Modeling of a membrane integrated catalytic microreactor for efficient DME production from syngas with CO2

Conversion of syngas (CO + CO2 + H-2) to dimethyl ether (DME) with in-situ steam separation is modeled in a membrane integrated, isothermal catalytic microchannel reactor. Reaction channel, involving washcoated form of physically mixed Cu-ZnO/Al2O3 and HZSM-5 catalysts, is separated from the permeate channel by a supported sodalite (SOD) membrane layer. Conservation of momentum and mass within the porous washcoat and the channels, and cross-membrane material transport are modeled in two dimensions at steady-state to elucidate the effects of temperature, pressure, syngas composition and permeate flow properties. Dosing syngas to both channels at 523 K, 50 bar, CO2/COx (COx: CO + CO2) = 0.5 and H-2/COx = 2.0 gives CO and CO2 conversions, and DME yield of 33.2, 12.4 and 15.3 %, respectively, which are 29.9, 7.2 and 12.7 % without membrane. These findings are coherent with relaxed thermodynamic limitations on methanol synthesis and dehydration upon selective H2O removal. Higher permeate syngas flow rates promote steam efflux and H-2 influx across the membrane and further elevate CO2 conversion and DME yield up to 15.8 and 17.4 %, respectively. These metrics can be improved up to 23.4 and 22.9 %, respectively upon dosing pure H-2 as the permeate fluid. However, a positive pressure gradient from reaction to permeate channel does not improve reactor performance. Coherent with its higher dehydration activity, HZSM-5 responds to membrane assistance stronger than gamma-Al2O3.