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, circulation digester of a total volume of 0.10(m(3)) under a 2(k)+2k+1(k=4) central composite experimental design, and 20 out of the 25 designed experimental points were duplicated. Three response variables of pulp yield, Kappa number and the lignin content of black liquor have been statistically analyzed with respect to the four input variables of effective alkali, sulfidity, cooking temperature, and time-at-temperature. Four statistics were used to discriminate among models and the statistical criteria for development of predictive models were discussed and established. Predictive models for pulp yield, Kappa number and the lignin content of black liquor have been developed with reference to a full quadratic equation. All parameters in the predictive models were selected at a confidence level of 95% or higher. Response surface methodology was used to study the complex effects of pulping variables on each response variable. Detailed results and discussions are presented.