(640b) Facilitated Transport in Hydroxide-Exchange Membranes for Post-Combustion CO2 Separation

Facilitated transport, hydroxide-exchange membranes have been fabricated for the separation of CO₂ from post-combustion flue gas feed. First, a correlation between expected basicity of the fixed-site functional group and CO₂ separation performance is highlighted. Later, this observation is used to suggest that phosphonium may be a good candidate for achieving high separation performance. Separation tests show that quaternary phosphonium-based membranes achieve separation performance above Robeson’s Upper Bound, an empirical bound describing the inverse relationship between permeability and selectivity. Specifically, permeabilities as high as 1090 and selectivities as high as 275 have been achieved. As expected, increases in CO₂ permeability are observed when increasing the degree of functionalization. In contrast, there is an small decrease in CO₂/N₂ selectivity when increasing the degree of functionalization, attributed to the increasingly large water uptakes at higher degree of functionalization. The high performance found in the membrane can be attributed to the combination of the quaternary phosphonium moiety and efficient transport channels.