The role of non-phenolic lignin in chlorate-forming reactions during chlorine dioxide bleaching of softwood kraft pulp

The affect of phenolic hydroxyl groups on the reaction efficiency during chlorine dioxide pre-bleaching of a softwood kraft pulp was investigated. The removal of phenolic hydroxyl groups via pulp methylation did not adversely affect the chlorine dioxide bleaching efficiency or the amount of chlorate formed during exposure to chlorine dioxide. Ion analysis of the reaction systems revealed that the formation of chloride and chlorite ions during the bleaching process were very similar between the kraft and methylated kraft pulps. These results indicate that the kinetic rates of lignin oxidation by chlorine dioxide and its reduction products, chlorite and hypochlorous acid, are much faster than the rate of inorganic reactions leading to chlorate formation.