Synergy of Anthraquinone/Polysulfide Pulping: The Effect of Sulfidity, 2002 Kraft Pulp Yield Anthology

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The individual and combined effects of anthraquinone (AQ) and polysulfide (PS) on kraft pulping of western softwoodwere investigated in a laboratory batch digester. Previous studies have shown that an increase in active alkali is requiredwhen pulping with polysulfide to achieve the same kappa number as in conventional kraft cooks. In this study,anthraquinone was used to reduce the alkali requirements for the polysulfide pulping to constant kappa number. Thepurported synergistic effect of anthraquinone and polysulfide on pulp yield when pulping to constant kappa number wasalso investigated. Wood chips were cooked with polysulfide liquor at two different sulfidity levels to provide supportfor the hypothesis that the enhanced delignification with AQ in the presence of polysulfide is due to the increasedeffectiveness of anthraquinone at the lower effective sulfidity of the polysulfide liquor.