Vanadium oxide, hydrocarbon conversion

One of the most industrially important reactions using vanadium pentoxide(V205) catalyst is the partial oxidation of 1-butene to maleic anhydride [1]. Partial oxidation reactions are inherently unselective and often make by-products of little or no value. Oxygen-rich feeds result in low product selectivities and high hydrocarbon conversions [2]. Because partial oxidation and total oxidation always proceed competitively, the selectivity of maleic anhydride from 1-butene is low. Though fixed bed reactors or fludized bed reactors have been used for partial oxidation for the past 30 years, the selectivity of maleic anhydride has not been obtained higher than 69% [3]. Some attempts have been reported on a new type of reactor to overcome the above limit. This is a membrane reactor which offers some advantages. A membrane reactor plays a... 

In a concurrent effort. Ford workers screened a number of catalysts and focused on vanadium oxide catalysts for hydrocarbon conversion. A major advantage (at the time) claimed for this catalyst was its inefficiency in oxidizing carbon monoxide, which eliminated the need for a secondary air pump to provide oxygen this feature also would permit the use of lower-cost steels since the heat release associated with CO oxidation would be avoided (5.). Although this catalyst was further developed as part of a system (, 7 y ), it was to become decidely less attractive when California adopted exhaust standards in 1959 which included carbon monoxide (9). 

Ethylene represents the major feedstock for the petrochemical industry and is generally produced by ethane and propane steam cracking, which also produces a wide range of hydrocarbon products. Currently, there is much interest in developing a selective catalytic route for the oxidative conversion of ethane to ethylene. Supported vanadium oxide catalysts are particularly good for this process because... 

Ogonowski, J. and Skrzynska, E. (2008). Conversion of lower hydrocarbons in the presence of carbon dioxide The theoretic analysis and catalytic tests over active carbon supported vanadium oxide, Catal. Lett., 124, pp. 52-58. 

The selective oxidation of saturated hydrocarbons is a reaction of high industrial importance. Besides a variety of other oxidants, hydrogen peroxide as a very clean oxidant has also been used for these purposes . As an example, in 1989 Moiseev and coworkers reported on the vanadium(V)-catalyzed oxidation of cyclohexane with hydrogen peroxide (Scheme 146) . When the reaction was carried out in acetic acid cyclohexanol and cyclohexanone were formed, bnt conversions were very poor and did not exceed 13%. Employing CF3COOH as solvent, complete conversions could be obtained within 5 min-ntes. Here, cyclohexyl trifluoroacetate was the main product (85% of the products formed) resulting from the reaction of cyclohexanol (the primary product of the oxidation) with CF3COOH. 

V-containing silicalite, for example, has been shown to have different catalytic properties than vanadium supported on silica in the conversion of methanol to hydrocarbons, NOx reduction with ammonia and ammoxidation of substituted aromatics, butadiene oxidation to furan and propane ammoxidation to acrylonitrile (7 and references therein). However, limited information is available about the characteristics of vanadium species in V-containing silicalite samples and especially regarding correlations with the catalytic behavior (7- 6). 

The oxidation of butane (or butylene or mixtures thereof) to maleic anhydride is a successful example of the replacement of a feedstock (in this case benzene) by a more economical one (Table 1, entry 5). Process conditions are similar to the conventional process starting from aromatics or butylene. Catalysts are based on vanadium and phosphorus oxides [11]. The reaction can be performed in multitubular fixed bed or in fluidized bed reactors. To achieve high selectivity the conversion is limited to <20 % in the fixed bed reactor and the concentration of C4 is limited to values below the explosion limit of approx. 2 mol% in the feed of fixed bed reactors. The fluidized-bed reactor can be operated above the explosion limits but the selectivity is lower than for a fixed bed process. The synthesis of maleic anhydride is also an example of the intensive process development that has occurred in recent decades. In the 1990s DuPont developed and introduced a so called cataloreactant concept on a technical scale. In this process hydrocarbons are oxidized by a catalyst in a high oxidation state and the catalyst is reduced in this first reaction step. In a second reaction step the catalyst is reoxidized separately. DuPont s circulating reactor-regenerator principle thus limits total oxidation of feed and products by the absence of gas phase oxygen in the reaction step of hydrocarbon oxidation [12]. 

Reduction of the Catalyst. During the catalytic reaction, there is a progressive reduction of the catalyst. Summarized in Fig. 4 is the change in the conversion of hydrocarbon during the catalytic tests in l butene oxidation at 120°C over Pd Og/alumina and the valence state of vanadium determined by chemical analysis. 

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. 

