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Methanol toluene alkylation reaction

Since their development in 1974 ZSM-5 zeolites have had considerable commercial success. ZSM-5 has a 10-membered ring-pore aperture of 0.55 nm (hence the 5 in ZSM-5), which is an ideal dimension for carrying out selective transformations on small aromatic substrates. Being the feedstock for PET, / -xylene is the most useful of the xylene isomers. The Bronsted acid form of ZSM-5, H-ZSM-5, is used to produce p-xylene selectively through toluene alkylation with methanol, xylene isomerization and toluene disproportionation (Figure 4.4). This is an example of a product selective reaction in which the reactant (toluene) is small enough to enter the pore but some of the initial products formed (o and w-xylene) are too large to diffuse rapidly out of the pore. /7-Xylene can, however. [Pg.95]

A comparative study with various types of zeolite showed that Cs-exchanged X and Y zeolites were active for toluene alkylation but primarily catalyzed the decomposition of methanol to CO.431 L and Beta zeolites, in turn, were less active and required higher reaction temperature but were much more selective, providing only very little CO. Adding boron to Cs-exchanged zeolites promotes the alkylation reaction 432 It appears that boron reduces the decomposition of methanol to CO without inhibiting active sites for side-chain alkylation. [Pg.267]

Recently, we investigated the associative alkylation reaction of toluene with methanol catalyzed by an acidic Mordenite (see Figures 13 and 14) by means of periodic ab initio calculations." We observed that for this reaction some transition selectivity occurred, and induced sufficiently large differences in activation energies to explain the small changes in the para/meta/ortho distribution experimentally observed on large pore zeolites. Thepara isomer is the more valuable product as it is an important intermediate for terphthalic acid, an important polymer monomer." The steric constraints obtained for the transition state structures could be estimated from local intermediates for which the orientations of the toluene molecule were similar as the ones observed for the transition states (see Figure 14). [Pg.16]

Figure 13. Geometries of the associative mechanism transition states of the alkylation reaction of toluene with methanol catalyzed by H-MOR as obtained from the DFT periodic structure calculations that lead to the formation of the different xylene isomers and water. ... Figure 13. Geometries of the associative mechanism transition states of the alkylation reaction of toluene with methanol catalyzed by H-MOR as obtained from the DFT periodic structure calculations that lead to the formation of the different xylene isomers and water. ...
These data support the experimental study of Ivanova et al. or the theoretical cluster approach study of Blaszkowski et al. ". It is known that the alkylation of toluene with methanol can proceed via two reaction routes. The first one involves an associative protonation of methanol, which induces the methyl jump to toluene (see Figures 13 and 14), whereas the second one is a consecutive reaction pathway, which initiates with the formation of a methoxy species and a water molecule. The second step in the consecutive reaction is an alkylation reaction between toluene and the methoxy species. However,... [Pg.20]

These effects have been used to explain the case of toluene alkylation by methanol in large zeolites, but other reactions are also being studied, and the results obtained so far are in agreement with the theoretical development. [Pg.745]

When refering to shape selectivity properties related to diffusivity, it seems obvious that the larger the zeolite grain, the higher will be the volume/sur f ace ratios and the shape selectivity, since the reaction will be more diffusion controlled. The external surface area represents different percents of the total zeolite area depending on the size of the grains which could be important if the active sites at the external surface also play a role in the selectivity. For instance in the case of toluene alkylation by methanol, the external surface acid sites will favor the thermodynamical equilibrium due to isomerization reactions (o m p-xylene - 25 50 25 at 400 C) while diffusivity resistance will favor the less bulky isomer namely the para-xylene. It may therefore be useful to neutralize the external surface acidity either by some bulky basic molecules or by terminating the synthesis with some Al free layers of siliceous zeolite. [Pg.267]

