Continuous production of biodiesel from rapeseed oil by ultrasonic assist transesterification in supercritical ethanol

In Europe, rapeseed is a renewable raw material which has been widely used for the production of biodiesel by various processes. The transesterification reaction of rapeseed oil with ethanol to biodiesel in supercritical fluid conditions was investigated using several heterogeneous catalysts and preliminary ultrasonic emulsification of the reaction mixture, to run the reaction at mild conditions. Phase equilibrium of fatty acids in supercritical ethanol was study to determine the operating condition in supercritical states. Transesterification experiments were carried out under a pressure of 30 MPa, with ethanol to oil molar ratio (in the range of 12:1⿿20:1), temperature (623 K to 653 K), and the catalyst loading level and type were the main parameters. The most important characteristics of Al 2 O 3 support catalyst and the impregnation method with aqueous solution of metal nitrates are also described. Yields of Fatty Acids Ethyl Ester (FAEE) are reported for different ZnO/Al 2 O 3 , MgO/Al 2 O 3 , SrO/Al 2 O 3 catalysts in different experimental conditions. The higher yield of 97.46% was obtained under the optimal conditions 623 K, 30 MPa, 12:1 ethanol/FAEE molar ratio, with SrO/Al 2 O 3 (2 wt.% SrO) impregnated catalyst.