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Using a Berty-type CSTR reactor, Ji (2007. Kinetics and mechanism of oxygen delignification, Ph.D. thesis. The University of Maine) obtained oxygen delignification kinetics first order in lignin when neglecting the higher initial delignification phase. In the present study the same Berty/CSTR reactor with an improved temperature control was used to determine the oxygen delignification kinetics of Southern Pine kraft pulp, with the kinetics now corrected for lignin removed by oxygen-free alkaline leaching. This removes the initial high delignification rate peak so that the kinetics over the entire lignin range can be modelled as first order in "reactive" lignin, which is lignin corrected for a small amount of unreactive lignin. It suggests that softwood pulp oxygen delignification consists of two contributions; phenolic delignification and alkaline leaching. The initial alkaline leaching phase is mathematically described by semi-infinite alkaline diffusion of dissolved lignin trapped in the cell wall after pulp washing. For phenolic delignification, the reaction orders in alkali concentration and oxygen of the power law delignification equation are 0.3 and 0.44 respectively, while the activation energy is 63 kJ/mol. Taking into account the unreactive HexA, the small amount of unreactive lignin, and the lignin removed by alkaline leaching, the kappa number is well predicted by the new delignification kinetics. [ABSTRACT FROM AUTHOR]

The objective of this work was to determine the effect of sodium methyl mercaptide (SMM) as an additive on the minimization of carbohydrate peeling reactions in Rock/Hard Maple (Acer saccharum) chips during kraft pulping. Two methods were evaluated for SMM addition to the pulping process: 1) pre-treatment before pulping and 2) co-addition with white liquor. The experimental results showed about 2.5% (on wood basis) increase in the kraft pulp yield after pre-treatment with 4.38% SMM (on wood basis) or the co-addition of the same amount of SMM with white liquor. The use of 4.38% SMM allowed a decrease in the white liquor effective alkali charge of 3% (on wood basis) to produce the target 14–15 kappa pulp. The 4.38% SMM charge was determined to be the optimum for both pre-treatment and co-addition. The increase in kraft pulp yield was mostly due to increased retention of cellulose (about 0.8% on wood) and xylan (about 1.8% on wood). The retention of glucomannan was insignificant in all cases. Based on the increase in intrinsic viscosity, it is concluded that the increased cellulose yield with SMM addition is caused by both reduced primary peeling and faster delignification rate (less alkaline hydrolysis followed by secondary peeling). The increased xylan retention is due to the lower effective alkali concentration during kraft pulping with SMM addition. [ABSTRACT FROM AUTHOR]