MODELING OF 2-METHYLPENTANE CRACKING - THE APPLICATION OF ADSORPTION EQUILIBRIUM-CONSTANTS ESTIMATED USING PROTON AFFINITIES

This article presents a practical approach for estimating adsorption e quilibrium constants, K-p, for inclusion in Eley-Rideal type rate expr essions, using van't Hoffs isochore equation, RTlnK(p) = Delta H-ad T Delta S-ad. The heats of adsorption, -Delta H-ad, have been calculat ed using proton affinites and heats of condensation, and the entropy o f adsorption, Delta S-ad, has been calculated using the Sackur-Tetrode equation. The equilibrium constants have been incorporated into a mod el for 2-methylpentane cracking that is based on a previously publishe d reaction mechanism. The predicted behavior of the model compares wel l with published experimental data for a range of catalyst to oil rati os, This new model is also capable of predicting surface coverages of reaction intermediates; for an overall conversion of 10%, over 80% of the catalyst surface is covered with adsorbed C-6 olefin. In addition, the model predictions compare well with published experimental result s for dilution of the feed stream with a nonpolar species such as nitr ogen. (C) 1996 Academic Press, Inc.