GB366022A - Manufacture of acetic acid - Google Patents

Abstract

In the oxidation of liquid acetaldehyde to acetic acid the gases or vapours leaving the reaction vessel are scrubbed with a liquid, and the scrubbings passed to the reaction liquor. Preferably the scrubbing is effected continuously during the oxidation, e.g. by means of a condenser, scrubbing tower, or the like through which the scrubbing liquor flows and arranged so that the scrubbing liquor flows therefrom into the vapour space above the liquid in the reaction vessel. Several such scrubbing vessels may be employed, arranged for instance in series, in which case the scrubbing liquid may be passed successively through the vessels of the series. Any liquid which does not deleteriously affect the oxidation may be used for the scrubbing, but it is preferred to use acetic acid, particularly glacial acetic acid or a reaction liquor containing acetic acid, particularly a liquor containing 40-50 per cent of acetic acid. The acetaldehyde to be oxidized need not be pure, e.g. mixtures of acetaldehyde and acetic acid may be treated, but the aldehyde should be as free as possible from water. The oxygen may be pure or admixed with inert gases, as in air, and is preferably introduced into the reaction liquid in the form of fine bubbles, this finely divided state being further promoted by agitation of the liquid. The reaction liquor may contain any catalyst capable of promoting the oxidation of aldehyde to acetic acid, e.g. manganese compounds such as manganous acetate, uranium dioxide, ferric oxide, ferric acetate, chromium sesquioxide, or vanadium pentoxide, or the catalysts described in Specifications 154,304 and 154,680, [both in Class 2 (iii), Dyes &c.], i.e. china clay or kaolin, or the residue which remains after igniting animal charcoal, or mixtures thereof with sodium acetate. The oxidation may be performed under ordinary or raised pressures, for example 20-40 pounds per square inch, or more, the use of raised pressure being especially useful in cases where air or other gaseous mixture containing oxygen is employed. The temperature may be between 0 DEG and 50 DEG C., low temperatures up to 20 DEG C. being useful when oxygen is employed, while with air or like mixtures temperatures between 20 DEG and 50 DEG C. are employed. During the initial stages, and intermittently throughout the reaction, the vapour space or the reaction space or both may be cooled to low temperatures, e.g. 0-5 DEG C., and the scrubbing vessels are preferably provided with water or brine cooling. Any aldehyde escaping condensation may be covered e.g. by subjecting the gases to scrubbing with acetic acid, water, or the like. In the example, the oxidation is effected in an aluminium vessel, and the vapours are scrubbed with glacial acetic acid, which passes to the reaction vessel.