GB684852A - Process for the purification of lower aliphatic aldehydes - Google Patents

Abstract

Aqueous solutions of aliphatic aldehydes containing from 1 to 5 carbon atoms, the aldehyde solution containing unsaturated alcohols, other odour bodies, and acids, are purified by subjecting the solutions to a liquid phase extraction treatment with a solvent selected from the group consisting of ethers and esters having the formula ROR1 and RCOOR1, respectively, in which R and R1 are alkyl radicals containing not more than 5 carbon atoms, separating the solvent from the aldehyde solution and recovering an essentially purified aldehyde solution. Specified solvents are diethyl ether, diisopropyl ether, dibutyl ether, di-isobutyl ether, ethyl acetate and butyl acetate. The process is particularly suitable for the purification of formaldehyde solutions, the preferred solvent being diisopropyl ether. The extraction treatment is preferably effected at 60 DEG to 80 DEG F. and it is preferred to use four volumes of solvent per volume of formaldehyde solution. The extraction treatment may be carried out by treating the aldehyde solution with the solvent in counter-current. Where the acid values of the aldehyde solution to be purified are low the extraction may be operated essentially for odour removal and in this case solvent ratios of 0.5 : 1 to 2 : 1 by volume are suitable. After contacting the formaldehyde solution with the solvent the raffinate may be flash distilled at 190 DEG to 210 DEG F. to recover any solvent present as an overhead product for recycle to the system. In examples: (1) an aqueous solution of formaldehyde containing a small amount of formic acid and unsaturated bodies is contacted at 70 DEG F. with diisopropyl ether (4 volumes solvent per volume of aldehyde solution) in a column, the solvent passing upwards in counter-current to the aldehyde solution. The formaldehyde solution withdrawn from the bottom of the column has a reduced acid and unsaturated body content. The formaldehyde raffinate is then flash distilled at a temperature of 206 DEG F. to yield an overhead product containing isopropyl ether and a small amount of aqueous formaldehyde solution which is separated in a separator and returned to the bottoms product from the flash still. The isopropyl ether from the separator is added to the isopropyl ether recovered at the top of the contacting column and the impure isopropyl ether fractionated to recover pure isopropyl ether which is recycled to the contacting column; (2) the procedure of (1) is repeated except that the volume ratio of isopropyl ether to formaldehyde is 1 : 1, the treatment being directed essentially for odour removal. The impure isopropyl ether from the contacting column is then purified by treatment with an aqueous solution containing sodium bicarbonate and sodium carbonate and the alkaline water wash is then subjected to flash distillation at 175 DEG to 210 DEG F. to recover the ether dissolved therein. The residual acidity of the treated aldehyde solutions may be removed or reduced by treatment with ion exchange resins. The purification of aqueous acetaldehyde solutions containing acetic acid by treatment with diisopropyl ether is also referred to.