GB743991A - Production of aliphatic acids - Google Patents

Abstract

Acetic acid and other aliphatic acids are obtained by oxidizing in the liquid phase at elevated temperature a paraffin of the formula C2H5.CH(CH3).R, where R is an alkyl group of at least two carbon atoms with a gas containing or consisting of molecular oxygen. Suitable paraffins include 3-methyl pentane, 2,3-dimethyl pentane, 3-methyl hexane and 3,4-dimethylhexane. The paraffinic hydrocarbons employed may be in the form of the pure materials separately or in combination, or in the form of mixtures with hydrocarbons, paraffinic or otherwise, provided that the paraffinic hydrocarbons of the above formula constitute a substantial proportion of the mixture. Inert diluents may also be present. The oxidizing gas may be in the form of air or of mixtures poorer or richer in oxygen than is air. Part of the molecular oxygen may be in the form of ozone. In order to maintain the reactants in the liquid phase the use of high pressures may be necessary. Preferred oxidation temperatures are 130 DEG to 200 DEG C. and the process may be carried out batchwise or continuously. The oxidation may be carried out in the presence or absence of an oxidation catalyst. Suitable oxidation catalysts include the oil-soluble organic acid salts of manganese, cobalt, nickel, vanadium and copper, or the catalyst metal may be added in the form of an anion, whether as the free acid or a salt thereof, e.g. as a vanadate. In examples: (1) a stainless steel reactor is charged with 3-methyl pentane containing manganese naphthenate and oxidation effected with air at 150-160 DEG C. and 200 lbs. per square inch pressure. The liquid products are circulated through a cooler and the lower aqueous acid layer is withdrawn as product and replaced with fresh 3-methylpentane to keep the total volume of liquid constant. The oxidation is completed in batchwise manner and the product is distilled to recover first nonacidic material after which the lower aliphatic acids and water are distilled from the high boiling residues. The mixture of wet acids is then dehydrated and distilled to yield acetic acid, together with some formic, propionic, and butyric acid. If 2-methylpentane and normal hexane, respectively, are used instead of 3-methylpentane the yield of acetic acid is reduced in each case; (2) to (4) as in (1) except that the hydrocarbons used are 3-methyl hexane, 2,3-dimethyl pentane and 3,4-dimethyl hexane, respectively, and the oxidation temperature is 150-155 DEG C. Specification 743,989 is referred to.