Addition of dissolved wood components to improve the delignification rate and pulp yield in hardwood kraft pulping

This study investigates the effects on the rate of delignification, HexA content and pulp yield of dissolved wood components (DWC) in the cooking liquor during the kraft pulping of Eucalyptus urograndis. The cooking was carried out with and without the addition of 50% DWC, in the form of black liquor, and also with and without the addition of a lignin-like model compound using a so-called constant composition cooking technique. The results show that the presence of DWC leads to an increase in the rate of delignification which makes it possible to reach kappa number 18 with an H-factor 40% less. Due to the faster delignification, 20% less HexA was formed at kappa number 18 when DWC was added than in the absence of added DWC. The presence of DWC also leads to a yield increase of up to two percentage points measured as lignin-free yield.