Increase In CO2 Permeability Research Articles

Interpenetrating networks of mixed matrix materials comprising metal-organic polyhedra for membrane CO2 capture

Mixed matrix materials (MMMs) comprising porous fillers in polymers can exhibit superior gas separation properties, yet their practical use has been limited by poor interfacial compatibility between the two components. Herein we report a bottom-up approach to synthesize the MMMs by dispersing a metal-organic polyhedron (MOP-3) in monomer solutions before rapid photopolymerization to form interpenetrating networks (IPNs), where the porous MOP-3 nanoparticles serve as molecular dopants. Specifically, MOP-3 with particle sizes of ≈5 nm was dispersed in and infiltrated by either a macromonomer of poly(ethylene glycol) diacrylate (PEGDA) or poly(1,3 dioxolane) acrylate (PDXLA). The introduction of the MOP-3 in the polyethers decreases their glass transition temperatures and even induces the crystallization of polyPDXLA at high loadings. Increasing the MOP loading increases CO2 permeability with a slight decrease in CO2/gas selectivity. For example, as the MOP content increases from 0 to 30 mass% in polyPDXLA, CO2 permeability increases from 190 Barrer to 580 Barrer, and CO2/N2 selectivity decreases from 70 to 62 at 35 °C. These IPNs-based MMMs exhibit separation properties above the Robeson's upper bounds for CO2/N2 and CO2/H2 separation. As the MOPs are soluble in solvents, this approach can be easily integrated into industrial membrane fabrication processes to produce MMMs-based composite membranes in large-scale.

High gas permeability of nanoZIF-8/polymer-based mixed matrix membranes intended for biogas purification

Abstract The production of biomethane from the biogas purification process depends on the capacity of the separation technique employed to separate methane from carbon dioxide. Mixed matrix membranes (MMMs) combine the benefits of polymeric and inorganic materials, and it is believed that the trade-off between gas permeability and selectivity in polymeric membranes can be hampered by MMMs. Until recently, the development of MMMs for the biogas purification process has been constrained in lab scales. To be applied in large scales, the increase in gas permeability as well as the membrane performance under the influence of CO2 plasticization needs to be investigated. This paper reports the evaluation of gas permeability and CO2/CH4 gas separation performances of nano zeolitic imidazolate framework (ZIF)-8/Pebax-1657 to be used for biogas purification processes. In addition, the study on the CO2 plasticization behavior of MMMs fabricated with co-polymer Pebax was investigated. The incorporation of nanoZIF-8 particles inhibited the increase of CO2 permeability due to the reduced polymer flexibility. In addition, the diffusional selectivity of ZIF-8 improves the permeation behavior of both gases through MMMs. With nanoZIF-8/Pebax-1657 MMMs, the incorporation of particles improves the gas permeability with a slight decrease in gas selectivity, indicating a potentiality of the membranes used for biogas purification processes.

Glassy PEEK-WC vs. Rubbery Pebax®1657 Polymers: Effect on the Gas Transport in CuNi-MOF Based Mixed Matrix Membranes

Mixed matrix membranes (MMMs) are seen as promising candidates to overcome the fundamental limit of polymeric membranes, known as the so-called Robeson upper bound, which defines the best compromise between permeability and selectivity of neat polymeric membranes. To overcome this limit, the permeability of the filler particles in the MMM must be carefully matched with that of the polymer matrix. The present work shows that it is not sufficient to match only the permeability of the polymer and the dispersed phase, but that one should consider also the individual contributions of the diffusivity and the solubility of the gas in both components. Here we compare the gas transport performance of two different MMMs, containing the metal–organic framework CuNi-MOF in the rubbery Pebax®1657 and in the glassy poly(ether-ether-ketone) with cardo moiety, PEEK-WC. The chemical and structural properties of MMMs were investigated by means of FT-IR spectroscopy, scanning electron microscopy and EDX analysis. The influence of MOF on the mechanical and thermal properties of both polymers was investigated by tensile tests and differential scanning calorimetry, respectively. The MOF loading in Pebax®1657 increased the ideal H2/N2 selectivity from 6 to 8 thanks to an increased H2 permeability. In general, the MOF had little effect on the Pebax®165 membranes because an increase in gas solubility was neutralized by an equivalent decrease in effective diffusivity. Instead, the addition of MOF to PEEK-WC increases the ideal CO2/CH4 selectivity from 30 to ~48 thanks to an increased CO2 permeability (from 6 to 48 Barrer). The increase in CO2 permeability and CO2/CH4 selectivity is maintained under mixed gas conditions.

