The transport properties of CO2 and CH4 for trimethylsilylated polysulfone membrane

The transport properties of CO₂ and CH₄ for TMSPSf (bisphenol A trimethylsilylated polysulfone) were measured, and compared with the values for PSf (bisphenol A polysulfone) and MPSf (bisphenol A methylated polysulfone) to explain the effect of molecular structure of polysulfones on gas transport properties. The permeability coefficients of three polysulfones rank in the order: TMSPSf>PSf>MPSf. TMSPSf is several times more permeable than PSf. The effect of the substituents on chain packing was related to the gas transport properties. The ranking of permeability coefficient correlates well with fractional free volume. The variation of d-spacing is also reasonably consistent with the permeability coefficient. The effects of pressure on the sorption and permeation properties of polysulfones were examined. The permeation properties for a mixture of CO₂ and CH₄ were also measured and these results were compared with the values of pure gases. The sorbed concentrations and permeability coefficients are well fitted to dual mode model. The permeability coefficients of each gas of binary mixture are reduced than those for pure gases, and the extent of reduction in permeability coefficient is the smallest for TMSPSf, which has the highest value of Langmuir capacity constant.     

The transport properties of CO2 and CH4 for brominated polysulfone membrane

The sorption and permeation properties of CO₂ and CH₄ for synthesized brominated polysulfone, BPSf (bromobisphenol A polysulfone) were measured, and compared with the values for PSf (bisphenol A polysulfone), MPSf (bisphenol A methylated polysulfone) and TMSPSf (bisphenol A trimethylsilylated polysulfone) to investigate the structure-property relationships. Especially, the effect of polarity of substituents on the transport properties was studied. The effect of operating pressure on the permeation properties of polysulfones was examined. The permeation properties for a mixture of CO₂ and CH₄ were also measured, and these results were compared with those obtained from the experiments of pure gases. The sorbed concentrations and permeability coefficients are well fitted to the dual mode model. The permeability coefficients of each gas of a binary mixture are less than those of pure gases, and the extent of reduction in permeability coefficient is larger for less permeable polymer. The ideal separation factor for four polysulfones increases in the following order: TMSPSf< PSf< BPSf< MPSf. The ideal separation factor for BPSf is higher than other polysulfones having similar permeability coefficients of CO₂ with BPSf. It can be explained that the strong polarity of bromine in BPSf increases cohesive energy density of polymer, and reduces the chain packing-inhibiting ability. The ranking of permeability coefficient correlates well with fractional free volume. The variation of d-spacing is not consistent with the permeability coefficient.     

The transport properties of CO2 and CH4 for chemically modified polysulfones

The sorption and transport properties of pure CO₂ and CH₄ for a series of polysulfones were measured. The effects of molecular structure of polysulfones on transport properties were studied using chemically modified polysulfones, including TMSPSF (bisphenol‐A trimethylsilylated polysulfone), BPSF (bromobisphenol‐A polysulfone), and BTMSPSF (bromobisphenol‐A trimethylsilylated polysulfone). The effects of operating pressure on the sorption and permeation properties of polysulfones were examined. The permeation properties for a mixture of CO₂ and CH₄ were also measured and these results were compared with those obtained from the experiments of pure gases. The sorbed concentrations and permeability coefficients are well fitted to a conventional dual‐mode model. The permeability coefficients of each gas of a binary mixture are lower than those of pure gases, which shows the competition effect between each component. The permeability coefficients of polysulfones rank in the following order, TMSPSF > BTMSPSF > bisphenol‐A polysulfone (PSF) > BPSF. The effect of the substituents on chain packing was related to the gas‐permeation properties. Fractional free volume (FFV) calculations and X‐ray diffraction were used to judge chain packing. In comparison with PSF, the higher values of permeability coefficients for TMSPSF and BTMSPSF are due to higher FFV and d spacing. The lower permeability coefficients for BPSF is attributed to the strong induced dipole interchain interaction. Addition of bromo substituents to TMSPSF is also found to decrease the permeability coefficients for BTMSPSF, suggesting that the potential increase in FFV due to packing–disrupting bulky trimethylsilyl groups is overridden by the increase in cohesive energy density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 391–400, 2000     