The only aromatic components that appeared at reaction temperatures below 300 °C were toluene and p-xylene. In the case of the small-crystalline H-ZSM-5(M), however, some m- and o-xylene were present in the product mixture even at 245 °C (WHSV = 6 h- ). This can be explained by xylene isomerization at the outer zeolite surface. At conditions where the para-selectivity was high (more than 90% para), the amount of p-ethyl-toluene (PET) in the product were one order of magnitude greater than that of any other Cg-component, but when it was low, the ratio 1,2,4-trimethyl-benzene (124TMB) PET was found to be about 10 1. These experimental facts indicate that 124TMB is mainly formed by secondary xylene alkylation with methanol. Toluene, p-xylene, PET and perhaps ethyl-benzene are more likely to be the primary aromatic products formed in the MTG-reaction. To confirm this suggestion the molar product ratios EB/PX,... [Pg.198]

Acidity of the materials has been determined by ir and thermodesorption of ammonia and their catalytic properties for toluene alkylation with methanol have been studied. Relations between acidic strength, diffusion rate, catalytic shape selectivity and structural features are discussed. It is suggested that the microporous framework has to be considered as a "living material" under catalytic reaction conditions. [Pg.66]

The production of para-xylene is of interest to the petrochemical industry because of its use as monomer in polyester production. In addition to Cg aromatic isomerization, there are a number of important routes to para-xylene including the alkylation of toluene with methanol and the disproportionation of toluene. The catalytic properties of the SAPO molecular sieves for toluene methylation reactions have been described(11). While both large and medium pore SAPO s were active for the alkylation reaction, the medium pore materials were distinguished by remarkably high selectivity for methylation reactions, with disproportionation of the toluene feed representing less than 2% of the total conversion. By comparison, large pore SAPO-5 had nearly 60% disproportionation selectivity and the zeolite reference LZ-105 had nearly 80% disproportionation selectivity. The very low disproportionation activity of the medium pore SAPO s, attributed to their mild acid character, resulted in reduced losses of toluene to benzene and increased xylene yields relative to LZ-105 and SAPO-5. [Pg.521]

Figure 3. Catalytic activity of uncoated H-ZSM-5 for the alkylation of toluene with methanol circles, toluene conversion squares, para-selectivity. Toluene/methanol = 1.0. Reaction temperature = 673 K. W/F = 0.06 kg-catalyst h mol ... Figure 3. Catalytic activity of uncoated H-ZSM-5 for the alkylation of toluene with methanol circles, toluene conversion squares, para-selectivity. Toluene/methanol = 1.0. Reaction temperature = 673 K. W/F = 0.06 kg-catalyst h mol ...
Figure 4.16. Mechanism of the alkylation reaction of toluene by methanol catalyzed by an acidic zeolite. Figure 4.16. Mechanism of the alkylation reaction of toluene by methanol catalyzed by an acidic zeolite.
Figure 4.17. Zeolite transition-state selectivity. Toluene alkylation with methanol catalyzed by H-MOR showing the energies of the key reaction intermediates . Reaction energy diagram for ortho-, meta- and para-xylene are compared. Figure 4.17. Zeolite transition-state selectivity. Toluene alkylation with methanol catalyzed by H-MOR showing the energies of the key reaction intermediates . Reaction energy diagram for ortho-, meta- and para-xylene are compared.
Initiahy, the enantioselective reduction and alkylation reaction of trans-cirmamaldehyde (196, R =R =H) was investigated, with ethyl Hantzsch ester 187 and bis(4-dimeth-ylamino-phenyl)-methanol (195, Ar=4-dimethylamino-phenyl) in the presence of different catalysts using toluene as a solvent. It was notable that the combination of catalysts 197 and 198 gave the formation of desired product (199, Ar=4-dimethylamino-phenyl) with the best result of 95% yield and 87% ee (Schane 2.65). [Pg.56]

Vos, A. M., Rozanska, X., Schoonheydt, R. A., van Santen, R. A., Hutschka, F., Hafner, J. (2001). A theoretical study of the alkylation reaction of toluene with methanol catalyzed by acidic mor-denite. Journal of the American Chemical Society, 123, 2799. [Pg.610]

