Study On The Electrochemically Mediated Delignification And Bleaching And Its Mechanism Of Triploid Of Polulus Tomentosa Kraft Pulp

The toxic organochlorine compounds generated in pulp chlorine-containing bleaching have strong damages to environment. In order to resolve this problem and make paper industry in sustained growing, the new elemental chlorine free bleaching (ECF) and totally chlorine free bleaching (TCF) technology must be developed. The electrochemically mediated delignification (E_M) is one of new pulp bleaching methods. To find proper electrodes with high efficiency, high catalysis performance and mediators with high efficiency and high delignification selectivity is the key of setting up the electrochemically mediated delignification system, and it is also a key and difficult point of electrochemical bleaching research. In this thesis, the preparations and choices of different material electrodes and mediators, elecrochemically mediated delignification process, bleaching sequences including E_M stage and their mechanism were investigated, which would offer technical and theoretical support for appliction of this bleaching method in pulp and paper industry.The results of electrochemical chlorine-containing bleaching showed that the optimal technology conditions for one-stage electrochemical bleaching were as follows: initial pH value 8.0, temperature 40℃, voltage 3.5V, time 120min, NaCl 3.5%, pulp consistency 1%. The electrolyte could be recycled. The optimal techology conditions for two-stage electrochemical chlorine-containing bleaching were as follows: first stage: initial pH value 1.0, room temprature, current desity 0.1 A/cm², time 40min, NaCl 1.5%, pulp consistency 1%; second stage: initial pH value 8.0, temperature 40℃, current density 0.06A/cm², time 120min, NaCl 1.5%, pulp consistency 1%. Commpared with CEH bleaching, the electrochemical bleaching could reduce bleaching time when getting the same brightness, 80%ISO. The bleaching effluents from electrochemical bleaching had lower CODcr content than that from CEH.The electrode must be chosen on the basis of electrode potential and catalysis capablity. In this research, all the prepared electrodes with different material such as Ti/SnSbO_x, Ti/SnSbO_x/MnO₂, Ti/RuTiO_x, Ti/SnSbO_x/Pt and Ti/SnSbO_x/PbO₂ had catalysis crystal. The coated layer was smooth and dense. Among these electrodes, the electrodes of Ti/SnSbO_x/PbO₂ and Ti/SnSbO_x/Pt had highest electric potential. The electrode of Ti/SnSbO_x/MnO₂ had lowest electric potential. For violuric acid (VIO) mediated electrochemical delignification the electrode of Ti/RuTiO_x had best...