Study On Bleaching Process And Reactivity Of Prehydrolysis Kraft-based Softwood Dissolving Pulp

The reactivity is a key quality parameter of viscose-grade dissolving pulp.It influences the production process, the final quality, the cost associated with the production, the environmental protection and the production efficiency of viscose rayon. In this paper, since the reactivity of the prehydrolysis kraft softwood dissolving pulp that produced in Fujian Qingshan Paper Industry Co., Ltd. was poor, the bleaching process was optimized in lab in order to improve the reactivity of the dissolving pulp.In this paper, the prehydrolysis softwood kraft pulp which was produced in the mill was used as the raw material.The original bleaching sequence was O-D0-EOP-D1-A, and the ultimatel bleaching sequence was replaced by OD0-E-D1-X through process optimization. Measured by performance optimization process to obtain a reaction slurry (Fock reaction performance and viscose filtering value), and other performance indicators and performance with a final-stage bleaching pulp production line performance comparison. At the same time by measuring the molecular weight and distribution of cellulose, cellulose crystallinity, fiber morphology analyze relevant mechanism slurry reactor with improved performance.Different bleaching stage processes, including oxygen delignification, chlorine dioxide bleaching, and alkali treatment, were optimized based on the brightness, kappa number, viscosity, metal ion content, and ?-cellulose content. Finally, the reactivity of the dissolving pulp which was bleached with the above optimized bleaching process was determined. The reactivity included the Fock reactivity, and viscose filtration value, In addtion other quality parameters of dissolving pulpwere also determined. The quality of dissolving pulp obtained in lab was compared with that produced in mill. Meanwhile, the mechanism associated with improved reactivity of dissolving pulp was analyzed, as according to cellulose molecular weight and distribution, crystallinity, and fiber morphology.The results showed that, the optimum conditions of oxygen delignification were as followed:NaOH dosage 2.5%, oxygen pressure 0.7MPa, temperature 90?,reaction time 75min, MgSO4 dosage 0.5%, pulp consistency 10%. The pulp properties under the optimum conditions were as followed:kappa number 3.6, viscosity 430.44 mL/g,pentosan content 3.69%, a-cellulose content 92.92%, brightness49.8%ISO. The optimum parameters of the first chlorine dioxide bleaching process were as followed:1.8% of CIO2 dosage, reaction time 60min, reaction temperature 60?, pulp consistency of 10%. The pulp properties under these optimum conditions were as followed:kappa number 1.4, viscosity 408.86 mL/g, pentosan content 4.42%, a-cellulose content 92.63%, brightness 71.5%ISO. The optimum parameters of alkaline treatment process were as followed:8% of NaOH dosage, reaction temperature 70?, reaction time 70min. The pulp properties under the optimum conditions were as followed:kappa number 0.9, viscosity 366.63mL/g, pentosan content3.37%, a-cellulose content 93.19%, brightness 75.2%ISO. The optimum parameters of the second chlorine dioxide bleaching process were as followed:0.5% of ClO2 dosage, reaction temperature 70 ?, reaction time 130min, pulp consistency of 10%. The pulp properties under these optimum conditions were as followed:viscosity 312.52 mL/g, pentosan content3.5%, a-cellulose content 93.73%, brightness 87.0%ISO. The optimum parameters of enzyme treatment process were as followed:enzyme dosage 0.01%, reaction temperature 50?, reaction time 60min, pH5.0, The Fock reactivity of enzyme-treated pulp was increased from 65.40% to 79.05%, and the viscose filtration value was only 75s. The production cost might be reduced by18RMB per ton pulp using the optimized bleaching sequence compared with the original bleaching sequence in mill.