Corn Stover Pretreatment by Ionic Liquid and Glycerol Mixtures with Their Density, Viscosity, and Thermogravimetric Properties

As a green, low-pressure pretreatment for biomass, ionic liquids (ILs) have great potential, but their high cost has limited commercial application to date. Glycerol, a safe byproduct of the growing biodiesel industry, was investigated as an IL cosolvent. In this study, the ILs 1-ethyl-3-methylimidazolium formate ([C2mim][O2CH]) and 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) were diluted with up to 75% glycerol and used to pretreat corn stover (CS) at 145 degrees C and ambient pressure. The pretreated CS residues were enzymatically hydrolyzed, yielding over 90% of the cellulose in the raw CS as glucose and 80% of the xylan as xylose. These mixture pretreatments gave yields 40% higher than the pure IL pretreatments. Fourier transform infrared spectroscopy indicated that lignin had been removed by the glycerol IL pretreatments. Compared to the ILs used, glycerol's viscosity was an order of magnitude higher at ambient temperature, but at the processing temperature used the viscosities of the ILs and their mixtures with glycerol were quite similar. An explanation for enhanced pretreatment may relate to the positive excess molar volume of the mixtures.