Pure Gas Permeation Research Articles

Hydrogen separation and purification using crosslinkable PDMS/zeolite A nanoparticles mixed matrix membranes

The transport properties of gases in polydimethylsiloxane (PDMS)/zeolite A mixed matrix membranes (MMMs) were determined based on pure gas permeation experiments. MMMs were prepared by incorporating zeolite 4A nanoparticles into a PDMS matrix using a new procedure. The permeation rates of C3H8, CH4, CO2, and H2 were evaluated through a dense homogeneous pure PDMS membrane and PDMS/4A MMMs to assess the viability of these membranes for natural gas sweetening and hydrogen purification. SEM investigations showed good adhesion of the polymer to the zeolite in MMMs. Permeation performance of the membranes was also investigated using a laboratory-scale gas separation apparatus and effects of feed pressure, zeolite loading and pore size of zeolite on the gas separation performance of the MMMs were evaluated. The MMMs exhibited both higher selectivity of H2/CH4 and H2 permeability as compared with the neat PDMS membrane, suggesting that these membranes are very promising for gas separations such as H2/CH4 separation.

Mixed gas and pure gas transport properties of copolyimide membranes

AbstractCopolyimides were synthesized from dianhydride of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with various diamine contents of 4,4′‐oxydianiline (ODA) and 2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (TeMPD) by chemical imidization in a two‐step procedure. Polyimides (PIs) were characterized using thermogravimetric analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, as well as specific volume and free volume. The gas transport properties for pure gas and blends of CO2 and CH4 for the homopolymers and 6FDA‐ODA/TeMPD copolymers were investigated at 35°C and 150 psi pressure. In pure gas permeation, permeability of CO2 and CH4 increased with increasing TeMPD content in the diamine moiety, whereas the ideal selectivity decreased with increasing TeMPD content. In the mixed gas permeation, permeabilities and separation factor were measured as a function of CO2 feed molar fraction for five PI membranes. The behavior of pure gas and mixed gas permeabilities and separation factor of CO2/CH4 mixtures as the chemical nature of the diamine and the CO2 molar fraction in the feed gas were varied and are discussed in detail. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013

Fabrication variables affecting the structure and properties of supported carbon molecular sieve membranes for hydrogen separation

Abstract A high molecular weight polyimide (Matrimid) was used as a precursor for fabricating supported carbon molecular sieve membranes without crack formation at 550–700 °C pyrolysis temperature. A one-step polymer (polyimide) coating method as precursor of carbon layer was used without needing a prior modification of a TiO2 macroporous support. The following fabrication variables were optimized and studied to determine their effect on the carbon structure: polymeric solution concentration, solvent extraction, heating rate and pyrolysis temperature. Two techniques (Thermogravimetric analysis and Raman spectroscopy) were used to determine these effects on final carbon structure. Likewise, the effect of the support was also reported as an additional and important variable in the design of supported carbon membranes. Atomic force microscopy and differential scanning calorimetry quantified the degree of influence. Pure gas permeation tests were performed using CH4, CO, CO2 and H2. The presence of a molecular sieving mechanism was confirmed after defects were plugged with PDMS solution at 12 wt%. Gas selectivities higher than Knudsen theoretical values were reached with membranes obtained over 650 °C, showing as best values 4.46, 4.70 and 10.62 for H2/N2, H2/CO and H2/CH4 ratio, respectively. Permeance values were over 9.82×10−9 mol/(m2 Pa s)during pure hydrogen permeation tests.

