Pure Gas Permeation Research Articles

Controlled Dip-coating Times for Improving CO2 Selective of PI/NCCbased Supported Carbon Membrane

Carbon membrane can be regarded as the future separation media in gas separation process due to its high gas separation performance, easy processability, and moderate energy requirement compared to conventional separation process. In this study, the fabrication of tubular carbon membrane prepared from PI blends with nanocrystalline cellulose (NCC) was investigated. The influence of dip-coating duration (15, 30, 45, and 60 min) towards the physicochemical properties and CO2/CH4 and O2/N2 separation was explored. The process of carbonization was conducted at 800°C with rate of heating at 3°C/min under argon gas flow (200 mL/min). Pure gas permeation tests were performed to investigate the prepared carbon membrane’s mechanism of transport at ambient temperature and a feed pressure of 8 bar. The carbon membrane with CO2/CH4 and O2/N2 selectivity of 68.23 ± 3.27 and 9.29 ± 2.54 and CO2 and O2 permeance of 213.56 ± 2.17 and 29.92 ± 1.44 GPU, respectively, were obtained when applying 45 min dip-coating.

Gas permeation and separation properties of large-sheet stacked graphene oxide membranes

Graphene oxide (GO) membranes offer attractive gas separation properties. However, the gas separation mechanism for GO membranes is unclear due to inconsistent permeation and separation results reported in the literature. In this work, pure gas permeation and separation of equimolar (H2/CO2) mixture experiments were conducted on GO membranes made from large GO sheets of different sizes (33 and 17µm) to understand the gas permeation and separation characteristics of these membranes. At room temperature the permeation of large molecules (CH4, N2 and CO2,) through GO membranes exhibits Knudsen–like diffusion characteristics, with the permeance for the small sheet GO membrane about twice that for the large sheet GO membrane. The smaller gases (H2 and He) exhibit much higher permeance, showing additional transport in additional pathway. The GO membranes show good H2/CO2 selectivity for both pure and binary gas feeds, without CO2 pore blockage effect for mixture separation found for crystalline microporous membranes. An inter-sheet and inner-sheet two-pathway model is proposed which can explain the results obtained in this work. Gas permeation in GO membranes, more complex than in crystalline microporous membranes, is determined by solubility (surface properties), diffusivity (relative molecular size to pore size), porosity and tortuosity of both the inter-sheet pores and inner-sheet defect pores. These properties are strongly influenced by synthesis method and conditions for GO sheets and membranes.

Mixed matrix membranes of polyurethane with nickel oxide nanoparticles for CO2 gas separation

We developed highly selective polyurethane (PU) membranes with incorporated NiO nanoparticles for gas-phase carbon dioxide separation. PU was synthesized with polytetramethylene glycol and isophoronediisocyanate, and 1,4-butandiamine/1,4-butandiol as the chain extender (1:3:2 molar ratio). Mixed matrix membranes (MMMs) composed of PU and NiO nanoparticles were fabricated using the solution casting method. Scanning electron microscopy (SEM) confirmed the even distribution of NiO in the PU matrix at the nanoscale. Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) were used to examine the phase separation between the soft and hard domains of PU, and the distribution of NiO nanoparticles in both domains. DSC and X-ray diffraction (XRD) pattern confirmed that the crystalline structures in both soft and hard segments are changed by NiO incorporation. The effects of NiO nanoparticles on the gas permeability, diffusivity, and solubility of pure CO2, CH4, O2, and N2 gases were studied at various temperatures and feed pressures. A large increase in the CO2/N2 permselectivity with a simultaneous reduction in the gas permeability of CH4, O2, and N2 was observed. When the NiO content was low (1wt%), the CO2/N2 permselectivity increased by 79.21%, and the CO2 permeability increased by 1.57%. Increasing the nanoparticle load to 5wt% increased the CO2/N2 permselectivity by 161.1%, while the CO2 permeability was decreased by 3.31%.

