Selective Cleavage of the Aryl Ether Bonds in Lignin for Depolymerization by Acidic Lithium Bromide Molten Salt Hydrate under Mild Conditions

Abstract

The present study demonstrates that the concentrated lithium bromide (LiBr) solution with acid as catalyst was able to selectively cleave the β-O-4 aryl ether bond and lead to lignin depolymerization under mild conditions (e.g., in 60% LiBr with 0.3 M HCl at 110 °C for 2 h). Four industrial lignins from different pulping and biorefining processes, including softwood kraft lignin (SKL), hardwood kraft lignin (HKL), softwood ethanol organosolv lignin (EOL), and acid corncob lignin (ACL), were treated in the LiBr solution. The molecular weight, functional group, and interunit linkages of the lignins were characterized using GPC, FTIR, and NMR. The results indicated that the β-O-4 aryl ether bonds of the lignins were selectively cleaved, and both LiBr and HCl played crucial roles in catalyzing the cleavage of the ether bonds.

Alkaline Sulfite Anthraquinone and Methanol (ASAM) Pulping Process of Tropical Bamboo (Gigantochloa scortechinii)

“…This results from the fact that solution of acid soluble lignin contributed to lignin dissolution. The relatively low pH of spent liquor at high temperature results in the partial cleavage of α-ether bonds in lignin [40,41]. On the other hand, the use of alkaline sodium sulfite as an additive in the ASAM process produces a low Kappa number, high pulp yield and high brightness.…”

“…More lignin is eliminated in the period of bulk delignification phase. This elimination occurs much more quickly than the third stage (residual delignification) [41,42]. As a result, the proportion of lignin removal in polysaccharides happens slowly.…”

An uncondensed lignin depolymerized in the solid state and isolated from lignocellulosic biomass: a mechanistic study

“…In addition, when the technical lignins from different pulping and biorefining processes were treated in the ALBTH system under mild conditions, the cleavage of the aryl ether bonds was also observed, leading to further reductions in molecular weight. 29 It is therefore of significant interest to investigate the chemical changes of lignins in the ALBTH system, to provide new insights into the lignin depolymerization mechanisms and to determine the characteristics and potential utilization of the ALBTH lignin. In this study, the native lignin in different lignocellulosic feedstocks and lignin model compounds (LMCs) were utilized to elucidate the mechanisms and pathways of lignin depolymerization and condensation in the ALBTH system.…”

Structural Characterization and Antioxidant Activity of Milled Wood Lignin from Xylose Residue and Corncob

“…The 1120 cm −1 band corresponds to an aromatic C-H in plane deformation. The intensity of the 1030 cm −1 C-O-C band was decreased after acid pretreatment, indicating that a partial ether bond was cleaved during the diluted acid treatment [19]. The lignin isolated from corncob contains a considerable number of β-ether unit (A), with some detectable phenylcoumaran (C) [16].…”