Abstract: A countercurrent, cooling crystallization and purification method for a multi-component molten mixture wherein the mixture is treated by a purification system comprising one or more crystallizers (1A, 1B) each having, at the respective upper portion, a clarifying portion (10A, 10B) and a purifier (2) arranged in series to the crystallizer or crystallizers and having, at its upper portion, a clarifying portion (20), the crystallizer or crystallizers and the purifier having a temperature difference therebetween and disposed in the order of temperature. The starting mixture is fed to one of the crystallizers and subjected to crystallization there, and the resulting crystals are taken out from the bottom of the crystallizer and fed to another crystallizer or a purifier of higher temperature while the clarified liquid, i.e., mother liquor positioned at the clarifying portion of the crystallizer is led to another crystallizer of lower temperature or discharged out of the system.

Abstract: A mixture containing monochloroacetic acid and dichloroacetic acid as the main components are admixed with 5-25% by weight of water on the basis of sum total of monochloroacetic acid, dichloroacetic acid and water, and subjected to adiabatic cooling under a pressure of 133 to 2,660 Pa, whereby monochloroacetic acid is crystallized with a high purity.