GB465199A - Improvements in or relating to the manufacture of acetaldehyde by hydration of acetylene and the production of a catalyst for use in this process - Google Patents

Abstract

Acetaldehyde is prepared by subjecting acetylene to reaction with steam in the presence of a cadmium metaphosphate catalyst in the form of a compact mass of microscopic particles. The volume of steam may be from 2 to 15 times that of the acetylene. The latter may be pure or diluted with other gases, for example, hydrogen or hydrocarbons such as methane. Commercial gas mixtures such as are obtained in the cracking of hydrocarbons, and containing say less than 10 per cent of acetylene may be used. An example discloses the use of an acetylene-hydrogen mixture containing 7,6 per cent of the former. The reaction is effected at 250--350 DEG C., the gases preheated if desired, being passed over the catalyst contained for example in an iron tube. The cadmium metaphosphate is prepared by reacting orthophosphoric acid or a substance yielding orthophosphoric acid, for example, an ammonium orthophosphate or a mono- or dialkyl ester of orthophosphoric acid in amount necessary to form acid cadmium orthophosphate, with a cadmium compound, and evaporating water from and heating the reaction product to form the metaphosphate. Thus, orthophosphoric acid of sp. gr. 1,75 is slowly added to a cream of cadmium carbonate at 60--80 DEG C., with stirring. Stirring is continued whilst the mixture is evaporated to a pasty mass. The product is dried at 250--350 DEG C., broken into pieces, and preferably heated to incipient fusion. The particles should be of less than 0,01 mm. diameter. The catalyst may be reactivated by blowing hot air thereover, if desired after sieving it free from dust. The catalyst should not contain foreign substances, for example, alkali metal compounds. For this reason, monosodium orthophosphate cannot be used in its preparation.ALSO:Cadmium metaphosphate in the form of a compact mass of microscopic particles for use as a catalyst in the reaction between acetylene and steam to produce acetaldehyde is prepared by reacting orthophosphoric acid or a substance yielding orthophosphoric acid, for example, an ammonium orthophosphate or a mono- or dialkyl ester of orthophosphoric acid in amount necessary to form acid cadmium orthophosphate, with a cadmium compound, and evaporating water from and heating the reaction product to form the metaphosphate. Thus, orthophosphoric acid of sp. gr. 1,75 is slowly added to a cream of cadmium carbonate at 60--80 DEG C., with stirring. Stirring is continued whilst the mixture is evaporated to a pasty mass. The product is dried at 250--350 DEG C., broken into pieces, and preferably heated to incipient fushion. The particles should be of less than 0,01 mm. diameter. The catalyst may be reactivated by blowing hot air thereover, if desired after sieving it free from dust. The catalyst should not contain foreign substances, for example, alkali metal compounds. For this reason, monosodium orthophosphate cannot be used in its preparation.