Gas permeabilities of CO2 and CH4 for polysulfones substituted with bromo and trimethylsilyl groups

Bromobisphenol A trimethylsilylated polysulfone (BTMSPSf) was synthesized, and the effect of bromo and trimethylsilyl groups on the pure CO₂ and CH₄ transport properties of polysulfone was examined. The ideal separation factor for BTMSPSf is reduced by about 10% than that for unmodified polysulfone (PSf), but BTMSPSf is about two times more permeable than PSf. The effect of the substituents on chain packing was related to the gas permeation properties. Fractional free volume (FFV) calculation, d-spacing and cohesive energy density were used to judge chain packing. In comparison with PSf, the higher values of permeability coefficients for BTMSPSf are due to higher FFV and d-spacing. The small decrease in ideal separation for BTMSPSf is explained as follows: the potential increase in FFV due to packing-disrupting bulky trimethylsilyl groups is overridden by the increase in cohesive energy density attributed to the addition of bromo substituents.     

Transport properties of gases through integrally skinned asymmetric composite membranes prepared from date pit powder and polysulfone

Studies were conducted on transport properties and separation performance of date pit/polysulfone composite membranes for CO₂, CH₄, N₂, He, and H₂ gases. Date seeds were obtained and processed into powder. Asymmetric flat sheet membrane was prepared by solvent casting method with 2–10 wt % date pit powder. Membrane characterization was done using high pressure gas permeation, X‐ray diffraction, thermogravimetric, and scanning electron microscope analyses. The separation performance and the plasticization resistance property were evaluated in terms of gas permeability, selectivity, and plasticization pressure, respectively. Time dependent performance properties were evaluated up to a pressure of 40 bar for 75 days. Results obtained showed the highest selectivity values of 1.54 (He/H₂), 3.637 (He/N₂), 2.538 (He/CO₂), 2.779 (He/CH₄), 3.179 (H₂/N₂), 3.907 (H₂/CO₂), 1.519 (CH₄/N₂), 1.650 (CO₂/N₂), and 1.261 (CO₂/CH₄) at 10 bar and 35 °C feed pressure and temperature, respectively. The resulting composite membrane showed about 39.50 and 66.94% increase in the selectivity of He/N₂ and CO₂/CH₄, respectively, as compared to the pure polysulfone membrane. Thus, the membrane composites possess some potentials in membrane gas separation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43606.     

Study of transport of pure and mixed CO2/N2 gases through polymeric membranes

The permeations of pure CO₂ and N₂ gases and a binary gas mixture of CO₂/N₂ (20/80) through poly(dimethylsiloxane) (PDMS) membrane were carried out by the new permeation apparatus. The permeation and separation behaviors were characterized in terms of transport parameters, namely, permeability, diffusion, and solubility coefficients which were precisely determined by the continuous‐flow technique. In the permeation of the pure gases, feed pressure and temperature affected the solubility coefficients of CO₂ and N₂ in opposite ways, respectively; increasing feed pressure positively affects CO₂ solubility coefficient and negatively affects N₂ solubility coefficient, whereas increasing temperature favors only N₂ sorption. In the permeation of the mixed gas, mass transport was observed to be affected mainly by the coupling in sorption, and the coupling was analyzed by a newly defined parameter permeation ratio. The coupling effects have been investigated on the permeation and separation behaviors in the permeation of the mixed gas varying temperature and feed pressure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 179–189, 2000     

Characterization of the permeation properties of CO2N2 gas mixtures in silicone rubber membranes

The separation characteristics of silicone rubber membranes are determined for CO₂N₂ gas mixtures. The analysis is performed as a function of composition, flow rate and pressure of the feed gas. Results are presented in terms of the variation in component permeability and separation factor as a function of the above parameters. Component permeabilities are calculated using the complete mixing model. Data analysis over the studied pressure range shows that the permeability coefficient of pure CO₂ gas in silicone rubber is 15 times higher than that of pure N₂ gas. This behaviour is completely altered for a mixture of the gases, where the calculated separation factors at low feed pressures and low CO₂ mole fractions in the feed stream are two- to three-fold lower than the separation factors for the pure gases. At higher feed pressures and high CO₂ mole fractions in the feed stream, the above behaviour is reversed; the separation factors for the gas mixture are now higher than those for the pure gases. Comparison of the permeation characteristics of silicone rubber and cellulose acetate membranes for CO₂N₂ gas mixtures shows similar ranges and values for the gas permeabilities and separation factors. However, much higher separation factors are obtained for the cellulose acetate membrane in the case of pure gas permeation.     

