GB520170A - Improvement in activation of silver catalysts - Google Patents

Abstract

520,170. Preparation of catalysts; olefine oxides. CARBIDE & CARBON CHEMICALS CORPORATION. Oct. 14, 1938, No. 29757 Convention date, Oct. 30, 1937. [Class 1 (i)] [Also in Group IV] Silver catalysts, particularly for use in the direct oxidation of olefines to olefine oxides at temperatures of 150‹-400‹C., are activated by treatment with a compound acting as a repressant which at small concentrations is gaseous between 150‹ and 400‹C. and which will react with the silver surface to form compounds capable of conversion to silver oxide or hydroxide by metal hydroxides, followed by treatment with barium or strontium hydroxide. Suitable repressants are ethylene dichloride, chlorine, sulphur chloride, sulphur trioxide, nitrogen peroxide or other chlorine-containing or acid-forming material. Preferably the silver catalyst has a roughened surface and it may be supported on granular inert material, e.g. silica stone, ceramically bonded alumina or sandstone, generally in the proportion of 4-20 per cent. by weight. The increase of activity is dependent upon the number of times the treatment with repressant and hydroxide is performed. This treatment is preferably carried out during the actual conversion of the olefines. The reaction may be carried out in iron tubes, wound for electrical heating and the temperature is regulated by boiling an organic liquid in a surrounding jacket. Half of the tube is packed with silica stone as a preheating section, and the gas mixture preferably contains 10 per cent. ethylene and 90 per cent. air. Examples describe the results obtained with catalysts containing silver, silver and barium peroxide, silver and strontium hydroxide initially, then after the addition of a repressant such as ethylene dichloride or sulphur trioxide and finally after activation one or several times with barium or strontium hydroxides. After several reactivations, the efficiency decreases and may be restored by leaching with hot water and repeating the activation. The reaction may be carried out at normal, increased or decreased pressure. Specifications 517,332, 517,333 and 518,823 are referred to.