Characterisation of pulp demethylation during chlorine dioxide bleaching

Chlorine Dioxide Bleaching

“…It is formed from the reaction of hypochlorous acid with chlorite ions (Ni et al, 1993;Germgard et al, 1981;Asplund and Germgard, 1991;Lindgren and Nilsson, 1975;Bergnor et al, 1987). Chlorate does not react with the pulp and also represents a loss of bleaching potential (Nilsson and Sjöström, 1974;Rapson and Anderson, 1977;Reeve and Rapson, 1981;Germgrad et al, 1981;Bergnor et al, 1987;Reeve, 1996). Chlorate formation is proportional to chlorine dioxide consumption and is strongly dependent on the bleaching pH.…”

“…Several studies have been conducted on the generation of organochlorine compounds during reaction of chlorine dioxide with unbleached pulp (Ni et al, 1992(Ni et al, , 1994aAxegard, 1987;Solomon et al, 1994;Morgan et al, 1991;Smith et al, 1995;Kolar et al, 1983;Dahlmann et al, 1995;Wallis and Wearne, 1994). About 50% of the applied chlorine dioxide is converted to hypochlorous acid (Kolar et al, 1983).…”

“…Attempts to reduce the amount of AOX formed during D0 stage generally result in a parallel decrease in delignification efficiency, for example when additives are used (Joncourt et al, 1995;Ni et al, 1994b). One way to reduce the AOX, while maintaining the same delignification efficiency, is to apply chlorine dioxide in neutral conditions (pH 6-8), which generates chlorite.…”

“…The organochlorine compounds are formed by the reaction of lignin and hypochlorous acid (Ni et al, 1994a). All the organically bound chlorine (in the pulp and in the liquor) is produced in the first 10 minutes of the reaction (Ni et al, 1992). Substitution of chlorine dioxide for chlorine in a bleaching sequence reduces the AOX level in the bleaching filtrates, and also changes the nature of the organochlorines formed during bleaching (Axegard, 1987).…”

“…About 50% of the applied chlorine dioxide is converted to hypochlorous acid (Kolar et al, 1983). The organochlorine compounds are formed by the reaction of lignin and hypochlorous acid (Ni et al, 1994a). All the organically bound chlorine (in the pulp and in the liquor) is produced in the first 10 minutes of the reaction (Ni et al, 1992).…”