GB669760A - Improvements in the synthesis of aliphatic carboxylic acids - Google Patents

Abstract

Aliphatic carboxylic acids are prepared by maintaining aliphatic hydroxy compounds and carbon monoxide under a pressure of at least 100, preferably 250-350 atmos., and at below 200 DEG , e.g. 130-190 DEG C., in presence of water and an iodide of nickel, cobalt or iron. A carbonyl of the metal, and iodine are equivalent to the iodide. Acetic acid may be produced directly from methanol synthesized from CO and H2 and containing the latter. Tungsten, vanadium, antimony, and bismuth are additional catalysts. The water is preferably 15-30 per cent of the weight of iodide, e.g. nickel iodide, used, and may be provided by water of crystallization, e.g. in the hexahydrate. Some anhydrous iodide, e.g. 5-20 mole per cent of the hydrated iodide, is preferably present to initiate the reaction. Acetic acid may be included in the initial charge for the synthesis from methanol. The latter may be obtained from CO and H2 using a zinc chromate catalyst at 300-320 DEG C., and the same pressure as used for the acid production, e.g. 300 atmos. A ratio of H2:CO of 2:1 may be used to initiate the methanol synthesis, tail gas from the acid synthesis then being fed with make-up gas having a H2 : CO ratio of 1 : 1. Propionic acid may be synthesized from ethanol and adipic acid from 1,4-butanediol. In examples, methanol is synthesized from CO+ H2 and the products contacted with NiI2, part anhydrous, with or without acetic acid. After distilling acetic acid, the residue of NiI2 may be mixed with acetic acid and water, and with methyl iodide and nickel carbonyl obtained as first runnings during distillation of the acetic acid, the mixture being charged to the second stage with the product of the methanol synthesis. Specification 283,989, [Class 2 (iii)], is referred to.