Conversion of mono/di/polysaccharides into furan compounds using 1-alkyl-3-methylimidazolium ionic liquids

The one-pot hydrolysis/dehydration of mono/di/polysaccharides into furfural (FUR) or 5-hydroxymethyl-2-furaldehyde (HMF) in the presence of an acidic ionic liquid, 1-ethyl-3-methylimidazolium hydrogen sulfate ([EMIM][HSO4]), at 100 °C, was investigated and the results were compared with those using 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), with or without CrCl3 or H2SO4. The ionic liquid [EMIM][HSO4] is effective in converting xylose and fructose or related polysaccharides into FUR (e.g. from xylose: 84% yield at 6 h) or HMF (e.g. from fructose: 88% yield at 30 min), but not glucose and polymers containing these units, which contrasts to that observed for the [BMIM][Cl]/CrCl3 system. The latter is quite effective in converting glucose and related disaccharides into HMF, but not the polysaccharides cellulose and starch. For the latter feedstocks, the addition of H2SO4 or [EMIM][HSO4] to cellulose/[BMIM][Cl]/CrCl3 enhances HMF yields, presumably by accelerating the hydrolysis step, although the selectivity of the dehydration of glucose monomers seems rather poor (HMF yield < 13 wt.%). In the case of the xylose to FUR conversion in [EMIM][HSO4], two systems involving the reaction and simultaneous separation of the target product were investigated, namely reaction/solvent extraction and reaction/evaporation systems, and for both the ionic liquid could be recovered and reused without a significant drop in FUR yield in recycling runs.

The ionic liquid [EMIM][HSO4] is promising for furfural and 5-hydroxymethyl-2-furaldehyde production from xylose, fructose or related polysaccharides, under relatively mild conditions. For more challenging polysaccharides such as cellulose and starch, the addition of [EMIM][HSO4] to the system cellulose/[BMIM][Cl]/CrCl3 enhances 5-hydroxymethyl-2-furaldehyde yields. Reaction/solvent extraction and reaction/evaporation systems were investigated for simultaneous reaction and product separation, and for both the acidic medium could be reused successfully.Figure optionsDownload as PowerPoint slide