Naphthalene, oxidation to phthalic anhydride

Ioffe and Sherman (149) studied the kinetics of naphthalene oxidation to phthalic anhydride on a more complex vanadium-potassium-sulfate catalyst over a wide range of conversions and temperatures. The naphthalene oxidation was found to be independent of naphthalene concentration. This reaction is first order with respect to oxygen concentration and is inhibited with reaction products. 

Either naphthalene or ortho-xylene is an acceptable starting material for partial oxidation to phthalic anhydride, but current raw materials costs favor the former as a starting material. Both fixed and fluidized bed processes have been used on a commercial scale, but you are to focus your attention on the former. Figure 13.5 is a schematic flow diagram of the proposed process. Most research groups that have studied the catalytic oxidation of naphthalene over vanadium pentoxide agree that the principal reactions are... 

In the older method, still used in some CIS and East European tar refineries, the naphthalene oil is cooled to ambient temperatures in pans, the residual oil is separated from the crystals, and the cmde drained naphthalene is macerated and centrifuged. The so-called whizzed naphthalene crystallizes at ca 72—76°C. This product is subjected to 35 MPa (350 atm) at 60—70°C for several minutes in a mechanical press. The lower melting layers of the crystals are expressed as liquid, giving a product crystallizing at 78—78.5°C (95.5—96.5% pure). This grade, satisfactory for oxidation to phthalic anhydride, is referred to as hot-pressed or phthalic-grade naphthalene. 

In the vapor phase oxidation of benzene to maleic anhydride an active catalyst is necessary to force oxidation to rupture the ring without leading to complete destruction. Vanadium pentoxide or vanadium compounds such as tin vanadate have been successfully used for this purpose.26 In the oxidation of alkylated benzene compounds to benzaldehyde, benzoic acid, or phthalic anhydride, a milder form of catalyst is effective. The oxidation of naphthalene to naphthaquinone would also require a mild form of catalyst to prevent ring rupture caused by too severe oxidation. However, oxidation to phthalic anhydride may be realized under ordinary conditions by the use of such catalysts as have been found effective in benzene oxidation, i.e., oxides of the metals of the fifth and sixth groups of the periodic system, especially the oxides of vanadium and molybdenum. 

The alkyl naphthalenes, such as methyl naphthalene, may be oxidized to phthalic anhydride in the same manner as naphthalene, thus making it possible to use cruder grades of naphthalene. Thus, crude naphthalene obtained by centrifuging the oils from the proper cut from the distillation of coal-tar (whizzed naphthalene) consisting principally of naphthalene to the extent of 50 to 80 per cent and usually containing considerable quantities of alkyl naphthalenes and other ring compounds may be treated in a manner similar to that used in the oxidation of pure naphthalene. The reaction products contain phthalic anhydride, benzoic acid, naphthoic acids and anhydrides, etc.81... 

Pure naphthalene (mp > 80 0) is introduced in the liquid state at the base of a catalyst bed contained in the reactor. It is immediately vaporized and dispersed in the solid medium, where it enters into contact on the hot catalyst with air introduced below a grid placed at the base of the system. Naphthalene is vaporized and oxidized to phthalic anhydride at a uniform temperature, ranging between 340 and 385 C, due to the intense agitation of the reaction medium engendered by the fluidized bed. The catalyst consists of vanadium oxide on sflka geL... 

The stability of the naphthalene structure is such that, at temperatures up to 400-500 C, a catalyst is necessary for commercial rates of oxidation with air as the oxidizing agent. Theoretically, nine atoms of oxygen is required per molecule of naphthalene for oxidation to phthalic anhydride. This means that 64.5 cu ft of dry air measured at room temperature is theoretically required for the oxidation of 1 lb of naphthalene to phthalic anhydride. In practice, considerable excess air is used, up to three times that theoretically required. Thus, 20-60 moles of air must be used per mole of naphthalene oxidized. 

Naphthalene Is oxidized to phthalic anhydride, a rubber cure retarder. 

Naphthalene Is oxidized to phthalic anhydride to produce DOP and DIDP synthetic ester plasticizers, which are used in specialty elastomer-based compounds. 

Xylenes are used inter alia as solvents, for example in the USA 180,000 t p.a. [13] and in Japan 90,000 t [33], particularly in the paint and printing ink industries (see also [5]). In eastern Europe it is also used for numerous applications in the shoe industry, o-xylene (besides naphthalene) is mainly oxidized to phthalic anhydride from which dyestuffs, phthalodinitrile and - by esterification with alcohols - plasticizers and raw materials for paints and varnishes are obtained [36, 38]. p-xylene is oxidized and processed with methanol to terephthalic acid dimethyl ester, from which polyesters are made [36, 38, 39]. For example, in 1972 2.9 million t polyester fibres were produced worldwide [39] and in 1979 more than 5 million t, which corresponds to 2.8 million t of p-xylene [30 a]. Polystyrene and copolymers (including expanded plastics) in particular are polymerized from styrene, and the world annual production of these products around 1975 was about 5 million t [39, 40],... 

Most of the naphthalene produced is oxidized to phthalic anhydride [2, 36]. In addition, naphthalene is used as the basis for other intermediates - primarily as initial products for dyestuffs - [36], or it is used besides and with p-dichlorobenzene as mothproofing agent and insecticide. Products similar to diesel oil - such as Aerotox 3470 - together with alkylated benzenes and naphthalenes are also used as solvents for pesticides, and are then introduced into the environment by spraying [44]. 1,1-phenyl-xylyl-ethane and diisopropyl naphthalene are PCB substitutes [45]. 

