Investigação das propriedades elétricas em petróleo por espectroscopia de impedância

Abstract

The petroleum and petroleum products characterization is vital for decisionmaking in the oil industry. Electrical properties have been used for quality and safety control, indirect characterization and investigation of some physicochemical properties of petroleum and by-products. The Impedance Spectroscopy was used to investigate the electrical conductivity and the dielectric constant behavior, at 30 and 50 °C, for some samples: (i) two oils (labelled as alpha and beta, considered heavy and medium oils, respectively); (ii) its aviation kerosene (QAV), diesel and atmospheric residue cuts obtained by distillation; (iii) blends of QAV/petroleum, diesel/petroleum and QAV/residue; and (iv) 10, 30 and 50 % weight water-in-oil emulsions. An unconventional electrochemical cell of two parallel platinum electrodes (99.9% purity) was used. The Nyquist diagram for oil, cuts and blends was characterized by a single semicircle; two semicircles were observed for emulsions, one assigned to the oil phase and the other to the emulsion. It was observed that an increase in temperature, for all the samples, causes an increase in electrical conductivity and a decrease for dielectric constant. The highest values of electrical conductivity and dielectric constant were observed for the alpha oil, which has the highest viscosity and polar compounds. For QAV, diesel and residue cuts, it was observed that the electrical conductivity decreases and the dielectric constant increases for higher boiling range cuts (QAV < diesel < residue). For blends, the incorporation of oil or residue into the QAV or diesel caused an increase in electrical conductivity up to a maximum point. It was observed that the dielectric constant increases linearly with the addition of oil or residue and that it can be used to infer the viscosity of these mixtures using exponential regression. The water incorporation caused a decrease in electrical conductivity and a linear increase in the dielectric constant for both oils. This last result implies that one can predict emulsions viscosity using the dielectric constant results.