Selective membrane application for the industrial one-step DME production process fed by CO2 rich streams: Modeling and simulation

The integration of a microporous zeolite membrane, highly selective to steam water in a one-step DME synthesis reactor, is modeled and assessed. The membrane reactor performance and the comparison with a conventional reactor, are studied mainly for a CO2-rich feedstock, i.e. derived from a biogas-derived syngas. The continuous removal of water from the reaction environment reduces the inhibition effect of H2O on the CO2 hydrogenation and methanol dehydration reactions, thus allowing the achievement of high conversions, DME yield and selectivity even at large CO2 composition in the inlet feedstock. If a CO2/CO ratio equal to 3 is imposed in the inlet stream, the DME yield reaches a value of 0.75 vs. 0.57 in a conventional reactor operating at the same conditions, the XCOx and XCO2 are 0.75 and 0.69, with an improvement of 15.4% and 30.2%, and the DME selectivity is close to 1. The membrane reactor behavior is assessed by a one-dimensional, non-isothermal model. Fixing industrial scale parameters, the effect of the main operating conditions as temperature and pressure in the reactor environment, the Gas Hourly Space Velocity (GHSV), the feedstock composition in terms of CO2/CO and H2/COx ratios, the pressure and flow rate downstream to the selective membrane are analyzed and discussed. The simulations confirm the improvement of the reactor performance, within large ranges of operating conditions, derived from the integration of the selective membrane. On this basis, membrane reactor for one-step DME synthesis process can be included in the “CO2 valorization” framework since the greenhouse gas CO2 can be used as a reactant in an industrial process and thus converted into a useful and marketable product.