Table 3 Overview of scientific studies concerning laccase/LMS or DES on the selective depolymerization of lignin
From: Laccase-catalyzed lignin depolymerization in deep eutectic solvents: challenges and prospects
Conditions of lignin depolymerization | Lignin type or source | Laccase origin or DES | Main results or limitations | References |
|---|---|---|---|---|
Two-step chemoenzymatic depolymerization containing LMS/IL/Buffer and aqueous alkaline solution | Lignin from beech wood | Trametes versicolor (Lcc2-M3) | A T. versicolor laccase variant (Lcc2-M3) catalyzed the essentially selective α-oxidation of the β-O-4 linkage to β-hydroxyketones at room temperature | (Liu et al. 2019b) |
Laccase-catalyzed degradation in ILs aqueous solution | Alkaline lignin | Trametes versicolor (Lcc2) | Alkaline lignin was majorly depolymerized into vanillin, acetosyringone, syringaldehyde, and acetovanillone | (Stevens et al. 2019) |
Laccase-catalyzed degradation | Rice straw, corn stover, reed, kraft lignin, and organosolv lignin from rice straw | Caldalkalibacillus thermarum | C. thermarum laccase efficiently depolymerized lignin into seven high-value benzaldehyde chemicals from lignocellulosic biomass and commercial lignin samples | (Yang et al. 2019) |
Alkaline lignin and milled wood lignin | Bacillus ligniniphilus | The B. ligniniphilus laccase can effectively degrade G-lignin even without a mediator, and the removal rate of G-lignin is higher than that of S-lignin. With the aid of mediator, laccase inreceased the removal rate of H-lignin | (Zhu et al. 2020) | |
Milled wood lignin | Amycolatopsis sp. 75iv2 | The laccase degradade 58% of S-lignin over 16Â h. The combination of ABTS with laccase reduced the selectivity for S-lignin over G-lignin | (Vuong et al. 2021) | |
Laccase-catalyzed degradation at low pH | Lignin model compounds and technical lignin | Obba rivulosa | In the presence of both N–OH-type and phenolic mediators, the laccases selectively oxidized lignin in acidic reaction conditions, and in the laccase-TEMPO system, the syringyl-type lignin units were preferred | (Kontro et al. 2020) |
Electrochemical degradation of lignin in a DES system | Kraft lignin | ChCl:ethylene glycol and ChCl:urea | Guaiacol and vanillin were the two most abundant detected products | (Di Marino et al. 2016) |
Metal-based DES catalysis of lignin | Organosolv lignin from herbaceous biomass | ChCl:FeCl3 (1:2) | Lignin was directedly degraded into methyl p-hydroxycinnamate as the sole product with high yield and selectivity (105.8 mg g−1 and 74.1%, respectively) | (Li et al. 2020) |
Chemocatalysis of lignin in a DES system | Alkaline lignin | ChCl:methanol | A high total yield of acetovanillone and acetic acid (87.12%) was obtained from alkaline lignin under mild conditions | (Yu et al. 2020) |
Catalytic hydrogenolysis using DES | Lignin from castor seed coats | ChCl:ethylene glycol, ChCl:glycerol, and ChCl:propylene glycol | High selectivity towards 4-propyl catechol was observed | (Liu et al. 2021b) |
A combination of chemical depolymerization by DES and bioconversion by Bacillus australimaris | Alkali lignin | ChCl:glycerin | ChCl:glycerin released more soluble small molecules from lignin, and confirmed improvement in lignin valorization via the combination of chemical and biological methods | (Yu et al. 2021) |
Catalytic hydrogenolysis and acidolysis using DES | Lignin from birch | ChCl:oxalic acid:ethylene glycol | The obtained ethylene glycol protected lignin displays high β-O-4 content and can be readily depolymerized to distinct monophenolic products | (Liu et al. 2021c) |