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This work introduces a phenomena-based model for delignification in the kraft pulping process. The solubilization of lignin is described as a set of chemical reactions representing the entire chemistry of lignin degradation as well as dissolution of the degraded lignin. For modeling, reaction mechanisms and reactions kinetics derived mainly from the literature were used. Each reaction was simulated separately and then combined for the overall degradation. The model was validated with experimental results from pine wood meal pulping under a wide range of reaction parameters. The experimental data presented a good fit with the model. With the aid of the model, the structure and the amount of wood components, in fibers and black liquor, can be determined at any pulping stage. Several engineering parameters can be computed from the detailed chemical composition of liquor and wood or chemical pulp. These include, e.g., kappa number, brightness, yield, active alkali, effective alkali, sulfidity, and higher heating value.

The article introduces a detailed model for carbohydrate chemistry in kraft pulping. This article is continuation to the modeling work carried out for hot water extraction and chemical pulp bleaching. The model includes galactoglucomannan, xylan, and cellulose acid-base equilibria, in addition to peeling, stopping, and alkaline hydrolysis reactions of the same carbohydrates, as well as hexenuronic acid formation and degradation reactions. The Arrhenius parameters were applied from the literature or regressed against experimental data in the present study. The model is very successful in predicting the experimental data of carbohydrate reactions during kraft pulping. Many features of the pulping-related model can be applied to specific fractionation chemistry considerations. The detailed knowledge on carbohydrates composition at any stage of pulping gives possibility for further development of biorefinery cases based on kraft pulping, such as biofuel and chemicals production.

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The effect of pH, ionic strength, and temperature on the kinetics of oxidation reactions between residual lignin and polyoxometalate (POM) anions ([AlMn III (OH 2 )W 11 O 39 ] 6and [SiMn III (OH 2 )-W 11 O 39 ] 5-) in a pulp suspension of unbleached softwood kraft pulp at varying conditions was investigated. According to the results, cation concentration and pH have a remarkable effect on reactivity of the POMs. At cation concentrations e0.10 mol L -1 , no reaction was observed during the first 5000 s; at 0.30 mol L -1 , the reactions were significantly more rapid, and the rate correlated strongly with increasing pH for both POMs. The activation energies (E a ) of the oxidation reactions at 0.30 mo L -1 cation concentration varied between ∼27 and 68 kJ mol -1 for [AlMn III (OH 2 )W 11 O 39 ] 6-, depending on pH and reaction time; the respective values for [SiMn III (OH 2 )W 11 O 39 ] 5were ∼17 to 82 kJ mol -1 . The reasons for the observed decrease in E a along with increasing pH and cation concentration are discussed.

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