A one-parameter model of catalyst deactivation for FCC modelling

Abstract

A one-parameter model of catalyst deactivation, based on the distribution of acid site strengths, is proposed. The model describes the deactivation rate as a function of time-on-stream (TOS) and accounts for the very fast initial rate of decay observed in commercial FCC. All of the model parameters are temperature-invariant and are shown to apply to feeds and catalysts not too different from the base case. The proposed model can be used to generate the catalyst deactivation profile at very short times-on-stream (TOS<6s) from experimental data obtained at relatively large TOS (>30 s). The same data is fitted using two forms of the TOS decay function. An examination of the resultant parameters indicates that decay in the first few seconds of TOS, is of a high kinetic order. Subsequently, the catalyst decays by processes which remove active sites by reactions of a lower order, one which is probably related to the chemical mechanism of catalyst poisoning. It is this change in kinetics which will not allow a valid extrapolation to short on stream times when the conventional TOS function, θ=(1+ Gt) −N, is applied to data at t>30 s.