Two-stage acid-catalyzed fractionation of lignocellulosic biomass in aqueous ethanol systems at low temperatures

Abstract

Wheat straw was fractionated into cellulosic fibres, hemicellulose sugars and solid lignin oligomers through a two-stage, acid-catalyzed process. During the first stage, raw material was treated with dilute H 2SO 4 (0·5–2·5 n) at reflux temperature (99·5 ± 1·0°C) for 10–60 min. Subsequently, delignification was conducted with H 2SO 4 (2 n) in aqueous ethanol (62·5–87·5% EtOH v/v) at reflux temperature (81·0 ± 2·0°C) for 90 min. Selective hydrolysis of about 50% of the straw hemicelluloses (w/w on original straw hemicelluloses), converted to water-soluble oligo- and monosaccharides (first stage), followed by delignification in 87·5% v/v EtOH (second stage), led to optimal component fractionation efficiency with negligible cellulose loss (less than 2% w/w on original straw cellulose) and high lignin removal (more than 70% w/w on original straw lignin). By this two-stage process, high overall fibre yields (more than 60% on original raw material) and good pulp mechanical properties were achieved.