Fractionation and characterization of lignins from Miscanthus via organosolv and soda pulping for biorefinery applications

Abstract

The structural complexity of lignins necessitates characterization and isolation methodologies for assessing their appropriateness for thermo-chemical systems and material applications. Lignins prepared via two pulping methods (organosolv and soda) were comprehensively investigated by analyzing the properties, including lignin purity, yield, and thermal and chemical properties. The extracted organosolv lignin has high purity (93.13–98.12%), however, the purity of soda lignin was relatively low (87.58–89.61%). Organosolv lignin produced the highest heating value of 26.79–26.95 MJ kg−1, with a fixed carbon content of 39.47–41.06 wt%, high purity, and low ash content, making it suitable for biofuel applications. The content of total phenolic OH groups was higher for the organosolv lignins; however, for the phenolic OH groups, the 4-vinylphenol content was significantly higher in the soda lignins, and increased with increasing NaOH concentration. Overall, the thermal and chemical properties related to the lignin structure changed with the fractionation method and solvent concentration, which in turn influences the design of lignin valorization strategies for prospective depolymerization and material applications.