Direct synthesis of dimethyl ether: A simulation study on the influence of the catalyst configuration

Abstract

The direct synthesis of dimethyl ether (DME) from synthesis gas (STD) via methanol as an intermediate is a promising option for implementation of the Power-to-X concept, involving the storage of renewable electrical energy via hydrogen or synthesis gas in synthetic fuels or chemicals. The STD reaction shifts the equilibrium conversion dictated by thermodynamics to higher values compared to methanol synthesis alone at given conditions. Notwithstanding, proper catalyst materials and a suitable configuration have to be found that would support high CO-conversion as well as high DME-selectivity. In this work, different catalyst configurations obtained by combining CuO/ZnO/Al2O3 (CZA) for methanol synthesis with zeolite H-ZSM-5 (Z) for its dehydration are investigated via simulation based on a crystallite-pore network model, able to describe e.g. the polycrystalline anisotropic zeolite. In this way, hybrid particles with proximity of the two catalysts in both, the micrometer-scale (medium proximity, CZA+Z) and in the sub-micrometer-scale (close proximity, CZA&Z) as well as structured core@shell particles (CZA@Z) were investigated for a tubular reactor. Moreover, their planar (coated) counterparts, namely the hybrid layered systems with medium (CZA#Z) and close proximity (CZA&/Z) and a structured double layer system (CZA//Z) were investigated for a wall-coated microchannel reactor. The performance of these systems in the STD reaction was studied focusing on the influence of the CZA/Z ratio and the operational parameters (temperature, GHSV, feed composition). According to this study, hybrid particles with close proximity of the two catalysts as well as the double layer structures showed the best performance in terms of CO-conversion and DME-selectivity.