BLANKING PROCESS WITH PEROXIDE OF CELLULOSIC AND CELLULOSIC MATERIALS

摘要

A method for bleaching cellulosic and lignocellulosic pulp using hydrogen peroxide as a bleaching reagent, utilizes a three stage reaction, viz. two short high temperature peroxide bleaching steps (50,160) at a pressure sufficient to suppress boiling and an interstage treatment (90) including a longer atmospheric pressure reduced temperature bleaching step. The two short peroxide bleaching stages include the steps of introducing pulp, at a consistency of 10%-18%, to a mixer (20,130) in which the pulp is heated to a temperature above 100 degree Celsius; adding sufficient sodium hydroxide (32,142) to bring the pulp to a pH of 8.5; adding sufficient hydrogen peroxide (33,143) to equal from about 0.5%-5.0%, by weight, of the pulp; passing the pulp through a pressurized reactor column (50,160) at a rate providing a reaction time in the column of less than 45 minutes, cooling the pulp and discharging the cooled pulp to a washer. It may be desirable to introduce the pulp to a mixer and add alkali to reactivate residual hydrogen peroxide by bringing the pulp to a pH of at least 9 after the first bleaching stage, deposit the pulp in a reaction tower and allowing the reaction to proceed until a substantial portion of the residual hydrogen has been consumed. IMAGE