DFT to study sugar dehydration reactions during cellulose fast pyrolysis

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

Submitted to: American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/18/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: Pyrolysis is a promising technology for producing clean fuels, chemicals, and materials from biomass (things like wood, grass, and agriculture plant wastes). A major challenge with pyrolysis, however, is that the chemical reactions involved can produce a very complicated mixture of products that is difficult to characterize. By improving our ability to understand the molecules that make up pyrolysis products, we will be able to more easily develop pyrolysis technologies to produce the fuels or chemicals that we want. In this research, we are studying the pyrolysis of cellulose, the primary building block of most biomass. Using some new laboratory techniques (specifically, high resolution mass spectrometry), we can analyze certain important pyrolysis products with much greater detail; however, there isn't a clear understanding of all the results that we get from this analysis. The goal of this work is to use our theoretical understanding of pyrolysis to study it with computational techniques (specifically, density functional theory) and compare the results we get in the laboratory to the results we get from the computer. The major focus of this poster will be to highlight the ways in which laboratory/experimental and computational results are complimentary and to show how this provides new insight for our research area. Preliminary results from our computational analysis will be presented. Future work for more laboratory analysis will also be discussed.

Technical Abstract: Dehyrdation is known to be among the most important reactions to occur during cellulose pyrolysis. This is in consonant with high-resolution mass spectrometry results from Pecha, et al. on the nature of secondary reactions in the liquid intermediate during cellulose fast pyrolysis, which revealed that dehydration is the major reaction pathway to form parent molecules (Ind. Eng. Chem. Res., 2017, 56(15), 4288-4301). This experimental work is the basis of our computational analyses with density functional theory (DFT), aiming to explore the energetics (Gibbs free energy, change in enthalpy and entropy) and have deeper understanding of the dehydration reactions of glucossacharides (particularly glucose, cellobiose and cellotriose). Dehydration of anhydrosugars (levoglucosan, cellobiosan, cellotriosan and cellotetrosan) is also being investigated. The goal of this presentation is to synthesize high-resolution mass spectrometry (specifically, FT-ICR MS) results of experimental cellulose pyrolysis with computational DFT results for cellulose dehydration. Calculations for sequential dehydrations of these model compounds is ongoing. Dehydration is performed via Maccoll elimination mechanism, where a C-O bond is broken with a concerted proton loss from a beta position, moving to the oxygen atom to form double bond and eliminate water. Geometry optimization and frequency calculations of all reactants, intermediates and products are done using DFT with the Gaussian 16 program suite at MO6-2X functional and 6-311++G(d,p) level of theory. All calculations are performed at the ground state and energy calculations are after zero-point energy corrections. The presentation will highlight the ways in which new insights can be taken from coupling experimental/analytical characterization (FT-ICR MS) and computational analyses (DFT) for cellulose pyrolysis. Future efforts will explore extending this approach to the analysis of lignin and whole lignocellulosic biomass pyrolysis.