Incorporation of thermally labile additives in carbon membrane development for superior gas permeation performance

Incorporating thermally labile polymer additives into carbon membrane development is highly practical due to its process simplicity and effective approach. In this study, different polymer composition of thermally labile additives such as polyvinylpyrrolidone (PVP), microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC) were introduced into the BTDA-TDI/MDI (P84-copolyimide) polymer solution. The P84-copolyimide based carbon tubular membranes were fabricated using dip-coating method and characterized in terms of its thermal stability, structural morphology and gas permeation properties. Initially, the NCC was introduced as a pore performing agent in the carbon membrane fabrication for carbon dioxide (CO2) separation. Our finding indicated that the use of NCC as pore performing agent significantly promoted an increment of pore structure channel in carbon membrane. As a result, the high permeance as well as high selectivity was demonstrated in this study. Pure gas permeation tests were performed using CO2, CH4, O2 and N2 at room temperature. The increment of both gas permeance and selectivity were observed in the NCC-containing carbon membranes prepared with a composition of 7 wt%. The promising CO2/CH4 selectivity of 68.23 ± 3.27, CO2/N2 selectivity of 66.32 ± 2.18 and O2/N2 selectivity of 9.29 ± 2.54 with respect to neat carbon membrane were presented. Thus, upon further investigation, the potential of NCC as thermally labile additive in carbon membrane was assured.

Polysulfone mixed-matrix membrane incorporating talc clay particles for gas separation

Mixed-matrix membranes (MMMs) have showed advantages in membrane-based gas separation in recent years. However, there is still intensive demand for the development of membranes incorporated by proper fillers for further enhancement of gas separation performance. In this study, mixed-matrix membrane (MMMs) has been synthesized by incorporating of different content of talc into polysulfone (PSf) polymer specifically upon the separation of carbon dioxide from methane. The influence of filler content on the gas separation performance of the fabricated membranes was studied. The prepared MMMs were analyzed by thermal gravimetric analysis (TGA), X-ray diffraction (XRD), derivative thermo-gravimetric (DTG), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and pure gas permeation testing. XRD analysis suggested that talc layers crystalline structure was changed slightly due to blending and just limited PSf chain intercalation occurred. The results showed that the rate of gas permeation increased with increasing talc content while the selectivity declined at 0.5 wt% due to filler agglomeration as confirmed by FESEM. The best results were obtained at 0.1 wt% talc compared to neat PSf with superior gas separation behavior.

Gas permeation properties of cellulose acetate/silica nanocomposite membrane

AbstractIn this study, the effects of silica nanoparticles on the permeability of pure CO2, O2, and N2 gases in cellulose acetate (CA) membrane have been studied. Silica particles were prepared via the sol–gel method through the hydrolysis of tetraethyl orthosilicate (TEOS). CA and CA/silica nanocomposite membranes were prepared by thermal phase inversion method. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Fourier transfer infrared (FTIR) analyses were employed to characterize the CA and CA/silica nanocomposite membranes. Gas permeation experiments showed an increase in the permeability of CO2 from 6.32 to 7.3 barrer and a reduction in the permeability of N2 from 0.18 to 0.09 barrer with the increment in silica content of the prepared composite membranes up to 20 wt%. Therefore, CO2/N2 selectivity of the nanocomposite membranes increased by increasing the silica content in the polymer matrix from 30 to 80 for 20 wt% load of silica.

