Extraction of polyunsaturated fatty acid methyl esters by imidazolium-based ionic liquids containing silver tetrafluoroborate - Extraction equilibrium studies.

The extraction/enrichment of omega-3 polyunsaturated fatty acid methyl esters (PUFAMEs) by hydrophobic ionic liquids (ILs) containing silver salts as the extraction phase has been extended to include equilibrium studies. The extraction time, organic solvents, IL structures, and AgBF4 concentrations all influence the organic/ionic liquid biphasic extraction equilibrium. Each of these parameters was studied. The PUFAME distribution ratios, partition coefficients and the PUFAME-Ag+ complex stability constants were determined from gas chromatography (GC) analyses. When AgBF4 dissolved in [hmim][PF6] was used as the extraction phase, both the distribution ratios of PUFAMEs and the stability constants of PUFAME-Ag+ complexes increased significantly with an increase in the degree of unsaturation of the PUFAMEs. Investigation of the IL structures indicated that larger PUFAME distribution ratios were obtained when AgBF4 was dissolved in hydrophobic ILs than in hydrophilic ILs. Higher PUFAME distribution ratios occurred using shorter chain alkanes as the organic solvents. The extraction isotherms for PUFAME uptake were obtained from which saturated extraction capacities were determined. Compared with previous aqueous AgNO3 extractions, a more efficient extraction of PUFAMEs was obtained by using a hydrophobic IL containing AgBF4. Much higher extraction capacities and significant shorter operation times were also achieved.