OP-II-3

PP-I-25transformations. In this work, we have compared a traditional silver catalyst with aAu/TiO 2 one. The silver/α-alumina catalyst was prepared by thermally decomposingγ-alumina and further silver impregnating it with Ag by the incipient wetness method.The catalyst was succesively washcoated in the microplates as described in [3]. TheAu/TiO 2 catalyst was deposited on the microplates by atomic layer deposition (ATD).A gas-phase microreactor was used for the synthesis of EO using a total gas flowrate of 6 ml/min. The varied parameters for the kinetic modelling were pressure (1-5bar), oxygen and ethylene concentrations (1-25 vol.%) and temperature (220-300°C). The effluent gases were analyzed by a Agilent 3000A Micro. Conversions ofethylene up to 40% were achieved at high pressures (5 bar). The selectivity towardsethylene oxide for silver-alumina catalysts reached 70%. As Au/TiO 2 was used,activities up to 40% and selectivities up to 60% were reached. Fig. 1 presents theconversions and selectivities towards ethylene oxide when using silver/aluminamicrochannels at atmospheric pressure. Ethylene and oxygen concentrations had apositive effect on both the rate of ethylene oxide formation and carbon dioxideformation. For the kinetic modelling a steady-state plug-flow reactor model wasassumed. The influence of the reaction products and internal diffusion limitationswere considered but found to be negligible.Fig. 1. Conversion and selectivity towardsethylene oxide over Ag/α-Al 2 O 3 coatedmicrochannels. 20 vol.% ethylene, 10 vol.%oxygen, total flow 6.0 ml/min, p = 1 bar.A competitive Langmuir-Hinshelwoodmodel was used with the surface reactionbetween adsorbed ethylene anddissociatively adsorbed oxygen as therate-limiting step. The kinetic fit of themodel and the parity plots (degree ofexplanation of 97%) are presented in the full manuscript.References[1]. Gavriilidis, A.; Angeli, P.; Cao, E.; Yeong, K. K.; Wan, Y. S. S. Technology and applications ofmicroengineered reactors. Chem. Eng. Res. Des. 2002, 80, 3.[2]. Stankiewicz, A. I.; Moulijn, J. A. Process intensification: Transforming Chemical Engineering.Chem. Eng. Prog. 2000, 96, 22.[3]. Stefanescu, A.; van Veen, A.C.; Mirodatos, C.; Beziat, J.C.; Duval-Brunel, E. Wall coatingoptimization for microchannel reactors, Catal. Today 2007, 125, 16.266