Rigorous kinetic models for catalyst deactivation by coke deposition: Application to butene dehydrogenation

Abstract

Recently developed models describing catalyst deactivation in terms of coverage of active sites and blockage of pores are extended and applied to published data on the dehydrogenation of butene on a chromia-alumina catalyst. The textural and catalytic properties of the catalyst are determined by classical physicochemical techniques. Regression of the coke versus time-on-stream curves allows the estimation of fundamental properties of the coke such as molecular mass and enables an insight into the mechanism of coke formation to be obtained. The best regression results are obtained by considering two stages in the coke formation sequence: there is a first stage of site coverage by coke precursor accompanied by instantaneous growth up to an intermediate size and a second stage of further growth at a rate of the same order of magnitude as the rate of coke formation corresponding to the first stage. Some 15% of the catalyst surface becomes inaccessible by blockage of the smallest pores. The deactivation of the dehydrogenation itself is predicted in a satisfactory way by using the parameter estimates derived from the coking data only.