Using Glycerol As a Co-Solvent for Ionic Liquid Pretreatment of Rice Hulls

Over 100 million tons of rice hulls (husks) are generated each year at rice processing centers around the world. These cannot be easily composted and often end up in landfills.  They can be pretreated with ionic liquids (ILs) prior to enzymatic hydrolysis to produce glucose or xylose, which can be fermented for biofuel production. However, the present high cost of ILs is a deterrent to large scale use.  The non-chloride containing ILs 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium formate, 1,3-dimethylimidazolium dimethylphosphate, and 1-ethyl-3-methylimidazolium diethylphosphate diluted with glycerol were investigated for rice hull (husk) pretreatment.  When diluted with up to 75% glycerol and used for a 110 °C, three hour pretreatment, 1-ethyl-3-methylimidazolium formate was found to give glucose and xylose yields after enzymatic hydrolysis similar to those of pure 1-ethyl-3-methylimidazolium formate. Diluting with glycerol was also found to decrease solvent viscosity and promote solvent recovery. Such findings suggest that glycerol dilution in IL-biomass pretreatment may, in some cases, enhance pretreatment.