Development and characterization of homopolymers and copolymers from the family of polyphenylene oxides

Poly(2,6‐dimethyl‐1,4‐phenylene oxide), PDMPO, poly(2,6‐diphenyl‐1,4‐phenylene oxide), PDPPO, as well as their copolymers of different compositions, having both random and block structures, have been synthesized and characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and gel permeation chromatography. Solution‐cast films were prepared from all synthesized polymers using chloroform as a solvent. The thermal properties of the resulting films were characterized by differential thermal analysis and differential scanning calorimetry, whereas their morphology was investigated using X‐ray diffraction. Ultimately, the potential of the synthesized polymers for gas separation was studied by examining gas permeation properties of the respective thin films in single gas permeation tests involving N₂, O₂, CH₄, and CO₂. In general, the O₂ and CO₂ permeability coefficients decrease with the PDPPO content. However, the largest drop in the permeability coefficients occurs between PDMPO and a copolymer having the lowest PDPPO content, and the permeability coefficients PDPPO are comparable or even lower than the permeability coefficients of the copolymers having the largest PDDPO content. On the basis of combination of the permeability coefficients and their ratios for CO₂/CH₄ and O₂/N₂, random copolymers appear to be a better candidate for gas separation membranes than their block counterparts. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The gas permeation properties of 6FDA-2, 4, 6-trimethyl-1, 3-phenylenediamine (TMPDA)/1, 3-phenylenediamine (mPDA) copolyimides

Summary The gas permeation behavior of 2, 2’-bis (3, 4’dicarboxyphenyl) hexafluoropropane dianhydride(6FDA)- 2, 4, 6-Trimethyl-1, 3-phenylenediamine (TMPDA)/1,3-phenylenediamine (mPDA) polyimides was investigated by systematically varying the diamine ratios. The physical properties of the copolyimides were characterized by IR, DSC and TGA. All the copolyimides were soluble in most of the common solvents. The gas permeabilities and diffusion coefficients decreased with increasing mPDA content; however, the permselectivity of gas pairs such as H₂/N₂, O₂/N₂, CO₂/CH₄ was enhanced with the incorporation of mPDA moiety. The permeability coefficients of H₂, O₂, N₂, CO₂ and CH₄ were found to decrease with the increasing order of kinetic diameters of the penetrant gases. Moreover, all of the copolyimides studied in this work exhibited performance near, lying on or above the existing upper bound trade-off line between permselectivity and permeability.     

Investigation of Methane and Carbon Dioxide Gases Permeability Through PEBAX/PEG/ZnO Nanoparticle Mixed Matrix Membrane

This paper presents a new kind of mixed matrix membrane using polyethylene glycol (PEG) as organic filler. In this mix, PEG and ZnO nanoparticles (as inorganic modifier) were added to a PEBAX polymer matrix at different concentration to study their effects on the morphology, permeability and selectivity of the membrane. To characterize the chemical structure of samples FTIR and for morphological characterization, XRD and SEM were employed. The permeability of pure gases CO₂ and CH₄ in PEBAX, and PEBAX/PEG/ZnO with different ZnO and PEG contents were determined by the constant pressure-variable volume method. Also influences of temperature and pressure on permeation properties of these membranes were studied. The results were indicative of an increase in gas permeability and enhancement which for neat PEBAX membrane, CO₂/CH₄ permeability of 44.6 and 2.193 Barrer and selectivity of 20.39 were obtained. The permeability of PEBAX/PEG (40 wt.%)/ZnO (4 wt.%) membrane was enhanced to 94.49 Barrer for CO₂ and 3.933 for CH₄. The selectivity of PEBAX/ZnO(4 wt.%) improved to 31.58 for the CO₂/CH₄ gas pair.     

