GB997340A - Working-up process for cyclohexane oxidation residues - Google Patents

Abstract

Lactones are separated from the alkaline saponification liquors of the by-products of the liquid phase oxidation of cyclohexane with air by (1) acidifying the saponification liquors with dilute mineral acid, preferably sulphuric acid, so that the pH of the liquors is between 0.5 and 4, preferably between 1.5 and 3, permitting the resultant liquors to separate into two layers, the upper layer being designated solution A, and the lower layer solution B, and separating the two layers; (2) extracting the solution B with a hydrocarbon solvent, permitting the resultant liquors to separate into two layers, the upper layer being designated solution C and the lower layer solution D, and separating the two layers; (3) extracting solution A with a hydrocarbon solvent, permitting the resultant solution to separate into two layers, the upper layer being designated solution E and the lower layer solution F, and separating the two layers; (4) combining solutions F and D and extracting the combined solution with a solvent for dicarboxylic acids and lactones, permitting the resultant liquors to separate into two layers the upper layer being designated solution G; (5) distilling the solvent for dicarboxylic acids off from solution G and recycling the solvent, and (6) separating the dicarboxylic acids present in the solutions resulting from the distillation from the lactones by recrystallization, and preferably including the additional step of distilling off first the hydrocarbon solvent and then the monocarboxylic acid from solution E and adding the resultant solution to the solution from which the dicarboxylic acids are separated by crystallization. Solution C may form all or part of the hydrocarbon extractant employed for solution A. The preferred hydrocarbon solvent is cyclohexane. The preferred solvent for the dicarboxylic acid and lactones is cyclohexanone. The invention is described with reference to a flow sheet (not shown) and in the example, the following specified materials are recovered: N-butyric acid, N-valeric acid, N-caproic acid, adipic acid, and a mixture of lactones. Alternative hydrocarbons which may be used consist of saturated or unsaturated aliphatic hydrocarbons containing 5 to 9 carbon atoms, saturated and unsaturated cycloaliphatic hydrocarbons containing 5 to 7 carbon atoms and aromatic hydrocarbons containing from 6 to 8 carbon atoms. Alternative solvents for dicarboxylic acids and lactones are straight chain ketones containing from 5 to 9 carbon atoms, straight chain and branched ethers containing from 4 to 8 carbon atoms, and aliphatic and aromatic halogen substituted hydrocarbons having low water solubility and having a boiling point below 150 DEG C.