Abstract
Journal of Materials Chemistry A 2024, 12, 29138-29144
Kinetic H2S/CO2 Selectivity in an Exceptionally Sterically Hindered Amine Membrane
S. Rao, X. Deng, C. Zou, B. Prasad, Y. Han, L.-C. Lin, and W.S.W. Ho
Facilitated transport membranes (FTMs) show great promise for H2S/CO2 separation, an industrially important yet challenging process. Herein, we report FTMs with excellent H2S/CO2 separation performance and investigate how contradictory thermodynamic and kinetic reaction preferences affect FTM selectivity. For membranes based on an extremely sterically hindered di-tert-butylamine carrier, CO2聽transport occurs exclusively via聽a slow bicarbonate pathway. Reducing the membrane thickness shifts the reaction preference from the thermodynamically favored bicarbonate pathway to the kinetically favored amine-H2S reaction, leading to a 10-fold improvement in H2S/CO2聽selectivity. This unusual trend of increasing selectivity with decreasing thickness, the opposite of typical FTMs, enables simultaneous improvements in membrane permeance and selectivity. This translates to an exceptional H2S/CO2聽permselectivity of 20, and an overall separation performance surpassing the H2S/CO2聽upper bounds.