1,2,4-Trimethylbenzene Transformation Reaction Compared with its Transalkylation Reaction with Toluene over USY Zeolite Catalyst

Abstract

Abstract1,2,4-Trimethyl benzene (TMB) transalkylation with toluene has been studied over USY-zeolite type catalyst using a riser simulator that mimics the operation of a fluidized-bed reactor. 50:50 wt% reaction mixtures of TMB and toluene were used for the transalkylation reaction. The range of temperature investigated was 400-500 o C and time on stream ranging from 3 to 15 seconds.The effect of reaction conditions on the variation of p-xylene to o-xylene products ratio (P/O), distribution of trimethylbenzene (TMB) isomers (1,3,5-to-1,2,3-) and values of xylene/tetramethylbenzenes (X/TeMB) ratios are reported. Comparisons are made between the results of the transalkylation reaction with the results of pure 1,2,4-TMB and toluene reactions earlier reported. Toluene that was found almost inactive, became reactive upon blending with 1,2,4-TMB. This shows that toluene would rather accept a methyl group to transform to xylene than to loose a methyl group to form benzene under the present experimental condition with pressures around ambient. The experimental results were modeled using quasi-steady state approximation. Kinetic parameters for the 1,2,4-TMB disappearance during the transalkylation reaction, and in its conversion into isomerization and disproportionation products were calculated using the catalyst activity decay function based on time on stream (TOS). The apparent activation energies were found to decrease as follows: E transalkylation > E isomerization > E disproportionation . February 2007Keywords: Trimethyl benzene transalkylation, toluene reaction, fluidized-bed reactor, USY-zeolite, xylene yield * Corresponding author. Tel.: +966-3-860-1429; Fax: +966-3-860-4234 e-mail address: skhattaf@kfupm.edu.sa 2 Introduction:The demand for xylenes as a raw material for polyester fibers and films continues to grow and drive the search to increase xylene production processes. In the year 1999, the world consumption of mixed xylene was about 24 million tons, and is expected to grow at a rate of 6.2% to 35.9 million tons by the year 2007. This indicates that xylenes are still gaining importance in the petrochemical market. Among the three xylene isomers, p-xylene is the most demanded and thus most expensive, followed by o-xylene.One common way for xylene production is the conversion of the lower value toluene (C 7 ) and trimethylbenzene (C 9 ) into xylenes via toluene disproportionation, trimethyl benzene (TMB) disproportionation and transalkylation with toluene. Thus, these processes offer a way to utilize the low cost toluene and TMB to produce much more attractive product xylene. TMB disproportionation, and toluene-TMB transalkylation. They found that the zeolite beta has excellent stability and transalkylation selectivity. In TMB disproportionation, blending toluene into feedstocks can shift the production selectivity of TeMB to xylene, whereas in toluene disproportionation, mixing TMB into feedstocks not only reduced the reaction temperatures but also raised the xylene yield. Das et al.[4] also studied the t...

Comparison of Activity and Selectivity of SSZ-33 Based Catalyst with other Zeolites in Toluene Disproportionation

“…Toluene is also an important component for transalkylation with trimethylbenzenes to provide xylenes. 1,2,4-Trimethylbenzene (TMB) transalkylation with toluene has been studied over USY zeolite type catalyst [22]. Reaction mixture of 50:50 wt% TMB and toluene was used.…”

Chemical Imaging of the Binder‐Dependent Coke Formation in Zeolite‐Based Catalyst Bodies During the Transalkylation of Aromatics

“…[13][14][15] However, it was found that medium-pore zeolites, like ZSM-5, have a higher selectivity towards p-xylene. Firstly, the pores need to be large enough for the diffusion of the bulky TMB species.…”

Effect of zeolite pore structure on the diffusion and catalytic behaviors in the transalkylation of toluene with 1,2,4-trimethylbenzene

“…This is conrmed by Krejčí and coworkers. 21 Al-Khattaf et al 22 reported that USY gave high xylene yield in the transalkylation of toluene with 1,2,4-TMB that was carried out in a riser simulator reactor. Lee et al 23 investigated the catalytic activity of zeolites with 12-MR in the transalkylation reaction and found that MOR zeolite showed high activity and stability, especially aer dealumination.Čejka et al 24 attributed the high catalytic activity of large-pore zeolites to accommodation of more reactants inside their channel systems, which led to an increase in the probability of occurrence of bimolecular reaction.…”