Efficient fractionation of lignin from Camellia oleifera shell by acidic deep eutectic solvent under mild conditions

In this study, ethylene glycol-oxalic acid deep eutectic system (DES) was used for delignification of Camellia oleifera shell (COS). The effects of treatment temperature and time on lignin removal rate, lignin purity and yield were investigated. At the treatment temperature and treatment time of 90 °C and 6 h, the residue rate, lignin removal rate and yield values of 42.33 %, 67.79 % and 45.84 %, respectively. The structure of lignin was ascertained by performing Fourier transform infrared spectroscopy (FT-IR) and two-dimensional nuclear magnetic resonance spectroscopy (2D HSQC NMR), the spectra of which indicated that COS lignin mainly comprises guaiacyl (G) units, followed by syringyl (S) units. Thermal analysis of lignin was conducted based on thermogravimetric analysis (TG) and differential scanning calorimetry (DSC), and the glass transition temperature of lignin was determined to be between 90 and 130 °C. The results in this study indicated that ethylene glycol-oxalic DES system can be used to facilitate the efficient delignification of COS.