Lipid Aggregation Thermodynamics and Kinetics in Ionic Liquid/Co-Solvent-Based Extractions

The extensive use of ionic liquids (ILs) is a significant achievement 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, the main highlight being auto-partitioning of extracted lipids into a separate phase.¹ While the efficacy of these IL/PCM mixtures has been demonstrated experimentally, our previous efforts focused on understanding the thermodynamic and structural properties of the basic co-solvent mixtures.

Experimental results showed that intermediate compositions of IL/PCM mixtures are desired for maximum lipid extraction yields.² Molecular dynamics (MD) simulations are conducted to predict the lipid aggregation behavior of triolein, a model lipid compound, at various concentrations of IL/PCM mixtures. MD generated radial distribution functions (rdfs) and lipid clustering analysis provide an estimate of the thermodynamics and kinetics of lipid aggregation and are compared to light scattering data. Clustering analysis and simulation snapshots indicates that the lipids are aggregating in these IL/co-solvent mixtures, a simulation finding that is supported by light scattering experiments and correlates well with auto-partitioning. A correlation between the extent of triolein aggregation and the experimental extraction yields as a function of co-solvent composition is also explored.

These efforts provide an improved understanding between the molecular-level behavior and macroscopic thermodynamic properties of lipid aggregation and auto-partitioning in IL/PCM mixtures, to characterize these new tailored solvent mixtures for bioprocessing separation applications.

References

[1] G. Young, F. Nippgen, S. Titterbrandt, and M. J. Cooney, “Lipid extraction from biomass using co-solvent mixtures of ionic liquids and polar covalent molecules”, Separation and Purification Technology, 2010, 72, 118.

[2] G. Severa, G. Kumar, M. Troung, G. Young and M. J. Cooney, (2013). “Simultaneous extraction and separation of phorbol esters and bio-oil from Jatropha biomass using ionic liquid–methanol co-solvents”, Separation and Purification Technology, 2013, 116, 265.