CO₂-Selective Membranes Containing Sterically Hindered Amines for CO₂/H₂ Separation

This work exploited amine steric hindrance effect to developing next-generation CO 2 -selective facilitated transport membranes for H 2 purification for fuel cells. The new membrane was synthesized by incorporating moderately hindered poly-N-isopropylallylamine as a fixed-site carrier along with mobile carriers into cross-linked polyvinylalcohol-poly(siloxane) network. The new membrane exhibited high CO 2 permeability of greater than 6500 Barrers, CO 2 /H 2 selectivity of more than 300, and CO 2 /N 2 selectivity of at least 650 at 110 °C and a feed pressure of 2 atm. Better membrane separation results were achieved as the sweep-side water content was increased. The membrane also showed good stability of at least 430 h at 110 °C and 2 atm. The membrane performance reduced as temperature was increased from 107 to 180 °C as a result of the reduction of water retention ability of the membrane; however, it still held a good CO 2 /H 2 selectivity of about 34 at 180 °C.