Hydrogen and Methanol Formation Utilizing Bioprocesses

Abstract

Increases in the atmospheric levels of carbon dioxide and methane are the main causes of global warming, so measures to reduce the emissions of both gases are essential. A process converting carbon dioxide and methane into methanol was investigated combining three systems as follows, photolysis of water with solar energy, conversion of carbon dioxide and hydrogen into methane, and conversion of methane into methanol. Photolysis of water with solar energy and conversion of methane into methanol with methanotroph are described. Two different systems were attempted to achieve the photoinduced cleavage of water: photoinduced hydrogen evolution combined with Photosystem I and hydrogenase, and the combination of oxygen evolution and photoinduced hydrogen evolution systems. The oxygen evolution system contains grana and an electron carrier such as NAD and NADP. Photoinduced hydrogen evolution systems contain an electron donor, a photosensitizer, an electron carrier and a catalyst such as hydrogenase. Methane was converted into methanol by methane-oxidizing bacteria, methanotrophs which utilize methane monooxygenase to catalyze hydroxylation of methane to methanol. Using methanotrophs for methanol production, accumulation of methanol was not detected, because the methanol is subsequently oxidized by methanol dehydrogenase. The cell suspension of methanotrophs was treated by cyclopropanol as a selective inhibitor of methanol dehydrogenase, leading to extracellular methanol accumulation. The conditions of methane hydroxylation were optimized and semicontinuous methanol synthesis was achieved.