Catalyst Deactivation by Active Site Coverage and Pore Blockage

Abstract

A mechanism for catalyst deactivation by active site coverage and pore blockage with coke was developed by assuming that the main reaction (in petroleum refining or petrochemical processes) and the coke deposition occurred on the same active sites (AS); that the growth of coke molecules was infinitely fast with respect to the formation rate of the coke precursors on the AS's; and that no diffusional limitations existed on the rate of the main reaction. Mathematical relationships were derived for the AS coverage or coke content (C/sub c/) and the number of AS's made inaccessible by coke molecules blocking the pores. The coke content vs. time and deactivation function (q) vs. time relations derived for single pores open on one or both ends, a set of parallel pores, and various networks of interconnected pores were used to explain the exponential relations between q and C/sub c/ previously observed in n-pentane isomerization on a platinum reforming catalyst and in 1-butene dehydrogenation on a chromia-alumina catalyst. The theory was applied to the kinetic analysis of a deactivating catalytic system and to the design of an isothermal tubular reactor.