Vanadium pentoxide oxidation over

Vapor-phase oxidation over a promoted vanadium pentoxide catalyst gives a 90% yield of maleic anhydride [108-31-6] (139). Liquid-phase oxidation with a supported palladium catalyst gives 55% of succinic acid [110-15-6] (140). 

Oxidation. Naphthalene may be oxidized direcdy to 1-naphthalenol (1-naphthol [90-15-3]) and 1,4-naphthoquinone, but yields are not good. Further oxidation beyond 1,4-naphthoquinone [130-15-4] results in the formation of ortho- h. h5 ic acid [88-99-3], which can be dehydrated to form phthaUc anhydride [85-44-9]. The vapor-phase reaction of naphthalene over a catalyst based on vanadium pentoxide is the commercial route used throughout the world. In the United States, the one phthaUc anhydride plant currently operating on naphthalene feedstock utilizes a fixed catalyst bed. The fiuid-bed process plants have all been shut down, and the preferred route used in the world is the fixed-bed process. 

Durene. The oxidation of durene (4) yields pyromeUitic acid [89-05-4] (17) or pyromeUitic dianhydride [89-32-7] (18) directly. The oxidation can be carried out with dilute nitric acid ia solution, with air and catalyst either ia the vapor phase over a soHd vanadium pentoxide-based catalyst or ia the... 

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... 

At present, almost all sulfuric acid is made by the contact process, which has been in use since 1831. The first step is exothermic air oxidation of SO2 catalyzed by vanadium pentoxide (V2O5) or platinum (reaction 10.5). The yield of SO3 is limited on the first pass to some 60% because the temperature rises to 600 °C or more usually, three more passes over the catalyst are made, and the yield can be increased to 98%. The SO3 vapor is then absorbed into 100% H2SO4 (reaction 10.6), and water is added to the resulting mixture of disulfuric (H2S207) and sulfuric acids (known as oleum) until the H2S2O7 is all hydrolyzed to H2SO4 (reaction 10.7). This obviates the aerosol problem. 

Maleic anhydride production. The oxidation of benzene to maleic anhydride over a vanadium pentoxide electrode has been studied by Pizzini et... 

Vanadyl Dibromide, VOBr2, is obtained by passing bromine vapour or, preferably, a mixture of sulphur bromide, SaBra, and bromine over a mixture of vanadium pentoxide and sulphur at a red heat the product is heated in vacuo at 240° C., whereupon the vanadyl dibromide is obtained as a yellow powder.8 An alternative method of preparation consists in heating vanadium oxytribromide, VOBr3, to 180° C.9 Vanadyl dibromide is no doubt present in the blue solution which results when hypovanadic oxide, VOa, is dissolved in hydrobromic acid. 

An alternative method for the preparation of crystalline vanadium pentoxide consists in heating a mixture of the amorphous oxide and calcium fluoride to red heat in an open crucible over which is suspended another crucible, inverted, to act as a receiver. The inside of the latter becomes coated with shining, needle-shaped, yellow crystals, which also become reddish-brown on being heated.4... 

Oxidation. The vapor-phase reaction of naphthalene over a catalyst based on vanadium pentoxide is the commercial route used throughout the world to funu plillialic anhydride. In the United Stales, the one phthalic anhydride plant currently operating on naphthalene feedstock utilizes a fixed catalyst bed, the preferred route worldwide. 

Indeed, this pathway is followed in many gas phase oxidations over metal oxide catalysts, such as vanadium pentoxide and bismuth molybdate. It is generally referred to as the Mars-van Krevelen mechanism after its original... 

Although the forward reaction is favored by increase in pressure, this is not employed in practice since 97 to 99% conversion of sulfur dioxide to sulfur trioxide can be accomplished at the temperature specified here, provided suitable catalysts are used. The first catalyst used for this reaction consisted of finely divided platinum dispersed in asbestos, anhydrous magnesium sulfate, or silica gel. Other catalysts were later discovered. Mixtures of ferric and cupric oxides are useful, but these are less efficient than platinum. Certain mixtures containing vanadium pentoxide (V205) and other compounds of vanadium appear to be as good as or better than platinum. There has been much controversy over the relative merits of platinum and vanadium catalysts, and only time will provide the answer as to which is best. 

Maleic acid and anhydride are recovered as by-products of the oxidation of xylenes and naphthalenes to form phthalic acids, and are also made specifically by the partial oxidation of benzene over a vanadium pentoxide (V205) catalyst. This is a highly exothermic reaction, and several modifications of the basic process exist, including one using butylenes as the starting materials. 

