Process for preventing scale deposition

摘要

A scale deposition from an aqueous slurry of naphthoquinone and phthalic acid can be prevented by adding fine crystals of phthalic acid to the aqueous slurry of naphthoquinone and phthalic acid collected, which slurry is obtained by contacting a gas resulting from a catalytic gas phase oxidation of naphthalene with water or a mother liquor recycled. The fine crystals of phthalic acid have diameters of less than 100 mu , preferably 10 to 40 mu , and can be in an aqueous slurry of phthalic acid pulverized by a pulverizer.