Separation and recovery of carboxylic acids from water

Abstract

A lower carboxylic acid such as acetic acid is separated and recovered from an aqueous medium by the steps which include contacting, in an extraction zone, the aqueous medium with an extracting agent such as trioctyl phosphine oxide dissolved in an organic solvent such as a mixture of paraffins having a boiling range of about 160.degree. C. to 175.degree. C., withdrawing from the extraction zone an aqueous raffinate having a greatly reduced concentration of acid and substantially free of organic solvent and of extracting agent, withdrawing the remainder from the extraction zone which is in the form of a mixture comprising the organic solvent, extracting agent, acid, and remainder of the water, passing the mixture to a first distillation zone to produce a first stream which includes a substantial amount of the water and a second stream which includes substantially all the organic solvent, extracting agent, acid, and remainder of the water, passing the second stream to a second distillation zone to form a third stream comprising substantially all of the organic solvent and extracting agent and a fourth stream comprising acid, water, and remainder of the organic solvent, and passing the fourth stream to a third distillation zone to form a fifth stream comprising water and organic solvent and a sixth stream comprising acid substantially free of water and of organic solvent. The aqueous medium can contain up to about 20 weight percent lower carboxylic acid and the aqueous raffinate will have as little as 50 ppm lower carboxylic acid.