Kinetic modelling of dimethyl ether synthesis from (H2 + CO2) by considering catalyst deactivation

A kinetic model has been established for the transformation of (H-2 + CO2) into dimethyl ether (DME) on a CuO-ZnO-Al2O3/gamma-Al2O3 bifunctional catalyst with excess gamma-Al2O3 acid function. The model considers the attenuation of methanol synthesis and the formation of paraffin byproducts due to CO2 and water in the reaction medium. Furthermore, the catalyst's low deactivation (lower than for (H-2 + CO) feed) is quantified by means of an equation that considers coke deposition on the metallic function due to the degradation of oxygenates (methanol and DME) in the reaction medium as the cause of deactivation. Deactivation attenuates as water and CO2 concentrations in the reaction medium are increased. The model fits the experimental results for the evolution with time on stream of both CO2 conversion and the yields of DME, methanol and paraffins in the range of operating conditions studied: 225-325 degrees C; 20-40 bar; H-2/CO2 molar ratio in the feed, between 2/1 and 4/1: time on stream, up to 30 h. The following operating conditions are suitable by striking a balance between activity at zero time on stream and deactivation: temperature, 275 degrees C: pressure, 40 bar: H-2/CO2 molar ratio in the feed, 4/1. (C) 2011 Elsevier B.V. All rights reserved.