Ethylene oxide synthesis in a wall-coated microchannel reactor with integrated cooling

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Ethylene oxide (EO) synthesis in a cooling function integrated microchannel reactor is studied via detailed modeling. The reactor is composed of parallel groups of cooling and catalyst coated reaction channels involving counter-current flows of air and reactive mixture, respectively. Upon its validation by the experimental data, the model accounting for the steady-state, 2D conservation of momentum, heat and species mass together with the reactive transport within porous catalyst layer is used to elucidate the impacts of reactor intensification on ethylene conversion, EO selectivity and yield. Significance of in-situ heat removal in intensified EO synthesis, which is not studied in the literature, is demonstrated by the complete elimination of ∼50 K adiabatic temperature rise. Increasing the reactant inlet temperature from 503 to 553 K elevates ethylene conversion from 4.5% to 12.5% but reduces EO selectivity from 62.2% to 56.8%. This trend is also observed by reducing C2H4/O2 from 3.0 to 0.25 that increases conversion and decreases selectivity by ∼6.5% and ∼0.8%, respectively. These findings are coherent with the responses of the competing rates of partial and total oxidation of ethylene. The operation is sensitive to the inlet air temperature which should be kept 5 K below that of the reactants to ensure uniform cooling along the channel. Use of thicker walls between the channels and thermally conductive reactor materials promotes isothermal behavior. However, impact of these structural parameters on reactor performance remains negligible. Efficient cooling by air even at O2-rich feeding, which offers up to two times increase in EO yield, but not preferred in conventional EO synthesis due to safety concerns, is well correlated with the superior heat transfer characteristics of the microchannel units.