Integrated Co‐Electrolysis and Syngas Methanation for the Direct Production of Synthetic Natural Gas from CO₂ and H₂O

Abstract

The concept of an integrated power-to-gas (P2G) process was demonstrated for renewable energy storage by converting renewable electrical energy to synthetic fuels. Such a dynamically integrated process enables direct production of synthetic natural gas (SNG) from CO 2 and H 2 O. The produced SNG can be stored or directly injected into the existing natural gas network. To study process integration, operating parameters of the hightemperature solid oxide electrolysis cell (SOEC) producing syngas (H 2 + CO) mixtures through co-electrolysis and a fixed bed reactor for syngas methanation of such gas mixtures were first optimized individually. Reactor design, operating conditions, and enhanced SNG selectivity were the main targets of the study. SOEC experiments were performed on state-of-the-art button cells. Varying operating conditions (temperature, flow rate, gas mixture and current density) emphasized the capability of the system to produce tailor-made syngas mixtures for downstream methanation. Catalytic syngas methanation was performed using hydrotalcite-derived 20 %Ni-2 %Fe/(Mg,Al) O x catalyst and commercial methanation catalyst (Ni/Al 2 O 3 ) as reference. Despite water in the feed mixture, SNG with high selectivity (� 90 %) was produced at 300°C and atmospheric pressure. An adequate rate of syngas conversion was obtained with H 2 O contents up to 30 %, decreasing significantly for 50 % H 2 O in the feed. Compared to the commercial catalyst, 20 %Ni-2 %Fe/(Mg,Al)O x enabled a higher rate of CO x conversion.

Syngas Production from CO2 and H2O via Solid-Oxide Electrolyzer Cells: Fundamentals, Materials, Degradation, Operating Conditions, and Applications

“…Owing to its higher current density at the maximum efficiency, coelectrolysis is more suitable than independent H 2 O electrolysis for producing more methane. ,− SOEC-coupled methane production should upgrade biogas to pipeline quality and could enhance the system’s ability to integrate sufficient renewable energy through the natural gas network. , The exothermic methanation reaction is perfectly matched to the endothermic electrolysis reaction, which enables an overall slightly exothermic stack operation at moderate polarization voltages …”

Mechanistic and Compositional Aspects of Industrial Catalysts for Selective CO2 Hydrogenation Processes

“…Studies show high selectivities of pure CO 2 methanation, with a possible coproduction of small amounts of CO due to the rWGS reaction. In the presence of CO, the conversion of CO 2 is inhibited, but the conversion of CO to methane occurs [99,126]. Reactor modeling studies suggest that, despite the high temperature, at moderate pressures, the amount of CO will always be very low in CO 2 hydrogenation reactors [111,127].…”

Co-electrolysis SOEC and internal reforming SOFC for achieving a carbon-neutral society

“…Methanation is used to produce synthetic natural gas, 17 with the advantage of utilizing existing pipelines and infrastructure. However, the SOFCs using synthetic natural gas require a high temperature of 790 °C for methane reforming.…”