Benzenes 1.4- diethylbenzene

Beilstein Handbook Reference) AI3-15336 Benzene, diethyl- BRN 1903396 Diethyl-benzene Diethylbenzenes... 

Alkylation Benzene to ethyl benzene, diethylbenzene or cumene. 

Xylene Isomerization. After separation of the preferred xylenes, ie, PX or OX, using the adsorption or crystallization processes discussed herein, the remaining raffinate stream, which tends to be rich in MX, is typically fed to a xylenes isomerization unit in order to further produce the preferred xylenes. Isomerization units are fixed-bed catalytic processes that are used to produce a close-to-equiUbrium mixture of the xylenes. To prevent the buildup of EB in the recycle loop, the catalysts are also designed to convert EB to either xylenes, benzene and lights, or benzene and diethylbenzene. 

Mobil s Low Pressure Isomerization Process (MLPI) was developed in the late 1970s (123,124). Two unique features of this process are that it is Operated at low pressures and no hydrogen is used. In this process, EB is converted to benzene and diethylbenzene via disproportionation. The patent beheved to be the basis for the MLPI process (123) discusses the use of H-ZSM-5 zeoHte with an alumina binder. The reaction conditions described are start-of-mn temperatures of 290—380°C, a pressure of 273 kPa and WHSV of 5—8.5/h. The EB conversion is about 25—40% depending on reaction conditions, with xylene losses of 2.5—4%. The PX approach to equiHbrium is about 99 ndash 101%. The first commercial unit was Hcensed in 1978. A total of four commercial plants have been built. 

A second Mobil process is the Mobil s Vapor Phase Isomerization Process (MVPI) (125,126). This process was introduced in 1973. Based on information in the patent Hterature (125), the catalyst used in this process is beHeved to be composed of NiHZSM-5 with an alumina binder. The primary mechanism of EB conversion is the disproportionation of two molecules of EB to one molecule of benzene and one molecule of diethylbenzene. EB conversion is about 25—40%, with xylene losses of 2.5—4%. PX is produced at concentration levels of 102—104% of equiHbrium. Temperatures are in the range of 315—370°C, pressure is generally 1480 kPa, the H2/hydrocatbon molar ratio is about 6 1, and WHSV is dependent on temperature, but is in the range of 2—50, although normally it is 5—10. 

Many different catalysts are available for this reaction. AlCls-EiCl is commonly used. Ethyl chloride may be substituted for EiCI in a mole-for-mole basis. Typical reaction conditions for the liquid-phase AICI3 catalyzed process are 40-100°C and 2-8 atmospheres. Diethylbenzene and higher alkylated benzenes also form. They are recycled and dealky-lated to EB. 

Benzene, toluene, ethylbenzene, p-xylene, m-xylene, o-xylcne. butylbenzene, styrene, o-, m-, and p-diethylbenzenes... 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

El 25 0 1 49 9 Telrakisisilldiethylbenzene (II) Tris(sil)diethylben/ene (II) Bi.s(sil)diethylbenzene (2) Hcxakis(sil)ben7.eiie llraee) Penlakisisil(benzene (81 Tetrakis(sil)benzcne (7) Tris(sil)benzene (5) Bis(sil)benzene (trace)... 

Polyethylbenzenes (diethylbenzene, triethylbenzene, etc.) are also formed as unwanted by products through reversible reactions in series with respect to ethyl benzene but parallel with respect to ethylene. For example ... 

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 Friedel-Crafts reaction has one major drawback. It doesn t stop at the mono-substitution stage. That is, the catalyst works so well, that the benzene will pick up two, three, or more ethylene molecules, forming diethylbenzene, triethylbenzene, or higher polyethylbenzenes. See Figure 8 2.) The problem is that chemically its easier to alkylate EB than it is benzene. One way to control the problem is to carry out the reaction in the presence of a large excess of benzene. When an ethylene molecule is in the neighborhood of one..EB molecule and 20 benzene molecules, chances are that the ethylene will hook up with benzene, even though it prefers EB. 

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. 

As was pointed out by Bell and Norem (2) and Crafts and Reiber (4), toxicity increases with the addition of side chains on the benzene nucleus. This increase in toxicity, however, may be due to changes in physical properties—e.g., decreased volatility— rather than direct chemical effect. The data in Figure 1 suggests a tempering effect from side chains on the benzene ring. For example, isopropylbenzene, diethylbenzene, and triethylbenzene appear to be less toxic than aromatics which have similar boiling points but shorter or no side chains. 

Because ethylbenzene is used almost exclusively to produce styrene, the product specification on ethylbenzene is set to provide a satisfactory feedstock for styrene production. Levels of cumene, -propylbenzene, ethyltoluenes and xylenes in ethylbenzene are controlled to meet the required styrene purity specification. A typical sales specification is as follows purity, 99.5 wt% min. benzene, 0.1-0.3 wt% toluene, 0.1-0.3wt% ort/io-xylene + cumene, 0.02 wt% max. meto-xylene + para-xylene, 0.2 wt% max. allylbenzene + a-propylbenzene + ethyltoluene, 0.2 wt% max. diethylbenzene, 20 mg/kg max. total chlorides (as chlorine), 1-3 mg/kg max. and total organic sulfur, 4 mg/kg max. (Coty et al., 1987). 

