Toluene xylene from

MTPX [Mobil toluene to /7-xylene] A catalytic process for making / -xylene from toluene, developed by Mobil Corporation in 1995. First installed at Mobil s plant in Fairfax, VA. 

Toluene disproportionation is a catalytic process in which 2 moles of toluene are converted to 1 mole of xylene and 1 mole of benzene. Although the mixed xylenes from toluene disproportionation are generally more costly to produce than those from catalytic reformate or pyrolysis gasoline,... 

A further improvement of the approach of Wei [107] was reported in 1989 by Hashimoto et al. [42], which considered not only adsorption effects, but also the nonselective reactions occurring at the outer surface of the crystallites. The nonselective influence of these reactions has also been recognized by Fraenkel [35] in 1990, who studied the formation of xylene from toluene on a HZSM-5 catalyst. Fraenkel assumed that inside the crystallite only />-xylene is formed, whereas the ortho and meta isomers are sterically inhibited there. Hence, he concluded that the amount of o- and m-xylene observed during his experiments must be due to the isomerization of p-xylene at the outer surface of the crystallites. This two-step mechanism was first suggested in 1987 by Paparetto et al. [82] for the ethylation of toluene. It may also be worth noting that Fraenkel s model took into account not only the isomerization but also the nonselective alkylation at the outer crystallite surface. 

HDA1—hydrodealkylation of toluene to produce benzene CYHEX1—cyclohexane production by hydrogenation of benzene STYR1—styrene production from ethylbenzene XYL1—production of m-xylene from toluene... 

Application The technology produces benzene and xylenes from toluene and C9 streams. This technology features a proprietary zeolite catalyst and can accommodate varying ratios of feedstock, while maintaining high activity and selectivity. 

The Tatoray process unit is capable of processing feedstocks ranging from 100 wt% toluene to 100 wt% Ag+. The optimal concentration of Ag+ in the feed is typically 40-60 wt%. The Tatoray process provides an ideal way to produce additional mixed xylenes from toluene and heavy aromatics. 

GT-TolAlk A process for making p-xylene from toluene and methanol, using a high-silica zeolite catalyst. Operated in a fixed bed at 400 to 450°C in the presence of hydrogen and water in a specific molar ratio. Developed by Indian Petrochemical and licensed to GTC Technology. 

P10-19j With the increasing demand for xylene in the petrochemical industry, the production of xylene from toluene disproportionation has gained attention in recent years [Ind. Eng. Chem. Res., 26, 1854(1987)]. This reaction. 

Based on fundamental studies that revealed the important variables in controlling the selectivity, we have been able to modify the ZSM-5 catalyst to produce para-xylene from toluene with much greater selectivity. Actually, what we ve done is partially plug the pore openings in ZSM-5 to make it more difficult for the bulkier meta-xylene and ortho-xylene molecules to come out. 

One of the most important industrial alkylations is the production of 1,4-xylene from toluene and methanol (Reaction 2). ZSM-5, in the proton exchanged form, is used as the catalyst because of its enhanced selectivity for para substituted products. para-Xylene is used in the manufacture of terephtha-lic acid, the starting material for the production of polyester fibres such as Terylene. The selectivity of the reaction over HZSM-5 occurs because of the difference in the rates of diffusion of the different isomers through the channels. This is confirmed by the observation that selectivity increases with increasing temperature, indicating the increasing importance of diffusion limitation. The diffusion rate of para-xylene is approximately 1000 times faster than that of the meta and ortho isomers.14... 

Benzene and Xylenes from Toluene Toray proeess... 

Evidence which was consistent with the postulate of methylene-insertion reactions in the formation of hexanes from pentane and xylene from toluene (both in the liquid phase) has already been mentioned. The formation of the three labeled hexanes from pentane in strict ratio relative to the number of available hydrogen positions on pentane strongly suggested that hot methylene was involved. The butanes product from propane by recoiling C (MacKs,y el cd., 1961) were also found in a ratio corresponding to what might he expected from the reaction of the species in the gas phase. 

Product selectivity. When one reaction has several outcomes, such as the production of xylenes from toluene and methanol, only the smaller molecules can diffuse out of the zeolite, again reducing the percentage of the larger product that is formed as they are hindered by the pore openings. 

