METHOD FOR PURIFYING METHACRYLIC ACID

PURPOSE:To readily and effectively remove maleic acid or aldehydes contained in very small amounts and purify methacrylic acid, by subjecting crude methacrylic acid to contact treatment with 2,4-diaminodiphenylamine or toluylenediamine, distilling and purifying the resultant treatment product. CONSTITUTION:Isobutylene, tertiary butanol, methacrolein or isobutyl aldehyde is catalytically oxidized in the vapor phase to provide methacrylic acid. In the process, crude methacrylic acid obtained by the reaction is subjected to contact treatment with 2,4-diaminodiphenylamine or m-toluylenediamine (preferably in a molar amount of 3 times or more of carboxylic acid and aldehyde groups based on unsaturated dibasic acid contained in the crude methacrylic acid), distilled and purified to purify the methacrylic acid.