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
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
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. Salimâs current affiliation: Membrane Technology and Research, Inc. (MTR), Newark, CA