GB791044A - Purification of aliphatic acids - Google Patents

Abstract

C2-4 Aliphatic monocarboxylic acids produced by the liquid phase oxidation of C4-8 paraffin hydrocarbons, prepared for example by the processes described in Specifications 743,989 and 743,990, are purified by catalytic hydrogenation, preferably after being substantially freed from formic acid. In a preferred embodiment, acetic acid recovered by the process described in Specification 771,992, [Group III], is used. The hydrogenation may be carried out in the liquid or vapour phase, preferably liquid. A wide range of temperature and pressure is suitable, generally room temperature and atmospheric pressure. Preferred catalysts are of the platinum or palladium groups. After treatment the acid product may be recovered by conventional methods, e.g. filtration or distillation. In Examples (1), (2), (3), (5) and (6), an aqueous solution of C2-4 acids containing also formic acid, obtained by oxidation of paraffins, is first subjected to a multiple distillation purification process, then dehydrated by distillation with isopropyl ether, freed from formic acid by distillation with toluene, and acetic acid distilled off; this is redistilled to remove traces of toluene and formic acid and hydrogenated using platinum oxide, palladium/charcoal and palladium/"Celite" (Registered Trade Mark) catalysts in the liquid phase at atmospheric pressure and room temperature. In Example (4), propionic acid obtained by batch distillation of the residue remaining after recovery of the acetic acid is similarly hydrogenated using a platinum oxide catalyst.