Oxidative depolymerization of lignin improved by enzymolysis pretreatment with laccase

A new lignin depolymerization approach for improving the yield of aromatic monomers（YAM） by enzymolysis pretreatment was investigated, in which lignin was pretreated with laccase followed by oxidative depolymerization. It was found that lignin depolymeirzation was enhanced significantly by enzymolysis. The oxidative depolymerization contributed to 21.37% of YAM after the enzymolysis pretreatment,whereas the conventional oxidative depolymerization only gave 14.10% of YAM. The addition of ethanol in enzymatic pretreatment process improved the efficiency of enzymolysis, which effectively improved the solubility of pretreated lignin and depolymerization degree（DD） of lignin. The enzymolysis pretreatment increased the content of syringyl（S） style aromatic monomers, which hindered the recondensation among polymerized products. As lignin has low solubility in acidic aqueous solution, ethanol was added into enzymolysis system to improve the efficiency. However, the enzymolysis of lignin should be carried out for a limited period of time to prevent the inactivation of laccase.

Scission of C–O and C–C linkages in lignin over RuRe alloy catalyst

The performance of lignin depolymerization is basically determined by the interunit C–O and C–C bonds.Numerous C–O bond cleavage strategies have been developed, while the cleavage of C–C bond between the primary aromatic units remains a challenging task due to the high dissociation energy of C–C bond.Herein, a multifunctional Ru Re alloy catalyst was designed, which exhibited exceptional catalytic activity for the cleavage of both C–O and C–C linkages in a broad range of lignin model compounds(β-1, a-5, 5–5,β-O-4, 4-O-5) and two stubborn lignins(kraft lignin and alkaline lignin), affording 97.5% overall yield of monocyclic compounds from model compounds and up to 129% of the maximum theoretical yield of monocyclic products based on C–O bonds cleavage from realistic lignin. Scanning transmission electron microscopy(STEM) characterization showed that Ru Re(1:1) alloy particles with hexagonal close-packed structure were homogeneously dispersed on the support. Quasi-in situ X-ray photoelectron spectroscopy(XPS), and X-ray absorption spectroscopy(XAS) indicate that Ru species were predominantly metallic state, whereas Re species were partially oxidized;meanwhile, there was a strong interaction between Ru and Re, where the electron transfer from Re to Ru was occurred, resulting in great improvement on the capability of C–O and C–C bonds cleavage in lignin conversion.

Efficient conversion of lignin to alkylphenols over highly stable inverse spinel MnFe_(2)O_(4) catalysts

The aromatic properties of lignin make it a promising source of valuable chemicals and fuels.Developing efficient and stable catalysts to effectively convert lignin into high-value chemicals is challenging.In this work,MnFe_(2)O_(4) spinel catalysts with oxygen-rich vacancies and porous distribution were synthesized by a simple solvothermal process and used to catalyze the depolymerization of lignin in an isopropanol solvent system.The specific surface area was 110.5 m^(2)∙g^(–1),which substantially increased the active sites for lignin depolymerization compared to Fe3O4.The conversion of lignin reached 94%,and the selectivity of alkylphenols exceeded 90% after 5 h at 250℃.Underpinned by characterizations,products,and density functional theory analysis,the results showed that the catalytic performance of MnFe_(2)O_(4) was attributed to the composition of Mn and Fe with strong Mn–O–Fe synergy.In addition,the cycling experiments and characterization showed that the depolymerized lignin on MnFe_(2)O_(4) has excellent cycling stability.Thus,our work provides valuable insights into the mechanism of lignin catalytic depolymerization and paves the way for the industrial-scale application of this process.

Application of Generalized Standard Addition Method and Ultraviolet Spectroscopy to Quantify Electrolytic Depolymerization of Lignin

Industrial lignin waste is an important byproduct of bio-refineries and the paper industry.Depolymerization of industrial lignin could generate useful aromatic compounds.This group has focused on electrolytic decomposition of biorefinery lignin.To quantify electrolytic decomposition of the lignin in a highly caustic solution,ultraviolet(UV)spectroscopy provides a useful probe.The conversion of the neat lignin to the oxidized products achieved by the electrolytic reactor may be measured by quantifying the amount of unreacted neat lignin that remains in the effluent.Because the properties of electrolytic decomposition products are largely unknown,a useful approach to quantify decomposition of the neat lignin is to use a multivariate calibration method referred to as the generalized standard addition method(GSAM).In this approach,the electrolytic decomposition products represent a background interference and the neat lignin that remains can be quantified.This approach allows the conversion of the neat lignin to be calculated in a solution that is a complex mixture.

CeCl_(3)-Promoted Simultaneous Photocatalytic Cleavage and Amination of C_(α)–C_(β)Bond in Lignin Model Compounds and Native Lignin

It remains challenging to achievevaluableplatformchemicals from lignin because of itscomplicated polymeric structure and inherent inert chemical activities.So far,only a fewexamples have been reported for the selective cleavage of C–C bonds in lignin due to their intrinsic inertness and ubiquity.Here,we present a simple and commercially available cerium(Ⅲ)chloride(CeCl_(3))-promoted photocatalytic depolymerization strategy to realize the simultaneous cleavage and amination ofC_(α)–C_(β)bond in a variety of lignin model compounds at room temperature.This procedure does not require any pretreatments and breakdown of C–O bonds or loss ofγ-CH_(2)OHgroup to generate aldehydes(up to 97%)and N-containing products(up to 95%)in good to excellent yields.Additionally,this CeCl_(3)-based photocatalyst system could maintain excellent catalytic performance even after 10 sequential cycles with newstarting materials.Moreover,this approach realizes the precise control over the reaction via switching the external light stimuli on/off.Further,this method is effective for the depolymerization of real lignin,thus affording the corresponding cleavage and amination products of C_(α)–C_(β)bonds.