Regenerability of the CuO–ZnO–MnO/SAPO-18 catalyst used in the synthesis of dimethyl ether in a single step

Abstract

The study has focused on the regenerability of the CuO–ZnO–MnO/SAPO-18 (CZMn/S) bifunctional catalyst used in the direct synthesis of dimethyl ether (STD process) from H2 + CO + CO2 feeds. The runs have been conducted in a fixed bed reactor under the following conditions: 250–300 °C; 10–40 bar; 1.25–10.18 gcat h molC−1; time on stream, 5–30 h; CO2/CO molar ratio, 0–1; feeding H2 + CO + CO2 with a H2/COx molar ratio of 3. Coke deposition has been determined as the main deactivation cause, and both the measurement of the coke content and the identification of three types of coke have been carried out by means of temperature programmed oxidation analyses. Reaction-regeneration cycle runs have been carried out in a fixed bed isothermal reactor, concluding that it is possible to regenerate the bifunctional catalyst by the combustion of coke with air, at 300 °C (48 h). Under these conditions, the catalyst undergoes a slight Cu sintering in the first reaction-regeneration cycle but recovers completely the remaining activity in the successive cycles.