Methyl chloride synthesis over Al₂O₃ catalyst coated microstructured reactor-Thermodynamics, kinetics and mass transfer

Selective synthesis of methyl chloride from methanol and hydrochloric acid was performed in an alumina-coated microreactor. Conversions from 4% to 83% were achieved in the investigated temperature range of 280-340. °C. This demonstrated that the reaction is fast enough to be successfully performed in a microreactor. A model based on kinetic experiments and thermodynamic calculations was developed for the system. The influence of the reactant adsorption on the catalyst surface was investigated performing transient experiments and comparison of kinetic models. A model taking into account HCl adsorption on the catalyst surface was able to describe the data most precisely. Kinetic models advanced in this work were compared with a previously published model. With the obtained kinetic parameters, a selectivity analysis was performed. The activation energy for the methyl chloride and dimethyl ether formation was 108. kJ/mol and 118. kJ/mol respectively. The former value is ca. two fold higher than the previously published, indicating a sign for diffusion limitations in previous studies. A detailed modeling of the diffusion in the porous catalyst layer confirmed that the kinetic constants determined in the microreactor represent the intrinsic kinetics and that methyl chloride formation is limited by diffusion starting from catalyst coating thicknesses of 50 μm.