Effect of pore size and aluminium content on the production of linear alkylbenzenes over HY, H-ZSM-5 and H-ZSM-12 zeolites: Alkylation of benzene with 1-dodecene

Abstract

H-ZSM-5 (Si/Al = 15 and 30), H-ZSM-12 (Si/Al = 80) and HY zeolites (Si/Al ratios in the range 2.7-26.4) were evaluated in the benzene alkylation reaction with 1-dodecene for linear alkyl-benzene-LAB production. A series of dealuminated Y-zeolites was prepared under strictly controlled conditions by treatment with silicon tetrachloride. The materials thus obtained were washed and exchanged with ammonium chloride. The catalysts were characterized by X-ray diffraction, infrared spectroscopy of the framework vibrations, 29Si and 27Al-nuclear magnetic resonance. Temperature-programmed desorption of ammonia and elemental analysis. H-ZSM-5 and H-ZSM-12 catalysts showed very low activity. H-ZSM-12 zeolite exhibits both product and transition state type shapeselectivity, favouring the formation of the least bulky 2-phenyl isomer. With HY-zeolites, the alkylation activity increased linearly with the number of lattice Al per unit cell over a range of Si/Al ratios from 2.7 to 26.4, so a practically constant turnover frequency is obtained. The HY-zeolites also gave 97–98% selectivity towards LAB and produced branched dodecene, traces of branched alkylates and dialkylbenzenes as by-products. Neither dialkyltetralins nor dialkylindanes were found among the products. HY-zeolites did not exhibit shape-selectivity effects. The apparent activation energy was 15 kcal/mol. Small changes in the low Na content of the zeolites were responsible for considerable increases in activity. Dealuminated HY zeolites showed the highest selectivity towards 2-phenyldo-decane. In this case we suggest that the alkylation reaction competed effectively with the migration of the double bond across the chain, so that some of the initial alkylcarbenium ions formed alkylated benzene without undergoing isomerization. The isomerization of the phenylalkane was not observed after alkylation.