METHOD FOR PURIFYING METHACRYLIC ACID

PROBLEM TO BE SOLVED: To provide a method for stably purifying methacrylic acid in an aqueous solution of methacrylic acid without contamination of apparatus. SOLUTION: This method for purifying methacrylic acid comprises mixing an aqueous solution of methacrylic acid, which is obtained by subjecting isobutylene, tertiary butyl alcohol or methacrolein to contact oxidation with a molecular oxygen-containing gas to give a formed gas and quenching the formed gas and from which a low-boiling component is removed, with a specific extracting solvent to selectively extract methacrylic acid, separating an extracting solvent phase from a water phase by a decanter, cooling the water phase to 0-40 deg.C, separating and removing a precipitating solid material, extracting methacrylic acid with an extracting solvent from the water phase from which the solid material is removed, recovering the extracting solvent from the extracting solvent phase thus obtained and the extracting solvent phase from the decanter by distillation to give methacrylic acid.