Synthesis, antioxidant properties, and oil solubility of a novel ionic liquid [UIM0Y2][C6H2(OH)3COO] in biodiesel

Abstract

To promote the practical applications of biodiesel, an antioxidant of biodiesel is designed and synthesized in this study. The antioxidant is a 1-(2-cyanoethyl)-2-undecyl imidazole gallate ionic liquid, referred to as [UIM0Y2][C6H2(OH)3COO], which is synthesized from gallic acid (GA) and 1-(2-cyanoethyl)-2-undecyl imidazole. The synthesized samples are characterized by proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy. The effects of [UIM0Y2][C6H2(OH)3COO] on the oxidation stability, metal corrosion, gum formation of Jatropha biodiesel, and oil solubility in biodiesel are also explored. The results reveal that [UIM0Y2][C6H2(OH)3COO] has an excellent oil solubility of 0.0425 g·(100 mL)−1 at 25 °C because of its non-polar structure, which is 85 times that of GA. The oxidation stability of Jatropha biodiesel is significantly improved by [UIM0Y2][C6H2(OH)3COO]. After adding 0.2‰ [UIM0Y2][C6H2(OH)3COO], the induction period of Jatropha biodiesel is enhanced by 76% and reaches the European standard (6 h). In addition, [UIM0Y2][C6H2(OH)3COO] can also inhibit the corrosion of copper and galvanized iron sheets by Jatropha biodiesel as well as the formation of gum. The amount of gum formation decreases by 37% when the concentration of [UIM0Y2][C6H2(OH)3COO] is 0.5‰. These findings indicate that [UIM0Y2][C6H2(OH)3COO] is a promising material for enhancing the oxidation stability of biodiesel.