I to 5. 0 mol per mol of hydroperoxide. The presence of sodium naphtheoate, by prevenling side reaction, helps to reduce the excess propylene required (from lO/l to 2/1 in moles). In the Shell technology, epoxidation is catalyzed by metallic oxides (molybdenum, vanadium, titanium, etc.) supported on sih cau The liighiy exothe c reaction takes place around 100 to 130 at 3.5.10 Pa absolute. Hydroperoxide conver> sion is very hi (> 97 per cent). Propylene oxide molar selectivity exceeds 70 per cent and that of the styrene precursors 93 per cent As for propylene, its once-through conversion is about 15 per cent, for a oxide molar selectivity greater than 90 per cent, and the main by-products are dimers and heavier hydrocarbons. 

Other oxidizing agents have been used. Sodium chlorate with vanadium pentoxide catalyst attacks anthracene readily but is not powerful enough for the conversion of hydrocarbons of the naphthalene and phenanthrene series. An acetic acid solution of 30% hydrogen peroxide has also been used. °... 

Characteristic features of vanadium containing heteropoly catalysts for the selective oxidation of hydrocarbons have been described. MAA yield ftom isobutyric acid was successfully enhanced by the stabilization of the vanadium-substituted heteropolyanions by forming cesium salts. As for lower alkane oxidation by using vanadium containing heteropoly catalysts, it was found that the surface of (V0)2P207 was reversibly oxidized to the Xi (8) phase under the reaction conditions of n-butane oxidation. The catalytic properties of cesium salts of 12-heteropolyacids were controlled by the substitution with vanadium, the Cs salt formation, and the addition of transition metal ions. By this way, the yield of MAA from isobutane reached 9.0%. Furthermore, vanadium-substituted 12-molybdates in solution showed 93% conversion on H2O2 basis in hydroxylation of benzene to phenol with 100% selectivity on benzene basis. 

The conversion of methane into formaldehyde, ethylene, and higher hydrocarbons by a process of oxidation has been claimed.1 - A mixture ot air and methane is heated in the presence ot a copper gauze catalyst under pressure to give formaldehyde, which by reaction with methane forms ethylene with removal of water in the presence of catalysts of iron, cobalt, nickel, chromium, vanadium, etc., at 500° C.—and under extremely high pressures. 

As in all conversions of this type, which are autocatalytic, the induction period is relatively long. Catalysts are used to shorten it. These catalysts are soluble salts of cobalt, chromium, vanadium or manganese, usually acetates. The oxidation rate rises with the number of carbon atoms in the hydrocarbon and with the extent to which the chain is linear. Thus, if it is l for ethane, it is as high as 100 for propane, 500 for n-butane and 1000 for n-pentane. 

Hydrocarbon oxidation. A metal catalyst is usually required. By adding bis(/-riphenylsilyl) chromate," diphenylmethane is oxidized to benzophenone, and vanadium-pillared montmorillonite " catalyzes the conversion of arylacetic esters to arylglyoxylic esters by f-BuOOH. The presence of calcined ZnCrOj-hydrotalcite enables the selective generation of benzylic hydroperoxides from aralkanes."... 

Noncatalytic oxidation of the aromatic hydrocarbons is slow at temperatures below 500 C. Benzene is not vigorously oxidized in glass apparatus until temperatures near 700°C are reached. Under similar conditions, toluene is noticeably oxidized at 650 0, and xjdene at 575 0. Even with an active catalyst such as vanadium pentoxide, a temperature of 400-450 0 is required for the commercial oxidation of naphthalene to phthalic anhydride by air. Furthermore, quantities of air from one to three times that theoretically necessary for the conversion must be used. This means that 20-60 moles of air must be used per mole of naphthalene in the reaction mixture. 

The oxidation of inexpensive olefins to maleic anhydride is of economic interest, since apparently it is competitive with the oxidation of benzene to maleic anhydride in some locations. As yet, however, oxidation of C4 hydrocarbons to maleic anhydride has given only about 50 % of the theoretically possible conversion to the desired product. Bretton, Wan, and Dodge 12) examined the oxidation of several C4 olefins over silver and silver oxide catalysts, but found only traces of products other than COg and HgO. With a vanadium catalyst prepared by decomposition of ammonium metavanadate on low-area alumina, substantial yields of intermediate products were found. Longfield and Dixon 57) and Matsumoto and co-workers 156) reported similar results a summary is given in Table XIV. These reactions were usually... 

The same authors 160) reported a process study of ra-butene oxidation to maleic anhydride using an unspecified vanadium catalyst. The catalyst was said to be different from that suitable for benzene oxidation. From the data presented, the reaction appears to be first order in hydrocarbon. A temperature of 430-470° was optimum. On the basis of this study the following conditions for oxidation of w-butenes were recommended butene concentration, 0.9-1.2% by volume temperature, 430-450° gas hourly space velocity, 4000. These conditions give a conversion of butenes of about 80%, a selectivity of 52%, and a yield C X 81100 of 41.6%. This relatively high yield, compared to that reported by others, may in part result from inclusion of about 8% butadiene in the feed. However, Societe d Electrochemie 160a) report C X SjlOO — 49% with butenes over a V-1.2 P catalyst at 470°. 

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