Studies On Hydrogen Peroxide Displacement Bleaching Processes And Mechanisms Of E. Globulus CTMP

The one- and two-stage H₂O₂ displacement bleaching processes and pretreatment processes before bleaching of E.globulus chemithermomechnical pulp (CTMP) were studied in this dissertation. Better processes of one-stage H₂O₂ displacement bleaching and chelating pretreatment of E.globulus CTMP were brought forward. The multi-stage (more than two-stage) H₂O₂ displacement bleaching process was simulated. Meanwhile, mechanisms of chelating pretreatment and H₂O₂ displacement bleaching were investigated in this dissertation.Influence of various factors on two-stage H₂O₂ displacement bleaching of Eglobulus CTMP was investigated .The results showed that the pH of H₂O₂ displacement bleaching should be lower than that of H₂O₂ conventional bleaching. H₂O₂ concentration in bleach liquor should not be too high. The temperature of 70℃ was a transition temperature to bleaching efficiency of E.globulus CTMP H₂O₂ displacement bleaching. The bleaching efficiency under 70℃ was higher than that of more than 70 ℃.It was totally different from H₂O₂ conventional bleaching that the bleaching efficiency dropped down rapidly along with the increase of pulp consistency. The H₂O₂ consumption decreased effectively when both sodium silicate and magnesium sulphate were present in bleach liquor. The better conditions were: 10% pulp consistency, pH 10.6,bleach liquor containing 10g/l H₂O₂,2-4g/l Na₂SiO₃ and 0.10g/l MgSO₄.The study on one-stage H₂O₂ displacement bleaching and chelating pretreatment showed that the phenomenon of channeling was relatively serious in laboratory displacement bleaching reactor. The volume of bleach liquor of using to displace the liquor in the pulp pad completely was about twice as much as the volume of the liquor in the pulp pad. Brightness and H₂O₂ consumption decreased along with the increase of superficial velocity, but bleaching efficiency increased along with the increase of superficial velocity. The effect of DTPA chelating pretreatment by displacement method was better than that of EDTA and DTPA chelating pretreatment by conventional method. The influencing sequence of various factors on H₂O₂ consumption was as following:...