Shape-selective methylation of 4-methylbiphenyl with methanol into 4,4,-dimethylbiphenyl. II. Effects of zeolite type, the SiO₂/Al₂O₃ mol ratios and phosphorus modification

The effects of zeolite type, the SiO₂/Al₂O₃ mol ratio of HZSM-5 on the methylation of 4-methylbiphenyl (4-MBP) with methanol were investigated by using a fixed-bed down-flow reactor. The results show that the products of methylation of 4-MBP with methanol catalyzed by zeolites with 12-membered ring, such as HY, HM and Hβ, yield all the possible isomers, no selectivity of the target product 4, 4-dimethylbiphenyl (4,4'-DMBP) is observed. The 10-membered ring zeolite ZSM-5 catalyst showed moderate selectivity to 4,4'-DMBP. The conversion of 4-MBP decreased and the selectivity to 4,4,-DMBP increased with the increase of the SiO₂/Al₂O₃ mol ratio of ZSM-5. With HZSM-5 (n(SiO₂)/n(Al₂O₃)=80) as the precursor, HZSM-5 zeolites with different phosphorus loading were prepared by impregnation method modified with ammonium hydrogen phosphate (AHP) and tri-phenyl phosphine (TPP), respectively. The prepared samples were characterized by XRD, TPD, N₂ low-temperature physical adsorption and evaluated with methylation of 4-MBP with methanol. The results show that both inorganic and organic phosphorus modification greatly improve the selectivity to 4,4'-DMBP.