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

A kinetic model has been established for the transformation of (H2 + CO2) into dimethyl ether (DME) on a CuO–ZnO–Al2O3/γ-Al2O3 bifunctional catalyst with excess γ-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 (H2 + 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 °C; 20–40 bar; H2/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 °C; pressure, 40 bar; H2/CO2 molar ratio in the feed, 4/1.

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► The kinetic model suitably predicts the evolution of CO2 conversion and yields of DME, methanol and paraffins with time on stream.
► Catalyst deactivation is caused by coke deposition on the metallic function and is attenuated by feeding CO2.
► Suitable conditions are: 275 °C, 40 bar, H2/CO2 molar ratio of 4/1.