Chromium oxide dehydrogenation catalyst

Jibril, B.Y. Propane oxidative dehydrogenation over chromium oxide-based catalysts. Appl. Catal. A General 2004, 264, 193-202. 

The first industrial plant for the dehydrogenation of butane to butenes was built by COP I Universal Oil Products) on the iCl (Imperial Chemical Industries) complex at Billingham (United Kingdom) in 1939/1940. The UOP process featured a multitube reactor operating with a chromium oxide/aloinma catalyst, at 570°C and 0.8.10 Pa absolute at the inlet, with a pressure drop of 0l5.10 Pa absolute in the tubes (5 m long, 7.5 cm diameter). Once-through conversion was 215 per cent with a molar selectivity of 80 to 90 per cent... 

B. Grzybowska, J. Sloczynski, R. Grabowski, K. Wcislo, A. Kozlowska, J. Stoch and J. Zielinski, Chromium oxide alumina catalysts in oxidative dehydrogenation of isobutane, J. Catal, 178(2), 687-700, 1998. 

J. Sloczynski, B. Grzybowska, R. Grabowski, A. Kozlowska and K. Wcislo, Oxygen adsorption and catalytic performance in oxidative dehydrogenation of isobutane on chromium oxide-based catalysts, Phys. Chem. Chem. Phys., 1(2), 333-339, 1999. A. Bielanski and J. Haber, Oxygen in catalysis, Dekker New York, 1991. 

Zhang X, Yue Y, Gao Z (2002) Chromium oxide supported on mesoporous SBA-15 as propane dehydrogenation and oxidative dehydrogenation catalysts. Catal Lett 83 19-25... 

Dehydrogenation of /i-Butane. Dehydrogenation of / -butane [106-97-8] via the Houdry process is carried out under partial vacuum, 35—75 kPa (5—11 psi), at about 535—650°C with a fixed-bed catalyst. The catalyst consists of aluminum oxide and chromium oxide as the principal components. The reaction is endothermic and the cycle life of the catalyst is about 10 minutes because of coke buildup. Several parallel reactors are needed in the plant to allow for continuous operation with catalyst regeneration. Thermodynamics limits the conversion to about 30—40% and the ultimate yield is 60—65 wt % (233). 

The reaction kinetics for the dehydrogenation of ethanol are also weU documented (309—312). The vapor-phase dehydrogenation of ethanol ia the presence of a chromium-activated copper catalyst at 280—340°C produces acetaldehyde ia a yield of 89% and a conversion of 75% per pass (313). Other catalysts used iaclude neodymium oxide and samarium hydroxide (314). 

Reactions over chromium oxide catalysts are often carried out without the addition of hydrogen to the reaction mixture, since this addition tends to reduce the catalytic activity. Thus, since chromium oxide is highly active for dehydrogenation, under the usual reaction conditions (temperature >500°C) extensive olefin formation occurs. In the following discussion we shall, in the main, be concerned only with skeletally distinguished products. Information about reaction pathways has been obtained by a study of the reaction product distribution from unlabeled (e.g. 89, 3, 118, 184-186, 38, 187) as well as from 14C-labeled reactants (89, 87, 88, 91-95, 98, 188, 189). The main mechanistic conclusions may be summarized. Although some skeletal isomerization occurs, chromium oxide catalysts are, on the whole, less efficient for skeletal isomerization than are platinum catalysts. Cyclic C5 products are of never more than very minor impor-... 

Hitachi Cable Ltd. (35) has claimed that dehydrogenation catalysts, exemplified by chromium oxide—zinc oxide, iron oxide, zinc oxide, and aluminum oxide—manganese oxide inhibit drip and reduce flammability of a polyolefin mainly flame retarded with ATH or magnesium hydroxide. Proprietary grades of ATH and Mg(OH)2 are on the market which contain small amounts of other metal oxides to increase char, possibly by this mechanism. 

