Dimethyl Ether Synthesis via Reforming of Steam/Carbon Dioxide and Methane

Abstract

Dimethyl ether (DME) synthesis via the reforming of methane (CH4) by carbon dioxide (CO2) and steam (H2O) was investigated using a model synthesis gas obtained by the reforming of CH4. Reforming of CH4 over Ni/α-Al2O3, Ru/α-Al2O3, Ni/MgO-Al2O3 and Ru/MgO-Al2O3 catalysts showed that CH4 conversion was strongly affected by temperature, but not by CO2/CH4 and H2O/CH4 molar ratios. CO2 conversion was strongly affected by temperature, and CO2/CH4 and H2O/CH4 molar ratios. M value [H2/(2CO + 3CO2) molar ratio] was strongly affected by temperature and CO2/CH4 molar ratio, but not by H2O/CH4 molar ratio. Using Ni/MgO-Al2O3 and Ru/MgO-Al2O3 catalysts, CH4 conversion almost reached equilibrium in 800 h durability tests, and carbon deposition on the catalyst was very low. DME synthesis was investigated using the model synthesis gas obtained by the reforming of CH4 by CO2 and H2O through two reactions, the one-step reaction with a hybrid catalyst structure and the two-step reaction with separated catalysts. The 2000 h durability tests showed that (methanol + DME) yield through the one-step reaction was higher in the first stage than through the two-step reaction, and decreased gradually with time. However, the (methanol + DME) yield hardly decreased through the two-step reaction for the whole test time. DME selectivity was stable in both one-step and two-step reactions for 2000 h. Moreover, the two-step reaction gave 20% or more higher (methanol + DME) yield and DME selectivity from the model gas containing CO compared to those from the mixed gas of H2 and CO2 not containing CO.