The conversions of 1,3,5-trimethylbenzene over beta zeolite: Effect of SiO₂/Al₂O₃ ratio

A series of beta zeolites with various SiO₂/Al₂O₃ ratios has been synthesized. These samples were characterized with respect to crystallinity, particle size, acidity and sorption capacities of water, n-hexane and cyclohexane. The conversion of 1,3,5-trimethylbenzene (TrMB) was conducted in a fixed bed reactor at 493-743 K and atmospheric pressure. The conversion of 1,3,5-TrMB decreased with an increase in the SiO₂/Al₂O₃ ratio of the zeolite. The zeolites with low SiO₂/Al₂O₃ ratio favored the disproportionation and the zeolites with high SiO₂/Al₂O₃ ratio favored the isomerization. These can be interpreted by the acid concentration of zeolite. In the isomerization, all zeolites produced more 1,2,4-TrMB than 1,2,3-TrMB. In the disproportionation, the selectivity of tetramethylbenzene (TeMB) was in the order of 1,2,3,5- > 1,2,4,5- > 1,2,3,4-TeMB. The concentration of 1,2,4,5-TeMB is greater than that at equilibrium. The results show that shape selectivity comes into effect. The reaction temperature and the reaction time on stream also affect the selectivity significantly due to coke formation in the zeolites.