Transalkylation reaction

Other species that are also present in the feed, such as ethylbenzene and methylethylbenzenes will also undergo transalkylation reactions. These reactions tend to approach an equiUbrium that depends on the operating conditions. 

The transalkylation reaction is essentiaHyisothermal and is reversible. A high ratio of benzene to polyethylbenzene favors the transalkylation reaction to the right and retards the disproportionation reaction to the left. Although alkylation and transalkylation can be carried out in the same reactor, as has been practiced in some processes, higher ethylbenzene yield and purity are achieved with a separate alkylator and transalkylator, operating under different conditions optimized for the respective reactions. 

Mol et al. (61) analyzed the products formed in the heterogeneously catalyzed metathesis of propene labeled with 14C. With propene labeled in the 2-position there will be, in the case of a transalkylation reaction, an equal distribution of the radioactivity over the products ... 

In experiments with [2- 4C] propene in the presence of a Re207-Al2C>8 catalyst, the ethene formed showed no radioactivity, while the butene showed a specific radioactivity twice as high as that of the starting material. This result is completely consistent with a transalkylidenation scheme, and excludes a transalkylation reaction. Similar results were obtained by Clark and Cook (62) in experiments with radioactive propene on a M0O3-C0O-AI2O3 catalyst. 

A Pt/Z12 sample with ZSM-12 structure having a SiCVA Os ratio of 100 and containing ca. 200 ppm Pt was prepared following the impregnation procedures reported earlier [6], Transalkylation reaction tests were conducted in a continuous flow... 

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.

Figure 1. Effects of H-Beta ratio (y) in the dual-bed catalyst Pt/Z12(x) HB(y) on (a) benzene purity and (b) product yields during transalkylation reaction (see text) at 623 K.

Figure 5. Transalkylation reactions in the ethylbenzene-xylene system.

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.)... 

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. 

Rozanska, X., Saintigny, X., van Santen, R.A., and Hutsdika, F.A. (2001) DFT smdy of isomerization and transalkylation reactions of aromatic spedes catalyzed by addic zeolites. /. Catal, 202,141-155. 

The concentrations are reported as a fraction of the toluene extract from the transalkylation reaction. As a result of oxidation, concentrations of the most abundant bridges, namely methylene, ethylene, methyl methylene, and ethyl methylene groups are reduced by factors of 6, 14, 6, and 9, respectively. The differences in the... 

The formal gas phase transmethylation reaction, the sole transalkylation reaction available to us (equation 1), is thermoneutral to within 5 kJmol . 

In this paper, we report on the shape selective isomerization of l methylnaphthalene in suitable zeolite catalysts in which the undesired transalkylation reaction is suppressed. Furthermore, new results concerning the alkylation of 2-methylnaphthalene with methanol are presented in an endeavor to contribute to a critical evaluation of Fraenkel s model. At the same time, the potential of shape selective catalysis for the manufacture of... 

Transalkylation Reaction. The alkylation reaction of potassium ferrocyanide with alkyl bromides activated at the a-carbon by a double bond (14) gave in each case good conversions to the corresponding isonitrile complexes. Since this method is limited to alkyl halides activated at the Qj-carbon by a double bond, it was of interest to develop a general method for the preparation of aliphatic isonitrile complexes. 

The mechanism of the transalkylation reaction is complex because of the many products involved and the possibility of internal rearrangement within the complex. The first step in the reaction may be the alkylation of I to III (Equation 6) or elimination of benzyl bromide to form II or IV. Since the transalkylation of II and III with p-nitrobenzvl bromide is slower than the total transalkylation of I with the same agent, I —> IV seems to be the slow step in the reaction. 

Transalkylation reactions are observed in Y zeolites partially exchanged with ethyl-, diethyl-, and triethylammonium cations (EA, DEA, and TEA, respectively) heated above 150° C in air or under vacuum, in the presence of residual water molecules. The main reactions may be depicted schematically as follows (EA) Y — (DEA)Y > (NHt+)Y, (DEA)Y - (EA)Y > (TEA)Y, and (TEA)Y - (DEA)Y > (EA)Y, iAc main constituent in the gas phase being CJh. They are similar to those observed in montmorillonite in the presence of a water vapor pressure of a few torr. It is proposed that in both cases the transalkylation processes are acid catalyzed, the residual water molecules and the surface oxygen being the active spots recycling the protons in montmorillonite and zeolite, respectively. 

Cobalt(II) compounds also undergo transalkylation reactions with organocobalt(III) compounds, probably via a transition state in which the two cobalt centres are bridged by the alkyl group. 

The primary examples of this class of compounds are the 1,2-dialkylcycloalkenes (24 n, R1, R2). The simplest thermochemical comparison we can make is with the corresponding unsubstituted cycloalkene, i.e. R1 = R2 = H. A suitable probe of the effect of the dialkylation is the enthalpy of the formal transalkylation reaction... 

Relevant examples of 1,2-dialkylcycloalkenes with which to test our conjecture about reaction 12 are disappointingly few. The simplest example of this class of compounds is 1,2-dimethylcyclopropene (24, n = 3, R1 = R2 = Me), and indeed, the requisite thermochemical data are available. Using the derived enthalpy of formation of 1,2-dimethylcyclopropene from Reference 56, we find this reaction to be 32 kJmol-1 endothermic. A posteriori, we are not surprised that this reaction is endothermic. After all, if it is part of the folklore of cyclopropanes that they are said to have olefinic character, then cyclopropenes are also said to have acetylenic character. Indeed, the related transalkylation reaction involving acetylenes... 

Bicycio[m. .0]alkenes (25 in. n) with the double bond linking the bridgehead carbons are another class of relevant compounds. Enthalpy-of-formation data are available for the m = n = 1 case through analysis of gas-phase acidity and electron-affinity measurements76, and for m = 2, n = 2, 3 and 4 from hydrogenation data54 from reaction in a thermochemically innocuous hydrocarbon solvent. Parallelling the earlier transalkylation reactions (equation 14), perhaps the simplest comparison we can make is to use the enthalpy of the reaction of the bicyclic species with ethylene to form two mono-cyclic ones. 

Another important synthesis method is transalkylation reactions with other oxonium ions.95 However, these reactions are reversible to a certain extent. The equilibrium between two oxonium salts and the corresponding ethers in solution is established by both differences in solubility and stability of the oxonium salts (Scheme 4.4). By an exchange reaction of this type, the trimethyloxonium salt 31 can be... 

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. 

A further variation on the transalkylation reaction described above is the cocondensation of different phosphorus esters (8) as shown in the following equation ... 

Many surface acid catalyzed reactions have been described (16-17). A typical one is the transalkylation reaction of alklammonium which can be schematically described as follows (18),... 

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