO₂-emission could be the combination of plasma technology with a separation process for CO₂ splitting.

Here, we present the use of MIEC hollow fiber membranes to separate oxygen from a CO₂ plasma. In the plasma the CO₂ is converted into CO which can be used as a platform chemical for different syntheses (e.g. Fischer-Tropsch).

In this project, various perovskite hollow fibers (LCCF, BCFZ) were manufactured using a phase inversion process. Subsequently, the hollow fibers were sintered to receive gastight membranes. The oxygen permeation within the fiber is given by the presence of defects in the crystal structure of the MIEC membranes.

The permeation of the LCCF hollow fibers were tested in a normal furnace and in a microwave induced atmospheric plasma torch under a CO₂ atmosphere. Therefore, we are especially interested in the behaviour of the capillaries under CO₂ containing atmospheres. In the furnace, the oxygen permeation is constant over time in a gas composition with 50% CO₂ (see figure 1).

Figure 1: Longterm O₂ permeation test of a LCCF hollow fiber

In the plasma the capillaries are repeatedly heated to temperature above 1000°C within seconds without any damage and no degradation could be observed in the CO₂ plasma after long time treatment (see figure 2).

Figure 2: O₂ permeation in a CO₂ plasma over time

Measurements with the stable LCCF hollow fibers in the plasma underline the splitting of CO₂ into CO and O₂. Accordingly, a plasma coupled membrane reactor is a reasonable option to separate oxygen and prevent the back reaction of CO₂ to generate CO.

Hyper-cross-linked ultrathin hybrid inorganic-organic polyimide membranes show exceptional results for H₂/CO₂ selectivities at temperatures up to 300°C [1]. These membranes have been prepared by interfacial polymerization of amine functionalized polyhedral silsesquioxane (POSS) and a dianhydride (for instance, 6-FDA) on top of the γ-alumina support, followed by a thermally induced imidization.

In this work, we use two different types of amine functionalized POSS building blocks to demonstrate that the molecular structure and the gas separation performance of the final membranes are affected by the nature and concentration of the counterions of their functional groups, i.e., protons or cations such as Na⁺, K⁺, Li⁺. We discuss how the nature of these ions effect: 1) the film formation during interfacial polymerization, via the characteristics of the interface between the organic and aqueous solvent, 2) the transformation of the amic acid to imide groups during thermal treatment, which requires the presence of protons, and 3) the effect of charges persisting in the molecular network during final application, which results in enhanced hygroscopic character.

The results indicate that the presence of non-proton cations, in particular, sodium, can help to enhance the permeance of the hybrid network membranes. On the other hand, the attendance of protons provides higher selectivity of H₂/CO₂ at the temperature of 200˚C. This is mainly because of the formation of carboxylate salts during interfacial polymerization with polyamic acids. This phenomenon leads to reduce the hydrogen bonding between polyamic acids, the yield of imidization, and eventually alter the performance of the membranes. These insights allow for further optimization of the next generation of hybrid POSS based polyimide membranes.

Acknowledgments

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 760899. This publication reflects only the author’s views and the European Union is not liable for any use that may be made of the information contained therein.

References

[1] Raaijmakers, M. J. T., Wessling, M., Nijmeijer, A. Benes, N. E., Chem. Mater., 26, (2014) 3660.

The process of separating components of natural gas is one of the most significant issues in the gas and oil industry, particularly to improve separation efficiency. Graphene-based membranes have inherent applications in the separation processes. In the present research, graphene-based nanostructures are used to separate components of the CH4/CO2 mixture. Molecular Dynamics Simulation approach is a powerful methodology able to provide characteristics of systems from the atomistic level. In this study, Molecular Dynamics is employed to examine the atomic structure and calculations. The atomistic configuration includes a mixture of CH4 and CO2 passing through a two-layer graphene-based membrane with defined compositions under applied pressure with a specified direction. Numerous interlayer spacing of graphene layers and gap size are considered to ascertain the effective interlayer distance as well as gap size which gives the biggest CH4/CO2 separation. The simulation results reveal the flux and permeability of the molecules along with the number of molecules separated. Furthermore, the number of layers could affect the separation process. Hence, the number of graphene layers are examined for investigating higher separation efficiency. The outcomes of this study could be beneficial because of the importance of carbon dioxide sequestration and shale gas production.

Typically, industrial H₂ is produced through an SMR-WGS process. The effluent, mainly of H₂ and CO₂, needs to be separated in order to produce a H₂ stream with purity determined by the intended application. To this end, membrane technology provides an alternative to the conventional energy and capital cost intensive PSA process. Currently, nanoporous ceramic membranes are being explored for the separation of H₂ at elevated temperatures and chemically aggressive environments instead of Pd-based membranes. Especially at temperatures of 100-400^oC such membranes could be superior to Pd ones in terms of stability and permeability, comparable in terms of selectivity and are more cost-effective. Despite the many studies on synthesis and characterization of nanoporous gas separation ceramic membranes, most of them relate to single gas permeation measurements and ideal selectivities. There is lack of reports with real gas separation data, assessing the effect of process parameters and the whole separation process potential.

In this study we present results of nanoporous ceramic membranes synthesis through modification of commercial membranes via a novel CVI method at 250 ^oC and characterization through real gas separation tests. Moreover, a 2-D isothermal model is developed in order to determine the concentration variation of components in both compartments by coupling the retentate and permeate zones' flow behavior with appropriate boundary conditions, while accounting for an adjusted permeance for each component through all membrane layers. The developed model is compared with real gas separation experimental results and used to assess the gas separation potential at representative conditions.

Figs 1 and 2 summarize experimental gas separation test results for a synthesized membrane with beyond the state-of-the-art performance and high separation potential (H₂ permeance: 1.57^.10^-7 mol^.m^-2.s^-1.Pa^-1 and H₂/CO₂ permselectivity: 61.4, at 250 ^oC). The results clearly demonstrate the high potential of the synthesized membranes in high purity H₂ production processes.

Fig.1: Process stage cut and selectivity with the applied pressure difference

Fig. 2: H₂ recovery and purity with the total feed gas flow rate

During the production and processing of the natural and associated gas, as well as in the processes of oil refining, petro-, gas, and coal fuel chemistry emerges a task of separation of hydrocarbon gas mixtures with a broad composition. Recently a simplified one-stage synthesis of polyalkylmethylsiloxanes (PAMS) with the increased hydrocarbon ideal separation selectivity was proposed [1]. In this work we studied the properties of dense and composite membranes based on polyalkylmethylsiloxanes, namely polyhexylmethylsiloxane (PHexMS), polyoctylmethylsiloxane (POMS), and polydecylmethylsiloxane (PDecMS) during the separation of eight component hydrocarbon mixture which models the composition of the associated petroleum gas (CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, i-C₄H₁₀, n-C₄H₁₀, CO₂). PDecMS membrane showed the highest selectivity for all of the gas mixture components with respect to methane: 3.0, 2.8, 7.0, 6.1, 7.6 and 18.2 for C₂H₄, C₂H₆, C₃H₆, i-C₄H₁₀ and n-C₄H₁₀, respectively. Composite membranes were formed employing two supports of ultra- and microfiltration type (UFFK and MFFK-1, respectively). Membranes with MFFK-1 support demonstrated higher С₂₊/СН₄ separation selectivity. The separation of the same multicomponent hydrocarbon mixture was studied through MDK-3 (ZAO STC “Vladipor”, Russia) and POMS (HZG, Germany) commercial composite membranes. It was revealed that PDecMS/MFFK showed a 40% higher selectivity for n-butane/methane gas pair (16.7) in comparison with MDK-3 (10.1) and a 20% higher selectivity in comparison with POMS–HZG (13.9).

This work was carried out in the A.V. Topchiev Institute of Petrochemical Synthesis (Russian Academy of Sciences) and was funded by the Russian Science Foundation, grant number 19-19-00647.

[1] Grushevenko E.A., et al. Reactive and functional polymers 134 (2019): 156-165.

PIM-1 shows great potential for use as a membrane material to separate CO₂ from other gases such as CH4.[1] The CO2/CH4 separation is important for industrial applications including the production of biogas and the purification of natural gas. Besides the promising results shown by PIM-1, it undergoes physical aging causing a reduction in permeability over time. This phenomenon leads to a loss in free volume due to the relaxation of the polymer chains towards an equilibrium state. Therefore, the long-term instability of PIM-1 represents an obstacle for its commercial use.

In this work, the physical aging of PIM-1 membranes and mixed matrix membranes (MMMs) of PIM-1 containing graphene-based materials were studied. Graphene oxide (GO) was synthetised through a modified Hummer’s method, functionalized with two different alkylamines (octylamine (OA) and octadecylamine (ODA)) and further reduced. These membranes were tested for CO₂/CH₄ (50:50 vol.%) over 155 days. At the end of this testing period, aged purely polymeric PIM-1 membranes showed a CO₂ permeability of (2.0 ± 0.7) × 10³ Barrer, which corresponds to a CO₂ permeability reduction of 68% from the value obtained right after their fabrication. The incorporation of alkyl-functionalised GO was shown to be an efficient strategy to hinder the physical aging of those membranes; filler loadings as low as 0.05 wt.% of reduced octyl-functionalized GO showed a CO₂ permeability of (3.5 ± 0.6) × 10³ Barrer after 5 months, which is almost three quarters higher than that of pure PIM-1 membrane aged for the same time period and represents a reduction of just 39% from its initial value. In terms of selectivity, membranes became more selective as they aged. Moreover, the addition of graphene-based materials to PIM-1 did not affect its mechanical properties.[2]

Reference:

[1] J. Membr. Sci., 251, 1-2, 263-269 (2005)

[2] J. Membr. Sci., 563, 513-520 (2018)

Permeability of gases through thin composite membrane tend to deviate from its intrinsic value as the thickness of the dense surface layer is reduced. For a highly porous (non-resistant) substrate and in the absence of surface defects, these differences can be caused by the porous – dense layer interactions. While the influence of coating solution’s pore intrusion is well known, recent advancement in computational modelling also suggested that lateral diffusion can significantly influence the gas permeability across a thin, supported dense layer, depending on the nature of the substrate’s surface pore architectures. Hence, in this work, composite membranes of different dense polydimethylsiloxane (PDMS) thicknesses were fabricated on pristine and 4 wt.% LiCl modified polyethersulfone (PES) substrates, which having different but measured surface pore structures. PDMS solution mixed in heptane was poured in a fixed weight in a custom-made mould and let to dry up. Both the PDMS solution’s pore intrusions and lateral diffusions were calculated and experimentally verified. Preliminary results suggested that while the selectivity barely changes with PDMS thickness, the composite membranes had a significant reduction in permeance for pristine substrate’s as compared to LiCl modified substrate’s composite membrane. These differences were then compared to the resistance-in-series model and then modified to include the lateral diffusion factors. The modified model was then compared to several other resistance-in-series model alterations.

Polymers of intrinsic microporosity (PIMs) show great potential for cost-effective and scalable membranes for CO₂ separation because of their inherent high gas permeability. We report the synthesis and improvement of PIM-Pyridine, the least-investigated PIM sub-class, incorporated with zeolitic imidazolate framework (ZIF-8) and hybrid in-situ grown ZIF-8 on graphene oxides (GOs) nanosheets, as mixed matrix membranes. The high porosity PIM-PY (BET surface area 712 m²/g) performs similarly to PIM-1, with CO₂ permeability of ~5,000 Barrer and comparable CO₂/N₂ (α = 15.3) and CO₂/CH₄ (α = 9.1) selectivities. The integration with the as-synthesized ZIF-8 nanoparticles (~50 nm) and ZIF-8/GO nanosheets was systematically studied. The in-situ grown ZIF-8/GO was characterized by XRD, sorption analysis and SEM, showing good integration with the GO nanosheets. Gas separation performance was evaluated using both single gas (CO₂, N₂, CH₄) and 50%:50% CO₂:CH₄ binary mixture at a feed pressure difference of 2 bar, at 25°C. CO₂/N₂ and CO₂/CH₄ selectivity improvements of 63% (α = 25.1) and 40% (α = 12.7), respectively, were achieved with optimum loading of ZIF-8/GO nanosheets, surpassing the 2008 Robeson upper bound for CO₂/N₂.

Graphical abstract: CO₂/N₂ separation performance of PIM-PY MMMs with ZIF-8 and hybrid ZIF-8/GO.

The presence of CO₂ in biogas affects its performance as fuel, which also increases pumping costs and corrodes the pipelines that carry biogas to the end-use applications. Gas separation using membranes, particularly hollow fiber membranes, has several attractive advantages, such as low cost of operation, low foot-print, and ease of scale-up and operation. The main objective of this study is to evaluate the effect of in-situ grown zeolitic imidazolate framework-67 (ZIF-67) nanoparticles on polysulfone-graphene oxide hollow fiber mixed matrix membranes (Psf-GO HFMs) toward efficient CO₂ separation. In this study, the pristine Psf-GO HFMs were prepared in an in-house fiber spinning facility by a non-solvent induced phase transition method. Next, ZIF-67 nanoparticles were in-situ grown on the prepared Psf-GO HFMs (termed as the modified or ZIF-67/Psf-GO HFMs) under optimized conditions. The different HFM samples were characterized using different microscopy and spectroscopy techniques, which confirmed the in-situ growth of ZIF-67 nanoparticles on the lumen-side of the pristine HFMs, which would act as a separating layer in the gas separations. Single and mixed gas permeation studies were carried out using CO₂ and CH₄, at 24 ± 2 °C and at 1 bar transmembrane pressure. Interestingly, a ~3 times increase in the ideal gas (CO₂/CH₄) selectivity was measured with the modified HFMs (19.8) as compared to that with the pristine HFMs (6.4). Moreover, in the mixed gas studies, the CO₂/CH₄ selectivity increased by ~2.5 times with the modified HFMs (41.8) as compared to that with the pristine HFMs (16.2). The CO₂ permeance was 81.5 GPU and 36.5 GPU in single and mixed gas studies, respectively, for ZIF-67/Psf-GO HFMs. Therefore, it is evident from these results that the novel membranes prepared by in-situ growing ZIF-67 nanoparticles on Psf-GO HFMs are suitable for the efficient CO₂/CH₄ separation.

Metal-organic frameworks (MOFs) incorporated composite membranes is proven to be a promising candidate for gas separations. However, the partial inorganic structure of MOF limits the compatibility with the polymer matrix, which tends to agglomerate on the membrane surface. Finely tailoring the interfacial interaction between the MOF and polymer matrix is crucial to reduce the defective structure on the membrane surface. Herein, an interfacial strategy is exhibited by coating MOF cores with ionic liquids (ILs) to prepare MOF@IL hybrids as nano-fillers to improve polymer and filler compatibility. ILs will act as an interfacial binder with the polymer matrix, thereby preventing the formation of non-selective voids and nanofillers agglomeration. In the present study, MIL-53 (Al) and IL coated MIL-53(Al) hybrid is obtained by hydrothermal process and characterized by X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Hybrid nanoparticles used as a filler to prepare polysulfone (PSF) composite membranes for the separation of CO₂/CH₄ and CO₂/N₂ gas mixtures at different pressures ranging from 1-10 bar. Robeson plots were applied to assess the performance of the prepared membranes for single and mixed gas separations. The composite membranes show better permeability and selectivity with improved flexibility and mechanical resistance. The ILs coating on the cores of the MOF structure could be an effective strategy to eliminate the defects in the membrane surface, which opens up the selection to a wide range of large-sized fillers in the membrane fabrication.

