Kinetic H2S/CO2 selectivity in an exceptionally sterically hindered amine membrane

Abstract

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 transport occurs exclusively via 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 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 permselectivity of 20, and an overall separation performance surpassing the H₂S/CO₂ upper bounds.