Integrated alkaline and deep eutectic solvent-based green strategy for lignin fractionation and thermochemical valorizationOA

In this work,an efficient and green strategy for selective extraction and high-value utilization of lignin was proposed.Most of the hemicellulose in the feedstock was first removed by alkaline pretreatment to create a favorable structural environment for subsequent lignin dissolution.Subsequently,an acid-alcohol deep eutectic solvent(DES)system based on FeCl_(3)-ethylene glycol(FeCl 3-EG)was developed to achieve efficient and selective lignin dissolution.The results of characterization by Fourier transform infrared(FT-IR)spectroscopy,X-ray diffraction(XRD),and BrunauerEmmett-Teller(BET)showed that the lignin was removed significantly after the treatment,the cellulose structure was preserved,and the crystallinity and specific surface area were increased to 73.46% and 2.764 m^(2)/g,respectively.The highest delignification rate of 96.53% was achieved when EG:FeCl_(3)=1:0.3.Gas chromatography-mass spectrometry(GC-MS)detected a variety of low molecular phenolic products.In-situ Raman spectroscopy revealed the dynamic process of lignin dissolution from the cell wall.The regenerated lignin was systematically characterized by FTIR,thermogravimetry(TG),elemental analysis,and two-dimensional heteronuclear single quantum coherence-nuclear magnetic resonance(2D HSQC-NMR),and it was found that as the FeCl_(3) content in DES increased,the β-O-4 content decreased,and the thermal stability of lignin increased.The pyrolysis properties were further analyzed by in-situ infrared(IR)spectroscopy,pyrolysis gas chromatography-mass spectrometry(Py GC-MS),and U-tube device,which showed that the regenerated lignin pyrolysis products had a high yield of the liquid phase and good phenol selectivity(40.94%),which demonstrated good selectivity and application prospects.This study provides a theoretical basis and process reference for the green extraction of lignin and its platform compound conversion.