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Effect of wetting on catalytic gas-liquid reactions
Abstract
Most trickle-bed reactors utilize cocurrent, downward flow of gas and liquid reactants through a fixed bed of catalytic particles. Under trickling flow conditions, the liquid travels down the bed over the surfaces of the packings, whereas the gas flows through the remaining void space. For sufficiently low liquid flowrates, the external surfaces of the catalysts may only be partially liquid covered. The degree of wetting of the individual pellets can have a significant effect on the external transport rates of the reactants and thus on the overall reaction rate. The major objectives of this thesis are first to study the impact of partial wetting on reaction at the single-pellet level and then to use this information to develop an improved reactor-scale model. To this end, a two-dimensional, diffusion-reaction model is developed for a partially wetted catalyst. A range of conditions and several different bimolecular, intrinsic rate forms are considered. In general, the maximum reaction rate occurs under partial wetting conditions, if the system is mass transport controlled and the limiting reactant is mainly present in the gas phase. For reactions following multiple-site Langmuir-Hinshelwood kinetics, partial wetting may induce reaction rate multiplicity. A single-pellet experiment, which simulates the local environment of the trickle-bed, corroborates the predictions of the diffusion-reaction model. The key feature of the setup is that the degree of wetting is directly measurable under reaction conditions. Under certain operating conditions, an incompletely wetted pellet provides a conversion more than ten times greater than one that is totally wetted. Based upon these single-pellet studies, a trickle-bed reactor model is developed that accounts for the flow on and reaction within every catalyst particle. The impact of partial wetting on the overall reactor performance is demonstrated. In addition, the model is used to investigate the effect of liquid maldistribution on reaction by simulating different liquid-inlet configurations. Finally, the qualitative trends of these predictions are confirmed with a packed-bed experiment in which liquid is injected onto a bed of catalyst spheres from either one or three inlet tubes.
Subject Area
Chemical engineering
Recommended Citation
Funk, Gregory Allen, "Effect of wetting on catalytic gas-liquid reactions" (1990). Doctoral Dissertations Available from Proquest. AAI9022684.
https://scholarworks.umass.edu/dissertations/AAI9022684