A Comprehensive Review of Green Methane Production from Biogas and Renewable H2 and Its Techno-Economic Assessment: An Australian Perspective

Green methane has been deemed as a low CO2 emission gas. The cost to produce green methane varies considerably by location and technologies (USD 15/GJ to USD 60/GJ). Although green methane has higher price than the average price of market natural gas in Australia (USD 11–40/GJ between 2019 and 2023), it is currently significantly lower than the production cost for green hydrogen, with the levelized cost of hydrogen (LCOH) at USD 6.6/kg. Green methane production can utilise different processing steps. Separation processes require energy to separate CO2, with the remaining issue of safely storing the captured CO2 or venting it to the atmosphere. Direct catalytic biogas methanation (e-methane) does not require the separation of CO2 but converts CO2 together with CH4 to a purer stream of CH4, converting the CO2 to an energy product. E-methane consequently can be considered as an alternative energy carrier to store off-peak electricity from the grid, commonly called power-to-gas technology (P2G). Furthermore, injecting green methane into gas pipelines does not require significant gas infrastructure upgrading and has no upper limit, as it is compatible with natural gas. Here we review the status of biogas and direct green methane production from biogas around the world and assess technologies that are used to produce green methane via separation or direct catalytic conversion. We evaluate their techno-economic assessment results, with a particular focus on e-methane, identifying the opportunity as a pathway to supply low-emission gas with the perspective of a future e-methane industry within Australia.