The One Stage Extending Delignification Of Kraft Pulping Of Wheat Straw And TCF Bleaching Of Low-kappa-number Pulp

The supplies of material are shortage at present; it can be resovel by making good use of abundant grass resources rationally for papermaking industry. The grass is the most important material of pulping and paper making industry, but the discharge of chloride water in bleaching is one of the most serious pollution, in order to lighten the pollution of the waste water, the one stage extended delignification of Kraft pulping was applied to yield low-Kappa-number pulp of wheat straw in the paper, and the totally chlorine free (TCF) bleaching sequences was used.The one stage extended delignification of Kraft pulping of wheat straw used the same machinery and sequence. The rules were that the viscocity of delignification was faster than the degradation of carbohydrate under low temperature and sodium sulfide and the additive can increase the selectivity of delignification. In order to find the most important factor, the orthogonal methods were used at four factor and three levers. The compatible conditions for the one stage extended delignification of Kraft pulping of wheat straw were: total alkali charge 14%, sulfidity 15%, liquor-to-wood ratio 1:5, maximum temperature 140℃, time at cooking temperature 120 minutes ,additive charge 0.3%. The kappa number of the pulp in the conditions was 11.3, the yield was 54.8%, and the viscosity was 1171ml/g.tn the paper TCFp and TCFz bleaching sequences were used for low-kappa-number pulp that was yield by the one stage extending delignification of Kraft pulping.1. The compatible conditions for the hydrogen peroxide bleaching at higher pressure and higher temperature (Pn) were: reaction temperature 125℃; pressure 0.5Mpa; NaOH1.5%; reaction time 60min; pulp consistency 10%; Na₂SiPO₃: 3%; MgSO₄: 0.5%. The brightness of bleached pulp in the conditions was 76% SBD, the viscosity was 986 ml/g, and the kappa number was 2.56, respectively.2. The compatible conditions for the ozone bleaching were: ozone dosage 0.73%; pH 2; pulp consistency 13%; reaction temperature 25℃. The brightness of bleached pulp was 64.6%, viscosity 957 ml/g; kappa number 2.9 (there was an acid pretreatment before bleaching, and add 2.5% glycol into the pulp).3. The lignin in the pulp could protect the carbohydrate in ozone bleaching, and the lignin was the natural protector of the carbohydrate.4. The brightness of bleached pulp could be achieved 86.2%( SBD), and 86.9%(SBD) after AQ (P_N) Y and AZEYP, and it had better strength. AQ (P_N) P and AZEYP is a better choice for wheat straw pulp mill of low -kappa-number kraft pulp.