Numerical Analysis of CO<sub>2</sub>-to-DME Conversion in a Membrane Microchannel Reactor
H. Hasan Koybasi, Ahmet K. Avcı
Abstract
Direct DME synthesis via CO2 hydrogenation in a membrane-integrated microchannel reactor is modeled. The proposed reactor comprises rectangular permeate and reaction channels separated by layers of sodalite membranes, permitting only H2O and H2 transport. Reaction channels, dosed with CO2 and H2, are washcoated with a physical mixture of methanol synthesis (Cu-ZnO/Al2O3 (CZA)) and dehydration (HZSM-5) catalysts. Pure H2-fed permeate channels host the steam transported from reaction channels. The mathematical model of the isothermal, steady-state reactor involves conservation equations in catalyst and fluid phases, catalytic reactions, and membrane separation. The model is successfully benchmarked against literature-based experimental data. Differences between isothermal and non-isothermal models remain negligible. At 543 K, 50 bar, and H2/CO2 = 3, cross-membrane H2O and H2 transport increases membraneless CO2 conversion and DME yield values by more than 2-fold, i.e., up to ∼73 and ∼35%, respectively. Counter-current flow configuration offers more H2O separation than the co-current one. The sweep-to-reactive stream inlet velocity ratio affects cross-membrane mass transfer significantly. Reactor performance is positively correlated with the CZA/HZSM-5 mass ratio. A ∼7 m3-sized reactor can transform ∼1 × 103 tons/year of CO2 into 2.76 × 102 tons/year of DME.