Abstract

A novel one-step process for co-production of dimethyl ether (DME) and methanol, in the liquid phase was first conceived by the UA researchers, as an advance over the liquid phase methanol synthesis process (LPMeOHtm). The one-step, direct 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 γ-Al2O3. The favorable thermodynamic and kinetic coupling of methanol dehydration reaction (very rapid and at/near thermodynamic equilibrium) with the methanol synthesis reaction (slower kinetics and highly thermodynamic) leads the beneficial “chemical synergy”. This synergy helps to overcome the limitation on thermodynamic equilibrium conversion, and increases the per-pass syngas conversionand reactor productivity. The catalyst deactivation phenomena in LPDMEtm processes 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, we review the salient developments in the LPDMEtm process since its inception, first at UA research laboratories and elsewhere including Air Products and Chemicals, Inc. First, we demonstrate the rationale of the LPDMEtm process, and 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. We then briefly discern the intrinsic kinetics of the LPMeOHtm and LPDMEtm systems, and also shed light of the catalyst deactivation phenomena in these processes. In closing, we outline the reactor design/scale-up and plant operational experience of the 3 commercial technologies, as currently practiced by JFE holdings, BP-AMOCO, and Halder-Topsoe.

Keywords: Natural gas; Steam reforming; Coal; Syngas; Methanol; DME, Bi-functional catalysts; Cu/ZnO/Al2O3; γ-Al2O3, Slurry reactors; Bubble column reactors; Chemical synergy; Methyl equivalent productivity (MEP); Intrinsic kinetics; Phase equilibrium; Chemical reaction equilibrium; Catalyst deactivation