Gas Separation Properties of Metal Organic Framework (MOF-5) Membranes

Permeation and separation properties of CO2/H2 and CO2/N2 mixtures for high quality, thin (∼14 μm) MOF-5 membranes prepared by the secondary growth method were studied at different temperatures, feed pressures, and feed composition. The MOF-5 membranes offer selective permeation for CO2 over H2 or N2 with CO2/H2 or CO2/N2 mixture feed under the experimental conditions studied. Compared to pure gas permeance data, the presence of the strongly adsorbing CO2 in the binary mixture separation suppresses less adsorbing H2 or N2, similar to what was observed for zeolite membranes. The MOF-5 membranes exhibit a separation factor for CO2/H2 of close to 5 with a feed CO2 composition of 82% and a separation factor for CO2/N2 greater than 60 with a feed CO2 composition of 88% at 445 kPa and 298 K. With the mixture feed, CO2 permeance increases and N2 (or H2) permeance decreases, and hence the CO2/N2 (or H2) separation factor increases, with increasing CO2 partial pressure (through the change of composition or feed pr...

Separation performance of CO2 through Supported Magnetic Ionic Liquid Membranes (SMILMs)

Ionic liquids (ILs) have reached an enormous interest as CO2 solvents due to their unique properties such as negligible vapour pressure and selectivity, making them very attractive in order to obtain stable supported liquid membranes. ILs containing magnetic metals in their anion are known as Magnetic Ionic Liquids (MILs) and they may show different behaviour in the presence of an external magnetic field.This work evaluates the preparation and use of a new class of supported liquid membranes based on Magnetic Ionic Liquids: Supported Magnetic Ionic Liquid Membranes (SMILMs) for CO2 separation/concentration. Four paramagnetic ionic liquids have been studied: [P6,6,6,14]2+[CoCl4]2−, [P6,6,6,14]+[FeCl4]−, [P6,6,6,14]2+[MnCl4]2− and [P6,6,6,14]3+[GdCl6]3; in combination with a hydrophobic or a hydrophilic PVDF porous support. An evaluation of the membrane stability was carried out and CO2, N2 and air permeabilites for stable SMILMs were experimentally determined. CO2/N2 and CO2/air selectivities were estimated and introduced in the Robeson diagram for a comparison with previous reported materials. Pure gas permeation results demonstrate that these SMILMs show much higher CO2 permeabilities when comparing with N2 and air. This selectivity may indicate a potential application of using SMILMs for the selective removal/recovery of CO2 from a gas stream and further work will perform the evaluation of an external magnetic field in the separation behaviour.

Zeolitic imidazolate framework (ZIF-8) based polymer nanocomposite membranes for gas separation

As synthesised ZIF-8 nanoparticles (size ∼ 60 nm and specific surface area ∼ 1300–1600 m2 g−1) were directly incorporated into a model polymer matrix (Matrimid® 5218) by solution mixing. This produces flexible transparent membranes with excellent dispersion of nanoparticles (up to loadings of 30 wt%) with good adhesion within the polymer matrix, as confirmed by scanning electron microscopy, dynamic mechanical thermal analysis and gas sorption studies. Pure gas (H2, CO2, O2, N2 and CH4) permeation tests showed enhanced permeability of the mixed matrix membrane with negligible losses in selectivity. Positron annihilation lifetime spectroscopy (PALS) indicated that an increase in the free volume of the polymer with ZIF-8 loading together with the free diffusion of gas through the cages of ZIF-8 contributed to an increase in gas permeability of the composite membrane. The gas transport properties of the composite membranes were well predicted by a Maxwell model whilst the processing strategy reported can be extended to fabricate other polymer nanocomposite membranes intended for a wide range of emerging energy applications.

High performance membranes based on ionic liquid polymers for CO2 separation from the flue gas

