Sustainable DME synthesis from CO2–rich syngas in a membrane assisted reactor–microchannel heat exchanger system

Abstract

One–step syngas–to–dimethyl ether (DME) conversion is modeled in a cascade of packed–bed reactors (PBRs) and microchannel heat exchangers (micro–HEXs). Each reactor, loaded with mixtures of Cu–ZnO/Al2O3 and HZSM–5 for adiabatic syngas hydrogenation and methanol dehydration, respectively, is connected to a micro–HEX for cooling PBR effluent. HEXs involve layers of sodalite membrane allowing selective H2O and H2 exchange between reactive stream and cooling channels. Membraneless and membrane–integrated systems are simulated at inlet syngas conditions of 50 bar, 523 K, and ∼0.8 mol/s, resembling syngas throughput of a pilot–scale gasifier. Although PBR effluents become H2O–lean in syngas–cooled membrane–integrated HEXs, CO2 conversion and DME yield remain almost identical with those of the membraneless (benchmark) case (∼6 and 10 %, respectively), suggesting that reactions are not constrained by steam. Cooling by pure H2 allows its penetration into reactive stream. H2–enriched PBR feeds are transformed under kinetic and thermodynamic promotions giving CO2 conversion and DME yield up to ∼72 and ∼57 %, respectively. Improved metrics occur at elongated contact of the fluids with membrane, necessitating voluminous HEX units. Nevertheless, membrane aided molar DME production and CO2 consumption per volume remain up to 1.6 and 2.3 times higher than the benchmark values. Membrane assistance also improves benchmark catalyst weight–based DME productivity and CO2 utilization by factors up to 7 and 13, respectively. Proposed cascade system allows scalable and sustainable DME production via increased CO2 valorization.