Perfluorosulfonic acid (PFSA) membranes are known to have high water vapor performance [1,2] and used in membrane dehumidifiers. The water vapor permeance of PFSA membranes reportedly depends on temperature and humidity, and basic studies are important for optimal design of modules. In this study, the water vapor permeance of the PFSA capillary membranes commercially available (sunsep^TM) was measured in a wide range of temperature of 10 - 40°C and feed relative humidity of 0 - 90%, and the water vapor solubility coefficient and the water vapor diffusion coefficient were obtained from the water content measured by the gravimetric method to clarify the temperature-humidity dependency of their water vapor permeance. 

Fig. 1 shows the water vapor flux and water vapor permeance of the PFSA membranes as a function of the relative humidity in feed. The water vapor permeance reached 10^-5 mol/(m² s Pa), which was higher than those in previous studies [1, 2] because the difference between feed-in and sweep-in was set to RH 20% or less to minimize the relative humidity difference across the membranes, for suppressing asymmetric profile of water vapor permeability due to the relative humidity distribution. As the relative humidity increased, the water vapor flux and the water vapor permeance increased. However, the water vapor flux showed a higher value as the temperature increased, whereas the water vapor permeance showed a lower value as the temperature increased. The solubility coefficient shown in Fig.2 (a) increased with decreasing temperature, and showed the lowest around RH 60%, and increased with lower and higher humidity, indicating the effect of temperature was greater than that of humidity. The water vapor diffusion coefficient shown in Fig. 2 (b) increased as the temperature and humidity increased, and the effect of humidity was greater than that of temperature. It was shown that the temperature and humidity dependence of the water vapor permeance is determined by the solubility coefficient and the diffusion coefficient, respectively.

References

[1] P. Majsztrik et al., J. Phys. Chem. B. 112 (2008) 16280–16289

[2] H. Azher et al., J. Memb. Sci. 459 (2014) 104–113

Membrane-based gas separation is considered as energy efficient process however, many challenges remain in the fabrication of high separation performance membranes able to replace conventional separation approaches.

In this work we report the investigation of gas transport in new fluorinated metal organic framework (NbOFFIVE-1-Ni) based mixed matrix membranes (MMM). The performance of MMM in respect to CO₂, N₂, O₂ and H₂ gases transport as well as mixed CO₂/N₂ formulations was studied.

We demonstrate that ultramicroporous fillers in CO₂-phillic polymer (Pebax-1657) are making big impact on gas transport only when the particle sizes are decreased significantly by post-synthesis ball milling to reach sub-micron size range. Considerable increase of the CO₂/N₂ selectivity (from ~60 in polymer to >100 in MMM) is observed with the increase of filler loading. The results demonstrate the ultra CO₂-selective nature of the NbOFFIVE-1-Ni MOF. This improvement is very important for the efficient membrane-based CO₂ capture processes, especially post-combustion CO₂ capture.

Further efforts of particle size reduction and mixed matrix membrane thinning are essential for effective utilization of the excellent molecular sieving properties of NbOFFIVE-1-Ni. This work’s key question is whether the high sorption selectivity of fluorinated MOFs towards CO₂ will result in high transport selectivity of CO₂ through the membrane containing particles as fillers or MOF-based crystalline layer.

High free volume glassy polymers are attractive membrane materials for gas separation due to their high mass-transfer parameters together with good mechanical and film-forming properties. The major drawback of these polymers is rather low gas selectivity, since the interconnected free volume elements with a size of about 0.4-1.2 nm play a major role in the gas transport through the membrane. In this study, thin film composite (TFC) membranes have been developed with high CO₂ permeance and superior CO₂/N₂ selectivity due to a strong synergistic effect. The TFC membranes, comprising a thin layer (0.29-0.42 µm) of PIM-1 atop a cross-linked PTMSP gutter layer (2.07-3.44 µm) on a porous backing material, were fabricated by coating PIM-1 solution on the cross-linked PTMSP support. A key element is that for coating PIM-1 a mixed solvent of chloroform and trichloroethylene (1:1) was successfully implemented for the first time. All membranes demonstrated a strong synergistic enhancement of CO₂/N₂ selectivity (=35.8-55.7) compared to PIM-1 (=18.5) and cross-linked PTMSP (=3.7). A SEM, TEM and laser interferometry study revealed that the synergistic enhancement of gas selectivity in the TFC membranes is most likely due to the creation of a very thin boundary layer between PIM-1 and the cross-linked PTMSP gutter layer. The aged TFC membranes (after three months) showed a severe drop in gas permeance while keeping nearly the same high selectivity. However, the physical aging of high free volume glassy polymers can be mitigated by introduction of porous nanoparticles. This talk will be focused on a new strategy for preparation of high performance TFC membranes with enhanced CO₂/N₂ selectivity, and the long-term performance of TFC membranes with the selective layer loaded with PAF nanoparticles.

This research was supported by the Russian Science Foundation (project No. 18-19-00738). The authors acknowledge I.Borisov, D.Bakhtin, L.Kulikov, V.Polevaya, J.Luque, E.Prestat and P.Gorgojo.

Gas separation membranes are constrained by the tradeoff between selectivity and permeability. Considering the effect of pressure ratio and multistage cascade process design, along with effect of pressure drop generated by gas passing through membrane cartridges, we point out that high membrane selectivity is critically needed for industry applications while the influence of membrane productivity is limited.

The process economics for gas separation membranes depends on several important factors: feed gas impurity concentration, product gas impurity requirement and product gas recovery rate, energy consumption, and pressure ratio (θ). For many practical applications, such as CO2 capture from flue gas, multistage cascade membrane process design, two or three stage, is required. The cascade process design can be significantly simplified using two types of membranes with different selectivity and productivity based on feed gas concentration and available pressure ratio. A relatively low selectivity and high productivity membrane is more advantageously utilized for the pressure ratio limiting stage. The membrane process economics can be improved significantly with high membrane selectivity for the membrane selectivity limiting stage. In many cases, a three stage process can be reduced into a two stage process and gas recycle ratio can be dramatically decreased, if a membrane with sufficient high selectivity is available for the membrane selectivity limiting stages.

Advanced membranes are fabricated into the hollow fiber configuration and packed into pressure shells. Shell side pressure drop can be modeled using Ergun pressure drop equation and bore side pressure drop can be modeled by Hagen-Poiseuille equation. The level of pressure drop depends on pressure differential and membrane productivity. Excessive membrane productivity will generate excessive pressure drop and negatively impacts the membrane process.

In conclusion, emphasis should be placed on membrane selectivity for the future membrane material development rather than membrane productivity.

Commercially available membranes for CO₂ separation have typically a limit on their performance known as the Robeson Upper Bound implying that there is a trade-off between selectivity and permeability. Hybrid membranes (polymers containing inorganic materials) may give improvements compared to their purely polymeric counterparts. Current hybrid membranes are based only on the physical mixing of polymer and particles, and there has been little work to achieve an active distribution and alignment of the particles in the membrane. Modelling has shown that optimal alignment of the nanoparticles in the plane or across the plane makes it possible to fully utilize their effect and thereby achieve maximum membrane performance.

The objective of the current work is to develop and optimize polymeric nanocomposite membranes for gas separation. We employ a patented alignment technology that uses electric fields to carefully control the orientation of the nanoparticles, allowing the full exploitation of their selective features. The technology enables alignment of the particles either through the plane or in the plane of the membrane film.

Many combinations of particles, polymers and solvents have been evaluated to optimize the particle dispersion and membrane performance. Permeability measurements have been performed on both free-standing and asymmetric membrane samples. Permeation properties are shown to be affected both by the electric field alignment of particles and the concentration of particles. For graphite-containing samples, through plane alignment (TPA) increased the permeability, whereas in plane alignment (IPA) decreased it. This is because in the IPA-sample the electric field aligns and orients the two-dimensional graphite particles parallel to the membrane plane, creating a barrier for the CO₂ molecules. In the TPA alignment the particles are oriented in a way that blocks the gas to the lowest degree.

Acknowledgements

This work is funded by the Norwegian RD&D CCS programme (CLIMIT) under grant agreement nº 281846.

It is well-known that natural gas is the principal feedstock of the chemical industry, whereas the raw natural gas contains a wide range of CO₂. Therefore, capturing and separating CO₂ become a research hot spot in 21st century. The SSZ-13 zeolite membrane has the appropriate pore size (0.38 × 0.38 nm) and and is a prospective membrane for CO₂ separation. In our previous studies, the high silica SSZ-13 zeolite membrane were successfully prepared on the mullite support, and the acid post-treatment had a great effect on the single gas permeance of the membranes.

In order to improve the gas separation performance of the high silica SSZ-13 zeolite membrane, effects of the support and acid post-treatment on the gas separation performance of the membrane are investigated in this work. The membranes are prepared on the home made α-Al₂O₃ support and mullite support by secondary hydrothermal synthesis, and the preparation method and acid post-treatment of the membranes are identical with our previous work. The molar composition of the precursor synthesis gel was SiO₂ : 100 Na₂O : 2.5Al₂O₃ : 100 TMAdaOH : 80000 H₂O, and the acid treatment conditions of the zeolite membranes are 25 ℃, 0.2 M H₂SO₄ and 0.5 h.

Table 1 summarizes the single gas permeance and ideal selectivity of the fresh and acid-treated membranes with different support. In comparison to mullite support, the α-Al₂O₃ supports was favor for preparing the SSZ-13 zeolite membranes with a high CO₂ permeance and CO₂/CH₄ ideal selectivity. Although the CO₂ permeance of the acid-treated membranes was few lower than the fresh membranes, and the selectivity of the membrane were greatly improved by the acid post-treatment.

Table 1. Single gas permeance and ideal selectivity of the fresh and acid treated SSZ-13 zeolite membranes with different support. (0.2 MPa, 25 °C)

Note: S_CO2/CH4 is the CO₂/CH₄ ideal selectivity.

Recently, hyper-crosslinked nanoscale hybrid materials derived from alternating polyhedral oligomeric silsesquioxanes and aromatic imide bridges showed promising performance for H₂ purification applications¹. Ultrathin films (< 100 nm) obtained via interfacial polymerization on γ-alumina discs allowed to achieve high H₂ permeance while the inorganic nature of the POSS fraction ensures a thermal stability exciding the one of traditional polymeric membranes.

In the present work, the potential of novel polyPOSSimide (iPOSS) membranes designed for the purification of H₂ from a coke gas (from steelmaking industry) is investigated. Aiming at upscaling the membrane fabrication, tubular single channel and multi-channel element membranes were prepared, using amine-modified POSS nanostructures and 6FDA as precursors. In particular, different types of amine-modified iPOSS have been produced in order to increase the performance and thermal stability of the selective layer. The gas separation performance has been investigated by means of single gas and quaternary (H₂, CH₄, CO₂, N₂) mixtures, the latter used to simulate the conditions expected at the membrane module inlet under real operation conditions. Preliminary results showed that the fabricated membranes can achieve high H₂ selectivity (H₂/N₂ > 40, H₂/CH₄ > 50, H₂/CO₂ > 7) in the temperature range 150 to 250 ºC, maintaining proper H₂ permeances (> 1000 GPU). The selectivity of these upscaled membrane samples meets the performance of those previously obtained for the disc-shaped lab-scale membranes, paving the way for a successful upscaling to larger membrane areas.

Figure 1 PolyPOSSimide membrane performance at varying temperature, feed pressure equal to 10 bar.

Acknowledgements

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 760899. This publication reflects only the author’s views and the European Union is not liable for any use that may be made of the information contained therein.

References

[1] Raaijmakers, M. J. T., Wessling, M., Nijmeijer, A. Benes, N. E., Chem. Mater., 26, (2014) 3660.

Purified and methane enriched Biogas, can be used for household applications, automobile fuel or electricity generation, by removing CO₂ (which constitutes 40%) from Biogas. Among several technologies for CO₂ separation, Membrane-based technologies have an edge over others because of the scale, easy operation and energy efficiency. Mixed Matrix Membranes (MMMs) have exhibited enhanced permeation performance along with higher thermal and structural stability as compared to polymeric membranes. Metal−organic frameworks (MOFs) having tunable porosities are promising filler candidates for the fabrication of MMMs. Here, we explore the potential of a MMM using Polysulfone (PSf) as polymeric phase and an Mg-based MOF as filler. The choice of the MOF is based on its preferential adsorption for CO₂ in relation to CH₄, which is expected to further augment the selectivity and flux characteristics of PSf in biogas enrichment. Both flat sheet as well as hollow fiber configurations have been fabricated and tested.

The Mg-based MOF was synthesized by an adaption of the methods proposed in the literature. To prepare the dope suspension for the spinning of Mg-based MOF/PSf membranes, the synthesized MOF was dispersed in the mixture of NMP–THF–EtOH followed by addition of PSf. The flat sheet membranes were made from this dope by phase inversion. For the preparation of hollow fiber MMMs, a Dry−wet spinning process was adopted. Neat-PSf membranes were also prepared using same solvent system for comparison. The spinning conditions of the fibers were kept constant.

The synthesized MOF and developed membranes were characterized by XRD, FEGSEM etc. Finally, the gas permeation properties of the membranes were studied with pure gases and gas mixtures (simulated composition of Bio-gas), over a range of pressures. Presence of Mg-based MOF showed substantial enhancement in gas permeation properties compared to Neat-PSf membranes, and indicate a high potential for further development.

Polybenzimidazole (PBI) is one of the highly thermostable polymers. PBI has been used in space, aviation, fire protection, firefighting, heat resistant fibers due to its unique heat resistance and durability. More recently, it has been applied as a membrane material for nanofiltration and gas separation, while PBI has been reported to exhibit the exceptional hydrogen separation of a gas mixture from water-gas-shift reaction at an elevated temperature.

Since synthesis of aromatic PBI has been reported by H. Vogel and C. S. Marvel in 1961, the well-known one-step synthetic route is to use polyphosphoric acid (PPA). It has the advantage of one-step process at high temperature of 200 deg C, but the usage of a strong acid has an environmental issue and thus complicated post-treatments to obtain fiber, powder, film, and sheet, etc.

We have prepared PBI using an alternative method to substitute the acid for a common organic solvent an to reduce the synthetic temperature. The reaction of an aldehyde with diaminobenzidine yields benzimidazole ring at 160 to 180 deg C, and the PBI synthesized through this method has been characterized for gas separation especially for hydrogen separation.

Carbon molecular sieves (CMS), hosting slit-like nanopores formed by a disordered packing of aromatic carbon strands driven by the volume exclusion effects, have emerged as a highly promising membrane material.^1–3 CMS can be synthesized with a narrow pore size distribution, yielding attractive sieving performances with a sub-angstrom resolution in molecular differentiation. However, the permeance of the CMS membranes remains low due to the micron-thick selective layer. A challenge with the reduction in the thickness is that the molecular selectivity is often compromised due to the increased contribution of transport from the defective pathways in the film. To the best of our knowledge, CMS films with thickness below 300 nm, yielding attractive gas separation performance have not been reported. Moreover, currently, there is no room temperature pore modification route to tune the molecular selectivity from the CMS membranes.

Herein, two membrane fabrication routes were developed, namely transfer and masking techniques, ⁴ leading to 100 – 200 nm CMS film by preventing the infiltration of the CMS precursor in the pores of the membrane support. The 100-nm-thick CMS film yielded attractive gas-sieving performances with H₂ permeance reaching up to 3060 gas permeation units (GPU) with corresponding H₂/CH₄ selectivity of 18 at 150 ^oC. Furthermore, a rapid and highly-tunable post-synthetic modification method based on room temperature ozone treatment was developed. Gas selectivity could be improved by several folds by shrinking the CMS micropores by a fraction of an angstrom. The optimized membranes yielded H₂ permeance of 507 GPU and H₂/CH₄ selectivity of 50.7. Other membrane yielded H₂ permeance of 453 GPU and H₂/CH₄ selectivity of 106.

Fig. 1. a) Cross-section SEM image of a 100nm-thick CMS film. b) XPS spectra from the oxygen functionalized CMS film. c) Gas selectivity of CMS membranes before and after the ozone treatment.

