Free Radical Formation in Lignin During Pyrolysis

Avni, E.; Suib, Steven L.

doi:10.1515/hfsg.1985.39.1.33

Cited by 12 publications

(13 citation statements)

References 8 publications

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“…These behaviors suggest that the coupling between the biomass radicals is greatly inhibited by the hydrogen donation of DHP, which is similar to that reported by Avin et al for the pyrolysis of lignin under a H 2 atmosphere. 13 The initial increase and then decrease in R D of the biomass in the presence of DHP in 30 min may indicate that the radicals generated in the early stage of the pyrolysis are high in concentration and are not well mixed with DHP locally, which allows some of the biomass radicals to couple with each other to form large-sized products that trap radicals. These products, however, are not stable and undergo further pyrolysis, during which the trapped radicals are exposed to DHP and can acquire hydrogen from it.…”

Section: Methodsmentioning

confidence: 99%

Cleavage of Covalent Bonds in the Pyrolysis of Lignin, Cellulose, and Hemicellulose

et al. 2015

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This study examines the cleavage of covalent bonds and the radical behavior in the pyrolysis of lignin, cellulose, and hemicellulose at 350, 400, and 440°C. In the presence of a sufficient amount of a hydrogen donor solvent, i.e., 9,10-dihydrophenanthrene (DHP), the quantity of covalent bonds cleaved is determined, and the quantity of stable radicals formed is measured. It is found that more than 99.9% of the radicals generated in the pyrolysis are coupled to hydrogen donated by DHP. The pyrolysis of the biomass can be characterized as cleavage of two types of covalent bonds, weak and strong. The cleavage of the weak bonds dominates the pyrolysis in the early stage, less than 10 min at 440°C, whereas that of the strong bonds becomes significant in the later stage, and its rate is promoted by DHP. The amounts of the weak bonds are 0.89 × 10 −2 , 0.63 × 10 −2 , and 0.68 × 10 −2 mol/g in lignin, cellulose, and hemicellulose, respectively. These values correspond to the sum of the C al −O and C al −C al bonds linking the unit structure in lignin and the C al −O bonds in the glucosidic linkage in cellulose and hemicellulose, respectively. Activation energies for the cleavage of these bonds in lignin, cellulose, and hemicellulose are 90.5, 129.7, and 126.5 kJ/mol, respectively.

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Section: Methodsmentioning

confidence: 99%

Cleavage of Covalent Bonds in the Pyrolysis of Lignin, Cellulose, and Hemicellulose

et al. 2015

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“…It was claimed that the stable free‐radical species were substituted phenoxy and semiquinone radicals 12. 13 Studies of free radicals involved in the pyrolysis of lignin are mostly limited to ex situ measurements of pyrolytic chars 11d. 13d, 14 The recently published work of Dellinger et al.…”

Section: Introductionmentioning

confidence: 99%

In situ Observation of Radicals and Molecular Products During Lignin Pyrolysis

et al. 2014

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Lignin pyrolysis is a promising method for the sustainable production of phenolic compounds from biomass. However, detailed knowledge about the radicals involved in this process and their influence on the molecular products is missing. Herein, we report on the pyrolysis of hard- and softwood Klason lignins under inert gas conditions in a temperature range between 350-550 °C. During the pyrolysis process, the formed radicals were detected by in situ high-temperature electron paramagnetic resonance spectroscopy. The overall formation of volatile products during lignin pyrolysis was determined using thermogravimetric analysis. The volatile molecular products were characterized and quantified using GC-MS analysis. Major differences were observed between hardwood and softwood lignins. Hardwood lignins form more radicals and volatile products than softwood lignins at temperatures from 350 to 450 °C. In the late stages of the pyrolysis process at 550 °C radical quenching reactions become dominant in hardwood lignins. We identified the disproportionation of two semiquinone radicals to quinone and hydroquinone species as the most likely quenching reaction. Our results show that both the pyrolysis temperature and the type of lignin source have a major influence on radical formation and the molecular products during the depolymerization of lignin.

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“…Actually, thermal decomposition gives rise to cleavage of methoxyl groups or leads to bond breakage (Avni, Suib, Coughlin 1985). In the case of hotpressing with corn cob powders catalyzed by a mixture of NH 4 C1 and (NH 4 ) 2 SO 4 , the presence of ethylbenzene with 1.5 mole water in the resin matrix could have originated from the lignin fraction contained in corn cobs (äs can be seen in Table 1).…”

Section: Discussionmentioning

confidence: 99%

Salt Catalyzed Wood Bonding with Hemicellulose

zu-shan¹,

Paszner²

1988

Holzforschung

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Corn cobs, which contain the highest hemicellulose content among agricultural and forestry residues, were used äs carbohydrate source for investigation of their bonding properties. This study establishes the feasibility of direct use of powdered corn cob äs a resource of adhesive for bonding Douglas-fir veneers into plywood. Ammonium Sulfate and ammonium Chloride catalysis of hightemperature conversion of corn cob powder was found to provide waterproof bonds of 3-ply Douglas-fir plywood, showing shear strength and wood failure equivalent to that of commercial 3-ply Douglas-fir plywood. Improved resin penetration into lathe checks was obtained on using catalyzed liquid sugar concentrate (syroups) mixed with corn cob powder äs the liquid resin. Ethylbenzene with 1.5 mole of water has been positively identified äs an important solvent-soluble fraction of the high-temperature conversion product of corn cob powder by two spectroscopic techniques: infrared (IR) and nuclear magnetic resonance (including hydrogen proton and 13 C analysis) spectroscopy. In light of the findings, requirements for the best performance of plywood glue lines pressed at 220°C (good wet and dry shear strength) are discussed.

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Free Radical Formation in Lignin During Pyrolysis

Cited by 12 publications

References 8 publications

Cleavage of Covalent Bonds in the Pyrolysis of Lignin, Cellulose, and Hemicellulose

Cleavage of Covalent Bonds in the Pyrolysis of Lignin, Cellulose, and Hemicellulose

In situ Observation of Radicals and Molecular Products During Lignin Pyrolysis

Salt Catalyzed Wood Bonding with Hemicellulose

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