UNSTEADY-STATE OPERATION OF CATALYTIC PARTICLES WITH CONSTANT AND PERIODICALLY CHANGING DEGREE OF EXTERNAL WETTING

A dynamic model is developed to describe two parallel reactions betwee n one gaseous and two non-volatile components on partially wetted cata lysts with a time-dependent welting efficiency. This simulates the per formance of catalytic particles in a trickle-bed reactor operating in the pulsing-flow regime. The periodically varying external surface cov erage results in periodically varying mass transfer rates to the surfa ce of the particle. No a priori assumption is made about a rate limiti ng reactant. The results show the effect of interface and intraparticl e mass transfer resistances as well as of the wetting efficiency and t he frequency with which it varies on catalyst performance. It is shown that the wetting efficiency, the location of the wetted zones and the frequency need to be specified in order to determine the time-average d effectiveness factors. For the same time-averaged wetting efficiency , pulse-flow can significantly enhance catalyst performance. Condition s are determined under which the effectiveness factors are maximized. The model is applied to a typical HDS process of heavy gas oil. (C) 19 98 Elsevier Science Ltd. All rights reserved.