Studies on dealkylation of alkyl aromatic hydrocarbons Part II- Demithylation of xylene isomers and ethylebezene to benzene

Abstract

The demand for benzene is increasing. The possibilities of preparing it from substituted benzene by dealkylation are investigated in the present work. From the literature pertaining to dealkylation processes, the vapour?phase catalytic hydrodealkylation of xylenes and ethylbenzene was selected for detailed study. It was proposed to study the xylenes and ethylbenzene individually. The dealkylation of xylenes and ethylbenzene is a two?step reaction. In the first step the xylene or ethylbenzene is dealkalkylated to toluene and in the second step toluene is dealkylated to benzene. The thermodynamical calculations indicated that all the reactions are exothermic reactions. For this study nickel on silica gel was used as the catalyst. The catalyst characterization such as surface area was carried out. In the first part of the investigation, a conventional experimentation procedure was followed with temperature of the reaction, time?factor, mole ratio and catalyst bed height as parameters. The process optimization was done with a central composite factorial design of experiments. From these experiments, a quadratic model was proposed for each of these systems. The quadratic models were analysed to see the effect of each variable on the process at the optimum level in the experimental region by ridge analysis. The main objective of much experimentation is to give an appropriate model for that system. A model was built for the rate of reaction by means of model?building technique with nonlinear estimation of the parameters on a statistical approach. From the model the energy of activation and the frequency factor for the systems were calculated. For the systems investigated a mechanism was proposed with the Langmuir–Hinshelwood approach.