New high permeable polysulfone/ionic liquid membrane for gas separation

In this study, the effects of 1-Ethyl-3-methylimidazolium tetrafluoroborate ionic liquid on CO₂/CH₄ separation performance of symmetric polysulfone membranes are investigated. Pure polysulfone membrane and ionic liquid-containing membranes are characterized. Field emission scanning electron microscopy (FE-SEM) is used to analyze surface morphology and thickness of the fabricated membranes. Energy dispersive spectroscopy (EDS) and elemental mapping, Fourier transform infrared (FTIR), thermal gravimetric (TGA), X-ray diffraction (XRD) and Tensile strength analyses are also conducted to characterize the prepared membranes. CO₂/CH₄ separation performance of the membranes are measured twice at 0.3 MPa and room temperature (25 °C). Permeability measurements confirm that increasing ionic liquid content in polymer-ionic liquid membranes leads to a growth in CO₂ permeation and CO₂/CH₄ selectivity due to high affinity of the ionic liquid to carbon dioxide. CO₂ permeation significantly increases from 4.3 Barrer (1 Barrer=10^-10 cm³(STP)·cm·cm^-2·s^-1·cmHg^-1, 1cmHg=1.333kPa) for the pure polymer membrane to 601.9 Barrer for the 30 wt% ionic liquid membrane. Also, selectivity of this membrane is improved from 8.2 to 25.8. mixed gas tests are implemented to investigate gases interaction. The results showed, the disruptive effect of CH₄ molecules for CO₂ permeation lead to selectivity decrement compare to pure gas test. The fabricated membranes with high ionic liquid content in this study are promising materials for industrial CO₂/CH₄ separation membranes.     

Structural and transport properties of polydimethylsiloxane based polyurethane/silica particles mixed matrix membranes for gas separation

Mixed matrix membranes of synthesized polyurethane (PU) based on toluene diisocyanate (TDI), polydimethylsiloxane (PDMS) and polytetramethylene glycol (PTMG) with polyvinyl alcohol based polar silica particles were prepared by solution casting technique. The homogeneity and thermal properties of the prepared PDMS-PU/silica membranes were characterized using scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The SEM micrographs confirmed the distribution of silica particles in the polymer matrix without agglomerations. Gas permeation properties of membranes with different silica contents were studied for pure CO₂, CH₄, O₂, He and N₂ gases. The obtained results indicated the permeability of the condensable and polar CO₂ gas was enhanced whereas permeability of other gases decreased upon increasing the silica content of the mixed matrix membranes. The permeability of CO₂ and its selectivity over N₂ was increased from 68.4 Barrer and 22 in pure PDMS-PU to 96.7 Barrer and 64.4 in the mixed matrix membranes containing 10 wt% of the silica particles.     

Fluorinated copolyimide membranes for sour mixed-gas upgrading

Three random and two block 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)-based copolyimides with different 6FpDA:Durene molar ratio varying from 25 to 80% were prepared and characterized. The pure-gas permeation data of their membranes were investigated at 100 psi and 22 °C. The CO₂/CH₄ ideal selectivity coefficient increased to around 47 with the increase of the 6FpDA content to 80% in the copolymer backbone while the CO₂ permeability coefficient found to be the highest (378 barrer) with highest Durene content copolymer. Based on its attractive pure-gas permeation properties(CO₂/CH₄ = 47), 6FDA-6FpDA/6FDA-Durene (4:1) block copolyimide was selected for further analyses, where the effect of pressure and temperature on its gas transport properties was evaluated. Furthermore, the mixed-gas permeation properties were investigated using multicomponent sweet and sour gas mixtures prepared from N₂ (30% or 10%), CH₄ (59%), C₂H₆ (1%), CO₂ (10%), and H₂S (0% or 20%)accordingly. The sweet mixed-gas CO₂/CH₄ selectivity and CO₂ permeability coefficients of 6FDA-6FpDA/6FDA-Durene (4:1) are around 39 and 45 barrer, respectively, at elevated pressure (800 psi). The polymer, however, showed nonideal behavior when subjected to high H₂S-content gas mixture (20 vol. % H₂S), where the CO₂/CH₄ selectivity value dropped to around 21 and the H₂S/CH₄ selectivity coefficient is 13. The CO₂ and H₂S permeability coefficients are 42 and 26 barrer, respectively, at an upstream pressure up to 500 psi. When plotted on the combined acid gas permeability-selectivity curve, the polymer separation efficiency was nearby the high-performing polymers reported in the literature, and way superior to the industrial standard glassy polymer, cellulose acetate, used currently in gas separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48336.     

