AUTHOR=Tou Maria , Grylka Adrian , Schuller Arnaud , Bulfin Brendan , Steinfeld Aldo , Michalsky Ronald 

TITLE=Dual Hydrogen- and Oxygen-Transport Membrane Reactor for Solar-Driven Syngas Production

JOURNAL=Frontiers in Energy Research

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2020.570884

DOI=10.3389/fenrg.2020.570884

ISSN=2296-598X

ABSTRACT=<p>A novel thermochemical dual-membrane reactor is considered with the goal of efficiently converting CO<sub>2</sub> to fuels using concentrated solar energy as the process heat source. In contrast to the temperature-swing redox cycle, in this isothermal system the thermolysis of H<sub>2</sub>O at above 1,800 K is assisted by removal of O<sub>2</sub> across an oxygen-permeable membrane and of H<sub>2</sub> across a hydrogen-permeable membrane. The latter is consumed by a stream of CO<sub>2</sub><italic>via</italic> the reverse water-gas shift reaction to re-form H<sub>2</sub>O and continuously generate CO. The net reaction is the splitting of CO<sub>2</sub> to CO and <inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>. Because reactions at such high temperature are expected to be thermodynamically controlled, thermodynamic models are developed to calculate the equilibrium limits of the proposed dual-membrane configuration. For comparison, two reference configurations comprising either a single oxygen-permeable membrane or a single hydrogen-permeable membrane are analyzed. At 1,800 K, 1 bar total pressure, and (not applicable for the hydrogen-membrane reactor) 10 Pa O<sub>2</sub>, the equilibrium mole fraction of fuel is 2% with a single oxygen membrane, 4% with a single hydrogen membrane, and 15% in the dual-membrane system. In all cases, total selectivity of CO<sub>2</sub> to CO and O<sub>2</sub> is obtained. Assuming thermodynamic equilibrium, the solar-to-fuel energy efficiency realistically attainable is 4% with a single oxygen membrane, 8% with a single hydrogen membrane, and 17% in the dual-membrane configuration at the aforementioned conditions. By increasing the pressure of the feed of steam to 100 bar, the dual-membrane model system could theoretically approach full mass conversion of CO<sub>2</sub> and reach up to 26% solar-to-fuel energy efficiency. However, developing appropriate and stable ceramic materials for such a system poses a significant challenge.</p>