(253f) Structure and Properties of Ionic Liquid/Organic Co-Solvent Mixtures

Bandlamudi, S., South Dakota School of Mines & Technology
Cooney, M., University of Hawaii
Chupas, P., Argonne National Laboratory
Benjamin, K. M., South Dakota School of Mines and Technology

The extensive use of ionic liquids (ILs) is a significant achievement in extraction processes, especially in extracting lipids and proteins from biomass for bio-fuel production from algae and other bio-based feedstocks.  The particular effectiveness of ionic liquids combined with polar-covalent molecules (PCM), such as methanol, as an extraction solvent mixture in extracting bio-oils from micro-algae has been demonstrated successfully by Young et al., 2010, the main highlight being auto-partitioning of extracted lipids into a separate phase.  While the efficacy of these IL/PCM mixtures has been demonstrated experimentally, there is no current molecular-level understanding of the structural and thermodynamic properties of these mixtures.

The thermodynamic and structural properties of IL/PCM mixtures are explored using both molecular simulation and computational quantum chemical methods.  Molecular dynamics (MD) simulations are conducted to predict mixture volumetric, thermal, and structural properties.  MD simulations of thermodynamic mixing properties for IL/PCM binary mixtures show virtually ideal mixing behavior, while excess heats of mixing are predicted.  In addition, MD predictions of structural properties like radial distribution functions and structure factors, supported by simulation visualization, provide information on local fluid structure and interactions between ionic liquid and polar-covalent molecules, including the change in ion aggregation with mixture composition.  These simulation predictions are compared to small angle X-ray scattering (SAXS) and polarization data for model validation.  Lastly, density functional theory (DFT) quantum chemical calculations are used to probe the shift in frequency of O-H stretch in methanol at various concentrations of IL/methanol mixtures, and compared to FTIR measurements.

These efforts provide an improved understanding between the molecular-level behavior and macroscopic thermodynamic properties of IL/PCM mixtures, to characterize these new solvents mixtures for separation applications.