Ionic liquids screening for lignin dissolution: COSMO-RS simulations and experimental characterization

As the second most abundant terrestrial polymer, lignin has emerged as a major sustainable source for the production of fuels, chemicals, and materials. However, efficient screening of solvents for lignin dissolving faces great challenges. In this work, COSMO-RS was used to screen 3886 ionic liquids (ILs) composed of 58 cations and 67 anions, to find out the most effective ones for lignin dissolving by considering the critical items of logarithmic infinite dilution activity coefficient (lnγ∞) and σ-profiles. The substantial improvement of lignin dissolution was achieved in [PMpyrr][OAc] IL by both simulations and experiments validations. Moreover, it was found that the anions dominate the dissolution process and the strongly polar anions exhibit better dissolution ability. Furthermore, the underlying mechanism originated from the hydrogen bond (H-bond) between ILs and lignin was also revealed and systemically analyzed from donor and acceptor ability, indicating that high lignin solubility is reached in the ILs with stronger ability to form H-bond acceptors. This work leads to possible ways toward developing more selective and efficient lignin dissolution methods based on solvent properties.