In 1980, the last year for which a breakdown has been pubUshed, the amount of benzene derived from coal in the United States was 168,000 t or 2.5% of domestic benzene production. Coal-derived toluene was 0.8% of production, and xylenes from coal were only 0.1% of total chemical production (9). The amounts and proportions of BTX components derived from coal in the United States are expected to be nearly the same today as in 1980. Based on information submitted to the International Trade Commission, approximately 25 companies participated in the coal-tar industry in the United States in 1990. 

Benzene, toluene, and a mixed xylene stream are subsequently recovered by extractive distillation using a solvent. Recovery ofA-xylene from a mixed xylene stream requires a further process step of either crystallization and filtration or adsorption on molecular sieves. o-Xylene can be recovered from the raffinate by fractionation. In A" xylene production it is common to isomerize the / -xylene in order to maximize the production of A xylene and o-xylene. Additional benzene is commonly produced by the hydrodealkylation of toluene to benzene to balance supply and demand. Less common is the hydrodealkylation of xylenes to produce benzene and the disproportionation of toluene to produce xylenes and benzene. 

Aromatic Hydrocarbons. Sulfolane is used principally as a solvent for extraction of benzene, toluene, and xylene from mixtures containing aHphatic hydrocarbons (33—37). The sulfolane process was introduced in 1959 by SheU Development Company, and that process is Hcensed by Universal OH Products. A sulfolane extraction process is also Hcensed by the Atlantic Richfield Company. In 1994, worldwide consumption was estimated at ca 6974 t/yr of sulfolane for 137 sulfolane extraction units (see Bix processes Extraction, liquid-liquid Xylenes and ethylbenzene). 

Rapid, simple, quaUtative methods suitable for determining the presence of benzene in the workplace or surroundings have been utilized since the 1930s. Many early tests offered methods for detection of aromatics but were not specific for benzene. A straightforward test allowing selective detection of benzene involves nitration of a sample to y -dinitrobenzene and reaction of the resultant ether extract with an ethanoHc solution of sodium hydroxide and methyl ethyl ketone (2-butanone), followed by the addition of acetic acid to eliminate interferences from toluene and xylenes. Benzene imparts a persistent red color to the solution (87). The method is claimed to be sensitive to concentrations as low as 0.27 ppm benzene from 10 mL air samples. 

Has been purified by co-distillation with ethylene glycol (boils at 197.5°), from which it can be recovered by additn of water, followed by crysm from 95% EtOH, benzene, toluene, a mixture of benzene/xylene (4 1), or EtjO. It has also been chromatographed on alumina with pet ether in a dark room (to avoid photo-oxidation of adsorbed anthracene to anthraquinone). Other purification methods include sublimation in a N2 atmosphere (in some cases after refluxing with sodium), and recrystd from toluene [Gorman et al. J Am Chem Soc 107 4404 1985]. 

First, the kinetics of the reactions of 0-, m-, and p-xylene as well as of toluene were studied separately (96) at various combinations of initial partial pressures of the hydrocarbon and hydrogen. From a broader set of 23 rate equations, using statistical methods, we selected the best equations for the initial rate and determined the values of their constants. With xylenes and toluenes, these were Eqs. (17a) and (17b). 

A further procedure will be described only for m-xylene, for which we obtained the following values of the constants fci = 173.7, fc2 = 84.2 mole hr-1 kg-1 atm-1 K — 20.6, Ko = 25.8 atm-1. The conclusions drawn from the study of consecutive hydrodemethylation were similar for all the three xylenes studied (100). The influencing of individual reactions by products and by the intermediate product was determined experimentally, by measuring their effect on the reaction of m-xylene and toluene. The adsorption coefficients, which express this effect, are listed in Table III. 

Once we know the partial rate factors, we can predict the proportions of isomers to be obtained when two or more groups are present on a ring, if we make the assumption that the effect of substituents is independent. For example, if the two methyl groups in m-xylene have the same effect as the methyl group in toluene, we can calculate the theoretical partial rate factors at each position by multiplying those from toluene, so they should be as indicated ... 

As illustrated in Figure 10.6, the high para-selectivity in the toluene disproportionation is caused by the selective removal of p-xylene from the silica-alumina particles, which leads to an apparent equilibrium shift between the xylene isomers. 

The excellent high para-selectivity can be explained by the selective escape of p-xylene from the H-ZSM-5 catalyst and inhibition of isomerization on the external surface of catalysts by silicalite-1 coating. In addition to the high para-selectivity, toluene conversion was still high even after the silicalite-1 coating because the silicalite-1 layers on H-ZSM-5 crystals were very thin. 

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