Alkylation of deactivated aromatic compounds on zeolites. Adsorption, deactivation and selectivity effects in the alkylation of bromobenzene and toluene with bifunctional alkylating agents

Abstract

The alkylation of bromobenzene and toluene on zeolite H-USY (Si/Al 15) was studied using a high-throughput frontal analysis experimental setup. Adsorption properties of the involved components were determined using the batch technique. Reactions were performed using allyl alcohol, allyl acetate, 1-octen-3-ol, and allyl chloride as alkylating agents at 200 °C in the liquid phase. The reaction products could be divided into 3 fractions: (1) light components formed in side reactions of the alkylating agent; (2) primary alkylation products resulting from the alkylation of bromobenzene or toluene and subsequent rearrangement reactions; and (3) a heavy fraction consisting of secondary alkylation products and polyaromatics. Whereas the use of allyl chloride and 1-octen-3-ol as alkylating agents resulted mainly in the formation of undesired side products, bromobenzene was efficiently alkylated with allyl alcohol and allyl acetate, resulting in the formation of allyl bromobenzene, cis-2-propenyl bromobenzene, and trans-2-propenyl bromobenzene. The greatest product selectivity was obtained with allyl acetate, which is explained by the more favorable intrapore distribution of the alkylating agent and the aromatic substrate using allyl acetate as compared with allyl alcohol. Significant catalyst deactivation occurred in these reactions, attributed to pore blocking by very strong adsorption of side products in the zeolite micropores. With toluene, the product stream was dominated by heavy components, formed in secondary alkylation reactions.