[1] M. Rungta, et al. Carbon. 2017, 115, 237–248.

[2] J. S. Adams, et al. Carbon. 2019, 141, 238–246.

[3] D.Y Koh, et al. Science. 2016, 353, 804-807.

[4] S. Huang, et al. ACS Appl. Mater. Interfaces, 2019, 11, 16729-16736.

Ceramic membranes using SiO₂ or TiO₂-ZrO₂ materials were promising for gas separation.^1,2) SO₂ membranes have excellent gas permeability and selectivity, but are likely damaged in water vapor. TiO₂ and ZrO₂ are in general chemically stable, however, there is a problem of lower permeability and selectivity. In this study, we aim at more precise pore size control of TiO₂-ZrO₂ composite membrane by using various organic chelating ligands with aromatic ring in TiO₂-ZrO₂ material. TiO₂-ZrO₂-aromatic organic chelating ligand (aOCL) composite membranes were prepared by the sol-gel method, and the permeation characteristics of gas molecules with different molecular diameters were examined.

Titanium (IV) isopropoxide (Ti(OC₃H₇)₄) and Zirconium (IV) butoxide (Zr(OC₄H₉)₄) as metal alkoxides, and Methyl Gallate (MG) or Ethyl Ferulate (EF) as OCLs were well mixed in 1-propanol solvent with small amount of acid as catalyst. Then, TiO₂-ZrO₂-(aOCL) composite sols were obtained by hydrolysis and condensation polymerization reaction. The prepared sols were dried and fired to prepare gel powder samples. FT-IR and XRD measurements were carried out on the powder samples to characterize the composite materials. TiO₂-ZrO₂ composite membranes were prepared by coating the sols on SiO₂ intermediate layer prepared on alumina porous supports and by firing at 300 ºC in nitrogen atmosphere.

FT-IR measurement showed that C=C bond of the aromatic ring could be remained in the gel calcined at 300 ˚C in N₂. XRD analysis suggested that the TiO₂-ZrO₂-(aOCL) composite samples had amorphous structure (Fig. 1). TiO₂-ZrO₂-(aOCL) membranes exhibited better molecular sieving properties as compared with the intermediate layer and TiO₂-ZrO₂ membranes at 200 ˚C (Fig. 2). In addition, different gas permeation characteristics was observed for TiO₂-ZrO₂-(MG) and TiO₂-ZrO₂-(EF) membranes. The difference in side chains of each aOCL would possibly affect to the difference in microporous structure of the resultant TiO₂-ZrO₂-(aOCL) membranes.

1) N. W. Ockwig et al., Chem.Rev, 107 (2007) 4078-4110.

2) T. Fukumoto et al., J. Membr. Sci., 461 (2014) 96-105.

Freeze casting is a well-known method to get highly porous bodies, particularly for the preparation of a support layer of membranes because the technique generally produceses macroscopic pores and low tortuosity [1]. However, the support layer of membranes should have good mechanical stability, where freeze cast structures usually possess low mechanical stability. Reinforcing aids, such as fibres, whiskers, might be mixed to improve strength. For instance, mullite, 3Al₂O₃·2SiO_2, only stable phase in the Al₂O₃-SiO₂ binary system and has excellent physicochemical properties with acicular crystal morphology, see Figure 1 , is a suitable candidate for this purpose [2].

Figure 1. Mullite single crystals in acicular shape.

In this work, highly porous alumina-mullite whisker composite membrane support layers were prepared by a freeze casting technique and adding a various amount of mullite whiskers as a reinforcing agent. Tert-butanol is used as a freezing media and 4K/min cooling rate is applied. Shrinkage, mechanical stability, porosity and water permeability of freeze cast alumina-mullite whisker composite support layers investigated as a function of mullite whisker content using several characterization techniques such as XRD, BET, compressive testing, and porosimetry.

References:

1. Deville, S. (2008). Freeze‐casting of porous ceramics: a review of current achievements and issues. Advanced Engineering Materials, 10(3), 155-169.
2. Okada, K., & Otuska, N. (1992). Synthesis of Mullite Whiskers and Their Application in Composites. ChemInform, 23(3).

In the recent development of membrane materials for water and wastewater treatment, TiO₂ has been used as a photocatalyst, a dopant or component in composite membranes or as an inorganic membrane material itself. Recently, coloured TiO₂ has received much attention in many other applications due to its enhanced electronic properties, which predicts its potential as a photocatalytic ultrafiltration membrane material in surface water treatment. Herein, a supported Ti³⁺ self-doped anatase TiO₂ membrane was prepared by partial sintering and hydrogenation, and its photocatalytically enhanced antifouling performance in surface water ultrafiltration was examined.

In this work, hydrogenation of the TiO₂ membrane effectively boosted its photocatalytic activity towards humic acid (HA) degradation and improved its anti-fouling capability. Upon UV irradiation, the hydrogenated TiO₂ membrane (TiO₂_H30, by 30 hours of hydrogenation) demonstrated 60% enhancements in HA removal efficiency, compared with pristine TiO₂. During subsequent filtration tests, the TiO₂_H30 membrane with UV pre-treatment showed 50% higher residue normalized flux over that of pristine TiO₂, and a tripling of residue normalized flux as compared to tests performed without UV pre-treatment. Through a combination of materials characterization techniques, the enhanced fouling resistance and improved photocatalytic activity of the hydrogenated TiO₂ membranes can be attributed to its improved carrier trapping, inhibited recombination, and improved conductivity, due to the hydrogenation-induced surface disorder and Ti³⁺ self-doping.

Over the last decades, the development of 'smart' membranes, which transport properties can be tuned or switched by an external impact, has attracted a lot of research attention. For ions, such a tuning can be realized with the help of electric field created by the conductive pore surface [1–3]. The applications of such structures include separation and purification processes, chemical sensors, and synthetic analogues of biological ion channels [4,5].

In this work, we investigate two types of nanoporous membranes with conductive surface for switchable ion transport. The first type (C-Nafen) is prepared by vacuum filtration from Nafen alumina nanofibers with the diameter of 10–15 nm followed by the deposition of conductive carbon layer by CVD [6]. The second type (C-PAAO) is represented by porous anodic alumina membranes with carbon nanotubes, which are synthesized inside the pores reducing their size to 5–10 nm. The electrochemical stability windows of C-Nafen and C-PAAO membranes are determined. It is shown experimentally that the selectivity of C-Nafen and C-PAAO membranes can be switched from cation to anion by changing the potential of membrane surface [7]. The theoretical model of ion transport derived from Navier-Stokes, Nernst-Planck, and Poisson equations showed good agreement with experimental results [8].

The work is funded by the Russian Foundation for Basic Research, project 18–38–20046.

References

1. Martin C.R. et al. Advanced Materials, 2001, 13, 1351–1362.
2. Gao P. and Martin C.R. ACS Nano, 2014, 8 (8), 8266–8272.
3. X. Zhang et al. Environmental Science and Technology, 2019, 53, 868.
4. Tagliazucchi M., Szleifer I. Materials Today, 2015, 18, 131.
5. Hou X. et al. Chemical Society Review, 2011, 40, 2385.
6. Solodovnichenko V.S. et al. Advanced Engineering Materials, 2017, 19, 1700244.
7. Lebedev D.V. et al. Petroleum chemistry, 2018, 58, 474–481.
8. Ryzhkov I.I. et al. Membranes and Membrane Technologies, 2020, 2(1), 10–19.

Introduction: Solid alkaline fuel cell and alkaline water electrolysis using anion exchange membrane (AEM) attract increasing attention since non-noble metal electrode catalyst can be used in this system. However, development of chemically durable membrane is critical for practical device application. Ether free AEM consisting of only aromatic component and anion exchange group such as polyphenylene AEM is potential candidate for highly durable membranes¹, but such membranes are often suffered from low molecular weight for synthesis and low mechanical property derived from less polymer entanglement nature of the highly rigid backbone.

Fig1. Chemical structure of the designed ether free AEM

In this work, we have synthesized an ultra-high molecular weight ether free AEM (Fig 1). We expected that AEM with both high mechanical strength and chemical durability can be obtained by using this membrane.

Method: Target membrane was synthesized by polymerization of the fluorene and the tetrafluorophenylene monomers and successive quaternization (Fig 1). Structure and molecular weight of the polymer were evaluated by ¹H-NMR spectra and GPC, respectively. Ion conductivity was measured by alternative impedance spectroscopy using 4-probe method. Alkaline stability of the membrane was investigated in 8M NaOH aq at 80 ^oC for 168 h.

Results and Discussion:

From GPC analysis, weight-average molecular weight of the polymer is 178 kDa.Due to this quite high molecular weight, the membrane is flexible and mechanically strong.

Chloride ion conductivity of this membrane shows 133 mS/cm under RH95% and 18 mS/cm under RH60% at 80 ^oC indicating highly conducing nature of the material. After the alkaline stability test, the membrane keeps its ion conductivity and mechanical flexibility. These results indicate that the developed membrane is promising for fuel cell and water electrolysis application.

Fig 2. Chloride conductivity of the membrane at 80 ^oC as a function of relative humidity

1. Shoji Miyanishi, Takeo Yamaguchi, J. Mater. Chem. A 7, 2219-2224 (2019)

Nowadays, a number of studies have been focusing on the zirconia-based oxygen permeable membranes, since zirconia has high mechanical strength and ionic conductivity that makes it suitable for large capacity manufacture of the membrane. However, the zirconia-based dual-phase membranes typically exhibit low oxygen permeation flux due to the inter-diffusion reaction between zirconia and rare-earth metals in the composite. In this study, a novel strategy for significantly improving the oxygen flux of the zirconia-based membrane by adopting a new surface coating material has been proposed. The Ruddlesden–Popper layered perovskite, which shows low reactivity with zirconia and a high surface exchange kinetics, was used as a new coating material to enhance the surface exchange reaction on surface. The bare zirconia-based composite membrane exhibited a low oxygen flux under an air/He atmosphere. On the other hand, the oxygen permeation flux of the membrane with coating of Ruddlesden–Popper perovskite was considerably improved by about two orders of magnitude. This permeation flux value is much higher than that of membrane with coating of lanthanum strontium cobaltate, which is a representative coating material with high surface exchange kinetics for the membrane. The resistances of oxygen permeation have been also investigated as a function of oxygen partial pressure by using the oxygen permeation model in order to understand the mechanism of permeability improvement by coating of Ruddlesden–Popper perovskite. The effects of surface exchange kinetics on the enhanced oxygen permeability in the zirconia-based composite membrane will be discussed.

Complex oxides with structure of perovskite can exchange oxygen with the environment. It allows to use such oxides as materials for oxygen permeable membranes. Change in oxygen content leads to change in crystal structure. This research aims to study crystal structure of oxygen permeable membrane in working conditions by XRD on example of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF).

Hollow fiber composed of LSCF was set in the diffractometer. Gas mixtures of oxygen and nitrogen were blown inside the membrane. Pure argon was blown outside the membrane. Then the gas flows were interchanged. The working temperature of membrane was reached by immediate AC heating. Temperature measurement was carried out by infrared pyrometer. Gas flow rates were controlled by gas mixer. The gas composition at the outlet was determined by mass-spectrometer. The gas flow rate was 50 ml/min inside the membrane and 200ml/min outside the membrane. The oxygen contents of gas mixtures are 5, 20 and 50 vol.%.

For detailed data analysis it is necessary to get phase diagram of LSCF. This work suggests the obtaining of such phase diagram.

Full profile analysis was carried out by Rietveld refinement using Topas 4.2. Obtained data allows to plot the lattice parameters versus the oxygen content in the gas mixture. It was shown that lattice parameters near the inner surface are different from parameters near the outer surface of membrane.

The difference between lattice parameters of inner and outer sides of membranes means existence of oxygen content gradient along the membrane. The stronger the oxygen content in the environment changes, the greater the gradient of oxygen content in the membrane.

Introduction

Oxygen-permeable membranes (OPM’s) based on the oxides with mixed ionic-electronic conductivity (MIEC) are widely used in various innovative technologies. They are 100% selective for oxygen and can be applicable to high-temperature processes.

The operating temperature range of OPM’s is above 600°C, since at these temperatures the membrane materials have both high electronic and ionic conductivities. This makes it possible to heat directly OPM by passing electric current through it. In our previous study [1], the perspectives of OPMs heating by passing AC through membranes have been shown. This way allows us to enhance the membrane energy efficiencies and to give the fast-response control of the reactor temperature. Such path also opens the access to the surface of the operating membrane and therefore makes it possible to study the mechanism of oxygen permeability in situ by different physicochemical techniques.

Methods

Ba_0.5Sr_0.5Co_0.75Fe_0.2Mo_0.05O_3-δ hollow fiber membranes were produced by phase inversion method.The surface modification of OPM with Ag was believed to result in an increase in the oxygen permeation [2]. Silver nanoparticles synthesized in high-boiling solvents were used for preparing colloidal solution [3]. After coating the surface with silver, the membranes were resistively AC heated and then the oxygen fluxes were measured.

Results and Discussion

The study is devoted to a research of the AC heating effects on the oxygen permeability of OPM with Ag-modified surface.

Acknowledgements

This research was carried out within the state assignment to ISSCM SB RAS (project AAAA-A17-117030310277-6).

References

1. Popov M.P., Bychkov S.F., Nemudry A.P. // Solid State Ion. – 2017. – V. 312. – P. 73-79.

2. Da Costa L., et al. // J. Membrane. Sci. – 2009. – V. 340. – P. 148-153.

3. Titkov A.I., et al. // J. Incl. Phenom. Macro. – 2019. – V. 94. – P. 287-295.

With the transition from fossil fuels to renewable energy sources and its inherent fluctuating supply it is necessary to improve existing and to develop new kinds of energy storage systems. One possible solution to tackle this problem is the conversion of electrical energy into hydrogen as a chemical energy carrier by water electrolysis and the subsequent re-electrification. Modern water electrolyzers work usually under acid conditions and are based on proton exchange membranes, but this comes at the price of high investment costs. For a widespread usage of water electrolysis as part of energy storage systems it is indispensable that electrolyzer systems consist of inexpensive materials. These requirements are met by implementation of alkaline water electrolysis with anion exchange membranes (AEMs). AEMs enable the usage of less expensive non-PGM cell materials but have the challenge of rapid degradation in alkaline media and poor mechanical integrity.

This presentation will give brief insights into Evonik’s current development of anion conducting polymers, which provide an outstanding ionic conductivity combined with an excellent stability under alkaline conditions. The resulting AEMs were characterized by in-plane conductivity, ion exchange capacity (IEC), water uptake, dimensional stability, hydrogen crossover and long-term stability tests, supported by ¹H-NMR and DSC analyses. The characterization revealed ionic conductivities of 103 mS/cm @ 60 °C (Fig. 1), an IEC of 1.76 mmol/g and a remarkable alkaline stability with a total loss of ionic conductivity of 24% (Fig. 2) and IEC of 10% after 2000 h immersion in 2 M KOH @80 °C. The water uptake is 21% and the swelling is below 9%, both @ 60 °C in H­₂O. 

This AEM with a high ionic conductivity and alkaline stability combined with a good dimensional stability and low water uptake meets the requirements for an industrial application and a widespread usage in alkaline water electrolyzers. 

Self-crosslinking 2D MOF nanosheet membranes for H2 recovery

Yuan Peng*^,1, Hongling Song^1,2, Weishen Yang*^,1

¹ Dalian Institute of Chemical Physics, Chinese Academy of Sciences, China

² University of Chinese Academy of Sciences, China

E-mail address: pengyuan@dicp.ac.cn

2D MOF nanosheet membranes have gained great attention for the gas separation applications owing to the abundant in-plane apertures for precise molecular sieving and the ultrathin thickness for minimized membrane transport resistances. Self-crosslinking of the MOF nanosheet could evoke the defect healing of these nanosheet membranes by retarding the permeation of impurities, leading to the enhancement of the membrane separation performance.

