Determination of oxygen penetration rate in medium-consistency kraft pulps

摘要

In medium-consistency oxygen delignifi-cation processes, dissolved oxygen must diffuse to lignin located within the fibre for reaction to occur. In this study, we measured the extent of oxygen penetration into kraft pulp pads as a function of pad consistency and oxygen pressure. The penetration distance was followed using the oxidation of sulfite by molecular oxygen in the presence of a catalyst. We found that, under atmospheric conditions, the penetration rate of oxygen through medium consistency pulp suspensions was 2 to 4 mm/h, similar to that measured previously for pulp chlorination. This penetration rate increases to 4 to 6 mm/h when typical oxygen pressure conditions are used. A shrinking-core reaction model largely explained the diffusion of oxygen through the pulp pad.