Orthoxylene Oxidation

As the petrochemical industry developed orthoxylene became widely available as a feedstock for phthalic anhydride. In the 1940s, Chevron became the first company to manufacture phthalic anhydride coimnercially by the oxidation of o-xylene, obtained as a by-product from a hydioforming plant. As o-xylene became available from platformers and demand for phthalic anhydride increased, it became the major feedstock. About 90% of the phthalic anhydride used in 1990 was produced from o-xylene. 

Catalyst 10% VjOs/P/o K2SO4 on 10%V2O5/l% K2SO4 on 9% V2O5 

The inclusion of titania was beheved to inhibit the desorption of the many intermediates involved in the overall reaction and is now a key component of the preferred o-xylene oxidation catalyst. 

Titanium dioxide catalysts were first described in the 1940s and 1950s, when mixed oxide catalysts were being investigated and used in a number of oxidation reactions. Mixtures of vanadium pentoxide with titanium dioxide gave better operation and longer life as phthalic anhydride demand increased. An early catalyst that did not sinter and clearly increased the stability of vanadium pentoxide was described in a patent as Ti0(V03)2. At about the same time vanadium pentoxide/phosphorous pentoxide mixtures were also being developed for use in maleic anhydride processes. 

A common feature of the new vanadium catalysts, including those used in sulfuric acid production, was the need to reduce pentavalent vanadium by reaction with hydrochloric or oxalic acid solutions before the active compounds that improved catalyst performance were formed. It was well known, especially from sulfuric acid catalysts, that tetravalent vanadium also formed during operation. 

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It remained for Massimilla (1973) to provide laboratory research demonstrating the higher contacting efficiency that a turbulent fluid bed affords. Wainwright and Hoffman (1974) reported excellent contacting for oxidation of orthoxylene in what was probably a fast fluid bed. 

Figure 10) - 129-Xe NMR chemical shift as a function of sorbed Xe of dealuminated HY zeolites. coked during orthoxylene cracking then partiallly and totally reoxidized. fresh sample 8.7 % coke pyrolyzed O oxidized, 4.8% coke oxidized, 1.6% coke A oxidized, 0% coke .(from reference 14).

Two mononitroxylenes can be derived, theoretically, from orthoxylene, three from metaxylene, and but one from paraxylene. It follows, therefore, that the xylene boiling at 142°, from which two mononitro derivatives can be prepared, is orthoxylene, and that the ones boiling at 139° and 138° have the meta and para structure, respectively. The application of the so-called absolute method leads to the establishment of the structure of the three xylenes, which can serve, therefore, as reference-compounds. The three hydrocarbons yield three dibasic acids on oxidation orthoxylene gives phthalic acid, metaxylene gives isophthalic acid, and paraxylene gives terephthalic acid. The three phthalic acids become, thus, reference-compounds. Other compounds can be readily converted into xylenes or phthalic acids, and can, therefore, be used in the determination of structure. Thus, the three dibromobenzenes can be converted into the three xylenes by Fittig s synthesis. The transformations establish the structure of the halogen derivatives. From these other compounds may be prepared. An example will be instructive. The dibromobenzene which melts at 89° is converted into paraxylene when treated with methyl iodide and sodium —... 

The Cindu Phthalic Anhydride Plant, Uithoorn, Holland Nearly 300 tons of steel was used in 1961 to construct this facility, which consists of a distillation plant and an oxidation plant. Phthalic anhydride is made by catalytic oxidation of naphthalene or orthoxylene. Therefore, the atmosphere in and around the open steelwork of the plant is polluted by steam vapors, phenol, naphthalene, and acid phthalic anhydride, together with sulfur dioxide from oil burners. Some of the resinous residues, however, have a certain protective action on limited areas (e.g., around valves, vents, and resin sprayers). 

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