Depolymerization and Demethylation of Kraft Lignin in Molten Salt Hydrate and Applications as an Antioxidant and Metal Ion Scavenger

Abstract

To improve the reactivity and enrich the functionality of lignin for valorization, kraft lignin was depolymerized and demethylated via cleaving aryl and alkyl ether bonds in acidic lithium bromide trihydrate (∼60% LiBr aqueous solution). It was found that the cleavage of the ether bonds followed the order of β-O-4 ether > aryl alkyl ether in phenylcoumaran > dialkyl ether in resinol > methoxyl (MeO). The depolymerization via β-O-4 cleavage occurred under mild conditions (e.g., <0.5 M HCl at 110 °C), while sufficient demethylation of the lignin needed harsher conditions (>1.5 M HCl). Both depolymerization and demethylation generated new aromatic hydroxyl (ArOH). With 2.4 M HCl, MeO content dropped from 4.85 to 0.95 mmol/g lignin, and ArOH content increased from 2.78 to 5.09 mmol/g lignin. The depolymerized and demethylated kraft lignin showed excellent antioxidant activity and Cr(VI)-scavenging capacity, compared with original kraft lignin and tannins.

Structural properties and antioxidation activities of lignins isolated from sequential two-step formosolv fractionation

“…28–30 However, the FA-induced depolymerization of lignin into lower mass molecular fractions could amend the solubility and mobility of lignin, thereby increasing the chance of their condensation. 31 Therefore, sequential two-step formosolv fractionation had a significant influence on the molecular weight of lignin specimens.…”

“…condensation. 31 Therefore, sequential two-step formosolv fractionation had a signicant inuence on the molecular weight of lignin specimens.…”

“…13,16 Lignin fraction enriched with reactive groups, including phenolic hydroxyl, methoxyl, aliphatic hydroxyl and double bond in the side chain, can be used as an efficient antioxidant. 17 In order to shed light on the direct relationship between lignin structural properties and its antioxidant activity, in this present study, a sequential two-step formosolv fractionation of Triarrhena lutarioriparia biomass is proposed to obtain four specic lignin fractions with different solubility in FA solution. As a native potential C 4 -plant, T. lutarioriparia grows well in wet environments, it is plenteous along Tongting Lake with the output of 920 000 tons per year in Hunan province, China.…”

“…13,16 Lignin fraction enriched with reactive groups, including phenolic hydroxyl, methoxyl, aliphatic hydroxyl and double bond in the side chain, can be used as an efficient antioxidant. 17…”

Enhanced production and separation of short-chain glucan oligomers from corn stover in an unacidified LiBr molten salt hydrate via pre-extraction of hemicellulose

“…With the addition of xylan for the hydrolysis of pre-extracted corn stover, a slight decrease in the glucan oligomer yield from 79.5% to 75.5% was observed, possibly due to the degradation of xylan to formic acid 43,44 which can promote the degradation of glucan oligomers. Enzymatic lignin addition also showed a negligible effect on the production of glucan oligomers, suggesting that the aromatic hydroxyl groups generated from the MSH hydrolysis 45 cannot facilitate glucan oligomer degradation. In contrast, with the addition of 35 mg of acetic acid, which equals the acetic acid dosage released from hemicellulose deconstruction, a significant decrease in the glucan oligomer yield from 79.5% to 13.3% was observed.…”