Pyrolysis kinetics for lignocellulosic biomass-to-oil from molecular modeling

Westmoreland, Phillip R.

doi:10.1016/j.coche.2019.03.011

Cited by 14 publications

(15 citation statements)

References 46 publications

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“…This lower apparent barrier was consistent with computed energies for a mechanism where vicinal hydroxyl groups on neighboring cellulose chains promote facile proton transfer during transglycosylation, thus leading to a hydroxyl-catalyzed mechanism . These studies indicate that H-bonding in the vicinity of the reaction center can increase or decrease the activation kinetics depending on the conditions, i.e., solid crystal versus reacting melt, respectively, as has been noted in a recent review by Westmoreland . Such a significant influence of the H-bonding environments has been observed and is also prevalent in other biomass conversion reactions, particularly in the acid-catalyzed conversion of biomass-derived sugars. , …”

Section: Introductionsupporting

confidence: 85%

“…19 These studies indicate that H-bonding in the vicinity of the reaction center can increase or decrease the activation kinetics depending on the conditions, i.e., solid crystal versus reacting melt, respectively, as has been noted in a recent review by Westmoreland. 20 Such a significant influence of the H-bonding environments has been observed and is also prevalent in other biomass conversion reactions, particularly in the acid-catalyzed conversion of biomass-derived sugars. Alternatively, the vicinal hydroxyl reaction environment in cellulose can also be modified by the presence of natural metal impurities.…”

Section: ■ Introductionmentioning

confidence: 92%

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Cooperative Activation of Cellulose with Natural Calcium

Facas

Maliekkal

Zhu

et al. 2021

JACS Au

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Naturally occurring metals, such as calcium, catalytically activate the intermonomer β-glycosidic bonds in long chains of cellulose, initiating reactions with volatile oxygenates for renewable applications. In this work, the millisecond kinetics of calcium-catalyzed reactions were measured via the method of the pulse-heated analysis of solid and surface reactions (PHASR) at high temperatures (370–430 °C) to reveal accelerated glycosidic ether scission with a second-order rate dependence on the Ca 2+ ions. First-principles density functional theory (DFT) calculations were used to identify stable binding configurations for two Ca 2+ ions that demonstrated accelerated transglycosylation kinetics, with an apparent activation barrier of 50 kcal mol –1 for a cooperative calcium-catalyzed cycle. The agreement of the mechanism with calcium cooperativity to the experimental barrier (48.7 ± 2.8 kcal mol –1 ) suggests that calcium enhances the reactivity through a primary role of stabilizing charged transition states and a secondary role of disrupting native H-bonding.

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Section: Introductionsupporting

confidence: 85%

Section: ■ Introductionmentioning

confidence: 92%

Cooperative Activation of Cellulose with Natural Calcium

Facas

Maliekkal

Zhu

et al. 2021

JACS Au

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“…Understanding the influence of these environments on the measured reactivity, however, is challenging due to the dynamics of the local cellulose structure as noted in a recent review. 32 The previous DFT studies discussed above have used static clusters to examine the effects of vicinal hydroxyl groups, and therefore little is known about the dynamic changes that occur at high temperatures, the entropies and free energies associated with such changes, or their influence on the reaction kinetics.…”

mentioning

confidence: 99%

Glycosidic C–O Bond Activation in Cellulose Pyrolysis: Alpha Versus Beta and Condensed Phase Hydroxyl-Catalytic Scission

2020

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Mechanistic insights into glycosidic bond activation in cellulose pyrolysis were obtained via first principles density functional theory calculations that explain the peculiar similarity in kinetics for different stereochemical glycosidic bonds (β vs α) and establish the role of the three-dimensional hydroxyl environment around the reaction center in activation dynamics. The reported activating mechanism of the α-isomer was shown to require an initial formation of a transient C1-O2-C2 epoxide, that subsequently undergoes transformation to levoglucosan. Density functional theory results from maltose, a model compound for the α-isomer, show that the intramolecular C2 hydroxyl group favorably interacts with lone pair electrons on the ether oxygen atom of an α-glycosidic bond in a manner similar to the hydroxymethyl (C6 hydroxyl) group interacting with the lone pair electrons on the ether oxygen atom of a β glycosidic bond. This mechanism has an activation energy of 52.4 kcal/mol, which is similar to the barriers reported for non-catalytic transglycosylation mechanism (~50 kcal/mol). Subsequent constrained ab initio molecular dynamics (AIMD) simulations revealed that vicinal hydroxyl groups in the condensed environment of a reacting carbohydrate melt anchor transition states via two-to-three hydrogen bonds and lead to lower free energy barriers (~32-37 kcal mol-1) in agreement with previous experiments. File list (2) download file view on ChemRxiv ChemRxiv_Narrative_Vineet_AlphaBeta_ver_05.pdf (0.92 MiB) download file view on ChemRxiv Vineet_theory_GBactivation_SI_ver_02.pdf (576.67 KiB)

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“…The contribution of hemicellulose to thermal pyrolysis is different from cellulose because the crystalline structure of cellulose has to be disrupted thermally to free the carboxyl groups at a certain temperature, whereas the hemicellulose chains are amorphous and disrupted at a lower temperature [16,79]. The degradation of hemicellulose mainly happens at a low temperature and the major weight loss occurs at 220-315 • C with higher CO 2 and char yields [80][81][82]. However, the maximum weight loss has been observed at 310 • C [23].…”

Section: Hemicellulose Pyrolysismentioning

confidence: 99%

Recent Insights into Lignocellulosic Biomass Pyrolysis: A Critical Review on Pretreatment, Characterization, and Products Upgrading

et al. 2020

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Pyrolysis process has been considered to be an efficient approach for valorization of lignocellulosic biomass into bio-oil and value-added chemicals. Bio-oil refers to biomass pyrolysis liquid, which contains alkanes, aromatic compounds, phenol derivatives, and small amounts of ketone, ester, ether, amine, and alcohol. Lignocellulosic biomass is a renewable and sustainable energy resource for carbon that is readily available in the environment. This review article provides an outline of the pyrolysis process including pretreatment of biomass, pyrolysis mechanism, and process products upgrading. The pretreatment processes for biomass are reviewed including physical and chemical processes. In addition, the gaps in research and recommendations for improving the pretreatment processes are highlighted. Furthermore, the effect of feedstock characterization, operating parameters, and types of biomass on the performance of the pyrolysis process are explained. Recent progress in the identification of the mechanism of the pyrolysis process is addressed with some recommendations for future work. In addition, the article critically provides insight into process upgrading via several approaches specifically using catalytic upgrading. In spite of the current catalytic achievements of catalytic pyrolysis for providing high-quality bio-oil, the production yield has simultaneously dropped. This article explains the current drawbacks of catalytic approaches while suggesting alternative methodologies that could possibly improve the deoxygenation of bio-oil while maintaining high production yield.

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Pyrolysis kinetics for lignocellulosic biomass-to-oil from molecular modeling

Cited by 14 publications

References 46 publications

Cooperative Activation of Cellulose with Natural Calcium

Cooperative Activation of Cellulose with Natural Calcium

Glycosidic C–O Bond Activation in Cellulose Pyrolysis: Alpha Versus Beta and Condensed Phase Hydroxyl-Catalytic Scission

Recent Insights into Lignocellulosic Biomass Pyrolysis: A Critical Review on Pretreatment, Characterization, and Products Upgrading

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