The Study Of H₂O₂Bleaching Catalyzed By Molybdate On Old Newsprint Pulp

H2O2bleaching of deink pulp of ONP catalyzed by molybdate was studied in this paper. The emphasis is on the effect of bleaching catalyzed by molybdate of deink pulp, and by comparing with the alkaline hydrogen peroxide bleaching to make sure of the effect of molybdate.The result indicates that adding molybdate to the bleaching stage of weak acidic H2O2can improve the brightness compared with pure weak acidic H2O2bleaching. The optimal conditions are as follows:dosage of molybdate is30ppm, pH value is5, the temperature is70℃, time is2hours.The brightness after pure weak acidic H2O2bleaching is45.8%ISO. After catalysis of sodium molybdate and ammonium molybdate, the brightness are47.2%ISO and46.7%ISO, the viscosity are767ml/g and774ml/g, the tensile index are25.95N· m/g and26.35N· m/g respectively. The effect of ammonium molybdate is lower than sodium molybdate on brightness, but it can protect the fiber well.After alkaline hydrogen peroxide bleaching, the brightness is49.9%ISO which is3%ISO higher than weak acidic hydrogen peroxide bleaching catalyzed by molybdate, but40ml/g lower on viscosity. By reducing the pH, the brightness is lower, but we will get better viscosity, that means, we can reduce the produce of anion.In order to improve the brightness of catalyzed axidic H2O2bleaching, we added TAED in the bleaching process. For alkaline hydrogen peroxide bleaching and catalyzed axidic H2O2bleaching, the brightness changed from49.9%ISO and47.2%ISO to52.8%ISO and49.8%ISO. TAED is effective to both alkaline hydrogen peroxide bleaching and catalyzed acidic H2O2bleaching.The highest brightness is under the ratio of0.5:1of TAED:H2O2. The bleaching result is better under the activation of TAED. The reaction rate is higher than the bleaching without TAED, the brightness is improved in40min, there is highest brightness in60min. less time will be taken. After adding TAED, the PC number is1.02%which is lower than the bleaching process without TAED. Then, TAED is effective for the stabbility of brightness.The result of alkaline hydrogen peroxide bleaching for the first section and FAS bleaching for the second bleaching has better brightness,56.8%ISO. Through catalyzed acidic H2O2bleaching and FAS bleaching, the brightness is54.1%ISO. So, in the weak acidic condition, the brightness can be improved under suitable conditons. It is an available way for hydrogen peroxide bleaching.