Reaction Course and Kinetics in NH_4OH-KOH Pulping of Wheat Straw

The reaction course and kinetics in NH 4OH KOH pulping of Shanghai wheat straw were studied in pulping experiments carried out under constant and well defined conditions. The results showed that three distinct delignification phases occurred during this pulping process of wheat straw, namely, the initial delignification phase from the beginning of the cook to 100 °C , the bulk delignification phase from 100 °C to 155 °C kept 45 minutes and the residual delignification phase at 155 °C kept 45 minutes to the end of the cook. It is found that about 65% of the lignin is dissolved in the initial phase. The delignification during the initial delignification phase is found to be pseudo first order with respect to residual lignin and 0.34 with respect to residual alkali. The activation energy of the delignification reaction is 29.75 kJ/mol and rate equation of delignification is -d L d t =7.602×10 2exp(-3 577 T ) Lc 0.34 OH - for first delignification phase.