The morphology and gas‐separation performance of membranes comprising multiwalled carbon nanotubes/polysulfone–Kapton

The development of desirable chemical structures and properties in nanocomposite membranes involve steps that need to be carefully designed and controlled. This study investigates the effect of adding multiwalled nanotubes (MWNT) on a Kapton–polysulfone composite membrane on the separation of various gas pairs. Data from Fourier transform infrared spectroscopy and scanning electron microscopy confirm that some studies on the Kapton–polysulfone blends are miscible on the molecular level. In fact, the results indicate that the chemical structure of the blend components, the Kapton–polysulfone blend compositions, and the carbon nanotubes play important roles in the transport properties of the resulting membranes. The results of gas permeability tests for the synthesized membranes specify that using a higher percentage of polysulfone (PSF) in blends resulted in membranes with higher ideal selectivity and permeability. Although the addition of nanotubes can increase the permeability of gases, it decreases gas pair selectivity. Furthermore, these outcomes suggest that Kapton–PSF membranes with higher PSF are special candidates for CO₂/CH₄ separation compared to CO₂/N₂ and O₂/N₂ separation. High CH₄, CO₂, N₂, and O₂ permeabilities of 0.35, 6.2, 0.34, and 1.15 bar, respectively, are obtained for the developed Kapton–PSF membranes (25/75%) with the highest percentage of carbon nanotubes (8%), whose values are the highest among all the resultant membranes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43839.     

Gas transport properties of polyaniline membranes

The transport properties of He, H₂, CO₂, O₂, N₂, and CH₄ gases in solvent cast, HCl doped, and undoped polyaniline (PANi) membranes were determined. Measurements were carried out at 40 psi pressure from 19°C to 60°C. An excellent correlation was found between the diffusion coefficients and the molecular diameters of gases. The solubility coefficients of gases were found to correlate with their boiling points or critical temperatures. The sepa-ration factors for CO₂/N₂ and CO₂/CH₄ are dominated by the high solubility of CO₂. These correlations enable us to predict the permeability, diffusion, and solubility coefficients of other gases. After the doping-undoping process, the fluxes of gases with kinetic diameters smaller than 3.5 Å increased but those of larger gases decreased. This results in a higher separation factor for a gas pair involving a small gas molecule and a larger one. © 1996 John Wiley & Sons, Inc.     

Separation of binary mixtures of carbon dioxide and methane through sulfonated polycarbonate membranes

Polycarbonate (PC) was sulfonated to varying degrees using acetyl sulfate. FTIR and NMR experiments were carried out to confirm sulfonation. The membranes were characterized by DSC and TGA to assess thermal stability. Ion exchange capacity (IEC) and degree of sulfonation (DS) were determined and their effect on permeation of CO₂ and CH₄ gases was investigated. Free volume fractions (FVF) of the membranes were found to decrease from 0.31 to 0.19 as the DS increased from 0 to 39.4%. Single gas permeation studies revealed that sulfonated PC exhibited higher selectivities than unmodified PC at reduced permeability. For a DS of 14.4%, sulfonated PC exhibited a selectivity of 36.1, which was 1.7 times that of unmodified PC, whereas the permeability dropped from 8.4 to 4.7 Barrers. In case of binary CO₂/CH₄ mixture permeation through PC membrane of the same DS, an increase in CO₂ feed concentration from 5 to 40 mol % produced an increase in permeability from 0.24 to 2.0 Barrers and a rise in selectivity from 11.7 to 27.2 at constant feed pressure (20 bar) and temperature (30°C). A rise in the feed pressure from 5 to 30 bar at a constant feed composition of 5% CO₂ resulted in a reduction in permeability from 0.38 to 0.2 Barrers and selectivity from 15.6 to 10.2. Sulfonated PC was found to be a promising candidate for separation of CO₂ from CH₄. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Gas separation performance of 6FDA-based polyimides with different chemical structures

