Theoretical Study on the Kinetics of Thermal Decomposition of Guaiacol and Catechol

Furutani, Yuki; Dohara, Yuki; Kudo, Shinji; Hayashi, Jun Ichiro; Norinaga, Koyo

doi:10.1021/acs.jpca.7b08112

Cited by 17 publications

(16 citation statements)

References 66 publications

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“…Alternatively, hydrogenation of catechol requires 6.83 kcal/mol of activation energy to produce structure 2_b1 . The gas phase activation energy for this conversion is almost equal with 8.1 kcal/mol . Structure 2_b1 then undergoes dehydroxygenation to produce phenol releasing 17.32 kcal/mol of energy in the aqueous phase as compared to 19.7 kcal/mol in the gas phase .…”

Section: Resultssupporting

confidence: 93%

“…The gas phase activation energy for this conversion is almost equal with 8.1 kcal/mol . Structure 2_b1 then undergoes dehydroxygenation to produce phenol releasing 17.32 kcal/mol of energy in the aqueous phase as compared to 19.7 kcal/mol in the gas phase . Reaction Scheme a ( RS 2a ) is more likely to proceed over reaction Scheme ( RS 2 ) due to the lower activation energy of formation of structure 2_b1 .…”

Section: Resultsmentioning

confidence: 99%

“…BDE analysis shows that the direct cleavage of any other functional group will require high energy. Thus in reaction Scheme ( RS 3 ), guaiacol is first hydrogenated to produce structure 3_a which is energetically similar in the gas phase . Then the methoxy group is cleaved from structure 3_a which requires 6.93 kcal/mol of energy to produce phenol.…”

Section: Resultsmentioning

confidence: 99%

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Thermochemical Conversion of Guaiacol in Aqueous Phase by Density Functional Theory

2019

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The conversion of guaiacol to benzene, toluene and o‐cresol along with several important intermediates like phenol, catechol and others in aqueous phase has been theoretically studied under the framework of density functional theory (DFT). The bond dissociation energy (BDE) calculation has been performed on optimized structures of guaiacol, phenol and anisole; and accordingly several reaction pathways have been proposed. The thermochemical parameters like Gibb's free energy change and enthalpy change of the reactions have also been reported using M06‐2X functional. In BDE study of the three compounds, i. e., guaiacol, phenol and anisole, it is observed that the scission of H. at fifth carbon position of an aromatic ring is the highest energy demanding dissociation, whereas the cleavage of bond from the functional group attached to the aromatic ring has the least BDE. The formation of phenol from guaiacol is more likely to occur by simultaneous hydrogenation and demethoxylation of guaiacol amongst all proposed pathways in aqueous phase. Further, decomposition of phenol to benzene is likely to occur via direct dehydroxylation of phenol. The simultaneous hydrogenation and dehydroxylation of guaiacol in aqueous phase are most likely to produce anisole which can further be reduced to phenol by direct cleavage of methyl group followed by hydrogenation. Further, free energy change landscape shows the conversion of guaiacol to phenol to be kinetically most favourable conversion at low temperature and high pressure in the aqueous phase. Finally, the increase in temperature causes a decrease in Gibb's free energy change and enthalpy change of overall reactions, thereby increasing favourability of most of the reactions in aqueous phase. Furthermore, the comparison between gaseous and aqueous phase results have been made wherever applicable.

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Section: Resultssupporting

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Thermochemical Conversion of Guaiacol in Aqueous Phase by Density Functional Theory

2019

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“…In case of the secondary homogeneous vapor‐phase cracking, our research group has established a DCKM involving thousands of elementary reaction channels and hundreds of chemical species . The DCKM was employed to conduct the numerical simulation of the vapor‐phase reactions of volatiles derived from fast pyrolysis of lignin at 773−1223 K .…”

