Relevance of the acidic 1-butyl-3-methylimidazolium hydrogen sulphate ionic liquid in the selective catalysis of the biomass hemicellulose fraction

Abstract

The ability of acidic 1-butyl-3-methylimidazolium hydrogen sulphate ionic liquid (IL) to hydrolyse and convert wheat straw into pivot compounds without additional catalyst was scrutinised. The pre-treatment with this IL allowed to obtain a liquor rich in hemicellulosic sugars, furans and organic acids, and a solid fraction constituted mainly of cellulose and lignin was obtained. Pre-treatment conditions such as temperature and residence time were set to produce xylose or furfural at a fixed 1/10 (w/w) biomass/IL ratio and 1.24% (w/w) water content in the pre-treatment process. Statistical modelling based on Doehlert experimental design was applied to establish optimal conditions to produce xylose and furfural. Temperature demonstrated a greater effect on the production of xylose, rather than the time of pre-treatment, and it was significantly incisive on furfural formation as well. To compare the reaction conditions, the severity factor for the studied IL was proposed and applied in this work. Furthermore, water was verified to have a large influence on the equilibrium of the hemicellulose hydrolysis. The increase of the water content close to 10% (w/w) in the system disfavoured xylose dehydration and thus allows increasing significantly the production of hemicellulose-derived monosaccharides. At last, an important disclosure in the reaction of biomass with [bmim][HSO₄] is the formation of humins for high severity pre-treatment.