EPR detection of key radicals during coking process of lignin monomer pyrolysis

Zhou, Qingguo; Luo, Zhongyang; Li, Guoxiang; Li, Simin

doi:10.1016/j.jaap.2020.104948

Cited by 31 publications

(8 citation statements)

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“…The methylated aromatic oligomer structures become quinone products according to the mechanism used in this study, as shown in Figure c. They were specifically benzoquinones, which can be an intermediate compound or a final product in lignin thermal decomposition in the biomass pyrolysis process, as suggested in earlier work. , These types of compounds have been found to be intermediate products during biomass pyrolysis. , This mechanism is also proposed for trimers and tetramers, and their difference lies in the methoxy groups available for demethylation reactions once the molecule is balanced. The mechanism of trimers and tetramers can be observed in Figures S1 and S2 of the supplementary material.…”

Section: Resultsmentioning

confidence: 54%

“…They were specifically benzoquinones, which can be an intermediate compound or a final product in lignin thermal decomposition in the biomass pyrolysis process, as suggested in earlier work. 45,46 These types of compounds have been found to be intermediate products during biomass pyrolysis. 47,48 This mechanism is also proposed for trimers and tetramers, and their difference lies in the methoxy groups available for demethylation reactions once the molecule is balanced.…”

Section: Simulated Structuresmentioning

confidence: 99%

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Elucidating Biomass-Derived Pyrolytic Lignin Structures from Demethylation Reactions through Density Functional Theory Calculations

et al. 2023

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Pyrolytic lignin is a fraction of pyrolysis oil that contains a wide range of phenolic compounds that can be used as intermediates to produce fuels and chemicals. However, the characteristics of the raw lignin structure make it difficult to establish a pyrolysis mechanism and determine pyrolytic lignin structures. This study proposes dimer, trimer, and tetramer structures based on their relative thermodynamic stability for a hardwood lignin model in pyrolysis. Different configurations of oligomers were evaluated by varying the positions of the guaiacyl (G) and syringyl (S) units and the bonds βO4 and β5 in the hardwood model lignin through electronic structure calculations. The homolytic cleavage of βO4 bonds is assumed to occur and generate two free radical fragments. These can stabilize by taking hydrogen radicals that may be in solution during the intermediate liquid (pathway 1) formation before the thermal ejection. An alternative pathway (pathway 2) could occur when the radicals use intramolecular hydrogen, turning themselves into stable products. Subsequently, a demethylation reaction can take place, thus generating a methane molecule and new oligomeric lignin-derived molecules. The most probable resulting structures were studied. We used FTIR and NMR spectra of selected model compounds to evaluate our calculation approach. Thermophysical properties were calculated using group contribution methods. The results give insights into the lignin oligomer structures and how these molecules are formed. They also provide helpful information for the design of pyrolysis oil separation and upgrading equipment.

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Section: Resultsmentioning

confidence: 54%

Section: Simulated Structuresmentioning

confidence: 99%

Elucidating Biomass-Derived Pyrolytic Lignin Structures from Demethylation Reactions through Density Functional Theory Calculations

et al. 2023

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“…70% in N 2 headspace (Figure S25), and a set of very weak EPR signals appear which are probably assigned to the phenoxy radical ( g = 2.0044) with short lifetime (Figure S27). − The abovementioned results indicate that the phenolic hydroxyl group is an electron donor that accelerates the CQD-mediated redox of Fe(II/III) which can bond with the carboxyl group via H-bond. KIE test was carried out to investigate the role of H(D)–O bond energy on the kinetics of Fe(II/III) step in CQDs Fenton-like catalysis (Figure d).…”

Section: Resultsmentioning

confidence: 98%

Overcoming Acidic H₂O₂/Fe(II/III) Redox-Induced Low H₂O₂ Utilization Efficiency by Carbon Quantum Dots Fenton-like Catalysis

Zhang

Wen

Pan

et al. 2022

Environ. Sci. Technol.

