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 degrees 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.