Transalkylation of toluene

Table 4. Tatoray Transalkylation of Toluenes and Aromatic Compounds, Relative Wt Units...

The Xylene Plus process of ARGO Technology, Inc. (95,96) and the FINA T2BX process (97) also use a fixed-bed catalyst in the vapor phase for transalkylation of toluene to produce xylenes and benzene. The Mobil low temperature disproportionation (LTD) process employs a zeoHte catalyst for transalkylation of toluene in the Hquid phase at 260—315°C in the absence of hydrogen (98). 

The catalytic performances obtained during transalkylation of toluene and 1,2,4-trimethylbenzene at 50 50 wt/wt composition over a single catalyst Pt/Z12 and a dualbed catalyst Pt/Z 121 HB are shown in Table 1. As expected, the presence of Pt tends to catalyze hydrogenation of coke precursors and aromatic species to yield undesirable naphthenes (N6 and N7) side products, such as cyclohexane (CH), methylcyclopentane (MCP), methylcyclohexane (MCH), and dimethylcyclopentane (DMCP), which deteriorates the benzene product purity. The product purity of benzene separated in typical benzene distillation towers, commonly termed as simulated benzene purity , can be estimated from the compositions of reactor effluent, such that [3] ... 

There are two methods of manufacture of the xylenes. The major one is from petroleum by catalytic reforming with a platinum-alumina catalyst. The second method (which has been developed recently) is by processes involving the disproportionation of toluene or the transalkylation of toluene... 

Benzene is also produced by the transalkylation of toluene in which two molecules of toluene are converted into one molecule of benzene and one molecule of mixed xylene isomers. 

C6H5CH3 + C6H6 + C6H4(CH3)2 or by the transalkylation of toluene with trimethylbenzenes. 

The feed to an aromatics complex is normally a C6+ aromatic naphtha from a catalytic reformer. The feed is split into Cg+ for xylene recovery and C7 for solvent extraction. The extraction unit recovers pure benzene as a product and C7+ aromatics for recycling. A by-product of extraction is a non-aromatic C6+ raffinate stream. The complex contains a catalytic process for disproportionation and transalkylation of toluene and C9+ aromatics, and a catalytic process for isomerization of C8 aromatics. Zeolitic catalysts are used in these processes, and catalyst selectivity is a major performance factor for minimizing ring loss and formation of light and heavy ends. The choice of isomerization catalyst is dependent on whether it is desired to isomerize ethylbenzene plus xylenes to equilibrium or to dealkylate ethylbenzene to benzene while isomerizing the xylenes. Para-selectivity may also be a desired... 

Wu and Leu, ° and Bursian et have carried out disproportionation and transalkylation of toluene with pseudocumene, using various modifications of mordenite zeolite catalysts. The disproportionation... 

Derivation (1) Hydrodealkylation of toluene or pyrolysis of gasoline (2) transalkylation of toluene by disproportionation reaction (3) catalytic reforming of petroleum (4) fractional distillation of coal tar. 

Earlier hydrodealkylation of toluene into benzene, disproportionation of toluene into benzene and xylenes and transalkylation of toluene and C9 aromatics into xylenes were developed and commercialized to strike a right balance in desired aromatic... 

Application The S-TDT process can produce mixed xylenes and benzene in an aromatics complex through disproportionation of toluene and transalkylation of toluene and Cg+ aromatics (Cg+ A) using toluene and Cg+ A as feedstocks. 

China Petrochemical Technology Co., Ltd. Xylenes and benzene Toluene and Cg+A S-TDT process produces mixed xylenes and benzene in a aromatics complex through the disproportionation of toluene and transalkylation of toluene and C,+ aromatics (C, A) 6 NA... 

The transalkylation of toluene with trimethylbenzenes (TMB) takes place on solid acid catalysts and it is part of a complex network of reversible reactions. The transalkylation reaction is mainly in equilibrium with the disproportionation reaction and the isomerization of polymethylbenzenes also takes place [2,3]. The distribution of the several isomers is governed by kinetics factors like the reactivity of the... 

The transalkylation of toluene with trimethylbenzenes (TMB) is one of the most important reactions of conversion of methylaromatics aiming at the xylene production. However, with the recent market reduction of benzene as a consequence of environmental restrictions, benzene transalkylation with C9 aromatics emerges as a potentially important reaction for commercial applications and its investigation has attracted increasing attention. 

Shape Selectivity. Analogous to the example in Figure 10.4, one possible route to synthesizing xylenes is the transalkylation of toluene over ZSM-5, that is. 

The acid ZSM-5 zeolite can be modified to selectively convert toluene into benzene and paraxylene. which is the least bulky of the xylenes. This modification requires the following 1) reducing access to the channels by the two other xylenes through a suitable chemical or coking treatment 2) passivating the external surface of the zeolite and 3) limiting conversion to around 30%. When xylenes are produced by transalkylation of toluene and C9+ polymethylbenzenes, the ZSM-5 zeolite is unsuitable. 

Despite the results illustrated in Example 2.1. benzene has been produced for the last 50 years and is a viable starting material for a host of petrochemical products. Therefore, how is this possible We must conclude that benzene can be produced via at least one other route, which is less sensitive to changes in the price of toluene, benzene, and natural gas. One such commercial process is the disproportionation or transalkylation of toluene to produce benzene and a mixture of para-, ortho-, and meta-xylene by the following reaction. 

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