The novel MOF nanosheet was fabricated following a bottom-up strategy, and the as-synthesized nanosheets were closely stacked onto a porous alumina substrate taking advantage of self-leveling of liquid. The crosslinking degrees and the stacking structures of the nanosheets were carefully controlled, which had great influences on the ultimate membrane performances.

Despite the lack of an obvious crystallinity of the MOF nanosheet, the novel nanosheets exhibited large lateral sizes and flexible belt-like morphologies (Figure 1a). AFM image revealed the high aspect ratio of the nanosheet with a thickness of 2 nm (Figure 1b). The corresponding nanosheet membrane testified the closely linking nanosheet morphology and the well-distributed coverage on the porous substrate (Figure 1c). Membranes prepared with different nanosheet amounts and post-synthetic drying processes demonstrated a wide range of H₂/CO₂ separation performances (Table 1), which all far exceeded those of the 2D MOF membranes reported to date.

Figure 1. SEM (a) and AFM images (b) of the MOF nanosheets. The inset in (b) shows the height profile along the black line. (c) SEM image of the top view of the MOF nanosheet membrane. The yellow arrows emphasized the boundaries of the adjacent nanosheets.

Table 1. The separation performances of membranes prepared at different conditions.

A new class of metal-organic frameworks (MOFs), known as hybrid ultramicroporous materials (HUMs) with high CO₂ adsorption capacities [1], have been recently introduced to solve the problems related to water stability, using strong interactions based on tight fitting. They have pore apertures, which are often less than 0.5 nm [2-4].

From the existing HUMs, TIFSIX-3-Ni (for simplification; TIFSIX from now on) is one of the most promising candidate that has one of the highest CO₂ capacities (40 cm³ g^-1 at 2 mbar CO₂ pressure) [5,6].

Powder form of TIFSIX has been investigated for gas separation and purification [7] whilst TIFSIX film synthesis procedure has not studied yet. The transfer of powder synthesis to membrane synthesis is often challenging. Additional properties such as film thickness and roughness have to be considered in order to create high quality films. Furthermore, the formation of films and membranes of MOFs is highly dependent on the specific structure to be studied, the nature of the substrate and the interaction between the two [8-10].

In this study, the thin-film synthesis of TIFSIX on glass substrates are reported by employing several methods including dip-coating, seeding/secondary growth, vapour-assisted conversion, rapid thermal deposition and in-situ coating. Using the in-situ approach with DMF as solvent, we were able to grow homogeneous TIFSIX films at relatively low temperatures and reduced reaction times.

We present the thin-film formation of TIFSIX by a straightforward in-situ synthesis without a need of surface modification on a glass support via SEM, XRD and XPS. We also reported a fabrication methodology based on seeding and secondary growth for TIFSIX films on ceramic tubular substrates and CO₂ and CH₄ permeabilities.

References

1 O. Cheung and N. Hedin, RSC Adv., 2014, 4, 14480–14494.

2 L.-Y. Lin and H. Bai, Micro. Meso. Mat., 2010, 136, 25–32.

3 M. M. Maroto-Valer, Z. Tang and Y. Zhang, Fuel Process. Technol., 2005, 86, 1487–1502.

4 S. Choi, J. H. Drese and C. W. Jones, ChemSusChem, 2009, 2, 796–854.

5 M. Kandiah, M. H. Nilsen, S. Usseglio, S. Jakobsen, U. Olsbye, M. Tilset, C. Larabi, E. A. Quadrelli, F. Bonino and K. P. Lillerud, Chem. Mater., 2010, 22, 6632–6640.

6 X. Y. Chen, V.-T. Hoang, D. Rodrigue and S. Kaliaguine, RSC Adv., 2013, 3, 24266–24279.

7 H. S. Scott, A. Bajpai, K.-J. Chen, T. Pham, B. Space, J. J. Perry and M. J. Zaworotko, Chem. Commun., 2015, 51, 14832–14835.

8 A. Cadiau, K. Adil, P. M. Bhatt, Y. Belmabkhout and M. Eddaoudi, Science, 2016, 353, 137–140.

9 L. T. Ngyen, K. K. LE and N. T. PHAN, Chinese J. Catal., 2012, 33, 688–696.

10 A. R. Millward and O. M. Yaghi, J. Am. Chem. Soc., 2005, 127, 17998–17999.

The separation of multicomponent, complex liquid mixtures, which are mixtures without a clear singular solvent, is an important, emerging area of membrane science. Transport models for polymeric materials have typically been applied to systems with three or fewer species; however, many critically important separations challenges involve complex mixtures containing dozens if not thousands of compounds. Here, we experimentally examine the ability of Maxwell-Stefan models to accurately predict complex mixture permeation in polymeric membranes based only on single component sorption and diffusion data. We specifically investigate the separation of a complex mixture of hydrocarbons covering a range of classes such as alkanes, cycloalkanes, alkyl aromatics, and polyaromatics. We observe strong sorption-based selectivity for aromatic compounds while diffusion-based selectivity dominates for aliphatic molecules. We utilize these experiments to test simplifying hypotheses regarding the estimation of sorption and diffusion coefficients of any arbitrary hydrocarbon in our polymer material. These simplifying hypotheses potential enable extension of our predictive capabilities to any N-component mixture of hydrocarbons, of which there are many industrially-relevant streams.

The purpose of this work is to develop a new monomer system for the synthesis of thin film composite (TFC) membranes via interfacial polymerization (IP) for solvent resistant nanofiltration (Figure 1). By combining the concept of PIMs with molecular adjustable monomers while making TFC membranes, it is aimed to obtain a thin active layer, with a high free volume and good permeance for organic solvents while retaining high retentions for the solute. IP ensures the formation of a thin selective layer while the rigid and contorted structure of the monomers ensures an enhanced free volume.

Figure 1. Schematic representation of the membrane, polymer network structure and monomers used.

First, the optically pure, methyl-linked binaphthalene di(acid chloride) was combined with various amine monomers to study the influence of the number and position of the amine functionalities (Figure 1). The membrane performance was determined using a high-throughput filtration module. The quality of the SRNF membranes is expressed in terms of permeance and solute retention (Figure 2).

Figure 2. Filtration data of the membranes prepared with different amines.

Second, the influence of changing the binaphthalene di(acid chloride) was studied by successively varying the dihedral angle and the enantiomeric excess. In both cases, 1,2,4TA&MPD was used as amine monomer (Figure 3).

Figure 3. Results of the influence of the binaphthalene di(acid chloride) on the membrane performance

From these results, it can be concluded that a 20 times higher permeance was obtained when the binaphthalene di(acid chloride) was combined with 1,2,4TA&MPD as amine in comparison to the standard MPD/TMC membrane. Moreover, the best filtration results were obtained with the methyl linked (1L-BN-AC) binaphthalene di(acid chloride) and when the optically pure (100% e.e.) of the acid chloride was used. Overall, it can be concluded that the newly formed polyamide membranes give a high permeance, while maintaining a good retention, especially for acetonitrile.

A novel hydrophobic thin film composite (TFC) membrane was prepared via interfacial polymerization of plant-based tannic acid (TA) and priamine monomers. The ultra-thin selective layer was successfully formed on a porous support prepared from recycled polyethylene terephthalate (PET) through Schiff-base reaction and Michael-addition reaction (Fig. 1). The reaction mechanism was demonstrated by solid-state NMR, XPS and ATR-FTIR analysis. The optimization of the membrane performance was conducted at different reaction time, tannic acid and priamine concentrations. TA/priamine-based TFC membrane showed excellent acetone permeance and styrene dimer rejection efficiency, which can provide new upperbound for the performance. In addition, compared to the literature, higher permeance for hydrophobic solvents including heptane and toluene was observed due to its hydrophobic property imparted from the long aliphatic chains of priamine. The hydrophobic TFC membrane was prepared using plant-based monomers and less toxic solvent, and recycled plastic material as a support, which is a good candidate for sustainable materials.

Fig. 1. TFC membrane prepared using plant-based monomers and recycled PET support.

Two-dimensional (2D) covalent organic frameworks (COFs) continue to attract intense interests due to their excellent properties, including chemical and thermal stabilities, well-defined and tunable pores, and atomic thicknesses. These inherent properties make 2D COFs ideal membrane materials with high selectivity, permeability, and chemical resistance for organic solvents. Currently, there are limited number of reports of applying COF membranes for OSN applications. Additionally, there lacks systematic experimental study on transport and separation mechanism of COF membranes for complex liquids such as organic solvents. In this talk, we report composite membranes having thin layers of COFs (~ 1 mm) as selective layers for OSN that showed high selectivity and permeance. Specifically, two categories of COFs will be investigated: 1) COFs with the same backbone structure, but varied functional groups lining the pore; and 2) COFs with the same functional group inside the pore, but varied backbone structures. The tunable nature of these COF membranes provides experimental evidence for us to further understand the solid-liquid surface interactions between organic solvents and membrane pores that lead to the differences in the pore microenvironments, and, consequently, selectivity among COF membranes. For example, Janus membranes, consisting of hydrophobic backbone with hydrophilic functional groups lining the pores, demonstrated high permeability to both polar and non-polar solvents. In the case of neat solvent filtration experiments, the Janus COF composite membranes showed permeance of 4160 ± 243 and 2778 ± 126 L m^-2 h^-1 bar^-1 for n-hexane and methanol, respectively. For non-polar solvent separation application, COFs with hydrophobic pores resulted in enhanced n-hexane permeance of 6000 L m^-2 h^-1bar^-1. Finally, the COF membranes are stable in various solvents for more than 7 days. As such, the reported COF membranes may be used for purification and recycling of solvents, catalysts, and products in chemical, pharmaceutical, and refinery industries.

Organic solvent nanofiltration (OSN) is a crucial industrial process for selective removal of pollutants and recovery of valuable chemical products. Due to the advantageous scalability of membrane nanofiltration technology, recent research studies have been devoted to developing functionalized membrane materials with precise molecular separations. Here in this work we present a series of highly-selective microporous ultra-thin polyamide (PA) nanofilm membranes synthesized from interfacial-polymerization between aromatic acyl chlorides and triptycene-derived amine monomers. The membranes were characterized with a range of techniques such as gas adsorption, SEM, and AFM. Rejection experiments were performed using acetone solvent in cross-flow systems with PA membranes captured on PAN support. The nanofiltration performance was evaluated in pressurized dead-end filtration cells and cross-flow systems. The membranes show sharp molecular cut-off in rejection experiments. This work is of vital importance for developing new OSN membranes for molecular separations and pharmaceutical production.

Solvents derived from fossil fuels such as hexane, n,n-dimethylformamide (DMF) and 1-methyl-2-pyrrolidone (NMP) are widely used in the polymer industry, including membrane fabrication. The use of these solvents are highly regulated by the European Chemical Agency (ECHA) [Regulation (EC) no. 1907/2006], due to their reprotoxicity, carcinogenicity and mutagenicity.

To overcome the limitation on solvent usage, the polymer membrane community has deployed bio-renewable solvents during membrane fabrication. To date, this approach has been proven successful with producing porous support layers of thin film composite (TFC) membranes or asymmetric membranes for microfiltration or ultrafiltration.

Here we extend this approach to report for the first time the replacement of such fossil fuel-derived solvents with bio-renewable alternatives derived from plants in the fabrication of TFC membranes that are suitable for organic solvent nanofiltration. We replaced hexane with 2-methyltetrahydrofuran as the organic phase during interfacial polymerisation of polyamide selective layers, while regenerated porous cellulose supports were produced using Cyrene™ via a one-step deacetylation process. Compared to TFC membranes produced using petroleum-derived solvents, the ethanol permeances of our TFC membranes were 300% higher, reaching 11.2 L m^-2 h^-1 bar^-1, while molecular dye rejection rates reached 98.5%.

The separation performances of our TFC membranes fabricated using renewable solvents outperformed those of polymer membranes produced using petroleum-derived solvents when ethanol and Rose Bengal were used as components of the feed solution. The use of bio-renewable solvents to fabricate high-performance polymer membranes via well-established processes provides an alternative to using complex protocols and additives for yielding high-performance polymer membranes.

In conclusion, following principles of green chemistry, we have successfully replaced fossil fuel-based solvents and polymers with renewable feedstocks – Cyrene^TM, 2-MeTHF and cellulose to fabricate high-performance TFC membranes suitable for OSN applications. Our approach may potentially transform the polymer membrane industry into a more sustainable industry.

Organic solvents are indispensable in chemical-science based industries which in range in scale from refining to pharmaceutical production. It is generally accepted that 40-70% of capital and operating costs in these industries can be reduced by replacing conventional concentration and purification technology to alternatives. Though one of the fascinating alternatives, the membrane-based system, has been successfully commercialized in desalination, it is still challenging to expand membrane operation into organic solvent systems. To replace the conventional processes such as evaporation, liquid extraction, adsorption, crystallization and chromatography, membranes must offer resilience in organic environments, display attractive selectivities, and have desirable permeance. In addition, the membrane fabrication process should create as little burden on the environment as possible.

In this study, a new green and compact production method is introduced for (a) fabricating a robust membrane which is capable to do its function in a wide range of organic solvents with attractive selectivity of target molecules and (b) minimizing waste disposal and production time. In contrast to the conventional membrane fabrications, a spray-coating method was employed to fabricate a thin film composite membrane with high temperature stability and high solvent permeance. The proposed fabrication method can reduce usage o polymer and solvents, and eliminate the time-consuming coagulation and washing steps, accordingly minimizing substantial amounts of solvent-contaminated wastewater (up to 50billion liters per year). Furthermore, a green solvent (dimethyl sulfoxide) is used to bypass conventional N,N-dimethyl formamide and N-methyl-2-pyrrolidone, and can simultaneously fabricate a membrane ready to use within a half-day. The resulting membrane exhibited remarkably stable performance for the separation of solutes in N,N-dimethyl formamide, even at elevated temperatures not feasible with conventional polymeric membranes, and so it is a candidate for potential use in the pharmaceutical and fine chemical industries.

Intensification of the hydroformylation process to produce 12-oxo-dodecanenitrile (route to polyamide) from 10-undecenitrile was studied by coupling the reaction with OSN for both the recycling of the catalytic system (Rh-catalyst & P-ligand) and the product extraction.

This system was first studied in toluene [1-3]. Among the P-ligands tested, Biphephos was the best compromise in terms of reaction performances and OSN selectivity by the Pervap4060 PDMS membrane. By coupling reaction (0.25 mol substrate, 1 mol.L^-1) & OSN (VRR=5, 10 bar), up to 3 reaction-OSN cycles were efficiently performed in toluene.

Knowing that substrate and products are liquids, a solvent-free overall process appeared more sustainable if OSN is efficient in solvent-free mixtures.By coupling reaction (1.25 mol pure substrate, 5 mol.L^-1) & OSN (VRR=5, 10 bar) in solvent-free mixtures, up to 2 reaction-OSN cycles were performed. A single cycle allowed to reach the same TON as two cycles in toluene. The catalyst recycling feasibility was proved, however, the OSN optimum was evidenced to be different from that in toluene [3].

Finally, integration of OSN in the overall production process is discussed aiming at the proposal of a hybrid separation process involving combination of OSN and distillation for an energy intensive global separation step. The optimum OSN conditions being different in toluene and solvent-free process, the best strategy for a given productivity was evidenced to be different: advantages and drawbacks of toluene and solvent-free processes must be balanced in a technical and economic analysis for the final selection.

[1] T. Renouard, A. Lejeune, M. Rabiller-Baudry, Sep. Purif. Technol. 2018, 194, 111-122.