To overcome the problems encountered in the homogeneous Wacker oxidation of higher alkenes several attempts have been undertaken to develop a gas-phase version of the process. The first heterogeneous catalysts were prepared by the deposition of palladium chloride and copper chloride on support materials, such as zeolite Y [2,3] or active carbon [4]. However, these catalysts all suffered from rapid deactivation. Other authors applied other redox components such as vanadium pentoxide [5,6] or p-benzoquinone [7]. The best results have been achieved with catalysts based on palladium salts deposited on a monolayer of vanadium oxide spread out over a high surface area support material, such as y-alumina [8]. Van der Heide showed that with catalysts consisting of H2PdCU deposited on a monolayer vanadium oxide supported on y-alumina, ethene as well as 1-butene and styrene... 

The reaction of gaseous SO2 with molecular oxygen in the contact process seems to proceed over two independent mechanisms [13] one of which is the direct oxidation of a vanadium pentoxide-sulfur dioxide adduct by oxygen and the other proceedings via a redox cycle involving V4+ and V3+ intermediate species [13-15]. 

Oxidation of individual hydrocarbons may be exemplified by the work of Medvedev (232) who has been studying these reactions for a number of years and has more recently investigated the effect of oxygen on polymerization reactions. Neutral phosphates of aluminum, tin or iron, tin borate, etc., were found to be suitable for the conversion of methane to formaldehyde at 500°C. A practical aspect of this research is represented by the homogeneous oxidation of petroleum stocks in the presence of naphthenates which was developed by Petrov into an industrial process to supply fatty acids for the soap making and grease making industry (298,299). Kreshkov oxidized methane to formaldehyde in the presence of chlorine and steam over chlorides of copper or barium or over vanadium pentoxide on carbon (179), but his yields were low. 

Example 8.8 Entropy production in a homogeneous chemical system The oxidation of sulfur dioxide to trioxide over a vanadium pentoxide catalyst is... 

Under extreme conditions, the benzene ring can be oxidized to other products. Maleic anhydride is prepared industrially by passing a mixture of benzene and air over a vanadium pentoxide catalyst t 420 "C,... 

PSC-fi The selective oxidation of toluene and methanol over vanadium pentoxide-sup-ported alkali metal sulfale catalysts was studied recently [AlChE 27(1), 41... 

P5C-6 The selective oxidation of toluene and methanol over vanadium pentoxide-sup-ported alkali metal sulfate catalysts was studied recently fAIOiEJ., 27(1), 41 (1981)]. Examine the experimental technique used (equipment, variables, etc.) in light of the mechanism proposed. Comment on the shortcomings of the analysis and compare with another study of this system presented in AZOiE J., 25(5), 855 (1982). 

In some cases a catalyst consists of minute particles of an active material dispersed over a less active substance called a support. The active material is frequently a pure metal or metal alloy. Such catalysts are called supported catalysts, as distinguished from unsupported catalysts, whose active ingredients are major amounts of other substances called promoters, which increase the activity. Examples of supported catalysts are the automobile-muffler catalysts mentioned above, the platinum-on-alumina catalyst used in petroleum reforming, and the vanadium pentoxide on silica used to oxidize sulfur dioxide in manufacturing sulfuric acid. On the other hand, the platinum gauze for ammonia oxidation, the promoted iron for ammonia synthesis, and the silica-alumina dehydrogenation catalyst used in butadiene manufacture typify unsupported catalysts. 

A classical example of the dehydrogenative formation of a carbon-carbon double bond conjugated with an aromatic ring is the dehydrogenation of ethylbenzene to styrene at 500-600 °C over a complex catalyst containing oxides of zinc and chromium [1090] or at 625 °C over vanadium pentoxide on alumina [478]. 

Gibbs phthalic anhydride process. Oxidation of naphthalene to phthalic anhydride with air at 360C over vanadium pentoxide and other catalysts. 

Important commercial reactions that are carried out in multistage adiabatic reactors include 1) the oxidation of SO2 to SO3 over a vanadium pentoxide catalyst, which is the key step in sulfuric acid manufacture, and 2) the silver-catalyzed oxidation of methanol to... 

Sulfur Dioxide to Sulfur Trioxide Process. The manufacture of sulfuric acid involves the oxidation of elemental sulfur to SO2, followed by the catalytic oxidation of SO2 to SO3 over vanadium pentoxide. The next step involves the absorption of SO3 with water to form H2SO4. The SO2 oxidation reaction to... 

Binary vanadium-titanium oxide catalysts with various ratios of vanadium oxide and titania, as well as individual oxides of vanadium and titanium were examined in oxidation of P-picoline. Nicotinic acid, 3-pyridinecarbaldehyde, and CO2 were the reaction products over all the catalysts. The binary catalysts and individual vanadium oxide were highly selective for nicotinic acid, the most effective in P-picoline oxidation were the samples containing 20% and more of vanadium pentoxide. A regular stacking of crystallites of V2O5 and Ti02 was found to be the characteristic feature of the structure of the most effective compositions. 

---