GB721301A - Improvements in or relating to the separation of acetic acid from aqueous mixtures of organic compounds by distillation - Google Patents

Abstract

Acetic acid is separated from mixtures of lower fatty acids containing formic acid and water in addition to acetic acid, by adding acetic anhydride to the mixture in an amount in excess of that required to react with all the water present to form acetic acid, and simultaneously or thereafter submitting the mixture to fractional distillation whereby an acetic acid fraction, substantially free of formic acid, is obtained after formic acid has been distilled over. At the temperature at which the distillation is carried out formic acid decomposes at an appreciable rate into carbon monoxide and water; it is therefore desirable to use sufficient anhydride to react not only with the water originally present in the mixture but also with that produced by decomposition of formic acid. Feedstocks for the process may contain ketones and esters in addition to fatty acids and water. Thus a suitable feedstock is the crude product obtained by the partial aerial oxidation of lower hydrocarbons.ALSO:Acetic acid is separated from mixtures of lower fatty acids containing formic acid and water in addition to acetic acid, by adding acetic anhydride to the mixture in an amount in excess of that required to react with all the water present to form acetic acid, and simultaneously or thereafter submitting the mixture to fractional distillation whereby an acetic acid fraction, substantially free of formic acid, is obtained after formic acid has been distilled over. At the temperature at which the distillation is carried out formic acid decomposes at an appreciable rate into carbon monoxide and water; it is therefore desirable to use sufficient anhydride to react not only with the water originally present in the mixture but also with that produced by decomposition of formic acid. Feedstocks for the process may contain ketones and esters in addition to fatty acids and water. Thus a suitable feedstock is the crude product obtained by the partial aerial oxidation of lower hydrocarbons. An initial azeotropic distillation, using hexane or toluene as entrainer, will separate most of the formic acid, esters and water as an overhead fraction, leaving a bottoms fraction containing acetic and propionic acids, together with the remaining formic acid and water. This bottoms product is then treated with excess acetic anhydride as described above. In an example, a mixture containing acetic acid (86.8 per cent), formic acid (11.2 per cent) and water (2 per cent) was distilled in the presence of 14 per cent (based on the feed) of acetic anhydride using a column equivalent to 40 theoretical plates. Distillate was removed until the overhead temperature reached 113 DEG C., and this left a bottoms product of acetic acid containing only 0.15 per cent of formic acid.