To obtain an α,ω-dicarboxylic acid useful as a cross-linking agent in a coating material composition by purifying the α,ω-dicarboxylic acid produced by a fermentation method of a normal paraffin as a raw material until the nitrogen content of minor impurities therein reaches a specific value.
A solvent having functions to dissolve at least a part of, e.g. an α,ω-dicarboxylic acid produced by a fermentation method of a normal paraffin as a raw material and having ≥500 ppm nitrogen content, e.g. brassilic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid and octadecanedioic acid (e.g. isopropyl acetate, n-propyl acetate or methyl isobutyl ketone) is mixed with the α,ω-dicarboxylic acid to deposit and remove impurities insoluble in the above solvent and impurities soluble in the solvent are adsorbed on active carbon and removed therefrom. The α,ω-dicarboxylic acid dissolved in the solvent is then recovered to thereby purify the α,ω-dicarboxylic acid until the nitrogen content reaches 0-100 ppm.
GOTO TAKAKUNI
MIYAWAKI TAKAHISA
KIKUTA YOSHIO
MITSUI CHEMICALS INC
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