Fractionation and characterization of lignin from wood biomass using ionic liquid and alkaline ethanol solvent

摘要

Lignocellulosic biomass is a new source of renewable and carbon neutral materials for biofuel andbioenergy production. However, we note the recalcitrance of lignocellulosic for bioconversion. Thepresence of lignin is a barrier to enzymatic hydrolysis of cellulose by cellulases, as well as inhibitingfermentation to form products such as ethanol and butanediol. Lgnin is a three-dimensionalamorphous polymer based on methoxylated phenylpropanoid units, and is crosslinks to differentpolysaccharides with covalent bond. The use of ionic liquids (ILs) in biomass pretreatment hasreceived considerable attention recently because of their effectiveness at decreasing biomassrecalcitrance to subsequent enzymatic hydrolysis. ILs pretreatment has been shown to reduce thelignin and hemicelluloses content, as well as the cellulose crystallinity. Certain ILs completelydissolved wood, agricultural waste, and other biopolymers at moderate temperatures and ambientpressure. In this article, we investigate the lignin extraction uses a purpose designed ionic liquid1-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 thebiomass by precipitation in acetone after IL treatment, allowing the IL to be recycled. The resultsindicated that exceeding 89.6% of regenerated biomass obtained. After that, the regenerated biomasswas subsequently extracted with alkaline ethanol solvent. It was indicated that the IL-organosolvlignin had a higher molecular weight (M_w, 1270-7810 g/mol) than the alkali-ethanol lignin (M_w,2440-3020g/mol). This comparison revealed that organic solvents considerably affect the M_w. Thisresult probably due to the viscosity and inhomogeneity of IL mixed with different organic solvents.Moreover, the lignin fractions were characterized by high-performance anion exchangechromatography (HPAEC) and Fourier transform infrared (FT-IR). It should be note that a smallamount of hemicelluloses loss during the IL extraction procedure. These results indicated a potentialapproach in further optimization of the choice of ILs/organic solvents for the efficient utilization ofthe lignocellulosic biomass, and all constituents can be fully recovered and further processed.