Kinetic Studies of Kraft Pulping (Part 3)
Effect of Initial Phase on Selectivity of Delignification
1983 Volume 37 Issue 11 Pages 999-1004
Details
1983 Volume 37 Issue 11 Pages 999-1004
The kraft cook can be divided into three stages so called initial phase, bulk delignification phase and final phase. The initial phase comprises the pulping treatment up to a temperature of about 150°C and results in dissolution of 2030% of the total amount of lignin. The rate of carbohydrates loss (rate constant ; KC) and the delignification rate (rate constant ; KL) during the initial phase and the bulk delignification phase are firts order with respect to carbohydrates and lignin content respectively, The value of KL/KC ratio for the initial phase is lower that for the bulk delignification phase. This indicates that the selectivity (carbohydrates yield at given kappa number) of kraft cooking can be improved by the cooking schedule in which the cooking temperature goes up to over 150°C as soon as possible. The above prediction is comfirmed by the kraft cooking carried out on matchstick-like wood chips so that liquor penetration and diffusion would not be rate-controlling steps.
