in Wiley Online Library (wileyonlinelibrary.com).Recently a homogeneous liquid-phase ethylene oxide (EO) process with nearly total EO selectivity, catalyzed by methyltrioxorhenium with H 2 O 2 as an oxidant, was reported. Fundamental mass transfer and kinetic studies of this reaction are reported in the present work. Volumetric expansion studies revealed that the liquid reaction phase (methanol þ H 2 O 2 / H 2 O) is expanded by up to 12% by compressed ethylene in the 20-40 C range and up to 50 bars. This represents an increase in ethylene solubility by approximately one-order of magnitude, attributed to the unique exploitation of nearcritical ethylene (P c ¼ 50.76 bar; T c ¼ 9.5 C). Interphase mass-transfer coefficients for ethylene dissolution into the liquid phase were obtained experimentally. Operating at conditions that enhanced the ethylene solubility and eliminated interphase mass-transfer limitations maximized the EO productivity (1.61-4.97 g EO/h/g cat), rendering it comparable to the conventional process. Intrinsic kinetic parameters, estimated from fixed-time semibatch reactor studies, disclosed the moderate activation energy (57 AE 2 kJ/mol). (a) Ethanol þ methanol binary system; (b) (ethylene þ methanol þ 50 wt % H 2 O 2 /H 2 O) ternary system. Initial composition of liquid phase ¼ 0.748 mol methanol þ 0.134 mol H 2 O 2 þ 0.253 mol H 2 O. Initial volume of liquid phase ¼ 15 mL. The size of the plotted data points represents the experimental uncertainty. Ethylene P ¼ 50 bars; T ¼ 40 C; MTO amount ¼ 0.361 mmol; methanol ¼ 0.748 mol; H 2 O 2 ¼ 0.116 mol; H 2 O ¼ 0.220 mol; acetonitrile ¼ 0.0191 mol; pyridine N-oxide ¼ 2.19 mmol; batch time ¼ 5 h; agitation speed (Ä : 1,200 rpm, h: 400 rpm).

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Multimolar CO2 concentrations are achieved in acetonitrile solutions containing supporting electrolyte at relatively mild CO2 pressures (<5 MPa) and ambient temperature. Such CO2‐rich, electrolyte‐containing solutions are termed as CO2‐eXpanded Electrolytes (CXEs) because significant volumetric expansion of the liquid phase accompanies CO2 dissolution. Cathodic polarization of a model polycrystalline gold electrode‐catalyst in CXE media enhances CO2 to CO conversion rates by up to an order of magnitude compared with those attainable at near‐ambient pressures, without loss of selectivity. The observed catalytic process intensification stems primarily from markedly increased CO2 availability. However, a non‐monotonic correlation between the dissolved CO2 concentration and catalytic activity is observed, with an optimum occurring at approximately 5 m CO2 concentration. At the highest applied CO2 pressures, catalysis is significantly attenuated despite higher CO2 concentrations and improved mass‐transport characteristics, attributed in part to increased solution resistance. These results reveal that pressure‐tunable CXE media can significantly intensify CO2 reduction rates over known electrocatalysts by alleviating substrate starvation, with CO2 pressure as a crucial variable for optimizing the efficiency of electrocatalytic CO2 conversion.

Modeling and simulation reveal the mechanistic basis for the pressure-tunable rates of CO2 reduction at elevated pressures of CO2.