Temperature-dependent gas transport and its correlation with kinetic diameter in polymer nanocomposite membrane

Activation energies for permeation of polymer nanocomposite membrane have not been reported so far. A trade-off relation between permeability and selectivity shows that as permeability increases, the selectivity decreases. Attempts have been made to see this trade-off relation at relatively higher temperature. It is found that selectivity decreases drastically with increasing temperature. A polymer–matrix composite was prepared by adding silica nanoparticles using casting method. Pure gas permeability was measured using a constant volume–variable pressure method at different temperature ranges from 35 to $$70^{\circ }\hbox {C}$$ . The Van’t Hoff relation was used to estimate the activation energy for permeation. It is found to decrease as compared with virgin polycarbonate and it increases with kinetic diameter. For the first time, the permeability and selectivity for nanocomposite membrane are reported as a function of temperature. Activation energies for different gases have been calculated for nanocomposite membrane and compared with that of virgin polymer membrane. Decrease in activation energies for permeation ( $$E_\mathrm{p}$$ ) with increasing kinetic diameter has been observed for both the membranes. Selectivity reduces with temperature for both the membranes. Mechanical and thermal properties of nanocomposite membrane have been investigated using a dynamic mechanical analyser and differential scanning calorimetry, respectively. Scanning electron microscopy has been used to study surface morphology. The results show modification in physical properties due to incorporation of silica nanoparticles.

Physical aging, CO2 sorption and plasticization in thin films of polymer with intrinsic microporosity (PIM-1)

Physical aging of both thick and thin films of “high free-volume” glassy polymer, PIM-1 (polymer with intrinsic microporosity) was studied by monitoring changes in pure gas permeability of O2, N2 and CH4 at a fixed temperature of 35°C. Permeability of PIM-1 is very sensitive to film thickness, post-treatment (methanol soak, water soak or dried) and casting solvent (chloroform and ortho-dichlorobenzene). Thin films of PIM-1 undergo accelerated aging, leading to initial permeability lower by an order of magnitude compared to thick films. The relative permeability for thin films of PIM-1 was decreased by 67% compared to 53% decrease for thick films at 1000h of aging due to the higher aging rates in thin films. The effect of casting solvent (vapor pressure and boiling point) is more pronounced on aging and selectivity of thin films with initial permeability almost two times higher for the film casted from chloroform (CHCl3) compared to that prepared from ortho-dichlorobenzene (o-DCB) solvent. The effect of casting solvent on the initial permeability is less prominent for thick films. The film thickness, casting solvent and CO2 exposure protocols also have significant effect on the absolute CO2 permeability and plasticization behavior of both thick and thin films. The thin films undergo significant increase in the relative permeability upon plasticization compared to thick films and permeability was found to increase even during CO2 depressurization. The long time, constant pressure CO2 exposure study revealed dominant aging effect in thin film where aging overcomes the CO2 plasticization effect just within 1.2min of the CO2 exposure compared to 10h for thick film. The ellipsometry measurements showed that the CO2 solubility in thin films decreases with increases in the aging time and temperature, and with decrease in the molecular weight. A strong correlation was observed for the Langmuir sorption capacity, CH' and solubility at infinite dilution, S0 with the aging time, temperature and molecular weight of PIM-1.

Enhanced gas separation performance of mixed matrix hollow fiber membranes containing post-functionalized S-MIL-53

Mixed matrix hollow fiber membranes (MMHFMs) filled with metal-organic frameworks (MOFs) have great potential for energy-efficient gas separation processes, but the major hurdle is polymer/MOFs interfacial defects and membrane plasticization. Herein, lab-synthesized MIL-53 was post-functionalized by aminosilane grafting and subsequently incorporated into Ultem®1000 polymer matrix to fabricate high performance MMHFMs. SEM, DLS, XRD and TGA were performed to characterize silane-modified MIL-53 (S-MIL-53) and prepared MMHFMs. Moreover, the effect of MOFs loading was systematically investigated first; then gas separation performance of MMHFMs for pure and mixed gas was evaluated under different pressures. MMHFMs containing post-functionalized S-MIL-53 achieved remarkable gas permeation properties which was better than model predictions. Compared to pure HFMs, CO2 permeance of MMHFM loaded with 15% S-MIL-53 increased by 157% accompanying with 40% increase for CO2/N2 selectivity, which outperformed the MMHFM filled with naked MIL-53. The pure and mixed gas permeation measurements with elevated feed pressure indicated that incorporation of S-MIL-53 also increased the resistance against CO2 plasticization. This work reveals that post-modified MOFs embedded in MMHFMs facilitate the improvement of gas separation performance and suppression of membrane plasticization.

