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Increasing hardwood kraft pulp yield using sodium methyl mercaptide

Ravikant Patil and Adriaan van Heiningen
From the journal Holzforschung


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.

Corresponding author: Ravikant Patil, Department of Chemical and Biomedical Engineering, University of Maine, Orono, ME 04469, USA, E-mail:


The authors acknowledge the helpful discussions with the technical members of APPTI, the technical management of Amy Luce, the Technology Research Center Manager of the Forest Bio-Products Research Institute (FBRI) at the University of Maine, and the assistance of Amos Cline of the University of Maine in setting up the MDOB equipment used in this work.

  1. Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

  2. Research funding: This work was funded by the Alliance for Pulp & Paper Technology Innovation (APPTI), Washington, DC, USA.

  3. Conflict of interest statement: The authors have no relevant financial or non-financial conflict of interests to disclose regarding this article.


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Received: 2021-06-29
Accepted: 2022-02-11
Published Online: 2022-03-23
Published in Print: 2022-06-27

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