Methane to methanol in supercritical water

Abstract

We examined the feasibility of producing methanol from the partial oxidation of methane in near-critical and supercritical water. Oxygen was always the limiting reactant. The parameter space investigated experimentally included temperatures between 349 and 481 °C, batch holding times between 1 and 9 min, water densities between 0.15 and 0.35 g mL−1, initial methane to water molar ratios between 0.05 and 0.27, and initial methane to oxygen molar ratios between 10 and 26. Experiments within this parameter space led to methane conversions up to 6%, and oxygen conversions up to 100%. Methanol, carbon monoxide, and carbon dioxide were the major products. The methanol selectivities ranged from 0.04 to 0.75, with the highest selectivities occurring at the lower conversions. The highest methanol yield was 0.7%. Reactions performed in glass-lined reactors proceeded to higher conversions than did reactions in stainless-steel reactors under otherwise identical conditions. A detailed chemical kinetics model showed that the methanol selectivity increased with temperature and with the methane to oxygen molar ratio, but decreased with increasing oxygen conversion. The methanol yield showed the same trends with temperature and the methane to oxygen ratio, but the yield increased with oxygen conversion.