EFFECT OF RESIDUAL EFFECTIVE ALKALI ON EUCALYPTUS KRAFT PULP YIELD AND CHEMISTRY

Abstract

The impact of residual effective alkali (REA) and pulp delignification degree on Eucalyptus kraft pulp yield and chemistry was investigated. The study was carried out with Eucalyptus globulus x Eucalyptus nitens hybrid, Eucalyptus nitens, Eucalyptus globulus and Eucalyptus urophylla x Eucalyptus grandis hybrid.  The chips were cooked to kappa numbers of 14±1, 18±1, 22±1 and 26±1 using two different ranges of REA, namely: low-REA (1-2 g L^-1) and high-REA (8-9 g L^-1). In general, the low-REA cooks lead to pulps of higher yield, viscosity and xylans content and lower brightness and HexA content, in relation to the high-REA cooks. In addition, the low-REA cooks required about 20% less effective alkali to achieve the target kappa, in spite of demanding about 50% more H-factor. Similar trends were observed for the other woods and kappa values evaluated, but the level of gains varied substantially among woods and delignification degrees. Among the various woods, E. globulus was the easiest to delignify.  There was a trend of higher brown pulp yield for the cooks terminated at higher kappa in the range of 14-26, but the lignin-HexA free screen yields were about similar in the kappa range of 18-26 for a given wood type.