Pilot-scale demonstration of an integrated Membrane–Biomethanation process for post-combustion CO2 capture and utilization with green hydrogen

Carbon capture technologies are crucial for reducing CO2 emissions from lignite-fired power plants, which remain among the largest contributors to GHG emissions globally. That was the case of Agios Dimitrios TPP, an active lignite-fired power plant of Public Power Corporation of Greece, where a membrane pilot-scale carbon capture unit was installed and operated. This work presents the development and evaluation of a hybrid process for carbon dioxide (CO2) capture and utilization, where a membrane system was designed and implemented to operate under long-term conditions, targeting the efficient removal of CO2 from CO2/N2 mixtures, which simulate coal-fired power plant emissions. The concentrated CO2 stream was linked to a biological methanation unit, where it was combined with water electrolysis hydrogen, producing a high–purity biomethane stream. The results obtained demonstrated that increasing CO2 concentrations in the feed significantly improved the purity of the recovered CO2 (>90%), while biomethane production consistently exceeded 95% purity with stable, long-term operation and proper control of nutrients and pH. The successful integration of membrane separation, electrolysis, and biomethanation steps underlines the system's potential as a combined carbon capture and utilization pathway for sustainable energy transition, valorizing industrial CO2 emissions for synthetic natural gas generation.