Enhanced H2S and CO2 selectivities through bromo-substitution of polyimide membranes for sour natural gas upgrading

Abstract

Hydrogen sulfide (H₂S) removal from sour natural gas streams via polymeric membranes is a challenging process. Membranes are prone to H₂S-induced plasticization at high gas feed pressures which reduces their separation properties (i.e., H₂S/CH₄ selectivity). In this work, we report the preparation of CARDO(Br)-containing polyimides that form membranes with increased polarity due to the presence of bromo groups in their backbones. Gas separation performance was evaluated of membranes prepared from 6FDA-Durene/CARDO(Br) (1:1) copolyimide using a quinary gas mixture containing ∼20 mol.% H₂S at a high gas feed pressure of 500 psia. Such conditions are of great importance to assess polymeric membrane performance since they mimic those encountered in industrial sour natural gas purification. The presence of the bromo groups [6FDA-Durene/CARDO(Br) (1:1) copolyimide] improved H₂S/CH₄ and CO₂/CH₄ selectivity coefficients by 42 % and 49 %, respectively, compared to its non-brominated [6FDA-Durene/CARDO (1:1)] copolyimide, while maintaining high H₂S and CO₂ permeability coefficients. The findings from this work avail polymeric membranes with attractive performance for implementation in membrane-based sour natural gas upgrading applications.