Interactions between Low- and High-Molecular-Weight Portions of Lignin during Fast Pyrolysis at Low Temperatures

Chua, Yee Wen; Wu, Hongwei; Yu, Yun

doi:10.1021/acs.energyfuels.9b02813

Cited by 11 publications

(5 citation statements)

References 47 publications

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“…These results are in agreement with the report of Chua et al, who made a crude separation by lignin dissolution in THF. They observed that both the THF-soluble and -insoluble fractions, presumably of low and high MWs, respectively, produced significantly less char upon pyrolysis than the original lignin, i.e., similar to what we observed for all MW fractions [71].…”

Section: Quantitative Profiles Of Sec Fractionssupporting

confidence: 89%

Unfolding of Lignin Structure Using Size-Exclusion Fractionation

LaVallie,

Andrianova,

Schumaker

et al. 2023

Polymers

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The heterogeneous and recalcitrant structure of lignin hinders its practical application. Here, we describe how new approaches to lignin characterization can reveal structural details that could ultimately lead to its more efficient utilization. A suite of methods, which enabled mass balance closure, the evaluation of structural features, and an accurate molecular weight (MW) determination, were employed and revealed unexpected structural features of the five alkali lignin fractions obtained with preparative size-exclusion chromatography (SEC). A thermal carbon analysis (TCA) provided quantitative temperature profiles based on sequential carbon evolution, including the final oxidation of char. The TCA results, supported with thermal desorption/pyrolysis gas chromatography–mass spectrometry (TD-Py-GC-MS) and 31P NMR spectroscopy, revealed the unfolding of the lignin structure as a result of the SEC fractionation, due to the disruption of the interactions between the high- and low-MW components. The “unraveled” lignin revealed poorly accessible hydroxyl groups and showed an altered thermal behavior. The fractionated lignin produced significantly less char upon pyrolysis, 2 vs. 47%. It also featured a higher occurrence of low-MW thermal evolution products, particularly guaiacol carbonyls, and more than double the number of OH groups accessible for phosphitylation. These observations indicate pronounced alterations in the lignin intermolecular association following size-exclusion fractionation, which may be used for more efficient lignin processing in biorefineries.

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Section: Quantitative Profiles Of Sec Fractionssupporting

confidence: 89%

Unfolding of Lignin Structure Using Size-Exclusion Fractionation

LaVallie,

Andrianova,

Schumaker

et al. 2023

Polymers

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“…This abstract representation of coal structure is similar to the lignin representation described by Hou et al as a set of single-ring aromatics with two attributes (type of propanoic side chain and the nature of methoxy phenol) . Chua et al used THF extraction as a means to quantify low and high molecular weight lignin fractions . The authors showed that most of the carbon residue formed is due to the high molecular weight fraction.…”

Section: Lignin Structure Overviewmentioning

confidence: 71%

“…109 Chua et al used THF extraction as a means to quantify low and high molecular weight lignin fractions. 110 The authors showed that most of the carbon residue formed is due to the high molecular weight fraction.…”

Section: Lignin Structure Overviewmentioning

confidence: 99%

A Review on Lignin Liquefaction: Advanced Characterization of Structure and Microkinetic Modeling

Terrell

Dellon

Dufour

et al. 2019

Ind. Eng. Chem. Res.

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Lignin liquefaction microkinetics is a move toward a more first-principles (i.e., ab initio)-based understanding at the molecular level in reaction engineering. While the microkinetic modeling of reactions to obtain kinetic rate parameters of chemical reactions have been widely used in the field of gas phase combustion and heterogeneous catalysis, this approach has not been as thoroughly developed in the area of biomass thermochemical reactions (e.g., lignin pyrolysis, hydrothermal liquefaction). The difficulties in establishing the structure of complex heterogeneous materials, like lignin, is perhaps the main challenge in developing rational microkinetic descriptions of biomass thermochemical reactions. In this manuscript, we review the current state of the art and the challenges to develop microkinetic models for lignin liquefaction technologies (e.g., pyrolysis, hydrothermal liquefaction, solvolysis). A general strategy for the development of microkinetic models for lignin liquefaction technologies is discussed. The first hurdle is to obtain sufficiently rich experimental data of lignin underlying polymeric structure and methodologies to use this data to build realistic lignin structural representations. Some analytical techniques for lignin structural characterization and their associated data, as well as a correlation for calculating the degree of macromolecular lignin branching, are discussed. The presence of small lignin oligomeric structures and the role of these structures in lignin pyrolysis is also addressed. The ways in which elementary deconstruction and repolymerization reactions occur within this structure to form a liquid intermediate and how these deconstruction products continue to interact with each other until they are removed from the liquid intermediate is thoroughly discussed. Further, experimental work with model compounds and the effect of reaction parameters (e.g., temperature, pressure, vapor residence time) are reviewed. Another major challenge to develop microkinetic models of lignin liquefaction is to describe product removal mechanisms (e.g., evaporation, solubilization, thermal ejection) from the liquid intermediate. Group contribution methods are presented for estimation of thermophysical parameters, like normal boiling point and heat of vaporization for model structures. Once the products have been removed from the liquid intermediate, they continue reacting in the aerosol droplets, in vapor phase, or in the solvent depending on the liquefaction technology studied. These “secondary reactions” need to be included in realistic microkinetic models. Based on this review, we can state that with careful implementation, high-quality microkinetic models can be developed to simulate thermochemical lignin liquefaction.

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“…Some literature takes advantage of the comparatively low temperature, e.g., 400 °C, due to the relatively high reactivity of biomass char and also to avoid the volatilization of AAEMs or the thermal-annealing change of char structure. , Meanwhile, the interactions between low- and high-molecular-weight portions of lignin also affect the properties of char during pyrolysis at low temperature. Chua et al investigated the interactions between low- and high-molecular-weight portions of lignin during fast pyrolysis at 100–300 °C, indicating that the interactions made char structures more condensed due to the polymerization reactions of oxygenated functional groups and aromatic structures with fused 2–5 rings. Chua et al further found that the low-molecular-weight portion was largely decomposed into volatiles and the high-molecular-weight portion intended to initiate polymerization reactions.…”

Section: Factors Affecting Biomass Char Gasificationmentioning

confidence: 99%

A Review on Biomass Gasification: Effect of Main Parameters on Char Generation and Reaction

et al. 2020

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Reactions between char and gasifying agents are usually the controlling step and of a core role for the overall biomass gasification process due to the relatively low reaction rate. Char reactivity will be greatly affected via interacting with volatiles, such as steam, hydrocarbons, tarry compounds, and other light gas species. By taking the updraft/downdraft moving bed and fluidized bed gasifier as examples, this review discussed the effects of char generation and evolution in various reactor environments on its following reaction behaviors. The characteristics of biomass and subsequent char gasification are further examined in terms of feedstock types and their inherent inorganics. Then, the effects of operation conditions and gasifying reagents on biomass gasification are outlined mainly from the point of char production and the subsequent volatiles−char interaction. Finally, some directions and suggestions considering char conversion and utilization are addressed for the design and betterment of the biomass gasification process.

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Interactions between Low- and High-Molecular-Weight Portions of Lignin during Fast Pyrolysis at Low Temperatures

Cited by 11 publications

References 47 publications

Unfolding of Lignin Structure Using Size-Exclusion Fractionation

Unfolding of Lignin Structure Using Size-Exclusion Fractionation

A Review on Lignin Liquefaction: Advanced Characterization of Structure and Microkinetic Modeling

A Review on Biomass Gasification: Effect of Main Parameters on Char Generation and Reaction

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