4.5 Shape-selective Isopropylation of Naphthalene and Biphenyl over Dealuminated H-Mordenites

Abstract

Abstract Dealumination of H-mordenite enhanced catalyst performance in the isopropylation of naphthalene and biphenyl. The activity for naphthalene and biphenyl to diisopropylnaphthalene (DIPN) and diisopropylbiphenyl (DIPB) isomers was increased by the dealumination, but further alkylation to polyisopropylated compounds was inhibited. The selectivity of 2,6-DIPN and 4,4′-DIPB increased with the increase of SiO 2 /Al 2 O 3 (Si/Al 2 ) ratio. The enhancement of catalytic activity by the dealumination is ascribed to the decrease of coke deposition because of the decrease of acid sites and strength. The increase of the selectivities of 2,6-DIPN and 4,4′-DIPB is due to the decrease of acid sites at the external surface. The selectivity of 4,4′-DIPB was varied with the change of propylene pressure in the isopropylation of biphenyl over a highly dealuminated mordenite HM220. The selectivity of 4,4′-DIPB was achieved up to 90 % under high propylene pressures such as 10 kg/cm 2 , whereas the decrease of the selectivity of 4,4′-DIPB due to the isomerization to 3,4′-DIPB was observed during the reaction under low propylene pressure such as 0.8 kg/cm 2 . Propylene prevents the isomerization because of its preferential adsorption on acid sites. The yield of 4-IPBP reached maximum at 50-60 % conversion, whereas the yield of 3-IPBP increased monotonously. These results are explained by two-stage alkylation mechanism: in the first stage, biphenyl is alkylaied to IPBP isomers, in which 4-IPBP is predominant. 4-IPBP only participates in the second stage alkylation, to yield 4,4′-DIPB shape-selectively. Coke deposition occurred rapidly at the early stages in the isopropylation of biphenyl over HM220. However, the oligomerization of propylene began after the yield of DIPB isomers reached 20 %. Propylene adsorbed on acid sites is preferentially consumed by the isopropylation, especially at the early stages. Principal biphenyl derivatives encapsulated in HM pore were identified as 4-IPBP and 4,4′-DIPB.