Computational Study of Bond Dissociation Enthalpies for Lignin Model Compounds. Substituent Effects in Phenethyl Phenyl Ethers

Beste, Ariana; Buchanan, A. C.

doi:10.1021/jo9001307

Cited by 158 publications

(165 citation statements)

References 21 publications

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“…Recently, many papers have reported theoretical calculations of the bond dissociation energies (BDEs) for linkages in lignin related compounds [61][62][63][64][65][66][67][68][69][70]. These include calculations of α-O-4, β-O-4, 4-O-5, β-aryl, phenylcoumaran, pinoresinol, dibenzodioxocin type dimers.…”

Section: Bond Dissociation Energymentioning

confidence: 99%

Lignin pyrolysis reactions

2017

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Section: Bond Dissociation Energymentioning

confidence: 99%

Lignin pyrolysis reactions

2017

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“…First-principles simulation can provide valuable insight on the energetics and products of bond cleavage pathways. Previous computational efforts have focused on studying model compounds that contain the abundant β-O-4 ether lignin linkage by evaluating homolytic bond dissociation energies [35][36][37][38][39] , mechanical properties [40][41][42][43] , intramolecular hydrogen bonding 44 . More recently, some kinetic modeling and analysis has been carried out, particularly to model fast pyrolysis [45][46][47][48][49][50] .…”

Section: Introductionmentioning

confidence: 99%

Depolymerization Pathways for Branching Lignin Spirodienone Units Revealed with ab Initio Steered Molecular Dynamics

Mar

Kulik

2017

J. Phys. Chem. A

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Lignocellulosic biomass is an abundant, rich source of aromatic compounds, but direct utilization of raw lignin has been hampered by both the high heterogeneity and variability of linking bonds in this biopolymer. Ab initio steered molecular dynamics (AISMD) has emerged both as a fruitful direct computational screening approach to identify products that occur through mechanical depolymerization (i.e., in sonication or ball-milling) and as a sampling approach. By varying the direction of force and sampling over 750 AISMD trajectories, we identify numerous possible pathways through which lignin depolymerization may occur in pyrolysis or through catalytic depolymerization as well. Here, we present eight unique major depolymerization pathways discovered via AISMD for the recently characterized spirodienone lignin branchinglinkage that may comprise around 10% weight of all lignin in some softwoods. We extract representative trajectories from AISMD and carry out reaction pathway analysis to identify energetically favorable pathways for lignin depolymerization. Importantly, we identify dynamical effects that could not be observed through more traditional calculations of bond dissociation energies. Such effects include thermodynamically favorable recovery of aromaticity in the dienone ring that leads to near-barrierless subsequent ether cleavage and hydrogen bonding effects that stabilize newly formed radicals. Some of the most stable spirodienone fragments that reside at most 1 eV above the reactant structure are formed with only 2 eV barriers for C-C bond cleavage, suggesting key targets for catalyst design to drive targeted depolymerization of lignin.2

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“…The thermally weak bonds are mainly hydroxyl groups attached to b or g carbons and ether bonds including b-O-4, which are most abundant linkage type in most lignin structures. 14, 42 Their bond cleavages contribute to a high production of water and condensable volatile products at low temperature. The methoxyl groups are more resistant against thermal degradation than the ether linkages which allows for the formation of a large fraction of methoxyl phenols such as guaiacol and syringol among condensable volatile products.…”

Section: Introductionmentioning

confidence: 99%

Kinetics and reaction chemistry for slow pyrolysis of enzymatic hydrolysislignin and organosolv extracted lignin derived from maplewood

et al. 2012

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The kinetics and reaction chemistry for the pyrolysis of Maplewood lignin were investigated using both a pyroprobe reactor and a thermogravimetric analyser mass spectrometry (TGA-MS). Lignin residue after enzymatic hydrolysis and organosolv lignin derived from Maplewood were used to measure the kinetic behaviours of lignin pyrolysis and to analyse pyrolysis product distributions. The enzymatic lignin residue pyrolyzed at lower temperature than that of organosolv lignin. The differential thermogravimetric (DTG) peaks for pyrolysis of the enzymatic residue were more similar to the DTG peaks for pyrolysis of the original Maplewood than DTG of the organosolv lignin. The condensable liquid volatile products were collected from a Pyroprobe reactor with a liquid nitrogen trap. The primary monomeric phenolic compounds were guaiacol, syringol, and vanillic acid. However, only 14-36 carbon% of the sample could be detected by GC-MS. Over 60 carbon% of the condensable products were heavy tar molecules that are not detectable by GC-MS. These heavy tar molecules are the primary products from pyrolysis of lignin. Intermediate solid samples were also collected at various pyrolysis temperatures and characterized by elemental analysis, FT-IR, DP-MAS 13 C NMR, and TOC. The methoxy groups and ether linkages decreased and the non-protonated aromatic carbon-carbon bonds increased in the solid residues as the pyrolysis temperature increased. The carbon content of the initial lignin feed (derived from enzymatic hydrolysis) and the solid polyaromatics residue (obtained at 773 K) was 58 wt% and 74 wt% respectively. This polyaromatic residue contained about 69 wt% of the original lignin feed. The solid polyaromatics undergo further slow decomposition accompanied by a constant release of carbon dioxide as the pyrolysis reaction continues. The pyrolysis of the enzymatic lignin residue was modelled by two reactions in series. In the first pyrolysis step the lignin was decomposed with an apparent activation energy of 74 kJ mol -1 and a heat of reaction of -8,780 kJ kg -1 . The second pyrolysis step had an apparent activation energy of 110 kJ mol -1 and a heat of reaction of -2,819 kJ kg -1 . Lignin pyrolysis has lower activation energies and higher heats of reaction than cellulose pyrolysis.

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Computational Study of Bond Dissociation Enthalpies for Lignin Model Compounds. Substituent Effects in Phenethyl Phenyl Ethers

Cited by 158 publications

References 21 publications

Lignin pyrolysis reactions

Lignin pyrolysis reactions

Depolymerization Pathways for Branching Lignin Spirodienone Units Revealed with ab Initio Steered Molecular Dynamics

Kinetics and reaction chemistry for slow pyrolysis of enzymatic hydrolysislignin and organosolv extracted lignin derived from maplewood

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