GB281827A - Improved method of concentrating aqueous solutions of acetic or formic acid - Google Patents

Abstract

281,827. Haworth, W. N., and Nelson, Ltd., J. Oct. 19, 1926. Acetic and formic acids.-Aqueous acetic and formic acids are concentrated by adding an acetate or formate respectively, distilling off the water, and then distilling off the strong acid, at least part of the distillation being under reduced pressure. In an example, 30 per cent acetic acid is distilled with anhydrous sodium acetate at a vacuum of 15-25 mm., at as low a temperature as possible; when most of the water is removed, the temperature is raised to distil off the strong acid. In the first stage of the distillation heated air may be employed to remove some of the water, but the first stage should be concluded under reduced pressure; the second stage may be effected at atmospheric pressure, but reduced pressure is preferable. The acetic acid vapour may be led through a mass of hot solid sodium or potassium acetate. It is preferred to provide in the still means for breaking up lumps, for instance a rotary still with scrapers may be employed, or a fixed still with agitating or grinding devices. In another example, formic acid of 30 pent cent distilled with anhydrous sodium formate at 50-55‹ C. and 10-20 mm. to distil off the water, and the strong acid is distilled at 130-140‹ C. at the same pressure, the receiver being cooled to -10‹ C.