Patent GB-841692-A (GB)
Title: Purification of aliphatic acids
Filed: 1957-01-30
Abstract: Acetic acid or propionic acid obtained by partial liquid phase oxidation of an aliphatic hydrocarbon is purified by passing the vapour of the acid upwardly through a downwardly flowing stream comprising an hydroxylamine salt of acetic or propionic acid.  It is preferred to use the hydroxylamine salt of the acid to be purified. The hydroxylamine salt is advantageously used in the form of a solution in acetic or propionic acid according to which acid is being purified.  In a preferred embodiment, acetic or propionic acid vapours obtained by the partial purification, by distillation, of the crude acid are introduced into the bottom of a distillation column while a solution of the hydroxylamine salt is fed in at the top of the column, the resulting purified acid vapours being drawn off from the top without reflux.  The process is generally carried out at about the boiling point of the acid being purified.  Thus when operating at atmospheric pressure the temperature will be about 120 DEG  to 140 DEG  C. although higher and lower pressures with correspondingly higher and lower temperatures respectively may be used.  An example is given for the purification of crude acetic acid obtained by liquid phase partial oxidation of n-butane with air or other source of molecular oxygen in acetic acid solution containing a cobalt salt as catalyst.  The crude acid is first distilled to give a stream of partially purified acetic acid vapours which are then fed into the bottom of a distillation column into the top of which is fed a stream of a 10% solution of hydroxylamine acetate in acetic acid, the column being operated with no reflux and at atmospheric pressure.ALSO:Acetic acid or propionic acid obtained by partial liquid phase oxidation of an aliphatic hydrocarbon is purified by passing the vapour of the acid upwardly through a downwardly flowing stream comprising a hydroxylamine salt of acetic or propionic acid. It is preferred to use the hydroxylamine salt of the acid to be purified.  The hydroxylamine salt is advantageously used in the form of a solution in acetic or propionic acid according to which acid is being purified.  In a preferred embodiment acetic or propionic acid vapours obtained by the partial purification, by distillation, of the crude acid are introduced into the bottom of a distillation column while a solution of the hydroxylamine salt is fed in at the top of the column, the resulting purified acid vapours being drawn off from the top without reflux.  The process is generally carried out at about the boiling point of the acid being purified, thus when operating at atmospheric pressure the temperature will be about 120 to 140 DEG C. although higher and lower pressures with correspondingly higher and lower temperatures respectively may be used.  An example is given for the purification of crude acetic acid obtained by liquid phase partial oxidation of n-butane with air or other source of molecular oxygen in acetic acid solution containing a cobalt salt as catalyst.  The crude acid is first distilled to give a stream of partially purified acetic acid.  Vapours which are then fed into the bottom of a distillation column into the top of which is fed a stream of a 10% solution of hydroxylamine acetate in acetic acid, the column being operated with no reflux and at atmospheric pressure.