H2 gas-liquid mass transfer: A key element in biological Power-to-Gas methanation

Power-to-Gas technologies are considered essential for a green transition of the global energy system by producing fossil-free fuel from renewable electricity and CO2. Biological methanation can be used as a Power-to-Gas technology by harnessing hydrogenotrophic methanogenic archaea to produce CH4 from CO2 and electricity-derived H2. Advancing biological Power-to-Gas methanation technologies to full-scale requires a dedicated focus on H2 gas-liquid mass transfer, which generally limits the conversion of H2 to CH4. Process and reactor design and operation have accordingly received much research attention in recent years, but technology development is still characterized by a broad investigation of various system configurations and operational conditions, mainly in lab-scale. This review gives an extensive summary of the current biological methanation capacities of different reactor types in the context of Power-to-Gas and critically examines the influence of operational parameters on H2 gas-liquid mass transfer based on the two-film theory. The review provides a basis for critical comparison of reactor performances among biological methanation studies, which often vary in key process parameters that have a direct influence on H2 gas-liquid mass transfer and, therefore, product gas quality. The review hereby compiles knowledge essential to realize the microbial potential for biological Power-to-Gas methanation and support the technology's development to an industrially relevant scale.