Patent GB-260305-A (GB)
Abstract: 260,305. Consortium f³r Elektrochemische Industrie Ges. Oct. 26, 1925, [Convention date]. Acetaldehyde. - The manufacture of acetaldehyde by the reaction between acetylene and water in presence of a mercury compound is improved by conducting the reaction in the presence of an organic solvent for acetylene, containing hydroxyl or carbonyl groups, but no carboxyl group. Suitable solvents are mono- and polyhydric alcohols, phenols, and ketones. Substances capable of yielding hydroxyl or carbonyl compounds, e.g. acetals or esters, may also be used. The acetaldehyde may be separated from the mixture of vapours leaving the reaction vessel by fractional condensation, the condensed alcohol or other solvent being returned to the vessel. The separation of the acetaldehyde may be promoted by rapid vaporization of the reaction mixture, which may be effected by passing a current of gas, particularly an excess of acetylene, through the mixture. The excess of acetylene is freed from acetaldehyde by a condensation or washing process and returned to the apparatus. The flow of acetylene through the mixture may also serve for purposes of agitation and temperature regulation, the surplus heat evolved by the reaction being absorbed by vapourization. The process may also be carried out under pressure, and at a high temperature. As catalysts. inorganic or organic mercury salts may be used, in the presence or absence of free acid. The reaction mixture may be circulated, whereby its composition and temperature may be more effectively controlled and the spent or partially spent catalyst may be removed continuously or periodically and regenerated catalyst returned to the system. In one example, acetylene is continuously circulated through a vessel provided with a stirrer and fractionating column, and containing an emulsion of mercury sulphate in water and ethyl alcohol, further quantities of an emulsion of mercury sulphate in water being added, partly continuously and partly periodically. The excess of acetylene, freed from acetaldehvde, is returned to the reaction vessel by means of a circulating pump, fresh acetylene being added according to its consumption, while a part of the circulating gas is removed according to the impurities it contains. Acetaldehyde is washed out from the acetylene and recovered by distilling the wash water, the latter fractions being returned to the reaction mixture, while the residue is used again for cooling. The reaction mixture remains practically free from resin, and the mercury separating can be readily removed and regenerated. In another example, methanol is used as the solvent. In a third example, liquid is removed continuously during the reaction, passes into a settling chamber where the spent catalyst separates, is emulsified with regenerated mercury sulphate, and is returned to the reaction chamber by means of a pump. The mercury separating in the settling vessel is dissolved in nitric acid, converted into sulphate, and returned to the emulsifying apparatus. The regeneration of the catalyst may be carried out in a. continuous manner by adding an iron salt, chromate or the like to the circulating reaction liquid, or it may be regenerated during the reaction by means of an electrolytic oxidation process. The Specification as open to inspection under Sect. 91 (3) (a) also includes the use of carboxylic acids as the solvents for acetylene. This subjectmatter does not appear in the Specification as accepted.