The relationship of pretreatment pulping parameters with respect to selectivity: optimization of green liquor pretreatment conditions for improved kraft pulping

Green liquor ( GL ) was used as a sulfide rich liquor to impregnate Southern pine wood chips in a pretreatment step for kraft pulping. A central composite experimental design was applied to investigate relationships between pretreatment conditions, chemical absorption, pulping selectivity, and primary pulp qualities. The derived equations provided a correlation between the independent cooking variables and described their influence on chemical absorption, pulp qualities, and other pulping parameters. The results indicate that a higher concentration of pretreatment liquor has the most significant impact for improving pretreatment and pulping processes as well as enhancing various pulp qualities. Since the chemicals in GL display different absorption characteristics in wood, pretreatment conditions can be optimized for higher sulfide absorption ratios. The experimental results revealed some notable trends between chemicals absorption and pulp properties. Sulfide absorption not only correlates with delignification, but also influences pulping selectivity and pulp yield. The sulfide to alkali ratio absorbed in wood chips is critical for improving pulping selectivity and enhancing pulp qualities. Finally, a higher hydrosulfide to hydroxide ratio is a key parameter for the benefit of pulping.