GB590479A - Production of olefin oxides - Google Patents

Abstract

Silver catalysts for use in catalytic production of olefine oxides comprise silver metal and silicon, with or without a bonding material such as clay or alumina. The silica may be present in the amorphous or crystalline condition. Porous aggregates of catalyst are conveniently prepared by fusing the silicon with a ceramic bonding material and crushing the resulting mass into chips or particles of the desired size prior to depositing thereon the metallic silver. The deposition may be effected by impregnating the catalyst base prepared as above with a solution or suspension of a reducible silver compound. The preferred material is silver nitrate, but the oxide, chloride, carbonate, cyanide or salts of carboxylic acids may be used. The reduction may be carried out by means of hydrogen or a gaseous reducing agent containing hydrogen, or by heat alone. If a particularly active catalyst is required, the carrier material is impregnated with a thermally decomposable organic compound of silver such as a silver salt of a carboxylic acid, and the mass heated. Compounds mentioned are silver acetate, propionate, butyrate or oxalate. A preferred type of catalyst is prepared by reducing an ammoniacal solution or suspension of a silver compound. This is carried out by treating the carrier or support containing silicon with a silver salt, then with ammonia or ammonium hydroxide, then with a strongly alkaline reagent such as sodium hydroxide, then with a further quantity of ammonia or ammonium hydroxide, and finally with a reducing agent such as glucose. Such a procedure gives a deposit of silver in the form of a mirror. The order of addition of ingredients may be modified if desired. The activity of the catalysts may be increased by the addition of a compound known to increase or modify the action of silver metal. Compounds mentioned for this purpose include metals such as gold, copper, platinum, nickel and iron, metal oxides, hydroxides and carbonates, particularly of the alkali or alkaline earth metals, and some halogen compounds. In some cases the catalyst activity is further increased by the addition of a sodium compound which may be added as an aqueous solution which is poured over the silvered supports. It is stated that a more active catalyst is formed if the silver is deposited on a support which has been previously treated with a dilute solution of hydrofluoric acid. In an example a catalyst is prepared by adding a silver nitrate solution to washed crystalline silicon followed by ammonium hydroxide and sodium hydroxide. A reducing solution prepared by adding ethyl alcohol and a small amount of concentrated nitric acid to an aqueous cane sugar solution and boiling for about five minutes was then added. The catalyst mass was allowed to stand, the liquids decanted and the catalyst washed.ALSO:Olefine oxides are prepared by reacting an olefine with oxygen in the presence of a solid catalyst comprising silver metal and silicon as a support for the silver, with or without a bonding material such as clay or alumina. The silicon may be present in the amorphous or the crystalline condition. Porous aggregates of catalyst are conveniently prepared by fusing the silicon with a ceramic bonding material and crushing the resulting mass into chips or particles of the desired size prior to depositing thereon the metallic silver. The deposition may be effected by impregnating the catalyst base, prepared as above, with a solution or suspension of a reducible silver compound. The preferred material is silver nitrate, but the oxide, chloride, carbonate, cyanide, or salts of carboxylic acids may be used. The reduction may be carried out by means of hydrogen, or a gaseous reducing agent containing hydrogen, or by heat alone. If a particularly active catalyst is required, the carrier material is impregnated with a thermally decomposable organic compound of silver, such as a silver salt of a carboxylic acid and the mass heated. Compounds mentioned are silver acetate, propionate, butyrate or oxalate. A preferred type of catalyst is prepared by reducing an ammoniacal solution or suspension of a silver compound. This is carried out by treating the carrier or support containing silicon with a silver salt, then with ammonia or ammonium hydroxide, then with a strongly alkaline reagent such as sodium hydroxide, then with a further quantity of ammonia or ammonium hydroxide, and finally with a reducing agent such as glucose. Such a procedure gives a deposit of silver in the form of a mirror. The order of addition of the ingredients may be modified if desired. The activity of the catalysts may be increased by the addition of a compound known to increase or modify the action of silver metal. Compounds mentioned for this purpose include metals such as gold, copper, platinum, nickel and iron, metal oxides, hydroxides and carbonates, particularly of the alkali or alkaline earth metals, and some halogen compounds. In some cases, the catalyst activity is further increased by the addition of a sodium compound which may be added as an aqueous solution which is poured over the silvered supports. It is stated that a more active catalyst is formed if the silver is deposited on a support which has been previously treated with a dilute solution of hydrofluoric acid. The olefins which form the starting material for the present invention may be obtained from any petroleum refining operation such as distillation, thermal cracking, hydrogenation, dehydrogenation or polymerization of hydrocarbon fluids. It is preferred to use oxygen in slight excess of the stoichiometric amount. The oxygen may be introduced as such, or in admixture with diluents such as nitrogen steam or carbon dioxide. Temperatures used are in the range of from 100-500 DEG C., and the preferred pressure is atmospheric. In an example, silver nitrate solution was added to washed crystalline silicon followed by ammonium hydroxide and sodium hydroxide. A reducing solution prepared by adding ethyl alcohol and a small amount of concentrated nitric acid to an aqueous cane sugar solution and boiling for about five minutes was then added. The catalyst mass was allowed to stand, the liquids decanted and the catalyst washed. An ethylene-air mixture was then passed over the catalyst at about 300 DEG C. at a rate of 60 ccs. per minute, to give a maximum yield of 80 per cent of ethylene oxide based on the total ethylene consumed.