A mechanistic model for Kraft pulping

A new mechanism is proposed for the heterogeneous delignification process during Kraft pulping. The mechanism consists of three key kinetic steps: adsorption of hydroxide and hydrosulfide ions on the lignin; chemical reaction on the solid surface to produce degraded lignin products; desorption of degradation products from the solid surface. The most important step for the delignification process is the surface reaction, rather than reactions occurring in the liquid phase. A kinetic model has thus been developed based on the proposed mechanism. The derived kinetic model shows that the mechanism can be employed to predict the pulping behavior under a variety of conditions with good accuracy.