Kinetic Of Pulp Bleaching By Hydrogen Peroxide

Abstract

As the result of increasing environmental concern, new technologies for bleaching pulps have been developed. Chlorine containing bleaching agents have been replaced by more environmentally benign chemical, and the importance of hydrogen peroxide in pulp bleaching has rapidly increased. This paper reports the results of experimental and kinetics studies of pulp bleaching. About 20 g of dry pulp was treated by using sulfuric acid and ethylene diamlne tetra acetate (EDTA) at chelating stage. The treatment was carried out in plastic bags placed in a pre-heated water bath. The bleaching was performed with addition of H2O2 and NaOH at 70°C and 90°C. After the bleaching, the pulp was dewatered and washed carefully. The filtrate obtained from the initial dewatering was used to determine the pH and residual H2O2. The pulp was analyzed its lignin content. Two kinetics models were proposed. Both models assume that the process consist of two consecutive reactions, which are decomposition of H2O2 producing HOO- and reaction of lignin with HOO-. Further, the first model assumes that decomposition of H2O2 producing H2O and O2 does not occur, while the second model does. The results of the two models were verified by the experimental data. It turns out that the first model works well at the temperature up to 70°C, while the second model work well until 90°C.