Tert-Butylation of biphenyl over H-Y and H-beta zeolites; formation and identification of main and by-products

Abstract

tert-Butylation of biphenyl with tert-butanol has been studied over large-pore H-Y (15) and H-beta (25) zeolites under liquid phase conditions using cyclohexane as a solvent. The identification of main and by-products has been performed by GC-MS analysis. The main products of the alkylation reaction were mono- tert-butylbiphenyls and di-( tert-butyl)biphenyls with preferential formation of para- and para, para′-isomers. Higher alkylbiphenyls with alkyl group from C 4 to C 10′ were identified as by-products. These compounds can be formed by alkylation of biphenyl and/or mono- tert-butylbiphenyls with different alkenes, generated by dehydration of tert-butanol, followed by oligomerisation and disproportionation of the formed isobutylene. A peculiar effect of the small change in dimensions of micropores of H-beta (elliptic pores 0.76 nm×0.64 nm) in comparison with H-Y zeolite (circular pores 0.74 nm) has been reflected by the transalkylation of mono- tert-butylbiphenyls to cyclohexylbiphenyls and methylcyclopentylbiphenyls over the more acid H-beta zeolite catalyst, whereas this transalkylation has been not monitored in the experiments with H-Y zeolite. The occurrence of transalkylation reactions has been supported by thermodynamic analysis and calculations.