Enhancement of ionic liquid-aided fractionation of birchwood. Part 1: autohydrolysis pretreatment

Abstract

Ionic liquid-cosolvent systems have been proposed as selective solvent media for lignocellulosic materials. We present the ionic liquid-aided fractionation of silver birch (Betula pendula) combined with an autohydrolysis pretreatment. Contrary to untreated birchwood meal, autohydrolyzed birchwood meal reveals quantitative dissolution in 1-ethyl-3-methylimidazolium acetate and distinct separation into the individual wood polymers upon regeneration in acetone/water. The process yields two main fractions, a cellulose-rich precipitate with a residual lignin content of 13–15% and another virtually pure lignin fraction. No cellulose yield loss is observed during the ionic liquid processing step. A comprehensive mass balance of the process, including insoluble material, wash waters, and soluble residues, is provided. The product fractions are characterised for their chemical compositions, molar mass distributions and structural characteristics by Klason lignin and sugar analysis, ¹³C NMR, GPC and WAXS. The study investigates the effects of wood particle size and autohydrolysis intensity on fractionation efficiency and selectivity.