Abstract
Kraft pulping is the predominant technology in the pulp and paper industry for removing lignin from wood carbohydrates to produce paper, board, packaging, tissue, and specialty cellulose. However, the kraft process is energy intensive and expensive, and its yield is limited by the degradation of carbohydrates. Pretreatment can increase carbohydrate yield by limiting degradation via primary peeling of reducing end groups. However, protection of galactoglucomannan (GGM), the primary hemicellulose component of softwood, is minimal when conventional pretreatments are used. Here, we investigated the effectiveness of sodium methyl mercaptide pretreatment on southern pine wood chips under a range of experimental conditions. We found that pretreatment of biomass with 4.38% sodium methyl mercaptide at pH 12 and 105 °C for 60 min provided small but significant increases in xylan and cellulose yields relative to control conditions, but preservation of GGM was minimal. To provide insight into molecular-scale details of primary peeling, pretreatment, and alkaline hydrolysis, we performed classical molecular dynamics (MD) simulations under selected process conditions and quantum mechanical (QM) calculations of selected reactions. MD simulations showed that C1 of the GGM reducing end is more readily accessible by HO- and CH3S- ions than in cellulose. The free energy barrier for peeling calculated with QM is lower for GGM than for cellulose, indicating increased susceptibility to peeling. In addition, we found that GGM may be more susceptible to internal chain cleavage than cellulose. Thus, even though reducing end groups may be protected initially through pretreatment, new unprotected reducing end groups may be generated through alkaline hydrolysis. Taken together, these findings show the promise of methyl mercaptide as a pretreatment technology for cellulose retention and also provide molecular insight for improving its effectiveness toward GGM.
Original language | English |
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Pages (from-to) | 11571-11580 |
Number of pages | 10 |
Journal | ACS Sustainable Chemistry and Engineering |
Volume | 9 |
Issue number | 34 |
DOIs | |
State | Published - Aug 30 2021 |
Funding
This research was supported by the High-Performance Computing for Manufacturing Project Program (HPC4Mfg), which is managed by the U.S. Department of Energy (DOE), Advanced Manufacturing Office, within the Energy Efficiency and Renewable Energy Office. This work was partially authored by the Alliance for Sustainable Energy, LLC, the manager and operator of NREL for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes. Computer time was provided by the National Renewable Energy Laboratory Computational Sciences Center supported by the DOE Office of EERE under Contract No. DE-AC36-08GO28308. This research also used resources of the Compute and Data Environment for Science (CADES) at ORNL, which is managed by UT-Battelle, LLC, for the U.S. DOE under Contract No. DE-AC05-00OR22725.
Keywords
- Alkaline hydrolysis
- Biomass
- DFT
- Degradation
- Kraft pulping
- MD
- Peeling
- Pretreatment