Preparation and Characterization of Polybenzimidazole-Based Hollow Fiber Membranes for Pre-Combustion Carbon Dioxide Capture

Pre-combustion carbon dioxide capture from synthesis (syn) gas in an integrated gasification combined cycle (IGCC) power production scheme provides significant opportunity for membrane-based technologies.  The high pressure of the process stream and high partial pressure of CO₂ in that stream provide the driving force necessary for energy efficient separation if the membrane-based separation system is integrated at realistic process conditions and provides adequate flux.  The high temperature (>200 °C) and presence of H₂S and steam in syn gas present a very challenging operating environment for any separation system.   Previous studies by our group have demonstrated the utility of polybenzimidazole (PBI)-based membranes for syn gas separations in these environments.  PBI-based membranes have commercially attractive H₂/CO₂ selectivity, exceptional thermal stability (T_g > 400 °C), and exhibit tolerance to steam and H₂S.  The H₂ permeability of the-state-of-the-art PBI-based materials mandates ultra-thin selective layers and high surface area membrane deployment platforms such as hollow fibers. Our aim is to develop PBI-based hollow fiber membranes (HFMs) with a thickness optimized selective layer to achieve high H₂ perm-selectivity while retaining thermo-mechanical stability and durability.

In this work, we demonstrate development and characterization of PBI-based composite HFMs for H₂/CO₂ separation at elevated temperature. These PBI HFMs are prepared using a phase inversion technique and their microstructure is optimized for an outer integral selective skin with porous support layer. The effects of the fiber spinning parameters on morphological and micro-structural changes in the PBI HFMs are evaluated and optimized.  The pure gas perm-selectivity data obtained on PBI HFMs at operating temperatures exceeding 250 °C are discussed.