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Bridging the Gap in Biomass Conversion: Understanding Enzymatic Hydrolysis of Cellulose and Hydrogenative Degradation of Lignin at the Molecular Level

Yue, Conghui
http://orcid.org/0000-0003-1399-6938
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627661055938336

Abstract Details

2021, PhD, University of Cincinnati, Arts and Sciences: Chemistry.
Abstract This dissertation focuses on biomass conversion, including the investigation of the effects of lignin structure on enzymatic hydrolysis, and lignin valorization to valuable chemicals under mild conditions. In this work, four different types of lignin model polymers have been synthesized and employed in enzymatic hydrolysis to understand their effects on glucose release. A cobalt-based catalytic system has also been developed to cleave the ether C–O bonds in lignin model compounds and organosolv lignin. The lignin structure is complicated to allow in-depth studies of structure-reactivity relationships. Thus, the use of lignin model systems can simplify the analysis, representing a viable strategy in this research field. On the other hand, overly simplified lignin model compounds may not necessarily reflect how real lignin behaves. Herein four lignin model polymers bearing ß-O-4 and/or ß-ß linkages and guaiacyl and/or syringyl units have been synthesized, which involves polymerization, further derivatization, and polymer purification. With medium complexity in structures, these polymers are expected to bridge the gap between overly simplified lignin model compounds and real lignin in terms of understanding the biomass conversion. Lignin model polymers I and IV contain ß-O-4 linkages with syringyl and guaiacyl units, respectively. Lignin model polymer II is composed of ß-O-4 and ß-ß with the syringyl unit only. Lignin model polymer III is composed of ß-O-4 and ß-ß with both syringyl and guaiacyl units. The complexity in lignin structure plays a crucial, yet not well-understood, role in sugar production from biomass via enzymatic hydrolysis. To understand the well-defined lignin structure’s influence, the aforementioned four lignin model polymers were employed in enzymatic hydrolysis. Lignin model polymers I and IV increase the glucose yield by 6% and 11%, while lignin model polymers II and III decrease the glucose yield by 3% and 2%, respectively. The adsorption isotherms of four lignin model polymers show that the lignin model polymers I and IV has lower bonding affinity and capacity than the lignin model polymers II and III. Unlike the ß-O-4 linkage, the ß-ß linkage presents an inhibitory effect on enzymatic hydrolysis. A catalytic system was developed to cleave the aliphatic and aromatic C–O bonds under milder conditions. The catalyst is produced through reduction of cobalt(II) bromide with Sodium triethylborohydride in toluene and the catalytic performance is enhanced by the additive Potassium tert-butoxide. The cobalt catalyst can promote the reductive cleavage of 4-O-5, ß-O-4, and a-O-4 bonds in lignin model compounds. The reductive degradation of organosolv lignin derived from loblolly pine and poplar, as well as a lignin model polymer has also been conducted under the catalytic conditions. This catalytic system is a potential method for lignin valorization to valuable chemicals with low costs.
Hairong Guan, Ph.D. (Committee Chair)
Allan Pinhas, Ph.D. (Committee Member)
Maobing Tu, Ph.D. (Committee Member)
Peng Zhang, Ph.D. (Committee Member)
156 p.
Chemistry
Lignin; Enzymatic hydrolysis; catalysis; model

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Citations

  • Yue, C. (2021). Bridging the Gap in Biomass Conversion: Understanding Enzymatic Hydrolysis of Cellulose and Hydrogenative Degradation of Lignin at the Molecular Level [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627661055938336

    APA Style (7th edition)

  • Yue, Conghui. Bridging the Gap in Biomass Conversion: Understanding Enzymatic Hydrolysis of Cellulose and Hydrogenative Degradation of Lignin at the Molecular Level. 2021. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627661055938336.

    MLA Style (8th edition)

  • Yue, Conghui. "Bridging the Gap in Biomass Conversion: Understanding Enzymatic Hydrolysis of Cellulose and Hydrogenative Degradation of Lignin at the Molecular Level." Doctoral dissertation, University of Cincinnati, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627661055938336

    Chicago Manual of Style (17th edition)

ucin1627661055938336
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This open access ETD is published by University of Cincinnati and OhioLINK.