Performance of three delignifying pretreatments on hardwoods: hydrolysis yields, comprehensive mass balances, and lignin properties

Journal Article · 09 September 2019 · Biotechnology for Biofuels

DOI: https://doi.org/10.1186/s13068-019-1546-0 · OSTI ID:1618770

Bhalla, Aditya ^[1]; Cai, Charles M. ^[2]; Xu, Feng ^[3]; Singh, Sandip K. ^[4]; Bansal, Namita ^[1]; Phongpreecha, Thanaphong ^[1]; Dutta, Tanmoy ^[3]; Foster, Cliff E. ^[1]; Kumar, Rajeev ^[2]; Simmons, Blake A. ^[3]; Singh, Seema ^[3]; Wyman, Charles E. ^[2]; Hegg, Eric L. ^[1]; Hodge, David B.  ^[5]

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1. Michigan State Univ., East Lansing, MI (United States)
2. Univ. of California, Riverside, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
4. Montana State Univ., Bozeman, MT (United States)
5. Michigan State Univ., East Lansing, MI (United States); Montana State Univ., Bozeman, MT (United States); Lulea Univ. of Technology, Lulea (Sweden)

Background: In this work, three pretreatments under investigation at the DOE Bioenergy Research Centers (BRCs) were subjected to a side-by-side comparison to assess their performance on model bioenergy hardwoods (a eucalyptus and a hybrid poplar). These include co-solvent-enhanced lignocellulosic fractionation (CELF), pretreatment with an ionic liquid using potentially biomass-derived components (cholinium lysinate or [Ch][Lys]), and two-stage Cu-catalyzed alkaline hydrogen peroxide pretreatment (Cu-AHP). For each of the feedstocks, the pretreatments were assessed for their impact on lignin and xylan solubilization and enzymatic hydrolysis yields as a function of enzyme loading. Lignins recovered from the pretreatments were characterized for polysaccharide content, molar mass distributions, β-aryl ether content, and response to depolymerization by thioacidolysis. Results: All three pretreatments resulted in significant solubilization of lignin and xylan, with the CELF pretreatment solubilizing the majority of both biopolymer categories. Enzymatic hydrolysis yields were shown to exhibit a strong, positive correlation with the lignin solubilized for the low enzyme loadings. The pretreatment-derived solubles in the [Ch][Lys]-pretreated biomass were presumed to contribute to inhibition of enzymatic hydrolysis in the eucalyptus as a substantial fraction of the pretreatment liquor was carried forward into hydrolysis for this pretreatment. The pretreatment-solubilized lignins exhibited significant differences in polysaccharide content, molar mass distributions, aromatic monomer yield by thioacidolysis, and β-aryl ether content. Key trends include a substantially higher polysaccharide content in the lignins recovered from the [Ch][Lys] pretreatment and high β-aryl ether contents and aromatic monomer yields from the Cu-AHP pretreatment. For all lignins, the ¹³C NMR-determined β-aryl ether content was shown to be correlated with the monomer yield with a second-order functionality. Conclusions: Overall, it was demonstrated that the three pretreatments highlighted in this study demonstrated uniquely different functionalities in reducing biomass recalcitrance and achieving higher enzymatic hydrolysis yields for the hybrid poplar while yielding a lignin-rich stream that may be suitable for valorization. Furthermore, modification of lignin during pretreatment, particularly cleavage of β-aryl ether bonds, is shown to be detrimental to subsequent depolymerization.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC02-05CH11231; FC02-07ER64494; AC05-00OR22725; DOE BER DE-AC02-05CH11231; SC0018409
• OSTI ID: 1618770
• Alternate ID(s): OSTI ID: 1572794
• Journal Information: Biotechnology for Biofuels, Vol. 12, Issue 1; ISSN 1754-6834
• Publisher: BioMed CentralCopyright Statement
• Country of Publication: United States
• Language: English