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 degrees 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.