Mixed Gas Experiments Research Articles

Effect of Temperature-Induced Aging on the Gas Permeation Behavior of Thin Film Composite Membranes of PIM-1 and Carboxylated PIM-1.

Polymers of intrinsic microporosity (PIMs) are a class of promising gas separation materials due to their high membrane permeabilities and reasonable selectivities. When processed into thin film composite (TFC) membranes, their high gas throughput aligns closely with industrial requirements, but they are prone to physical aging and plasticization effects. TFC membranes based on the prototypical PIM-1 and its carboxylated derivative cPIM-1 exhibit temperature-dependent gas permeation behavior, which has not been extensively studied before. In single CO2 permeation tests, measurable physical aging occurred when the temperature was raised to 55 °C within a period of 90 min, and the aging rate accelerated as temperature was raised further. TFC membranes prepared from cPIM-1 exhibited a faster aging rate compared to PIM-1 at the same temperature. The decreased permeance could be at least partially recovered through a 5 day methanol vapor treatment. In mixed gas experiments, all membranes showed decreased permselectivities at elevated temperatures. The plasticization pressure of TFC membranes occurred at around 1 bar of CO2 partial pressure, independent of temperature. Significant plasticization was particularly evident for cPIM-1 TFC membranes under CO2/CH4 conditions with increasing temperature, which resulted in increased gas permeance for both components.

Gas separation properties of PIM-1 films treated by elemental fluorine in liquid perfluorodecalin

Gas transport properties of PIM-1 films treated by elemental fluorine in a liquid perfluorodecalin were investigated. The investigation included an estimation of fluorine content in a fluorinated layer, pure and mixed gas permeability, diffusion and solubility coefficients measurement, ideal selectivity assessment and analysis of fluorination time effect on gas transport properties. An increase of treatment duration resulted in an increase of concentration of fluorine in the fluorinated layer as well as a depth of fluorination. The depths of fluorination linearly increased with square of fluorination time indicating a diffusion of fluorine in the fluorinated layer to be a restrictive stage of kinetics of fluorination. The effect of the drop in gas permeability was demonstrated to be dependent on the kinetic size of the penetrant. The comparison of liquid-phase and gas-phase regimes was performed, and it was shown that sharp decrease in gas permeability is observed for gas-phase regime at short times of fluorination already, whereas this decrease is more gradual for liquid-phase fluorination. According to a Barrie method, the gas transport parameters of the fluorinated layer of the modified PIM-1 films were calculated, which turned out to be much lower than those for the virgin PIM-1 polymer and slightly lower than the gas transport parameters for dry Nafion. The reduction of the gas permeability coefficients is mostly induced by a sharp decrease in the gas diffusion coefficients. According to combination of permeability and selectivity, the fluorinated PIM-1 samples show excellent results exceeding the 2008 Robeson upper bounds for H2/CH4, H2/CO2, H2/N2, He/CH4 and others gas pairs. Mixed gas experiments were also conducted for hydrogen-containing mixtures and fluorinated PIM-1 samples have demonstrated good separation characteristics for the model binary mixtures attaining separation factors as high as 115–143 (H2/CH4), 4.4–6.7 (H2/CO2) and 49–146 (He/CH4), which makes these materials promising for helium recovery from natural gas and hydrogen recovery from various catalytic and biohydrogen production mixtures. Ten-months aging of the PIM-1 sample fluorinated during 30 min showed a decline of permeability by 25 and 40%, respectively and a slight decrease of ideal selectivity.

