Production Of Biodiesel From Soybean Oil Over CaO-ZrO₂ Solid Base Catalysts

Biodiesel, generally known as fatty acid methyl ester (FAME), is becoming an alternative energy resource to fossil fuels for its superior properties in regeneration and environmental protection. Biodiesel is the product of transesterification of vegetable oil and/or fats with methanol in the presence of a suitable catalyst. The performance of the catalysts is a key factor for the transesterification reaction. Currently, researchers focus on the heterogeneous catalysts, especially the solid base catalysts.CaO-ZrO2 mixed oxide solid base catalysts were prepared via the combustion techniques and tested in the transesterification reaction in this paper. The influences of the Ca/Zr mole ratio and the addition of La on the properties of CaO-ZrO2 catalysts were investigated in detail. The relationship between the physicochemical and catalytic properties was discussed. The main conclusions obtained are listed as follows:1. The method of glycerol titration is not a good method for determining the products of transesterification reaction because it is complex and time-consuming. Furthermore, there is a defect in principle. A lot of standard samples are required for chromatography method. A method based on nuclear magnetic resonance (NMR) technology is relatively easy, accurate and repeatable.2. With the increase in Ca/Zr mole ratio, the BET surface area of catalysts decreased. However, the amount of alkali sites increased firstly and then decreased, and a maximum was obtained as the Ca/Zr is 8:2. With increasing the Ca/Zr mole ratio, the strength of basic sites increases resulting in a high TOF. Under the optimum reaction conditions (1.25 wt.% catalyst, methanol/oil ratio of 25:1, reaction temperature of 65℃), the FAME yield are 93.9% and 98.0% after 2 and 3 h reaction, respectively.3. Urea-nitrate combustion method is a rapid and effective method for the preparation of solid base catalyst. The amount of fuel is 150% of the stoichiometric, and the ignition temperature is 500 ℃. There is no further calcinations for the products after combusting.4. With the addition of La, the BET surface area, the diameter of pore and the volume of pore increase. The reaction time for the FAME yield of 90% is 0.5 h over the 5%LCgZ2 catalyst. The improvement of catalytic performance is attributed to the increase in the pole diameter and SBET.5. The life of CaO-ZrO2 solid base improves with the addition of La. The FAME yield over the La-doped CaO-ZrO2 is 90% after 1 h reaction with the addition of 15% water in the reactant, while the FAME yield is less than 15% over the undroped CaO-ZrO2 catalysts. The 5%LC8Z2 catalyst can be recycled for catalyze the transesterification reaction more than 6 times.