Characterization of Eucalyptus Lignin Fractionation from a MIBK-Based Solvothermal Process

In this study, the effects of sulfuric acid on cellulose yield, lignin removal, and lignin recovery in solvothermal fractionation of eucalyptus (EC) were studied. An acid concentration of 0.04 M sulfuric acid (H2SO4), temperature of 180 °C and residence time of 30 min resulted in maximum lignin removal from the solid phase, at 87.7 %. Lignin recovery in the organic phase under optimum conditions was 84.6 %. It should be noted that H2SO4 was the best catalyst in the optimal solvothermal process, and it increased the cellulose yield to 95.2 % in the solid phase. Additionally, the physicochemical and structural properties of the extracted lignin were analyzed using FTIR, TGA, elemental analysis, GPC, and Py-GCMS methods. Thermal degradation analysis showed that recovered lignin is primarily composed of syringyl, guaiacyl and p-hydroxyphenyl units cross-linked by C–C, inter-unit α-O-4, β-O-4 linkages. The weight average molecular weight (Mw) analysis of recovered lignin demonstrated a low molecular weight for recovered lignin (2.19 g/mol). However, the main phenolic derivatives in the extracted lignin obtained from EC were S-units (i.e., syringol, 4-methylsyringol, 4-vinylsyringol). In addition, G-units (4-vinylguaiacol, 4-methylguaiacol, phenol, 2-methylphenol, and 4-methylphenol) were obtained after release from H-units. Py-GCMS analysis showed the predominance of G-units (32.8 %) over S-units (57.4 %). This work demonstrated the potential of fractionated lignin in the production of valuable chemicals in biorefineries. HIGHLIGHTS Eucalyptus was fractionated with solvothermal process with different conditions The maximum lignin removal of 87.7 % was achieved in the presence of catalyst of 0.04 M Organosolv fractionation enabled an extensive and selective delignification The structural changes of lignin were characterized comprehensively GRAPHICAL ABSTRACT