Electrical and ultrasonic properties of vegetable oils and biodiesel

Abstract

Electrical properties (permittivity and conductivity) and speed of sound were determined in commercial vegetable oils from sunflower, corn, soybean, grape, cotton, olive, canola and chia, and in biodiesel from these oils. Electrical properties were measured in the frequency range from 20 Hz to 2 MHz at temperatures between 300 K and 343 K. The calibration uncertainty of the measuring system was below 1%. The speed of sound was determined at the frequencies of 1.53 MHz, 5.66 MHz and 9.43 MHz. The uncertainty of the results was below 0.05%. In all the measurements in this work, the temperature of the samples was stabilized within ±0.1 K. The experimental data for the speed of sound and permittivity of vegetable oils and biodiesel samples fit very satisfactorily to a linear dependence with temperature, whereas the conductivities follow an Arrhenius law. In all the samples, the fitting parameters of the real part of the relative permittivity, the activation energy of the conductivity and the speed of sound allow to distinguish between the vegetable oil and the biodiesel obtained from it. Within the temperature range studied in this work, a linear correlation is found between the speed of sound and the permittivity of vegetable oils and biodiesel.