Synthesis of Dimethyl Ether from Syngas on the Catalysts with the ZSM-5 Zeolites

Resumo

Several bifunctional catalysts for dimethyl ether (DME) synthesis from syngas are prepared on the basis of commercial methanol-synthesis Megamax 507 catalyst. Commercial HZSM-5 zeolites with a SiО₂/Al₂О₃ ratios of 23, 80, and 307 and γ-alumina were used as dehydration components. Physicochemical characteristics of zeolites and alumina are studied: temperature-programmed desorption of ammonia, the porosity, and the specific surface area. The activity of catalyst in DME synthesis is studied in a microcatalytic flow-type setup at a pressure of 3 MPa in a temperature range of 200–260°С with a productivity based on syngas of up to 30000 L \({\text{kg}}_{{{\text{cat}}}}^{{ - 1}}\) h^–1. The composition of syngas was (vol %): CO, 21; CO₂, 6; Н₂, 67; N₂, 6 . It is shown that zeolites, especially with silica/alumina ratios of 23 and 80, are more active than alumina in methanol dehydration to DME, but in the presence of these zeolites, traces of hydrocarbons were detected at 260°С. The zeolite with a silica/alumina ratio of 307 is the most interesting of the studied zeolites. Hydrocarbons are almost not formed on it, and its activity in methanol dehydration is somewhat higher than that of alumina. The behavior of the methanol-synthesis component of the bifunctional catalyst is studied: the apparent activation energy of methanol synthesis and the degree of approaching to equilibrium are estimated depending on the catalyst load.