Plant extracts such as pine nut shell, peanut shell and jujube leaf improved the antioxidant ability and gas permeability of chitosan films

In order to develop the antioxidant and gas permeability packaging film, the effects of three plant extracts (pine nut shell, peanut shell and jujube leaf) on the physical, antioxidative and structural properties of chitosan based biodegradable films were studied. The results showed that three plant extracts improved the antioxidant capacity of films. The DPPH radical scavenging activity of chitosan-jujube leaf films increased by 3.8 times compared with the control films. The chitosan-pine nut shell films had the highest water vapor and oxygen permeability, while chitosan-peanut shell films showed greatest increase in CO2 permeability with a value of 1.71 × 104 cm3/(m2·24h) under standard test. In addition, three plant extracts reduced the homogeneity and caused porous structure of chitosan films. Chitosan-peanut shell films had the highest thermal stability compared with the control and other two films. X-ray diffraction and FTIR indicated three plant extracts changed the hydrogen bonding of film matrix and caused the changes of crystal and chemical structure. The study provided a reference for the preparation of polysaccharide-based active films with strong antioxidant and gas permeability.

Using lantern Zn/Co-ZIF nanoparticles to provide channels for CO2 permeation through PEO-based MMMs

To reduce the diffusion resistance of CO2 and enhance its permeability in mixed matrix membranes (MMMs), lantern Zn/Co-ZIF nanoparticles were loaded in-situ into semi-interpenetrating cross-linked poly(ethylene oxide) (XLPEO) membranes to provide efficient channels for CO2 permeability. TEM and SEM results showed that the Zn/Co-ZIF nanoparticles (diameter 490–550 nm) treated at 145 °C possessed a lantern structure with hollow cores (diameter 380–450 nm) and thin shells (thickness 20–85 nm). XRD and BET results indicated that the nanocrystal structure and porosity of the Zn/Co-ZIF remained intact after etching at 145 °C. Peaks shifts in the infrared spectra confirmed that the Zn/Co-ZIF nanoparticles were well integrated with the XLPEO membrane through hydrogen bonds. Therefore, doping 15 wt% lantern Zn/Co-ZIF nanoparticles into the membrane dramatically increased CO2 permeability by 72% to 761.9 ± 3.0 barrers, while the CO2/N2 selectivity was above the upper bound established by Robeson in 2008.

Modulator-Mediated Functionalization of MOF-808 as a Platform Tool to Create High-Performance Mixed-Matrix Membranes.

Modulator-mediated functionalization (MoFu) is introduced as a new and versatile platform tool to improve the separation performance of metal-organic framework (MOF)-based membranes, exemplified here by the creation of mixed-matrix membranes (MMMs) with enhanced CO2 separation efficiency. The unique structure of MOF-808 allows incorporation of CO2-philic modulators in the MOF framework during a one-pot synthesis procedure in water, thus creating a straightforward way to functionalize both MOF and corresponding MMM. As a proof of concept, a series of fluorinated carboxylic acids [trifluoroacetic acid (TFA), pentafluoropropionic acid (PFPA), and heptafluorobutyric acid (HFBA)] and nonfluorinated alkyl carboxylic acids (acetic acid (AA), propionic acid (PA), and butyric acid (BA)) were used as a modulator during MOF-808 synthesis. Two of the best MMMs prepared with 30 wt % MOF-TFA (100% increase in CO2/CH4 separation factor, 350% increase in CO2 permeability) and 10 wt % MOF-PFPA (140% increase in CO2/CH4 separation factor, 100% increase in CO2 permeability) scored very close to or even crossed the 2008 and 2018 upper bound limits for CO2/CH4. Because of its facile functionalization (and its subsequent excellent performance), MOF-808 is proposed as an alternative for widely used UiO-66, which is, from a functionalization point-of-view and despite its widespread use, a rather limited MOF.

