Modelling of carbon and hydrogen oxidation kinetics of a coked ferrierite catalyst

Abstract

The hydrocarbons in an alkene skeletal isomerisation process cause catalyst deactivation by forming coke that blocks the active sites. Oxidation of the coke is carried out in a regeneration unit to reactivate the catalyst. A kinetic model for the combustion is essential for purposes of designing the regeneration unit, since the highly exothermic oxidation releases heat that can damage the catalyst and the unit. Kinetic models were derived and tested by non-linear regression against the results of temperature programmed oxidation experiments with a coked ferrierite catalyst. Two methods for the measurement of carbon oxides in the reactor outflow – a direct analysis by mass spectrometry and an indirect analysis by a methanation method – were compared, and both were found appropriate. The determination of water by mass spectrometry was found adequate. The derived models cover the oxidation of both coke carbon and hydrogen. A power law model with an oxygen concentration order of half in carbon oxidation and zero order in hydrogen oxidation described the experimental results well. Two other models, in which active intermediate species are formed in fast equilibrium reactions, performed as well as the power law model. The estimated parameters of the models were in the physically meaningful range.