In the middle thirties the reactions of naphtha and certain compounds known to be present in naphtha were being studied in university and industrial laboratories. One of the problems was to find a catalyst that was capable of synthesizing an aromatic from a paraffin. It was reasoned that the hydrogenation-dehydrogenation oxide-type catalysts such as molybdenum oxide and chromium might possess suitable activity at temperatures well below those employed in thermal reforming. 

In a more recent study of the dehydrogenation of cyclohexane to benzene over a chromium oxide catalyst at 450°C., Balandin and coworkers (Dl) concluded that benzene was formed by two routes. One of these, the so-called consecutive route, involves cyclohexene as a gas phase intermediate, while the other proceeds by a direct route in which intermediate products are not formed in the gas phase. It was concluded that the latter route played a larger role in the reaction than did the former. These conclusions were derived from experiments on mixtures of cyclohexane and Cl4-labeled cyclohexene, which made it possible to evaluate the individual rates Wi, BY, Wt, and Wz in the reaction scheme... 

In contrast with chromia supported on alumina, pure chromium oxide is a poor catalyst for the nitroxidation of hydrocarbons as it deactivated rapidly with time on stream and favoured deep oxidation at the steady state (ref. 3), althouoh it exhibits good dehydrogenation properties (ref. 2). It was concluded that alumina prevents the segregation of chromia phase and thus favours the formation of... 

A copper-chromium oxide on pumice catalyst has particular value for the dehydrogenation of primary and secondary alcohols to the corresponding carbonyl compounds (see Section 5.6.1, p. 581). Dissolve 10.4g of barium nitrate (AnalaR) in 280 ml of water at about 80 °C and add to this hot solution 87 g of copper(n) nitrate trihydrate (AnalaR) stir the mixture and heat until a homogeneous solution results. Prepare a solution of 50.4 g of recrystallised ammonium dichromate in a mixture of 200 ml of water and 75 ml of concentrated ammonia solution (d 0.880). To the ammonium chromate solution at 25-30 °C add the hot (80 °C) nitrate solution in a thin stream with stirring. Allow the mixture to cool and filter off the yellowish-brown precipitate with suction press with a glass stopper and suck as dry as possbile. Transfer the... 

Satisfactory yields of simple aldehydes are also usually obtained when the vapour of the primary alcohol is dehydrogenated by passage over a heated catalyst of copper-chromium oxide deposited on pumice (Expt 5.75). 

Styrene (phenyl ethylene, vinyl benzene freezing point -30.6°C, boiling point 145°C, density 0.9059, flash point 31.4°C) is made from ethylbenzene by dehydrogenation at high temperature (630°C) with various metal oxides as catalysts, including zinc, chromium, iron, or magnesium oxides coated on activated carbon, alumina, or bauxite (Fig. 1). Iron oxide on potassium carbonate is also used. 

In the discussion of the subject Balandin mentions (15) that Fischer previously postulated that methylene radicals may be produced as an intermediate in the formation of hydrocarbons by his method (116). This mechanism of carbon deposition on platinum supported on oxides of nickel and chromium (oxidized nichrome) through the intermediate formation of methylenes was thought by Balandin to be similar to the mechanism of dehydrogenation over this type of catalyst in that both occur on the boundaries of platinum-nickel and of platinum-chromia and were brought in agreement by him with his multiplet theory (26). 

Metal chromium(III) oxides are often used as catalysts, especially dehydrogenation catalysts hence it is important to prepare them as powders.5 The synthesis described here involves the double-decomposition reaction between lithium chromium(III) oxide and molten divalent metal chlorides, and produces finely divided powders. 

The dehydrogenation catalyst must be sufhciently active to allow for very short contact times and the use of low temperatures, to minimize thermal cracking reactions. Carbon deposits are eliminated by heatihg in the presence of a gas containing oxygen. -This means that the catalyst must be thermally stable to avoid being deactivated during the oxidation of the deposits. The best catalysts contain alamina and chromium oxide, but these cannot be employed in the presence of steam. Operations are conducted at a temperature between 550 and 700 C, and low pressure, less than 0.1.10 Pa absolute. 

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