Softwood lignocellulose is a potential feedstock for the production of biofuels and bioproducts. However, the highly cross-linked nature of softwood lignocellulose restricts enzyme access to its sugars. Thus, harsh pretreatment conditions (180-280 °C) and/or high enzyme loading are required to unlock sugars. These requirements negatively affect the economic viability of softwoods in biorefineries. Here we show that H3PO4 pretreatment of pine and Douglas fir under a mild reaction temperature (50 °C) and atmospheric pressure enabled a high (∼80%) glucan digestibility with low enzyme loading (5 filter paper units (FPU)/g glucan). The dissolution and regeneration of softwoods disrupted the hydrogen bonding between cellulose chains, thereby increasing the cellulose accessibility to cellulase (CAC) values by ∼38-fold (from ∼0.4 to 15 m2/g biomass). Examination of H3PO4-pretreated softwoods by cross-polarization/magic angle spin (CP/MAS), 13C- nuclear magnetic resonance (NMR), and Fourier-transform infrared spectroscopy (FTIR) revealed that breaking of the orderly hydrogen bonding of crystalline cellulose caused the increase in CAC (higher than 11 m2/g biomass), which, in turn, was responsible for the high glucan digestibility of pretreated softwoods. The H3PO4 pretreatment process was feedstock independent. Lastly, 2D 13C-1H heteronuclear single quantum coherence (HSQC) NMR showed that the lignin was depolymerized but not condensed; thus, the lignin can be available for producing high-value products.
|Original language||English (US)|
|Number of pages||15|
|Journal||Industrial and Engineering Chemistry Research|
|State||Published - Dec 23 2019|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: A part of this work was supported by the National Science Foundation under Cooperative Agreement No. 1355438. Materials characterization was performed in part at the Conn Center for Renewable Energy Research at the University of Louisville, which belongs to the National Science Foundation NNCI KY Manufacturing and Nano Integration Node, supported by ECCS-1542174. This work was part of the DOE Joint BioEnergy Institute (http://www.jbei.org) supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, through Contract DE-AC02-05CH11231 between Lawrence Berkeley National Laboratory and the U.S. Department of Energy. The publisher, by accepting this article for publication, acknowledges that the United States Government retains a
nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, and allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). The authors would like
to thank Dr. Howard Fried for his valuable comments and suggestions on the manuscript.