Improved CO2 transport properties of Matrimid membranes by adding amine-functionalized PVDF and MIL-101(Cr)

The effect of addition of ammoniated PVDF (NH2-PVDF) and amine-functionalized metal organic framework (MOF) NH2-MIL-101(Cr) were investigated on the gas permselectivity and plasticization behavior of Matrimid-based membranes for CO2/CH4 separation. The NH2-PVDF was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The NH2-MIL-101(Cr) nano-sized particles were synthesized and investigated via XRD, field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller (BET) and dynamic light scattering (DLS). Then, the particles were dispersed in Matrimid/NH2-PVDF blend to produce ternary mixed matrix membrane (MMM). The membrane microstructures were examined by FTIR and XRD, while the uniform particle dispersion was confirmed by FESEM. Differential scanning calorimetry (DSC) showed that the Matrimid/NH2-PVDF blend is miscible up to 3 wt% of NH2-PVDF and the glass transition temperature increased with MOF content. Single-gas permeability measurements revealed that the best separation performance was obtained for the blend membrane with 3 wt% of NH2-PVDF with increased CO2 permeability and CO2/CH4 ideal selectivity by 39% and 33% respectively, over the neat Matrimid values. Much higher improvements (125% and 136% respectively) were obtained when 5 wt% of NH2-MIL-101(Cr) was added. Also, the plasticization pressure was increased from 12 to 26 bar by adding 3 wt% of NH2-PVDF and 7 wt% of MOF in the neat Matrimid.

Fabrication of Amino-Functionalized CAU-1/Cellulose Acetate Mixed Matrix Membranes for CO<sub>2</sub>/N<sub>2</sub> Separation

In this work, a new type of mixed matrix membranes comprising of amino-functionalized CAU-1 as filler and cellulose acetate as polymer phase were fabricated for CO2 separation from N2. The crystallinity and morphology of the resultant fillers were verified by using X-ray diffraction (XRD) and scanning electron microscope (SEM). The energy-dispersive X-ray (EDX) results showed that, sedimentation and agglomeration of fillers were found at loading of more than 5 wt%. Subsequently, the gases permeation results revealed that, an increase in CO2 permeability and CO2/N2 selectivity of 149% and 81%, respectively, were achieved for the membrane loaded with 5 wt% of CAU-1-NH2, as compared to pure cellulose acetate membrane.

Enhancing the CO2 Separation Performance of Matrimid 5218 Membranes for CO2/CH4 Binary Mixtures

AbstractThe effect of CO2‐philic additive polyethylene glycol (PEG) 200 in Matrimid 5218 on the separation performance of prepared membranes was evaluated in a binary gas mixture. Matrimid/PEG 200 flat‐sheet blended membranes with low PEG concentrations were prepared by the dense film‐casting method. Pure Matrimid and blended membranes were characterized by FTIR spectroscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and permeation measurements. The addition of 4–5 % of PEG enhanced considerably the CO2 permeability of the Matrimid matrix. The best formulation, Matrimid/PEG 200 (96/4), showed in comparison to pure Matrimid a more than threefold increase in CO2 permeability and an increase in separation factor of about 40 %.

