Switchable Ionic Liquids as Delignification Solvents for Lignocellulosic Materials

The transformation of lignocellulosic materials into potentially valuable resources is compromised by their complicated structure. Consequently, new economical and feasible conversion/fractionation techniques that render value-added products are intensely investigated. Herein an unorthodox and feasible fractionation method of birch chips (B.pendula) using a switchable ionic liquid (SIL) derived from an alkanol amine (monoethanol amine, MEA) and an organic super base (1,8-diazabicyclo-[5.4.0]-undec-7-ene, DBU) with two different trigger acid gases (CO2 and SO2) is studied. After SIL treatment, the dissolved fractions were selectively separated by a step-wise method using an antisolvent to induce precipitation. The SIL was recycled after concentration and evaporation of anti-solvent. The composition of undissolved wood after MEA-SO2-SIL treatment resulted in 80wt% cellulose, 10wt% hemicelluloses, and 3wt% lignin, whereas MEA-CO2-SIL treatment resulted in 66wt% cellulose, 12wt% hemicelluloses and 11wt% lignin. Thus, the MEA-SO2-SIL proved more efficient than the MEA-CO2-SIL, and a better solvent for lignin removal. All fractions were analyzed by gas chromatography (GC), Fourier transform infrared spectroscopy (FT-IR), C-13 nuclear magnetic resonance spectroscopy (NMR) and Gel permeation chromatography (GPC).