HYDROCARBON HYDROGEN MIXED-GAS PERMEATION IN POLY(1-TRIMETHYLSILYL-1-PROPYNE) (PTMSP), POLY(1-PHENYL-1-PROPYNE) (PPP), AND PTMSP/PPP BLENDS/

The gas permeation properties of poly(1-trimethylsilyl-1-propyne) (PTM SP), poly(1-phenyl-1-propyne) (PPP), and blends of PTMSP and PPP have been determined with hydrocarbon/hydrogen mixtures. For a glassy polym er, 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 composit ion in the blend increased from 0 to 100%, n-butane permeability incre ased by a factor of 2600, and n-butane/hydrogen selectivity increased from 0.4 to 24. Thus, both hydrocarbon permeability and hydrocarbon/hy drogen selectivity increase with the PTMSP content in the blend. The s electivities measured with gas mixtures were markedly higher than sele ctivities calculated from the corresponding ratio of pure gas permeabi lities. The difference between mixed gas and pure gas selectivity beco mes more pronounced as the PTMSP content in the blend increases. The m ixed gas selectivities are higher than pure gas selectivities because the hydrogen permeability in the mixture is much lower than the pure h ydrogen permeability. For example, the hydrogen permeability in PTMSP decreased by a factor of 20 as the relative propane pressure (p/p(sat) ) in propane/hydrogen mixtures increased from 0 to 0.8. This marked re duction in permanent gas permeability in the presence of a more conden sable hydrocarbon component is reminiscent of blocking of permanent ga s transport in microporous materials by preferential sorption of the c ondensable component in the pores. The permeability of PTMSP to a five -component hydrocarbon/hydrogen mixture, similar to that found in refi nery waste gas, was determined and compared with published permeation results for a 6-Angstrom microporous carbon membrane. PTMSP exhibited lower selectivities than those of the carbon membrane, but permeabilit y coefficients in PTMSP were nearly three orders of magnitude higher. (C) 1996 John Wiley & Sons, Inc.