Comparison of various hardwood kraft pulp pre-bleaching techniques

We examined five pre-bleaching methods with the same starting hardwood kraft brownstock pulp to determine their effects on reducing bleaching costs. each pretreated pulp was subjected to a D(EP)D bleaching sequence. A D-1 brightness curve as a function of the percent applied chlorine dioxide (ClO2) was obtained for each of these pre-bleaching methods and for a baseline pulp sample. For each of the pre-bleaching methods, we calculated the amount of ClO2 required to obtain D-1 stage 79.1% ISO brightness and determined the net cost savings for each sequence. pre-bleaching methods that produced a net savings in the D1 stage were also subjected to a four-stage bleaching sequence of D(EP)DD to 89% ISO brightness. We also determined net cost savings resulting from pretreatment of the fully bleached pulps. The methods examined were mild acid pretreatment, xylanase enzyme pre-bleaching, brownstock peroxide pretreatment, acidic brownstock peroxide treatment, and xylanase enzyme followed by acidic peroxide pretreatment. enzyme pretreatment and small applications of acidic peroxide pretreatment resulted in net D-1 stage cost savings at 79.1% ISO brightness. only enzyme pretreatment resulted in a net savings at 89% ISO.