Open-cocoon zeolitic imidazolate framework nanoparticles introduce low-resistance path for CO2 transport in crosslinked poly(ethylene oxide) membrane

To break through the permeability-selectivity trade-off in solution-diffusion membranes, novel three-dimensional hollow zeolitic imidazolate framework (ZIF) nanoparticles like open cocoons were built and then in-situ embedded in cross-linked poly(ethylene oxide) backbone by a simple one-step untraviolet polymerization. Those nanoparticles, which were evenly distributed in the polymer, acted as a “CO2 transport promoter” and developed low-resistance inner channels for CO2 Knudsen diffusion in the solution-diffusion membrane. Simultaneously, embedded nanoparticles broke the crosslinking of poly(ethylene oxide), thereby reducing the crystallinity of the polymer and then increasing the flexibility of polymer chains. Therefore, adding open-cocoon ZIF nanoparticles exponentially increased CO2 permeability with small changes in CO2/H2, CO2/CH4 and CO2/N2 selectivity. Specifically, adding 10 wt% open-cocoon ZIF nanoparticles in the polymer increased CO2 permeability by ∼190%, from ∼ 130 Barrers to ∼373 Barrers, with a 15% increase in CO2/H2 selectivity and a 10% decrease in CO2/N2 selectivity.

Facilitating CO2 Transport Across Mixed Matrix Membranes Containing Multifunctional Nanocapsules.

Mixed matrix membranes (MMMs) have exhibited advantages in overcoming the trade-off effect, although it is still intensively demanded in the design of multifunctional fillers to improve CO2 separation performance. At present, MMMs with transport channels present an effective strategy to obtain ultrahigh CO2 permselectivity. In this work, Pebax-based MMMs was fabricated by incorporating nanocapsules (NCs), whose exterior, interior and transverse shell surfaces contained abundant carboxylic acid groups. NCs, similar to vesicles in cells, provide favorable physical and chemical microenvironments to the constructed CO2 transport channels, enhancing the CO2 permselectivity via both a facilitated transport mechanism and a solution-diffusion mechanism. CO2 permselectivity of MMMs doped with 20 wt % NCs surpassed the 2008 Robeson limit; an increase in CO2 permeability was up to 1431 ± 35 Barrer for pure gas, which was a 362% enhancement from the pure membrane, and an increase of the CO2/CH4 and CO2/N2 ideal selectivities to 46 ± 1.4 and 69 ± 2.7, corresponding to 44% and 23% enhancements from the pure membrane, respectively. This study provides an ingenious strategy to enhance the gas permselectivity of MMMs.

Block copolymer membranes with catecholic bolaamphiphile assemblies

We report the first use of the assemblies of catecholic bolaamphiphilic compound, i.e., bis-(N-α-amido-3,4-dihydroxyphenylalanine)−1,7-heptane dicarboxylate (DOPA-C7), as an organic filler for gas separation membranes. Specifically, the membranes were prepared by adding the assembly fillers to a block copolymer matrix, i.e., nonpolar polystyrene-b-polybutadiene-b-polystyrene (SBS) or polar poly (ether-b-amide) (PEBAX). The interaction between the filler and matrix was investigated regarding the structure, morphology, and CO2/N2 separation performance. The strongly interacting PEBAX/DOPA-C7 membranes showed a typical trade-off behavior, i.e., a decrease in CO2 permeability and increase in CO2/N2 selectivity with the filler contents. In contrast, the weakly interacting SBS/DOPA-C7 interestingly showed an improved CO2/N2 selectivity, from 14.1 to 21.1, with a slight increase in CO2 permeability (from 347.5 to 349.7 Barrer) owing to the catechol group of DOPA-C7 that can function as a Lewis base. This indicates that very strong interactions between the polymeric matrix and filler could have a negative impact on the gas separation performance. This work not only explores the importance of a polymer matrix, but also opens up the feasibility of using a catecholic compound in gas separation membranes.