Polyurethanes containing Poly(arylene ether sulfone) and Poly(ethylene oxide) segments for gas separation membranes

Poly(arylene ether sulfone) and poly(ethylene oxide) (PEO)-based segmented polyurethanes were synthesized as potential gas separation membrane materials. Poly(arylene ether sulfone) oligomers with controlled molecular weights (15,000 and 20,000 g/mol Mn) were prepared with phenol endgroups by nucleophilic aromatic substitution step growth polymerization of 4,4'-dichlorodiphenylsulfone with a calculated excess of 4,4'-(propane-2,2-diyl)diphenol (bisphenol A). The oligomers with phenolic endgroups were subsequently reacted with ethylene carbonate to obtain aliphatic hydroxyethyl terminal functionality. The hydroxyethyl terminated polysulfone oligomers and hydroxy-terminated PEO were reacted with 4,4'-methylene diphenyl diisocyanate (MDI) to obtain segmented polyurethanes. Compositions with high poly(arylene ether sulfone) content relative to the hydrophilic PEO blocks were of particular interest due to their mechanical integrity. Size exclusion chromatograms confirmed that the polyurethanes had high molecular weights with unimodal molecular weight distributions. DMA and DSC thermograms revealed polyurethanes containing 30 wt % PEO have two distinct Tg's. Pure gas permeabilities of membranes were measured using a series of gases having different kinetic diameters including H2, He, CO2, O2, N2, and CH4. Gas transport measurements showed changes in permeabilities as the PEO content in the polyurethane increased. The CO2/N2 and CO2/CH4 gas selectivity of membranes increased systematically as PEO content increased in the polyurethanes.

Polydimethylsiloxane/postmodified MIL‐53 composite layer coated on asymmetric hollow fiber membrane for improving gas separation performance

ABSTRACTComposite layer containing postmodified MIL‐53 (P‐MIL‐53) was exploited to be coated on as‐fabricated asymmetric hollow fiber membrane for improving gas separation performance. The morphology and pore size distribution of P‐MIL‐53 particles were characterized by SEM and N2 adsorption isotherm. The EDX mapping and FTIR spectra were performed to confirm the presence of P‐MIL‐53 deposited on the outer surface of hollow fiber membranes. The results of pure gas permeation measurement indicated that incorporation of P‐MIL‐53 particles in coating layer could improve permeation properties of hollow fiber membranes. By varying coating times and P‐MIL‐53 content, the membrane coated with PDMS/15%P‐MIL‐53 composite by three times achieved best performance. Compared to pure PDMS coated membrane, CO2 permeance was enhanced from 29.96 GPU to 40.24 GPU and ideal selectivity of CO2/N2 and CO2/CH4 also increased from 23.28 and 26.95 to 28.08 and 32.03, respectively. The gas transport through composite membrane was governed by solution‐diffusion mechanism and CO2 preferential adsorption of P‐MIL‐53 contributed to considerable increase of CO2 solubility resulting in accelerated permeation rate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44999.

Extending effective medium theory to finite size systems: Theory and simulation for permeation in mixed-matrix membranes

We present a novel theory for estimation of the effective permeability of pure gases in flat mixed-matrix membranes (MMMs), in which effective medium theory (EMT) is extended to systems with finite filler size and membrane thickness. We introduce an inhomogeneous filler volume fraction profile, which arises due to depletion of the filler in regions adjacent to the membrane ends, into the MMM permeation model. In this way, the effective medium approach (EMA) can still be applied to systems where the dispersant size is not small in comparison to the membrane thickness, and for which a permeability profiles arises in the MMM that is dependent on both filler size and membrane thickness, besides the filler-polymer equilibrium constant. It is found that increase in particle size reduces the effective membrane permeability at fixed membrane thickness, and that the effective membrane permeability increases with increase of the membrane thickness to asymptotically reach the value predicted by existing models. The present theory is validated against detailed simulations of the transport in MMMs, and theoretical predictions are found to be in agreement with those obtained from the exact calculations. Further, comparison of the exact effective permeability at different filler volume fractions is made for different packing configurations, showing variations in dispersant packing structure to have only a very weak effect on MMM performance.

