Methane Synthesis Characteristics of H2O/CO2 Co-Electrolysis in Tubular Solid Oxide Electrolysis Cells

Producing methane by H₂O/CO₂ co-electrolysis through solid oxide electrolysis cell (SOEC) is a promising method to store unstable renewable power and reduce CO₂ emission simultaneously. Theoretically, methanation reaction is possible to happen in standard condition when temperature is lower than 600^oC. Tubular solid oxide electrolysis cell (TSOEC) has great potential for large-scale application due to easily sealing and high strength. Moreover, gradient distribution of temperature in flow direction is beneficial to CH₄ production. In this paper, CH₄ synthesis characteristics in TSOEC is studied in the temperature range of 500-650^oC by combining experiment and simulation. Experiment demonstrates the addition of H₂ increases the outlet molar fraction of CH₄ from 0 to 2.85% at 600^oC, and from 0.01% to 8.77% at 550^oC. In addition, it’s found that electricity significantly promotes CH₄ production, especially when H₂ is added. The applied voltage of 1.5V just increases CH₄ production ratio by <0.04% in the absence of H₂. But when 20% H₂ is fed in cathode, CH₄ production ratio is improved by 3-4%. Finally, the optimal operating condition, thermal distribution and reaction active zones are simulated by a well validated thermal model. The thermal distribution can be changed by outer boundary condition. CH₄production can be further improved by increasing the temperature of upstream zone and reducing that of downstream zone.

Fig.1 Methane synthesis schematic in TSOEC