Gas transport properties of PDMS-coated reverse osmosis membranes

We report a systematic study of the adaptation of polyamide reverse osmosis (RO) membranes for gas separation applications. The RO membranes examined in this study contained defects or pores in the polyamide selective layer that compromised gas selectivity. These membranes were surface-coated with poly(dimethylsiloxane) (PDMS) to caulk the defects, and pure-gas permeances of He, H2, CO2, and CH4 were measured at 35 °C, and upstream pressure ranging from 3 to 16 atm. After a PDMS coating was applied, the pure-gas selectivities increased and were comparable to those of typical aromatic polyamide membranes. Pure-gas permeances of coated RO membranes were also constant or slightly decreased with increasing upstream pressure, suggesting that PDMS had filled and eliminated the defects. In addition, CO2 and CH4 mixed-gas (50/50) permeation tests were performed at 35 °C and fugacities ranging from 3 to 15 atm. CO2 did not appear to plasticize the thin polyamide selective layer of the coated RO membranes. CO2/CH4 mixed-gas selectivities were about 20% higher than pure-gas selectivities, presumably due to dual-mode competitive sorption effects.