Bifunctional temperature-sensitive amphiphilic acidic ionic liquids for preparation of biodiesel

Abstract

Several water-stable bifunctional temperature-sensitive amphiphilic Bronsted-acidic ionic liquids with an alkane sulfonic acid group and a polyether group were synthesized through polyethylene glycol monomethylether as raw material. The properties and structures of the ionic liquids were experimentally characterized. Esterification of oleic acid with methanol to biodiesel was investigated in various bifunctional temperature-sensitive amphiphilic acidic ionic liquids. The amphiphilicity, temperature-sensitive, polymerization degree, acidity and activity correlation for the ionic liquids were studied. It was found that their structures were consistent with the designed structure and their purities were high. Among all these ionic liquids, the ionic liquid – MPEG-350-ILs showed the best catalytic activity that is near to that of concentrated sulfuric acid, which is ascribed to its strong Brønsted acidity and amphiphilicity. The catalytic activity of each ILs is dependent on the polymerization degree of polyether cation. The catalytic activity decreased with lengthening polyether chain of ionic liquids. These ionic liquids exhibited temperature-sensitive property. The produced biodiesel could be separated via simple decantation and the ionic liquids could be reused.