GB718305A - Improvements in or relating to catalytic reduction - Google Patents

Abstract

Anthraquinhydrones or anthraquinols are formed by reduction with hydrogen of a solution of an anthraquinone in a solvent mixture containing an aliphatic ester of a cyclohexanol or of an alkyl cyclohexanol in the presence of a palladium catalyst which has a particle size corresponding to a screen aperture between 0.001 and 0.1 inch and is in free suspension in the solution, the catalyst having been formed by the reduction of one or more palladium compounds. The reduction is described as part of a cyclic process for the preparation of hydrogen peroxide (see Group III). Cyclohexanol acetate or propionate or methyl cyclohexanol acetate or propionate are suitable solvents, and are used mixed with a liquid hydrocarbon, e.g. benzene, toluene, or xylene. The catalyst is preferably supported on alumina and may be prepared by p the method described in Specification 718,306, [Group III]. The reduction may be carried out in the hydrogenator described in Specification 718,307. Catalyst may be added to the hydrogenator during the process to maintain a constant rate of reduction. The anthraquinone used may contain alkyl and/or aryl substituent groups, 2-ethyl anthraquinone and 2-tertiarybutyl anthraquinone being mentioned. The process claimed in Specification 718,307 is disclaimed. Specifications 508,081, 686,574, and 695,779, [all in Group III], also are referred to.ALSO:Hydrogen peroxide is prepared by a cyclic process in which an anthraquinhydrone or anthraquinol is autoxidized with oxygen in a solvent containing an aliphatic ester of a cyclohexanol or an alkyl cyclohexanol, hydrogen peroxide is removed, the anthraquinone formed in solution is reduced by hydrogen in the presence of a palladium catalyst suspended in the solution, and the reduced solution is separated from the catalyst and returned for oxidation; the catalyst has a particle size corresponding to a screen aperture between 0.001 and 0.1 inch and is prepared by reduction of a palladium compounds. Cyclohexanol acetate or propionate or methylcyclohexanol acetate or propionate are suitable solvents, and are used mixed with a liquid hydrocarbon, e.g. benzene, toluene, or xylene. Hydrogen peroxide is recovered by countercurrent extraction of the solution with water in a plate column. The catalyst is preferably supported on alumina and may be prepared by the method described in Specification 718,306 or by evaporation of an aqueous solution of sodium chloropalladite in the presence of finely divided precipitated alumina. Catalysts are also prepared by impregnating magnesium oxide and activated charcoal with palladium chloride solution. The reduction may be carried out in the hydrogenator described in Specification 718,307. Catalyst may be added to the hydrogenator during the process to maintain a constant rate of reduction. Regeneration of the catalyst is effected by washing with benzene, heating in an oxygen-containing gas, and then reducing. The anthraquinone used may contain alkyl and/or aryl substituent groups, 2-ethyl anthraquinone and 2-tertiary-butyl anthraquinone being mentioned. The process claimed in Specification 718,307 is disclaimed. Specifications 508,081, 686.574 and 695,779 also are referred to.