Experimental investigations and model-based optimization of CZZ/H-FER 20 bed compositions for the direct synthesis of DME from CO2-rich syngas

Abstract

Experimental kinetics studies and model-based optimization were performed for the direct synthesis of dimethyl ether (DME) in a wide range of process conditions, including various CuO/ZnO/ZrO₂ : H-FER 20 bed compositions. Thus, in order to improve the DME productivity using fluctuating CO/CO₂ gas feeds such as those that could be used in power-to-fuel technologies, a series of experiments was carried out at 30 bar by varying the CO₂/CO_x inlet ratio (0.4–0.9), temperature (483–513 K), gas hourly space velocity (2.78, 3.57 s⁻¹), and the weight ratio of the catalyst components CuO/ZnO/ZrO₂ and H-FER 20 (from 1 to 70.4). A lumped kinetic model for the methanol synthesis from the literature was extended for the direct DME synthesis. With only eight fitted parameters, the model adequately simulates an extensive array of data points measured with a six-fold parallel reactor setup. The resulting model was applied to optimize the CuO/ZnO/ZrO₂ : H-FER 20 ratio and the obtained optimization results were validated experimentally, confirming the simulated performance enhancement. For a CO₂-rich feed (CO₂/CO_x = 0.9), the optimum volumetric CuO/ZnO/ZrO₂ : H-FER 20 ratio under kinetic operating conditions is 91.5/8.5 vol%. Extrapolation based on the new model for industrially relevant operating cases show an optimal H-FER 20 volume fraction below 5 vol%, resulting in a CO_x conversion of 47% at a DME selectivity of 88%.