Integration of hemicellulose recovery and cold caustic extraction in upgrading a paper-grade bleached kraft pulp to a dissolving grade

In this study, a hemicellulose recovery process was integrated with a cold caustic extraction (CCE) process in upgrading paper-grade bleached kraft pulp to dissolving grade. Under the conditions of 15% NaOH, 10% pulp consistency, 30℃ and 1 h, a paper-grade softwood bleached kraft pulp was purified to a dissolving-grade pulp with 97.57% α-cellulose and 1.67% pentosan contents. The spent liquor from the cold caustic extraction process was sequentially extracted with ethanol to precipitate and recover the dissolved hemicelluloses, followed by evaporation to recover the ethanol. After the recovery of hemicelluloses and ethanol, the spent liquor can be reused as the caustic solution for the CCE process without compromising the resulting pulp properties. The results demonstrated that it is feasible to integrate hemicellulose production with the cold caustic extraction process of dissolving pulp production, based on the concept of biorefinery.