The influence of temperature on delignification and carbohydrate degradation in soda-AQ pulping of softwood

The effect of temperature on both delignification rate in the bulk and residual phases and on carbohydrate degradation in soda-AQ pulping of softwood has been evaluated. Extremely high liquor-to-wood ratios were used in order to maintain constant chemical compositions throughout the cooks. The delignification in soda-AQ pulping was described by a model in which the delignification is regarded as first order reactions occurring in all three delignification phases simultaneously. It was assumed that the amount of residual lignin was independent of pulping temperature. The activation energies for the bull: and residual phases were calculated to 110 kJ/mole and 158 kJ/mole, respectively. The carbohydrate yield loss was described by two first order reactions with respect to easily and slowly dissolved carbohydrates. The dissolution of different types of carbohydrates was found to be temperature dependent. A possible explanation for this behaviour could be that AQ decomposes at higher cooking temperatures. The activation energies for both slowly and easily dissolution were calculated for two temperature ranges respectively. This resulted in two activation energies for loss of easily dissolved carbohydrates, 130 kJ/mole for temperatures 160-180 degreesC and 100 kJ/mole for temperatures 140-150 degreesC. The activation energy for loss of the slowly dissolved carbohydrates was calculated, 150 kJ/mole for temperatures 160-180 degreesC and 190 kJ/mole for temperatures 140-150 degreesC.