Kinetic Modeling of a Vacuum Gas Oil Hydrocracking in a Semi-Batch Reactor : Approach By Distribution
Résumé
A model for hydrocracking a VGO over a bifunctional catalyst at 400°C and 120 bar in a semi-batch reactor has been constructed based on the experimental work of Henry et al.. In this work liquid phase composition was analysed by two dimensional gas chromatography (GC x GC) and, to model these results, the reaction mixture is lumped into pseudo-components by both molecular structure and carbon number. The rate constants are represented using probability distributions including the product distribution published by Weitkamp for ideal hydrocracking. Reactivity is calculated as a function of carbon number.
The model uses the Grayson-Streed activity coefficient model combined with the Peng-Robinson equation of state to represent the vapour-liquid equilibrium in the reactor and also takes into account internal and external mass transfer resistances.
The results of this model show that the assumptions regarding the molecular structure of the naphthenes and aromatics are important to successfully represent the experimental data and, in particular, to simulate
the over-cracking observed experimentally for the iso-paraffins. The same effect could not be achieved by adjusting only the mass transfer coefficients.