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Cellulose triacetate (CTA) is a workhorse polymeric membrane material for industrial CO 2 /CH 4 separation. This study investigates the doping of CTA with ionic liquids (ILs) to reduce the crystallinity of the CTA and enhance its affinity with CO 2 , thus increasing CO 2 permeability and CO 2 /light gas selectivity. CTA films doped with 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF 4 ]) and 1-ethyl-3-methylimidazolium dicyanamide ([emim][dca]) were prepared; and the effect of IL loading on properties of the CTA, such as crystallinity, density, degradation temperature, glass transition temperature, and gas transport properties, were determined. The IL doping reduces the glass transition temperature and degree of crystallinity of CTA, increasing gas diffusivity and permeability. The IL doping also increases CO 2 /CH 4 solubility selectivity and CO 2 /N 2 permeability selectivity, due to the affinity of these ILs with CO 2 , compared to light gases such as CH 4 and N 2. This study demonstrates a promising route in manipulating the morphology and gas transport properties of semi-crystalline polymers by doping with ILs.

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The gas permeation properties of poly(1‐trimethylsilyl‐1‐propyne) (PTMSP), poly(1‐phenyl‐1‐propyne) (PPP), and blends of PTMSP and PPP have been determined with hydrocarbon/hydrogen mixtures. For a glassy polymer, PTMSP has unusual gas permeation properties which result from its very high free volume. Transport in PPP is similar to that observed in conventional, low‐free‐volume glassy polymers. In experiments with n‐butane/hydrogen gas mixtures, PTMSP and PTMSP/PPP blend membranes were more permeable to n‐butane than to hydrogen. PPP, on the other hand, was more permeable to hydrogen than to n‐butane. As the PTMSP composition in the blend increased from 0 to 100%, n‐butane permeability increased by a factor of 2600, and n‐butane/hydrogen selectivity increased from 0.4 to 24. Thus, both hydrocarbon permeability and hydrocarbon/hydrogen selectivity increase with the PTMSP content in the blend. The selectivities measured with gas mixtures were markedly higher than selectivities calculated from the corresponding ratio of pure gas permeabilities. The difference between mixed gas and pure gas selectivity becomes more pronounced as the PTMSP content in the blend increases. The mixed gas selectivities are higher than pure gas selectivities because the hydrogen permeability in the mixture is much lower than the pure hydrogen permeability. For example, the hydrogen permeability in PTMSP decreased by a factor of 20 as the relative propane pressure (p/psat) in propane/hydrogen mixtures increased from 0 to 0.8. This marked reduction in permanent gas permeability in the presence of a more condensable hydrocarbon component is reminiscent of blocking of permanent gas transport in microporous materials by preferential sorption of the condensable component in the pores. The permeability of PTMSP to a five‐component hydrocarbon/hydrogen mixture, similar to that found in refinery waste gas, was determined and compared with published permeation results for a 6‐Å microporous carbon membrane. PTMSP exhibited lower selectivities than those of the carbon membrane, but permeability coefficients in PTMSP were nearly three orders of magnitude higher. © 1996 John Wiley & Sons, Inc.