Routes of catalytic oxidation of o-xylene to phthalic anhydride

Relative reactivity of o-xylene, o-tolualdehyde, phthalide, and phthalane and the rate of phthalic anhydride formation from them have been determined. The main route of o-xylene oxidation to phthalic anhydride is due to the o-arrangement of methyl groups, proceeding through bicyclic products, such as dihydrobenzofuran (phthalane) and 3,4-benzofuran.

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-, - , , . - - : () 3,4-.

     

Catalyst optimization strategy: selective oxidation of o-xylene to phthalic anhydride

The oxidation of o-xylene and/or naphthalene to phthalic anhydride is one of the important industrial processes based on catalytic selective oxidation reactions. Vanadia--titania catalysts have been used in the industrial phthalic anyhdride process for the last 50 years. The operation parameters like the temperature range of operation, reactor inlet pressures, contact times, o-xylene loadings, etc. were constantly improved during this period of continuous process optimization so as to optimize catalyst performance and increase its life time. However, a fundamental understanding of the mutual interaction of the rather complex reaction network and the catalyst formulation is still missing. Recently, a detailed study of by-product formation as function of process conditions allowed us to develop a novel, improved reaction scheme for the catalytic oxidation of o-xylene. Based on this understanding, a detailed investigation was conducted for the first time of the by-product formation under varying operation conditions and as a function of the active mass variation exploiting high-throughput, as well as bench scales reactors. This high-throughput testing allowed us to relate reaction kinetics to novel catalyst formulations.     

o-Xylene oxidation to phthalic anhydride over unsteady state catalysts

o-Xylene oxidation in a non-isothermal fluidized bed has been studied. Phthalic anhydride yield appears to be significantly higher than in an isothermal fluidized bed or in ideal mixing and plug flow reactors. A higher yield is caused by an unsteady state of the catalyst resulting from a chaotic particle movement in the temperature field.     

Reactivation of vanadium-titanium oxide catalysts foro-xylene oxidation to phthalic anhydride

Reactivation with sulfur containing compounds of vanadium-titanium oxide catalysts for partial oxidation ofo-xylene is studied. The efficiency depends on the kind and quantity of sulfur additives. Most proper reactivation towardso-xylene is reached with sulfur in concentrations of 0.20 wt.%.     

Lithium-promoted V2O5?TiO2 catalysts for o-xylene oxidation to phthalic anhydride

A V₂O₅–Li₂O–TiO₂ (a) based catalyst for o-xylene oxidation to phthalic anhydride has been synthesized. The activity and selectivity of the specimen obtained are comparable with those of industrial catalysts.     

Vapor phase oxidation of o-xylene on carbon catalysts

A mechanism is proposed for the mild oxidation of o-xylene on carbon catalysts. A characteristic feature of all stages of the mechanism is that they take place on basic (electron donor) centers, to which are bonded all the organic molecules and molecular oxygen participating in the reaction. The strong oxidation of o-xylene also takes place in parallel with the mild oxidation. A substantial difference between the mechanisms of phthalic anhydride and carbon dioxide formation may be caused by the different orientations of o-xylene during its adsorption, which predetermines the different directions of the subsequent attack by the oxygen. A comparison has been made of the catalytic properties of different carbons, and they have been compared with the catalytic properties of an industrial V₂0₅ catalyst.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 22, No. 5, pp. 619–625, September–October, 1986.     

Mechanosynthesis and mechanochemical treatment of bismuthdoped vanadium phosphorus oxide catalysts for the partial oxidation of n-butane to maleic anhydride

Three Bi-doped vanadyl pyrophosphate catalysts were prepared via dihydrate route （VPD method）, which consisted of different preparation methods including mechanosynthesis, mechanochemical treatment, and the conventional reflux method. The catalysts produced by the above three methods were characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, and temperature programmed reduction （TPR）. Catalytic evaluation for the partial oxidation of n-butane to maleic anhydride （MA） was also carried out. The XRD patterns of all the Bi-doped catalysts showed the main peaks of pyrophosphate phase. Lower intensity peaks were observed for the mechanochemically treated Bi-doped catalyst （VPDBiMill） with two additional small peaks corresponding to the presence of a small amount of V5＋ phase. The TPR profiles showed that the highest amount of active oxygen species, i.e, V4＋–O- pair, responsible for n-butane activation, was removed from VPDBiMill. Furthermore, from the catalytic test results, the graph of selectivity to MA as a function of the conversion of n-butane demonstrated that VPDBiMill was the most selective catalyst. This suggests that the mechanochemical treatment of vanadium phosphate catalyst （VPDBiMill） is a potential method to improve the catalytic properties for the partial oxidation of n-butane to maleic anhydride.     

Kinetics of the vapor-phase oxidation of o-xylene over a vanadium oxide catalyst

(Pt–Sn)/Al₂O₃. , , , , .

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The catalytic and adsorption properties of the (Pt–Sn)/Al₂O₃ system have been studied. The results of benzene hydrogenation, cyclohexane dehydrogenation and temperature-programmed hydrogen desorption show that the introduction of tin into the Pt/Al₂O₃ catalyst significantly changes the dispersity and electronic state of supported platinum.