[2] A. Lejeune, M. Rabiller-Baudry, T. Renouard, B. Balannec, Y. Liu, J. Augello, D. Wolbert, Chem. Eng. Sci. 2018, 183, 240-259.

[3] A.Lejeune, L. Le Goanvic, T. Renouard, J.-L. Couturier, J.-L. Dubois, J.-F. Carpentier, M. Rabiller-Baudry, ChemPlusChem 2019, 84, 1744-1760.

The Layer-by-Layer (LbL) technology presents a powerful tool to modify porous membranes and their rejection behaviour. With this method, it is possible to achieve thin films on membrane surfaces which can be tailored to required needs due to the thickness and density of the layer or surface charges.

Aim of this study is the characterization of LbL- coated capillary ultrafiltration membranes and further understanding of rejection mechanisms.

Key characterization methods for membranes in general are the molecular weight cut-off (MWCO) and zeta potential measurement – giving information about the molecular separation limit and surface charge. Both of these properties have to be taken into account to understand the annexation mechanisms and the influence on the rejection.

Therefore capillary polyethersulfone membranes (INGE GmbH) were coated with double layers (DL) of Poly(diallyldimethylammonia)chloride and Poly(styrenesulfonate). With 8 DL coatings a permeability of around 12 L/(m²hbar) and a rejection of 70-80 % for a divalent ion solution (MgSO₄) was achieved, while the virgin membranes have shown less than 5 % rejection at a permeability of approx. 850 L/(m²hbar).

For the coated membranes MWCO decreases from 100,000 Da to less than 400 Da, resulting in a calculated pore diameter of approx. 1.6 nm – in the range of nanofiltration membranes. At the same time the negative zeta potential of the virgin membrane (-40 mV at pH 7) shifts to less negative values (Figure 1), reaching ‑15 mV at pH 7. Accordingly the isoelectric point was reached around pH 3. Filtration at this pH shows a collapse in rejection (MgSO₄) to 30 %, leading to the assumption that both mechanisms have a major impact on the filtration characteristic and the rejection of divalent anions.

Further research will focus on the build-up of the LbL-film to determine the influence of polyelectrolytes configuration within the film on membrane properties.

Membrane assisted crystallization is a well-known technology where microporous hydrophobic membranes are used not as selective barriers but to promote the water vapor transfer between phases inducing supersaturation in solution [1]. This has been successfully tested in the crystallization of ionic salts, low molecular organic acids, and proteins [2]. Although some experimental studies probed the early stage of crystals formation, thanks to advanced techniques such as cryo-TEM [3], atomic force microscopy [4], molecular modelling helped to investigate the mechanism of nucleation and crystals growth [5,6].

In this paper we will present a detailed computational analysis of the crystal nucleation and growth of sodium chloride in contact with hydrophobic polymer surfaces at a supersaturated concentration of salt.

The amorphous polyvinylidene fluoride (PVDF) surface together with the alpha and beta phases analysed in this work will provide new insight into peculiarities of their influence in crystal formation mechanism.

The salt nucleation is faster with amorphous PVDF model then α and β PVDF and can be attributed to difference in the ability of  amorphous membrane to induce supersaturation in less time. Molecular models confirm the highly efficient packing of the alfa nd beta polymer chains,  in comparison to the amorphous one resulting in greater diffusion of water molecules. Furthermore, the rate of aggregation for Na+ Cl- ions was higher for the amorphous PVDF  leading to a much more massive nucleation and crystallization.

[1] E. Drioli et al., Current Opinion in Chem. Eng. 1 (2012) 178-182

[2] G. Di Profio et al., J. Crystal Growth, 257 (2003) 257-263

[3] T. Yamazaki et al., PNAS USA, 114 (2017) 2154–2159

[4] S. Chung et al., PNAS USA, 107 (2010) 16536–16541

[5] D. Chakraborty et al., Chem. Phys. Letters, 587 (2013) 25–29

[6] J.H. Tsai et al., Applied Sci., 8 (2018), 2145-2152

The use of biopolymers instead of fossil-fuel-derived materials represents a growing area to produce membranes, but their application is hindered by poor stability in aqueous environments.

Crosslinking is a strategy to improve biomaterial properties, but most crosslinking agents (e.g., glutaraldehyde) cause unwanted-functional changes in biopolymers or are hazardous. In this work, pectin (P) was employed for the first time as crosslinker to improve the stability and the mechanical properties of polyvinyl alcohol (PVA)-based membranes.

The membranes, crosslinked with different PVA/P ratio, were prepared by Evaporation-Induced Phase Separation (EIPS). These were characterized by Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Static-Water Contact Angle (SCA). Properties such as stability to high-temperature and to acid-basic solutions, antiradical and antibacterial activity and biodegradation level were determined. All these properties have been compared with those obtained from crosslinked PVA/citric acid membranes (PVA/CA).

SEM analysis confirmed that dense membranes were obtained, and SCA proved their hydrophilicity. The successful of crosslinking reaction (crosslinking degree of 65%) has been demonstrated by FTIR spectra that showed absorption bands of ester group and by TGA curves in which the temperature onset increased. Besides, results demonstrated that the membrane prepared with appropriate ratio PVA/P showed good performance in terms of stability to acid-basic solutions, high-temperature resistance and antiradical activity. Furthermore, the PVA/P membrane degradation was limited under soil burial conditions. In fact, after 20 days, they lost 4% wt, whilst PVA/CA lost 30% wt and PVA membranes were totally decomposed.

The crosslinking of PVA membrane with pectin, used instead of glutaraldehyde, has led to production of water-insoluble (at any tested pH) and high-temperature resistant (higher than 450 °C) membranes, with antiradical and antibacterial activity. Furthermore, the results on the uses of produced membranes as support for biocatalyst immobilization and development of biocatalytic membrane reactors will be highlighted.

Water filtration membranes coupled with photocatalysis has recently emerged as process for water treatment [1]. TiO₂ is the most common photocatalyst used in these hybrid processes subjected to UV light [1,2,3], being used as suspended nanoparticles, covering or embedded in the membranes [1].We evaluate the effect of UV exposure over polymeric membranes, namely Polyethersulfone (PES, 0.2 µm), Cellulose Acetate (CA, 0.45µm), Polyamide (PA, 0.45µm), DK and BW30, before and after modification. Figure 1 shows the membranes modification and UV exposure process performed with an UVH-lamp type Z that emits polychromatic light and housed in a shuttered box with PN310 quartz. Membrane discs were placed in a double-walled glass Petri dishes containing autoclaved and filtered (0.2µm) deionized water and the UV exposures were performed in quadruplicate for 3 or 6h for non-modified membranes and, 6h for modified membranes. Dark controls (without UV) were also obtained. All dried membranes (24h, 30°C) were characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) to check and compare their chemical-physical stability. Analysis of the water in contact with membranes were made using UV-Vis Spectroscopy and Nanoparticle Tracking Analysis (NTA). The results revealed that all non-modified membranes were dramatically affected by UV exposure whereas the modified membranes coated with SiO₂-TiO₂, preserved their integrity, indicating the positive effect of the surface modification towards membrane protection from the UV light. These membranes can be used to retain and degrade organic contaminants simultaneously.

Figure 1.Flow chart depicting the experimental procedures for sol-gel modification process of polymeric membranes with SiO₂-TiO₂ and UV exposure results.

References:

[1] Mozia, S. Sep. Purif. Technol. 2010, 73, 71–91.

[2] Sanches, S.et al J. Chem. Technol. Biot. 2016, 92, 1727–1737.

[3] Geltmeyer, J. et al Sep. Purif. Technol. 2017, 179, 533–541.

Acknowledgements

FAPESP (2019/04319-8); PTDC/ EAM-AMB/30989/2017; INTERFACE Programme.

The purpose of this study is to identify the connection between interfacial energy and crystal formation through induction time to establish the role of chemistry in membrane crystallisation. Membrane crystallisation is one of the most innovative processes for the recovery of valuable salts from effluents. Although the extensive research on the topic, there is still unclear how the membrane works with salt chemistry. For experimental purposes, flat sheet membrane cells were created and ePTFE hydrophobic membranes were used as a barrier to promote oversaturation. To create the feed solutions (90% undersaturated), five salts were selected. The solutions run with similar Reynolds number in both feed and permeate side (3100 – 400) and induction time was estimated with an FBRM particle tracker. The temperatures used were 40^oC and 25^oC. The differences in solubility for each salt, introduced differences in the permeate fluxes because of the different vapour pressures. These solubility differences among the five salts lead to different saturation levels where crystals appear downstream in the feed solution (induction), with the saturation level increasing according to the solubility of salt. This does not happen if the solubility is plotted against the time, which is something that the crystallisation theory suggests. Through these experiments it can clearly be seen that induction time establishes a linear trend against interfacial energy. Although the theory states that induction time is following a linear trend with solubility through different salts as proved with this work, it actually follows the trend of interfacial energy. Through this, we can now predict the induction time of all inorganic salts and control the process of membrane crystallization with better accuracy, while establishing the role of chemistry in it. This will help industries create more efficient crystallisers and get more effective in separation as well as resource reclaim.

Scale-up such a membrane crystallisation process is still insufficiently explored in terms of kinetic properties. Therefore, different polypropylene (PP) membrane modules configurations (i.e.1, 7, 19, 25, and 37 fibers) have been tested to identify the key parameters that strongly influence the kinetics properties when membrane scale increases. Operation conditions have been fixed in terms of velocity, feed concentration and temperature in the bulk as well as across the membrane. Based on tested modules, increasing hollow fiber number leading to less operation time, more treated volume with a high degree of supersaturation and high crystals yield. The crystal mass production in bulk stream using 37HF module is four-time higher than the 1HF module. 37HF module achieved a higher degree of saturation (1.14) while 1HF is the lowest (1.03) and 7, 19 and 25HF modules record 1.05, 1.08 and 1.12 respectively. This might be due to the load of the concentrated solution will be spread over a wide area as the effective membrane area increases. SEM photo approved that in which the crystals deposition and accumulation in 1HF module are extremely compared with other HF modules. Induction time and metastable zone were determined using a turbidity meter for better understanding of nucleation mechanism. 37HF module showed the lowest induction time (34 min) and the 1HF module showed the highest induction time (105 min) while the rest modules were in between. Hence, induction time decreases as effective membrane area increases where the supersaturation level is reached faster. Operation within the metastable zone is essential to avoid spontaneous nucleation and to control nucleation in which large crystals size can be produced.37HF can provide a wider metastable zone compared with other modules, as a result, the average crystal size produced by 37HF is approximately three times higher (103.2 µm) than the 1HF module (36.10 µm).

Membrane technology used in protein purification is hindered by the subsequent membrane fouling, and especially the decrease in flux during the application process have always restricted their rapid development. The ZrO₂ UF membranes with narrow pore size distribution are prepared through a modified wet chemical method, which effectively relieve the pollution of ceramic membrane. The pore size distribution and the permeance of the membrane are tunable via adjusting the fabrication parameters. The molecule weigh cut-off (MWCO) of the ZrO₂ UF membranes increased from 25 kDa (7 nm) to 66 kDa (10.9 nm) as the sintering temperature rised from 400 °C to 800 °C. Meanwhile, the permeance of the ZrO₂ UF membranes increased from 135 L·m^-2·h^-1·bar^-1 to 225 L·m^-2·h^-1·bar^-1. After testing the antifouling properties in the BSA molecules solution (0.5 g·L^-1), the ZrO₂ UF membrane with the heat treatment temperature controlled at the range of 400 °C to 600 °C displayed an almost 100 % retention of BSA molecules, and obtained a stable permeance of about 80-95 L·m^-2·h^-1·bar^-1. These membranes could have the same high rejection of BSA molecules, but have more than twice the permeance comparing previous works. The prepared ZrO₂ UF membrane will have a bright future in protein separation.

Polymer membranes with gas selectivity can be used for energy efficient industrial gas separations, and an open source database of such polymers would benefit the discovery of gas selective polymers. The Membrane Society of Australasia (https://membrane-australasia.org/) hosts the database for gas permeability of polymers collected from publications from 1950 to 2018. However, missing values exist in the database, making it difficult to generalize quantitative relationships among the permeability of different gases. If missing values in the database can be filled accurately, one can not only retrieve candidates with good gas selectivity that were not measured at the time of publication, but also get a more complete database for future experimental and theoretical study.  

In this study, missing values in the database were filled using machine learning (ML). The ML model was validated with published gas permeability data that are not recorded in the database. The rooted mean squared error (RMSE) between the ML prediction and experimental reports of the logarithm gas permeability were between 0.06 and 0.13 for polymers of intrinsic microporosity (PIM) and polyimides. In addition, the ML model could predict if the gas selectivity of polymer in the test set were above the Robeson upper bound with an accuracy of larger than 0.8.

Through filling in the missing data, we can reanalyse historical polymers and suggest potential “missed” candidates with desired gas selectivity. ML with sparse features was also performed, and we suggest that permeability of He, H₂, O₂, N₂ and CH₄ can be quantitatively postulated using the gas permeability of O₂ and/or CO₂. Primary insight on the gas permeability of polymers can thus be gained at the initial stage of experimental measurements and our model has the potential to rapidly identify polymer membranes worth further investigation.

Stimuli-responsive sulfonated polyaniline (S-PANI) membranes could have wide-ranging applications due to their electrical tunability, antifouling behaviour and chlorine resistance. However, design limitations of separation size range have hampered further development by allowing fabrication of S-PANI ultrafiltration (UF) membranes only, even if costly and laborious crosslinking post-membrane fabrication procedures were followed. This study presents a simple and scalable approach to produce the first nanofiltration (NF) S-PANI membrane. A systematic investigation of the variation in coagulation bath acidic strength and its effects on S-PANI membrane morphology (S-PANI reassembly process) was performed using a multitude of characterisation techniques. The obtained results revealed that controlling the acidic strength of the coagulation bath could promote a delay in the demixing rate of polymer, resulting in a tailored membrane morphology from finger-like shape to sponge-like shape and a denser skin layer. Tailoring the membrane morphology provided enhanced separation performance, including a substantial improvement in solute rejection of polyethylene glycol (PEG) and dye solutions. S-PANI membranes casted in 3M HCl aqueous solution showed an over 90% rejection of 1000 g.mol^-1 PEG solute compared to 12% rejection for the membranes produced in pure water coagulation bath. S-PANI membranes showed a stable in-filtration performance over time without acid leaching.

In comparison with commercial NF fluoropolymer membranes, NF S-PANI membranes showed a rejection of 91-100% for anionic dye solutes in the range of 320-1017 g.mol^-1 compared to 74-85% rejection of the commercial fluoropolymer membranes. In addition to better membrane performance, the S-PANI membranes casted at lower pH exhibited an increase in the membrane surface charge and a significant decrease in contact angle both enhanced the S-PANI membrane antifouling behaviour. Overall, the S-PANI membrane rejection performance and antifouling properties were significantly enhanced by exploiting a simple and fast coagulation bath kinetics approach without the need of using crosslinking agents.

Introduction: This study focuses on the development of electrospun fibres based on a family of processable microporous polymers (PIM), for use as adsorbent for toxic industrial chemical (TICs) and chemical warfare agents (CWA).

Methods:

PIMs were chemically modified in order to introduce highly nucleophilic reactive groups, such as amidoxime groups (AO-PIM-1), which are anticipated to react with CWA to decompose them. Then, these materials were processed into fibrous membrane using to an electrospinning process.

Results and discussion:

The influence of the feed solution (polymer concentration, solvent nature, presence of salt) and the electrospinning process conditions (flow rate, distance between the tip and the collector and voltage) have been investigated in order to obtain the optimal structure for the membrane, ie bead-free and thin fibres with small porosity. For instance, a minimum concentration of AO-PIM-1 was required to form thin fibres without beads. The presence of salt allowed the production of nanofibers at low polymer concentration. Moreover, the nature of solvent (DMF or DMSO) induced a different web structure.

