Influence of kraft pulping on the kinetics of oxygen delignification

Conventional kraft pulping was performed on mixed northeastern hardwood chi ps in a laboratory digester. Four pulps of kappa no. 15-16 were produced wi th the sulfidity held constant while the effective alkali charge and H-fact or were varied. The pulps were used in oxygen delignification experiments p erformed under industrially relevant conditions. Response variables were: k appa number, viscosity, COD, residual alkali, and final pH. Values were fou nd to depend on the effective alkali concentration used in pulping. The res ults suggest that more refractory lignin moieties occur during kraft pulpin g at low alkali levels and high H-factors. An alternative explanation is th at pulps with high xylan content are more difficult to delignify in an oxyg en stage.