Biodiesel production using supercritical alcohols and different vegetable oils in batch and continuous reactors

P. VALLE; A. VELEZ; P. HEGEL; E.A. BRIGNOLE

Barcelona, España

Congreso; 11th European Meeting on Supercritical Fluids. New perspectives in supercritical fluids: Nanoscience, Materials and Processing; 2008

ICMAB-CSIC

Abstract: Recent experimental studies on non-catalytic transesterification have shown that high reaction rates, which justify the commercial application of this process, can be obtained if the operating conditions are above the critical pressure and temperature of the alcohol. Even though it is generally agreed that temperatures above 550 K and high alcohol/oil ratios are required to obtain high conversions and high reaction rates, there is disagreement among the different authors regarding the operating pressure, the assumed phase conditions, the use of co-solvents and the justification of the sudden increase of the rate of reaction with temperature. In the present work, the reactor phase transitions are directly observed in a double windowed cylindrical reactor and the conversion to ethyl esters is measured. In these studies different oils, crude and refined, as well as the effect of water and free fatty acids, are studied. Also the effect of using methanol or ethanol and different co-solvents on the rate of reaction and efficiency of conversion are considered. The optimization of the process conditions was carried out based on a statistical design of experiments where the key process variables were studied over different ranges to obtain a reliable model for the efficiency of the reaction as a function of reactants residence time, temperature, pressure and molar ratio of alcohol/oil. The present results confirm preliminary studies that indicate that high conversions can be obtained at pressures of 10-15 Mpa at temperatures between 570 and 600 K using a molar ratio of 39. From direct observations and the modeling of the phase behavior, a better understanding of the supercritical ethanol transesterification process is obtained as well as the confirmation of the phase equilibrium predictions based on the GCA-EOS model.