Abstract

Green liquor (GL) pretreatment for kraft pulping technologies was modified by applying anthraquinone (AQ) during the pretreatment stage. Analysis of the pulp lignin contents and final pulp yields demonstrated that the addition of AQ improved delignification selectivity. A proposed mechanism for the behavior of AQ during the GL pretreatment is that it amplifies delignification rather than preserves hemicelluloses. An analysis of the pulp carboxylic acid groups indicated that AQ did not affect the total carboxylic acid content in the pulp, but provided a lower hexenuronic acid content at a specific level of lignin content. In general, green liquor pretreatment reduces the energy requirement for pulping and improves chemical reactivity during delignification. As a result, net pulping efficiency for a kraft pulping operation can be improved.