Three vinyl functionalized imidazolium based room-temperature ionic liquids (RTILs): 1-vinyl-3-ethylimidazolium dicyanamide ([veim][dca]), 1-vinyl-3-butylimidazolium dicyanamide ([vbim][dca]) and 1-vinyl-3-heptylimidazolium dicyanamide ([vhim][dca]) were synthesized and UV-polymerized to form free standing membranes. The pure gas permeabilities of CO2 and N2 of these newly developed membranes acquired at 1 atm 35 °C increased with an increase in the number of N-alkyl group in the monomers but their ideal CO2–N2 selectivities decreased. The three vinyl functionalized monomers were blended with three free RTILs: 1-ethyl-3-methylimidazolium dicyanamide ([emim][dca]), 1-ethyl-3-methylimidazolium tetracyanoborate ([emim][B(CN)4]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) and subsequently subjected to UV-polymerization to form the poly(RTIL)–RTIL composite membranes. The incorporation of free RTILs not only significantly increases the CO2 permeability but also greatly improves the CO2–N2 selectivity. The best separation performance is achieved for the poly([vbim][dca])–[emim][B(CN)4] (1 : 2) and poly([vbim][dca])–[emim][dca] (1 : 2) composite membranes, which have CO2 permeabilities of 340 and 273 barrers and CO2–N2 selectivities of 42 and 53, respectively, at 1 atm 35 °C. The mixed gas permeabilities of these two composite membranes are 297 and 253.5 barrers with corresponding CO2–N2 selectivities of 38.8 and 50.6, respectively, using a 50 : 50 CO2–N2 mixed gas at 2 atm 35 °C. These two composite membranes have separation performance very close to the 2008 “Robeson Upper Bound”, suggesting their potential for industrial applications, especially for the post-combustion flue gas treatment.

Fabrication and characterization of PEI/PVP‐based carbon hollow fiber membranes for CO2/CH4 and CO2/N2 separation

AbstractCarbon hollow fiber membranes derived from polymer blend of polyetherimide and polyvinylpyrrolidone (PVP) were extensively prepared through stabilization under air atmosphere followed by carbonization under N2 atmosphere. The effects of the PVP compositions on the thermal behavior, structure, and gas permeation properties were investigated thoroughly by means of differential scanning calorimetry, thermogravimetric analysis, X‐ray diffraction, and pure gas permeation apparatus. The experimental results indicate that the transport mechanism of small gas molecules of N2, CO2, and CH4 is dominated by the molecular sieving effect. The gas permeation properties of the prepared carbon membranes have a strong dependency on PVP composition. The carbon membranes prepared from polymer blends with 6 wt % PVP demonstrated the highest CO2/CH4 and CO2/N2 selectivities of 55.33 and 41.50, respectively. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3167–3175, 2012

Pilot plant performance of rubbery polymeric membranes for carbon dioxide separation from syngas

Pre-combustion carbon capture separates carbon dioxide from syngas before combustion. Rubbery polymeric membranes offer the ability to separate carbon dioxide from syngas, and in particular hydrogen, with reasonable selectivity. Here, the gas separation performance of three rubbery polymeric membranes, poly dimethyl siloxane (PDMS), cross-linked polyethylene glycol (PEG) and poly (ether-b-amide) (PEBAX 2533), are reported upon exposure to real unshifted syngas, as part of the CO2CRC Mulgrave capture project. At low temperatures, all three membranes were able to separate CO 2 from syngas; however competitive sorption by other syngas components significantly altered their performance relative to reported laboratory results. For PDMS, under syngas conditions CO 2 permeability was reduced compared to the pure gas permeability, but CO 2/H 2 and CO 2/N 2 selectivity were improved in the presence of syngas. This resulted in good CO 2 separation performance for this membrane. However over 24 h of exposure the performance decreased somewhat. In contrast, both PEG and PEBAX membranes demonstrated poor CO 2 separation performance upon exposure to syngas. In particular, low CO 2/H 2 selectivities where observed, indicating that both membranes upon exposure to syngas had poor selective ability.

High performance ZIF-8/6FDA-DAM mixed matrix membrane for propylene/propane separations