     

Mathematical simulation of the oxidation of ortho-xylene to phthalic anhydride in a fluidized catalyst bed

Kinetics and Catalysis - The oxidation of ortho-xylene to phthalic anhydride in a catalytic fluidized-bed reactor was simulated. The mathematical model implied that the reactor was separated into...     

Mechanism of phthalic anhydride formation in the oxidation of n-pentane on a vanadium-phosphorus oxide catalyst

The reaction paths of product formation in the partial oxidation of n-pentane on vanadium-phosphorus oxide (VPO) and VPO-Bi catalysts are considered. The condensed products of n-pentane oxidation were analyzed by chromatography-mass spectrometry, and the presence of C₄ rather than C₅ unsaturated hydrocarbons was detected. It was found that the concentration of phthalic anhydride in the products increased upon the addition of C₄ olefins and butadiene to the n-pentane-air reaction mixture. With the use of a system with two in-series reactors, it was found that the addition of butadiene to a flow of n-butane oxidation products (maleic anhydride, CO, and CO₂) resulted in the formation of phthalic anhydride. The oxidation of 1-butanol was studied, and butene and butadiene were found to be the primary products of reaction; at a higher temperature, maleic anhydride and then phthalic anhydride were formed. The experimental results supported the reaction scheme according to which the activation of n-pentane occurred with the elimination of a methyl group and the formation of C₄ unsaturated hydrocarbons. The oxidation of these latter led to the formation of maleic anhydride. The Diels-Alder reaction between maleic anhydride and C₄ unsaturated hydrocarbons is the main path of phthalic anhydride formation.     

Desorption of catalytic oxidation products of o-xylene from the surface of carbon catalysts

In a study of the oxidation of o-xylene on carbons (in the range of 523–573°K) under nonstationary conditions, it was found that considerable amounts of the reaction products (phthalic anhydride and CO₂) are adsorbed on the surface of the catalysts (phthalic anhydride more strongly than CO₂). The adsorption of the products is chemical in nature, like the adsorption of initial o-xylene. The bond between the adsorbates and the surface weakens with increase in the number of acidic groups on the surface. Since the active carbons are characterized by a higher basicity than the oxidized ones, in the first case the oxidation products of o-xylene are adsorbed more strongly and desorbed more slowly.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 499–503, July–August, 1986.     

Redox processes in o-xylene oxidation over V?Ti oxide catalysts

It has been established that fast relaxations are due to catalytic conversion and slow ones are due to the formation of structures with decreasing activity and selectivity.

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Complete oxidation of ethanol over vanadium based catalysts

V2O5/γ-Al2O3-TiO2 catalysts were prepared by the mixing sol-gel and co-impregnation method. The performance of the catalysts for complete oxidation of ethanol was performed in a conventional fixed-bed quartz reactor. And the effects of support, preparation methods and vanadium content have been investigated. The results showed that 5% V2O5 catalyst supported on γ-Al2O3-TiO2 possessed the best ethanol conversion under the considered temperature. This may be ascribed to the highly dispersible active component, mutual function between the active component and the carriers. The nature of the best performance for 5%V/γ-Al2O3-TiO2 catalyst may be related to the high V4+ amounts on the surface. And the surface V4+ species may play an important role in the formation of active site for the total ethanol oxidation.     

Nonsteady-state kinetic model of sulfur dioxide oxidation on vanadium catalysts

Rate constants and activation energies of individual steps for the previously suggested mechanism of SO₂ oxidation on vanadium catalysts have been determined from experimental data on nonsteady-state kinetics.

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Relaxation kinetic studies of sulfur dioxide oxidation over vanadium catalyst

Relaxation processes of approaching a steady state of the catalytic system in sulfurous anhydride oxidation over a vanadium catalyst have been studied by a transient response method. It is shown that the experimental results can be interpreted in terms of a two-route mechanism.

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Vapor-phase oxidation of 4-picoline to pyridine-4-carboxaldehyde on a vanadium phosphate catalysts

The vapor-phase oxidation of 4-picoline to pyridine-4-carboxaldehyde on (VO)₂P₂O₇ has been studied. VOHPO₄·0.5 H₂0 was used as catalyst precursor. The resulting aldehyde was trapped as oxime with hydroxylamine hydrochloride solution in a subsequent reaction. In the optimum temperature range (683–703 K), a high 4-picoline conversion with good selectivity for the aldehyde was observed.

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4- -4- (VO)₂P₂O₇. VOHPO₄·0,5H₂0. . (683–703 ) 4- .

     

Heat transfer in the desublimation of phthalic anhydride

The heat transfer in the desublimation of phthalic anhydride has been investigated experimentally for the purpose of modelling and developing the design calculation procedure.Experiments were performed on a pilot installation connected to the industrial plant. On the basis of the experimental data, new correlations for the equivalent local heat transfer resistance and the mean equivalent density of the condensate were obtained. The formula for the equivalent heat transfer coefficient in the gaseous phase and the diagram for determination of the efficiency of the process are also given. The validity of the proposed formulae was verified by comparison of the calculated temperature profiles along the condenser with the measured values.