The direct dimethyl ether (DME) synthesis process from syngas I. Process feasibility and chemical synergy in one-step LPDMEtm process

A novel one-step process for co-production of dimethyl ether (DME) and methanol, in the liquid phase, was conceived as an advance over the liquid phase methanol synthesis process (LPMeOHtm). This direct, one-step DME process (LPDMEtm) is based on the application of dual catalysis, where 2 functionally different yet compatible catalysts are used as a physical mixture, well-dispersed in the inert liquid phase. Three different reactions, methanol synthesis (via CO and CO2), water-gas shift, and methanol dehydration (to form DME) take place over the 2 catalysts, Cu/ZnO/Al2O3 and typically -Al2O3. The thermodynamic and kinetic coupling of methanol dehydration reaction (very fast and at/near thermodynamic equilibrium) with the methanol synthesis reaction (slower kinetics and highly thermodynamic) leads to the observed chemical synergy. This synergy helps overcome the limitation on thermodynamic equilibrium conversion, and increases the per-pass syngas conversion and reactor productivity. The catalyst deactivation phenomena in LPDMEtm proess is also greatly alleviated compared to methanol alone; the increase in syngas conversion and methyl equivalent productivity (MEP) are sustained over a longer on-stream time.Here, in this review, we survey the salient developments in the LPDMEtm process since its inception, first at UA research laboratories and elsewhere including Air Products and Chemicals, Inc. We demonstrate the rationale of the LPDMEtm process, and then outline briefly the research studies in the two processes, that illustrate the chemical synergy in the LPDMEtm process. This successful example of cooperative catalysis can be adapted in principle to many other organic reactions.