Concerted Reactions and Mechanism of Glucose Pyrolysis and Implications for Cellulose Kinetics

Abstract

Concerted reactions are proposed to be keys to understanding thermal decomposition of glucose in the absence of ionic chemistry, including molecular catalysis by ROH molecules such as H(2)O, other glucose molecules, and most of the intermediates and products. Concerted transition states, elementary-reaction pathways, and rate coefficients are computed for pyrolysis of β-D-glucose (β-D-glucopyranose), the monomer of cellulose, and for related molecules, giving an improved and elementary-reaction interpretation of the reaction network proposed by Sanders et al. (J. Anal. Appl. Pyrolysis, 2003, 66, 29-50). Reactions for ring-opening and formation, ring contraction, retro-aldol condensation, keto-enol tautomerization, and dehydration are included. The dehydration reactions are focused on bicyclic ring formations that lead to levoglucosan and 1,6-β-D-anhydrousglucofuranose. The bimolecular ROH-assisted reactions are found to have lower activation energy compared to the unimolecular reactions. The same dehydration reaction to levoglucosan should occur for cellulose going to cellosan (e.g., cellotriosan) plus a shortened cellulose chain, a hypothesis supported by the very similar activation energies computed when alternate groups were substituted at the C1 glycosidic oxygen. The principles of Sanders et al. that distinguish D-glucose, D-fructose, sucrose, and cellulose pyrolysis prove useful in providing qualitative insights into cellulose pyrolysis.

High-temperature decomposition of the cellulose molecule: a stochastic molecular dynamics study

“…One reason for the lack of LGA formation in our simulations may be the high temperatures, which could lead to radical chemistry dominating over the concerted routes to LGA. Another factor may be the absence of the chemical and electrostatic environment of crystalline (or amorphous) cellulose, especially since the presence of hydroxyl groups on neighbouring chains has been proposed to catalyse concerted reactions (Assary and Curtiss 2012;Seshadri and Westmoreland 2012).…”

Multiscale molecular modeling can be an effective tool to aid the development of biomass conversion technology: A perspective

“…Glucose, a monomer of cellulose, is the most common of them all. Seshadri and Westmoreland (2012) investigated the pyrolysis of beta-D-glucose and pathways for reactions such as dehydration, retro-aldol condensation and keto-enol tautomerization were proposed. Their studies suggested that bimolecular mechanisms, involving a water molecule or a neighboring R-OH molecule, have a lower activation energy barrier than unimolecular decomposition of glucose.…”

Quantitative Insights into the Fast Pyrolysis of Extracted Cellulose, Hemicelluloses, and Lignin

“…Indeed, the chemical aspect of biomass fast pyrolysis can be described as a combination of parallel and successive reactions of a nonionic and ionic nature 13. If radical mechanisms are invoked and are predominant in coal pyrolysis,14 recent experimental evidence6, 7, 15 and theoretical calculations16, 17 for biomass fast pyrolysis suggest the predominance of nonionic reactions during the primary pyrolysis stage. This ongoing discussion on the importance and predominance of the ionic and/or nonionic character of fast pyrolysis reactions13 has provided important clues that have not yet been used to rationalize the degradation modes.…”