Natural gas sweetening using TEGMC polyimide hollow fiber membranes

Raw natural gas contains a significant range of impurities, i.e. H2S, CO2, C2, C3, C6+ etc. The acidic H2S and CO2 are especially highly corrosive to processing and transporting equipment and cause serious environmental issues. In the current study, we investigated H2S and CO2 removal efficiency of TEGMC (TriEthylene Glycol Monoesterified Crosslinked) hollow fiber membranes under realistic natural gas sweetening conditions. The membranes had been stored under ambient condition over seven years but still show good gas separation performance without any particular regeneration treatments. Unexpectedly, the presence of various hydrocarbons, i.e. C2, C3, and toluene, in the feed gas enhances both H2S/CH4 and CO2/CH4 selectivity. Indeed, the condensable hydrocarbons suppress the CH4 permeation through competitive sorption with less effect on the permeation of H2S and CO2. Such a phenomenon is unique in membrane separations, suggesting that penetrant competition can be a useful tool rather than a problem to tune the membrane performance in some cases.