Phthalic anhydride. Naphthalene is oxidized by air to phthalic anhydride in a Bubbling flmdized reaclor. Even though the naphthalene feed is in liquid form, the reaction is highly exothermic. Temperature control is achieved by removing heat through vertical tubes in the bed to raise steam [Graham and Way, Chem. Eng. Prog., 58, 96 (Januaiy 1962)]. 

An alternative route to phthalic anhydride is the partial oxidation of naphthalene. The heat of reaction is — 430 kcal/mol. This reaction can be performed using a promoted V2O5 catalyst on silica, much like that considered in Example 9.1. Suppose In(fik) = 31.6800—19,100/T for the naphthalene oxidation reaction and that the subsequent, complete oxidation of phthalic anhydride follows the kinetics of Problem 9.3. Suppose it is desired to use the same reactor as in Example 9.1 but with a,>, = 53g/ m. Determine values for and T aii that maximize the output of phthalic anhydride from naphthalene. 

Fluidized bed reactors were first employed on a large scale for the catalytic cracking of petroleum fractions, but in recent years they have been employed for an increasingly large variety of reactions, both catalytic and non-catalytic. The catalytic reactions include the partial oxidation of naphthalene to phthalic anhydride and the formation of acrylonitrile from propylene, ammonia, and air. The noncatalytic applications include the roasting of ores and Tie fluorination of uranium oxide. 

Fires inside wood-packed benzene scrubbers in coke oven gas plants were attributed to saturation of the wood with naphthalene, and vapour-phase oxidation of the latter to phthalic anhydride, which participates in exothermic free radical chain reactions. 

Gibbs A process for oxidizing naphthalene to phthalic anhydride, using air as the oxidant and catalyzed by vanadium pentoxide. Invented in 1917 by H. D. Gibbs and C. Conover. 

LAR [Low air ratio] A process for oxidizing o-xylene or naphthalene to phthalic anhydride, using a titania/vanadia catalyst containing molybdenum. Developed by Alusuisse Italia in the 1980s. A plant was operated at Valdamo, Italy, in 1984. 

Extension of the Kunii-Levenspiel bubbling-bed model for first-order reactions to complex systems is of practical significance, since most of the processes conducted in fluidized-bed reactors involve such systems. Thus, the yield or selectivity to a desired product is a primary design issue which should be considered. As described in Chapter 5, reactions may occur in series or parallel, or a combination of both. Specific examples include the production of acrylonitrile from propylene, in which other nitriles may be formed, oxidation of butadiene and butene to produce maleic anhydride and other oxidation products, and the production of phthalic anhydride from naphthalene, in which phthalic anhydride may undergo further oxidation. 

For fitting such a set of existing data, a much more reasonable approach has been used (P2). For the naphthalene oxidation system, major reactants and products are symbolized in Table III. In this table, letters in bold type represent species for which data were used in estimating the frequency factors and activation energies contained in the body of the table. Note that the rate equations have been reparameterized (Section III,B) to allow a better estimation of the two parameters. For the first entry of the table, then, a model involving only the first-order decomposition of naphthalene to phthalic anhydride and naphthoquinone was assumed. The parameter estimates obtained by a nonlinear-least-squares fit of these data, are seen to be relatively precise when compared to the standard errors of these estimates, s0. The residual mean square, using these best parameter estimates, is contained in the last column of the table. This quantity should estimate the variance of the experimental error if the model adequately fits the data (Section IV). The remainder of Table III, then, presents similar results for increasingly complex models, each of which entails several first-order decompositions. 

Fluidised catalysts are also used in the synthesis of high-grade fuels from mixtures of carbon monoxide and hydrogen, obtained either by coal carbonisation or by partial oxidation of methane. An important application in the chemical industry is the oxidation of naphthalene to phthalic anhydride, as discussed by Riley(131). The kinetics of this reaction are much slower than those of catalytic cracking, and considerable difficulties have been experienced in correctly designing the system. 

So far, no reference has been made to the presence of more than one phase in the reactor. Many important chemicals are manufactured by processes in which gases react on the surface of solid catalysts. Examples include ammonia synthesis, the oxidation of sulphur dioxide to sulphur trioxide, the oxidation of naphthalene to phthalic anhydride and the manufacture of methanol from carbon monoxide and hydrogen. These reactions, and many others, are carried out in tubular reactors containing a fixed bed of catalyst which may be either a single deep bed or a number of parallel tubes packed with catalyst pellets. The latter arrangement is used, for exjimple, in the oxidation of ethene to oxiran (ethylene oxide)... 

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. 

With a particular catalyst and at a given temperature, the oxidation of naphthalene to phthalic anhydride proceeds as follows ... 

Another sulfur dioxide application 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 aliphatic hydrocarbons which are relatively insoluble in sulfur dioxide. Sulfur dioxide acts as a cocatalyst or catalyst modifier in certain processes for oxidation of 0-xylene or naphthalene to phthalic anhydride (324,325). 

The oxidation of aromatic hydrocarbons originating from coal is one of the first organic gas phase oxidation processes carried out on an industrial scale. The development of these processes was initiated by the discovery that the V2Os catalyst used for the oxidation of sulphur dioxide was also applicable to the partial oxidation of benzene to maleic anhydride and naphthalene to phthalic anhydride. Remarkably, V2Os-based catalysts are still used in these processes today as they appear superior to any other type of catalyst. 

The gas phase oxidation of naphthalene to phthalic anhydride over V2Os-based catalysts is one of the oldest successful partial oxidation processes and is still of industrial importance today. Common commercial catalysts are modified silica-supported V—K—S—O catalysts and catalysts similar to those used for benzene or o-xylene oxidation. Maximum phthalic anhydride yields of 80—85 mol. % (92—98 wt. %) at 350—400°C are reported. By-products are naphthoquinone (2—5%), maleic anhydride (2— 5%) and carbon oxides. 

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