(20g) Integrating a CO2-Selective Membrane Process into a Solid Oxide Fuel Cell System to Enhance H2 Utilization

The recovery of H₂ from the anode exhaust of a high-temperature solid oxide fuel cell (SOFC) system is an emerging method to increase the H₂ utilization, and a polymeric membrane with a high CO₂/H₂ selectivity is the key for this separation task. However, one of the challenges is to maintain the high selectivity at a high temperature of 120 °C. The membrane reported here contained a polyelectrolyte with quarternaryammonium ions as the cations bound to the polymer backbone. Fluoride was chosen as the counterion as it can catalyze the reaction between CO₂ and water for enhancing CO₂ permeance. The composition also included a boric acid to further catalyze the reaction as well as a hydroxide-based mobile carrier for the facilitated transport of CO₂. The membrane showed a CO₂ permeance of 100 GPU and a CO₂/H₂ selectivity of 116 at 120 °C. Moreover, CO₂ partial pressures and membrane hydration were systematically studied to generate membrane performance data for the design of a membrane system.

Next, a high-level techno-economic analysis was used to explore the integration of the membrane process into the SOFC system. Owing to the high selectivity of the membrane, a single stage membrane system was able to achieve a 99% H₂ recovery with a CO₂ removal of 46.9%. Based on the CO₂ permeance of 100 GPU and the CO₂/H₂ selectivity of 116, the CO₂ removal cost was calculated to be $62.8/tonne for a set of optimized parameters. In order to improve the process further, a vacuum has been proposed to be pulled on the permeate side so that the removed CO₂ can be captured, which will decrease the carbon emission of the SOFC process.

Dr. Salim’s current affiliation: Membrane Technology and Research, Inc. (MTR), Newark, CA