Cleavage of ethers and demethylation of lignin in acidic concentrated lithium bromide (ACLB) solution

Abstract

Methoxyl group is the most abundant functional group of lignin, which affects the property, reactivity, and application of lignin. Efficient demethylation is always of interest to the area of lignin...

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

“…It was found in our previous studies that the depolymerization and demethylation of lignin increased with LiBr concentration in the range tested (10−60 wt %). 29,30 Therefore, 60 wt % LiBr solution was used for the demethylation of guaiacol and kraft lignin in this study. Temperature was critical to the demethylation of guaiacol.…”

“…In addition, the decrease in the MeO content was more than the increase in the ArOH content (Figure 1C), probably because some ArOH groups were involved (consumed) in side reactions, for example, the transformation of β-O-4 to the benzodioxane (BD) structure or diaryl ether structure. 28,30 FTIR Study of Kraft Lignin before and after the ALBTH Treatment. The FT-IR spectra of five lignin samples before and after the ALBTH treatment shown in Figure 2 provide additional evidence of lignin depolymerization and demethylation in the ALBTH.…”

“…29 Furthermore, careful studies using model compounds and actual lignin samples (including hardwood organosolv lignin, softwood organosolv lignin, hardwood kraft lignin, and corn stover lignin) revealed that lignin can be demethylated in the ALBTH, and the ether bonds in β-5 and β−β structures except for the 4-O-5 bond in the diphenyl structure can be cleaved as well. 30 The effect of reaction conditions on the lignin reactions in the ALBTH system was investigated as well. For example, a higher LiBr concentration (e.g., 55−61 wt %) favors the demethylation and depolymerization but not the condensation of lignin.…”

“…The depolymerization (β-O-4 cleavage) of the native lignin in wood could occur at an acid concentration as low as 0.04 M, 28 while the depolymerization of isolated lignins needed 0.3 M acid. 29 On the other hand, the demethylation of lignin needed a much higher acid concentration of 1.3 M. 30 Kraft lignin is the most available industrial lignin produced in the paper industry. Tannin is a polyphenol that has been used as an antioxidant and metal adsorbent.…”

Progress in Bio‐Based Phenolic Foams: Synthesis, Properties, and Applications

“…It is difficult to formulate a general depolymerization protocol for lignin, due to its structural variability with the plant origin. Prevailing techniques include phenolation [71], demethylation [72], hydroxy methylation [73], and depolymerization processes such as pyrolysis [74], oxidation [75], hydrogenolysis [76], hot-compressed water liquefaction [77], catalytic hydrothermal treatments [78], and microbial conversion [79]. The yield and composition of the depolymerization product may vary with the reaction conditions and process type.…”