The impact of water, BTEX compounds and ethylene glycol on the performance of perfluoro(butenyl vinyl ether) based membranes for CO2 capture from natural gas

Abstract

Glassy perfluoropolymers offer a remarkable resistance towards many species that can alter the separation performance of conventional polymeric membranes. In this study, the performance of Cytop® and CyclAFlor™ random copolymers of perfluoro(butenyl vinyl ether) (PBVE) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD) are studied for the first time for carbon dioxide capture in the presence of impurities that are common in raw natural gas. Water vapor sorption isotherms were S-shaped for both polymers, indicating the formation of water clusters. The water permeability decreased with vapor activity in both perfluoropolymers as the formation of these clusters decreased water diffusivity. The presence of the water clusters, however, had no impact on the performance of Cytop® and poly(50%PBVE-co-50%PDD) for CO2/CH4 separation. Typical concave sorption isotherms were obtained for toluene and xylene in poly(50%PBVE-co-50%PDD), while convex isotherms were observed in Cytop®. It was speculated that this change in isotherm shape may have been due to the small number of larger free volume elements within Cytop®, as observed in x-ray diffraction analysis. Neither toluene nor xylene had a significant impact on CO2 and CH4 permeabilities in Cytop®, while a gradual decrease in both permeabilities was noted for poly(50%PBVE-co-50%PDD) as the vapor activity increased, due to either competitive sorption or pore blocking. Finally, liquid glycol carryover caused no change on the performance of Cytop® membranes, while a slight drop in the CO2/CH4 separation factor for poly(50%PBVE-co-50%PDD) was observed.