Production of xylenes from toluene and 1,2,4-trimethylbenzene over zsm-5 and mordenite catalysts in a fluidized-bed reactor

The production of various xylenes from toluene, heavy aromatics such as 1,2,4-trimethylbenzene (1,2,4-TMB) and their mixture was investigated over H-ZSM-5 (H-Z), H-mordenite (H-M) and a dual zeolitic catalyst comprising ZSM-5 and mordenite (H-ZM). The experiments were conducted in a riser-simulator reactor under different operating conditions to study the effect of temperature, reaction time and feed composition on conversion and product yields. At 400 °C, the conversion of toluene over the three catalysts yielded mainly benzene and xylenes with maximum conversion at 25% and a xylene yield of 12.5 wt% over the H-M catalyst. The transformation of 1,2,4-TMB doubled the conversion level and xylene yield and suppressed benzene formation. However, a considerable portion of the 1,2,4-TMB feed was isomerized into 1,2,3-TMB and 1,3,5-TMB accompanied by the formation of tetramethylbenzenes (TeMBs). The conversion of an equimolar mixture of toluene and 1,2,4-TMB over the three catalysts resulted in higher toluene conversion and double xylene yield in comparison with 1,2,4-TMB alone. The advantage of using a dual zeolitic catalyst was observed at an equimolar feed of toluene and 1,2,4-TMB, exhibiting maximum toluene conversion, higher xylene yield and the formation of lower levels of undesirable products.