Investigation On The Pulp Bleaching With Oxygen Cathode By Electrochemically Catalytic

With the development of pulp bleaching technology, electrochemistry bleaching arouse more and more people’s attention. During recent years, electrochemical hypochlorite bleaching and electrochemical mediator delignification have various degree of development. But there is rarely reported on the electrochemical bleaching with hydrogen peroxide. In our experiment, homemade graphite/PTFE gas diffusion electrode is used in the self-assembled electrolyzer to produce hydrogen peroxide and its electrochemical kinetics is discussed. Then H2O2-generation system with prepared gas diffusion electrode is used to bleach aspen kraft pulp and it proved that this system has a favorable effect in the applications. Moreover, different types of catalysts are mixed in the raw material of the gas electrode to form a new electrode and its various catalytic effect is discussed. We choose the catalytic electrode which has good properties to bleach populus Kraft pulp.The results showed that 2:1 of the mass ratio of graphite to PTFE and 300℃ of calcinations temperature are best conditions during the fabrication of gas diffusion electrode. Electrochemical treatment of Kraft pulp with the graphite/polytetrafluorothylene (PTFE) gas diffusion electrode through cathodic reduction of oxygen in alkaline aqueous solution was performed in a homemade electrolytic cell. The results illustrated delignification rate of 83.28% and brightness of 71.2% can be obtained under optimal conditions of 2.34mA/cm3 of electric current density,11.02 of electrolyte pH,6cm of anode-cathode distance and 240min of bleaching time.In this experiment, the electrochemistry kinetics about cathodic reduction of oxygen is discussed through electrochemical tests. Based on electrochemical parameters, we conclude that the gas adsorption plays an important role in the whole process. Cathodic oxygen reduction reaction itself is related to the gas-liquid solid phase. The adsorption rate oxygen to the electrode is slow and affects the entire reaction speed. So gas adsorption is speed controlled step. From that, we know optimizing the electrode structure is important in the electrode preparation process. If the electrode itself is porous, with a high oxygen adsorption, it is possible to efficiently produce high yields of hydrogen peroxide, and thus also it is conducive to populous kraft pulp bleaching.Cerium oxide, lanthanum oxide and zirconium are mixed in the carbon and PTFE with a certain appropriate to form a new electrode. The experiment indicates that the new electrode with zirconium showing good properties. It is founded that bleaching effect with the catalytic electrode is better than the original electrode. Kappa number of the bleaching pulp is decreased significantly and the rate of pulp viscosity loss can be controlled within 5%.