CO2 separation using thin film composite membranes of acid-hydrolyzed PIM-1

The polymer of intrinsic microporosity PIM-1 was synthesized with different topologies and negligible network content. A more rapid heating rate from room temperature yielded a predominantly di-substituted PIM-1 (D-PIM-1), whereas a marginally lower heating rate produced a more branched structure (B-PIM-1). Both polymers were acid-hydrolyzed to give carboxylic acid functionalization (cPIM-1), as indicated by FT-IR, 1H NMR, and elemental analysis. Both PIM-1 and cPIM-1 were processed into self-supported membranes and into thin film composite (TFC) membranes on a polyacrylonitrile support. For a 70% hydrolyzed polymer (D-cPIM-1-70%), the initial CO2 permeance reached 7700 GPU, with ideal selectivity of 56 for CO2/N2 and 37 for CO2/CH4. D-PIM-1 and D-cPIM-1-70% showed 85% and 52% CO2 permeance drop after 60 days’ aging, respectively. B-PIM-1, with initial CO2 permeance of 3100 GPU and ideal selectivity of 19 for CO2/N2 and 11 for CO2/CH4, showed only a 65% decrease. Polymer that was both branched and hydrolyzed (B-cPIM-1-73&81%), with CO2 permeance of 3200 GPU and selectivity of 64 for CO2/N2 and 45 for CO2/CH4, showed no decrease of CO2 permeance after 60 days. The branched structure is crucial for reducing membrane aging. Plasticization gave rise to reduced selectivity in mixed gas experiments, but nevertheless TFC membranes prepared from B-cPIM-1-81% were able to concentrate CO2 to 38% from a 10% CO2/90% N2 mixture at 4.8 bar.

In-situ growth of ZIF-8 nanoparticles in Pebax-2533 for facile preparation of high CO2-selective mixed matrix membranes

In this work, ZIF-8 nanoparticles were introduced into the Pebax-2533 via a novel “in-situ growth” synthesis approach for easy and fast fabrication of the mixed-matrix-membranes (MMMs) with superior CO2 separation performance. The ZIF-8 nanoparticles were grown and formed in the Pebax solution medium by reacting Zn and imidazole via a one-step procedure (without using any sonication in the preparation procedure). The in-situ prepared ZIF-8 particles in Pebax-2533 have suitable dispersion in the matrix and appropriate polymer-filler interfacial compatibility. As ZIF-8 in-situ synthesized, due to the formation of strong filler/polymer interfacial interactions, the crystallinity and Tg of the membrane severely increased, and FFV simultaneously decreased. The in-situ MMMs revealed promising gas separation performance via a synergistic enhancement in the CO2 permeability and selectivity and proved that they have premiere CO2 selectivity than the ex-situ MMMs. For example, the CO2 permeability, and CO2/N2 and CO2/CH4 selectivities enhanced from 57.5 Barrer, 23.4, and 10.6 for the neat Pebax membrane to 73.3 Barrer (28% enhancement), 82 (250%), 32.6 (208%) for the in-situ Pebax/ZIF-8 MMM containing 8 wt% of nano-filler. In the mixed gas experiments, the gas permeabilities were a little lower than the single gas permeabilities, while the selectivities enhanced due to the competitive sorption between the gas molecules, especially for the in-situ MMMs. The in-situ MMM containing 16 wt% of ZIF-8 also surpassed the upper bound-2019. Furthermore, this study indicated the undeniable potential of the in-situ synthesis approach for the fabrication of high CO2 separation performance membranes with a performance stability in the 24 h permeation test for industrial applications, which is available with a snappier and more convenient manufacturing method than the conventional MMMs.

Permeation of Ternary Mixture Containing H2S, CO2 and CH4 in Aquivion® Perfluorosulfonic Acid (PFSA) Ionomer Membranes.

Aquivion® E87-12S Perfluorosulfonated acid ionomer material (PFSA) has been studied as a membrane technology for natural gas sweetening from CO2, H2S due to its interesting chemical and mechanical stability and good separation performance for polar compounds in humid environments. In the present work, permeation of the H2S/CO2/CH4 ternary mixture in this short-side PFSA chain was investigated at pressures up to 10 bar, temperatures up to 50 °C, and in a range of relative humidity (RH) from 20% to 90%. The results obtained confirm the strong dependence of Aquivion® on water activity and temperature, and its ability to separate gases based on their water solubility without substantial differences between pure and mixed gas experiments. Indeed, even when tested in ternary mixture, the permeation behavior remains similar to that observed for pure components and binary mixtures. In particular, the permeability of H2S is higher than that of CO2 and methane CH4, reaching values of 500 Barrer at 50 °C and 80% RH, against 450 and 23 Barrer for the other two gases respectively. Additionally, when tested at higher pressures of up to 10 bar under humid conditions, the membrane properties remained largely unchanged, thus confirming the overall stability and durability of Aquivion® E87-12S in acid environments.

