Toluene methanol alkylation

Auroux observed that ammonia adsorption shifts from strong chemisorption for HZSM-5 to a process controlled by physisorption (shorter h/i) for boron-modified zeolites. The acidity found by this method correlated well with the modified catalytic reactivity shown for methanol conversion, toluene/methanol alkylation, and toluene disproportionation processes. Stradella (129) utilized the above techniques to suggest that a dissociative chemisorption of ammonia takes place on the strongest Lewis sites of reduced Bi203-MoOj whereas only relatively weak coordination occurs in that same region of reoxidized samples. 

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. ... 

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... 

When toluene is alkylated by methanol with a ZSM-5 catalyst, increase in the ciystallite size from 0.5 to 3 pm approximately doubles the amount of para-xylene produced. Suggest a possible explanation. 

Below is an example regarding the alkylation of toluene into xylene using methanol in presence of ZSM-5 (Fig. 3). Selectivity of p-xylene among xylene is plotted as a function of temperature, with various chemical modifications of the catalyst. In this example, the user has fixed the following constraints pressure = 1 atm, and toluene/methanol ratio = 2. The dialogue between the program and the user is reported hereafter. User input is given in bold. 

In hydrogenations with H2 in D20 the product showed only CHD— stretches in the infrared. This observation excludes a fast H/D exchange on Pd, and implies a monohydridic mechanism of hydrogenation. With the same catalyst in an aqueous (D20) solution, itaconic acid is reduced under H2 to yield multiply deuterated methyl succinic acid having 1.97 deuterons at C3, 0.66 at C2 and none at Cl (Eq. 32) [83]. On the other hand, in an H20/ethyl acetate biphasic solvent mixture, the catalyst prepared in situ from [Rh(cod)Cl]2 and TPPTS catalyzed the reduction (with D2) of dimethyl itaconate with deuterium incorporation at C3 (2.06), C2 (0.78) and at Cl (0.18) [84], Similar results were obtained in toluene/methanol (1 1) with the Rh(I)-BPPM cationic catalyst [85], Again, these findings could be explained by a fast /3-elimination from the intermediate Rh(I)-alkyl. 

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 ...

The gas phase alkylation of toluene with methanol was carried out in a fixed-bed tubular reactor at atmospheric pressure. Samples were sieved to retain particles with 0.35-0.40 mm in diameter for catafytic measurements. A mixture of toluene/methanol of 1 1 molar ratio was vaporized in a preheating section and delivered to the reactor. The reaction was carried out at 400 °C, employing a space velocity (WHSV) of 2 h. Toluene conversion (Xtoi) was calculated as Xtoi (%) = [EYj / (ZYj + Ytoi.)]100, where ZYj is the molar fiactions of the aromatic reaction products, including benzene, and Ytoi is the outlet molar fiaction of toluene. The selectivity to product j was determined as Sj (%) = [Y/EYj.lOO. The Sei-bz selectivity includes the sum of ethylbenzene and styrene, which are the side-chain alkylation products. In-situ poisoning experiments were carried out by doping the toluene/methanol mixture with either acetic acid or 3,5-dimethyl pyridine in a concentration range between 0-15000 ppm... 

Another instructive example of a reaction monitored in situ by transmission IR spectroscopy is the alkylation of the toluene ring by methanol reported by Lercher and coworkers [820,890,891 ]. This work was related to the investigation of adsorption and co-adsorption of toluene, methanol and ammonia on H-ZSM-5 and H, Na-ERI by the same group (vide supra and [127,652,814-821]). The authors used a continuously stirred tank reactor [892-895]. Some conclusions drawn by the authors from their results of combined IR spectroscopic and gas chromatographic experiments were reported as follows. 

Zeolite NU-87, if containing Bronsted-acid sites, is an active catalyst for a large variety of acid catalyzed reactions hke toluene disproportionation, alkylation of benzene with ethylene, amination of methanol to methylamines etc. [51]. Moreover, it was found to possess interesting shape selective properties in the conversion of m-xylene [52] and of polynuclear aromatics, e.g. methylnaphtha-lenes [53]. On non-acidic (i.e. Cs+-exchanged) zeolite NU-87, loaded with small amounts of platinum, n-alkanes like n-hexane or n-octane can be dehydrocycliz-ed in high yields to the corresponding aromatics [54]. 

