Fractionation and Characterization of Lignin From Wood Biomass Using Ionic Liquid and Alkaline Ethanol Solvent

Lignocellulosic biomass is a new source of renewable and carbon neutral materials for biofuel and bioenergy production. However, we note the recalcitrance of lignocellulosic for bioconversion. The presence of lignin is a barrier to enzymatic hydrolysis of cellulose by cellulases, as well as inhibiting fermentation to form products such as ethanol and butanediol. Lgnin is a three-dimensional amorphous polymer based on methoxylated phenylpropanoid units, and is crosslinks to different polysaccharides with covalent bond. The use of ionic liquids (ILs) in biomass pretreatment has received considerable attention recently because of their effectiveness at decreasing biomass recalcitrance to subsequent enzymatic hydrolysis. ILs pretreatment has been shown to reduce the lignin and hemicelluloses content, as well as the cellulose crystallinity. Certain ILs completely dissolved wood, agricultural waste, and other biopolymers at moderate temperatures and ambient pressure. In this article, we investigate the lignin extraction uses a purpose designed ionic liquid 1-butyl-3-methylimidazolium acesulfamate [BMIM]Ace at 120 °C and open atmosphere. The IL +organic solvents systems were also studied. The lignin was successfully fractionated from the biomass by precipitation in acetone after IL treatment, allowing the IL to be recycled. The results indicated that exceeding 89.6% of regenerated biomass obtained. After that, the regenerated biomass was subsequently extracted with alkaline ethanol solvent. It was indicated that the IL-organosolv lignin had a higher molecular weight (M_w, 1005-9050 g/mol) than the neat IL-lignin (M_w, 3700-6060g/mol) and alkali-ethanol lignin (M_w, 2440-3820g/mol). This comparison revealed that organic solvents considerably affect the M_w. This result probably due to the viscosity and inhomogeneity of IL mixed with different organic solvents. Moreover, the lignin fractions were characterized by high-performance anion exchange chromatography (HPAEC) and Fourier transform infrared (FT-IR). It should be note that a small amount of hemicelluloses loss during the IL extraction procedure. These results indicated a potential approach in further optimization of the choice of ILs/organic solvents for the efficient utilization of the lignocellulosic biomass, and all constituents can be fully recovered and further processed.