Synergy of high permeability and selectivity of superbase/choline chloride/urea solution impregnated membranes for CO2 capture

A new generation of solvents called ternary deep eutectic solvents have emerged as a promising candidate to replace ionic liquids (IL) in CO2 capturing due to its inherent advantages of both, superbase and deep eutectic solvents (DES). In this work, the binary and ternary DES were synthesized to investigate the effect of superbase on the performance of DES based membrane systems for acid gas capture. The reline DES system was chosen as binary DES and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was used as superbase. The ternary DES was prepared by mixing DBU in reline DES system in different molar ratios. The permeability and selectivity of the synthesized membrane for CO2, CH4, and N2 were investigated in pure and mixed gas experiments. Moreover, the effect of the DES molar ratio, operating conditions of feed on the DES based supported liquid membranes (SLMs) performance was studied comprehensively. These novel ternary DES SLMs showed significant permeability and selectivity values up to 38.12 Barrer and 58.65 respectively. These values were found to be significantly higher than the permeability and selectivity value of binary DES-SLM i.e. 31 Barrer and 51.67 respectively. The improved gas performance results of ternary DES can be attributed to the basicity and fast reaction kinetics of the superbase/DBU. The ternary DES can potentially alternate the ILs and commonly used binary DESs in CO2 capturing process due to their high affinity towards CO2 gas.

CO2/H2 separation through poly(ionic liquid)–ionic liquid membranes: The effect of multicomponent gas mixtures, temperature and gas feed pressure

This work presents mixed gas separation performance through PIL–IL membranes bearing pyrrolidinium-based PILs with [NTf2]– and [C(CN)3]– anions and different weight percentages of the corresponding ILs 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. COSMO-RS was successfully used to understand the separation behavior of the PIL–IL composites for the H2 + CO2 + N2 mixture. The effect of temperature between 20 °C and 80 °C and feed pressure between 1 bar and 4 bar was also studied and is here discussed. The increased of the mixed H2, CO2 and N2 permeabilities with increasing temperature was shown to be due to dominant role of gas solubility at low temperature, and diffusivity at high temperature. The small pronounced differences between mixed and ideal CO2/H2 permselectivities through the prepared PIL–IL composites indicated that membrane separation efficiency can be maintained, despite the competition effect between gases in mixed gas experiments. Depending on the operating conditions, the best mixed separation performance was obtained for PIL C(CN)3–60 [C2mim][C(CN)3], with a CO2 permeability of 324.7 Barrer and a CO2/H2 permselectivity of 11.4. The great potential of the studied PIL–IL membranes for biohydrogen separation is here clearly evidenced, since they revealed mixed CO2/H2 separation performances above the Robeson upper bound even at the highest temperature and feed pressure tested.

How is mixed-gas permeation through poly(1-trimethylsilyl-1-propyne) membranes influenced by elevated temperatures?

