Life Cycle Assessment of Power-to-Gas: Syngas vs Methane

Abstract

Power-to-Gas enables the integration of renewable electricity and carbon into the chemical industry. The electricity is used to produce hydrogen, which is subsequently converted with CO2 as the renewable carbon source. The resulting products can be used as feedstock for the chemical industry replacing current fossil-based feedstock. Because the integration of renewable electricity and carbon into the chemical industry is mainly environmentally motivated, we identify the conditions under which Power-to-Gas pathways are environmentally beneficial. The conditions are expressed as environmental threshold values for electricity supply. The threshold values are derived by a comparative life cycle assessment (LCA) of Power-to-Gas pathways to fossil-based processes. We analyze Power-to-Gas pathways to synthetic natural gas (Power-to-SNG) and to syngas (Power-to-Syngas). SNG is produced by the Sabatier reaction; syngas by reverse water gas shift (rWGS) and dry reforming of methane (DRM). The threshold values for electricity supply allow us to compare the environmental benefit of Power-to-SNG and Power-to-Syngas on an equal basis: how well they utilize the currently limited renewable electricity. Syngas production by the DRM process has the largest environmental potential. Both Power-to-Syngas pathways lead to larger environmental benefits than Power-to-SNG making syngas the more desirable product than methane as long as renewable electricity is limited.