Effect of lignin diffusion on kraft delignification kinetics as determinedby liquor analysis. Part I: An experimental study

This study provides an experimental evaluation of the effect of lignin diff usion on the kraft delignification kinetics of black spruce as determined b y liquor analysis. In this study, the measured lignin concentration in cook ing liquor was compared to the values calculated by using the delignificati on kinetics expressed through the well-known H factor: It was found that th e effect of temperature on the lignin concentrations from liquor analysis c ould not be described by using the classical value of 134 kJ/mol for the ac tivation energy for kraft cooking of black spruce. A lower activation energ y provided a better fit to the data. In addition, the measured rate was mor e than two times lower than the theoretical value at 180 degrees C. Diffusi on limitation, therefore, plays an important role in the delignification ra te as measured by liquor analysis. Cooking temperature or chip thickness or both have to be significantly reduced to eliminate the effect of diffusion on the measured rate.