Fundamental insight into the mechanism of oxygen delignification of kraft pulps. II. Application of surfactants

The use of commercial ethoxy-based alcohol surfactants for the efficiency of oxygen delignification of commercially manufactured softwood kraft pulps was investigated as part of a novel direction in oxygen research. The work described herein demonstrates that the surfactants can accelerate oxygen delignification (OD), without any adverse impact on the overall selectivity of the delignification reactions. In general, it was found out that the lower the molecular weight of the surfactant employed, the more pronounced was overall delignification. In order to increase the selectivity of oxygen delignification process, a selectivity enhancement system, catalytic in character, was employed in conjunction with the surfactants. Part of our study explored the limitations to OD as part of the surfactant and protector study. To this end, we embarked upon experiments that required very forcing OD conditions. When the kappa number was reduced to about 6 units, it was found out that the OD of pulps became extremely difficult. Under moderate mixing conditions (15-60 rpm), oxygen diffusion was seen as not being the controlling step of the OD process. Additionally, oxygen does not only react with the residual lignin in pulps, but also with the dissolved lignin in solution, while the oxygen consumption for the latter reaction is greater than that of the former.