Selective alkylation of biphenyl with t-butanol over large pore zeolites

Abstract

Alkylation of biphenyl with t-butanol under liquid phase conditions has been studied over HY and Hβ zeolites with different silicon to aluminum molar ratios as catalysts. HY zeolites have been shown to be more active than Hβ zeolites. A maximum of 58% for the biphenyl conversion has been obtained over HY (15) zeolite at 160°C. The initial catalytic activity of studied zeolites for t-butylation of biphenyl at 160°C can be set in the next order: HY (15)>HY (30)>Hβ (12.5)≅Hβ (25). Both types of zeolites showed a significant selectivity of the monoalkylation step versus di- and polyalkylation with a very high selectivity leading to the 4- t-butylbiphenyl derivative (4-TBB) (near 95% for HY and 87% for Hβ). Moreover, a high initial selectivity in 4,4′-di( t-butyl)biphenyl (4,4′-DTBB) was obtained (near 82% for HY and 90% for Hβ at 160°C). Such a selectivity remained constant with time over HY, while it dramatically decreased over Hβ. Higher temperatures and higher catalyst concentration led to an increase of secondary reactions, which have been evidenced as isomerization of 4-TBB to 3-TBB, 4,4′-DTBB to 3,4′- and 3,3′-DTBB, oligomerization of isobutylene, alkylation of biphenyl with oligomers to higher alkyl- and polyalkylbiphenyls together with disproportionation and transalkylation of alkylbiphenyls.