Oxidation of o-xylene to phthalic anhydride

Phthalic acid was discovered by the French chemist Auguste Laurent in 1836. During experiments with naphthalene, he discovered an acidic substance, which he called naphthalene acid . In 1869, Carl Graebe established that this naphthalene acid was, in fact, o-benzenedicarboxylic acid (phthalic acid). 

Commercial production of phthalic anhydride (PA) was taken up by BASFm 1872, by the oxidation of naphthalene with manganese dioxide and hydrochloric acid, to obtain the required base material (PA) for the manufacture of the dyestuffs fluorescein and eosine, and later for phenolphthalein however, the yield was only 5 to 7%. 

Despite considerable headway in the process, which involved the use of chromic acid and later oleum, and which increased the yield to around 15%, non-catalytic methods remained highly unsatisfactory. 

During research into the development of a commercial synthesis of indigo in 1891, Eugen Sapper discovered an important improvement by the use of a mercury sulfate catalyst the Sapper process remained in use until 1925. During World War I, Alfred Wohl in Germany and Harry D. Gibbs and Courtney Conover in the USA, independently discovered the catalytic gas-phase oxidation of naphthalene with vanadium pentoxide. 

As a consequence of the lengthy patent dispute arising from this parallel development, and restrictions on the importation of German PA during the war, a high temperature process for gas-phase oxidation of naphthalene, using mercury for heat transfer, was perfected in the USA in 1917. 

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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. 

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... 

Kinetic and mechanistic investigations on the o-xylene oxidation over V205—Ti02 catalysts were carried out by Vanhove and Blanchard [335, 336] using a flow reactor at 450°C. Possible intermediates like o-methyl-benzyl alcohol, o-xylene-a,a -diol, toluic acid and phthalaldehyde were studied by comparing their oxidation product distribution with that of toluene. Moreover, a competitive oxidation of o-methylbenzyl alcohol and l4C-labelled o-xylene was carried out. The compounds investigated are all very rapidly oxidized, compared with o-xylene, and essentially yield the same products. It is concluded, therefore, that these compounds, or their adsorbed forms may very well be intermediates in the oxidation of o-xylene to phthalic anhydride. The ratio in which the partial oxidation products are formed appears to depend on the nature of the oxidized compounds, i.e. o-methylbenzyl alcohol yields relatively more phthalide, whereas o-xylene-diol produces detectable amounts of phthalan. This... 

Grabowski et al.92 found that for V205/Ti02 catalysts the maximum selectivity for oxidation of o-xylene to phthalic anhydride was obtained at not too high vanadium contents of 2 to 15 wt% and at temperatures around 350°C. 

With OCFS, the lower pressure drop in the catalyst bed results in reduction in the energy costs associated with recirculation of gas streams and—in new plants—lower investment costs due to the possibility of using boosters rather than compressors. Further potential for savings lies in the reduction of the number of reactor tubes, due to the increased tube diameter made possible by more efficient radial heat transfer. Of greatest significance, however, for processes such as the oxidation of o-xylene to phthalic anhydride... 

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... 

C.R. Dias, M.F. Portela, M. Galan Fereres et al.. Selective Oxidation of o-Xylene to Phthalic Anhydride, Catal. Lett. 43(1-2), 117-121 (1997). 

When more than one reaction occurs the calculation procedures are similar to those illustrated in Example 13-6. A difference equation is written for each component, and these equations are solved simultaneously with the difference equation for the conservation of energy. Froment has used one- and two-dimensional models to predict conversion and temperatures in a fixed-bed reactor for the oxidation of o-xylene to phthalic anhydride, CO, and COj, with a V2O5 catalyst. The reaction scheme is... 

In many cases, the external mass and heat transfer resistances are negligible because of the high gas flow rate that destroys the external resistances (see for example the ammonia converter, ch. 6, sec. 6.3.3, and the steam reformer, ch. 6, sec. 6.3.4). A counter example is the case of the partial oxidation of o-Xylene to phthalic anhydride, ch. 6, sec. 6.3.6, where external mass and heat transfer resistances must be taken into consideration for precise modelling of these reactors. 

As an illustrative example, we present in detail the different mechanisms and kinetic rate equations for the catalytic partial oxidation of o-Xylene to phthalic anhydride. 

For multiple reactions, whether reversible and cyclic such as the steam reforming of methane or irreversible, consecutive and parallel such as the partial oxidation of o-Xylene to phthalic anhydride, the situation becomes rather complex. The full practical implication of these findings has not been explored. Both the partial oxidation of... 

For more complex reaction networks, these component effectiveness factors are the correct numbers to indicate the effect of diffusion on the yield and selectivity for the different components. For this reason it is the components effectiveness factors formulation which should be used in connection with complex reaction networks. It will be shown that in these cases not only rj> I are possible but also ij <0 are possible for some intermediate components. This phenomenon will be discussed in sections 5.1.9 and 5.2.2, in connection with the highly endothermic steam reforming reaction, and the highly exothermic partial oxidation of o-Xylene to phthalic anhydride. 

Fixed bed reactors for the partial oxidation of o-Xylene to phthalic anhydride. 

Metal oxide catalysts are extensively employed in the chemical, petroleum and pollution control industries as oxidation catalysts (e.g., oxidation of methanol to formaldehyde, oxidation of o-xylene to phthalic anhydride, ammoxidation of propylene/propane to acrylonitrile, selective oxidation of HjS to elemental sulfur (SuperClaus) or SO2/SO3, selective catalytic reduction (SCR) of NO, with NHj, catalytic combustion of VOCs, etc.)- A special class of metal oxide catalysts consists of supported metal oxide catalysts, where an active phase (e.g., vanadium oxide) is deposited on a high surface area oxide support (e.g., alumina, titania, ziiconia, niobia, ceria, etc.). Supported metal oxide catalysts provide several advantages over bulk mixed metal oxide catalysts for fundamental studies since (1) the number of surface active sites can be controlled because the active metal oxide is 100% dispersed on the oxide support below monolayer coverage,... 

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