Patent ID: 6306253
Filing Date: 2001-10-23
Classification: D21C

Abstract:
A method of sequentially treating cellulose pulp comprising:(a) digesting commminuted cellulosic fibrous material to produce cellulose pulp, and if necessary oxygen delignifying the pulp, to produce a cellulose pulp with a kappa number of less than 24; then(b) treating the digested pulp in at least one acid tower at a pH of between 2-5 at a temperature between 75-130.degree. C., and, in order to prevent the strength properties of the pulp from being deteriorated, at a retention time t in minutes between 30-300 minutes, wherein the treatment temperature T in degrees centigrade is T.sub.min <T<T.sub.max in which ##EQU4##andT.sub.max =T.sub.min +23ECin order to decrease the kappa number of the pulp 2-9 units;(c) treating the acid treated pulp in at least one treatment tower different from the at least one acid tower with chlorine dioxide; andpracticing steps (b) and (c) without an intermediate wash therebetween.