Synthesis and Transport Properties of Novel MOF/PIM-1/MOF Sandwich Membranes for Gas Separation.

Metal-organic frameworks (MOFs) were supported on polymer membrane substrates for the fabrication of composite polymer membranes based on unmodified and modified polymer of intrinsic microporosity (PIM-1). Layers of two different MOFs, zeolitic imidazolate framework-8 (ZIF-8) and Copper benzene tricarboxylate ((HKUST-1), were grown onto neat PIM-1, amide surface-modified PIM-1 and hexamethylenediamine (HMDA) -modified PIM-1. The surface-grown crystalline MOFs were characterized by a combination of several techniques, including powder X-ray diffraction, infrared spectroscopy and scanning electron microscopy to investigate the film morphology on the neat and modified PIM-1 membranes. The pure gas permeabilities of He, H2, O2, N2, CH4, CO2 were studied to understand the effect of the surface modification on the basic transport properties and evaluate the potential use of these membranes for industrially relevant gas separations. The pure gas transport was discussed in terms of permeability and selectivity, highlighting the effect of the MOF growth on the diffusion coefficients of the gas in the new composite polymer membranes. The results confirm that the growth of MOFs on polymer membranes can enhance the selectivity of the appropriately functionalized PIM-1, without a dramatic decrease of the permeability.

Mixed matrix membranes comprising polymers of intrinsic microporosity and covalent organic framework for gas separation

Polymers of intrinsic microporosity (PIMs) exhibit the inherent superior permeability over traditional commercial polymers, however, the relatively low selectivity restrict their broad application in gas separation. In this study, novel kinds of mixed matrix membranes (MMMs) combined covalent organic frameworks (COFs) and PIMs were prepared and utilized for improving the selectivity of carbon capture process. Covalent organic framework (SNW-1) was synthesized via Schiff base chemistry and incorporated into polymer of intrinsic microporosity (PIM-1) to prepare MMMs. Pure gas permeation tests and mixed gases separation performances of the MMMs were conducted. Owing to its proper porosity characteristics and good compatibility with PIM-1 matrix, the incorporation of SNW-1 significantly intensified the diffusion process of CO2 within the membrane. Compared with pure PIM-1 membrane, the prepared MMMs showed an increment of 27.4% and 37.6% in selectivity of CO2/CH4 and CO2/N2 along with an enhancement of 116% in CO2 permeability. The strategy of incorporating COFs into polymers of intrinsic microporosity may hold promising potential in preparing high performance MMMs for gas separation.

Ionic liquid-modified Pebax® 1657 membrane filled by ZIF-8 particles for separation of CO2 from CH4, N2 and H2

3-Di-n-butyl-2-mthylimidazolium chloride (DnBMCl) ionic liquid (IL) was synthesized and used for modification of Pebax 1657 surface. ZIF-8 particles synthesized by different molar ratios of precursors, were introduced into the matrix of IL-Pebax 1657 for fabrication of mixed matrix membranes (MMMs) by coating method. Synthesized ZIF-8 particles were characterized using laser particle size analyzer, SEM, XRD and N2 adsorption. SEM, DSC, FTIR, 13C NMR, TGA and gas permeation tests were applied for characterization and performance evaluation of MMMs. The modification of Pebax 1657 with DnBMCl lead to formation of possible Carbon-Carbon bonds between Pebax 1657 and DnBMCl and also between ZIF-8 and DnBMCl. Pure gas permeation tests showed that the higher ideal selectivities of CO2/CH4, CO2/N2 and CO2/H2 were observed for DnBMCl-modified MMMs compared to unmodified MMMs and neat Pebax 1657 membrane. Plasticization lead to inferior CO2 separation ability of MMMs in mixed gas condition compared to pure gas test. The DnBMCl-modified Pebax 1657/ZIF-8 MMMs showed superior CO2/CH4, CO2/N2 selectivities at feed pressures of 2 and 4bar.

