Kinetic non-reversibility of the cracking reactions and its accounting during mathematical modeling of industrial process

Abstract

The paper presents the approach to the catalytic cracking modeling with consideration of the reactions' reversibility/non-reversibility depending on the current concentrations and the cracking temperature. The thermodynamic analysis of the reactions using the quantum-chemical methods allows formulating a hydrocarbons conversion scheme at the thermal equilibrium temperature between the feedstock and the catalyst. The magnitude of the current chemical attraction of reactions is a criterion of thermodynamic non-reversibility of reactions, which is determined at each stage of the calculation. It has been shown that the change in the concentrations of conversion participants and cracking temperature have a significant effect on the catalytic cracking reactions. Thus, the cyclization reactions are non-reversible up to 512.9 °C (A[rij]=6.46 kJ/mol) during the processing of feedstock with saturated hydrocarbons to aromatics ratio is 2.1 and with further temperature increasing the contribution of reverse reactions rises. Also with increasing the saturated hydrocarbons to aromatics ratio from 2.1 to 3.2 in the feedstock, the equilibrium of the reaction shifts to low temperatures from 512.9 to 508.9 °C (A[rij]=6.497 kJ/mol). It is connected with the fact that intensification of the exotermic reactions (alkylation, condensation, coke formation) under certain conditions is possible. It is an important factor in terms of catalyst deactivation and has an effect on the desired product yield.