Fractionation of Wood with Binary Solvent 1-Butyl-3-methylimidazolium Acetate + Dimethyl Sulfoxide

It is suggested to use a binary solvent, 1-butyl-3-methylimidazolium acetate + dimethyl sulfoxide, for full dissolution of wood, followed by its separation into the polysaccharide and lignin components. The optimal conditions of the wood treatment process were determined (temperature 120°C, processing duration 6 h). A scheme is suggested for double-stage fractionation of the lignin‒cellulose biomass. The scheme is based on the successive precipitation of the dissolved components with acetone and water. The isolated polysaccharide and lignin fractions constituting, combined, 70% of the initial mass of wood were characterized by IR and NMR spectroscopy, exclusion chromatography, electron microscopy, and functional analysis. It was found that the polysaccharide fraction has the form of amorphous cellulose (2% degree of crystallinity) containing about 15% lignin. The isolated lignin contains no significant admixtures of polysaccharides, has a mass-average molecular mass of about 5 kDa, and is close to organosolvent lignins. It was found that the lignin fraction contains up to 35% residual ionic fluid. A suggestion is made about the possibility of chemical binding between lignin and butyl-3-methylimidazolium cations.