The performance of affordable and stable cellulose-based poly-ionic membranes in CO2/N2 and CO2/CH4 gas separation

The majority of commercial membrane units for large-scale natural gas sweetening are based on cellulose acetate (CA). However, the low selectivity and risk for and plasticisation affect adversely the performance of CA-based systems. Herein, we present a new class of CA-derived poly(ionic liquid) (PIL) as a thin film composite (TFC) membrane for CO2 separations. CA is modified with pyrrolidinium cations through alkylation of butyl chloride, substituting the hydroxyl group in the polymer backbone, and further anion exchange to bis(trifluoromethylsulfonyl)imide, P[CA][Tf2N]. The synthesised PIL material properties are extensively studied. The CO2 separation performance of the newly synthesised materials is evaluated by gravimetric gas sorption experiments, single gas time-lag experiments on thick membranes, and mixed-gas separation experiments on TFC membranes. The results are compared to the parent material (CA) as well as a reference PIL (poly(diallyldimethyl ammonium) bis(trifluoromethylsulfonyl)imide (P[DADMA][Tf2N])). The ideal CO2/N2 sorption selectivity of P[CA][Tf2N] is constant up to 10 bar. The single gas transport measurements in P[CA][Tf2N] reveal improved ideal CO2 selectivity for the CO2/N2 gas pair and increased CO2 permeability for the CO2/CH4 gas pair compared to the reference PIL. Mixed-gas permeation tests demonstrated that P[CA][Tf2N]-based membranes with a 5 µm thick selective layer has a two-fold higher CO2 flux compared to conventional CA. These results present CA modification into PILs as a successful approach promoting the higher permeate flows and improved process stability in a wide range of concentrations and pressures of CO2/N2 and CO2/CH4 gas mixtures.

Mixed-matrix membranes containing nanocage-like hollow ZIF-8 polyhedral nanocrystals in graft copolymers for carbon dioxide/methane separation

Abstract Nanocage-like, hollow ZIF-8 (H-ZIF) polyhedral nanocrystals were synthesized via the use of seed crystals, epitaxial ZIF-8 growth, and excavation of ZIF-67 sacrificial templates. The highly porous and hollow structure of the H-ZIF polyhedral nanocrystals was confirmed by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction (XRD), and Brunauer-Emmett-Teller analysis. The H-ZIF nanocrystals were distributed in an amphiphilic poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer matrix to form mixed-matrix membranes (MMMs) for CO2/CH4 separation. The microphase-separated nature of the structure of the PVC-g-POEM was induced by the solubility difference between the hydrophobic PVC backbone and the hydrophilic POEM side chains. Specific interactions between the micro-structured PVC-g-POEM polymer matrix and the imidazole moiety of the H-ZIF enhanced the interfacial contact and improved the dispersion of the H-ZIF within the MMM; this was confirmed by XRD, FE-SEM, and differential scanning calorimetry. The hollow structure of the H-ZIF reduced the gas diffusion resistance of the MMM, resulting in increased gas permeability. Moreover, the molecular sieving properties and CO2-philic amine groups in the imidazole linkers of the H-ZIF led to high CO2 separation performance. The PVC-g-POEM/H-ZIF MMM exhibited an approximately fivefold increase in CO2 permeability, with a value of 210.6 barrer, compared to 43.5 barrer for a pristine PVC-g-POEM membrane with a CO2/CH4 selectivity of 14.3, which is close to upper bound reported by Robeson in 2008.

