Supercritical Transesterification of Palm Oil and Hydrated Ethanol in a Fixed Bed Reactor with a CaO/Al2O3 Catalyst

Biodiesel production from palm oil and hydrated ethanol in a fixed bed reactor using CaO/Al 2O 3 as the catalyst was investigated and optimized using response surface methodology. The investigated parameters were temperature, pressure, ethanol/palm oil molar ratio, residence time and total mass flow rate. The approach was divided into two parts, a preliminary study using broad scale changes over a reasonable range of the above operating parameters and then, using this data to select a narrower range, a finer scale study to optimize the selected narrower operating parameters from the preliminary study. The resultant biodiesel obtained under the optimal conditions (285 °C, 20 MPa, 30:1 ethanol/oil molar ratio, 2 g/min flow rate and 4.85 min residence time) was measured for 11 fuel properties following the International Biodiesel Standard (EN14214), and was found to comply with this International Standard. Moreover, ZnO/Al 2O 3 and La 2O 3/Al 2O 3 catalysts were tested for their activity and stability. Although the La 2O 3/Al 2O 3 catalyst had a slightly higher initial activity than that of CaO/Al 2O 3, it is some 800-fold more expensive. Therefore, the CaO/Al 2O 3 catalyst has a greater industrial potential than La 2O 3/Al 2O 3, when comparing together the technical and economic benefits.