Fabrication, Characterization, and Hemocompatibility Investigation of Polysulfone Grafted With Polyethylene Glycol and Heparin Used in Membrane Oxygenators.

Polysulfone (PSF) was grafted chemically with polyethylene glycol (PEG) of different molecular weights (400, 2000, 10 000, and 20 000) and heparin to prepare PSF-PEG-Hep membranes (labeled as PSF-PEG400-Hep, PSF-PEG2000-Hep, PSF-PEG10 000-Hep, and PSF-PEG20 000-Hep). These membranes were synthesized via the following steps: (i) PSF chloromethylation; (ii) PEGylation; and (iii) heparin immobilization process. Water contact angle, critical water permeation pressure, ATR-FTIR, 1 H NMR, UV-visible spectrophotometry, and X-ray photoelectron spectroscopy were conducted to prove grafting success and to fix the optimal reaction parameters during chemical modification processes. To further evaluate the application potential of the PSF-PEG-Hep membrane in a membrane oxygenator, we conducted pure CO2 and O2 gas permeation tests and measured the gas exchange rates of CO2 and O2 through a membrane oxygenator using fresh porcine blood. Meanwhile, the hemocompatibility of the membrane was analyzed and compared by protein adsorption, platelet adhesion, and blood coagulation tests. Results of pure gas permeation experiments indicated that the excellent gas transmission properties through PSF membrane were preserved after modification. Blood oxygenation experiments through the PSF-PEG10 000-Hep membrane showed that when the flow rate of porcine blood was 1.5 L/min, CO2 and O2 exchange rates reached 102 and 110 mL/min, respectively, which could basically satisfy the gas exchange potential of commercial membrane oxygenators. Besides, the PSF-PEG-Hep membrane has demonstrated more prominent blood compatibility than PSF.

Highly permeable and aging resistant 3D architecture from polymers of intrinsic microporosity incorporated with beta-cyclodextrin

The polymers of intrinsic microporosity (PIM) incorporated with beta-cyclodextrin (β-CD) (referred to as PIM-CD) are prepared to investigate the effects of unique 3-dimensional (3D) hollow bowl structure of β-CD on gas separation performance and physical aging behavior. Compared with the pristine PIM membrane, the permeability of PIM-CD membranes increases with an increase in β-CD loading. Pure gas permeation tests reveal that the incorporation of a very small amount of β-CD into the PIM matrix can significantly enhance the CO2 permeability from 3368 to 8812 barrer, an increase of 162%, without too much sacrifice of gas selectivity. The gas separation performance of PIM-CD membranes can surpass the Robeson upper bound lines for almost all of the gases. Analyses from positron annihilation lifetime spectroscopy and wide angles x-ray diffraction confirm that the β-CD incorporation brings PIM-CD membranes with bigger micro-pores and higher fractional free volume, resulting in a higher gas permeability. In addition, the interactions between β-CD and PIM can restrict chain movement and make ultra-fine micro-pores difficult to collapse. Thus the PIM-CD membranes exhibit much greater resistance to physical aging than PIM membrane. These results may open up new avenues for molecular design of 3D architecture CD-based membranes for gas separation.

