NSF Award
9261401
This study will examine the permeability and selectivity for gas transport of isotropic polymeric membranes made of poly(trimethyl silylpropyne) (PTMSP; ?C(CH3)=C(SiCH3)3!n). Previous research on PTMSP membranes have shown that because of their large free volume, the solubility and diffusivity of gas molecules through the membrane is very large, and this results in a very high gas permeability. The high permeability is accompanied by relatively low selectivity (i.e. the ration of the flux of one species to that of the other). This lack of selectivity can be attributed again to the large free volume size which facilitates the easy passage of molecules of all sizes. Consequently, to date PTMSP membranes have not been of practical value in gas separations. The research points out, however, that the selectivity has been measured by passing pure gases through the membrane and taking the flux ratio under identical driving conditions. Recent experiments have shown that the membrane exhibits selectivity in co-permeation: In particular experiments at MTR demonstrate a 27:1 selectivity on n-butane in an n- butane/methane mixture at 24oC. The result of this research will be built by studying pure and mixed gas transport in PTMSP with a series of permanent gases such as methane or air, and closely related organic solvent vapors (CCl4, CF4, a series of freons and with hydrocarbon vapors such as butane and pentane if successful, the research will lead to membranes which can separate butane from methane (important in the natural gas industry), and organic vapors from air (an important separation in many environmental concerns).
