Extraction of biofuels and biofeedstocks from aqueous solutions using ionic liquids

The production from biomass of chemicals and fuels by fermentation, biocatalysis, and related techniques implies energy-intensive separations of organics from relatively dilute aqueous solutions, and may require use of hazardous materials as entrainers to break azeotropes. We consider the design feasibility of using ionic liquids as solvents in liquid–liquid extractions for separating organic compounds from dilute aqueous solutions. As an example, we focus on the extraction of 1-butanol from a dilute aqueous solution. We have recently shown (Chapeaux et al., 2008) that 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide shows significant promise as a solvent for extracting 1-butanol from water. We will consider here two additional ionic liquids, 1-(6-hydroxyhexyl)-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide and 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, as extraction solvents for 1-butanol. Preliminary design feasibility calculations will be used to compare the three ionic liquid extraction solvents considered. The ability to predict the observed ternary liquid–liquid equilibrium behavior using selected excess Gibbs energy models, with parameters estimated solely using binary data and pure component properties, will also be explored.