Shape-selective Methylation of 4-Methylbiphenyl to 4,4/-Dimethylbiphenyl with Supercritical Methanol over Zeolite Catalysts

摘要

The applicability of supercritical methanol was investigated to the selective para methylation of 4-methyl-biphenyl to produce 4,4'-dimethylbiphenyl,which has recently attracted much attention as a valuable monomer of thermotropic liquid crystals,engineering plastics and others.The effects of the catalysts,temperature,pressure,reaction time,initial molar ratio of methanol to 4-methylbiphenyl and initial weight ratio of catalyst to 4-methyl-biphenyl were evaluated using a batch-type reactor.The combination of supercritical methanol with SAPO-11 catalyst gave an excellent product selectivity of 70-85% of 4,4'-dimethylbiphenyl at 300°C,14-16 MPa,0.5 h reaction time,15-20 initial molar ratio of methanol to 4-methylbiphenyl and 0.4-0.6 initial weight ratio of catalyst to 4-methylbiphenyl.Comparing with supercritical and gaseous methanol,the selectivity of 4,4'-dimethyl-biphenyl in the supercritical phase was 1.5-3.4 times higher than that in the gas phase at the same conversion of 20-50% of 4-methylbiphenyl.The methylation almost stopped around 1 h due to coke deposition on the catalyst surface.