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Lignocellulosic biomass has a recalcitrant structure including interwoven cellulose, hemicelluloses, and lignin biomacromolecules that is challenging to deconstruct. Many ionic liquids (ILs), salts molten below 100 掳C, can be used to deconstruct lignocellulosic biomass and are less hazardous than the chemicals typically used. The environmentally-friendly ILs investigated in this study were 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium formate. While effective and recyclable, these ILs are expensive. To reduce costs, dilution with other safe compounds was desired. Glycerol, a food additive, is inexpensive and becoming even more so since it is a by-product of the expanding biodiesel industry.  When glycerol was added to these ILs to pretreat loblolly pine or rice husks, lignin was dissolved into the IL- glycerol mixture and crystalline cellulose in the residue had been converted to more easily hydrolyzed amorphous cellulose.  Lignin could subsequently be precipitated using an anti-solvent.

 To determine the reasons for their efficacy, IL- glycerol mixtures were investigated to determine pH, viscosity, and density. The ILs investigated were 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium formate, which were diluted with glycerol to give mass fractions of 0.25, 0.50, and 0.75. Values for pH for 1-ethyl-3-methylimidazolium acetate and its mixture with glycerol when diluted with water to be 10 mass% IL-glycerol mixture was 6.0, while 1-ethyl-3-methylimidazolium formate and its mixture with glycerol gave a pH of 8.3 when so diluted with water. Viscosity was measured for the IL-glycerol mixtures up to 140 掳C.  While quite different at room temperature, glycerol, ILs, and mixtures had similar viscosities between 110 掳C and 140 掳C, the typical range for biomass IL pretreatment. Density measurements showed the IL-glycerol mixtures that gave more effective pretreatments to have positive excess molar volumes.