Research Article 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 con- version 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 accompa- nied 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 conver- sion, higher xylene yield and the formation of lower levels of undesirable pro- ducts. Keywords: Disproportionation, Dual catalyst, Isomerization, Mordenite, Toluene, Transalkylation, Trimethylbenzenes, Xylenes, ZSM-5 Received: February 25, 2010; revised: March 23, 2010; accepted: April 27, 2010 DOI: 10.1002/ceat.201000083 1 Introduction The production of xylenes via the disproportionation of tolu- ene or the transalkylation of heavy aromatics (with or without toluene or benzene) offers refiners an excellent opportunity to add value to their product streams. Other advantages include compliance with the more stringent gasoline specifications (less heavy aromatics) and the expected decline in gasoline de- mand. The main applications of xylenes are in the production of synthetic fibers, plasticizers as well as solvents and gasoline blending. Commercial transalkylation processes such as Trans- Plus and Tatoray have become an essential part of the modern aromatics industry [1, 2]. Currently, p-xylene accounts for ca. 83 % of the global demand for xylenes, which exceeds 42 mil- lion tons per year, followed by o-xylene at 9 % of the total demand [3]. The conversion of toluene and heavy aromatics takes place on solid acid catalysts and is one part of several parallel con- secutive reversible reactions, mainly transalkylation and dis- proportionation. The list of equations in Tab. 1 summarizes some of the individual reactions and products that can be identified during the transalkylation reaction [4,5]. Toluene undergoes disproportionation to produce benzene and xy- lenes. TMBs get converted into xylenes and TeMBs and also undergo isomerization to an almost thermodynamic equilibri- um mixture. The utilization of zeolitic catalysts in the transfor- mation reaction plays a key role in the selective production of desirable xylene products. Various types of medium pore zeo- lites such as ZSM-5 [6], omega, erionite [7], NU-87 [8, 9], MCM-22 [9], and large pore zeolites such as ZSM-12 [10, 11], faujasites [12–17], beta [8, 17–19], mordenite [8, 11, 17], SAPO-5 [20], and zeolite L [21], have been tested for the transalkylation reaction. Coke formation and catalyst stability are among the various factors affecting the activity and selec- Chem. Eng. Technol. 2010, 33, No. 7, 1193–1202 © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Abdullah M. Aitani 1 Ashraf M. Ali 1 Saidu M. Waziri 1 Sulaiman Al-Khattaf 1 1 Center of Research Excellence in Petroleum Refining and Petrochemicals, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia. – Correspondence: Prof. S. Al-Khattaf (skhattaf@kfupm.edu.sa), Center of Research Excellence in Petroleum Refining and Petrochemicals, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran 31261, Saudi Arabia. Xylenes 1193