A series of room temperature ionic liquids (ILs), in which cholinium acts as the cation and amino acids as the anions, were prepared via a simple and green chemical route, and characterized. Most of the ILs dissolved lignin efficiently and selectively (with solubilities of 140-220 mg of lignin per g of IL). The solubility of xylan in these ILs (which ranged from <1 to 85 mg g -1 ) depended on the nature of the anion, while cellulose was scarcely soluble (<5 mg g -1 ). In addition, enzymatic hydrolysis of microcrystalline cellulose and rice straw was enhanced significantly after pretreatment using the IL [Ch][Gly].Room temperature ionic liquids (RTILs) have been attracting increasing attention as electrolyte materials, catalysts and solvents for synthesis, catalysis and extraction etc., due to their excellent properties such as low vapor pressure, nonflammability, high thermal and chemical stability, and outstanding ability to dissolve a wide range of compounds.

Cholinium amino acids ionic liquids ([Ch][AA] ILs), a novel type of bio-ILs that can easily be prepared from renewable biomaterials, were investigated for pretreatment of rice straw by selective extraction of lignin from this abundant lignocellulosic biomass material. Of the eight ILs examined, most were demonstrated to be excellent pretreatment solvents. Upon pretreatment using these ILs, the initial saccharification rates of rice straw residues were substantially improved as well as the extent to which polysaccharides could be digested (>90% for cellulose and >60% for xylan). Enzymatic hydrolysis of pretreated rice straw by Trichoderma reesei cellulase/xylanase furnished glucose and xylose with the yields in excess of 80% and 30%, respectively. Detailed spectroscopic characterization showed that the enhancement of polysaccharides degestibility derived mainly from delignification rather than changes in cellulose crystallinity. The yields of fermentable reducing sugars were significantly improved after individual optimization of pretreatment temperature and duration. With [Ch][Lys] as the solvent, the sugar yields of 84.0% for glucose and 42.1% for xylose were achieved after pretreatment at 90°C for 5 h. The IL [Ch][Lys] showed excellent reusability across five successive batches in pretreatment of rice straw. These bio-ILs performed as well as or better than previously investigated non-renewable ILs, and thus present a new and environmentally friendly way to pretreat lignocellulose for production of fermentable sugars and total utilization of the biomass.

In this work, 28 cholinium ionic liquids (ILs), most of which are good solvents for dissolving lignin, were used for rice straw pretreatment to improve subsequent enzymatic hydrolysis. The anion exerted a significant effect on the pretreatment effectiveness of the IL as well as the subsequent enzymatic hydrolysis efficiency of rice straw residues. The presence of the basic group(s) in the anion significantly enhanced the IL pretreatment effectiveness, while the carboxyl, hydroxyl and aromatic groups had a negative impact on IL delignification. Except for amino acid-based ILs, the delignification abilities of the ILs are linearly and positively correlated with the pKa values of the conjugate acids of the anions. Of the ILs tested, amino acid-based ILs, especially basic amino acid-based ILs, are the most effective pretreatment solvents. Satisfactory reducing sugar yields (81% for glucose and 26% for xylose) were obtained in the enzymatic hydrolysis of rice straw pretreated by cholinium argininate ([Ch][Arg]) under a pretty mild pretreatment severity (60°C, 6 h). The results presented in this work may be useful for rational design of novel and green ILs for delignification of lignocellulose.

In this work, sugar cane bagasse pretreatment by renewable cholinium amino acids ionic liquids ([Ch][AA] ILs) and subsequent enzymatic hydrolysis of the residues were conducted. Six ILs tested were found to be effective for sugar cane bagasse pretreatment. Upon pretreatment using these ILs, the enzymatic digestion of this lignocellulosic biomass was improved significantly due to extensive delignification. The IL cholinium lysine ([Ch][Lys]) displayed excellent pretreatment efficiency with sugar cane bagasse of various sizes as the substrates. The addition of water into [Ch][Lys] did not exert a negative effect on pretreatment effectiveness, although the delignification capacity of the IL decreased. The sugar yields of 80% for glucose and 84% for xylose were obtained in the enzymatic hydrolysis after the sugar cane bagasse without size reduction was pretreated with a biomass loading of 5 wt % by 50 g 50% [Ch][Lys]–water mixture at 90 °C for 6 h. A simple and atom-economic preparation approach to ILs was successfully developed for lignocellulosic biomass pretreatment, which may significantly reduce ILs costs, and the reactant contaminations in the IL–water mixture had no detrimental effect on the pretreatment efficiency.

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