Comparative life cycle assessment of power-to-methane pathways : process simulation of biological and catalytic biogas methanation

Power-to-Methane (P2M) pathways are proposed as an innovative solution to utilize surplus renewable electricity for long-term and long-distance storage. This electricity can produce hydrogen using electrolysis and, with the input of CO2 from biogas, be further used for the production of synthetic methane. The methanation reaction can be done with a biocatalyst or nickel catalyst, each with a different pathway of pre- and post-treatment steps. To date, only a limited number of studies have analysed the environmental impact of P2M pathways using life cycle assessment, and no study has directly compared the biological and catalytic P2M pathways. The goal of this research is to close this knowledge gap by quantifying the environmental impact of synthetic methane production and identifying differences between both pathways. Mass and heat balances of both pathways were simulated with AspenPlus and used as basis for a thorough life cycle inventory of the material and energy demand. The global warming potential per MWh synthetic CH4 is similar for the biological and catalytic pathways, but the impact is differently distributed between the processes. The catalytic pathway requires more sulfur removal, compression power and cooling demand. In the biological pathway, the bioreactor has a large impact due to its electricity and nutrient demand, whereas the catalytic reactor's impact is almost negligible