We report significantly enhanced propylene/propane (C 3H 6/C 3H 8) selectivity in mixed matrix membranes fabricated using 6FDA-DAM polyimide and a zeolitic imidazolate framework (ZIF-8). Equilibrium isotherms and sorption kinetics of C 3H 6 and C 3H 8 at 35 °C were studied on a 200 nm commercially available ZIF-8 sample produced by BASF. Mixed matrix dense films were formed with 6FDA-DAM and 200 nm BASF ZIF-8 particles. SEM imaging showed generally good adhesion between the ZIF-8 and 6FDA-DAM without the need for surface-treating ZIF-8. Pure gas permeation showed significantly enhanced mixed matrix ZIF-8/6FDA-DAM membrane C 3H 6/C 3H 8 separation performance over the pure 6FDA-DAM membrane performance. A C 3H 6 permeability of 56.2 Barrer and C 3H 6/C 3H 8 ideal selectivity of 31.0 was found in ZIF-8/6FDA-DAM mixed matrix membrane with 48.0 wt% ZIF-8 loading, which are 258% and 150% higher than the pure 6FDA-DAM membrane, respectively for permeability and selectivity. Permeation properties of C 3H 6 and C 3H 8 in ZIF-8 were back-calculated by the Maxwell model for composite permeability using pure gas permeation data, leading to a C 3H 6 permeability of 277 Barrer and C 3H 6/C 3H 8 selectivity of 122. Mixed gas permeation also verified that selectivity enhancements were achievable in mixed gas environment by ZIF-8.

Effect of quenching temperature on the performance of poly(vinylidene fluoride) microporous hollow fiber membranes fabricated via thermally induced phase separation technique on the removal of CO 2 from CO 2-gas mixture

The capture and utilization of carbon dioxide from flue gases and sweetening of natural gas, is currently a global issue. Hollow fiber membranes contactors are new emerged technology proposed for this purpose. In the present work hollow fiber membranes were fabricated and used as a membrane contactor and utilized in the absorption of carbon dioxide from natural gas. Poly(vinylidene fluoride) (PVDF) was used to fabricate microporous hollow fiber membranes. The fibers were prepared by using glycerol triacetate (triacetin) as solvent, and through thermally induced phase separation technique. The fabricated fiber membranes were investigated at various quenching temperatures. Characterization of the resulting membranes included scanning electron microscopy and differential scanning calorimetry. Microscopic observation showed that the membrane was composed of spherical clusters. The crystallinity increased with the quenching temperature. Permeation performance was also determined, including pure water permeability and gas permeation test. The results showed that at lower quenching temperatures, the structure of the membrane was dense. Therefore the water permeability and gas permeability were low. Complete removal of CO 2 was possible using PVDF hollow fiber membrane contactor enclosed of hollow fiber membranes fabricated at high quenching temperatures.

Facilitated transport effect of Ag + ion exchanged halloysite nanotubes on the performance of polyetherimide mixed matrix membrane for gas separation

This study investigated the facilitated transport effect of Ag + ion exchanged halloysite nanotubes (HNTs) as filler on the gas separation performance of asymmetric mixed matrix membranes (MMMs). The polymer matrix employed in this study was commercial polyetherimide (PEI) Ultem 1000. The modified HNTs were prepared by treating HNTs with N-β-(aminoethyl)-γ-aminopropyltrimethoxy silane (AEAPTMS) and silver nitrate. FESEM, XRD, FTIR, TGA, DSC, EDX and pure gas permeation testing were used to characterise the modified HNTs and the fabricated MMMs. Three protocols were performed: (i) S-HNT MMM (no Ag + ion exchange treatment), (ii) S-Ag-HNT MMM (first Ag + ion exchanging and then silylation of HNTs), and (iii) Ag-S-HNT MMM (first silylation and then Ag + ion exchanging of HNTs). FTIR and TGA showed that silylation occurred successfully. From XRD we found out that, the Ag + ion exchanging did not affect the HNT crystalline structure. EDX revealed that, Ag + ion exchanging after silylation of HNTs resulted in much higher concentration of Ag + ions in the Ag-S-HNT product. This in turn showed that AEAPTMS could successfully enhance the HNTs cation exchange capacity (CEC), which resulted in higher concentration of Ag + ions in the modified HNTs. DSC disclosed depression in the glass transition temperature ( T g) of MMMs possessed Ag + ions. Three major factors were discussed: (i) facilitated transport affect of Ag + ions, (ii) Knudsen diffusion and (iii) T g depression. By increasing the fillers loading, all of the factors exhibited an additive influence on the permeability. The order of closeness of the resultant MMMs to the ideal morphology was as follows: Ag-S-HNT MMM > S-Ag-HNT MMM > S-HNT MMM. Ag-S-HNT MMM exhibited outstanding performance among the three protocols.

