INVESTIGATION OF PULPING EFFECT ON PULP YIELD AND THE LIGNIN CONTENT OF BLACK LIQUOR WITH A CENTRAL COMPOSITE KRAFT PULPING DESIGN

Kraft pulping of slash pine has been conducted with a batch, circulati on digester of a total volume of 0.10(m(3)) under a 2(k)+2k+1(k=4) cen tral composite experimental design, and 20 out of the 25 designed expe rimental points were duplicated. Three response variables of pulp yiel d, Kappa number and the lignin content of black liquor have been stati stically analyzed with respect to the four input variables of effectiv e alkali, sulfidity, cooking temperature, and time-at-temperature. Fou r statistics were used to discriminate among models and the statistica l criteria for development of predictive models were discussed and est ablished. Predictive models for pulp yield, Kappa number and the ligni n content of black liquor have been developed with reference to a full quadratic equation. All parameters in the predictive models were sele cted at a confidence level of 95% or higher. Response surface methodol ogy was used to study the complex effects of pulping variables on each response variable. Detailed results and discussions are presented.