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Xylene transalkylation

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 ... [Pg.415]

There are several commercial processes that produce xylenes via disproportionation or transalkylation. These include UOP s Tatoray and PX-Plus,... [Pg.415]

Table 5. Xylenes Plus Transalkylation of Toluene and Aromatics Compounds, Relative Wt Units... Table 5. Xylenes Plus Transalkylation of Toluene and Aromatics 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). [Pg.52]

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... [Pg.52]

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). [Pg.53]

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... [Pg.42]

Another example of catalytic isomerization is the Mobil Vapor-Phase Isomerization process, in which -xylene is separated from an equiHbrium mixture of Cg aromatics obtained by isomerization of mixed xylenes and ethylbenzene. To keep xylene losses low, this process uses a ZSM-5-supported noble metal catalyst over which the rate of transalkylation of ethylbenzene is two orders of magnitude larger than that of xylene disproportionation (12). [Pg.201]

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 ... [Pg.285]

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. [Pg.265]

Transplus A transalkylation process for making mixed xylenes from heavy aromatics and toluene. Developed by Mobil Technology and Chinese Petroleum Corporation. [Pg.274]

The correlation between selectivity and intracrystalline free space can be readily accounted for in terms of the mechanisms of the reactions involved. The acid-catalyzed xylene isomerization occurs via 1,2-methyl shifts in protonated xylenes (Figure 3). A mechanism via two transalkylation steps as proposed for synthetic faujasite (8) can be ruled out in view of the strictly consecutive nature of the isomerization sequence o m p and the low activity for disproportionation. Disproportionation involves a large diphenylmethane-type intermediate (Figure 4). It is suggested that this intermediate can form readily in the large intracrystalline cavity (diameter. 1.3 nm) of faujasite, but is sterically inhibited in the smaller pores of mordenite and ZSM-4 (d -0.8 nm) and especially of ZSM-5 (d -0.6 nm). Thus, transition state selectivity rather than shape selective diffusion are responsible for the high xylene isomerization selectivity of ZSM-5. [Pg.276]

Production of p-xylene via p-xylene removal, i.e., by crystallization or adsorption, and re-equilibration of the para-depleted stream requires recycle operation. Ethylbenzene in the feed must therefore be converted to lower or higher boiling products during the xylene isomerization step, otherwise it would build up in the recycle stream. With dual-functional catalysts, ethylbenzene is converted partly to xylenes and is partly hydrocracked. With mono-functional acid ZSM-5, ethylbenzene is converted at low temperature via transalkylation, and at higher temperature via transalkylation and dealkylation. In both cases, benzene of nitration grade purity is produced as a valuable by-product. [Pg.278]

Figure 5. Transalkylation reactions in the ethylbenzene-xylene system. Figure 5. Transalkylation reactions in the ethylbenzene-xylene system.
This may be partly the result of increased steric crowding in the transition state of transalkylation. Another contributory factor to the increased selectivity in ZSM-5 is the higher diffusion rate of ethylbenzene vs m-/o-xylene in ZSM-5 and hence a higher steady state concentration ratio [EB]/[xyl] in the zeolite interior than in the outside phase. Diffusional restriction for xylenes vs ethylbenzene may also be indicated by the better selectivity of synthetic mordenite vs ZSM-4, since the former had a larger crystal size. [Pg.280]

In commercial xylene isomerization, it is desirable that the necessary ethylbenzene conversion is accompanied by a minimum conversion (transalkylation) of xylenes, since the latter constitutes a downgrading to less valuable products. The ability of ZSM-5 to convert ethylbenzene via transalkylation in high selectivity, as shown in Table II, leads to high ultimate p-xylene yields in a commercial process. With a simulated commercial feed containing 85% m- and o-xylene and 15% ethylbenzene, we have obtained the data shown in Table III. It is seen that for a given ethylbenzene conversion, the xylene loss... [Pg.280]

Figure 6. Transalkylation of an ethylbenzene-xylene feed over HZSM-4. TMB = trimethylbenzene, DMEB = dimethylethyl-benzene, DEB = diethylbenzene, and ETol = ethyltoluene. Feed 16% EB, 62% m-xylene, 22% o-xylene. Temperature ... Figure 6. Transalkylation of an ethylbenzene-xylene feed over HZSM-4. TMB = trimethylbenzene, DMEB = dimethylethyl-benzene, DEB = diethylbenzene, and ETol = ethyltoluene. Feed 16% EB, 62% m-xylene, 22% o-xylene. Temperature ...
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... [Pg.282]

We have shown that the high selectivity of ZSM-5 in xylene isomerization relative to larger pore acid catalysts is a result of its pore size. It is large enough to admit the three xylenes and to allow their interconversion to an equilibrium mixture it also catalyzes the transalkylation and dealkylation of ethylbenzene (EB), a necessary requirement for commercial feed but it selectively retards transalkylation of xylenes, an undesired side reaction. [Pg.299]

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.)... [Pg.35]

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%. [Pg.51]

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. [Pg.369]

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. [Pg.493]

All, S.A., Al-Nawad, K., Okomoto, T., and Ishikawa, K. (2005) Transalkylation of heavy aromatics for enhanced xylene production. Proceedings of 15th Saudi-Japan Joint Symposium,... [Pg.502]

The reaction of o-, m-, or -xylene with four equivalents of Ic affords an isomeric mixture of peralkylated xylenes consisting of tetrakis[(dichloromethylsilyl)ethyl]-xylenes and isomeric transalkylation products. With longer reaction times and... [Pg.54]

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... [Pg.232]


See other pages where Xylene transalkylation is mentioned: [Pg.2790]    [Pg.459]    [Pg.477]    [Pg.479]    [Pg.490]    [Pg.163]    [Pg.163]    [Pg.164]    [Pg.429]    [Pg.278]    [Pg.233]    [Pg.234]    [Pg.235]    [Pg.369]    [Pg.491]    [Pg.494]    [Pg.517]    [Pg.171]    [Pg.193]   
See also in sourсe #XX -- [ Pg.51 ]




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