Poly(1-trimethylsilyl-1-propyne) (PTMSP), one of the most permeable membrane materials, has been extensively studied for gas permeation in the past. Even though it is in a glassy state, PTMSP permeates larger molecules selectively over small inert gases. Its mixed-gas selectivity in gas mixtures containing condensable gases is preferential towards the condensable components. This peculiar behavior is due to its extremely high non-equilibrium frozen-in excess free volume. This behavior also makes PTMSP and its transport performance highly relevant to study the effect of the high free volume - often called intrinsic microporosity - for applications in natural gas treatment, petroleum processing, or membrane reactors. While condensability strongly depends on the temperature, a detailed analysis of the temperature behavior in terms of the enhanced mixed-gas selectivity has not yet been performed for polymers with intrinsic porosity.Within this work, pure- and mixed-gas experiments with 1-butene (C4H8) and nitrogen (N2) were conducted at different C4H8 partial pressures and for temperatures ranging from 20∘C up to 120∘C. At 20∘C, a minimal C4H8 partial pressure of 0.5 mbar already depressed the N2 flux through PTMSP membranes in C4H8/N2 mixtures. With increasing temperatures, the extent of the C4H8 influence on N2 permeation vanishes. Elevated temperatures caused the mixed-gas selectivity αC4H8/N2 to decrease, but even at 120∘C it remained above the pure-gas selectivity.PTMSP is a membrane material with high-excess non-equilibrium free volume, which makes it prone to aging. Therefore, the physical aging of PTMSP membranes was recorded throughout the experiments. For temperatures exceeding 50∘C, pronounced aging occurred. Although the physical aging was reversed to a small degree when contacted by C4H8, the resulting permeabilities remained below the initial values. For temperatures ≤50∘C however, an in-situ rejuvination of membrane permeabilities was possible with small concentrations of C4H8 in the gas mixture. This in-situ rejuvination makes the long-term use of PTMSP membranes possible at low temperatures where condensable gases are present at sufficiently high concentration in the polymer.

Comparative performance of commercial polymeric membranes in the recovery of industrial hydrogen waste gas streams

The application of membrane separation processes to industrial hydrogen-rich waste gases promotes the efficient recovery of this clean fuel. The first step to address and overcome this waste of resources is to assess the real performance of commercially available polymeric membranes for hydrogen separation in terms of hydrogen purity that meets the quality standards to be used in hydrogen-based applications. Therefore, this work makes a comparison of the performance of commercial flat hydrogen-selective membranes based on non-porous polymeric materials through the experimental assessment in a lab-scale set up that contains a gas permeation cell with the aim of recovering hydrogen from the most suitable multicomponent waste gaseous streams. To assess the mixed-gas permeation performance, the influence of the feed gas composition, temperature and pressure was examined. The results of experimental tests indicated that there is a strong dependency of H2 permeability on CO2 concentration, that induces a decay of H2/CO2 selectivity in mixed-gas experiments for the membranes under study. Accordingly, the permeability-selectivity trade-off in the state-of-the-art membranes defines the balance between H2 recovery and the product purity. Finally, it is worth noting that although H2 purities obtained are higher than 98% vol. H2 for APG and COG mixtures, which may indeed be used as a commodity chemical in many industrial processes, they are still far from fuel cell requirements.

Thin graphene oxide membranes for gas dehumidification

Thin graphene oxide (GO) membranes supported on porous anodic aluminum oxide (AAO) substrates prepared by spin-coating and pressure-assisted filtration are tested in gas dehumidification experiments. Graphene oxides with different specific nanosheet sizes ranged from 10 × 140 to 3300 nm synthesized by modified Hummer's method were used for membrane preparation. We have shown that 25–60 nm-thick GO membranes exhibit barrier properties towards most of the gases (CH4, N2, O2, C4H10), while revealing high permeance for water and water soluble vapors (CO2). The influence of the GO nanosheet size and the membrane preparation technique on the gas transport characteristics of the composite membranes are investigated. The best membrane performance has been achieved for membranes prepared from medium-flake-sized GO nanosheets providing high enough defect density at the surface to allow water entrance to the interlayer space and large enough nanosheet size to cover AAO nanochannels and create continuous barrier coating towards permanent gases on the surface. Water permeance and H2O/N2 selectivity measured in the relative humidity range of 10–80% shows strong humidity dependence due to the sorption of water vapors in the interlayer space of GO. Maximum H2O/N2 selectivity of 13,000 at water permeance of GO membranes of ~1.4 m3/(m2 h) has been achieved at standard conditions (298 K, 1 bar) and relative humidity of 80%. Water permeance of GO membranes strongly depends on the transmembrane pressure, diminishing an order of magnitude from equi-pressure conditions to 0.1 MPa pressure difference. The effect has been ascribed to a pressure-driven ousting of water molecules from the interlayer spacing of GO. Permeability of the GO membranes towards CO2 in humid mixed gas experiments has been shown to be enhanced strongly due to gas solubility in liquefied water enabling sweetening and dehumidification of natural and technological gases in a single stage.

