Investigation on the Kinetics of Residual Phases of Delignification at Pulping Process of Bagasse

The kinetics of the delignification at the residual phase of kraft pulping of bagasse was studied. Kraft pulping was carried out under chemical charge of %14.11 (as NaOH, based on O.D. bagasse), sulfidity of %25.11 and liquor to raw material ratio as 20: 1. The cooking maximum temperatures as 85, 70 and 55°C, were selected and reaction time varied from 0 to 720 min. based on maximum temperature. The initial Klason and acid soluble lignin content of bagaase were measured as %19.23 and %1.87, respectively. The rate of delignification was first order with respect to lignin yield based on oven dried raw material and the process at least can be divided into three delignification phases. The reaction rate constants of delignification varied with pulping maximum temperature. The values were 1.6×10-3 min-1, 1.5×10-3 min -1 and 1.4×10-3 min-1 for cooking maximum temperature of 85, 70 and 55°C, respectively. The activation energy of delignification was 4.27 kJ/mol for residual phases. Lignin content at the transition point of second and third phases was calculated as 4.66, 5.21 and 6.17 percent for the cooking times of 85, 70 and 55oC, respectively. Thus, at transition points, lignin content of the pulp is a function of pulping temperature and decreases with increasing of cooking temperature.