Three-Dimensional Numerical Modeling of a Low-Temperature Sabatier Reactor for a Tandem System of CO₂ Methanation and Polymer Electrolyte Membrane Water Electrolysis

The Sabatier reaction, which converts CO2 and H-2 into CH4 and H2O (methanation), is an attractive way to produce a hydrogen carrier for renewable energy and CO2 recycling. Also, for air revitalization in space missions, water electrolysis provides not only O-2, but also H-2, which can hydrogenate metabolic CO2 from human respiration using the Sabatier reaction, producing H2O for O-2 regeneration with the electrolysis. In this study, we have developed a three-dimensional finite element model of a test tandem cell combining a low-temperature Sabatier reactor working at around 220 degrees C with a proton exchange membrane water electrolyzer at around 120 degrees C. The model with our developed Sabatier reaction catalyst demonstrated that appropriate heat balance between the reactor and electrolyzer establishes a CO2 conversion above 90% and thermal self-sustainability. An appropriate thermal insulator between the reactor and electrolyzer maintains them at predetermined temperatures. The thermal analysis also shows thermal self-sustainability for a plurality of the tandem cells, simulating a cell in a stack. Exergy loss ascribed to the entropy production rate with the temperature drop between the Sabatier reactor and electrolyzer is also evaluated. (C) The Author(s) 2022. Published by ECSJ.