Reaction Conditions and Thermodynamics Study of a Transalkylation Reaction System

The reaction system of toluene disproportionation and trimethylbenzene transalkylation is a complex system for xylene preparation. In this paper, the equilibrium compositions of the products in this reaction system were carefully calculated and the equilibrium compositions at different temperatures and different feed compositions were analysed. The results show that as the temperature increases, the equilibrium conversions of toluene and trimethylbenzene decrease, and the equilibrium selectivity of xylene decreases as well. As Tol∶TMB value in the feed decreases from 9 to 1, the equilibrium conversions of toluene and trimethylbenzene decrease, while the equilibrium selectivity of xylene increases significantly. These results are due to the cooperation effect of toluene disproportionation and trimethylbenzene transalkylation. Using treated β zeolite as the catalyst, we analysed the reaction results and compared them with calculated equlibrium results. The results show that as the temperature increases, the aromatics conversions increase and approach to the equilibrium value, while xylene selectivity decreases markedly. It shows that there is an optimal point of Tol∶TMB value (60∶40) at which aromatics conversions and xylene selectivities achieve the maximum values.