Catalysis Preparation of Biodiesel from Waste <i>Schisandra chinensis</i> Seed Oil with the Ionic Liquid Immobilized in a Magnetic Catalyst: Fe₃O₄@SiO₂@[C4mim]HSO₄

Abstract

The purpose of this study was to synthesize a magnetic material that could be easily separated by a magnetic field and combined the catalytic function of an acid/base ionic liquid with silicon for biodiesel preparation. A kind of magnetic catalyst-immobilized ionic liquid was synthesized by a three-step method. The synthesis conditions in each step were optimized by single-factor analysis. Under the optimum conditions, 206.83 mg of ionic liquid (>43.63%) was immobilized on SiO₂ (per gram). Heating under reflux was applied to extract <i>Schisandra chinensis</i> seed oil with an average yield of 10.9%. According to the biodiesel yields, Fe₃O₄@SiO₂@[C4mim]HSO₄ was the most efficient catalyst in the methyl esterification reaction. Under the optimum reaction conditions, seed oil (10.0 g) was mixed with methanol (70 mL) under continuous mechanical stirring for 3 h, and the yield of biodiesel was 0.557 g/g (the catalyst efficiency was about 89.2%). Also, the thermal value was increased from 32.14 kJ/g (seed oil) to 38.28 kJ/g (biodiesel). The catalytic efficiency of Fe₃O₄@SiO₂@[C4mim]HSO₄ was 87.6% of the first being used after four reuse cycles, and 71.4% of the first being used after six reuse cycles in the methylation reaction. The yields and physical and chemical properties of biodiesel were determined.