The Effect of Green Liquor / Anthraquinone-modified Kraft Pulping on the Physical and Chemical Properties of Hardwoods

Modified kraft pulping of hardwood for the manufacture of linerboard grade pulp by using green liquor (GL) was investigated. The combination of GL and anthraquinone (AQ) to improve pulp qualities are discussed. More than 2 absolute percentage points of pulp yield increase was achieved by addition of AQ in the GL pretreatment at a Kappa number of 107 to 110. Furthermore, GL/AQ pretreatment modified kraft pulping also provided additional benefits in chemical savings and energy reduction. Approximately 23 to 26% of alkali saving and a lower H-factor compared to conventional kraft pulping were obtained in this modified kraft pulping process. The results indicate sulfide concentration in the post cook can play an important role on AQ function during pulping. A greater effect for AQ in GL pretreatment was achieved at a lower rather than higher sulfidity. The physical strength of the modified kraft pulp was also quite similar to conventional kraft pulp.