GB307868A - Process and apparatus for the continuous extraction of acetic acid from its aqueous solutions - Google Patents

Abstract

307,868. Soc. Anon. des Distilleries des Deux-Sevres. March 15, 1928, [Convention date]. Extracts, making.- Acetic acid is extracted from aqueous solutions thereof, for example solutions obtained in the manufacture of cellulose acetate, by passing the solution, in countercurrent to an extracting medium such as amyl acetate, through multistage apparatus, each stage of which comprises a mixer, in which the two phases are thoroughly emulsified, and a settling vessel in which they are allowed to separate, the enriched extraction medium being then passed to the one and the solvent to the other adjacent stage. The apparatus may be carried out at temperatures above or below atmospheric temperatures and at pressures greater or less than normal. The stages of the apparatus may be arranged in one or more rows, in circular formation, or the mixing and settling elements may be superposed to form two towers or may be combined into a single tower. Circulation of the fluids may be effected by pumps, by compressed gas or, as regards one of the phases, by gravity. The mixing apparatus may be made to serve as a pump for this purpose. As illustrated, the apparatus comprises mixing vessels M1 - - M5 and settling vessels D1 - - D5. The solution to be extracted, for example a 10 per cent aqueous solution of acetic acid, is delivered to mixer M5 through a pipe 34 and the extracting medium M1 through a pipe 36. The liquids pass in opposite directions through the apparatus, being at each stage thoroughly emulsified in the mixing vessels' and then delivered to the separating vessels. After separation the upper layer containing amyl acetate enriched with acetic acid is passed through pipes such as 10, 22 to the next lower mixing vessel and the lower layer is delivered through vessels G1 - - G5 and pipes such as 23, 24, 27 to the next higher mixing vessel. Delivery of the lower layer is effected by the injection action of compressed air supplied through pipes 25 from a reservoir 26. The used air is trapped in vessels HI - - H5 and delivered through pipes 28, 29 to a reservoir 30 whence it is returned in compressed condition to the reservoir 26 by a pump 31. The extractladen solvent is delivered from the apparatus by a pipe 33 and the extracted solution by a pipe 35. Where the solution contains precipitatable solid matter such as cellulose acetate this solid matter remains at the top or bottom of the setting vessels or at the surface of separation of the two liquids and may be removed as by periodical cleaning of the vessels. The Specification as open to inspection under Sect. 91 (3) (a) describes the invention as applicable to the extraction in general of substances dissolved in solvents, by means of extracting media insoluble or substantially insoluble in the solvent. This subject-matter does not appear in the Specification as accepted.