Thermally rearranged polypyrrolone membranes for high-pressure natural gas separation applications

The gas permeability performance of thermally rearranged polypyrrolone (PPL-450) membranes have been experimentally evaluated under similar industrial conditions of gas mixtures, pressures, and stage-cuts. The membranes were synthesized from 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 3.3′-diaminobenzidine (DAB). The thermal treatment of the PPL-450 was accomplished under vacuum at 450 °C. Several gas mixtures (binary, ternary and quaternary) were utilized to study the performance of the PPL-450 membranes for CO2 removal and helium recovery from natural gas streams. The quaternary feed gas-mixture was composed of 59% CH4, 30% N2, 10% CO2 and 1% C2H6, which represent a low quality natural gas. Three pressures (400, 600, and 800 psig) and five stage-cuts (1.2, 2.8, 4.2, 6.4, and 9.8%) were considered for the study. It was observed that the permeability values of all gases were decreased for mixed-gas experiments when compared to that of the single-gas permeability. On the other hand, CO2/CH4 permeability ratio was increased from 29, for pure gas, to 45 for quaternary gas-mixture. Likewise, the He/CH4 permeability ratio was increased from 33, for pure gas, to 46 for ternary gas-mixture. Furthermore, at 800 psig and 9.8% stage-cut, PPL-450 was able to remove 80% of CO2 from the quaternary gas-mixture. In another study of a very dilute helium-concentration (0.14%) more than 80% helium was recovered at 800 psig and 5% stage-cut. Moreover, in all gas mixtures containing CO2, the PPL-450 membrane demonstrated an outstanding resistivity to CO2-induced plasticization at high pressures.

Matrimid®/polysulfone blend mixed matrix membranes containing ZIF-8 nanoparticles for high pressure stability in natural gas separation

Abstract Plasticization is of important concern in high pressure natural gas separation. Majority of the pure polymers and MOF-MMM systems suffer from plasticization at low pressures. Combination of polymer blending and MMM approach could lead to plasticization resistant membranes with improved membrane performance. In this work, the gas separation performance of Matrimid® and PSF blend membranes containing ZIF-8 nanoparticles, were studied. The effect of ZIF-8 loading on the gas transport and plasticization behavior of the blend-MOF MMMs was investigated. Gas permeability measurements of PI/PSF-ZIF-8 MMMs showed significant improvements in permeability of both CO2 and CH4, compared to pure reference polymer membrane. At a high loading of 30 wt% ZIF-8, MMM showed an enhancement of 136% in CO2 permeability compared to the pure PI/PSF membrane, while the selectivity stayed constant. This increase in the permeability could be related to the moderate increase in sorption capacity and faster diffusion of gases through the ZIF-8 nanoparticles. More detailed analysis of the gas transport performance of the MMMs showed that the CO2 permeability and the CO2/CH4 selectivity were mainly governed by the increase in CO2 diffusion coefficient. Blend MMMs were considerably more resistant to plasticization phenomenon compared to the pure PI membrane. For pure gases, native PI/PSF blend membrane showed a plasticization pressure of ∼18 bar, which increased to ∼25 bar up to 30 wt% ZIF-8 loading. Short and long CO2 exposure time experiments, with different upstream pressures, showed that the permeability stayed constant in time at pressures below the plasticization pressure while a noticeable increase in permeability was recorded in time at higher pressures. Additionally, these experiments showed that the extent of dilation in the pure PI/PSF membrane was much higher compared to the PI/PSF-ZIF-8 MMMs. In mixed gas (50/50 mol% CO2/CH4) experiments, the pure PI/PSF membrane and the MMMs did not show plasticization over the pressure range investigated, as confirmed by a constant mixed gas CH4 permeability and nearly constant selectivity with pressure. While the pure PI and PI-ZIF-8 MMMs showed the plasticization behavior. Comparing the mixed gas performance of PI/PSF-ZIF-8 membranes with that of pure PI/PSF membranes at high pressures an increase of 197% in CO2 permeability and 30% in CO2/CH4 selectivity was obtained. These results showed that the combination of polymer blending and the mixed matrix membrane approach offers a simple and economically versatile tool to approach higher CO2 permeabilities and CO2/CH4 selectivities while maintaining a stable separation performance in processes involving higher CO2 partial pressures.

