Process of p-Xylene Production by Highly Selective Methylation of Toluene

Ind. Eng. Chem. Res., 2013, 52 (38), pp 13730–13737, DOI: 10.1021/ie401156x
Process of p-Xylene Production by Highly Selective Methylation of Toluene
Muhammad Tahir Ashraf , Rachid Chebbi *, and Naif A. Darwish
Department of Chemical Engineering, American University of Sharjah, P.O. Box 26666, Sharjah, United Arab Emirates
Abstract
p-Xylene is typically produced by cracking naphtha. With steadily increasing demand, however, it is necessary to create new and more cost-effective methods for the production.
Toluene alkylation with methanol over an alumino-silicate zeolite catalyst, such as ZSM-5, produces a mixture of xylene isomers with low p-xylene selectivity. Because of the very close boiling points of xylene isomers, it is quite expensive to separate them. There has been some success in enhancing p-xylene selectivity by modifying the ZSM-5 catalyst. This results in reduced separation cost, making toluene methylation a competitive process for p-xylene production.
Researchers describe an innovative process for the production of p-xylenes by the catalytic methylation of toluene followed by reactive distillation for the separation of p-xylene. They use Aspen Plus to create a complete process flow diagram simulation. Using the built-in optimization tool in Aspen Plus, they optimize reactor parameters for a maximum p-xylene selectivity of 97.7%. After separation, a p-xylene product stream purity of 99.7% is achieved. High p-xylene selectivity in the reactor and use of reactive distillation reduces the separation cost and renders the new process economically competitive.
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