ABSTRACT
Eucalyptus spp kraft pulp, due to its high content of hexenuronic acids, is quite easy to bleach. Therefore, investigations have been made attempting to decrease the number of stages in the bleaching process in order to minimize capital costs. This study focused on the evaluation of short ECF (Elemental Chlorine Free) and TCF (Totally Chlorine Free) sequences for bleaching oxygen delignified Eucalyptus spp. kraft pulp to 90% ISO brightness: PDP (Molybdenum catalyzed acid peroxide, chlorine dioxide and hydrogen peroxide), MOD/P (Molybdenum catalyzed acid peroxide, chlorine dioxide and hydrogen peroxide, without washing) D(PO) (Molybdenum catalyzed acid peroxide, chlorine dioxide and pressurized peroxide), D(EPO)DP (chlorine dioxide, extraction oxidative with oxygen and peroxide, chlorine dioxide and hydrogen peroxide), Q(PO) (Molybdenum catalyzed acid peroxide, DTPA and pressurized peroxide), and XP Q(PO) (Enzyme, molybdenum catalyzed acid peroxide, DTPA and pressurized peroxide). Uncommon pulp treatments, such as molybdenum catalyzed acid peroxide (P ) and xylanase (X) bleaching stages, were used. Among the ECF alternatives, the two-stage P D/P sequence proved highly cost-effective without affecting pulp quality in relation to the traditional D(EPO)DP sequence and produced better quality effluent in relation to the reference. However, a four stage sequence, XPQ(PO), was required to achieve full brightness using the TCF technology. This sequence was highly cost-effective although it only produced pulp of acceptable quality
Keywords:
ECF pulp; TCF pulp; xylanase; acid-catalyzed peroxide bleaching