Improved Pulp Yield by Optimized Alkaline Profiles in Kraft Delignification of Birch Wood, 1998 Breaking the Pulp Yield Barrier Symposium Proceedings

The use of hardwoods in kraft pulping has enjoyed a rapid increase recently, yet little information is available from the literature about effects of pulping process parameters on delignification and pulp properties. Against this background, laboratory kraft pulping of birch wood chips was carried out at Åbo Akademi University. The major objective of the study was to investigate the effect of effective alkali (EA)profiles on kraft pulp yield. Results from the study indicate that the EA concentration profiles significantly affect delignification and pulp yield. The results also indicate that pulp carbohydrate composition issignificantly affected by the alkaline concentration throughout the pulping process. A higher EA concentration in the early stages of a cook tends to decrease mainly cellulose yield, while a higher EA concentration toward the end of the cook decreases mainly the yield of xylans. The study also demonstrated that with split, multiple white liquor additions, it is possible to manipulate the effective alkali concentration in different stages of a kraft cook so as to optimise for pulp yield, pulp viscosity, brownstock brightness and/or bleachability.