This work reports the gas separation performance of several 6FDA-based polyimides with different chemical structures, to correlate chemical structure with gas transport properties with a special focus on CO₂ and CH₄ transport and plasticization stability of the polyimides membranes relevant to natural gas purification. The consideration of the other gases (He, O₂ and N₂) provided additional insights regarding effects of backbone structure on detailed penetrant properties. The polyimides studied include 6FDA-DAM, 6FDA-mPDA, 6FDA-DABA, 6FDA-DAM:DABA (3:2), 6FDA-DAM:mPDA (3:2) and 6FDA-mPDA:DABA (3:2). Both pure and binary gas permeation were investigated. The packing density, which is tunable by adjusting monomer type and composition of the various samples, correlated with transport permeability and selectivity. The separation performance of the polyimides for various gas pairs were also plotted for comparison to the upper bound curves, and it was found that this family of materials shows attractive performance. The CO₂ plasticization responses for the un-cross-linked polyimides showed good plasticization resistance to CO₂/CH₄ mixed gas with 10% CO₂; however, only the cross-linked polyimides showed good plasticization resistance under aggressive gas feed conditions (CO₂/CH₄ mixed gas with 50% CO₂ or pure CO₂). For future work, asymmetric hollow fibers and carbon molecular sieve membranes based on the most attractive members of the family will be considered.     

Mixed gas and pure gas transport properties of copolyimide membranes

Copolyimides 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     

Separation of CO2/CH4 through carbon molecular sieve membranes derived from P84 polyimide

The separation of CO₂/CH₄ separation is industrially important especially for natural gas processing. In the past decades, polymeric membranes separation technology has been widely adopted for CO₂/CH₄ separation. However, polymeric membranes are suffering from plasticization by condensable CO₂ molecules. Thus, carbon molecular sieve membranes (CMSMs) with excellent separation performance and stability appear to be a promising candidate for CO₂/CH₄ separation. A commercially available polyimide, P84 has been chosen as a precursor in preparing carbon membranes for this study. P84 displays a very high selectivity among the polyimides. The carbonization process was carried out at 550–800 °C under vacuum environment. WAXD and density measurements were performed to characterize the morphology of carbon membranes. The permeation properties of single and equimolar binary gas mixture through carbon membranes were measured and analyzed. The highest selectivity was attained by carbon membranes pyrolyzed at 800 °C, where the pyrolysis temperatures significantly affected the permeation properties of carbon membranes. A comparison of permeation properties among carbon membranes derived from four commercially available polyimides showed that the P84 carbon membranes exhibited the highest separation efficiency for CO₂/CH₄ separation. The pure gas measurement underestimated the separation efficiency of carbon membranes, due to the restricted diffusion of non-adsorbable gas by adsorbable component in binary mixture.     

Effect of doping treatment on gas transport properties and on separation factors of polyaniline memebranes

Gas permeation experiments of H₂, O₂, CO₂, N₂, and CH₂ were carried out with freestanding films of the conjugated polymer polyaniline (PANi). At first annealed to remove residual solvent, PANi membranes were doped (i.e., protonated) in a strongly acidic medium (HCl 4M), undoped in a basic medium (NH₄OH 1M), and redoped in a slightly acidic medium (HCl 10^?2M). Protonation and deprotonation kinetics were studied by elementary analysis Gas permeation experiments were performed with the annealed, doped, undoped, and redoped PANi films. The gas transport mechanism was clearly influenced by the diffusivity factor and it obeyed a Fickian diffusion model. From the variations in permeability coefficients with the doping treatment, gases could be divided in two subgroups comprising H₂, O₂, and CO₂ on one hand and N₂ and CH₄ on the other. After the doping–undoping–redoping process, gas fluxes were increased by 15% for the smaller gases and were decreased by 45% for the larger gases. As a consequence gas separation factors were approximately doubled for a gas pair involving the two subgroups and these were unchanged for a gas pair involving only one subgroup. The highest O₂/N₂ and CO₂/CH₄ selectivity coefficients were, respectively, equal to 14 and 78. © 1995 John Wiley & Sons, Inc.