Highly permeable mixed matrix materials comprising ZIF-8 nanoparticles in rubbery amorphous poly(ethylene oxide) for CO2 capture

Abstract Amorphous polymers containing poly(ethylene oxide) are leading membrane materials for CO2 capture from fossil fuel-derived flue gas and syngas, such as those prepared from poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) methyl ether acrylate (PEGMEA). This work shows that introduction of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles in these polymers increases CO2 permeability with minimal effect on CO2/H2 and CO2/N2 selectivity. Specifically, ZIF-8 nanoparticles with a size of 150–250 nm were synthesized and fabricated into mixed matrix materials (MMMs). The effect of ZIF-8 loading on gas transport properties at 35 °C in MMMs was systematically investigated. Adding 10 wt% ZIF-8 in the crosslinked PEGDA increases CO2 permeability from 130 Barrers to 320 Barrers unexpectedly by 170% without any reduction of CO2/light gas selectivity. While the CO2/light gas selectivity in the MMMs can be satisfactorily described using the Lewis-Nielsen model, the model underestimates the gas permeability. Despite a body of studies of MMMs comprising ZIFs, this work represents one of the few on the MMMs based on amorphous rubbery polymers elucidating the effect of ZIF-8 loading on the polymer properties and demonstrating their impact in achieving superior CO2/H2 and CO2/N2 separation properties.

CO 2 /N 2 gas separation using Fe(BTC)-based mixed matrix membranes: A view on the adsorptive and filler properties of metal-organic frameworks

Abstract The incorporation of a Metal-Organic Framework (MOF), Fe(BTC), into a polymeric membrane was assessed for CO2/N2 gas separation. The adsorptive and filler properties of the MOF in the Mixed Matrix Membranes (MMMs) produced were investigated as a strategy to separate CO2 from N2 and contribute to reduce CO2 emissions. Therefore, Fe(BTC) was firstly characterized by single-component adsorption equilibria measurements of CO2 and N2, to evaluate the MOF performance as an adsorbent for CO2/N2 separation and its adsorption role in the MMMs performance. Fe(BTC) was then incorporated in Matrimid®5218 at different loading percentages, and the MMMs produced were characterized by distinct techniques (SEM, TGA, puncture tests and contact angle essays). Finally, pure gas permeation experiments were carried out for CO2 and N2 at 303 K, 323 K and 353 K, to evaluate the temperature impact on both gas permeability and CO2/N2 ideal selectivity. The results show that an increase in CO2 permeability and CO2/N2 ideal selectivity can be advantageously achieved, especially at the higher operating temperature of 353 K. At these conditions, the Robeson upper-bound is surpassed, which is a clear indication of the high potential of using Matrimid®5218/Fe(BTC) MMMs in post-combustion streams at high-temperatures.

Mixed matrix membranes with fast and selective transport pathways for efficient CO2 separation

To improve CO2 separation performance, porous carbon nanosheets (PCNs) were used as a filler into a Pebax MH 1657 (Pebax) matrix, fabricating mixed matrix membranes (MMMs). The PCNs exhibited a preferential horizontal orientation within the Pebax matrix because of the extremely large 2D plane and nanoscale thickness of the matrix. Therefore, the micropores of the PCNs provided fast CO2 transport pathways, which led to increased CO2 permeability. The reduced pore size of the PCNs was a consequence of the overlapping of PCNs and the polymer chains penetrating into the pores of the PCNs. The reduction in the pore size of the PCNs improved the CO2/gas selectivity. As a result, the CO2 permeability and CO2/CH4 selectivity of the Pebax membrane with 10 wt% PCNs-loading (Pebax–PCNs-10) were 520 barrer and 51, respectively, for CO2/CH4 mixed-gas. The CO2 permeability and CO2/N2 selectivity of the Pebax–PCNs-10 membrane were 614 barrer and 61, respectively, for CO2/N2 mixed-gas.

