Xylene catalytic oxidation

Commercial production of acetic acid has been revolutionized in the decade 1978—1988. Butane—naphtha Hquid-phase catalytic oxidation has declined precipitously as methanol [67-56-1] or methyl acetate [79-20-9] carbonylation has become the technology of choice in the world market. By-product acetic acid recovery in other hydrocarbon oxidations, eg, in xylene oxidation to terephthaUc acid and propylene conversion to acryflc acid, has also grown. Production from synthesis gas is increasing and the development of alternative raw materials is under serious consideration following widespread dislocations in the cost of raw material (see Chemurgy). 

The U.S. naphthalene consumption by markets for 1992 is Hsted in Table 9. The production of phthaHc anhydride by vapor-phase catalytic oxidation has been the main use for naphthalene. Although its use has declined in favor of o-xylene, naphthalene is expected to maintain its present share of this market, ie, ca 18%. Both petroleum naphthalene and coal-tar naphthalene can be used for phthaHc anhydride manufacture. U.S. phthaHc anhydride capacity was 465 X lOM in 1992 (38). 

Vapor-phase catalytic oxidation of dutene is a mote direct route to the dianhydtide. Hbls in Europe apparently uses this route, which eliminates the need for a separate dehydration step and for handling of any oxidants or solvents. Continuous operation is faciHtated, corrosion is minimized, and product recovery is simplified. The vapor-phase oxidation of dutene is similar to that of o-xylene to phthaHc anhydtide, and phthaHc anhydtide units can be... 

Some catalysts exposed to air stripping off-gas were subject to deactivation. However, using a catalytic oxidizer at a U.S. Coast Guard faciUty (Traverse City, Mich.) for the destmction of benzene, toluene, and xylene stripped from the groundwater, the catalytic oxidization unit operated at 260 to 315°C, and was able to achieve 90% destmction efficiency (see Groundwatermonitoring). 

The prime function of the saturated acid is to space out the double bonds and thus reduce the density of cross-linking. Phthalic anhydride is most commonly used for this purpose because it provides an inflexible link and maintains the rigidity in the cured resin. It has been used in increasing proportions during the past decade since its low price enables cheaper resins to be made. The most detrimental effect of this is to reduce the heat resistance of the laminates but this is frequently unimportant. It is usually produced by catalytic oxidation of o-xylene but sometimes naphthalene and is a crystalline solid melting at 131°C. 

In the late 1950 s two groups - one at ICI (ref. 1) and the other at the Mid-Century Corporation (ref. 2) - independently discovered that p-xylene is oxidized to terephthalic acid in almost quantitative yield when soluble bromides are used together with cobalt and manganese catalysts in acetic acid solvent at temperatures > 130 °C (ref. 3). This discovery formed the basis for what became known as the Mid-Century process and later, when the Mid-Century Corporation was acquired by Amoco, as the Amoco MC process for the commercial production of terephthalic acid. A large part of the ca. 6 million tons of the latter that are manufactured annually, on a worldwide basis, are produced via this method. This makes it the most important catalytic oxidation process (ref. 4). 

Either naphthalene or ortho-xylene is an acceptable starting material for partial oxidation to phthalic anhydride, but current raw materials costs favor the former as a starting material. Both fixed and fluidized bed processes have been used on a commercial scale, but you are to focus your attention on the former. Figure 13.5 is a schematic flow diagram of the proposed process. Most research groups that have studied the catalytic oxidation of naphthalene over vanadium pentoxide agree that the principal reactions are... 

Heyden-Wacker A process for making phthalic anhydride by the catalytic oxidation of naphthalene or o-xylene. Offered by Lurgi. 

An aromatic compound which is employed along with glycerol in the production of alkyd resins is phthalic anhydride. The conventional process for the manufacture of this chemical has been from the catalytic oxidation of coal tar naphthalene, and annual production of the anhydride in recent years has been around 150,000,000 pounds. In 1946 production was started (4) in a plant of the Oronite Chemical Co. at Richmond, Calif., to produce phthalic anhydride by the oxidation of o-xylene produced in a hydroformer unit of the adjacent Standard Oil Co. of California refinery. The Oronite plant was reported to have a design capacity of 7,000,000 to 8,000,000 pounds per year of 99.7% pure phthalic anhydride. 

The influence of substituents on the catalytic oxidation of toluene was investigated by Trimm and Irshad [330]. Toluene, chlorotoluenes and xylenes were oxidized over a M0O3 catalyst at 350—500° C. Partial oxidation products are aldehydes, acids and phthalic anhydride (in the case of o-xylene). Unexpectedly, both xylenes and chlorotoluenes are oxidized faster than toluene. The authors conclude that apparently the electromeric effect of the chlorosubstituent is more important than its inductive (—I) effect. The activation energies of the xylenes and chlorotoluenes all fall in the same range (17—18 kcal mol"1), while a much higher value is reported for toluene (27 kcal mol 1). 

A major problem associated with such autoxidations is that they are largely indiscriminate, i.e. they exhibit poor chemo- and regio- selectivities. They are synthetically useful only with relatively simple substrates containing one reactive position, e.g. the oxidation of toluene to benzoic acid or p-xylene to terephthalic acid. Any catalytic oxidation has to complete with this non-catalytic pathway. Moreover, the situation is further complicated by the fact that transition metal ions also catalyze autoxidations by mediating the decomposition of trace amounts of hydroperoxides into chain-initiating radicals, via the so-called Haber-Weiss mechanism ... 

