Patent ID: 6942803

Claim:
A process for purifying lactic acid, comprising: providing an aqueous feed stream comprising free lactic acid and at least one contaminant, wherein the contaminant is selected from the group consisting of pyruvic acid, oxalic acid, maleic acid, malonic acid, fumaric acid, 2-ketobutyric acid, 2-hydroxybutyric acid, acetic acid, 2-hydroxy-3-methyl butyric acid, 4-hydroxy-phenylpyruvic acid, phenyl-pyruvic acid, 4-hydroxy-phenyllactic acid, phenyllactic acid, citraconic acid, citric acid, and mixtures thereof; contacting the aqueous feed stream with a lean liquid extractant comprising less than about 0.75 moles of an amine per kg of the lean liquid extractant, between about 0 and 0.5 moles of an enhancer per mol of the amine, and a diluent, whereby the majority of the contaminant becomes complexed with the lean liquid extractant; separating the complexed lean liquid extractant from the aqueous feed stream, thereby producing a first effluent stream that comprises free lactic acid and that has a greater ratio of free lactic acid to contaminant than the uncontacted aqueous feed stream; and contacting the first effluent stream with a rich liquid extractant, whereby a majority of the free lactic acid in the first effluent stream is complexed with the rich liquid extractant, wherein the rich liquid extractant comprises the same amine, enhancer, and diluent as in the lean liquid extractant, and the rich liquid extractant comprises more moles of the amine per kg of the rich liquid extractant than the moles of amine present per kg in the lean liquid extractant, and the rich liquid extractant comprises a higher ratio of moles of the enhancer to moles of the amine than in the lean liquid extractant, and wherein loading is such that the ratio of moles of free lactic acid in the first effluent stream to moles of amine in the rich liquid extractant is less than about 1.1.