Effective polarizability of vegetable oils

Abstract

Vegetable oils are the most important feedstock for biodiesel production. For pure substances and mixtures, such as vegetable oils (a mixture of triacylglycerols), the effective polarizability relates the refractive index with density, through the Lorentz – Lorenz equation. Although refractive index measurements are widely used in industrial settings, and also in the laboratory to characterize liquids, no published data of effective polarizability of vegetable oils could be found in the literature. This work reports the effective polarizability of eight different vegetable oils samples (soybean, corn, peanut, canola, grapeseed, linseed, chia, almond), calculated from measurements of refractive index and density, in the temperature range between 20°C and 45°C. For all the samples, the effective polarizability is 0.305 cm3/g (RMS uncertainty below 0.001 cm3/g). Remarkably, this value is the same (within the experimental uncertainty) for different vegetable oil types and pure triacylglycerols, and independent of temperature. Moreover, it agrees very well with the result calculated from experimental data of refractive index and density of different vegetable oils and pure triacylglycerols found in the literature. In contrast, the effective polarizability of biodiesel, determined in a previous work, is very close to 0.31, and for a wide variety of liquid hydrocarbons and crude oils is between 0.33 and 0.35 cm3/g, as reported by other authors. The results of this work are of interest for the analysis and numerical modeling of vegetable oils properties. They are also relevant for the detection of vegetable oil in biodiesel, the development of sensors, and to detect the adulteration of vegetable oils.