Ternary mixed-gas separation for flue gas CO2 capture using high performance thermally rearranged (TR) hollow fiber membranes

Abstract

A comprehensive study evaluated the mixed-gas (CO2/N-2/O-2) separation performance of thermally rearranged polybenzoxazole-co-imide (TR-PBOI-AD5) hollow fiber membranes fabricated in-house (pure-gas CO2 permeance of 481 GPU and ideal CO2/N-2 selectivity of 17.7). The criteria for the determining the two major operating conditions (pressure ratio and feed flow rate) were identified in order to deliver optimal separation performance with low process energy consumption. By varying the feed CO2 concentrations, it was found that a single-stage operation using TR-PBOI-AD5 (produced by bis-APAF and DAM as the TR-able and non-TR-able diamines, respectively, based on 6FDA) hollow fiber membranes was not sufficient to meet the required 90% permeate CO2 purity target, while a two-stage operation using the same membranes led to a permeate CO2 purity (81%) closer to the target value. The comparison study among the TR polymer membranes and three other polymer membranes highlighted the significance of an appropriate choice of a mixed-gas separation operating scheme to fully utilize the exceptional permeation properties of the recently developed high performance membranes such as TR polymeric membranes.