The effects of temperature, alkali charge and additives in the oxygen delignification in high kappa number eucalyptus pulp kraft

Abstract

The purpose of this paper was to evaluate the effect of temperature, alkali charge, anthraquinone and ethanol additives in oxygen delignification for kraft pulp of Eucalyptus grandis vs. Eucalyptus urophylla with high kappa number and rejects content. In pulp production, the conventional kraft cooking was used with 13% alkaline charge, 25% sulfidity, in addition to H factor of 580. To reduce the rejects content, the pulp was subjected to two passages through the disc refiner. The oxygen delignification occurred in medium consistency (10%) and oxygen pressure of 5 kgf·cm-2, in addition to the delignification with the combination of four alkaline charges (15, 30, 45 and 60 kg·t-1) and four temperatures (80, 100, 120 and 140°C). The additives effect evaluation was made with 0.05% of anthraquinone and ethanol separately, just like the treatments with no additives as a reference. The brown pulp kappa number produced was 63.9 with 8.7% of rejects content. The comparison between the alkaline charge and temperature factors shows that the first is more influential in the oxygen delignification process. However, by increasing the temperature it was possible to reduce the kappa number with lower drop in selectivity. In addition, the temperature is the activating agent of the process reactions, given that for any alkaline charge applied, the residual alkali concentration decreases with the temperature increase. Also, there was no great drop in yield with the increased alkali charge and temperature. Simultaneously, the conversion of rejects into pulp ensured the yield maintenance. The anthraquinone addition showed no gains in the yield and in the kappa number results, but the process became more selective. The addition of ethanol showed positive results in terms of kappa number and rejects reduction, and also an increased yield. The total of solids generated had no significant influence of additives action.