Complete dissolution of woody biomass using an ionic liquid

Abstract

Birch wood meal was added to the ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim][OAc])/dimethyl sulfoxide (DMSO) to investigate the conditions required for the complete dissolution of the lignocellulose. Cellulose was treated with [Emim][OAc], and its molecular weight distribution was analyzed by size exclusion chromatography as a model compound. The solubilities of lignocellulose were compared under different treatment conditions, such as the ball-milling time of the raw material and the temperature of the [Emim][OAc]/DMSO treatment. The insoluble fraction was analyzed by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) to investigate the lignin structure. Cellulose treated with [Emim][OAc] under a nitrogen atmosphere for 1 to 12 h was remarkably depolymerized. It was demonstrated that lignocellulose is easily dissolved when the temperature of [Emim][OAc]/DMSO and the ball-milling times of lignocellulose are increased; a ball-milled sample was completely dissolved in the ionic liquid. The well-dissolved sample had a low cellulose molecular weight. Ball-milling reduced the primary particle size of the sample and facilitated the dissolution and extraction of guaiacyl lignin units.