GB688515A - Process for preparing polyhydric alcohols by catalytic reduction of carbohydrates - Google Patents

Abstract

Polyhydric alcohols are produced by the continuous catalytic reduction of carbohydrates in which an aqueous carbohydrate trickles downwardly over a fixed nickel catalyst containing more than 20 per cent by weight of nickel at a temperature above 100 DEG C. in the presence of hydrogen under pressure. A nickel catalyst containing silica, prepared by precipitating nickel from a nickel salt solution as a silicate and mixing it with a carrier, may be used. Another suitable catalyst may be obtained by precipitating nickel from a solution of a nickel salt with an alkali silicate at a temperature above 60 DEG C. and ensuring that the atomic ratio of nickel to silicon is in the range of 1 : 1 to 1 : 3. The precipitate is dried and reduced with hydrogen. Suitable carriers are sintered kieselguhr, alumina, magnesium silicate, magnesium carbonate, magnesium oxide, barium sulphate, majolica, earthenware, active carbon, aluminas, aluminium and various clays, e.g. white bauxite. Glucose solutions are suitable as starting materials. These may be pure or impure solutions such as those obtained by hydrolysing starch as completely as possible. Dextrins may also be used as starting materials, e.g. those obtained by less thorough hydrolysis of starch. In the examples solutions of glucose were reduced according to the invention to sorbitol.ALSO:Catalysts used for the catalytic reduction of carbohydrates to polyhydric alcohols in the presence of hydrogen consist of a fixed nickel catalyst containing more than 20 per cent by weight of nickel. Preferably the catalyst contains silica and is supported on a carrier e.g. sintered kieselguhr, alumina, magnesium silicate, magnesium carbonate, magnesium oxide, barium sulphate, majolica, earthenware, active carbon, natural or artificial aluminas, metallic carriers such as aluminium, and various kinds of clay which may be acid-treated. White bauxite is especially suitable. The catalyst may, for example, be prepared by dissolving soda in water, adding sodium metasilicate and then nickel nitrate solution; the precipitate formed is filtered, dried and powdered: it is then mixed with white Surinam bauxite and graphite powder as lubricant. The mixture is tableted and reduced in hydrogen, Alternatively, the catalyst may be prepared by precipitating nickel from a solution of a nickel salt with an alkali silicate ensuring that the Ni : Si ratio is between 1 : 1 and 1 : 3 so that a nickel compound of the montmorillonite type is formed and at least half of the precipitate consists of nickel montmorillonite; the precipitate is filtered, dried and reduced with hydrogen.