The One Stage Extending Delignification Cooking And Bleaching For Europhylla Pulp

The carbohydrate loss in cooking is high when yield the low-kappa-number pulp by the conventional Kraft cooking. But it is possible to conduct high strength low-kappa-number pulp after people invented the technology of extended delignification .In the paper the one stage extended delignification of low-Kappa-number Kraft cooking technology was applied to yield low-Kappa-number Europhylla pulp. Compared with the conventional Kraft process, the technology used the same machinery but only change some process conditions. At first the practical process conditions (total alkali; sultidity; additive charge; time at maximum temperature) were studied by orthogonal comparisons. Then researched the influences of liquor-to-wood ratio and maximum temperature. So we could find the optimum of one-stage Kraft pulping conditions were: total alkali charge 20%, sulfidity 25%,liquor-to-wood ratio 1:5.5. maximum temperature 160 C, time at cooking temperature 120 minutes ,additive charge 0.2%. Results in the conditions were: Kappa number 14.7, viscosity 1057ml/L, yield 49.32%, brightness 38% SBD. The result indicated that the one stage extending delignification of low-Kappa-number cooking technology gave a better selectivity of delignification than the conventional Kraft cooking, the Kappa number of the pulp was 4 units lower and the yield was high by 2.5% than the kappa number of conventional at the same viscosity of pulp.Today the number one concern in bleaching has gradually became pollution abatement, so many scientists studied on totally chlorine free (TCF) bleaching sequences. It is the key to product high brightness pulp in efficiency that using suitable bleaching agents. In the paper TCFp(OpP) and TCFz bleaching sequences was used for low-kappa-number Europylla pulps which was yield by the one stage extending delignification technology. The results indicated that the low-kappa-number pulp could be bleached to high brightness by a TCFp (OpP) bleaching sequences after one stage oxygen bleaching. A bleached pulp of 81.6%SBD brightness and 840ml/g viscosity could be produced by OP bleaching sequence with a 2% H2O2 charge in peroxide bleaching. The optimum of ozone bleaching conditions were: ozone dosage 3.5%, pulp consistency 12%,temperature 20 C, PH 2, and the consequent results after the single bleaching sequence were: kappa number 5.0, viscosity 743ml/g, brightness 70.5%SBD. Adding H2O2 to the ozone bleaching could improve delignification degree and increase brightness of bleached pulp (for example with 1.5% H2O2 charge, delignification degree and pulp brightness could be increase 3.4% and 2.1 points respectively). The ozone bleaching with pretreatment was superior to that with non-pretreatment. (The kappa number of the bleached pulp was lower 25%, and the brightness increased by 3% SBD, the viscosity was raised by 10%). And the result of the ozone bleaching with the H2SO4 pretreatment was best. A brightness of bleached pulp could beachieved above 85%SBD by the QZEP, QZEPY, QZEYP bleaching sequences. Compared with Na2S2O4 bleaching, the H2O2 bleaching was better in raising brightness.