Temperature Dependence of Light Hydrocarbons Sorption and Transport in Dense Membranes Based on Tetradecyl Substituted Silicone Rubber

Solubility-selective polymer membranes are promising materials for C3+ hydrocarbons removal from methane and other permanent gas streams. To this end, a dense solubility-selective membrane based on crosslinked poly(tetradecyl methyl siloxane) was synthesized. Sorption of methane, ethane, and n-butane in the polymer was measured in the temperature range of 5-35 degrees C. An abnormal temperature dependence of sorption was detected, contradicting the generally accepted view of sorption as an exothermic process. In particular, methane shows minimal sorption at 5 degrees C. The abnormal temperature behavior was found to be related to crystallization of the alkyl side chains at temperatures below similar to 10 degrees C. Gas permeability determined by sorption and permeation methods are in reasonable agreement with each other and decrease in the order n-C4H10 > C2H6 > CH4. The solubility of these alkanes changes in the same order indicating that poly(tetradecyl methyl siloxane) is indeed the sorption-selective membrane. The diffusivities and permeabilities of studied alkanes declined with decreasing temperature, whereas the n-C4H10/CH4 permselectivity increases with decreasing temperature, reaching a value of 23 at 5 degrees C.

Automated summary

A solubility-selective membrane based on crosslinked poly(tetradecyl methyl siloxane) was synthesized to remove C3+ hydrocarbons from methane and other permanent gas streams. An abnormal temperature dependence of sorption was detected, contradicting the generally accepted exothermic sorption process. The sorption behavior is related to the crystallization of the alkyl side chains at temperatures below 10 degrees C. The gas permeability and solubility of alkanes decrease in the order n-C4H10 > C2H6 > CH4, indicating the selective properties of the membrane.