Fig. 1: AO-PIM-1 fibers with DMF (Left) and DMSO (Right) as solvent.

Fibrous mat with 1.5 micron diameter fibres and porosity below 10 micron have been fabricated. These fibre mats presented a hydrophobic character with contact angle superior to 90°. Moreover, they were breathable, permeable to moisture vapour but not permeable to liquid water, which is essential for use within protective gear (i.e. gas masks or protective clothing).

Fig.2: Waterproof and breathable material.

Conclusions:

The preparation of waterproof/breathable films based on AO-PIM-1 fibers was demonstrated and optimised. The electrospun mats can can be easily incorporated into protective gear for protection against CWA.

Innovative and progressive solutions to global challenges in the field of membrane technology require intensive research activities. The speed at which researchers can achieve scientific breakthroughs will increase exponentially through the development and implementation of novel machine learning algorithms. The most important prerequisite for this is the provision of complete, reusable research data sets.

Today, data generated in research is often inadequately structured and managed, making it difficult and time-consuming to retrieve the data for evaluation, analysis, and graphing. A systematic computer-aided reuse of data is usually not possible due to the lack of structure and complete metadata.

FURTHRresearch is a spin-off of RWTH Aachen University and is active in the field of research data management. A versatile software platform, FURTHRmind, has been developed with which data of research and development can be efficiently managed (see Figure). The use of the software supports the researchers to manage research data according to the FAIR (findable, accessible, interoperable and reusable) principle, to organize data management efficiently and to ensure the longevity of the data.

The first version of the software was developed within the framework of the EU project "LbLBRANE" and the software was a major driver for the time-efficient development of layer-by-layer coated nano-filtration hollow fiber membranes in the scope of the project. Using selected examples from membrane research, we show how the research data management software can significantly accelerate progress in research projects. Furthermore, we give an outlook on what is possible in the long term: Well recorded and complete data sets simplify knowledge transfer and are processable with machine learning algorithms.

Formaldehyde (HCHO) and ultrafine dust causes increasing concerns, because of their ubiquitous presence in the indoor environment and their carcinogenic nature, with regard to humans. The integrated catalysis and filtration process for get rid of these pollutants has increasing practical prospect. High activity catalyst carried nanofiber membranes are the most ideal material for simultaneously removal of HCHO and ultrafine dust at ordinary temperature. In this work, inspired by beads on the cobwebs, the Pd nanoparticles spatial distributed at the ZIF-8 was in situ synthesised on the electrospuned SiO₂ nanofibrous membrane by contra-diffusion. Varying the preparation conditions such as the Pd adding time, dosage, ZIF-8 precursors concentration, and reaction duration, the whole synthesis could be precisely controlled both for the Pd and ZIF-8 particles with changeable sizes and for the Pd@ZIF-8/SiO₂ membrane with tunable nanostructure and thickness. This Pd nanoparticles carried ZIF-8 beads hanging on the SiO₂ can significantly increase the specific surface area of the membrane, leading higher gas permeation and rejection rate for ultrafine dust. Also, the well dispersed Pd nanoparticles in the ZIF-8 possesses good ordinary temperature catalytic performance for HCHO. This noble metal@MOF nanomaterials hanged nanofibrous membrane demonstrate a new way for indoor air purification, and the synthesis route reported here may provide new strategies for preparing core@shell-structured metal@MOF nanomaterials on inorganic nanofibrous membranes.

Introduction:

Electron-beam induced grafting of membrane polymers such as polyvinylidene fluoride is a promising method to produce surface engineered membranes. This seminal technology is characterized by its sustainable and green approach (no organic solvents, catalysts, or initiators are necessary, just an aqueous solution), its capability to produce a permanent functionalization by formation of covalent bonds, as well as its upscalability to industrial applications (continuous throughput with instantaneous reaction). Most studies so far used vinyl compounds like acrylates or styrene for which the mechanism is well understood and known as “grafting from approach” (radical polymerization). However, such compounds are often harmful to health or to the environment as well as unstable and expensive. In recent years, the “grafting to approach” of a broad variety of substances ranging from alcohols (e.g. glycerine) to acids (e.g. malonic acid) and even proteins/enzymes were conducted. Due to lack of vinyl groups, the covalent coupling cannot be explained by the traditional “grafting from approach”. With this study, we aim to close the gap and present a possible mechanism regarding grafting of general organic molecules to a membrane polymer.

Methods:

For this study, theoretical and experimental approaches were combined. Static quantum chemical calculations (DFT, B3LYP*, COSMO) were conducted to evaluate possible reaction pathways. Experimentally, sets of irradiation studies were performed, and the released products were determined (e.g. fluoride using ion chromatography and UV/VIS spectrophotometry).

Results:

Electron-beam irradiation leads to the release of fluoride/HF from PVDF depending on the dosage applied. Irradiation experiments using dry and water-wetted membranes as well as scavenger chemicals showed differences between released amounts, and supported or dismissed, respectively, certain reaction pathways obtained by DFT calculations. The crucial effect of water, however, lies mainly in the secondary activation of the dissolved grafting substances. The formation of covalent bonds could be explained by radical recombination.

An important challenge of the industrialized world is the increasing contamination of water by various chemical products. These substances originate from industrial processes, agriculture, cosmetics or pharmaceuticals. However, conventional sewage treatment plants can't completely remove these micropollutants, hence they start to accumulate in surface, ground and even in drinking water.

In this project, porous mixed-matrix membrane adsorbers having different functional groups were developed for water purification. Such membranes can combine filtration and adsorption capabilities and furthermore enable the simple adaption to various contaminants. The work comprises the development of mixed-matrix membrane adsorbers and their testing for the simultaneous separation of several micropollutants from water.

Porous polyvinylidene fluoride hollow fiber membranes were fabricated via the nonsolvent-induced phase separation (NIPS) process. Polystyrene particles with various functional groups were directly incorporated into the membrane structure during NIPS process.

The performance of the mixed-matrix membrane adsorbers to separate simultaneously micropollutants like diclofenac, carbamazepine, metoprolol and sulfamethoxazole was determined by dynamic adsorption experiments.

Mixed-matrix membrane adsorbers were successfully produced by the NIPS process yielding a porous surface on a sponge-like structure (Figure 1). Functional polystyrene particles were distributed homogeneously over the cross-sectional area with particle loadings up to 40 %.

Figure 2 illustrates the adsorption capacities of the membrane adsorbers for the designated micropollutants. For membrane adsorbers with anion exchange functionality (F1) adsorption capacities up to 14 g m^-² of Diclofenac were achieved. Additionally, integration of different functionalities (F1 and F2) into the same membrane is possible without considerable impairment in adsorption capacity.

Also diclofenac in low concentration of 2 µg L^-1 was separated successfully from tap water, revealing a removal of > 99 %.

Figure 1. Cross-section of mixed-matrix membrane adsorber.

Figure 2. Adsorption capacities of membrane adsorbers with anion (F1) or cation (F2) exchange function for different micropollutants.

Recycling of secondary effluents with the simultaneous clean water production and the recovery of valuable nutrients are important circular economy aspects. During the last few decades, many various techniques have been used for wastewater treatment, and the most promising seems to be membrane technology due to its high scalability, low energy demand and good product quality. However, a serious problem in the membrane water treatment is the deposition of biological and organic components of treated effluents (fouling) and precipitation of minerals (scaling) on the membrane surface [1]. Both phenomena are responsible for a rapid decline of the permeate flux over time, and reduce the effectiveness and economic benefits of membrane processes [2]. To avoid membrane fouling and scaling, several solutions have been proposed, including the selection of proper chemical reagents, cleaning sequence and washing protocol.

This study aims at developing a high effective method of membrane cleaning after secondary effluent treatment in the ultrafiltration/nanofiltration/reverse osmosis integrated system located at the Wroclaw Wastewater Treatment Plant (Poland). Three washing approaches were tested, namely alkaline-acidic, acidic-alkaline and alkaline-enzymatic-acidic. During the cleaning, parameters such as pH and conductivity of the washing solution were being monitored. The effectiveness of washing was evaluated by comparing the permeate streams before and after cleaning for various transmembrane pressures. Sodium hydroxide, sodium hypochlorite, nitric acid (V), free nitrous acid, and the enzyme-based agent were used as cleaning substances. The optimal cleaning time for each cleaning stage was found to be 30 minutes. For UF membrane the most effective was alkaline-enzymatic-acidic approach, while for NF membrane alkaline-acidic cleaning. The enzymatic washing allowed for the regeneration of the membrane flux in 96%.

References

[2] Guo, W., Ngo, H.-H., Li, J. Bioresource Technology 122, 27-34 (2012).

[1] Zhang, J., Yang, L., Wang, Z., et al. Journal of Membrane Science 587, 117159 (2019).

Bioethanol recovery via membrane-based pervaporation has become one of the research hotspots in the field of renewable energy. Mixed matrix membranes (MMMs), composed of polymer and inorganic particles, are very promising to become bioethanol permselective membrane, since they combine the merits of both polymeric membrane and inorganic membrane. However, the dispersion and compatibility problems of inorganic particles in MMMs severely influence the separation performance.

Herein, to address above problems, a serious of PDMS/ZIF MMMs are developed for bioethanol recovery via pervaporation. First of all, dodecylamine-modified ZIF-90 (DLA-ZIF-90) nanoparticles with enhanced hydrophobicity and ZIF-8@GO composites with GO as the carrier are fabricated as the fillers in order to improve the dispersion and compatibility of ZIF into PDMS matrix. The best PDMS/DLA-ZIF-90 MMM shows a high separation factor of 15.1 and the optimal flux of 100 g/m²h, while the optimal PDMS/ZIF-8@GO MMM displays a prominent separation factor of 22.2 with a total flux of 444 g/m²h, attributed to super-hydrophobicity and sieving function of ZIF-8. Besides, we also prepare covalently-linked AZIF-8@PDMS MMMs by covalent linking among amine-functionalized ZIF-8 (AZIF-8), 3-glycidyloxypropyltrimethoxysilane (GOPTS), and PDMS. GOPTS as a covalent linking bridge can covalently link AZIF-8 to PDMS, improving the compatibility of AZIF-8 with PDMS matrix and eliminating interfacial defects between AZIF-8 and PDMS, thereby enhancing ethanol recovery ability. The MMM with 7 % AZIF-8 loading exhibits the optimal separation performance with the highest separation factor of 17.7 and comparable flux of 586 g/m²h.

In this study, a promising new UiO-66-NH₂/BTESE hybrid membrane has been developed and applied to the desalination of high-salinity water by pervaporation. Due to the incorporation of UiO-66-NH₂ into the BTESE networks, the membrane networks exhibited a higher water affinity and a narrower pore size distribution, leading to a simultaneous improvement in water permeance and NaCl rejection in water desalination. The salt rejection of the membrane was almost insensitive to the feed salinity and operating temperature in pervaporation. As shown in Figure 1 (left), the water permeance of the resultant membrane decreased by 22% as the NaCl concentration increased from 1 to 13 wt % in the feed. Whereas the observed NaCl rejection continued to exceed 99.9%, irrespective of the feed salt concentration, indicative of excellent structural stability. Figure 1 (right) presents the water permeance and NaCl rejection as a function of operating time. Throughout a continuous PV operation of as long as 200 h, there was no significant change in either water permeance (1.3 ± 0.3×10^-10 m³/(m² s Pa)) or salt rejection (>99.9%) for the membrane, suggesting no structural alteration occurred during the long-term exposure to high-salinity water. The UiO-66-NH₂/BTESE hybrid membranes explored in this study show great promise as a new class of highly efficient PV membranes for the desalination of high-salinity water.

Figure 1. (left) Influence of NaCl concentration on desalination performances of the membrane at 70 °C. (right) Stability of the membrane for PV desalination of 3.5 wt % NaCl feed solution at 30 °C.

As Membrane Distillation emerges as a promising energy saving method for desalination, using solar heat or waste heat, its efficiency still needs to be improved. A better understanding of the influent parameters on temperature and concentration boundary layers will help optimizing the process. University of Luxembourg Membrane Distillation experimental facility is designed and operated to validate its three-dimensional CFD air-gap membrane distillation (AGMD) heat and mass transfer numerical model. The facility is equipped with out-fluxes measurements as well as temperature and concentration polarization characterization. A heater and a cooler with PID control, allow to set a stable and designed temperature. A peristaltic pump feeds the circuit, with a maximum flux of 5.3l/min. A rectangular module has been designed to insure a good spatial resolution for the optical measurement methods and a steady state flow while reducing the hydraulic entry length, in order to be able to test both laminar and turbulent flows. Temperature at all inlets and outlets of both the hot and cold channels is monitored, as well as pressure and flux at the inlet of the two channels.

Transparent windows on the sides of the hot channel and air-gap allow to determine (later on simultaneously) the temperature and concentration gradients in the hot channel close to the membrane, as well as in the air-gap, thanks to the combination of optical methods. The module design provides sufficient flexibility to test the influence of different geometric configurations, like the size of the Air Gap or the orientation of the module, or different spacer designs, in order to characterize the convection phenomena.

Validation results comparing calculated and experimental data will be presented.

The overall goal is to provide numerical and experimental results to be used to optimize the output fluxes and energy efficiency of AGMD processes.

Superhydrophobic membranes for membrane distillation (MD) are of great interest, as they can prevent wetting and scaling from occurring. Currently, perfluorinated compounds have been intensively used to achieve superhydrophobicity in membranes. However, the environmental issues associated with the use of perfluorinated compounds, ranging from C5 to C12, raise important research questions regarding its sustainability. When C5-12 perfluorinated compounds degrade in the environment, they form perfluorooctanoic acid (PFOA) which is carcinogenic and persistent in the environment. Herein, we propose a benign and facile silicone nanofilaments coating with which MD membranes can achieve superhydrophobicity. Silicone nanofilaments were first discovered by Stefan Seeger in 2006 [1]. In the years since their discovery, silicone nanofilaments have been grown on different substrates for different purposes, such as clothes[2], glass slides[3] and porous materials for catalysis and oil/water separation [4]. Most recently, different silicone nanostructures have been synthesised on metal soap[5]. However, the synthesis of different silicone nanostructures on top of membrane by chemical vapour deposition has never been reported.

In this study, we present a salvinia effect-inspired excellent antiwetting membrane with a silicone nanofilament coating for Membrane Distillation. Water contact angle increased from 117.9 degree±1.6 degree (pristine commercial 0.45-micron PVDF membrane) to 167.9 degree±1.2 degree (salvinia shape of silicone nanostructures grew on commercial 0.45-micron PVDF membrane) and liquid entry pressure increased from 111.5 kPa±1.5 kPa (pristine commercial 0.45-micron PVDF membrane) to 129.5 kPa±2.9 kPa. For the membrane with salvinia structures, it was observed to withstand a 3.2 mM sodium dodecyl sulphate (SDS) and 3.5% NaCl feed solution, which represents a very high concentration of SDS. Additionally, the used membrane could be cleaned by sonication in a 60 Degree Celsius water bath under 200W power for 20 mins to restore its superhydrobicity.

References

[1] G.R.J. Artus, S. Jung, J. Zimmermann, H.P. Gautschi, K. Marquardt, S. Seeger, Silicone nanofilaments and their application as superhydrophobic coatings, Adv. Mater. 18 (2006) 2758–2762. doi:10.1002/adma.200502030.

[2] J. Zhang, S. Seeger, Polyester materials with superwetting silicone nanofilaments for oil/water separation and selective oil absorption, Adv. Funct. Mater. 21 (2011) 4699–4704. doi:10.1002/adfm.201101090.