Benzylic and allylic positions are hydroxylated by CPO in halide-dependent catalytic transformations. Toluene and p-xylene are oxidized to the respective aldehydes and carboxylic acids [247, 248]. Ethylbenzene and other substrates with longer alkyl chains form the respective benzylic/allylic alcohols with high enantio-selectivity. Straight-chain aliphatic and cyclic (Z)-alkenes are hydroxylated, favoring small unsubstituted substrates in which the double bond is not more than two carbon atoms from the terminus. Steric control is observed for benzylic hydroxylations. 

Crude terephthalic acid (1,2,3) CTA is produced by catalytic oxidation of p-xylene with air in the liquid phase using acetic... 

Escherichia coli (see Draths and Frost, 1994). Hydroquinone is a very practical intermediate in the manufacture of polymeric materials—almost 2 billion kg of adipic acid are produced from it and used annually in the manufacture of nylon 66. Most commercial syntheses of adipic acid utilize benzene as the starting material, derived from the benzene/toluene/xylene (BTX) fraction of petroleum refining. Benzene is hydrogenated over a metal catalyst to form cyclohexane, which is then oxidized over another catalyst that produces both cyclohexanone and cyclohexanol. See Figure 12.6. These molecules are catalytically oxidized in the presence of nitric acid to form adipic acid. 

A series of V205/Ti02 catalysts were prepared by coprecipitation, grafting, incipient wetness and dry impregnation. It was found that there were three types of vanadium species present on each of these catalysts with the relative amounts of each dependent on the method used for the preparation. >20 It was proposed that all three species are involved in the catalytic oxidation of o-xylene to phthalic anhydride (Eqn. 10.15), a reaction for which supported... 

Derivation Catalytic oxidation of o-toluic acid and oxidation of xylene. 

Catalytic oxidation of p-xylene with air is the chief commercial method used to produce terephthalic acid. A solution of p-xylene in acetic acid, together with manganese or cobalt derivative and heavy metal bromides, which serve as cocatalysts, is fed to a continuous reactor, vigorously stirred, and heated to 200°C while under about 25 atm pressure. Air is continuously fed into the reactor at the same time as a small stream of partially reacted solution is removed (Eq. 19.66). 

Although the obtained alkylphenols should be more reactive than the initial alkylbenzenes, their further hydroxylation and oxidation to alkylbenzoquinones is hindered for steric reasons. Since hydroxyl and methyl groups have similar dimensions, the lower conversions of p-xylene and p-ethyltoluene compared to toluene and ethylbenzene [6] suggest the effect of the steric restrictions in catalytic oxidation over TS-1. Products of oxidation both in the ring and in the aliphatic chain, could also be formed in principle. 

Although the oxidation affects only the alkyl group attached to the benzene nucleus, the presence of more than one methyl group accelerates the oxidation. Thus, in the liquid phase non-catalytic oxidation experiments of Stephens it was found that durene (sym.-tetra methylbenzene) was easily oxidized under conditions that scarcely affected toluene. However, in the presence of water the oxidation of m-xylene or mesitylene (1 3 4-trimethylbenzene) is almost entirely inhibited,128 a fact that Stephens interprets as showing the reversible elimination of water in one... 

Although little experimental data is available, numerous patents have been issued for the vapor phase catalytic oxidation of various other derivatives containing the benzene nucleus, as well as heterocyclic compounds Thus, fluorene (diphenyl methane) is oxidized to fluorenone with air in the presence of a catalyst containing iron vanadate or other suitable metal salt of the fifth or sixth group of the periodic system at a temperature of 360° to 400°.1,2 Maleic acid and anhydride are formed by the catalytic oxidation of compounds of the furan series, such as furan, furfural alcohol, furfural, methyl furfural, hydroxymethylfurfural, pyromucic acid or mixtures, with air over catalysts of molybdenum, vanadium, or other metals.133 Dimethyl benzaldehyde is formed by oxidizing pseudocumene with air at 550° C. in the presence of a tungsten oxide catalyst. Molybdenum, vanadium, or tantalum oxide catalysts may also be used to form aromatic aldehydes from o-, m-, or p-xylenes, mesitylene, p-cymene, or o-chlorotoluene by air oxidation. Times of contact of 0.3 to 0.4 seconds... 

Broeker, J.L., Partenheimer, W, and Rosen, B.I. (1995) Process for the manufacturing of aromatic dicarboxylic acids utilizing cerium to facilitate a low bromine to metals catalyst ratio. US Patent 5,453,538, Sept 26, 1995. Broeker, J.L. and Gong, WH. (1996) Low bromine />-xylene oxidations. 6th International Symposium on the Activation of Dioxygen and Homogeneous Catalytic Oxidation, Noordwijkherhout, The Netherlands, April 14-19,1996. 

Li, M. (2013) A spray reactor concept for catalytic oxidation of />-xylene to produce high-purity terephthalic acid. PhD Thesis. University of Kansas, p. 14. 

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