Reactor modelling and design for sorption enhanced dimethyl ether synthesis

Sorption Enhanced DiMethyl Ether Synthesis (SEDMES) is a promising option to overcome thermodynamic limitations of conventional DME production processes. In this work a 2D + 1D heterogeneous dynamic model of the reaction/adsorption step in a tube of an externally cooled multitubular fixed bed SEDMES reactor is developed in order to investigate the effect of design and operating parameters on thermal behavior and DME yield performances of the reactor. The model is validated by comparison with experimental results from a bench scale unit, including the dynamics of the outlet composition and the temperature trajectories in different points along the axial coordinate. Simulations with the validated model address the effect of the CO/CO2 ratio in the feed. The results confirm that, thanks to the effective in-situ H2O removal, the DME yield performances (65–70% in this work) of SEDMES are poorly sensitive on the CO/CO2 ratio. Accordingly, on increasing the CO2 content in the feed, SEDMES provides larger advantages with respect to conventional DME direct synthesis. Calculations of maximum temperatures achieved along the axial coordinate show that catalyst thermal stress in the hottest inlet zone of the SEDMES reactor slightly increases with the CO content in the feed due to faster kinetics of the DME production reactions. However, thanks to the dilution effect provided by the adsorption material, maximum bed temperature keeps ∼ 20–30 K below the catalyst stability limit reported in the literature (573 K). Accordingly, larger tube diameters (up to 46.6 mm) than in conventional reactors for the direct synthesis of DME can be adopted with less than 2% loss in DME yield.