H2S/CO2 separation using sterically hindered amine membranes

With the growing interest in carbon capture from syngas and natural gas, H2S/CO2 separation is gradually becoming important in the gas processing and carbon capture industries. This work describes the development of amine-based facilitated transport membranes (FTMs) suitable for syngas desulfurization. Six amino acid salt carriers with varying steric hindrance were synthesized and used to fabricate FTMs. Their H2S/CO2 separation performances were evaluated at 107 °C and 7 bar feed pressure, using a dry feed composition of 1.5% H2S and 98.5% CO2. H2S/CO2 selectivity improved significantly as amine steric hindrance was increased. While mildly hindered amines showed low H2S/CO2 selectivities of around 5, sterically hindered and tertiary amines showed substantially improved separation performance, with selectivities in the range of 10–20. A highly hindered carrier containing the di-tert-butyl amine moiety showed the highest selectivity of 19.6, along with an H2S permeance of 560 GPU. The di-tert-butyl amine-based FTM was used to study the effect of temperature and feed H2S content on H2S/CO2 separation performance. The performances of the newly devised FTMs exceed the H2S/CO2 upper bound, and the learnings shed light on the design of amine carriers for acid gas separations.