Mixed gas separation study for the hydrogen recovery from H 2/CO/N 2/CO 2 post combustion mixtures using a Matrimid membrane

In this work, the membrane separation of hydrogen from binary, ternary and quaternary mixtures of H 2, N 2, CO and CO 2 is presented. Hydrogen permeability through a polyimide Matrimid 5218 membrane was experimentally obtained using the constant pressure technique. The influence of the feed gas composition, temperature (30–100 °C), pressure range (up to 6 bar), and flow rates was experimentally analyzed. As expected, the pure gas permeability of H 2 was only slightly dependant on pressure and had an average value of 17.7 × 10 −14 m 3(STP) m m −2 s −1 kPa −1 at 30 °C. Hydrogen permeability was not affected by the presence of nitrogen and carbon monoxide, and as a result the mixed gas selectivities for the H 2/N 2/CO mixtures are very close to the selectivities calculated from pure gas permeation data. On the contrary, a strong dependency of the hydrogen permeability on CO 2 concentration was observed even at low concentrations of CO 2. A reduction of 42% of the hydrogen permeability coefficient was obtained when a mixture of 10/90 vol.% H 2/CO 2 was used as feed gas. Accordingly H 2/CO 2 selectivity decayed from a value of 4.2 calculated from pure gas permeabilities to 2.7 when permeation data were obtained in mixed gas experiments. The preferential sorption of CO 2 on the Langmuir sites of the excess free volume portion of the polymer allowed explaining and quantifying this phenomenon. The “dual-mode sorption, partial immobilization” model was used to describe H 2 and CO 2 permeation behavior of pure, binary, ternary and quaternary mixtures. The model sorption parameters for N 2 and CO 2 in the polymer Matrimid 5218 were obtained from the literature meanwhile those for H 2 and for CO were unknown and resulted from the fitting of the experimental data to the proposed model. Satisfactory agreement between predicted permeability results and experimental data with a correlation coefficient ( R) higher than 0.95 and mean squared relative error (MSRE) lower than 0.01 was attained. Thus, this work reports useful knowledge related to the intrinsic material properties, considering gas mixtures of industrial interest and essential when other membrane configurations like hollow fibers, mixed matrix membranes or polymer blends are proposed.

Microporous carbon membranes from sulfonated poly(phthalazinone ether sulfone ketone): Preparation, characterization, and gas permeation

Microporous carbon membranes (MCM) were prepared from sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) through stabilization and pyrolysis processes. The effects of sulfonation degree (SD) of SPPESK and the stabilization temperature on the structure and gas permeation of MCM were investigated. The thermal decomposition behavior of SPPESK was studied by thermogravimetric analysis-mass spectrometry. The evolution of functional groups on membrane surface was detected by Fourier transform infrared spectroscopy during heat treatment. The resultant MCM was characterized by X-ray diffraction, Raman spectroscopy, nitrogen adsorption technique and pure gas permeation test (including the gases of H2, CO2, O2, and N2), respectively. The results have shown that the removal of sulfonic acid groups in SPPESK leads to a weight loss stage in the temperature range of 250–450°C. The surface area, maximum pore volume, and gas permeability of MCM increase with the SD increasing from 59 to 75%, together with the reduction of selectivity. Similarly, the gas permeability of MCM also increases with elevating the stabilization temperature from 350 to 400°C at the loss of selectivity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Gas separation performance of polyethersulfone/multi-walled carbon nanotubes mixed matrix membranes

