Fractionation of autohydrolyzed birchwood in ionic liquid and co-solvent mixtures

Abstract

Ionic liquids are novel solvents that are solely composed of ions. The dissolution and fractionation of wood in ionic liquid has drawn much attention in the recent years. Ionic liquids show better properties than traditional wood solvents. However, drawbacks still remain, such as the high viscosity of the resulting solution and low fractionation selectivity. In the literature part of this thesis, the properties and applications of the ionic liquids are reviewed. Furthermore, the chemistry and the factors that affect the dissolution and fractionation of wood in ionic liquid are described.

The objective of the study was a comparative evaluation of the fractionation of untreated and autohydrolyzed (P-factor 500) birchwood meal into their polymeric constituents. Thereby, 25 g (autohydrolyzed) birchwood meal (0<=125 µm) was kneaded with l-ethyl-3-methylimidazoliurn acetate ([emim]OAc) at 5% consistency. The subsequent press filtration showed that complete dissolution was achieved when autohydrolyzed wood meal was used. By the addition of 1:1 v/v acetone-water and further evaporating the acetone, cellulose-rich (precipitate 1) and lignin-rich (precipitate 2) materials were separated. The lignin and hemicellulose content in precipitate 1 were lower than if using untreated wood, while the yield and purity of precipitate 2 increased significantly. The results showed that the selectivity of fractionation was significantly improved when birchwood meal was autohydrolyzed prior to the dissolution in [emim]OAc. The addition of DMP (dimethyl phthalate) as co-solvent did not Improve the selectivity of the fractionation, while addition of sulfolane contributed to a slight improvement.