Pure and mixed gas CH_4 and n-C_4H_(10) sprption and dilation in poly(dimethylsiloxane)

摘要

Pure and mixed gas n-C_4H_(10) and CH_4 sorption and dilation properties in poly(dimethylsiloxane) (PDMS) are reported at temperatures ranging from -20 to 50℃. CH_4 partial pressures range from 3.1 to 16 atm, and n-C_4H_(10) partial pressures range from 0.07 to 1.3 atm. Based on the mixed gas sorption results, the presence of n-C_4H_(10) in the polymer enhances CH_4 solubility. For instance, at 25℃, a 10% increase in CH_4 solubility, from 0.50 (pure gas) to 0.55 cm~3 (STP)/(cm~3 polymer atm), is observed when the n-C_4H_(10) activity goes from 0 to 0.29. At -20℃, as n-C_4H_(10) activity increases from 0 to 0.53, CH_4 solubility increases by almost 35%, going from 0.77 to 1.03 cm~3 (STP)/(cm~3 polymer atm). In contrast, n-C_4H_(10) sorption properties in these mixtures are not measurably affected by the presence of CH_4. The n-C_4H_(10)/CH_4 solubility selectivity in PDMS increases as temperature decreases and as n-C_4H_(10) activity in the mixture increases. For example, at 25℃, the solubility selectivity increases from 52 to 60 as n-C_4H_(10) activity increases from 0.11 to 0.34. At 0℃, n-C_4H_(10)/CH_4 solubility selectivity increases from 84 to 105 as n-C_4H_(10) activity increases from 0.09 to 0.33. Pure and mixed gas dilation results are used to calculate partial molar volumes of CH_4 and n-C_4H_(10) in the polymer. Dilation isotherms in mixtures agree with estimates based on pure gas sorption and dilation measurements.