No abstract

This study examines the effect of structural components of an ionic liquid (IL), including the choice of the anion, alkyl chain length on the cation, and substitution on the cation, on the mutual solubility with water and with 1-octanol. This is important because ionic liquids have been shown to be good replacements for organic extraction solvents in some liquid separations. In addition, we use the measured data to predict 1-octanol/water partition coefficients for the ionic liquids using the nonrandom two liquid (NRTL) and electrolyte nonrandom two liquid (eNRTL) excess Gibbs energy models. Specifically, the mutual solubilities of 15 different imidazolium, pyridinium, and quaternary ammonium ionic liquids with water were measured at (23.5 ± 1) °C. An increase in the alkyl chain length or the substitution decreases the mutual solubility with water. The [BF4]- and [B(CN)4]- anions are significantly more hydrophilic than [PF6]-, [(CF3SO2)2N]-, and [(CF3SO2)3C]-. The mutual solubilities of 10 ILs with 1-octanol were measured at (23.5 ± 1) °C. For these systems, the longer the alkyl chain, the more soluble the IL was in the alcohol, while ring substitution has little effect. From this data, 1-octanol/water partition coefficients of 10 ionic liquids were predicted using the NRTL and eNRTL models.

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.

A new asymmetric framework for modeling liquid−liquid equilibrium (LLE) in electrolyte/mixed-solvent systems is demonstrated, with focus on systems involving a dilute aqueous solution of an ionic liquid (IL). The extent to which this approach is able to predict ternary LLE, using parameters obtained from binary and pure-component data only, is evaluated. For this purpose, ternary IL/solvent/water systems are used as examples. Comparisons of predicted LLE are made to experimental data representing various types of ternary LLE behavior, as well as to predictions obtained from standard symmetric models. Results indicate that an asymmetric NRTL/eNRTL model provides better predictions of ternary LLE for systems containing ILs and water than standard symmetric models.

Accurate mass balance and conversion data from integrated operation is needed to fully elucidate the economics of biofuel production processes. This study explored integrated conversion of corn stover to ethanol and highlights techniques for accurate yield calculations. Acid pretreated corn stover (PCS) produced in a pilot-scale reactor was enzymatically hydrolyzed and the resulting sugars were fermented to ethanol by the glucose-xylose fermenting bacteria, Zymomonas mobilis 8b. The calculations presented here account for high solids operation and oligomeric sugars produced during pretreatment, enzymatic hydrolysis, and fermentation, which, if not accounted for, leads to overestimating ethanol yields. The calculations are illustrated for enzymatic hydrolysis and fermentation of PCS at 17.5% and 20.0% total solids achieving 80.1% and 77.9% conversion of cellulose and xylan to ethanol and ethanol titers of 63g/L and 69g/L, respectively. These procedures will be employed in the future and the resulting information used for techno-economic analysis.