Patent ID: 6153051
Filing Date: 2000-11-28
Classification: D21C

Abstract:
A method for the treatment of kraft pulp in preparation for its use in papermaking comprising the steps of:contacting said pulp while dispersed in an aqueous medium with an initial charge of a chlorine-based bleaching agent selected from the group consisting of chlorine dioxide, and mixtures of chlorine dioxide and chlorine, wherein the total chlorine dioxide present in said charge represents between about 100% and about 50% of the total charge, expressed as effective chlorine, the remainder of said charge being chlorine, said bleaching agent producing a substantial quantity of chlorine-containing moieties that are insoluble in an acid medium,thereafter, and prior to any intervening treatment of said pulp other than a wash, contacting said pulp with ozone, said ozone being present in an amount which provides a ratio of ""C"" factor to % ozone, based on dry weight of pulp, from about 0.036 to about 0.7 for a period of time sufficient to cause said ozone to oxidize substantial quantities of said chlorine-containing moieties and render the same soluble in the acid medium of said pulp,thereafter, separating said solubilized chlorine-containing moieties from said pulp, andwhereby there is obtained a pulp having substantially lower chlorine content, essentially no 2, 3, 7, 8 tetrachlorodibenzodioxin, essentially no 2, 3, 7, 8 tetra-chlorodibenzofuran, and substantially equivalent brightness and viscosity as the same pulp which has been bleached employing conventional chlorine-based bleaching sequences.