Xylene to phthalic

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. 

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... 

NON-ISOTHERMAL FIXED BED REACTOR OXIDATION OF 0-XYLENE TO PHTHALIC ANHYDRIDE STEADY-STATE AXIAL TEMPERATURE AND CONVERSION CONSTANT 6=4684 superf. mass velocity [kg/m2 h]... 

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. 

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... 

Three well known examples of processes employing fluidised-bed operations are the oxidations of naphthalene and xylene to phthalic anhydride using a supported V2O5 catalyst and ammoxidation of propylene utilising a mixed oxide composition containing bismuth molybdate. Typically, this latter reaction is executed by passing a mixture of ammonia, air and propylene to a fluidised bed operating at about 0.2 MPa pressure, 400—500°C and a few seconds contact time between gas and fluidised catalyst peirticles. 

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). 

This class of reactions, carried out in fluidized beds, involves parallel and series reactions, with reaction intermediates being the desired products. Industrial examples include partial oxidation of n-butane to maleic anhydride and o-xylene to phthalic anhydride. The vigorous solid mixing of fluidized beds is valuable for these reactions because they are highly exothermic. However, gas backmixing must be minimized to avoid extended gas residence times that lead to the formation of products of total combustion (i.e., CO2 and H2O). For this reason, fluidized bed catalytic partial oxidation reactors are operated in the higher velocity regimes of turbulent and fast-fluidization. 

Multitubular reactors are mainly used in gas-phase partial oxidation processes, such as the air oxidation of light olefins, paraffins, and aromatics. Examples of chemistries where these reactors are used include the partial oxidation of methanol to formaldehyde, ethylene to ethylene oxide, ethylene and acetic acid to vinyl acetate, propylene to acrolein and acrylic acid, butane to maleic anhydride, isobutylene to methacrolein and methacrylic acid, and o-xylene to phthalic anhydride. An overview of the multitubular reactor process for the partial oxidation of n-butane to maleic anhydride is given here. 

---