Synthesis of Dimethyl Ether over Modified H-Mordenite Zeolites and Bifunctional Catalysts Composed of Cu/ZnO/ZrO₂ and Modified H-Mordenite Zeolite in Slurry Phase

Abstract

Synthesis of dimethyl ether (DME) via methanol dehydration were investigated over various catalysts, and via direct CO hydrogenation over hybrid catalysts composed of Al-modified H-Mordenite zeolite and Cu/ZnO/ZrO₂. H-Mordenite zeolite exhibited the highest activity in dehydration of methanol. However, its selectivity toward dimethyl ether was rather low. For this reason, the H-Mordenite was modified. Modification of zeolites was performed by wet impregnation method and considered catalysts were characterized by AAS, XRD and NH₃-TPD analyses. Results of catalytic tests indicated that H-Mordenite modified with 8 wt% aluminum oxide was the best catalyst for synthesis of dimethyl ether from methanol, in which methanol conversion and DME selectivity were 99.8 and 96.8%, respectively, without noticeable change in catalyst stability. For direct synthesis of dimethyl ether from synthesis gas, hybrid catalysts were prepared by coprecipitation sedimentation method. It was found that optimum ratio of methanol synthesis catalyst to methanol dehydration catalyst is 2:1. In this case, CO conversion and DME selectivity were 64 and 78.8%, respectively, with good catalyst stability. Ultimately, it was concluded that the hybrid catalyst composed of Cu/ZnO/ZrO₂ and Al-modified H-Mordenite zeolite is an appropriate catalyst for direct synthesis of dimethyl ether from the synthesis gas.