Acidolysis of α-O-4 Aryl-Ether Bonds in Lignin Model Compounds: A Modeling and Experimental Study

Journal Article · Mon Jul 06 04:00:00 EDT 2015 · ACS Sustainable Chemistry & Engineering

DOI:https://doi.org/10.1021/acssuschemeng.5b00070· OSTI ID:1351580

Pelzer, Adam W.; Sturgeon, Matthew R.; Yanez, Abraham J.; Chupka, Gina; O’Brien, Marykate H.; Katahira, Rui; Cortright, Randy D.; Woods, Liz; Beckham, Gregg T.; Broadbelt, Linda J.

Lignocellulosic biomass offers a vast, renewable resource for the sustainable production of fuels and chemicals. To date, a commonly employed approach to depolymerize the polysaccharides in plant cell walls employs mineral acids, and upgrading strategies for the resulting sugars are under intense development. Although the behavior of cellulose and hemicellulose is reasonably well characterized, a more thorough understanding of lignin depolymerization mechanisms in acid environments is necessary to predict the fate of lignin under such conditions and ultimately to potentially make lignin a viable feedstock. To this end, dilute acid hydrolysis experiments were performed on two lignin model compounds containing the a-O-4 ether linkage at two temperatures concomitant with dilute acid pretreatment. Both primary and secondary products were tracked over time, giving insight into the reaction kinetics. The only difference between the two model compounds was the presence or absence of a methyl group on the a-carbon, with the former being typical of native lignin. It was found that methylation of the a-carbon increases the rate of reaction by an order of magnitude. Density functional theory calculations were performed on a proposed mechanism initiated by a nucleophilic attack on the a-carbon by water with a commensurate protonation of the ether oxygen. The values for the thermodynamics and kinetics derived from these calculations were used as the basis for a microkinetic model of the reaction. Results from this model are in good agreement with the experimental kinetic data for both lignin model compounds and provide useful insight into the primary pathways of a-O-4 scission reactions in acid-catalyzed lignin depolymerization. The distribution of primary and secondary products is interpreted as a function of two barriers of formation exhibiting opposite trends upon methylation of the a-carbon (one barrier is lowered while the other is increased). Such insights will be needed to construct a comprehensive model of how lignin behaves in a common deconstruction approach.

• Research Organization: NREL (National Renewable Energy Laboratory (NREL), Golden, CO (United States))
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 1351580
• Report Number(s): NREL/JA-5900-64929
• Journal Information: ACS Sustainable Chemistry & Engineering, Journal Name: ACS Sustainable Chemistry & Engineering Journal Issue: 7 Vol. 3; ISSN 2168-0485
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
77 NANOSCIENCE AND NANOTECHNOLOGY
a-O-4
density functional theory
ether bond
microkinetic modeling