Isopropylation of biphenyl over ZSM-12 zeolites

ZSM-12 zeolites, ZSM-12L and ZSM-12S, with MTW topology were synthesized by using methyltriethylammonium bromide (MTEABr) and tetraethylammnoium bromide (TEABr) as structure directing agents (SDA), respectively, for the isopropylation of biphenyl (BP) using propene as an alkylating agent. The particle sizes of the ZSM-12L and ZSM-12S were in the range of 5–10 μm and less than 0.5 μm, respectively. The selectivities for 4,4′-diisopropylbiphenyl (4,4′-DIPB) were 60–70% for ZSM-12L and 40–50% for ZSM-12S at lower temperatures below 275 °C, and rapidly decreased with further increase in temperatures to less than 20% at 350 °C over both zeolites. The kinetic controlled catalyses on external acid sites at lower temperatures were resulted in the formation of bulkier isomers, 2,x′-DIPB (x:2,3,4). The decreases in the selectivity for 4,4′-DIPB occurred by the isomerization of 4,4′-DIPB to stable isomers, 3,4′- and 3,3′-DIPB on external acid sites at higher temperatures. These catalyses were decreased remarkably over ZSM-12LD prepared by the dealumination of ZSM-12L with EDTA-3Na, because of effective removal of external acid sites.The isopropylation of BP over ZSM-12 zeolites was moderately shape-selective for the formation of 4,4′-DIPB at appropriate temperatures, particularly over ZSM-12L and ZSM-12LD. The formation of 4,4′-DIPB occurred primarily near pore-entrances but not deep in the channels. ZSM-12 channels are less effective for the selective formation of 4,4′-DIPB than MOR channels.

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► Shape-selective formation of 4,4′-diisopropylbiphenyl over ZSM-12 zeolites.
► Selectivities for 4,4′-DIPB were 60–70% of ZSM-12 with particle size of 5–10 μm.
► Non-selective formation of 2,x′-DIPB (x:2,3,4) and 3,4′-DIPB at external acid sites.
► Principal active sites for the formation of 4,4′-DIPB are near pore-entrances.
► ZSM-12 channels are a little bit narrow for the highly selective formation of 4,4′-DIPB.