Use of Oxidized White Liquor As a Caustic Replacement in O, EO, EOP, and E2 Bleaching Stages of Kraft Hardwood and Softwood Pulp, 1997 Pulping Conference Proceedings

With the high levels of chlorine dioxide usage to meet environmental regulations, many mills have either a surplus of white liquor or a caustic imbalance. The use of oxidized white liquor as an alkali source in bleaching sequences can serve to maintain a chlor-alkali balance while at the same time utilize any excess white liquor. If the oxidized white liquor is of sufficiently high quality (i.e. no sodium sulfide and limited thiosulfate present), it can be used as an alkali source in any bleaching stage which would normally require sodium hydroxide. The oxidized white liquor used in this study (Q-OWL TM ) was prepared at a pilot plant located at a kraft mill using a stream of the mill’s white liquor. Analysis of this oxidized white liquor gave results indicating no sodium sulfide present and greater than 90% conversion to sodium sulfate. This modified OWL was compared to both NaOH and unoxidized white liquor as a caustic source in O, EO, EOP, and E2 stages of kraft hardwood and softwood bleaching sequences. In all cases, the modified OWL resulted in equivalent or higher brightness and viscosity values than obtained using caustic and both the modified OWL and NaOH gave better results than those obtained using white liquor.