Acid Treatment Under Pressurized Oxygen Gas, 1999 Pulping Conference Proceedings

Yosuke Uchida, Takahiro Miura & Makoto Iwasaki

Oji Paper Co., Ltd.

We investigated the reduction of bleaching chemicals by acid treatment of oxygen-delignified hardwood kraft pulps. The results indicated that the reduction of chlorine dioxide was proportional to the reduction of kappa number (KN) with acid treatment, in case of chlorine dioxide in the first bleaching stage (for example, in D-E-D sequence). In contrast, the reduction of chlorine was less than that of KN, in case of chlorine in the first bleaching stage. (for example, C-E-H-D sequence).

The characteristics of acid-treated pulps were examined, in order to find out the reason of the difference between the reduction of chlorine dioxide and that of chlorine. The results suggested that the chromophores are generated, and phenolic hydroxyl groups content of residual lignin was increased during acid treatment.

We conducted the acid treatment of pulps under pressurized oxygen gas in order to prevent the generation of chromophores. As a result, the bleachability of acid-treated pulp was improved.