Continuous production of fatty acid ethyl esters from sunflower oil using supercritical ethanol

Abstract The production of first generation biofuels has increased in the last few years because of the rising price of fossil fuels and environmental policies. Biodiesel process alternatives have been proposed in order to achieve higher yields, non-catalytic and more environmentally friendly processes, a greater profit from by-products and particularly the possibility of using low quality and cheaper feedstocks. In this regard, one of the most studied technologies has been the non-catalytic supercritical transesterification of fats and raw vegetable oils. This work reports results on the continuous production of fatty acid ethyl esters (FAEEs) from the non-catalytic supercritical ethanolysis of sunflower oil. The reaction was carried out in the following range of operating conditions: (i) ethanol-to-oil molar ratio of 40:1; (ii) temperature and pressure range, 573–618 K and 165–200 bar and (iii) mass flow rates varying from 3 to 16 g/min. Given the high sensitivity of the specific density in supercritical mixtures, the mixture residence time in the reactor was estimated based on experimental data of the reactive mixture density. Moreover, we show here that overlooking the use of this experimental data and assuming ideal solution behavior for density calculation, which is usually done, may lead to important deviations in the kinetic model parameters. The mixture densities were correlated with the Peng–Robinson equation of state (PR-EoS). In the range of operating conditions studied in this work, up to 90% by mass fraction of fatty ester was obtained.