Oxidatively stable membranes for CO2 separation and H2 purification

CO2-selective facilitated transport membranes are well-known for providing remarkably high CO2/H2 selectivity along with high permeance at high temperatures (100 - 120 °C). This work demonstrates the development of a new class of facilitated transport membranes containing quaternaryammonium hydroxide small molecules and quaternaryammonium hydroxide- and fluoride-containing polymers as mobile carriers and fixed-site carriers, respectively, for CO2 separation and H2 purification. The active nature of tetramethylquaternaryammonium hydroxide as a mobile carrier was successfully demonstrated with high CO2 permeance. However, the membrane performance was improved significantly by the incorporation of quaternaryammonium hydroxide- and/or fluoride-containing polymers in the membrane. The resulting hydroxide- and fluoride-containing membranes exhibited CO2 permeance >50 GPU and CO2/H2 selectivity >100 at 120 °C using humid air as the sweep gas. The membrane composition was optimized, and the transport stability of the membrane was investigated. The membrane showed oxidative stability during the 145-h transport measurement at 120 °C using air as the sweep gas. Furthermore, the effects of sweep steam content and membrane thickness were investigated. As the sweep steam content was increased (especially for steam content >50%), both CO2 permeance and CO2/H2 selectivity increased. As the membrane thickness was reduced from 15 µm to 2 µm, a sharp drop in the CO2/H2 selectivity was observed whereas the CO2 permeance did not seem to increase as prominently as the H2 permeance. In addition, the membrane was successfully scaled up using a roll-to-roll continuous membrane fabrication machine, and the scale-up membrane showed similar performance as the lab-scale membrane.