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Fenton reaction has important implications in biology- and environment-related remediation. Hydroxyl radicals (•OH) and hydroxide (OH–) were formed by a reaction between Fe(II) and hydrogen peroxide (H2O2). The acidic H2O2/Fe(II/III) redox-induced low H2O2 utilization efficiency is the bottleneck of Fenton reaction. Electron paramagnetic resonance, surface-enhanced Raman scattering, and density functional theory calculation indicate that the unpaired electrons in the defects of carbon quantum dots (CQDs) and the carboxylic groups at the edge have a synergistic effect on CQDs Fenton-like catalysis. This leads to a 33-fold higher H2O2 utilization efficiency in comparison with Fe(II)/H2O2 Fenton reaction, and the pseudo-first-order reaction rate constant (k obs) increases 38-fold that of Fe(III)/H2O2 under equivalent conditions. The replacement of acidic H2O2/Fe(II/III) redox with CQD-mediated Fe(II/III) redox improves the sluggish Fe(II) generation. Highly effective production of •OH in CQDs-Fe(III)/H2O2 dramatically decreases the selectivity of toxic intermediate benzoquinone. The inorganic ions and dissolved organic matter (DOM) in real groundwater show negligible effects on the CQDs Fenton-like catalysis process. This work presents a process with a higher efficiency of utilization of H2O2 in situ chemical oxidation (ISCO) to remove persistent organic pollutants.

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“…Foram detectados alguns adutos de radicais livres como o hidroximetil, hidroxila e acetila, confirmados mediante a comparação com os dados obtidos na literatura (SARAVANAN, 2013;SUMI et al, 2012;ZHOU et al, 2020).…”

Section: Radicais Formadosunclassified

Análise dos processos de eletro-oxidação simples e foto-assistido usando ânodo de mistura de óxidos metálicos comercial em meio alcoólico e atrazina como composto modelo

Parra¹

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Water contamination has been extensively studied due to its scarcity, aggravated by poor management of water resources. One of the pollutants that has received the most attention is atrazine, a herbicide widely used in agriculture. Therefore, studies of new technologies for the treatment of effluents as electrochemical processes, have become important alternative methods to the conventional ones. However, considering the low concentrations (high dilution) of these pollutants in water, an inherent problem is the low effectiveness of these alternative methods and, consequently, the high energy consumption. Therefore, a new adsorption pre-concentration methodology that can be integrated into the degradation process is being implemented to avoid the limitations of direct electrochemical treatment. Atrazine is a poorly soluble in water, which, when nonaqueous solventes are used, facilitates desorption in a small volume for electrochemical treatment. In this work, atrazine was degraded in methanol media in the presence of different proportions of water (0%, 5% and 10%) using a commercial mixed metal oxide anode and sodium chloride as supporting electrolyte. The results obtained showed atrazines removals up to 99.8% after 1h of electrolysis. The variation of the current density during electrolysis demonstrated that atrazine is removed more quickly at high currents. The initial pH of the solution influences the process due to the formation of different species of active chlorine. The detection of the radicals produced helped to better understand the process and the species generated during the electro-oxidation in the methanol medium. On the other hand, the coupling of photo-assistance with electrooxidation showed a synergy between these processes, improving considerably the efficiency of atrazine degradation and demonstrating that the implementation of methanol as a medium is a promising method to degrade pollutants in effluents.

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EPR detection of key radicals during coking process of lignin monomer pyrolysis

Cited by 31 publications

References 51 publications

Elucidating Biomass-Derived Pyrolytic Lignin Structures from Demethylation Reactions through Density Functional Theory Calculations

Elucidating Biomass-Derived Pyrolytic Lignin Structures from Demethylation Reactions through Density Functional Theory Calculations

Overcoming Acidic H₂O₂/Fe(II/III) Redox-Induced Low H₂O₂ Utilization Efficiency by Carbon Quantum Dots Fenton-like Catalysis

Análise dos processos de eletro-oxidação simples e foto-assistido usando ânodo de mistura de óxidos metálicos comercial em meio alcoólico e atrazina como composto modelo

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EPR detection of key radicals during coking process of lignin monomer pyrolysis

Cited by 31 publications

References 51 publications

Elucidating Biomass-Derived Pyrolytic Lignin Structures from Demethylation Reactions through Density Functional Theory Calculations

Elucidating Biomass-Derived Pyrolytic Lignin Structures from Demethylation Reactions through Density Functional Theory Calculations

Overcoming Acidic H2O2/Fe(II/III) Redox-Induced Low H2O2 Utilization Efficiency by Carbon Quantum Dots Fenton-like Catalysis

Análise dos processos de eletro-oxidação simples e foto-assistido usando ânodo de mistura de óxidos metálicos comercial em meio alcoólico e atrazina como composto modelo

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Overcoming Acidic H₂O₂/Fe(II/III) Redox-Induced Low H₂O₂ Utilization Efficiency by Carbon Quantum Dots Fenton-like Catalysis