Technology And Mechanism On Simultaneous Silicon-remain Cooking Tn Bamboo Pulp Based On Extended Delignification

Reasonable use of non-wood raw materials have a greatsignificance to improve China’s papermaking raw material structure,however, non-wood raw materials have more silicon content than thewood raw materials, meanwhile, the silicon which easily lead to"silicon interference" in the pulping process. Research on mitigating"silicon interference" has a positive meaning on reasonablly use ofnon-wood raw materials. It was emphasized on the theoretic researchand technology optimizing of simultaneous silicon-remian cooking inbamboo pulping. Silica dissolution law is derived on the basis ofoptimized bamboo pulp cooking process in order to achieve the purposeof simultaneous silicon-remain cooking in bamboo pulping process,some chemical agents were added at different stages of cooking processaccording to the silica dissolution law, and the mechanism ofsimultaneous silicon-remain in cooking process was studied by modernanalytical instruments such as XPS, SEM, XRD.Optimized bamboo pulp cooking process as follows: alkali charge24%; sulfidity24%（NaOH）, the first stage/the second stage liquid ratio1:4/1:4.5; the first stage alkali charge10%, sulfidity charge12%,remaining alkali liquid added into the second cooking stage; cookingcurve: the temperature was heated from room temperature to100℃in60minutes, and then insulation60minutes at100℃; in the secondcooking stage, adding the remaining alkali liquid, and the temperature was reheated to143℃in30minutes, insulation90minutes at143℃,after that, temperature was reheated up to160℃in20minutes, and theninsulation60minutes at the cooking temperature. After the cookingprocess, the bamboo pulp Kappa value is26, the degree ofpolymerization is1267and the screened yield was46.71%.The silica dissolution law was studied based on the optimizedcooking conditions, the dissolution rate of silica from raw material inthe first stage was more than that in the second stage, the ratio of silicondissolution was48%in the first stage, and22.4%in the second stagewas. A large number of silicon dissoluted in the first stage because ofthe high pH value, and the pH value in the first stage was higher thanthat in the second stage, causing the dissoluted silicon precipitation onthe fiber.The results showed that sodium aluminate, aluminum sulfate,calcium oxide all had an effect on silicon-remain, and the effect ofcombination of aluminum sulfate and calcium oxide was better than theagent separately added in the first stage. Optimized bamboosimultaneous silicon-remain cooking technology as follows: alkalicharge24%, sulfidity24%（NaOH）, the first stage/the second stageliquid ratio1:4/1:4.5, and the first stage alkali charge10%, sulfiditycharge12%, calcium oxide2%, remaining alkali liquid added into thesecond cooking stage. Cooking curve: the temperature was heated fromroom temperature to100℃in60minutes, and then insulation60minutes at100℃; in the second cooking stage, adding the remainingalkali liquid and1.04%aluminum sulfate, and the temperature wasreheated to143℃in30minutes, insulation90minutes at143℃, afterthat, temperature was reheated up to160℃in20minutes, and theninsulation60minutes at cooking temperature. Under the cookingconditions, the total rate of silicon-removal was77.54%, and the silicacontent of bamboo pulp was0.6798%.The results abtained from SEM-EDAX showed that sodiumaluminate and calcium oxide had the effect on silicon-remain, however,the silicon-remain mechanism is not the same. Sodium aluminate and sodium silicate reaction generated of very small solid particlesadsorbing on the fiber, which distributed uniform on the fiber to preventthe silicon transfering into the black liquid, so that the agent had thesilicon-remain effect; and calcium oxide and sodium silicate reactiongenerated flaky particles adsorbed on the fiber, which unevenlydistributed; the particles generated by adding aluminum sulfate in thefirst stage and calcium oxide in the second stage, which was small andcomposition was similar to zeolite; the particles generated by addingcalcium oxide in the first stage and aluminum sulfate in the secondstage which was more complex and higher silicon content.The results abtained from XPS showed that calcium oxide andaluminum sulfate also had silicon-remain effect, however, the effect ofadding agent alone in the first stage was not obvious. The results ofadding calcium oxide in the first stage and adding aluminum sulfateshowed that this cooking process had the best silicon-remian effect, andXPS analysis showed that the particles distributed uniform in the cellwall, remaining in the pulp silicide were organic silicide and inorganicsilicide, and the inorganic silicides content was more than organicsilicides content, for the inorganic silicides, mainly of SiO₂, SiS₂silicates and K₂SiF₈, organic silicide was ETSiCl₃.