Pure and mixed gas CH4 and n-C4H10 permeability and diffusivity in poly (dimethylsiloxane)

Pure and mixed gas n-C4H10 and CH4 permeability coefficients in poly(dimethylsiloxane) (PDMS) are reported at temperatures from -20 to 50 degrees C. CH4 partial pressures range from 1.5 to 14.6 atm, and n-C4H10 partial pressures range from 0.09 to 1.8 atm. CH4 permeability increases with increasing n-C4H10 concentration in the polymer. For example, at -20 degrees C, CH4 permeability increases to approximately twice its pure gas value, from 730 to 1500 Barrer, as n-C4H10 concentration increases from 0 to 75 cm 3 (STP)/cm(3) polymer. In contrast, n-C4H10 permeabilities in the mixtures are essentially unaffected by the presence of CH4. Diffusion coefficients of n-C4H10 and CH4 in mixtures were calculated using mixture permeability data and mixture solubility data. n-C4H10-induced plasticization increases n-C4H10 and CH4 diffusion coefficients in mixtures. Mixed gas n-C4H10/CH4 permeability, solubility, and diffusivity selectivities are lower than those estimated from pure gas measurements due to the higher CH4 permeability, solubility, and diffusion coefficients in mixtures. The mixed gas permeability selectivity increases as n-C4H10 fugacity increases and temperature decreases. In contrast, mixture diffusivity selectivity varies little with temperature or n-C4H10 concentration. The increase in mixed gas permeability selectivity with increasing n-C4H10 activity and decreasing temperature is mainly due to increases in n-C4H10/CH4 solubility selectivity. Based upon a Maxwell-Stefan analysis, the influence of coupling effects on permeation properties were negligible. (C) 2007 Elsevier B.V. All rights reserved.