Transalkylation toluene

Xylenes Produetion Via Toluene Transalkylation and Disproportionation. The toluene that is produced from processes such as catalytic reforming can be converted into xylenes via transalkylation and disproportionation. Toluene disproportionation is defined as the reaction of 2 mol of toluene to produce 1 mol of xylene and 1 mol of benzene. Toluene transalkylation is defined as the reaction of toluene with or higher aromatics to produce xylenes ... 

By considering these aspeots, this work deals with the study of coke formation on H-mordenite during the benzene transalkylation with C9 aromatics, under several reaction conditions, in order to state the best condition to reduce catalyst deactivation in industrial processes. Although there are several publications and patents about the toluene transalkylation [10,13], there are very few works concerning the benzene transalkylation [1, 14]. Several industrial processes uses mordenite for toluene transalkylation with high performance [2]. 

None of these look to be dramatically unfavored, through one could argue the TS for the p-isomer is more linear, and perhaps thus easier to form in the pores of ZSM-5. In reahty this reaction is slow relative to the reaction of methanol + toluene to form xylene toluene transalkylation would not be significant. 

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

Xylenes. The main appHcation of xylene isomers, primarily p- and 0-xylenes, is in the manufacture of plasticizers and polyester fibers and resins. Demands for xylene isomers and other aromatics such as benzene have steadily been increasing over the last two decades. The major source of xylenes is the catalytic reforming of naphtha and the pyrolysis of naphtha and gas oils. A significant amount of toluene and Cg aromatics, which have lower petrochemical value, is also produced by these processes. More valuable p- or 0-xylene isomers can be manufactured from these low value aromatics in a process complex consisting of transalkylation, eg, the Tatoray process and Mobil s toluene disproportionation (M lDP) and selective toluene disproportionation (MSTDP) processes isomerization, eg, the UOP Isomar process (88) and Mobil s high temperature isomerization (MHTI), low pressure isomerization (MLPI), and vapor-phase isomerization (MVPI) processes (89) and xylene isomer separation, eg, the UOP Parex process (90). 

The Tatoray process, which was developed by Toray Industries, Inc., and is available for Hcense through UOP, can be appHed to the production of xylenes and benzene from feedstock that consists typically of toluene [108-88-3] either alone or blended with aromatics (particularly trimethylbenzenes and ethyl-toluenes). The main reactions are transalkylation (or disproportionation) of toluene to xylene and benzene or of toluene and trimethylbenzenes to xylenes in the vapor phase over a highly selective fixed-bed catalyst in a hydrogen atmosphere at 350—500°C and 1—5 MPa (10—50 atm). Ethyl groups are... 

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). 

Ethyltoluene is manufactured by aluminum chloride-cataly2ed alkylation similar to that used for ethylbenzene production. All three isomers are formed. A typical analysis of the reactor effluent is shown in Table 9. After the unconverted toluene and light by-products are removed, the mixture of ethyltoluene isomers and polyethyltoluenes is fractionated to recover the meta and para isomers (bp 161.3 and 162.0°C, respectively) as the overhead product, which typically contains 0.2% or less ortho isomer (bp 165.1°C). This isomer separation is difficult but essential because (9-ethyltoluene undergoes ring closure to form indan and indene in the subsequent dehydrogenation process. These compounds are even more difficult to remove from vinyltoluene, and their presence in the monomer results in inferior polymers. The o-ethyltoluene and polyethyltoluenes are recovered and recycled to the reactor for isomerization and transalkylation to produce more ethyltoluenes. Fina uses a zeoHte-catalyzed vapor-phase alkylation process to produce ethyltoluenes. 

Transall lation. Two molecules of toluene are converted iato one molecule of benzene and one molecule of mixed xylene isomers ia a sequence called transalkylation or disproportionation. Economic feasibiUty of the process strongly depends on the relative prices of benzene, toluene, and xylene. Operation of a transalkylation unit is practical only when there is an excess of toluene and a strong demand for benzene. In recent years, xylene and benzene prices have generally been higher than toluene prices so transalkylation is presendy an attractive alternative to hydrodealkylation (see also Btx... 

The catalytic disproportionation of toluene (Figure 10-13) in the presence of hydrogen produces henzene and a xylene mixture. Disproportionation is an equilihrium reaction with a 58% conversion per pass theoretically possible. The reverse reaction is the transalkylation of xylenes with henzene ... 

