Effects of SiO₂/Al₂O₃, MgO modification and hydrothermal treatment on the catalytic activity of HZSM-5 zeolites in the methylation of 4-methylbiphenyl with methanol

The objective of this work is to study the effects of SiO ₂/Al₂O₃ of HZSM-5, MgO modification and hydrothermal treatment on methylation of 4-methylbiphenyl (4-MBP) with methanol under fixed-bed down-flow conditions. The results show that, with an increase in the SiO₂/Al₂O₃ of HZSM-5 (from 50 to 150, molar ratio), the selectivity to 4,4′-dimethylbiphenyl (4,4′-DMBP) increases from 25 to 79%. MgO modification also increases the selectivity to 4,4′-DMBP, but leads as well to low catalyst activity and rapid deactivation. Hydrothermal treatment not only increases the selectivity, but also improves the stability. When CBV1502 (SiO₂/Al₂O ₃=150) catalyst was hydrothermally treated at 500°C, the selectivity to 4,4′-DMBP increased to 85%. The selectivity to 4,4′-DMBP was further improved to about 90% by the increasing in the amount of mesitylene in the feed as solvent.