Study on Optimization of Preparation Process of Biodiesel Using Sulfuric Acid as Catalyst by Response Surface Methodology

In this investigation, biodiesel was prepared by esterification reaction using the oleic acid as raw material and H₂SO₄ as catalyst. The effects of various parameters such as reaction time, temperature, mole ratio of alcohol/oleic acid, catalyst dosage on the conversion rate of oleic acid were investigated and the preparation process of biodiesel was optimized by using response surface methodology (RSM). The results showed that with the increase of reaction temperature, the conversion rate of oleic acid increased, when the reaction temperature reached 70 ℃, the conversion rate of oleic acid was not changed. The conversion rate of oleic acid increased with the increase of the catalyst dosage of H₂SO₄, and the conversion rate was close to the maximum when the increase of the catalyst dosage was 2% of the oleic acid. With the increase of reaction time, the conversion rate of oleic acid increased gradually, and the conversion rate of oleic acid stabilized after 4 h reaction. The continuous increase of the mole ratio of alcohol/oleic acid caused the conversion rate of oleic acid increased continuously. When the mole ratio of alcohol/oleic acid was 8 : 1, reaction tends to be gentle. Mathematical model of response surface regression between conversion rate of oleic acid (Y) and single factors was obtained by analyzed the test data with analysis software Design Expert 8.0. The optimum reaction conditions were determined: the reaction time of 3.77 h, the reaction temperature of 68.83 ℃, the catalyst dosage of 4.21%, the mole ratio of alcohol/oleic acid of 9.26 : 1 and predicted conversion rate of 98.26%.