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/Al₂O₃ 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/Al₂O₃ and La₂O₃/Al₂O₃ catalysts were tested for their activity and stability. Although the La₂O₃/Al₂O₃ catalyst had a slightly higher initial activity than that of CaO/Al₂O₃, it is some 800-fold more expensive. Therefore, the CaO/Al₂O₃ catalyst has a greater industrial potential than La₂O₃/Al₂O₃, when comparing together the technical and economic benefits.