Nanotube-reinforced facilitated transport membrane for CO2/N2 separation with vacuum operation

A novel facilitated transport membrane was synthesized in a composite membrane configuration with a 170-nm selective layer coated on a polyethersulfone nanoporous substrate. In the selective layer, poly(N-vinylformamide-co-vinylamine) with amino groups covalently bound to the polymer backbone was used as the fixed-site carrier and an aminoacid salt, synthesized by deprotonating sarcosine with 2-(1-piperazinyl)ethylamine, was blended as the mobile carrier. The membrane demonstrated a CO2 permeance of 975 GPU (1 GPU = 10-6 cm3 (STP) cm-2 s-1 cmHg-1) and a CO2/N2 selectivity > 140 at 57 °C with 1 atm feed and permeate pressures. The membrane performance was also characterized with a vacuum pulled on the permeate side to simulate actual separation process conditions. However, the rubbery selective layer of the synthesized membrane sank into the nanoporous substrate, resulting in a drastically reduced CO2 permeance. To address this issue, multi-walled carbon nanotubes (MWNTs) wrapped by a copolymer poly(1-vinylpyrrolidone-co-vinyl acetate) were dispersed in the selective layer as reinforcement nanofillers. The gas permeation measurements showed that the incorporation of MWNTs strengthened the polymer matrix and the selective layer penetration was refrained by a 3 wt% MWNT loading. The presence of MWNTs also mitigated the polymer compaction if the feed gas was compressed.