Mixed matrix membranes (MMM) comprised of multi-walled carbon nanotubes (MWCNTs) inside polyethersulfone (PES) matrix were fabricated and characterized for gas separation performance. The MWCNTs were purified with acid mixtures (HNO 3/H 2SO 4; v/v = 1:3) to remove carbonaceous impurities followed by surface functionalization with 3-aminopropyltriethoxylsilane (APTES) to allow well dispersion of the tubes in organic solvent such as N-methlypyrrolidone (NMP) during the preparation of PES/MWCNTs suspension. Effects of purification, functionalization and MWCNTs loading on the gas permeation properties of the MMM were investigated by varying the MWCNTs loading in the PES matrix from 0.5–3.0 wt.%. The fabricated MWCNTs/PES MMM were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA) and pure gas permeation test. Gas permeation measurement showed that MMMs embedded with different kinds of applied CNTs exhibited different separation performances. For example, gas permeation measurement showed that MMM embedded with 1.0 wt.% purified and functionalized MWCNTs possessed better performances in terms of permeability and selectivity in comparison to raw MWCNTs. The highest gas selectivity was achieved at 0.5 wt.% MWCNTs loadings ( α CO 2 / CH 4 = 250.13; α O 2 / N 2 = 10.65) and decreased as the loadings were increased from 1.0 to 3.0 wt.%. The reduction in performance possibly due to the presence of interface voids which became prominent at higher MWCNTs loading. The high selectivity of fabricated MMM suggested that the present works have a great potential to be utilized practically in gas separation technology.

Pure and mixed gas permeation through a composite polydimethylsiloxane membrane

AbstractA thin polydimethylsiloxane (PDMS) layer on polyethersulfone (PES) support was synthesized and pure and mixed gas permeation of C3H8, CH4, and H2 through it was measured. At first, a macroporous PES support was prepared by using the phase inversion method and characterized. Then, a thin layer of PDMS was coated over the support. Finally, permeation behavior of the synthesized composite membrane was investigated by pure and mixed gas experiments under various operating conditions. The synthesized PDMS/PES membrane showed much better gas permeation performance than others reported in the literature. Pure gas experiments showed that increase in the transmembrane pressure increases the permeability coefficient of heavier gases, C3H8, while decreases those of lighter ones, CH4 and H2. Exactly opposite behavior was observed in mixed gas experiments due to the competitive sorption and diffusion in the plasticized polymer matrix. Temperature was realized to induce similar effects on the permeability of pure and mixed gases. As expected, in rubbery membranes such as PDMS, permeability values of more condensable gases decrease with increasing temperature, whereas those of permanent gases increase. In the case of mixed gas experiments, increase in the C3H8 concentration in feed led to increase in the permeabilities of all the components due to the C3H8‐induced swelling of the PDMS film. High C3H8/H2 and C3H8/CH4 ideal selectivities of 22.1 and 14.7, respectively, at a transmembrane pressure of 7 atm as well as reasonable C3H8 separation factor (SF) values for all mixed gas experiments (in the range of 8.1–16.8) demonstrated the ability of the synthesized PDMS/PES membrane for the separation of organic vapors from permanent gases. Copyright © 2009 John Wiley & Sons, Ltd.

Mixed matrix membrane incorporated with large pore size halloysite nanotubes (HNT) as filler for gas separation: Experimental

This study investigated the gas separation and transport properties of asymmetric mixed matrix membranes (MMM) fabricated from polyetherimide (PEI); Ultem 1000 incorporated with raw and modified halloysite nanotubes (HNT) as filler. The modified HNTs; S-HNTs were prepared by treating HNTs with N-β-(aminoethyl)-γ-aminopropyltrimethoxy silane (AEAPTMS). FESEM, XRD, FTIR, TGA, DSC and pure gas permeation testing were used to characterise the S-HNTs and the fabricated MMMs. In the first part of the experiments, the effect of dope preparation factors such as: ultrasonic sonication period, filler wetting period and priming period were investigated. In the second part, the influence of silane concentration on the fabricated MMMs was studied. Results showed that, increasing the silane concentration, led to higher tendency in HNT agglomeration which resulted in poor separation properties but permeability enhancement. In the last part, the effect of S-HNTs loading was experienced. Our observations showed that the dispersion of nanoparticles decreased with an increase in the S-HNTs loading. Accordingly, 0.5% loading of silylated-HNT yielded the optimum MMMs in terms of permeability (27% increase) and selectivity (8% increase).

