| Oxygen delignification process has been used in the first stage bleaching of the cooked pulp. It also can be regarded as the continuation of cooking to further get rid of the residual lignin of pulp. Under normal conditions, the delignification rate of the single-staged oxygen delignification process should be keeped at 40%～50%. As increasing of the delignification rate, the degradation of carbohydrate will aggravate significantly.This paper mainly maked use of the reinforced effects of H2O2 to strengthen the delignification action of oxygen by adding slight H2O2 in the two-staged oxygen delignification process. In addition, the split addition of Alkali was adopted in this paper to balance the influncement of alkali on the delignification process by oxygen, thus the delignification process was moderated and the oxygen delignification rate was maximized at a relatively high viscosity of the pulp.In this paper, wheat straw Soda-AQ pulp, Acacia EMCC kraft pulp and the Masson pine KP pulp were used as the raw materials to rearchech the oxygen delignification process, the results indicated as folowes.The results of oxygen bleaching of wheat straw Soda-AQ pulp indicated:1. The optimal single-staged oxygen delignification conditions were: alkali charge 3.0%, oxygen pressure 0.6MPa, MgSO4 charge 0.3%, pulp concentration 10%, and reacted for 60min at 100℃.Under these conditions, the delignification rate can attain to 48.23%, the kappa number and viscosity of the bleached pulp were 9.78 and 944ml/g reapectively, brightness was 46.71%ISO.2. In the two-staged oxygen delignification process, the basic conditions of the reinforcing process were alkali charge 3.5-1.0%, oxygen pressure of 0.6-0.5MPa, reacted at 100℃for 30-60min. H2O2 was added under such conditions and the results showed O-Op was superior to Op-O; when H2O2 dosage was 1.0%, the delignification rate can reach 61.4% and the viscosity of the bleached pulp was 898ml/g, brightness was 55.71%ISO.The results of oxygen bleaching of Acacia EMCC pulp indicated:1. the optimal conditions of the reinforcing process of two-staged oxygen delignification were alkali charge 3.0-1.5%, oxygen pressure of 0.6-0.5MPa,and temperature 100℃.under such a condition, with increasing of H2O2 dosage, Op-O was superior to O-Op. When dosage of H2O2 was set at 1.0%, the delignification rate was 56.5%, decreasing rate of viscosity was 17.4%, brightness was 65.80%ISO. However, further increasing of H2O2 dosage would not lead to a higher removal of lignin, but the brightness of the pulp increased obviously.2. the split alkali addition mode was not superior to the two-staged oxygen delignification process foe the Acacia EMCC pulp. In this way the delignification rate can be only reached at 52%, while the viscosity and brightness of the pulp were similar to that of the two-staged pulp.so the split alkali addition during oxygen delignification was not suited to the low kappa number acacia pulp.The results of oxygen bleaching of Masson pine KP pulp indicated:1.The reinforcing effect of the untreated pulp was not obvious, but it became remarkable after the pretreatment of chelation (Q).When the dosage of H2O2 was1.0%, the delignification rate of the QOpO pulp was 73.0%, decreasing rate of viscosity was 18.7%, brightness was 49.85%ISO. The appropriate dosage of H2O2 was between 1.0% and 1.5%. The reinforcing effect was not remarkable under the high concentration and low total alkali dosage conditions.2.Under low total alkali dosage condition, the effect of alkali split addition during the oxygen delignification was not superior to the single or two-staged process when the alkali dosage was not very high. However, when the alkali dosage was set at 4.5%, this method can lead to a high level of lignin removal. The delignification rate can reach at 64.3% while the viscosity of the pulp can be keeped at a relatively higher level of 837ml/g. The optimum conditions for split addition of alkali during the oxygen bleaching process were as follows: alkali charge was O1:2.0%,O2:1.0%,O3:1.0%,O4:0.5%; temperature was 80℃,90℃,100℃,110℃respectively; reacting time was keeped for 20min and 30min in the first two stage,40 min and 60 min in the following two stage; oxygen pressure was 0.6MPa; MgSO4 charge was 0.3%and the pulp concentration was 10%. Under these conditions, the delignification rate of the unbleached pulp was 70.8%, and the viscosity of the pulp was 778ml/g, decreasing rate of viscosity was 27.6%, brightness was 46.44% ISO.This subject was subsidized by the National Natural Science Foundation of China'Projects"The Analysis about Mechanism of Pulp Oxygen Delignification Process & New Notion of Oxygen Delignification Maximization"(30671653)...
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