GB804132A - Process for the dehydrogenation of alcohols - Google Patents

Abstract

The invention comprises catalysts, optionally applied on to carriers, consisting of reduced copper containing small amounts of unreduced copper oxide and small amounts of chromium and/or at least one chromium oxide and an alkali metal oxide, the chromium content amounting to between 0.5 and 3 per cent by weight calculated as chromium oxide Cr2O3 based on the total amount of chromium and copper calculated, as oxides Cr2O3 and CuO, and the alkali metal oxide corresponding to at least double and at most six times the molar quantity of the chromium oxide Cr2O3. The catalysts may be prepared, for example, by impregnating reducible copper compounds, such as copper hydroxide, cuprous oxide or cupric oxide with an alkali metal salt of chromic or perchromic acid, the compounds being applied, if required, on to carriers and then dried; the material thus obtained is reduced, for instance by treatment with hydrogen at 200-300 DEG C. resulting in the substantial reduction of the copper oxide into copper. Suitable carriers are, for example, pumice and diatomaceous earth. If no carriers is present a binder, e.g. an aqueous solution of methyl cellulose, may be added to facilitate the production of shaped bodies or tablets.ALSO:Aldehydes or ketones are prepared by the dehydrogenation of saturated aliphatic or cycloaliphatic primary or secondary alcohols containing 2-6 carbon atoms at 250 DEG to 380 DEG C. in the presence of a copper catalyst optionally applied on to carriers, the copper catalyst being a reduced copper catalyst containing small amounts of copper oxide as well as 0.5 to 3 per cent by weight of chromium and/or a chromium oxide, the total chromium content being calculated as Cr2O3 and being referred to the total quantity of the copper and chromium content, calculated as oxides CuO and Cr2O3, and containing also from double to six times the molar quantity of alkali metal oxide referred to the chromium oxide. The catalyst may be prepared, for example, by impregnating reducible copper compounds, such as copper hydroxide, cuprous oxide or cupric oxide with an alkali metal salt of chromic or perchromic acid, the compounds being applied, if required, on to carriers, and then dried. The material, thus obtained, is reduced advantageously before the start of the reaction by heating with hydrogen at low temperatures. Any saturated primary or secondary alcohol, e.g. ethyl alcohol, isopropyl alcohol, butanol, secondary butanol, primary or secondary pentanols, cyclopentanol and cyclohexanol, may be used as starting material. For the dehydrogenation of secondary alcohols to the corresponding ketones preferred temperatures are in the range 250-360 DEG C. and for the dehydrogenation of primary alcohols to the corresponding aldehydes preferred temperatures are in the range 280-340 DEG C. In the examples: (a) isopropyl alcohol is passed over a catalyst, consisting of copper oxide which is present for the most part in reduced form, chromic oxide and sodium oxide on a pumic support, to give acetone; and (b) ethyl alcohol is passed over a similar catalyst to give acetaldehyde.