[3] J. Zimmermann, G.R.J. Artus, S. Seeger, Superhydrophobic Silicone Nanofilament Coatings, J. Adhes. Sci. Technol. 22 (2008) 251–263. doi:10.1163/156856108X305165.

[4] Z. Chu, S. Seeger, Multifunctional Hybrid Porous Micro-/Nanocomposite Materials, Adv. Mater. 27 (2015) 7775–7781. doi:10.1002/adma.201503502.

[5] G.R.J. Artus, S. Olveira, D. Patra, S. Seeger, Directed In Situ Shaping of Complex Nano- and Microstructures during Chemical Synthesis, Macromol. Rapid Commun. 38 (2017) 1–9. doi:10.1002/marc.201600558.

2m

Figure 1. 5kx SEM images Salvinia silicone nanostructures membrane

Figure 2. An antiwetting MD performance for salvinia silicone nanostructure membrane.

Figure 3. Restoration of hydrophobicity after sonication.

Ethylene glycol is a key chemical product widely used in the production of polyester fiber, polyester film and antifreeze. The purity of EG should be very high (95.0 wt% and above). Thus, pervaporation has been recognized as an effective alternative process, especially at relatively low concentrations of water in the feed.

Polymers have been widely used as membrane materials due to the superior membrane- forming properties and good thermal and chemical stability. One of the efficient modification methods is creating hybrid material in order to overcome drawbacks of trade-off between flux and selectivity. Assembly of nanomodifiers with polymer matrix leads to changes in structure and physical parameters of materials that leads to desired transport properties.

In order to solve the issue of incompatibility between inorganic nanoparticles and polymer matrix, hybrid membranes on the basis of a low cost and mechanically strong polymer poly (2,6- dimethyl-1,4-phenylene oxide) (PPO) and a star-shaped macromolecules (SM) with a small branching center of fullerene C60 and six arms of polystyrene and six arms of poly- tert-butyl methacrylate were prepared

The membrane structure war characterized by scanning electron microscopy (SEM) and X-ray phase analysis (XRD). The thermal stability was analyzed by thermogravimetric analysis (TGA). Contact angles were measured by sessile drop method.

The PPO/SM membranes were then applied to the pervaporation process for the dehydration of ethylene glycol. The effects of the SM content and the operating parameters on the pervaporation performance of the PPO/SM were investigated. The membranes under study were high selective with respect to water and show good transport properties. Membranes containing 2 and 5 wt.% of SM exhibited the best PV performance.

Acknowledgment: this work was carried out with financial support of Russian Science Foundation (RSF) (grant № 18-79-10116).

Membrane distillation (porous membrane) and thermopervaporation (membrane with non-porous selective layer) can be considered as an attractive approach for water desalination, or recovery of organic compounds from aqueous solutions since the low-temperature gradient between hot and cold liquid loops is already required for effective vapor transport. The drawback of membrane distillation process is a wetting of membrane pores in time that could dramatically reduce the process selectivity. Besides, such membrane contactor systems shall be operated vertically and have sufficient distance of the air gap to provide effective evacuation of condensed liquid from the condenser surface. Direct contact membrane distillation is the gravity-independent type of membrane distillation, but the feed and permeate solutions shall not wet the porous structure of the membrane that limits its applications.

In this work, we proposed the porous condenser made of stainless-steel in the membrane distillation process for the desalination of aqueous solutions of sodium chloride (5-42 g/l) and recovery of organic compounds from n-butanol/water solutions and ABE-fermentation model broth. In both cases, the porous condenser allowed using the permeate as a cooling agent that simplified the membrane module design. In the thermopervaporation process with the membrane contained the organophilic dense layer, continuous accumulation ofjrganics in the permeate led to the phase separation and, hence, provided additional enrichment of target components in organic-reach phase. The presentation will cover the results of the application of porous condenser in both applications.

The membrane distillation study was supported by RFBR (project № 18-58-80031), the thermopervaporation study was carried out within the State Program of TIPS RAS.

Membrane distillation is a thermally-driven desalination technology for separating water vapor from feed solution. The temperature difference between the two sides of the hydrophobicity membrane induces vapor pressure difference that causes water vapor in the hot feed side to permeate through the membrane pores. The technique works at low temperatures, low pressure, and achieves almost 100% salt rejection.

In the present work, two modifications are experimentally applied to the conventional water gap membrane distillation process and design to enhance its productivity. In the first modification, the gap water is circulated to enhance the heat and mass transfer inside the MD module. In the second modification, gap water is circulated while being cooled using a built-in heat exchanger coil within the cooling channel of the module that allows reduced gap temperature while circulation and eventually increases the system output flux. Investigated parameters included the water gap width, gap cooling, feed and coolant temperatures and flow rates, and gap circulation rate. Results showed that the feed temperature and flow rate are very effective operating variables with gap circulation and cooling due to their effects with enhanced heat and mass transfer coefficients in the WGMD. The specific energy consumption of the WGMD module with circulation and cooling portrayed high relative values at low feed temperatures. However, the SEC values decreased with increasing the feed temperature to be comparable to the case of gap circulation without cooling and little higher than conventional WGMD system. Corresponding values of maximum GOR between 0.4 and 0.5 were calculated for feed temperature between 70 and 80°C. For high system productivity, running the WGMD with gap circulation and cooling at high feed temperatures and flow rates is recommended. Additional studies on the gap width are recommended to optimize the performance of WGMD system.

Graphene oxide-Polysulfone (GO-PSF) membranes for direct contact membrane distillation (DCMD) were successfully synthesized using the method of wet-phase inversion. The membranes were prepared by varying the GO content in the casting solution, including 1.0 wt% GO, 5.0 wt% GO, and 10.0 wt% GO. The characterization of the synthesized and used membranes was made with SEM, Energy dispersive spectroscopy (EDS), Atomic force microscopy (AFM), and by using an optical tensiometer and Java Image processing software (ImageJ). This study demonstrated that the surface morphology, cross-section and roughness characteristics of the membranes, and the performance of desalination in DCMD were affected by the GO content. An increase of GO loading changed the dense skin of the top surface to a sponge-like structure and made the membrane more hydrophobic and rough, with lower porosity, and the permeate flux and salt rejection increased. The membrane with 5.0 wt% GO produced the highest flux (50.0 L/m²h) followed by the membranes with 10.0 wt% GO (48.2 L/m²h) and 1.0 wt% GO (21.7 L/m²h) when treating a solution containing 25,000 mg/L NaCl. The membrane with 10.0 wt% GO lost its mechanical stability after being exposed to the MD process. Therefore, there is a limit in the amount of GO that can be added to membranes being prepared by wet-phase inversion in order to obtained high MD performance and membrane integrity. These results are promising for producing GO-based membranes adaptable to MD for the treatment of high salinity water.

Introduction

Membrane distillation (MD) is a membrane based thermal distillation process capable of utilizing low-grade thermal energy to desalinate hypersaline brine water. To achieve an efficient MD process, a robust hydrophobic membrane is the key. Typical MD membrane materials are prone to fail in the MD process due to wetting and fouling. Besides, the water flux of the current MD membrane needs to be improved. Metal organic frameworks (MOFs) are a group of porous materials that have been recognized as an excellent platform for many applications. Since MOFs are highly porous and open to surface chemistry engineering because the surface ligands can be substituted, we expect that the incorporation of MOFs and polymeric membranes should offer higher overall porosity and tunable surface wettability. This type of hybrid membrane will be promising for MD application with high water flux, anti-wetting and/or anti-fouling features.

Methods:

ZIF-8 was synthesized through reported recipe with minor modification to achieve ZIF-8 nanoparticles. Different types of fluro-substituted organic ligands were reacted with the as-prepared ZIF-8 material to alter its surface wettability. The modified ZIF-8 was then mixed with polyvinylidene fluoride (PVDF) solution and electrospinning technique was used to fabricate the MD membrane. Detailed characterizations including material characterization and MD performance were carried out.

Results:

We have conducted preliminary tests on the ZIF8-PVDF membrane. The SEM image shows that the ZIF-8 nanoparticles were well distributed on the electrospun fibers (Figure 1). The MD test suggested that the hybrid membrane showed higher flux and more tolerant to membrane scaling compared with bare electrospun PVDF.

Discussion:

We are still working on the detailed characterizations. Our preliminary results indicated that the addition of ZIF-8 increased the water flux and changed the membrane wettability. Next, we will change the surface ligands of the ZIF-8 and complete the performance and mechanism study.

Figure 1. SEM image of the ZIF8-PVDF electrospun membrane

Until now, there is no uniform procedure or strategy to find humidifier membranes for fuel cell vehicles. Therefore, the aim of this work is to find suitable characterization methods for membranes for use in humidifier modules and to structure and apply them into a selection and evaluation methodology. For this purpose, characterization methods are first sought based on the technical requirements. In addition, selection and decision-making methods are compared on the basis of various evaluation criteria. The analysis techniques are to be incorporated into the selection and evaluation method. This shows that not only one method is sufficient in itself. For example, some membranes do not have to be completely tested and are selected beforehand. Therefore, several methods are combined and the evaluation method of the membrane is divided into two parts. In the first part, the performance properties, i.e. the basic suitability controlled by an EPC (event-driven process chain), is checked. The evaluation is carried out using a TOPSIS analysis (Technique for Order Preference by Similarity to Ideal Solution). This combination allows the membranes to be compared with each other and a ranking can be created. The appropriate membranes that pass this evaluation procedure are examined in the second part, the polymer analysis. This is about gaining understanding of the membrane and how it works. The test procedure can be controlled by a functional structure. Since the results of the analysis are intended to support the measurement results from performance measurement, but do not necessarily give a direct statement about performance, these should be evaluated with a SWOT analysis (strengths, weaknesses, opportunities, and threats) in order to identify risks and opportunities. The result is a comprehensive selection procedure in which the TOPSIS method is combined with an EPC. Finally, the membranes are evaluated in a SWOT analysis.

The oxygenates, such as alcohols and ethers, are widely used as high octane number boosters, high performance industrial antiknock additives, however, they are also pollutants. The traditional method for recovery of oxygenates from effluents is the distillation. Hydrophobic pervaporation has a number of advantages in solving such a separation task. However, in order to increase the efficiency of separation, it is necessary to develop membranes with enhanced selectivity. In this work, for the first time, a number of composite membranes with a selective layer based on polyalkylmethylsiloxanes, namely polyhexylmethylsiloxane (PHexMS), polyheptylmethylsiloxane (PHepMS), polyoctylmethylsiloxane (POMS) and polydecylmethylsiloxane (PDecMS) were fabricated using a commercial microfiltration support of the MFFK series. Membranes were prepared using a recently developed one-step method for the synthesis and vulcanization of polyalkylmethylsiloxanes. The pervaporation separation was carried out using the model mixture of 1% wt. BuOH, 1% wt. PrOH and 3% wt. EtOH in water, and 1wt. % MTBE in water. The performance of the developed composite membranes was compared with that of the following commercial membranes based on PDMS: Pervap 4060 (Sulzer Chemtech), Pervatech PDMS, (Pervatech), PolyAn POL_OR_M2 (PolyAn GmbH) and MDK-3 (ZAO NTC “Vladipor”). The PHepMS/MFFK composite membrane provided the highest BuOH/H2O selectivity (2.8) which is at least 3 times higher than that of commercial pervaporation membranes. Therefore, this membrane is a very promising option for the recovery of oxygenates from water.

This work was carried out in the A.V. Topchiev Institute of Petrochemical Synthesis (Russian Academy of Sciences) and was funded by the Russian Science Foundation, grant number 17-79-20296.

The quest for fresh water has been ever increasing since the inception of mankind on this planet. Membrane distillation process has proven to be very promising since it is less thermally intensive process. Several developments have been made to increase the productivity of the membrane distillation process. One such development is the integration of heat pump with direct contact membrane distillation (DCMD) module, the performance of which has been studied in this paper. An analytical model of the heat pump was designed to predict the performance parameters of the integrated system. The effects of feed and permeate inlet temperatures, volume flow rates, refrigerant mass flow rate, condenser and evaporator pressures have been investigated. The permeate flux increases with increase in refrigerant mass flow rate, feed inlet temperature and decreases with increase in condenser and evaporator pressures, feed flow rate, permeate inlet temperature. Comparisons between the theoretical data and experimental observations were drawn and it can be said that the analytical model proves to be a close approximation of the actual process i.e. the theoretical values were in good agreement with the experimental ones. It was also observed that the permeate flow rate did not have much effect on the overall flux produced by the system. The analytical model gave fairly precise results after taking into account, the non-ideal nature of the compressor of the heat pump. Better values of efficiency and flux can be obtained by proper optimization of the operating parameters of the system.

Integrated System Layout

Validation of the theoretical model

Variation of system Flux, thermal efficiency, and GOR with feed temperature

Aromatic hydrocarbons are important raw materials for organic synthesis, and are obtained by extraction of the gasoline fraction of catalytic cracking products, followed by regeneration of the solvent by distillation. This process is energy consuming and metal intensive. A more economical method for separating liquids is pervaporation. This method has the following advantages: no need to use high temperatures, the ability to use low-grade heat, modularity, compactness, reduced metal consumption.

To increase the productivity of the process, it is necessary to use highly selective and highly permeable membranes. In this work, we propose the process of separation of aromatic hydrocarbons from polar extractants using PIM-1 based membranes. This polymer has high permeability and good mechanical and film-forming properties, which allows the fabrication of both continuous and composite membranes with a thin selective layer.

It was found that sorption of aromatics onto PIM-1 was 1.5-1.8 g/g when sorption of triethylene glycol (TEG) was 1.09 g/g. To increase the stability of the membrane material, the cross-linking PIM-1 was performed using different methods. The crosslinking with aluminum chloride proved to be the most efficient for improving the stability of PIM-1 membranes in the presence of aromatics.

When conducting pervaporation experiments for a long time on a model mixture of toluene-TEG (75 wt.%/25 wt.%, respectively) at a temperature of 80ºC, it was found that the PIM-1 membrane shows stable toluene flux (0.7 kg/(m²·h)) and high separation factors (more than 20). Therefore, this membrane is very promising for the separation of aromatic hydrocarbons from polar solvents.

This work is supported by the Ministry of Science and Higher Education of the Russian Federation, project 14.616.21.0100 (project identifier RFMEFI61618X0100) and by an Institutional Links grant 351983438 (the grant is funded by the British Council and the Ministry of Science and Higher Education of the Russian Federation).

Introduction:

Membrane distillation has become a rapidly developing process with remarkable potential for treating highly saline waters, such as produced waters and reverse osmosis brine. However, due to the lack of suitable high flux membrane with both anti-wetting and anti-fouling properties, MD has not yet been well applied at the industrial level. In this study, a novel inner super-hydrophobic and external hydrophilic membrane was fabricated, characterized and applied in DCMD for highly saline water with oil and surfactant. Its high flux, anti-wetting and anti-fouling properties were investigated and explained.

Methods:

ZnO nanoparticles were in-situ grown on PVDF electrospun membrane (pristine) and later fluorinated to get inner superhydrophobic layer (FZP). Polydopamine was then deposited on outer sides of FZP. Inner super-hydrophobic and external hydrophilic membrane (PFZP) was thus obtained and characterized. DCMD experiments were conducted for several cycles (each lasted 10 h). The feed solutions of 10 g/L NaCl with and without surfactant-stabilized oil were used.

Results:

For 10 g/L NaCl solution, pristine membrane (~10 kg/m²h) only lasted 2 cycles while PFZP with higher flux of 18.6 kg/m²h lasted 5 cycles. This was due to the internal super-hydrophobicity and higher LEP of PFZP. For 10 g/L NaCl solution with surfactant-stabilized oil, PFZP lasted 3 cycles; while pristine membrane only lasted 20 min, and commercial HVHP and GVHP (Millipore) also lasted less than 40 min.