Fabrication and investigation of PEBAX/Fe-BTC, a high permeable and CO2 selective mixed matrix membrane

Mixed matrix membranes comprising commercial poly (ether-block-amid) or PEBAX® (1657) as continues phase and Fe-BTC metal organic framework as disperse phase are fabricated via phase inversion method. To investigate membrane structure various analysis including SEM, TGA, DLS and FTIR are performed. CO2 and CH4 permeability and Selectivity are measured for all membranes at 25°C and different pressures from 3 to 25bar. Moreover, mixed gas tests are implemented for 10/90 CO2/CH4 mixture. Cross section SEM images showed proper particles distribution and good interaction between polymer and particles. The replacement of various bounds in FTIR test confirmed the good compatibility of Fe-BTC with polymer matrix too. TGA results showed acceptable thermal resistance of all membranes. Membranes permeability increased with increase in particles loading percent due to high porosity of particles and also high adsorption capacity especially for CO2 molecules. The highest CO2 permeability was belong to PEBAX/Fe-BTC 40wt.% membrane which was 425.4 Barrer. Mixed matrix membranes showed selectivity enhancement too. However, PEBAX/Fe-BTC 20wt.% membrane had the best selectivity of 22.19, in membrane with higher loading percent particles agglomeration made interfacial voids which caused selectivity decrement specially in 40wt.% loading percent. All membranes showed permeability and selectivity growth till 7bar pressures however, selectivity decreased due to plasticization effect at higher pressures of 15 and 25bar. Membrane with 25wt.% loading percent showed 50% and 9% increase in CO2 permeability and selectivity at 7bar compare to base pressure of 3bar.

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

Carbon capture and storage (CCS) using membranes for the separation of CO2 holds great promise for the reduction of atmospheric CO2 emissions from fuel combustion and industrial processes. Among the different process outlines, post-combustion CO2 capture could be easily implemented in existing power plants. However, for this technology to become viable, new membrane materials have to be developed. In this article we present the development of high performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer matrix. The CO2/N2 separation performance was evaluated by mixed gas tests (15CO2:85N2) at 25°C and 1–4bar transmembrane pressure difference. The CO2 membrane permeability was increased by the addition of the ZIF-94 particles, maintaining a constant CO2/N2 selectivity of ~22. The largest increase in CO2 permeability of ~ 200% was observed for 40wt% ZIF-94 loading, reaching the highest permeability (2310 Barrer) at similar selectivity among 6FDA-DAM MMMs reported in literature. For the first time, the ZIF-94 metal organic framework crystals with particle size smaller than 500nm were synthesized using nonhazardous solvent (tetrahydrofuran and methanol) instead of dimethylformamide (DMF) in a scalable process. Membranes were characterized by three non-invasive image techniques, i.e. SEM, AFM and nanoscale infrared imaging by scattering-type scanning near-field optical microscopy (s-SNOM). The combination of these techniques demonstrates a very good dispersion and interaction of the filler in the polymer layer, even at very high loadings.

Evaluation of pectin-reinforced supported liquid membranes containing carbonic anhydrase: The role of ionic liquid on enzyme stability and CO2 separation performance

In this paper, pectin-reinforced, supported liquid membranes (SLMs) prepared with carbonic anhydrase (CA) were investigated for CO2/N2 separation. In the first part of the study, the effect of [Bmim][NTf2] ionic liquid (IL) – as possible solvent to fill the pores of cellulose acetate support during SLM fabrication – on enzyme activity was tested. It turned out that this particular IL caused rapid and severe loss of initial biocatalyst activity, which fact can be seen as a threat in the membrane process design. Afterwards, the stability of pectin-containing SLMs (containing CA but lacking the IL having adverse impact) was addressed and their improved resistance against higher transmembrane pressures (up to 7.2 bar) was found, representing an approx. 3-fold enhancement compared to their control. Thereafter, the performance of the membranes was tested under single and mixed gas conditions with carbon dioxide and nitrogen. Employing single gases, it was demonstrated that CA enzyme could notably increase CO2 permeability (from 55 to 93 Barrer), while that of N2 remained unchanged (1.6-1.7 Barrer). Thus, the highest CO2/N2 theoretical selectivity was attained as 54 using the pectin-reinforced SLMs enriched with CA biocatalyst. For comparison, the outcomes were plotted on the Robeson upper-bound.