GB832297A - Process and catalyst for the dehydrogenation of hydrocarbons - Google Patents

Abstract

A process for the dehydrogenation of a hydrocarbon comprises contacting each mole. thereof with 2 to 30 moles. of steam at not less than 580 DEG C. and with a catalyst containing:-(i) one or more iron oxides having an average degree of oxidation between Fe3O4 and Fe2O3, the total iron oxide content being at least 35% calculated as Fe2O3; (ii) at least one potassium compound other than the chloride which is either the carbonate or convertible thereto under the reaction conditions in an amount equivalent to at least 6% K2O; and (iii) a phosphate, or a compound which forms a phosphate under the reaction conditions, in an amount equivalent to 0.2 to 9% of phosphate groups, the percentages being by weight of the Fe2O3 + K2O + phosphate present. Potassium compounds specified are the hydroxide, nitrate, bicarbonate, sulphate and acetate. The phosphate may be added as an alkali metal or alkaline earth phosphate, e.g. tripotassium or dipotassium hydrogen phosphate, phosphoric acid, or phosphorus pentoxide, the K2O content of potassium phosphates counting towards (ii). Other ingredients mentioned are 0.5 to 4% of oxide of heavy metals, e.g. Cr, Mn, Bi, W, Mo and Ce. The catalyst ingredients may be compounded by mixing (e.g. ball-milling), coprecipitation, or impregnation of the iron oxide with the other components. The iron oxide may be calcined, before or after compounding with the other components at 550 DEG to 1050 DEG C. for at least one hour. The process is applicable to the dehydrogenation of n-butenes to butadiene and ethyl benzene to styrene. At dehydrogenation temperatures of 580 DEG to 700 DEG C. the catalysts are autoregenerative, side reactions producing the small amount of carbon dioxide required. In an example, n-butene-2 is dehydrogenated (35% conversion) with catalysts consisting of 62% Fe2O3, 2.2% Cr2O3, potassium phosphate and carbonate equivalent to 24.1% K2O and the following percentages of K3PO4:-2.2, 4.6, 7.5, 9.0, and 26.9, the K2CO3 content being varied to maintain the K2O content at 22.4% at 620-660 DEG C., 500 GHSV, and a steam : butene molar ratio of 12.ALSO:A process for the dehydrogenation of a hydrocarbon comprises contacting each mole. thereof with 2 to 30 moles. of steam at not less than 580 DEG C. and with a catalyst containing: (i) one or more iron oxides having an average degree of oxidation between Fe3O4 and Fe2O3, the total iron oxide content being at least 35% calculated as Fe2O3; (ii) at least one potassium compound other than the chloride which is either the carbonate or convertible thereto under the reaction conditions in an amount equivalent to at least 6% K2O; and (iii) a phosphate, or a compound which forms a phosphate under the reaction conditions, in amount equivalent of 0.2 to 9% of phosphate groups, the percentages being by weight of the Fe2O3+K2O+phosphate present. Potassium compounds specified are the hydroxide, nitrate, bicarbonate, sulphate and acetate. Other ingredients mentioned are 0.5 to 4% of oxide of heavy metals, e.g. Cr, Mn, Bi, W, Mo and Ce. The iron oxide may be calcined, before or after compounding with the other components at 550 DEG to 1050 DEG C. for at least one hour. The process is applicable to the dehydrogenation of n-butenes to butadiene and ethyl benzene to styrene. At dehydrogenation temperatures of 580 DEG to 700 DEG C. the catalysts are autoregenerative, side reactions producing the small amount of carbon dioxide required. In an example, n-butene-2 is dehydrogenated (35% conversion) with catalysts consisting of 62% Fe2O3, 2.2% Cr2O3, potassium phosphate and carbonate equivalent to 22.4% K2O, and the following percentage of K3PO4: 2.2, 4.6, 7.5, 9.0 and 26.9, the K2CO3 content being varied to maintain the K2O content at 22.4% at 620-660 DEG C., 500 GHSV, and a steam : butene molar ratio of 12.