Influence of the membrane properties on the catalytic production of dimethyl ether with in situ water removal for the successful capture of co2

Abstract

The incorporation of CO2 as reactant co-fed with syngas for the direct synthesis of dimethyl ether (DME) using a bifunctional (CuO–ZnO–Al2O3/γ–Al2O3) catalyst in a packed-bed reactor has been proposed. The presence of CO2 in this system favors H2O formation that hampers the reaction of methanol dehydration towards DME. Therefore, the employment of a zeolite membrane for the in situ H2O removal in a packed-bed membrane reactor (PBMR) has been theoretically evaluated. A mathematical model describing mass transport through the membrane of all the components involved in the DME synthesis has been developed. The model has been used to predict the process performance and to define the most favorable membrane characteristics, with feed and sweep streams flowing countercurrently in single-pass mode. The mass transport characteristics of the zeolite membranes proposed in the present study ranged from those permeable to all the components present in the DME reaction site, i.e. ZSM5, mordenite and silicalite, to those ideally permselective to water. Simulation runs predicted that the application of any zeolite membrane always promoted the transformation of CO2 into DME, although yields and conversions were highly dependent on membrane transport characteristics. Hence, membranes highly selective to H2O were required to reach sufficient conversions of CO2 into DME while, low H2O permeances (0.5–1.2×10−7molPa−1m−2s−1) procured an enhancement on DME yield. Our results highlight the relevance of further research and development of zeolite membranes with improved H2O permselectivity as one of the major challenges in processes for CO2 capture and transformation into DME.