Theoretical insights on the fragmentation of cellulosic oligomers to form hydroxyacetone and hydroxyacetaldehyde

Authors: DENSON, MELBA - Washington State University; Terrell, Evan; KOSTETSKYY, PAVLO - Northwestern University; BROADBELT, LINDA - Northwestern University; OLARTE, MARIEFEL - Pacific Northwest National Laboratory; GARCIA-PEREZ, MANUEL - Washington State University

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2023
Publication Date: 9/1/2023
Citation: Denson, M.D., Terrell, E., Kostetskyy, P., Broadbelt, L., Olarte, M., Garcia-Perez, M. 2023. Theoretical insights on the fragmentation of cellulosic oligomers to form hydroxyacetone and hydroxyacetaldehyde. Energy and Fuels. 37(18):13997-14005. https://doi.org/10.1021/acs.energyfuels.3c01924.
DOI: https://doi.org/10.1021/acs.energyfuels.3c01924

Interpretive Summary: One promising way to utilize biomass resources more effectively is through a thermochemical conversion process known as pyrolysis. In this process, biomass (e.g., wood, grass, agriculture residues) is heated in an inert environment and subsequently broken down into a bio-oil product. This bio-oil is comparable to petroleum and can be utilized for renewable energy and fuels; however, there is still significant research necessary to understand the key differences between biomass-derived and fossil-derived resources. In this work, the conversion of cellulose (a fraction of biomass) during pyrolysis is modeled using advanced computational techniques (i.e., density functional theory). In previous work, theoretical/computational work explored how cellulose breaks down from a larger polymer into smaller molecular fragments made up of several connected sugar units. In this study, the same theoretical/computational techniques are applied in order to understand how low-molecular weight compounds (with 2-4 carbon atoms) are produced during these reactions. These compounds are of interest for future development as renewable building blocks with a range of applications in green chemistry and engineering.

Technical Abstract: The presence of heavy unknown oligomeric sugar products in bio-oil is evidenced in experimental results reported in the literature. In this paper, we study the fragmentation reactions yielding acetol and glycolaldehyde from oligomeric sugars following previous work on dehydration reactions to propose structures of these oligomers. Acetol and glycolaldehyde are primary products of cellulose fast pyrolysis but the fragmentation reaction mechanism of these compounds from oligomers merits further study. The density functional theory (DFT) approach was employed to study this reaction. Results revealed that acetol and glycolaldehyde fragments are favorably removed from the non-reducing end based on their thermodynamic stabilities. As a result of this study, we propose chemical structures for new molecules. Theoretical FTIR and NMR spectra were calculated so that in the future when these molecules are separated, their experimental spectra and the theoretical ones herein reported can be used to confirm the structures of these oligomeric sugars. Also, the thermodynamics and physical properties of these compounds were estimated using the Group Contribution Method (GCM). These properties are essential in the design of technologies for bio-oil refining.