The direct dimethyl ether (DME) synthesis process from syngas II. Intrinsic kinetics and catalyst deactivation in one-step LPDMEtm process

Abstract

ABSTRACTIn Part I of this series, it was seen that the favorable thermodynamic and kinetic coupling in the one-step LPDMEtm process – of methanol dehydration reaction (very rapid kinetics and at/near thermodynamic equilibrium) with the methanol synthesis reaction (slower kinetics and under thermodynamic limitation) – leads the beneficial “chemical synergy”.In this part II of Series, we briefly discern the intrinsic kinetics of the LPMeOHtm and LPDMEtm systems, and also shed light of the catalyst deactivation phenomena in these processes. Among the many reports on intrinsic kinetics of the one-step LPMeOHtm and LPDMEtm processes, two illustrative kinetic studies, from the groups of University of Akron and Air Products and Chemicals, Inc. are highlighted and discussed further. For development of intrinsic kinetic models of LPMeOHtm and LPDMEtm systems, a detailed thermodynamic framework has been developed which allows one to compute the liquid phase concentrations of reactive species, at phase equilibria and at chemical reaction equilibria. The intrinsic kinetic models of the LPDMEtm system are mainly based on the independent, component kinetic models of methanol synthesis (van den Bussche and Froment, 1996) and methanol dehydration (Bercic & Levec, 1992). From an overarching analysis of the deactivation of supported copper catalysts for methanol synthesis and other reactions (methanol decomposition and methanol steam reforming), we propose that thermal sintering, i.e., increase in Cu particle size and loss of metal surface area, is the only cause of catalyst deactivation in methanol synthesis reactions over Cu/ZnO/Al2O3 industrial-type methanol catalysts.