Mass transfer and selectivity analysis of a dense membrane contactor for upgrading biogas

The mass transfer of a dense membrane contactor for the removal of CO2 from a biomethane-CO2 mixture was investigated in detail. Pure gas CO2 experiments as well as mixed gas experiments were conducted in order to determine the transmembrane flux and the selectivity of the contactor as a function of the pressure level and the transmembrane pressure difference. Two membranes, a PDMS coated and a Teflon-AF coated composite flat-sheet gas permeation membrane (PolyActive™) were tested in the self-constructed membrane module. The mass transfer was analyzed using a rigorous mass transfer model. With this model, it was possible to determine the mass transfer resistance of the membrane and the liquid boundary layer. It was found that both resistances do significantly contribute to the overall mass transfer resistance that is governing the membrane flux and the selectivity of the dense membrane contactor. Nevertheless, an increased driving force due to an increased pressure difference across the membrane could easily compensate for the additional mass transfer resistance of the membrane. A transmembrane pressure difference of up to two bars and absorbent liquid phase pressures at the permeate side of up to five bars were applied. It could be shown that a higher permeate pressure and a large transmembrane pressure difference is favorable for both, the permeance and the selectivity of the dense membrane contactor.

Pressure-dependent pure- and mixed-gas permeation properties of Nafion®

The permeation properties of Nafion® at 35°C are presented for pure gases H2, N2, O2, CH4, CO2, C2H6 and C3H8, as a function of pressure between 2 and 20atm. The effect of pressure on permeability and selectivity is analyzed to understand two observed phenomena: compression and plasticization. In pure-gas experiments, at increasing feed pressure, compression of the polymer matrix reduced the permeability of low-sorbing penetrants H2, N2, O2, and CH4. In contrast, permeabilities of more soluble penetrants CO2 and C2H6 increased by 18% and 46% respectively, as plasticization effects overcame compression effects. Permeability of C3H8 decreased slightly with increasing pressure up to 4.6atm as a result of compression, then increased by 3-fold at 9atm as a result of plasticization associated with high C3H8 solubility. Binary CO2/CH4 (50:50) mixed-gas experiments at total feed pressures up to 36atm quantified the effect of CO2 plasticization on separation performance. At 10atm CO2 partial pressure, CH4 permeability increased by 23% relative to its pure-gas value of 0.078 Barrer, while CO2 permeability decreased by 28%. Consequently, CO2/CH4 selectivity decreased to 19, i.e., 42% below its pure-gas value of 32.

Preparation and characterization of Ag+ ion-exchanged zeolite-Matrimid®5218 mixed matrix membrane for CO2/CH4 separation

