PROCESS FOR WHITENING CONIFEROUS SULFATE CELLULOSE Russian patent published in 1994 - IPC

FIELD: pulp-and-paper industry. SUBSTANCE: the process for whitening coniferous sulfate cellulose comprises treatment of the original cellulose suspension with a mineral acid at 70-95 C and a pH of 1.2-2.5, delignification with hydrogen peroxide with the addition of sodium hydroxide, the amount of hydrogen peroxide of 0.5-2.5% based on the weight of the absolutely dry cellulose at the same temperature and subsequent washing of the pulp with water. Prior to delignification with hydrogen peroxide, the cellulose suspension is pretreated with a sodium hydroxide-based alkali solution with the amount of 1-3% NaOH based on the weight of the absolutely dry cellulose for 0.5-1.0 hr at a pH of 10-11 followed by washing with water to a pH of 7-8. Sodium hydroxide is added in an amount of 2-4% in the stage of delignification with hydrogen peroxide to a pH of 10.0-12.0. The process is carried out with the ratio of sodium hydroxide in the stages of pretreatment and delignification with hydrogen peroxide ranging from 1:1 to 1:4, respectively. The alkali solution is sodium hydroxide or a mixture thereof with the spent solution resulting from the stage of delignification with hydrogen peroxide. The mineral acid is fresh sulfuric and hydrochloric acid or a mixture of fresh sulfuric or hydrochloric with the spent acid in a 1:1 ratio. EFFECT: improved properties of the sulfate cellulose. 4 cl, 1 tbl