Certain Mobil ZSM-5 type zeolites have pore openings with rings of 10 oxygen atoms (17). This structure permits access to reactant or product molecules with larger dimensions, such as substituted aromatic compounds, which can diffuse in and out of the catalyst. A mixture of toluene and alkylating agents, such as methanol or ethylene can easily enter the pores and react at an acidic site to produce the corresponding xylenes or ethyltoluenes In previously reported work, thermodynamic equilibrium mixtures of Isomers were produced (18). Furthermore, individual Isomers were Isomerized to the equilibrium mixture under alkylation conditions over a zeolite with similar properties (19). 

Gas-phase alkylation of toluene with alkyl chloroformate was also reported to be efficient. Due to the high reactivity of alkyl chloroformates, as compared to that of alcohols, higher yields of alkylation of toluene were obtained under the same reaction conditions. A 59% conversion of methyl chloroformate was observed in the alkylation of toluene at 573 K, as compared to about 10% conversion using methanol. 

Cata t deactivation during toluene alkylation with methanol over B-HZSM-5 catatyst Terrperature 600°C, WHSV =3.8, pressure = 0.1 MPa, and toluene-methanol molar ratio = 2 l. Toluene conversion (circles) jgiene wt% in or nic product (open squares) and / -3giene wt% of total xylenes (filW squares). 

Operation with the hi toluene-methanol ratios required to limit methanol side reactions means that product yield based on alkylbenzene feed is low and the reaction is limited by methanol Attempts to overcome this limitation have been made by use of composite methanol synthesis-HZSM-5 catalysts, and this approach has been demonstrated for /7-xylene alkylation to yield 1,2,4-trimethyIbenzene. Yashima et al [62] claimed that the efficiency of methanol usage as an alkylating agent is greater when the methanol is produced in situ on the Zn/Cr OTude catalyst than when the methanol is cofed with the /7- Q7lene. 

PMMA is not affected by most inorganic solutions, mineral oils, animal oils, low concentrations of alcohols paraffins, olefins, amines, alkyl monohahdes and ahphatic hydrocarbons and higher esters, ie, >10 carbon atoms. However, PMMA is attacked by lower esters, eg, ethyl acetate, isopropyl acetate aromatic hydrocarbons, eg, benzene, toluene, xylene phenols, eg, cresol, carboHc acid aryl hahdes, eg, chlorobenzene, bromobenzene ahphatic acids, eg, butyric acid, acetic acid alkyl polyhaHdes, eg, ethylene dichloride, methylene chloride high concentrations of alcohols, eg, methanol, ethanol 2-propanol and high concentrations of alkahes and oxidizing agents. 

The selective alkylation of toluene with methanol to produce -xylene as a predominant isomer can be achieved over shape-selective catalysts (99—101). With a modified ZSM-5 zeoHte catalyst, more than 99% -xylene in xylene isomers can be produced at 550°C. This -xylene concentration exceeds the equiHbrium concentration of 23% (99). The selective synthesis of -xylene using relatively low cost toluene is economically attractive however, this technology was not commercialized as of 1991. 

Figure 10.7 Pora-selectivity as a function in the conversion of the alkylation of methanol and toluene to xylene by bare and silicalite-coated H—ZSM5 catalyst particles.

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. 

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. 

Figure 4.28 Plot of CD intensities of poly -hexyl(j -/ -propoxyphenyl)silane (41) aggregates in toluene/series of (S)-primary chiral alkyl alcohols/methanol mixtures at 20°C. [For comparison, CD intensity with (A)-2-butanol is inserted.].

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... 

The retention indices, measured on the alkyl aryl ketone scale, of a set of column test compounds (toluene, nitrobenzene, p-cresol, 2-phenyl ethanol, and IV-methylaniline) were used to determine the changes in selectivity of a series of ternary eluents prepared from methanol/0.02M phosphate buffer pH 7 (60 40), acetonitrile/0.02 M phosphate buffer pH 7 (50 50) and tetrahydrofuran/0.02 M phosphate buffer pH 7 (25 65). The analyses were carried out on a Spherisorb ODS reversed-phase column. The selectivity changes were often nonlinear between the binary composition [83]. 

Other examples of systems that are likely to be governed by product shape selectivity effects include toluene disproportionation to para-xylene -i- benzene in favor of other xylenes r- benzene [61]. Toluene alkylation by methanol to give para-xylene in favor of other xylenes is yet another such example [76],... 

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