Gas separation performance of 6FDA-DAM-ZIF-11 mixed-matrix membranes for H2/CH4 and CO2/CH4 separation

Abstract In this study, gas separation performance of 6FDA-DAM-ZIF-11 mixed matrix membranes (MMMs) with various ZIF-11 percentages (0, 10, 20, 30 wt.%) were investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and particle size analysis were achieved to investigate ZIF-11 structure. SEM, Fourier Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC) and thermogravimetric (TGA) analysis were also carried out to characterize the membranes. In the SEM images of the MMMs, no apparent agglomeration between ZIF-11 particles and the 6FDA-DAM matrix was observed, even at 30 wt.% loading of the ZIF-11. The measured permeabilities for H2, CO2 and CH4 gases were found to be 272, 257 and 8.3 Barrers for 20 wt.% ZIF-11 containing MMMs measured at 30 °C and 4 bar. Pure gas permeation tests showed improvement in permeability of the MMMs but the ideal selectivity of gases remained almost constant for the various loadings. The permeability values increased as the ZIF-11 loading increased up to 20 wt.%. However, at higher loadings, 30 wt.%, the permeability decreased for all gases. The ideal selectivities of MMMs did not show significant change but the selectivity of 6FDA-DAM-ZIF-11 at 20 wt.% loading approached to the 2008 Robeson upper bound.

Mixed matrix membranes based on UiO-66 MOFs in the polymer of intrinsic microporosity PIM-1

Abstract This work presents a study of the gas transport properties for a novel class of mixed matrix membranes (MMMs) based on the polymer of intrinsic microporosity PIM-1 loaded with UiO-66 [Zr6O4(OH)4(O2CC6H4CO2)6] based metal-organic frameworks (MOFs). Three isoreticular MOFs were dispersed in the polymer matrix, standard UiO-66, UiO-66-NH2 (functionalized with an amino group) and UiO-66-(COOH)2 (functionalized with two carboxylic groups), in order to investigate the effect of the functionalization of the linker on the gas transport. The pure gas permeabilities of He, H2, O2, N2, CH4, CO2 were studied, for the as prepared membranes and after methanol treatment, focusing attention on the potential use of these membranes for CO2/CH4 separation. The pure gas transport of the MMMs was described on the basis of the Maxwell model. The predictions of the model are discussed and compared with the experimental permeability and selectivity of the MMMs and neat PIM-1. Mixed gas permeation tests were performed on a representative sample to investigate the actual separation performance with industrially relevant gas mixtures. These confirmed the good perspectives of these MMMs in applications like CO2 removal from biogas or from flue gas.

Aromatic block co-polyimide membranes for sour gas feed separations

Permeation properties of pure and gas mixture consisting of CO2, H2S, CH4, N2 and C2H6 through dense films of the block co-polyimides (6FDA-mPDA)-(6FDA-durene) are studied at 35–55°C and pressures of 100–500psi for combined separation of CO2, H2S and N2 from acid gas streams. The H2S composition in the gas mixture is up to 20vol%. This rigid block copolymer exhibits relatively constant or slightly decrease in pure gas permeability with increasing feed pressure for most of the penetrants. The pure gas CO2/CH4 and N2/CH4 selectivities are up to 61 and 2.6 respectively. The mixed gas studies also show relatively constant or slightly decrease in permeability coefficients with increase in pressure for most of the penetrants. One significant fact is that, at feed pressure of 500psi and 20vol% H2S in feed gas mixture (consisting of CO2, N2, CH4 and H2S), H2S/CH4 and CO2/CH4 separation factors are 23 and 27 respectively. These values are within the same order of magnitude or even better than those obtained in other state-of-the-art polymeric membranes that have been reported. Another unique feature of this co-polyimide is that, in addition to being selective to acid gas, it is also more selective to N2 as compare to CH4. Moreover, the CO2/CH4 separation factor does not suffer significant loss to the same degree as in the case of cellulose acetate (CA), even under these much more aggressive environments. This stability at moderate pressures and high H2S concentration is quite remarkable, as most reported studies are focused on low H2S concentrations and low pressures.