Application of silver-based dihydric alcohol to the extraction of methyl linolenate with high extractability and stability replacing ionic liquids

A novel silver-based dihydric alcohol extractant was substituted for ionic liquids to enrich methyl linolenate (C18-3) from tallow seed oil methyl ester in this study. The interactions among dihydric alcohol, Ag(I) and C18-3 were explored by FT-IR spectroscopy. The effects of dihydric alcohol structure, carrier Ag(I) concentration, temperature and initial feed concentration on extraction yield and selectivity were reported. The good extraction performance was achieved by 1,4-butanediol containing AgBF4. The complexation of Ag(I) with C18-3 was dominant in extraction operation rather than physical partition. Furthermore, a multi-step reverse extraction method was proposed to obtain C18-3 product and regenerate the extractant. 1-Hexene as the stripping phase can facilitate C18-3 reverse extraction. The content of C18-3 in the product was up to 93.36%, and the yield was 73.76%. This work opened a new route for the utilization of the dihydric alcohol properties to manipulate the carrier efficiency for extracting unsaturated fatty acid methyl esters at a lower cost.