Zinc chromite hydrogenation catalyst

Hydrogenation. Gas-phase catalytic hydrogenation of succinic anhydride yields y-butyrolactone [96-48-0] (GBL), tetrahydrofiiran [109-99-9] (THF), 1,4-butanediol (BDO), or a mixture of these products, depending on the experimental conditions. Catalysts mentioned in the Hterature include copper chromites with various additives (72), copper—zinc oxides with promoters (73—75), and mthenium (76). The same products are obtained by hquid-phase hydrogenation catalysts used include Pd with various modifiers on various carriers (77—80), Ru on C (81) or Ru complexes (82,83), Rh on C (79), Cu—Co—Mn oxides (84), Co—Ni—Re oxides (85), Cu—Ti oxides (86), Ca—Mo—Ni on diatomaceous earth (87), and Mo—Ba—Re oxides (88). Chemical reduction of succinic anhydride to GBL or THF can be performed with 2-propanol in the presence of Zr02 catalyst (89,90). 

The concentration theory completely fails to explain the selective nature of catalysis. Why, for example, does formic acid decompose into hydrogen and carbon dioxide with a zinc oxide catalyst, whereas with titanium oxide, it breaks down to carbon monoxide and water Or, to quote another example, why do carbon monoxide and hydrogen form methane in the presence of nickel, whereas quantitative yields of methanol are produced with a zinc chromite catalyst.6... 

Catalysts used for the hydrogenation step are usually copper chromite formulations, although copper oxide/zinc oxide catalysts have also been used. The process accounts for about half of the copper chromite catalysts used commer-dally. Both acid group and double bonds in the long carbon chain are hydrogenated during the reaction, which produces a saturated alcohol. When an unsaturated fatty alcohol is required, a more selective zinc chromite catalyst may be used. 

The catalyst copper chromite, used in all three processes, also hydrogenates all double bonds in the chain, and completely saturated alcohols are the result. With use of a zinc-containing mixed catalyst, the double bonds in unsaturated starting materials are retained to an extent of 98%. Highly unsaturated alcohols are recovered. 

Tishchenko (79), using a modified form of Raney nickel, obtained a 95.7 % yield of camphor from the dehydrogenation of borneol. Rutovskii, (80) received a 93.5% yield of camphor with Raney alloy. Reeves and Adkins (81), studying the dehydrogenation of primary alcohols, removed the hydrogen with ethylene. It was found that, though Raney nickel could be used for a catalyst for the reaction, the yields were low and, in general, the Raney nickel was inferior to a catalyst composed of copper, zinc, nickel, and barium chromite. 

Fatty alcohols are obtained by direct hydrogenation of fatty acids or by hydrogenation of fatty acid esters. Typically, this is performed over copper catalysts at elevated temperature (170°C-270°C) and pressure (40-300 bar hydrogen) [26], By this route, completely saturated fatty alcohols are produced. In the past, unsaturated fatty alcohols were produced via hydrolysis of whale oil (a natural wax occurring in whale blubber) or by reduction of waxes with sodium (Bouveault-Blanc reduction). Today, they can be obtained by selective hydrogenation at even higher temperatures (250°C-280°C), but lower pressure up to 25 bar over metal oxides (zinc oxide, chromium oxide, iron oxide, or cadmium oxide) or partially deactivated copper chromite catalysts [26],... 

The fractionated methyl esters can be converted into fatty alcohols by the high-pressure hydrogenation process in the presence of a catalyst. Usually, copper chromite catalyst is used. Copper chromite catalyst also converts any unsamrated carbon double bonds so that only saturated fatty alcohols are formed. If unsamrated fatty alcohols are desired, a special zinc-bearing catalyst is employed. 

Chromium copper arsenate as a wood preservative (uses 62% of the chromic acid in the United States) Catalyst for polymerization of ethylene Copper chromite catalyst for hydrogenation Zinc chromate near the zinc anode gives batteries 50-80% more shelf life... 

The search is on for catalysts to replace those containing toxic heavy metals. The addition of hydrogen chloride to acetylene to form vinyl chloride is catalyzed by mercuric chloride. Rhodium (III) chloride on activated carbon works just as well and is much less toxic 97 It should be tried also in other addition reactions of acetylene as well as in trans-esteriflcation reactions of vinyl acetate. The reduction of 2 ethyl-2-hexenal to 2-ethylhexanol can be catalyzed by a mixture of copper, zinc, manganese, and aluminum oxides in 100% yield.98 This is said to be a replacement for carcinogenic copper chromite. In Reaction 4.15, the amount of toxic chromium(II) chloride has been reduced from stoichiometric to catalytic (9-15 mol% chromium(II) chloride) by the addition of manganese metal.99... 

These reductive deaminations can be effected by hydrogenation over Raney nickel, palladium, or copper chromite catalysts, and also by means of sodium amalgam or zinc dust in aqueous-methanolic sodium hydroxide.344k... 

Hydrogenation is generally carried out at tanperatures of 250-280°C and pressures of 20-25 MPa. Catalysts include zinc oxide in conjunction with aluminum oxide, chromium oxide, or iron oxide, and possibly, other promoters copper chromite whose activity has been reduced by the addition of cadmium compounds and cadmium oxide on an alumina carrier. Selective hydrogenation can also be carried out in a homogenous phase with metallic soaps as catalysts. 

The main use of copper oxide/zinc oxide catalysts has been in dehydrogenation and hydrogenation reactions. These include the dehydrogenation of isopropyl alcohol to acetone as well as the hydrogenation of oxo-alcohols and fatty acid methyl esters. Although in many processes copper chromite catalysts are preferred to copper oxide/zinc oxide, the environmental problems involved in disposing of chromium wastes may reverse the situation. 

Fixed bed processes can be used for the l drogenation of fatty acid methyl esters. The methyl esters can be prepared direcdy from the fatty acid or by tra 5 -esterification of the triglyceride with methanol. The hydrogenation is carried out in a bed of solid copper chromite catalyst, which usually loses activity after operating for 3-6 months. Copper oxide/zinc oxide catalysts have also been used. 

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