The optimum delignification conditions and delignification course during the pretreatment process of poplar kraft pluping with green liquor pretreatment

In this paper, optimal pretreatment conditions were obtained by investigating the influences of temperature, time and green liquor doses on delignification during pretreatment stage in poplar green liquor pretreatment-Kraft pulping process with orthogonal experiments firstly. Then delignification course during pretreatment stage was obtained by conditional experiments after orthogonal experiments. Finally reaction course was analyzed by the changes of OH- and HS- in the pretreatment liquor. The results showed that the optimal conditions of delignification were as follows: maximum temperature, 120°C; green liquor dose, 1L/kg; holding time, 1h; liquor ratio, 1:4. The delignification process had three periods, which were the initial delignification stage, mass delignification stage and residual delignification stage. During the pretreatment the main function of NaOH was to open the channels for ion penetration, and provided suitable environment for the reaction between HS- and lignin. The main function of HS^- was to react with lignin molecular and made it dissolvable after fragmentation.