Using Lignin Monomer As a Novel Capping Agent for
Efficient Acid-Catalyzed Depolymerization of High Molecular Weight
Lignin to Improve Its Antioxidant Activity
posted on 2020-06-09, 15:37authored byShuang Qi, Guanhua Wang, Hao Sun, Lulu Wang, Qimeng Liu, Guozhi Ma, Ashak Mahmud Parvez, Chuanling Si
In
this work, a mild and efficient process for acid-catalyzed depolymerization
of lignin to improve its antioxidant activity was proposed using lignin
monomer, p-hydroxybenzyl alcohol (HBA), as a novel
capping agent. High molecular weight lignin (HMWL) with high β-O-4
linkage content was used as the feedstock for depolymerization, and
the products were further extracted by ethyl acetate to obtain the
depolymerized ethyl acetate soluble lignin (DESL) with high antioxidant
capacity. Moreover, the mechanism of the promoted depolymerization
through the utilization of the capping agent was proposed and verified
using a lignin dimer model with a β-O-4 linkage. The results
showed that the HBA substantially suppressed lignin condensation and
increased the DESL yield. When the HBA dosage was 3 mmol/g lignin,
the DESL yield obtained at 150 °C was 51.88%, which was 2.7 times
and 1.9 times those obtained at 150 and 210 °C without HBA addition,
respectively. Besides, the DPPH· scavenging capacity (IC50, 65.2 μg/mL) of DESL obtained at 150 °C with
HBA addition was significantly higher than that obtained without HBA
addition (125.7 μg/mL) and was close to that of commercial antioxidant
BHT (57.3 μg/mL). Accordingly, this work demonstrates that the
acid catalysis process using lignin monomer as a capping agent is
effective to produce depolymerized lignin with high antioxidant activity.
Furthermore, this study provides new insights for the efficient acid-catalyzed
depolymerization of lignin through condensation suppression using
lignin monomer as a capping agent.