Patent ID: 6042690
Filing Date: 2000-03-28
Classification: D21C

Abstract:
A process for the bleaching of a cellulosic pulp to a target brightness of at least about G. E. 75 and a viscosity of at least about 14 cP comprising:a first stage which includes contacting said pulp at a consistency of between about 2% and about 15% and a pH of between about 1.5 and about 3 with a chlorination agent including at least about 50% chlorine dioxide and a chlorination factor of between about 0.1 and about 0.25 and, thereafter, without an intervening treatment other than an optional water wash,a second stage subsequent to the first stage which includes contacting said pulp at a pH of about 5 or lower and a consistency of between about 1% and about 30% with ozone and, thereafter, without an intervening treatment other than an optional water wash,a third stage subsequent to the second stage which includes contacting said pulp with chlorine dioxide at a pH at the end of the stage of from about 2.5 to about 3.5, wherein the effluent from said bleaching process contains less colored matter and exhibits a lower COD than the effluent from a pulp bleaching process wherein there is employed an alkali extraction between either of said first or second stages.