Toluene alkylation with methanol using Friedel-Crafts catalysts results in mixed products since isomerization reactions and fiirther methylation of the desired products readily occur under these reaction conditions [49,50]. Recent work has therefore been aimed at the development of processes with high selectivity, and zeolite catalysts appear to have the most promise in this regard. [Pg.190]

Iron porphyrins containing vinyl ligands have also been prepared by hydromet-allation of alkynes with Fe(TPP)CI and NaBH4 in toluene/methanol. Reactions with hex-2-yne and hex-3-yne are shown in Scheme 4. with the former giving two isomers. Insertion of an alkyne into an Fe(III) hydride intermediate, Fe(TPP)H, formed from Fe(TPP)Cl with NaBH4, has been proposed for these reactions. " In superficially similar chemistry, Fe(TPP)CI (present in 10 mol%) catalyzes the reduction of alkenes and alkynes with 200 mol% NaBH4 in anaerobic benzene/ethanol. For example, styrene is reduced to 2,3-diphenylbutane and ethylbenzene. Addition of a radical trap decreases the yield of the coupled product, 2,3-diphenylbutane. Both Fe(lll) and Fe(II) alkyls, Fe(TPP)CH(Me)Ph and [Fe(TPP)CH(Me)Ph] , were propo.sed as intermediates, but were not observed directly. ... [Pg.247]

Among the wide variety of organic reactions in which zeolites have been employed as catalysts, may be emphasized the transformations of aromatic hydrocarbons of importance in petrochemistry, and in the synthesis of intermediates for pharmaceutical or fragrance products.5 In particular, Friede 1-Crafts acylation and alkylation over zeolites have been widely used for the synthesis of fine chemicals.6 Insights into the mechanism of aromatic acylation over zeolites have been disclosed.7 The production of ethylbenzene from benzene and ethylene, catalyzed by HZSM-5 zeolite and developed by the Mobil-Badger Company, was the first commercialized industrial process for aromatic alkylation over zeolites.8 Other typical examples of zeolite-mediated Friedel-Crafts reactions are the regioselective formation of p-xylene by alkylation of toluene with methanol over HZSM-5,9 or the regioselective p-acylation of toluene with acetic anhydride over HBEA zeolites.10 In both transformations, the p-isomers are obtained in nearly quantitative yield. [Pg.32]

It has been found that the disproportionation of toluene over ZSM-5 catalyst can be directed such that p-xylene is the predominant xylene isomer (14-17). This reaction, designated STOP, is one of several in which disubstituted aromatics rich in the para isomer are produced. Others are the alkylation of toluene with methanol to produce p-xylene (15,18) and with ethylene to produce p-ethyltoluene (19,20), as well as the aromatization of olefins (20), paraffins (20) and of methanol... [Pg.283]

No commercial process is offered at this time for side chain alkylation of toluene with methanol for styrene and ethylbenzene production. In the literature the reaction is typically carried out at toluene to methanol molar ratios from 1.0 7.5 to 5 1 from 350 to 450 °C at atmospheric pressures. In some cases inert gas is introduced to assist vaporizing the liquid feed. In other cases H2 is co-fed to improve activity, selectivity and stability. Exelus recently claimed 80% yields in their ExSyM process at full methanol conversion using a 9 4 toluene methanol feed ratio at 400-425 °C and latm (101 kPa) in a bench-scale operation. This performance appears to be... [Pg.515]


See other pages where Methanol toluene alkylation reaction is mentioned: [Pg.267]    [Pg.515]    [Pg.226]    [Pg.17]    [Pg.337]    [Pg.533]    [Pg.742]    [Pg.742]    [Pg.210]    [Pg.637]    [Pg.216]    [Pg.1621]    [Pg.543]    [Pg.593]    [Pg.1036]    [Pg.193]    [Pg.48]    [Pg.365]    [Pg.84]    [Pg.263]    [Pg.228]    [Pg.515]    [Pg.516]    [Pg.91]    [Pg.261]    [Pg.55]    [Pg.104]    [Pg.276]   
See also in sourсe #XX -- [ Pg.228 ]




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