Kawasaki Kasei Chemicals Ltd.

Tuneyasu Sato

Kazuaki Sakai

Kazuhiko Chiba

Ryo Matsuura

Yorinobu Yamada

Kowzo Bandow

A process for removing an anthraquinone type scale comprises condensing a steam evaporated from a black liquor obtained by separating pulp from a digested mixture of lignocelluloses containing an anthraquinone type digesting assistant; and contacting a heated aqueous solution of a base in the presence or absence of a reducing agent or an alkali resistant surfactant with a wall of a condenser of an evaporator on which said anthraquinone type scale is adhered.

Process for removing anthraquinone type scale

A crude naphthoquinone produced by an oxidation of naphthalene is purified by a reduced pressure distillation of a crude 1,4-naphthoquinone having an acid content of less than 5 equivalent % calculated as monobasic acid and the crude naphthoquinone is preferably treated by an oxidation of oxidizable impurities.

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Chigasaki, Japan

Tuneyasu Sato