Roy presents his paper entitled, "The Effect of Substituent Size and Shape on Gas Transport Properties in Substituted Polyacetylenes" at the 2004 North American Membrane Society (NAMS) meeting in Honolulu, Hawaii. Co-authors Roy Raharjo, H. Lee, and Benny D. Freeman (UT Austin) and T. Sakaguchi and T. Masuda (Kyoto University).
Abstract
Poly[1-phenyl-2-[p-(trimethylsilyl) phenyl]acetylene] (PTMSDPA) is a highly permeable, glassy, substituted acetylene polymer. Like poly(1- trimethylsilyl-1-propyne) (PTMSP), this polymer is more permeable to larger, more condensable hydrocarbons than to smaller, less condensable permanent gases. Therefore, it may be useful for separations such as the removal of higher hydrocarbons from natural gas or hydrogen streams. Although PTMSDPA has outstanding properties for such separations, PTMSDPA is soluble in common hydrocarbons and, therefore, would not be suitable for use as a commercial membrane in such applications. However, desilylation of this polymer renders it completely insoluble, thereby strongly improving its chemical resistance. The resulting polymer, poly(diphenylacetylene) (PDPA), has a fractional free volume (FFV) of 0.23, slightly lower than that in PTMSDPA (0.26). The pure gas permeation properties of various light gases and hydrocarbons in PTMSDPA and PDPA at 35oC are reported and compared to those in other substituted polyacetylenes. A significant decrease in gas permeability values, most likely due to the decrease in the FFV, is observed after desilylation. For example, the permeability of nitrogen is reduced by almost 50%, from 640 to 280 Barrers. The permeability of n- butane is reduced even more, from 16000 to 2400 Barrers. The permeability measurement was done at 35oC with an upstream pressure of 50 psig (4.46 bar) for all permanent gases, methane, ethane, and propane and 8 psig (1.56 bar) for n-butane. The downstream pressure was maintained at atmospheric.