In this work, the zeolite-Y was ion-exchanged by introducing silver cations into the framework of micro-sized nano-porous sodium zeolite-Y using a liquid-phase ion exchanged method. The Ag+ ion-exchanged zeolite, was then embedded into the Matrimid®5218 matrix to form novel mixed matrix membranes (MMMs). The particles and MMMs were characterized by ultraviolet-visible diffuse reflectance spectroscopy (UV–vis DRS), N2 adsorption–desorption isotherm, X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). Furthermore, the effects of filler content (0–20 wt%) on pure and mixed gas experiments, feed pressure (2–20bar) and operating temperature (35–75ºC) on CO2/CH4 transport properties of Matrimid/AgY MMMs were considered. Characterization results confirmed an appropriate ion-exchange treatment of the zeolites. The SEM results confirmed the superior interfacial adhesion between polymer and zeolites, particularly in the case of Matrimid/AgY membranes. This is due to the proper silverous zeolite/Matrimid functional groups’ interactions. The gas permeation results showed that the CO2 permeability increased about 123%, from 8.34 Barrer for pure Matrimid to 18.62 Barrer for Matrimid/AgY (15 wt%). The CO2/CH4 selectivity was improved about 66%, from 36.3 for Matrimid to 60.1 for Matrimid/AgY (15 wt%). The privileged gas separation performance of Matrimid/AgY (15 wt%) was the result of a combined effect of facilitated transport mechanism of Ag+ ions as well as the intrinsic surface diffusion mechanism of Y-type zeolite. In order to survey the possibility of using the developed MMMs in industry, the CO2-induced plasticization effect and mixed gas experiment were accomplished. It was deduced that the fabricated MMMs could maintain the superior performance in actual operating conditions.

The effects of aminosilane grafting on NaY zeolite–Matrimid®5218 mixed matrix membranes for CO2/CH4 separation

The aminosilane grafting on micro-sized nanoporous sodium zeolite Y particles was performed and novel mixed matrix membranes (MMMs) were fabricated by embedding the modified particles into the Matrimid®5218 matrix. The aminosilane grafting reaction was considered using 3-aminopropyl(diethoxy)methylsilane (APDEMS) as the silane coupling agent. DLS, BET, XRD, FTIR-ATR, CAM, SEM, and TG/DTG were investigated to characterize the pure zeolite (NaY), silane modified zeolite (Sm-NaY) and the fabricated MMMs. Moreover, the effects of filler content (0–20wt%) on pure and mixed gas experiments, feed pressure (2–12bar) and operating temperature (35–75°C) on CO2/CH4 transport properties of Matrimid/Sm-NaY were surveyed. The obtained results revealed that at 15wt% filler loading (the optimum condition), the CO2 permeability increased from 8.34 Barrer for Matrimid to 9.70Barrer (about 16%). The related CO2/CH4 selectivity was considerably increased from 36.3 to 57.1 (about 57%). This superior performance at 15wt% filler loading was related to the good dispersion of the silane modified NaY particles in the Matrimid matrix. The defect free polymer/filler interface was achieved by the aminosilanes grafted on the external surface of the zeolites.

Pure- and mixed-gas permeation of CO2 and CH4 in thermally rearranged polymers based on 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)

Permeability coefficients for pure CO2, pure CH4, and CO2/CH4 mixtures containing 50% CO2 are reported for a polyimide synthesized from 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and for three thermally-rearranged (TR) derivatives thereof. Permeability measurements were made at 35°C for fugacities ranging from 4 to 25atm. The permeability of CO2 and CH4 increased as the degree of TR conversion increased. For example, CO2 permeability at 10atm increased by a factor of 30 between the unconverted polyimide and its TR analog converted at 450°C. In pure-gas experiments, CO2 was observed to plasticize the unconverted polyimide, but it did not appear to plasticize the TR polymers. In mixed-gas experiments, dual-mode competitive sorption caused a depression in CH4 permeability, with very little change in CO2 permeability. In addition, plasticization by CO2 was evident in the CH4 mixed-gas permeability trends, but its impact was small in contrast with dual-mode competitive effects. Consequently, CO2/CH4 mixed-gas permeability selectivity was higher than the ideal selectivity, calculated as the ratio of pure gas permeability coefficients. The dual-mode sorption and permeation model was fit to the experimental data. Dual-mode model parameters and model predictions are reported, along with their confidence intervals. By comparing the dual-mode model predictions with the experimental mixed-gas data, the degree of CO2-induced plasticization was observed to decrease as the degree of TR conversion increased and was completely absent (within experimental uncertainty) for the TR polymer converted at 450°C.

