GB727078A - Purifying acetic acid by azeotropic distillation - Google Patents

Abstract

<PICT:0727078/III/1> Acetic acid is separated from formic acid in mixtures containing the two acids, water and higher boiling aliphatic acids, by subjecting the mixture to fractional distillation together with a paraffinic hydrocarbon liquid containing not more than 6 carbon atoms per molecule, whereby the formic acid and water distil over with the hydrocarbon and there is obtained as base product acetic acid containing the higher boiling acids but free from formic acid. Suitable hydrocarbons are pentane and hexane. A crude feed comprising acetic acid (64.6 per cent.), water (29.1 per cent.), formic acid (4.3 per cent) and higher boiling compounds (2 per cent.) including propionic, n-butyric and succinic acids, is introduced into column 1 through line 2 at the rate of 100 volumes per minute; while the column is heated by reboiler 3, and 98 volumes per minute of pentane are introduced into the column through line 4. The overhead product, taken off through line 5, is condensed; and the condensate is allowed to separate into two layers in decanter 6. The lower layer, which is an aqueous solution of formic acid, is withdrawn through line 7. The pentane layer is returned to column 1 through line 4. A mixture comprising acetic acid and the higher boiling compounds is withdrawn from reboiler 3, and passed through line 9 to column 11. A mixture comprising 83.3 per cent. of the higher boiling compounds and 16.7 per cent. of acetic acid is withdrawn from reboiler 12; while the distillate, which contains 99.5 per cent. of acetic acid, is passed to column 4. A final product containing 99.7 per cent. acetic acid is taken overhead from column 14, and is collected in receiver 15. The base product from column 14 contains 70 per cent. acetic acid, and is recycled through line 18 to column 11.