Petrochemical Processing disproportionation

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). 

Y. Y. Huang, M. P. Nicoletti, and R. A. Sailor, "The Mobil Selective Toluene Disproportionation Process (MSTDP)," 1990 Petrochemical evieiv DeWitt Company, Houston, Tex., Mar. Ill—70 1990. 

After the cmde BTX is formed, by reforming in this case, a heart cut is sent to extraction. Actually, the xylenes and heavier components are often sent to downstream processes without extraction. The toluene produced is converted to ben2ene, a more valuable petrochemical, by mnning it through a hydrodealkylation unit. This catalytic unit operates at 540—810°C with an excess of hydrogen. Another option is to disproportionate toluene or toluene plus aromatics to a mixture of ben2ene and xylenes using a process such as UOP s Tatoray or Mobil s Selective Toluene Disproportionation Process (STDP) (36). 

Industrial applications of zeolites cover a broad range of technological processes from oil upgrading, via petrochemical transformations up to synthesis of fine chemicals [1,2]. These processes clearly benefit from zeolite well-defined microporous structures providing a possibility of reaction control via shape selectivity [3,4] and acidity [5]. Catalytic reactions, namely transformations of aromatic hydrocarbons via alkylation, isomerization, disproportionation and transalkylation [2], are not only of industrial importance but can also be used to assess the structural features of zeolites [6] especially when combined with the investigation of their acidic properties [7]. A high diversity of zeolitic structures provides us with the opportunity to correlate the acidity, activity and selectivity of different structural types of zeolites. 

Intermediate pore zeolites typified by ZSM-5 (1) show unique shape-selectivities. This has led to the development and commercial use of several novel processes in the petroleum and petrochemical industry (2-4). This paper describes the selectivity characteristics of two different aromatics conversion processes Xylene Isomerization and Selective Toluene Disproportionation (STDP). In these two reactions, two different principles (5,j6) are responsible for their high selectivity a restricted transition state in the first, and mass transfer limitation in the second. 

Zeolites are integral components of petrochemical refineries that produce benzene, xylene isomers, ethylbenzene and cumene. These aromatics must be high in purity for downstream conversion to polyesters and styrenic or phenolic based plastics. Catalytic processes for producing aromatics employ zeolites for isomerization, disproportionation, transalkylation, alkylation, and dealkylation. 

Application The Tatoray process produces mixed xylenes and petrochemical grade benzene by disproportionation of toluene and transalk-lyation of toluene and C9+ aromatics. 

GT-STDP A process for disproportionating toluene into p-xylene and benzene, using a high-silica zeolite catalyst. Operated in the vapor phase at 390 to 400°C. Developed by Indian Petrochemical and licensed to GT Technology. 

The latest industrial application of metathesis was developed by Phillips who started up a plant in late 1985 at Cbannelview, Texas, on the L ondell Petrochemical Complex with a production capacity of 135,000 t/year of propylene from ethylene. This facility carries out the disproportionation of ethylene and 2-butenes, in the vapor phase, around 300 to 350°C, at about 0.5.10 Pa absolute, with a VHSV of 50 to 200 and a once-througb conversion of about 15 per cent 2-butenes are themselves obtained by the dimerization of ethylene in a homogeneous phase, which may be followed by a hydroisomerization step to convert the 1-butene formed (see Sections 13.3.2. A and B). IFP is also developing a liquid phase process in this area. 

Yamada, S, Ono, 1, Production of buttne-1 from ethylene BuU. cf Japan Petroleum Insu 12160 163 (1970). Izumt. JC, Now slash costs for maidsg Itoedr x-olefiss , Chem. Engng, 7f (21) 71-73 (1970)i Anderson, K. L, Brown, T. D, Olefin disproportionation. New routes to petrochemicals , Hyifrocorhofi Processing, 55 (8) 119-122 (1976). 

These catalysts provide three-dimensional microscopic media for reaction. The most important are the zeolites (see 14.2.2.2). Faujasites are used to crack petroleum for the manufacture of gasoline, and HZSM-5 to convert methanol into gasoline and in other petrochemical conversion processes including xylene isomerization and toluene disproportionation. ... 

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... 

A radical reaction or radical chain propagation (such as in alkene polymerization) is terminated by either the reaction of two radicals or by disproportionation of the radical into alkane and alkene (Scheme 2.2.6). The latter reaction plays the dominant role in petrochemical cracking processes. Alternatively, a radical reaction can be stopped by adding to the reaction mixture substances that react very easily with radicals by forming very stable radicals themselves so that the propagation reaction is terminated. Examples of such radical scavenger molecules are phenols, quinones, and diphenylamines. 

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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