GB741485A - Improvements in or relating to a distillation process for working-up reaction mixtures obtained by the oxidation of acetaldehyde - Google Patents

Abstract

<PICT:0741485/III/1> In a process for the oxidation of acetaldehyde to acetic acid and/or acetic anhydride, the product from the reactor is distilled to remove overhead the components boiling lower than acetic acid, i.e., unchanged acetaldehyde, methyl acetate, acetone and formaldehyde; and this volatile mixture is subjected to extractive distillation with water in order to strip formaldehyde therefrom. The vapours from the extractive distillation still, thus freed from formaldehyde, are condensed and/or subjected to rectification. The removal of formaldehyde in this manner obviates the deposition of paraformaldehyde in the cooler parts of the apparatus. The amount of water introduced is preferably such that the formaldehyde concentration in the aqueous effluent from the extractive distillation still is notmore than about one per cent. Water may be introduced at various points of the still, and/or the aqueous solution in the base of the still may be circulated, provided some fresh water is added above the feed point of the organic mixture. It is desirable to scrub with water the effluent gases from the oxidation reactor; and the scrubbing water is thereafter used, supplemented if necessary with fresh water, for the extractive distillation still. The liquid products from reactor 11 are fed to fractionating column 14 from which vapours containing 59 per cent acetaldehyde, 31 per cent methyl acetate, 7 per cent acetone and 2.75 per cent formaldehyde are removed overhead. These vapours are passed through line 15 to the 12th plate of extractive distillation column 13, which is equivalent to thirty-one theoretical plates. The effluent gases from reactor 11 are passed to scrubber 12 where they are contacted with a countercurrent flow of water to remove acetaldehyde, methyl acetate and acetone therefrom. The water discharged from scrubber 12 is fed on to the 19th plate of column 13. Live steam is introduced through line 21 into the base of column 13, and the pressure in the column is maintained at 2.2 atm. The vapours from the head of column 13 pass via line 22 into condenser 17. The condensate which contains 74 per cent acetaldehyde, 21 per cent methyl acetate, and 5 per cent acetone, but no formaldehyde, flows into divider 18 where it is divided into three parts. One part is supplied through line 16 as reflux to column 14, another part is returned through line 19 as reflux to column 13, and the remaining part flows to storage tank 20. The water discharged from the base of column 13 contains 0.07 per cent formaldehyde and 0.4 per cent acetic acid.