Functional Ionic Liquids Catalyzed the Esterification of Ricinoleic Acid with Methanol to Prepare Biodiesel: Optimization by Response Surface Methodology

An efficient route to preparing biodiesel by the esterification of ricinoleic acid (RA) with methanol was investigated in the work. Six kinds of functional ionic liquids (IL) were selected as catalysts. The effects of reaction variables (reaction time, temperature, IL load, and the ratio of reaction substrates) were also evaluated and optimized using response surface methodology (RSM). Among IL tested, 1-butylsulfonic-3-methylimidazolium trifluoromethanesulfonate showed the highest catalytic efficiency for the esterification. Reaction variables were optimized using RSM as follows: IL load 4 % (relative to the weight of RA), molar ratio of methanol to RA 9.2:1, 67 °C, and 28 min. Under the optimized conditions, the esterification degree of RA was 92.3 ± 1.7 %.