Oxidation of o-xylene

Example 13.1 Phthalic anhydride is an important intermediate for the plastics industry. Manufacture is by the controlled oxidation of o-xylene or naphthalene. The most common route uses o-xylene via the reaction... 

Figure 13.5 shows a flowsheet for the manufacture of phthalic anhydride by the oxidation of o-xylene. Air and o-xylene are heated and mixed in a Venturi, where the o-xylene vaporizes. The reaction mixture enters a tubular catalytic reactor. The heat of reaction is removed from the reactor by recirculation of molten salt. The temperature control in the reactor would be diflficult to maintain by methods other than molten salt. 

The first of the benzene polycarboxyUc acids to become a commercial product was phthabc acid, mosdy in the form of the anhydride. The anhydride is obtained by the catalytic vapor-phase air oxidation of o-xylene or naphthalene. The lUPAC name of phthabc anhydride is 1,3-isobenzofurandione... 

Another sulfur dioxide appHcation in oil refining is as a selective extraction solvent in the Edeleanu process (323), wherein aromatic components are extracted from a kerosene stream by sulfur dioxide, leaving a purified stream of saturated aHphatic hydrocarbons which are relatively insoluble in sulfur dioxide. Sulfur dioxide acts as a cocatalyst or catalyst modifier in certain processes for oxidation of o-xylene or naphthalene to phthaHc anhydride (324,325). 

In another example, Ti02 can be deposited on a siHca support body in order to obtain a stable high surface titania. This is necessary because Ti02 sinters badly on heating in the bulk oxide and loses surface area. The Ti02 Si02 combination is useful as a catalyst for the oxidation of o-xylene to phthaHc anhydride. 

Cataljdic reactions performed in fluid beds are not too numerous. Among these are the oxidation of o-xylene to phthalic anhydride, the Deacon process for oxidizing HCl to CI2, producing acrylonitrile from propylene and ammonia in an oxidation, and the ethylene dichloride process. In the petroleum industry, cataljdic cracking and catalyst regeneration is done in fluid beds as well as some hydroforming reactions. 

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. 

Currently, phthalic anhydride is mainly produced through catalyzed oxidation of o-xylene. A variety of metal oxides are used as catalysts. A typical one is V2O5 -1- Ti02/Sb203. Approximate conditions for the vapor-phase oxidation are 375-435°C and 0.7 atmosphere. The yield of phthalic anhydride is about 85% ... 

Liquid-phase oxidation of o-xylene also works at approximately 150°C. Cobalt or manganese acetate in acetic acid medium serves as a catalyst. 

Besides the technical method starting from naphthalene, phthalic acid and its substituted derivatives can be prepared by oxidation of o-xylene to phthalic acid with potassium permanganate. This compound can be subsequently transformed via an anhydride, imide, and amide to a derivative of phthalonitrile, which is the more convenient starting material for several coordination compounds. The synthesis of the ferf-butyl-substituted dicarbonitrile, which is a very common starting material for highly soluble phthalocyanines, is shown below.97,105... 

The reaction scheme is rather complex also in the case of the oxidation of o-xylene (41a, 87a), of the oxidative dehydrogenation of n-butenes over bismuth-molybdenum catalyst (87b), or of ethylbenzene on aluminum oxide catalysts (87c), in the hydrogenolysis of glucose (87d) over Ni-kieselguhr or of n-butane on a nickel on silica catalyst (87e), and in the hydrogenation of succinimide in isopropyl alcohol on Ni-Al2Oa catalyst (87f) or of acetophenone on Rh-Al203 catalyst (87g). Decomposition of n-and sec-butyl acetates on synthetic zeolites accompanied by the isomerization of the formed butenes has also been the subject of a kinetic study (87h). 

Either Friedel-Crafts disconnection will do, but o-toluic acid (27) is available from the oxidation of o-xylene so that route is preferred as no separation of o, p-isomers is involved. 

Harms G, K Zengle, R Rabus, F Aeckersberg, D Minz, R Rossell6-Mora, F Widdel (1999) Anaerobic oxidation of o-xylene, m-xylene, and homologous alkylbenzenes by new types of sulfate-reducing bacteria. Appl Environ Microbiol 65 999-1004. 

The aerobic oxidation of o-xylene to phthalic acid or anhydride at elevated temperatures is industrially important, and the flammability limits and explosion parameters at 350°C under a range of pressures have been redetermined. 

Oxidation of o-xylene over V20s/Si02 [6]. The rate enhancement was because of a temperature gradient of approx. 100 K in the catalyst bed. Reaction conditions a flow fixed-bed multi-mode reactor. 

It is required to determine the height (h) of a bubble-column reactor and the outlet partial pressure of oxygen (A, pAout) for the hquid-phase oxidation of o-xylene to o-methylbenzoic acid the column diameter (D) is 1 m. The reaction is... 

A pilot-scale reactor for the oxidation of o-xylene by air according to the following reaction has been constructed and its performance is being tested. 

ANHYD - Oxidation of O-Xylene to Phthalic Anhydride System... 

Steady-State Absorption Column Design 471 Oxidation of O-Xylene to Phthalic Anhydride 324 Continuous Stirred Tank Reactor Model of Activated 577... 

The gas-phase selective oxidation of o-xylene to phthalic anhydride is performed industrially over vanadia-titania-based catalysts ("7-5). The process operates in the temperature range 620-670 K with 60-70 g/Nm of xylene in air and 0.15 to 0.6 sec. contact times. It allows near 80 % yield in phthalic anhydride. The main by-products are maleic anhydride, that is recovered with yields near 4 %, and carbon oxides. Minor by-products are o-tolualdehyde, o-toluic acid, phthalide, benzoic acid, toluene, benzene, citraconic anhydride. The kinetics and the mechanism of this reaction have been theobjectof a number of studies ( 2-7). Reaction schemes have been proposed for the selective pathways, but much less is known about by-product formation. 

V20s/Ti02 oxidation of o-xylene to phthalic anhydride... 

Figure 9 Influence of humidity on the photocatalytic oxidation of o-xylene. (From Ref. 19.)...

Ameen and Raupp examined photocatalytic regeneration following photocatalytic oxidation of o-xylene at 25 ppmv and 80% relative humidity [19]. Exposure to clean flowing air and UV illumination for 12 hr was found to restore the titanium dioxide photocatalyst activity to levels observed with fresh catalysts. 

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. 

Phthalic Anhydride. Phthalic anhydride is manufactured by the catalytic vapor-phase oxidation of o-xylene [Eq. (9.182)] or naphthalene [Eq. (9.183)] ... 

Detailed mechanistic studies about both oxidations have been carried out.901,1006,1033 On the basis of the observed intermediates, a reaction network [Eq. (9.184)] was suggested in the oxidation of o-xylene indicating o-tolualdehyde as the first intermediate 1034,1035... 

Phthalic anhydride is the most important product in the oxidation of o-xylene, which has become competitive with naphthalene as a feedstock for the industrial production of this component. This process is carried out at 350— 400°C and the industrial catalysts consist of doped V2Os or V2Os—Ti02 mixtures, pure or supported. Maximum yields of 70—75 mol. % (95—105 wt. %) are reported. Carbon oxides are the main by-products, besides minor amounts of tolualdehyde and maleic anhydride. Tolualde-hyde is the main product at low conversion and an essential intermediate in the phthalic anhydride formation, while maleic anhydride is mainly formed as a side-product directly from o-xlyene. 

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