Tetralin, hydrogenation of, 12 Titanium compounds as catalysts, 188 Titanium dichloride, 192, 193 number of propagation centers, 198-200 Titanium trichloride, 193, 194 Toluene in exhaust gases, 67 Transalkylation, 141, 142 Transalkylidenation, 142 Transition metal compounds as catalysts, 174... 

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] ... 

Table 1. Product yields of transalkylation reaction of toluene and 1,2,4-trimethylbenzene (at 623 K) over Pt-supported single- and dual-bed catalysts.

Tatoray [Transalkylation aromatics Toray] A process for transalkylating toluene, and/or trimethylbenzenes, into a mixture of benzene and xylenes. Operated in the vapor phase, with hydrogen, in a fixed bed containing a zeolite catalyst. Developed jointly by Toray Industries and UOP and now licensed by UOP. First operated commercially in Japan in 1969 as of 1992, 23 units were operating and 6 more were in design and construction. 

Transplus A transalkylation process for making mixed xylenes from heavy aromatics and toluene. Developed by Mobil Technology and Chinese Petroleum Corporation. 

The xylenes are produced in an equilibrium mixture containing 24% p-, 54% m-, and 22% o-xylene (11) This is readily understandable. The transalkylation occurs via an electrophilic substitution of toluene by a benzyl cation. In the absence of steric constraints, p- and o-xylene are expected as predominant... 

In the case of toluene disproportionation, reduction to benzene occurs when a methyl group pops off (hydrodealkylation takes place) and oxidation to xylene occurs as that methyl group that popped off attaches itself to another toluene molecule (a transalkylation reaction.)... 

In the chapter on benzene and in Figure 2—7, you saw that toluene disproportionation yielded both benzene and mixed xylenes. When the catalyst-prompted methyl group removes itself from the toluene, it usually attaches itself to another toluene molecule in a way that it forms xylene. That s transalkylation. The freed methyl group might attach itself momentarily to another free benzene molecule, or it might attach itself to the methyl group of another toluene, forming ethylbenzene. However, the creation of benzene and xylenes predominates, and the combined yields of the two are 92-97%. 

Isomerization and transalkylation reactions to redistribute methyl groups on aromatic molecules are important processes in the production of benzene, toluene and xylenes (BTX). In particular, the production of para-xylene is preferred. The interconversion of C8 aromatics is covered in much greater depth in Section 14.3. 

The most common by-product losses are due to transalkylation, dealkylation, saturation and cracking. Transalkylation results in toluene, trimethylbenzenes, methylethyl benzenes, benzene and ClOAs. These are the best by-products to have, because they are the easiest to react back into C8A in a transalkylation unit (if the aromatics complex is so equipped) without any loss of carbon atoms [59-61]. Dealkylation results in benzene, toluene, methane and ethane. The benzene and toluene are aromatics and represent valuable by-products, but the C1-C6 nonaromatics represent carbons that are lost from the complex as less valuable LPG and fuel gas. 

Side Reactions One of the major side reactions that occurs during isomerization of Cg aromatics is transalkylation. This reaction produces species such as toluene, trimethylbenzene, methylethylbenzene, dimethylethylbenzene, benzene and diethylbenzene. The types and specific isomers of transalkylated products formed depend on the acidity and spatial constraints of the zeolitic catalyst used. These reactions can be controlled through modification of catalyst properties, especially pore size and external acidity, though these reactions are still among the major contributors to xylene losses. 

After the separator, the liquid product is sent to a deheptanizer to remove toluene, benzene and other lighter products. If this is an EB isomerization-style process, the deheptanizer operation may be constrained by the need to send the C8N to the bottoms, which also results in more toluene in the bottoms than would be present in an EB dealkylation system (which does not require C8N recirculation). The elevated toluene is not generally detrimental to catalyst performance, primarily acting as a diluent, although in some cases it may actually be beneficial, by pushing the toluene -i- C9A transalkylation equilibrium back toward C8A. 

Magnoux, Z.D. and Guisnet, M. (1999) Liquid phase alkylation of toluene with 1-heptene over a HFAU zeolite evidence for transalkylation between toluene and non-desorbed products. Appl Catal A, 182, 407-411. 

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