Description of the Delignification of Kraft Cooks, 1991 Forest Products Symposium Proceedings

The delignification reactions of the kraft cooking are very complex. In a diagram for polysaccharide yield versus lignin yield it seems that delignification could be divided into three separate phases, initial delignification, bulk delignification and final delignification.

In an attempt to describe the overall delignification of the kraft cook, irrespective of the many chemical reactions, it was proposed that the ratio between pulp yield and lignin content should be used as a relevant characteristic of the final delignification. A good cook should reveal high pulp yield and at the same time a low lignin content. By rearranging the ratio it transforms to l/(k * C), where k = the slope factor and C = the chlorine number, considered an adequate measure of the lignin content of the pulp.

The result of this experiment was that the digestion seemed to consist of two phases only rather than three. The initial phase achieved was more or less independent of the cooking conditions, as the final phase obtained, described by a straight line, located on different levels or had different slopes dependent on the initial effective alkali charged and the white liquor sulphidity.