Evaluation of biodiesel storage stability using reference methods

The recorded changes in 8 different samples of biodiesel (from 4 different feedstocks, both undistilled and distilled) during accelerated ageing are shown in this paper. ASTM D 4625 method for quick ageing of common diesel fuels, carried out at 43 °C, allows to simulate the changes taking place in fuel during a long-term storage. All quality parameters of biodiesel are changing during time, according to the storage stability of different samples. The changes in other parameters not included in CEN tentative specification such as polymer content and peroxide value were recorded and plotted against storage time. Samples were also evaluated in terms of insoluble formation (filterable + adherent) but in any case significant insoluble formation was observed. The conclusion was that polymers formed during storage of biodiesel in controlled conditions are soluble in oxidised biodiesel, thanks to its high polarity and become insoluble only when oxidised biodiesel is mixed with diesel fuel.