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Ionic liquids (ILs) can play multiple roles in lignocellulose biorefineries, including utilization as agents for the separation of selected compounds or as reaction media for processing lignocellulosic materials (LCM). Imidazolium-based ILs have been proposed for separating target components from LCM biorefinery streams, for example, the dehydration of ethanol-water mixtures or the extractive separation of biofuels (ethanol, butanol) or lactic acid from the respective fermentation broths. As in other industries, ILs are potentially suitable for removing volatile organic compounds or carbon dioxide from gaseous biorefinery effluents. On the other hand, cellulose dissolution in ILs allows homogeneous derivatization reactions to be carried out, opening new ways for product design or for improving the quality of the products. Imidazolium-based ILs are also suitable for processing native LCM, allowing the integral benefit of the feedstocks via separation of polysaccharides and lignin. Even strongly lignified materials can yield cellulose-enriched substrates highly susceptible to enzymatic hydrolysis upon ILs processing. Recent developments in enzymatic hydrolysis include the identification of ILs causing limited enzyme inhibition and the utilization of enzymes with improved performance in the presence of ILs.

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ABSTRACT:The acidic 1-butyl-3-methylimidazolium hydrogen sulfate ([bmim][HSO 4 ]) ionic liquid was explored as both a reaction medium and a catalyst in the furfural production from xylose. Preliminary experiments were carried out at 100−140°C for 15−480 min in systems containing just xylose dissolved in [bmim] [HSO 4 ] in the absence of externally added catalysts. More than 95% xylose conversion was achieved when operating at 120 or 140°C for 300 and 90 min, respectively; but just 36.7% of the initial xylose was converted to furfural. Operation in biphasic reaction systems (in the presence of toluene, methyl-isobutyl ketone or dioxane as extraction solvents) at 140°C under selected conditions resulted in improved furfural production (73.8%, 80.3%, and 82.2% xylose conversion to furfural for the cited extraction solvents, respectively).

Olive tree trimmings (OTT) were subjected to sequential stages of autohydrolysis (with hot compressed water) and ethanolÀwater mixtures (organosolv pulping), to obtain three separate streams containing hemicellulose-derived products (autohydrolysis liquors), lignin fragments (pulping liquors), and autohydrolyzed, delignified solids (denoted ADOTT) mainly made up of cellulose. Up to 42% of the polysaccharides contained in the raw material (accounting for about 25% of the OTT dry mass) were recovered in autohydrolysis liquors as valuable compounds, whereas ADOTT showed high susceptibility toward enzymatic hydrolysis and allowed the formulation of media in which saccharification and ethanol fermentation were carried out simultaneously at a high product yield. Ethanol conversions higher than 90% of the theoretical value (calculated from the ADOTT content of cellulose) were achieved, whereas the ethanol concentration of fermented media reached values up to 39 g/L.

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