| Research Abstract |
Direct oxidation of methane to methanol is a highly attractive process compared to the current process consisting of energy intensive conversion of methane by steam into synthesis gas. Methane monooxygenase (MMO) catalyzes single-step oxidation of methane to methanol. But MMO could not be used in methanol synthesis, because of instability. Thus methanol production from methane was tried with methanotroph. Methylosinus trichosporium OB3b, a methanotrophic bacterium, contains MMO and catalyzes hydroxylation of methane to methanol.
When the methane is oxidized, produced methanol is subsequently oxidized by methanol dehydrogenase containing in the same bacterium. To prevent further oxidation of methanol, the cell suspension was treated by cyclopropanol, which was found to be an irreversible inhibitor for methanol dehydrogenase by the previous study, leading to extracellular methanol accumulation. The purpose of this research is to increase methanol production and to improve methanol yield a
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nd the efficiency.
The batch type of methanol synthesis by M.trichosporium OB3b is terminated at c.a.6 mM of methanol, because MMO is inhibited by increasing methanol concentration. For prolonged methanol accumulation, a semicontinuous process was carried out in this study. A standard 50 ml ultrafiltration (UF) cell was used as semicontinuous reactor. The solution containing cyclopropanol treated cell suspension and sodium formate in phosphate buffer was introduced in to the UF cell attached with ultrafilter (Diaflo ultrafilter YM-100, Amicon, Inc.). The UF cell was incubated for 5 min at 30ﾟC,and the reaction was initiated by injecting methane into the UF cell with a gas-tight syringe. After incubation at 30ﾟC for 90 min, the reaction mixture was filtrated by nitrogen pressure, leading to separate a produced methanol from cell suspension. The methanol synthesis was repeated five times and stationary rate was 3.17 mumol h^<-1>mg^<-1>. The total produced methanol was 36.1 mumol, which is about twice amount of methanol produced by batch reaction under the same condition. Less
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