Application of ion-exclusion chromatography to alkaline pulping liquors; separation of hydroxy carboxylic acids from inorganic solids

Hydroxy carboxylic acids were separated from inorganic solids on a pilot-plant scale by using columns containing a strongly acidic polystyrene cation exchange resin with bed volumes of about 1000 and 200 dm³. The liquor samples were obtained from soda–anthraquinone pulping of pine wood and they were first acidified with sulfuric acid to precipitate most of the lignin and to liberate the hydroxy acids. Under appropriate conditions, using warm water (65°C) as eluent, the liquor sample could be resolved into two distinct fractions consisting mainly of hydroxy acids and sodium sulfate, respectively. This separation method seems promising as a complementary technique in connection with the recovery of aliphatic carboxylic acids from kraft black liquors, although further studies are required to optimize the conditions.