Ethylbenzene is almost exclusively (> 99%) used as an intermediate for the manufacture of styrene monomer. Styrene production, which uses ethylbenzene as a starting material, consumes approximately 50% of the world s benzene production. Less than 1% of the ethylbenzene produced is used as a paint solvent or as an intermediate for the production of diethylbenzene and acetophenone. The ethy lbenzene present in recovered mixed xylenes is largely converted to xylenes or benzene (Coty et al., 1987 Caimella, 1998). 

H2C CH.CcH4.CH CH,2 mw 130.18 exists as o-,m- and p-isomers. The commercial form contains the 3 isomers together with ethylvinylbenzene and diethylbenzene bivinyi-m-benzene, wh liq, easily polymerized sp gr 0.9289 at 20° fr p minus 66.9°, bp 199.5°. It can be prepd (with other products) by heating 1,3 dtethylbenzene or 3 ethyl-l-vinylbenzene superheated steam passed over a bed of activated charcoal at 700°... 

Benzene 22 Toluene 90 Ethylbenzene 115 m-Xylene% 120 Methylethylbenzene 138 Cumene (Isopropylbenzene) 137 Pseudocumene 152 tert-Butylbenzene 153 sec-Butylbenzene 156 Diethylbenzene 160 Cymene ( -Isopropyltoluene) 161 Methyldiethylbenzene 172 Ethylisopropylbenzene 177 Disopropylbenzene 191 sec-Amylbenzene 178 Triethylbenzene 188 Methyldiisopropylbenzene 203 Pi-sec-butylbenzene 222 Di-sec-amylbenzene 234 Hexaethylbenzene 235... 

Ethylbenzene disproportionates under the influence of excess HF-BF3 to benzene and 1,3-diethylbenzene ... 

The high acidity of the Nafion-H catalyst is further demonstrated by its ability to promote both polyalkylation and isomerization. In reaction between benzene and ethylene at 190°C, 20% of the alkylated products are diethylbenzenes.187 The isomer distribution of the diethylbenzenes is 1 % of the ortho, 75% of the meta, and 24% of the para isomers. This composition is very close to the equilibrium composition of diethylbenzenes determined in solution chemistry with AICI3 catalyst and indicates that the reaction is thermodynamically controlled. 

The predominance of meta-diethyl benzene in the isomerization of diethylbenzenes is easily rationalized. Since isomerization reaction proceeds via arenium ion intermediates, the cr-complex derived from mefa-diethylbenzene is the most stable one. Moreover, mefa-diethylbenzene is also the most basic of the isomeric diethylben-zenes. Therefore, more acidic catalysts increase the amount of the meta isomer at the expense of the para (and ortho) isomers, due to the increased stability of the substrate-catalyst complex. 

Nafion-H appears to be a very useful catalyst for transalkylation reaction as indicated in these studies. Transalkylation of benzene with diethylbenzenes, as well as with diisopropylbenzene, is efficiently catalyzed by Nafion-H in a flow system. The efficiency of the catalyst is, however, more limited when the transferring group is a methyl group.268 Beltrame and co-workers have also carried out269 detailed mechanistic studies on the isomerization of xylenes over Nafion-H. 

Table 5.22. Transethylation of Benzene with Diethylbenzene over Graphite-Intercalated Metal Halides.112...

Recently, the results of the isomerization and transalkylation of isomeric diethylbenzenes with benzene in the presence of triflic acid have been reported. The aim is to find the best condition for the preparation of ethylbenzene.283 285ort/ta-Diethylbenzene and benzene reacting in 1 1 molar ratio at 35°C gave ethylbenzene in 49% yield in 6h 285 An even higher yield was obtained with /mra-diethylbenzene (51% at 22°C), whereas meta-diethylbenzene produced ethylbenzene only in 29% yield.283 Both decreasing temperature and decreasing diethylbenzene/benzene ratio resulted in decreasing yields. 

Analytical Properties Does not separate diethylbenzene (DEB) isomers good separation of disubstituted benzene isomers Reference 13... 

In the case where there are two reactants, one of which is involved in an undesirable series reaction (A + B — C and C + B —> D), the concentration of B in the reactor can be kept small to improve selectivity. An important industrial example of this type of series reactions is in the production of ethylbenzene. The desired reaction is the formation of ethylbenzene from ethylene and benzene. The undesirable reaction is the formation of diethylbenzene from ethylene and ethylbenzene. To suppress this second series reaction, the concentration of ethylene is kept low and an excess of benzene is employed, which must be recovered and recycled. 

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