Catalyst screening and reaction kinetics of liquid phase DME synthesis under reactive distillation conditions

While conventional DME synthesis is exclusively operated in a gas phase heterogenous reaction system, reactive distillation unveils the potential for a process intensified, compact and efficient DME production. In a catalyst screening, various solid acid catalysts were examined in the liquid phase dehydration of methanol to DME. Ion exchange resins proofed to be more active than zeolites and more stable than perfluorsulfonic acids. Reaction kinetics on the two most promising commercial ion exchange resins, the oversulfonated resin Amberlyst® 36 and the chlorinated resin Treverlyst CAT400 were studied in a profile reactor setup over the full range of water fractions relevant for DME reactive distillation processes. CAT 400 was found to show a lower activity than Amberlyst® 36 at identical temperatures, however, due to the higher thermal stability, significantly higher conversions could be achieved. In the kinetic fitting, it was found that the conventional Eley-Rideal and Langmuir-Hinshelwood mechanisms are not capable to describe the experimental data over the wide range of water fractions due to the highly non-linear inhibition by water resulting from the distinct swelling properties of ion exchange resins. To account for this behavior, a new kind of kinetic model with dedicated water inhibition term is introduced and discussed. This model allows the precise description of reaction kinetics over the whole studied operating range for both investigated catalysts and reflects the temperature-dependent inhibition by water. The new kinetic model is an essential building block for the design of industrial scale DME reactive distillation processes.