Influência da matéria-prima nas propriedades elétricas de biodiesel e misturas diesel e biodiesel

Abstract

Were prepared biodiesel samples from four different oil sources: sunflower, soybean, canola and corn that were characterized by optical techniques (FTIR and Fluorescence), mechanical (viscosity measurements) and electrics (Impedance Spectroscopy - IS and Conductivity Spectroscopy). The electrical characteristics of biodiesel showed significant variations on electrical resistivity/conductivity and relaxation time of different biodiesels studied. The results showed that these variations are directly related to changes in viscosity of biodiesel, because it is an important factor for the mobility of charge carriers, being dependent on the structural profile of the carbon chain of fatty acids that make up biodiesel. The dielectric constant, on the other hand, did not show significant variations, basically suggesting little changes in the polarity of biofuels from different feedstocks. The diesel/biodiesel blends (DB) were characterized using the Molecular Fluorescence Spectroscopy and electrical measurements using the technique of Impedance Spectroscopy (IS) measurements with alternating electrical current (AC) and direct current electrical conductivity (DC). From the data of IS were obtained the conductivities of mixtures DB, in the limit of low frequencies and conductivities that are comparable to DC. The conductivity is, however, dependent on the feedstock oil seed as the biodiesel from different sources contains specific molecules in different concentrations. Variation in the composition may modify the electrical properties of the material and, in the case of the fatty acids that precede obtaining biodiesel, it is known that the acidity increases with the degree of unsaturation carbon chain and decreases with increasing them. By the electrical conductivity was possible to calculate a Intensification Factor (I), which compares the conductivity of the blends to the conductivity of pure diesel. With the increase of biodiesel content observed a linear increase in I evaluated compositional interval and in some cases may reach 300% increase. The EI has been described in the literature to quantify mixtures of DB by the electrical conductivity in the contrast based on dielectric constant measurements for these sensors. Finally, our results show that the DC technique yielded similar results to those obtained in AC results, making it possible to apply this method is simpler and cheaper replacing IS.