Study On The Recovery Treatment And Reaction Mechanism Of Black Liquid Alkali In Chemical Mechanical Pulp

In this study,the black liquor of chemical-mechanical pulp was used as raw material to analyze the characteristics of the black liquor.According to its characteristics,the calcification precipitation method was used to recover the alkali.The eucalyptus chemical mechanical pulp was produced through the direct recovery of alkaline liquor circulating cooking pulping process,and the paper-forming performance of paper preparation was discussed.A water flow model for wastewater reuse in the pulp mill was established and simulated and analyzed.By adding calcium oxide directly to the black liquor,they will undergo a calcification reaction to produce sodium hydroxide solution and mixed precipitation,so as to achieve alkali recovery,and obtain new materials such as lignin calcium,and explore the relevant reaction mechanism.(1)The physical characteristics of chemical mechanical pulping black liquor were analyzed,and the results showed that the solid content of chemical mechanical pulping black liquor was lower and the water content was larger than that of chemical pulping black liquor.According to the analysis of elemental composition,the high content of organic substance and sodium inblack liquor indicated that it could be treated with alkali recovery.According to infrared spectroscopy,the organic structure of black liquor contains functional groups such as benzene ring,carbonyl group,and hydroxyl group.At the same time,organic compounds including aromatic compounds,alcohols,and phenols exist,and the composition is relatively complex.(2)Explore a new process of alkali recovery for the reaction of chemical machine black liquor with calcium oxide,considering the influence of black liquor concentration,calcium oxide dosage and reaction time on the calcification reaction.With reference to the single-factor experiment results,the Design-Expert software was used to fit the orthogonal experiment plan,and the results were subjected to range analysis.The optimal process conditions obtained were: black liquor concentration 2.0%,calcium oxide dosage 2.5 g,reaction time 30 min.At this time,the COD removal rate,alkali recovery rate,color removal rate and lignin removal rate of the calcification solution were64.9%,54.17%,84% and 71.99%.(3)According to the circulating cooking experiment,the eucalyptus chemical mechanical pulp is prepared.The results showed that the pulp yield was 9.6 to 13.3% higher than that of the conventional non-circulating alkaline pre-cooking pre-treatment chemical machine pulp preparation method,and can ensure that the paper has excellent physical properties.By establishing a distribution model of pulping wastewater flow and using experimental data as the basis,the use of circular cooking technology can reduce the cooking andgrinding wastewater produced by the pulp mill by 90.6%.(4)By scanning electron microscopy analysis,the surface morphology of calcified lignin is irregularly granular,with a small particle size and a loose surface morphology.Based on the relevant chemical reaction theory and simulated precipitation experiments,it is preliminarily assumed that these three substances,sodium lignin,sodium resinate and sodium carboxylate,can react with calcium ions to form precipitates.The infrared spectroscopy contrast analysis of the calcification reaction precipitates shows that the main component of the calcification precipitates is lignin,which proves that calcium lignin is the main component of the precipitates.