GB735867A - Improvements in or relating to the concentration of fatty acids in aqueous solution and to the recovery of said acids from aqueous solutions thereof by azeotropic distillation - Google Patents

Abstract

<PICT:0735867/III/1> Aqueous solutions of aliphatic carboxylic acids containing 1 to 4 carbon atoms per molecule are concentrated by distilling the solution in a fractionating column operated in a continuous manner in the presence of a volatile hydrocarbon and an aliphatic ketone having 4 to 7 carbon atoms per molecule, whereby vapours comprising water, ketone and hydrocarbon pass over from the head of the column; these vapours are condensed, the condensate is allowed to separate into an aqueous phase and a non-aqueous phase, and the non-aqueous phase is returned to the head of the column. The aqueous phase is distilled in a separate column in order to recover a concentrated solution of the ketone, and this is blended with the aqueous acid fed to the main column. When using butanone as ketone, the preferred volatile hydrocarbons are benzene and cyclohexane. When using a C5 ketone, the preferred hydrocarbons are methylcyclohexane and n-heptane. Aqueous acid fed through line 9 is blended with concentrated aqueous ketone supplied through line 10; and the mixture is passed through preheater 1 into column 2 which is heated by reboiler 3. The overhead vapours are condensed in condenser 5, the condensate being collected in separator 6. The upper layer of the condensate is returned to column 2 through line 14. The lower layer is passed through line 15 to column 7 where it is stripped with steam introduced through line 19. Ketone vapours are removed overhead from column 7, and are condensed. Part of the condensate is returned as reflux to column 7, and the remainder is passed through line 10 to be blended with fresh aqueous acid entering the system. Concentrated acid is withdrawn through line 12 from the base of column 2. Waste water is withdrawn from the base of column 7 through line 18. In an example, an aqueous mixture of acetic and formic acids is concentrated using methyl ethyl ketone and cyclohexane as auxiliary liquids. A column equivalent to 40 theoretical plates is employed; and the feed is introduced half-way up the column. The temperature at the top of the column is maintained at 66.5 DEG C., and that at the base at 110.5 DEG C. The aqueous phase removed from the separator contains 9 per cent by weight of methyl ethyl ketone. This is distilled in a separate column to give the ketone/water azeotrope which is fed with the aqueous acids to the main column. The waste water contains no detectable quantity of formic or acetic acid. The acid mixture withdrawn from the base of the main column contains less than 0.32 per cent by weight of water, and less than 0.25 per cent by weight of methyl ethyl ketone.