Discussion：

Our study confirmed that the hydrophilic layer facing feed solution with water contact angle (CA) of 41.2° and underwater oil CA of 126.5° could provide the membrane anti-fouling property for low surface tension organic contaminants; the hydrophilic layer facing permeate side could enhance membrane flux; and the inner super-hydrophobic layer ensures its anti-wetting and long life-time for MD. The novel sandwich-like PFZP membrane has promising potential in DCMD for highly saline water with surfactant-stabilized oil.

The foulant-membrane hydrophobic attraction could result into severe membrane fouling/wetting issue to restrict the application of membrane distillation (MD). Many interesting, tailor-made MD membranes originate from the surface special wettability, whereas the foulant-membrane charge effect, supposedly to also affect the membrane fouling issue, is rarely studied. This work is to confirm a hypothesis that foulant-membrane charge repulsion is un-negligible and a novel anti-fouling membrane design based on it could be insightful.

A functional layer of CNT was homogeneously sprayed on the commercial PVDF hydrophobic micro-sized membrane to form an electrically conductive top surface with tuneable wettability due to the slight hydrophilic or hydrophobic additives. Then the as-prepared membrane was used as membrane cathode in a novel electricity-assisted DCMD module. Concentrated hexadecane in water emulsions (up to 2000 ppm) were used to challenge the membrane anti-fouling performance at different applied potentials.

Given no cell voltage applied, both the modified membranes (PVDF-M-CNT) exhibited a clearly slower flux decline compared to the pristine membrane (PVDF-V), with the hydrophilic CNT layer superior than the hydrophobic counter-part regarding the anti-oil fouling performance. Interestingly, given a cell potential from 1 to 3V, the superiority of PVDF-M-CNT was further improved, capably leading to a negligible flux decline. The robustness of electricity-assisted anti-fouling performance was confirmed in long-term operation and comparatively analysed regarding the membrane wettability. The increased negative surface charge of the membrane cathode is assumed to give a significant energy barrier to contributing to the anti-fouling performance.

Agreeing with the acknowledged significance of surface wettability in MD, our work shows the foulant-membrane charge interaction should not be neglected which has potential to reduce membrane fouling/wetting. Incorporation of small electricity input could be interesting as novel anti-fouling strategy to maximize the foulant-membrane charge repulsion towards the process long-term robustness.

Fouling and scaling for hydrophobic membranes has been one of the most important puzzles of membrane distillation (MD). In the last decade, tremendous effects on mitigation strategy lead to design of superhydrophobic or omniphobic membranes. Contemporary understanding of fouling/scaling for hydrophobic membranes has been adopted from hydrophilic membranes. Thermodynamic analysis indicates that increasing membrane hydrophobicity can decrease fouling/scaling formation. But, results sometimes are contradictory and frequently superhydrophobic membrane showed negligible or even detrimental effect on fouling/scaling mitigation.

The fundamental assumption of conventional fouling/scaling theory has been based on zero velocity at a solid-liquid interface. For a superhydrophobic membrane, we adopted a new view of slip at a liquid-solid-air interface. The new concept is based on Navier’s model suggesting that the flow velocity at the liquid-solid-gas interface is above zero (Fig. 1 right). By utilizing this model, we transformed the previous thermodynamic basis to a new hydrodynamic foundation in analysis of the fouling/scaling behavior of a superhydrophobic membrane in MD. In this study, the mechanism, validation, limits and opportunities of slippy surface in fouling mitigation will be discussed.

Fig. 1 (Left) Schematic for fabricating the micro-pillar PVDF membrane. (Right) Sketch of the slip length

Reference:

[1] Z. Xiao, R. Zheng, Y. Liu, H. He, X. Yuan, Y. Ji, D. Li, H. Yin, Y. Zhang, X.-M. Li, T. He, Slippery for scaling resistance in membrane distillation: a novel porous micropillared superhydrophobic surface, Water Research, 155 (2019) 152-161.

[2] Z. Xiao, Z. Li, H. Guo, Y. Liu, Y. Wang, H. Yin, X. Li, J. Song, L.D. Nghiem, T. He, Scaling mitigation in membrane distillation: From superhydrophobic to slippery, Desalination, 466 (2019) 36-43.

[3] J. Wang, H. He, M. Wang, Z. Xiao, Y. Chen, Y. Wang, J. Song, X.M. Li, Y. Zhang, T. He, 3-[[3-(Triethoxysilyl)-propyl] amino] propane-1-sulfonic acid zwitterion grafted polyvinylidene fluoride antifouling membranes for concentrating greywater in direct contact membrane distillation, Desalination, 455 (2019) 71-78.

[4] Y. Chen, R. Zheng, J. Wang, Y. Liu, Y. Wang, X.-M. Li, T. He, Laminated PTFE membranes to enhance the performance in direct contact membrane distillation for high salinity solution, Desalination, 424 (2017) 140-148.

[5] Y. Chen, M. Tian, X. Li, Y. Wang, A.K. An, J. Fang, T. He, Anti-wetting behavior of negatively charged superhydrophobic PVDF membranes in direct contact membrane distillation of emulsified wastewaters, Journal of Membrane Science, 535 (2017) 230-238.

Funding sources: NSFC(21676290、21978315、51861145313、21808236）and Newton Advanced Research Fellowship (NA170113）

The full implementation of membrane distillation (MD) for treatment of low surface tension industrial oily wastewaters is still hindered mainly due to major membrane issues such as wetting and fouling. In this study, a hierarchically assembled superomniphobic membrane with three levels of re-entrant structure was designed and fabricated to enable effective treatment of low surface tension, hypersaline oily wastewaters using direct contact MD. The overall structure is a combination of macro corrugations obtained by surface imprinting, micro spherulites morphology achieved through the applied modified phase inversion method and nano patterns obtained by fluorinated Silica nanoparticles (SiNPs) coating (Fig. 1). This resulted in a superomniphobic membrane (SOM) surface with remarkable anti-wetting properties repelling both high and low surface tension liquids.

Measurements of contact angle (CA) with DI water, an anionic surfactant, oil, and ethanol demonstrated a robust wetting resistance against low surface tension liquids showing both superhydrophobicity and superoleophobicity (Fig. 2). CA values of 160.8 ± 2.3° and 154.3 ± 1.9° for water and oil were obtained, respectively. Calculations revealed a high liquid-vapor interface for the fabricated membrane with more than 89% of the water droplet contact area being with air pockets entrapped between adjacent SiNPs and only 11% in contact with the solid membrane surface (Fig. 3). The high liquid-vapor interface endued the membrane with high liquid repellency, self-cleaning and slippery effects, characterized by a minimum droplet-membrane interaction and complete water droplet bouncing on the surface within only 18 milliseconds (Fig. 4). When tested in DCMD with synthetic hypersaline oily wastewaters, the fabricated SOM showed stable, non-wetting MD operation over 24 h, even at high concentrations of low surface tension 1.0 mM Sodium dodecyl sulfate and 400 ppm oil, potentially offering a sustainable option for treatment of low surface tension oily industrial wastewater.

Fig. 1. Hierarchically structured superomniphobic MD membrane.

Fig. 2. Wetting characteristics of the surface of commercial, superhydrophobic corrugated (SCM), and superomniphobic (SOM) membranes in terms of their contact angle with DI water, 5mM SDS, vegetable oil, and ethanol (A) immediately after the droplet was placed on the surface and (B) after 3 min of placing the droplet, along with (C) photographic images of the droplets on the membrane surface and (D) robustness of the SOM characterized by its CAs with DI water, 5mM SDS, vegetable oil, and ethanol before and after being subjected to physical and chemical stresses.

Fig. 3. (A) Images of the SOM liquid-repelling (1-2) and self-cleaning (3-4) properties, (B) estimation of the areas of solid-liquid and air-liquid interfaces on a projected area of unity for the commercial, SCM, and SOM along with (C) their schematic illustration of contact area between water droplet and the surface.

Fig. 4. Surface behavior upon first membrane surface interaction with a falling water droplet. (A) Images of a flat SOM droplet-bouncing showing two complete consecutive droplet bounces within 26 (frames 1-7) and 18.6 (frames 9-12) ms, for the first and second bounces, respectively. (B) Images of the SOM showing combined bouncing and slipping effect of a split water droplet. (C) The slipperiness of the SOM surface characterized by fast droplet movement away from the surface.

Proton exchange membrane fuel cell (PEMFC) is an energy conversion device that directly converts the chemical energy of a fuel into electricity and heat. The heart of a PEMFC, namely membrane electrode assembly (MEA) is composed of a polymer electrolyte membrane (PEM), 2 catalyst layers (CL) and 2 gas diffusion layers (GDL). There are two methods for making a MEA which is either coating an electrode directly on membrane or on GDL. The approach of making a MEA depends on electrode inks and coating techniques.

Although there is a lot of studies about the composition of electrode ink for improving PEMFC performance, there is only a few papers dealing with the homogeneity and thickness of catalyst coating layer and its impact on PEMFC performance.

In this work, we attempt to understand the relationship between the morphology of catalyst coating layer and its performance in PEMFC. For this purpose, we made some catalyst coating membranes (CCMs) using a commercial ultrasonic spray bench. After having optimized the spraying method, the coating surface and thickness of CCMs were characterized using SEM and profilometer techniques. The performance of CCMs were compared via CV curves obtained with a homemade fuel cell bench (figure 1).

Results show that the amount of Pt loading is not a key parameter for increasing the performance of a PEMFC. This latter depends mostly on the thickness of the coating layer, the ratio of Pt/C and the gas stoichiometry.

Figure 1. Roadmap of the work

Solid oxide fuel cells (SOFCs) have been highlighted as candidates to replace the current lithium ion battery market due to their high efficiency, fuel flexibility and environmentally friendly characteristics. However, due to the high operating temperature of SOFCs, there are critical disadvantages, such as material selection and component degradation. In order to lower the high operating temperature, it is necessary to reduce the ohmic loss and activation loss that will increase as the temperature is lowered. One way to reduce the ohmic loss is to apply materials with high ionic conductivity even at low temperatures, and reduce the thickness of the electrolyte.

In this work, CeO2 thin film was fabricated by plasma-enhanced atomic layer deposition (PEALD) as a preceding step for the fabrication of doped-ceria material thin films. Oxygen plasma was used to oxidize the precursor to widen the ALD window and to produce the highly crystalline CeO2 thin film. The growth rate of CeO2 was determined by controlling precursor and oxidizer exposure time, and the thickness of thin film per cycle was confirmed. The surface morphology was observed by scanning electron microscope (SEM), and dense and pinhole-free thin film surface was confirmed. In addition, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses were performed and the characteristic crystalline peaks and chemical compositions were compared with those of the thermal ALD CeO2 thin films. Fabricated CeO2 thin film was deposited between electrolyte and the cathode as an interlayer. Electrochemical performance was measured at 500℃ and increased compared to no interlayer cell. Electrochemical impedance spectroscopy (EIS) was investigated to determine the reasons of performance improvement of CeO2 interlayer cell.

Poly(tetrafluoroethylene) (PTFE) is an attractive membrane material due to its excellent thermostability, superior chemical resistance and high mechanical strength. However, the poor wettability of PTFE to liquid electrolyte impeded its utilization in Li ions battery (LIB). In this work, the PTFE porous membrane was modified into a LIB separator with higher affinity to electrolyte by the hybrid of polyethylenemine (PEI) and tetraethyl orthosilicate (TEOS), which can be in-situ biomineralized into SiO₂ nanoparticles. The prepared PTFE/PEI-SiO₂ separator showed a dynamic electrolyte contact angle decreased from 50.3° to 0° within 4s, along with 215% of the electrolyte uptake. The ionic conductivity and the interfacial resistance of the CR2032 cell equipped with the PTFE/PEI-SiO₂ separator was 9.12 mS/cm and 119.8Ω, respectively. In addition, the cell with the separator showed capacity of 163.5 mAh·g^-1 and a good cycle stability with capacity retention of 90.1% after 50 cycles, along with 98.3% capacity recovery. Especially, the cell with the PTFE/PEI-SiO₂ separator exhibited good thermal stability with 156.2 mAh·g^-1 of capacity after annealed at 120°C for 12 hours.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (21878003) and the National Natural Science Fund for Innovative Research Groups (Grant No. 51621003).

Antibiotics are reported from ng.L^-1 to mg.L^-1 in water, urban sewage and industrial wastewater. Conventional treatment processes can only partially remove these compounds, while membrane separation processes can obtain water for reuse. This study evaluates the performance of 2 nanofiltration membranes with different MWCO (Filmtec NF270 and Alfa Laval NF97), in experiments carried out in concentration mode, for the removal of norfloxacin (NOR) and sulfamethoxazole (SMX) from a sewage sample, collected on the outlet of the municipal effluent treatment plant of Porto Alegre, Brazil, which contains primary and secondary treatment (activated sludge). To these collected samples, with pH close to neutrality, were added 10 mg.L^-1 of each of the studied antibiotics. Sewage samples with added antibiotics were treated by NF at 6 bar and with a feed flow rate of 480 L.h^-1. For comparison purposes, synthetic solutions, prepared with NOR and SMX diluted in deionized water, were also treated under the same operating conditions. Working with synthetic solutions and achieving a 70% water recovery rate, the treatment with NF270 and NF97 membranes resulted in 42 and 16 L.h^-1.m^-2 permeate fluxes, 77% and 95% SMX as well as 95% and 98% NOR rejections, respectively. Considering the same water recovery rate, on the sewage treatment the permeate fluxes were slightly lower, 38 and 13 L.h^-1.m^-2, but the rejections were higher, being 97% SMX and NOR for the NF270 and 98% SMX and NOR for the NF97 membranes. In conclusion, the aqueous matrix affected the results. Since the sewage had a certain organic matter content (COD ~ 200 mg.L^-1), lower permeate fluxes were obtained, once this organic matter contributed to the incidence of concentration polarization and fouling. However, the organic matter also contributed to a greater rejection of antibiotics during nanofiltration, especially with the NF270 membrane, which is characterized as a broadband membrane.

Very large-scale molecular dynamics (MD) simulations have been aimed at studying mixed-gas transport of oxygen, nitrogen, carbon dioxide and methane in explicit dense polymer films. Air O₂/N₂ separation and natural gas CO₂/CH₄ sweetening are two of the most studied gas separations. Together, they represent more than half of the market. MD simulations of mixed-gas separation by macromolecular membranes are still rare, but they are obviously very pertinent with respect to experimental characterizations and industrial applications.

The glassy matrices were modelled as 50000-atom 6FDA-6FpDA polyimide thin-films, i.e. much larger than standard models, and with explicit reservoirs at either end. These large sizes prevented artefacts due to poor sampling. In a first step, air (Figure on left with N₂ in blue and O₂ in red) was inserted into the reservoirs at various pressures up to 50 bar. Both the sorption and the selective transport of O₂ and N₂ were simulated up to over 300 ns, i.e. 15-150 times longer than standard MD simulations. This allowed for the sorption of each gas to attain equilibrium, which was especially critical for N₂. This important increase in model size and timescale amounted to a total simulation time of ~700 000 CPU hours.

In a second step, CH₄ (5 bar) was inserted into the reservoirs along with molar fractions of CO₂ amounting to up to 20%. These simulations have now reached over 200 ns (Figure on right with CH₄ in purple/white and CO₂ in red/yellow) and are still undergoing.

Model characterizations will include for both O₂/N₂ and CO₂/CH₄ separations: the effects of their simultaneous sorption on the polymer, their solubility and diffusion selectivities, their low-energy sites, their trajectories along with their crossing times. We will show that state-of-the-art MD is able to efficiently complement experiments, which are particularly difficult and time-consuming under mixed-gas conditions.