Study On Process And Mechanism For Bleaching Eucalyptus Slad Edging Pulp With Ozone And Chlorine Dioxide At Medium Concentration

With the increasingly strict national and local paper industry related emission standards and the advancement of papermaking end treatment technology,the paper industry has made significant progress in cleaner production and pollution prevention.However,with the in-depth implementation of the national ecological civilization construction strategy,the requirements for ultra-low emissions in the industry are getting higher and higher.As the chemical pulping with the largest amount of water pollution,it is necessary to further reduce the amount of wastewater in the bleaching process and reduce the pollution load.However,the currently adopted element-free chlorine?ECF?and total chlorine-free?TCF?bleaching processes are difficult to meet the requirements of high brightness of pulp,low pollution emissions and low bleaching costs.Studies abroad have confirmed that ozone bleaching has many advantages in terms of product quality,wastewater discharge,and bleaching costs,but there are no successful application cases in China.In this study,the eucalyptus wood board pulp was used as the raw material,combined with the characteristics of the domestic chemical method of pulping,which basically used medium-concentration bleaching.Before the conventional medium-concentration chlorine dioxide bleaching,a section of medium-concentration ozone bleaching was added to discuss the medium-concentration ozone bleaching and subsequent dioxide.Chlorine bleaching process and its effect on pulp performance and wastewater indicators after bleaching.This project research can provide process reference and theoretical guidance for the engineering of ozone bleaching technology and the practical application of light ECF bleaching with ozone bleaching.The thesis mainly conducts research from the following three aspects:1.Design the pressure ozone bleaching experiment platform by yourself,imitate the actual production conditions under laboratory conditions,carry out pressure ozone bleaching on the medium-concentrated eucalyptus wood board pulp,and discuss the factors such as reaction temperature,bleaching time,acid dosage,ozone concentration and other factors on the pulp Effects of viscosity,Kappa number and brightness.The experimental results show that:under pressure,each bleaching process condition has a significant effect on the pulp performance after bleaching;ozone concentration has the greatest impact on the pulp performance.The best ozone bleaching process of eucalyptus wood board pulp is:sulfuric acid dosage 3%,ozone concentration 3 wt%,reaction time 3 min,temperature room temperature,the final brightness of eucalyptus wood board pulp is 41.81%ISO,Kappa value is 10.55 The viscosity is 563.29 m L/g and the COD of ozone bleaching wastewater is 406.41mg/L.2.Using the slurry obtained under the best ozone bleaching conditions as raw materials,follow-up research on the medium-concentration chlorine dioxide bleaching process will be conducted.First,through a single factor experiment,the effects of Cl O2 dosage,temperature,and reaction time on pulp performance were studied,and better conditions were established;on this basis,a three-factor five-level central combined experimental design method?CCD?was used to establish a pulp card Mathematical model between the primary value,brightness and the amount of Cl O₂,temperature and reaction time.The experimental results show that the degree of influence of the three factors on the Kappa number and brightness is arranged from large to small:Cl O₂ dosage>time>temperature;the chlorine dioxide bleaching process parameters optimized by the CCD method fitting equation model are:reaction The time was47 minutes,the bleaching temperature was 71?,the amount of Cl O₂ was 1.8%,and the verification experiment under this process condition showed that the pulp properties were brightness of 61.0%ISO and Kappa value of 2.8,which was basically consistent with the predicted value.3.The effects of two stages of bleaching process on p H,COD and AOX in wastewater were investigated.The results show that the bleaching time and the amount of chlorine dioxide have significant effects on the p H,COD,and AOX of the wastewater;the bleaching temperature has little effect on the p H and COD of the wastewater,and has a significant effect on the AOX of the wastewater.The study found that the purpose of controlling the discharge of harmful substances in bleaching wastewater can be achieved by changing the process parameters.4.Various analysis and detection methods are used to study the changes of the morphology,microstructure and functional groups of the pulp before and after bleaching.The results showed that with the progress of bleaching,the length and width of the pulp fibers changed little,the surface of the pulp fibers became rougher,the crystallinity of the pulp fibers changed little,and the composition of the functional groups in the pulp did not change significantly.