Section: Introductionmentioning

confidence: 99%

Computational Study on the Thermal Decomposition of Phenol‐Type Monolignols

Furutani

Dohara

Kudo

et al. 2018

Int J of Chemical Kinetics

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A detailed chemical kinetic model has been developed to theoretically predict the pyrolysis behavior of phenol‐type monolignol compounds (1‐(4‐hydroxyphenyl)prop‐2‐en‐1‐one, HPP; p‐coumaryl alcohol, 3‐hydroxy‐1‐(4‐hydroxyphenyl)propan‐1‐one, HHPP; 1‐(4‐hydroxyphenyl)propane‐1,3‐diol, HPPD) released from the primary heterogeneous pyrolysis of lignin. The possible thermal decomposition pathways involving unimolecular decomposition, H‐addition, and H‐abstraction by H and CH3 radicals were investigated by comparing the activation energies calculated at the M06–2X/6–311++G(d,p) level of theory. The results indicated that all phenol‐type monolignol compounds convert to phenol by side‐chain cleavage. p‐Coumaryl alcohol decomposes into phenol via the formation of 4‐vinylphenol, whereas HPP, HHPP, and HPPD decompose into phenol via the formation of 4‐hydroxybenzaldehyde. The pyrolytic pathways focusing on the reactivity of the hydroxyl group in HPP and producing cyclopentadiene (cyc‐C5H6) were also investigated. The transition state theory (TST) rate constants for all the proposed elementary reaction channels were calculated at the high‐pressure limit in the temperature range of 300–1500 K. The kinetic analysis predicted the two favorable unimolecular decomposition pathways in HPP: the one is the dominant channel below 1000 K to produce cyc‐C5H6, and the other is above 1000 K to yield phenol (C6H5OH).

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“…and Nguyen et al . The 2‐(2‐hydroxyethyl) phenol from the guaiacol demethylation reaction is not only an important intermediate for the formation of o‐methylphenol or o‐ethylphenol (Path 4) but also an important source for the formation of furans (Path 5) . Many other researchers also have explored the transfer behavior of free radicals like the methyl radical in guaiacol pyrolysis, which providing support for the mechanism shown in the Figure .…”

Section: Resultsmentioning

confidence: 75%

Catalytic Pyrolysis of Guaiacol over Ni/La–Modified Hierarchical HZSM‐5

Shen

Chen

et al. 2020

ChemistrySelect

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Catalytic pyrolysis of guaiacol as a model compound of lignin was conducted to explore the lignin pyrolysis mechanism in this study. The effects of catalyst and temperature on product distribution were studied. Five catalysts were tested including HZSM‐5, hierarchical HZSM‐5, metal‐modified hierarchical HZSM‐5 catalysts. And the Ni/La bimetallic hierarchical HZSM‐5 (NiLa/HZ‐SH) contributes to the achievement of high conversion and selectivity in catalytic pyrolysis of guaiacol. we obtained the yields of monocyclic aromatic hydrocarbons over NiLa/HZ‐SH (550°C): Phenol (23.01%), Benzofuran (6.68%), Salicylaldehyde (1.54%), 2‐Methylphenol (31.48%), 4‐Methylphenol (6.54%), 2‐Ethylphenol (14.89%), 4‐Vinylphenol (1.45%) and Catechol (8.67%), and the maximal yields of these monocyclic aromatic hydrocarbons is 94.26%. Moreover, the yield of polycyclic aromatic hydrocarbons (PAH) as the non‐target product reached a minimum of 1.46% over NiLa/HZ‐SH, while it was 16.88% without catalyst. In addition, catalyst stability was investigated, the reason that led to the decrease of target products could be the acidity and surface area of catalysts decreased as the coke blocked the pore channels, spent catalyst can be successfully regenerated through calcination treatment. Finally, based on the experiment results in this work and other published studies, a guaiacol pyrolysis mechanism was summarized and proposed aiming to understand the lignin pyrolysis process.

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Theoretical Study on the Kinetics of Thermal Decomposition of Guaiacol and Catechol

Cited by 17 publications

References 66 publications

Thermochemical Conversion of Guaiacol in Aqueous Phase by Density Functional Theory

Thermochemical Conversion of Guaiacol in Aqueous Phase by Density Functional Theory

Computational Study on the Thermal Decomposition of Phenol‐Type Monolignols

Catalytic Pyrolysis of Guaiacol over Ni/La–Modified Hierarchical HZSM‐5

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