Effects of montmorillonite nano-clay fillers on PEI mixed matrix membrane for CO 2 removal

This paper focuses on the effect of montmorillonite nano-clay fillers on polyetherimide (PEI) mixed matrix membrane, specifically upon the removal of carbon dioxide. Five different types of montmorillonite (MMT) nano-clays, including unmodified and industrially modified clays, were used as filler to fabricate asymmetric flat sheet mixed matrix membrane (MMM) via a dry/wet phase inversion technique. The five types of clay used were: raw MMT, Cloisite 15A, general MMT, hydrophobic MMT and hydrophilic MMT. The MMTs were characterized by X-ray diffractometry (XRD), thermal gravimetric analysis (TGA), Fourier-transform infrared (FTIR). The fabricated MMMs were characterized by differential scanning calorimetry (DSC), field emission scanning electron microscopic (FESEM) and pure gas permeation testing. The gas permeation results revealed the following order in terms of the permselectivity for CO 2/CH 4 separation: Cloisite 15A > general MMT > hydrophilic MMT > hydrophobic MMT > raw MMT. The best results were obtained at 0.5 wt.% Cloisite 15A loading where the selectivity enhancement was about 28% as compared to that of neat PEI.

Synthesis and characterization of bis (4-maleimidophenyl) fluorene and its semi interpenetrating network membranes with polyether imide (Ultem ® 1000)

A semi-interpenetrating network (semi-IPN) of bis (4-maleimidophenyl) fluorene (cardo-BMI) and polyether imide (PEI, Ultem ® 1000) was prepared. The structure of bis (4-maleimidophenyl) fluorene and the corresponding semi-IPNs was determined by nuclear magnetic resonance and Fourier transform infrared spectroscopy, respectively. The thermal properties of the cardo-BMI and semi-IPNs were evaluated by thermogravimetry and differential scanning calorimetry. The semi-IPNs exhibited thermal stability up to 480 °C. The morphology of the semi-IPNs was evaluated by scanning electron microscopy. Asymmetric membranes were prepared from the semi-IPN material by the wet phase inversion method. The pure gas permeation properties of the PEI and semi-IPN membranes were evaluated for oxygen (O 2), nitrogen (N 2), carbon dioxide (CO 2) and methane (CH 4) by the constant pressure and variable volume method at an absolute feed pressure of 0.69 MPa at 22 °C. The CO 2/N 2 selectivity of 39.2 ± 3.0 with a CO 2 permeance of 18.3 ± 4.0 GPU of semi-IPN membrane was higher than the PEI membranes (selectivity 21.6 ± 4.1 and CO 2 permeance 0.5 ± 0.1 GPU). The highest CO 2/CH 4 selectivity of the semi-IPN membrane was 49.3 ± 3.5 compared to 37 for a PEI dense film. Among the semi-IPN membranes, those with 5 wt% cardo-BMI exhibited better performance than the 1% and 10%.

Dual-sorption model for H2/CO2 permeation in glassy polymeric Matrimid membrane

This work deals with the membrane separation of hydrogen and carbon dioxide. Permeation experiments of pure and binary mixtures of H2 and CO2 were performed using the constant pressure technique and a planar membrane made of the commercial polyimide Matrimid 5218. For pure gases permeability values of 23.4 Barrer for hydrogen and of 5.2 Barrer for carbon dioxide were obtained leading to an ideal selectivity of 4.5 at 6 bar feed pressure. In the case of gas mixtures, H2 permeability decreases with increasing contents of CO2, while the permeability of carbon dioxide in mixtures presents similar values to pure gas permeabilities. As a result, the H2/CO2selectivity obtained from mixed gas experiments decays to an average value of 3. The dual-sorption model with a partial permeant immobilization was used to predict each component permeation behavior for pure gases and binary mixtures. The carbon dioxide diffusion coefficients through the Matrimid polymer in the Henry and Langmuir mode were obtained, DD CO2, 2....