Hydrogen production in concentrated solar driven membrane reactors - A conception design and numerical analysis

Perovskite-type mixed ionic-electronic conducting (MIEC) oxygen permeable membranes possess highly selective oxygen separation capabilities. These membranes can be synergistically integrated with the partial oxidation of biomethane to produce green hydrogen. The temperature range of these oxygen permeable membranes aligns seamlessly with that of commercial concentrated solar power (CSP) systems. Coupling photothermal conversion, oxygen separation, and partial oxidation of methane (POM) offers a novel, efficient, and environmentally friendly engineering solution for "solar fuel" production. This study introduces, for the first time, a compact membrane reactor design that integrates a porous ceramic (SiC) solar absorber with a MIEC oxygen permeable membrane assembly. The solar absorber facilitates photothermal conversion and heats the reaction gases (air), and maintains the MIEC membrane assembly at an optimal operating temperature with uniformity through thermal radiation. A mathematical model has been developed that couples radiation and heat transfer within the porous medium, along with the membrane separation and reaction processes. The pore parameters of the solar absorber have been optimized to enhance photothermal conversion efficiency and achieve a uniform outlet temperature distribution, thereby enhancing the temperature uniformity and stability of the membrane assembly. Taking the La0.6Sr0.4Co0.2Fe0.8O3-delta membrane assembly as a case study, simulations of the proposed reactor under densely packed conditions indicate that, following buffering and equalization by the solar absorber, the temperature distribution within the reactor exhibits improved uniformity both axially and radially, facilitating uniform and controlled POM. The overall solar-to-fuel and solar-to-hydrogen conversion efficiencies of the system reach 16.19% and 10.80%, respectively. Compared to high-temperature thermochemical cycles driven by solar thermal energy, these efficiencies demonstrate higher conversion efficiency and promising prospects for engineering applications.