Methane conversion into methanol by biotechnological processes: Challenges and perspectives

Methane is one of the most prominent greenhouse gases contributing to global warming. It is also a valuable source of energy and a raw material for the production of chemicals. Gas-to-liquid technologies for its conversion into methanol are particularly interesting, methanol being considered as a platform molecule for the chemical industry and a prospective fuel for low-emission transport. Methane oxidation into methanol is up to day carried out industrially under energy-consuming conditions, associated to significant CO₂ emissions. Methanotrophic catalysis has arisen as a promising greener alternative since methanotrophs are naturally-occurring microorganisms (bacteria and archaea) able to uptake methane under mild conditions. Methanotrophic bacteria express the Methane MonoOxygenase (MMO) enzyme, able to selectively hydroxylate methane. However, their large-scale implementation is currently hindered by both biological and process constraints. This review summarizes recent developments in bioprocesses for methanol production from methane, including methanotroph-based ones. Whole-cell methanotrophs, cell-free (enzymatic) processes and MMO heterologous expression have been covered.