Process integration of biological and catalytic CO2 methanation for biogas upgrading to SNG: A techno-economic analysis for PtG applications

The present study examines the integration of biological and catalytic CO₂ methanation process within the framework of Power-to-Gas (PtG) applications, a key technology for energy storage and decarbonization. The PtG concept involves converting surplus renewable electricity into synthetic natural gas (SNG) by utilizing CO₂ and green hydrogen (H₂) produced through water electrolysis. In this hybrid approach, the catalytic process, based on the Sabatier reaction, enables the rapid and efficient conversion of CO₂ to CH₄ at elevated temperatures using metal-based catalysts (Ni and Ru). Meanwhile, the biological process leverages methanogenic microorganisms (archaea) to facilitate CO₂ reduction at lower temperatures. Integrating these two methods aims to combine the high conversion efficiency of catalytic methanation with the operational flexibility and milder conditions of biological methanation. Catalytic methanation swiftly converts CO₂ and H₂ at high temperatures, whereas biological methanation offers advantages such as tolerance to impurities and the ability to operate under variable gas compositions. This study highlights key challenges associated with process integration by employing kinetic models from the literature in Aspen Plus environment for both biological and catalytic methanation. Specifically, methanogenic archaea are utilized in the biological step, while Ni- and Ru-based catalysts are applied in the catalytic section across three different configurations to gain valuable insights. The process is assessed at an industrial scale, based on a 7 MW PEM electrolyzer for green hydrogen production, corresponding to approximately 677 m³ /h of biogas and 783 m³ /h of hydrogen. A techno-economic analysis is carried out to evaluate the feasibility of the process and identify the most cost-effective configuration.