Ionic liquids for separation of lignin and transformation into value-added chemicals

Ionic liquids (ILs) represent a class of nonvolatile and thermally stable solvents. The versatility of ILs as a catalyst and solvent can be used at various stages of biomass valorization. The ILs effectively fractionate various biomass components in high purity owing to selective dissolution of the carbohydrate or lignin fraction. The tunable properties of ILs have recently led to the successful transformation of lignin into value-added chemicals such as vanillin, guaiacol, diethyl maleate ester, and so on, with high selectivity. Hence, the role of pH, acid-base ratio, cations/anions in ILs, and π-π and n-π interactions between IL and feedstock during the lignin isolation and depolymerization are discussed in this review. ILs properties for vanillin production and isolation are also summarized.