Study Of Pulping Black Liquor Lignin Extraction And Filtrate Was Used For Cooking Wood Chips

Pulping black liquor is a kind of viscous fluid generated in the process of chemical pulping. It contains large amounts of organic matter and inorganic salt. By adding acid, the pH value of black liquor can be reduced so that lignin can be separated out. Then, by using vacuum filtration, lignin can be separated from black liquor. It is the very filtrate without lignin that can be used for pulping.This paper is a study of precipitating the lignin from the black liquor by acidifying the black liquor with sulfuric acid. After filtering out the lignin from the black liquor, finally the acidified filtrate can be produced. Then, using the filtrate, instead of the cooking water, to cook the wood chips to explore the influence of the cooking temperature, sulfidity, dosage of alkali and the dosage of filtrate on filtrate cooking. In this way, the optimum technology solution will come into being. After testing the properties of pulp which comes from filtrate cooking, analyzing the performance of black liquor, and comparing the properties of the pulp and black liquor in the process of conventional cooking with the new method, the following conclusions are drawn.1. To work out the optimum process of pulping by changing the cooking conditions of pulping and analyzing the yield, the kappa number, the brightness of the pulp and black liquor’s yield. That is, the cooking temperature is160℃; the dosage of alkali is22%; the sulfidity is28%; the dosage of filtrate is30%; liquid ratio is1:4; the heating time is70min; and the holding time is160min.2. To arrive at the pulp’s yield by detecting its properties. That is,45.34%. The kappa number of the pulp is18.32, and its viscosity is834mL/g. And the folding strength, thickness, tearability, bursting strength, tensile strength, brightness of this kind of paper are16times,0.0987mm,478mN,363kPa,4.30kN/m and30.39%ISO, respectively. By comparing the properties of pulp and paper in the process of filtrate cooking and the properties of pulp and paper in the process of conventional cooking, to draw conclusions, the pulp and paper’s properties of filtrate cooking and the pulp and paper’s properties of conventional cooking are basically consistent.3. To get the main compositions and their content of the black liquor by analyzing the chemical elements included in it. That is, C:37.2%, H:3.61%, N:0.27%, S:4.52%, O:36.4%and Cl:1.62%. Then work out the specific content of residual alkali, sodium sulfate, sodium thiosulfate, sodium sulfide, sodium carbonate and ash by analyzing the inorganics and ash content of the black liquor. That is,11.41g/L,27.86g/L,15.97g/L,17.90g/L,8.59g/L and76.97%, respectively.