CO2-selective membranes containing amino acid salts for CO2/N2 separation

In this paper, facilitated transport membranes comprising polyvinylamine (PVAm) as fixed carrier and different amino acid salts (AAS) as mobile carriers were synthesized for post-combustion capture. The AAS carriers were prepared by deprotonating alanine (Ala), lysine (Lys), and proline (Pro) with 2-(1-piperazinyl)ethylamine (PZEA). CO2 separation performances of the membranes with these AAS carriers were compared, and the AAS effectiveness to facilitate transport of CO2 was in the order of PZEA-Pro > PZEA-Lys > PZEA-Ala. The membrane comprising 35 wt% PVAm and 65 wt% PZEA-Pro at 57 °C rendered a promising CO2 permeance of 936 GPU and a CO2/N2 mixed gas selectivity of 193. When the PVAm was reduced to 15 wt%, i.e., its 20 wt% was replaced by the mobile carrier of PZEA-Sar (sarcosinate), the permeance further improved to 947 GPU with a remarkable CO2/N2 selectivity of 210. Moreover, thermal gravimetric analysis showed a good thermal stability of the membrane, and membrane stability testing also gave stable transport performance. Furthermore, spectroscopic ellipsometry analysis exhibited a uniform membrane selective layer and an excellent agreement on the membrane thickness of ca. 170 nm measured independently by SEM. In addition, the membranes presented in this paper surpassed both the Robeson upper bound and the modified upper bound, indicating a great potential for CO2 capture.