A novel CO2-selective synthesized amine-impregnated cross-linked polyvinylalcohol/glutaraldehyde membrane: fabrication, characterization, and gas permeation study

In this paper, polyvinyl alcohol (PVA) membranes impregnated with amines (monoethanolamine and diethanolamine) were prepared for CO2/N2 separation. The cross-linking of DEA impregnated PVA by glutaraldehyde (GA) with different mass ratios (GA/PVA: 0.5, 1, 3, 5, 7%) were investigated with no use of acid catalyst or organic solvents. The effects of the amine type-concentration, cross-linking agent content, and feed pressure as well as stability were examined in both pure and mixed gases. Generally, CO2/N2 performance through the DEA-PVA membranes was higher than that of MEA-PVA membranes. The fabricated membranes were characterized by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The cross-linked membranes showed reasonable CO2/N2 permselectivities in comparison with uncross-linked membranes and these are recommended for high performance membrane for CO2/N2 separation. The best-yielding membranes (DEA-PVA/GA(1 wt%)/PTFE) represented the greatest CO2/N2 selectivity of 122.04 and 907.06 for pure and mixed gas experiments, respectively.

The effect of polyurethane on the structure and performance of PES membrane for separation of carbon dioxide from methane

In the present study, asymmetric gas separation membranes of polyethersulfone (PES) and polyethersulfone/polyurethane (PU) were prepared with different blend compositions. The prepared membranes were investigated for the separation of carbon dioxide from methane. The effect of PU on the microstructure and d-spacing of the membranes was studied by X-ray diffraction analysis and the miscibility of PES and PU was investigated using Differential Scanning Calorimetry (DSC). The thermal properties of PES and PES/PU were compared using Thermal Gravimetric Analysis (TGA). The effect of PES/PU blend composition on the morphology and porosity of the membrane was investigated by Scanning Electron Microscopy (SEM) and porosity experiments. Density Functional Theory (DFT) calculations were used to investigate the relative affinity of CO2, CH4 and H2O for PES and PU. Moreover, the effect of PU on the casting solution viscosity, gas sorption and mechanical properties of the PES membrane was investigated. For comparing gas separation performance of PES and PES/PU membranes, pure and mixed gas experiments were carried out. The obtained results indicated that the presence of PU in the casting solution increases the d-spacing and fractional free volume, and decreases the membrane porosity; Tg and thermal resistance, membrane gas sorption as well as CO2 induced plasticization by decreasing Langmuir capacity, and also increases strength at yield and elongation at yield of PES membrane.The presence of PU decreases the CO2 permeance and enhances the CO2/CH4 selectivity and plasticization pressure of the PES membrane. Furthermore, the presence of the PU changes the membrane behavior against the feed pressure, feed temperature and feed composition in the mixed gas experiments.

Synthesis and characterization of diethanolamine-impregnated cross-linked polyvinylalcohol/glutaraldehyde membranes for CO2/CH4 separation

In this research, the cross-linking of diethanolamine (DEA) impregnated poly(vinyl alcohol) (PVA) on polytetrafluoroethylene (PTFE) by glutaraldehyde (GA) with different blend compositions (GA/PVA: 0.5, 1, 3, 5, 7 ratio%) was performed in the absence of an acid catalyst and organic solvents in order to avoid any interference in CO2 facilitation reaction with DEA. The fabricated membranes were characterized by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). Furthermore, the effects of cross-linking agent content, feed pressure and composition as well as stability on CO2/CH4 transport properties were investigated in both pure and mixed gas experiments. The cross-linked membranes showed reasonable CO2/CH4 permselectivities in comparison with uncross-linked membranes. The best-yield CO2-selective membranes (DEA-PVA/GA(1wt%)/PTFE) represented the best CO2/CH4 selectivity of 91.13 and 665 for pure and mixed gas experiments, respectively.