An experimental and modeling study of phase transition and exothermic reaction in the multiphase catalyst pellet

摘要

The purpose of this research is to provide fundamental insight into the partial wetting of catalyst pellets under multiphase, nonisothermal conditions. In trickle-bed reactors, for example, the catalyst pellets may be only partially contacted by liquid due to flow maldistributions in the reactor bed. When the reactions under consideration are exothermic, and contain species that are volatile, condensation and vaporization may occur within the pores and on the catalyst pellet exterior. Acquiring a fundamental insight into the complicated multiphase environment and the chemical and physical processes of a single catalyst pellet by modeling and experiments is the goal of this research. Such insight can lead to an improved understanding of hot spot formation with trickle-bed reactors and to the development of new reactor types which exploit reaction induced phase transition.;Specifically, the situation where a single liquid rivulet partly wets the outside surface of a catalyst pellet is examined. Both the modeling and experiments carried out in this study indicate that heat generated by reaction can cause vaporization of the liquid reactant leading to partial pore filling of the catalyst pellet.;To this end, a one-dimensional, steady-state model is presented to capture the coupling between partial external wetting, imbibition, vaporization, and liquid- and gas-phase reactions. A range of conditions are considered to emphasize pressure buildup, temperature variation, and concentration gradients that can occur within the partially wetted catalyst pellet. In general, a multiplicity of states is predicted over a wide range of conditions.;A novel single pellet reactor was used to measure the liquid holdup, catalyst temperature, degree of wetting, and reaction rate. Dynamic experiments with $alpha$-methylstyrene hydrogenation and cyclohexene hydrogenation were carried out indicating coincident temperature rise with vaporization of the liquid reactant. Steady-state experiments using cyclohexene hydrogenation corroborate qualitatively the model predictions. Significantly higher reaction rates are obtained when the pellet is partly liquid-filled compared to when the pellet is completely filled.