Article
Measurement of the Refractive Index of Crude Oil and Asphaltene Solutions: Onset Flocculation Determination
Autor
Castillo, Jimmy
Gutiérrez, Héctor
Ranaudo, María Antonieta
Villarroel, Otsmar
Institución
Resumen
In this work, we measure the refractive index of crude oils and asphaltene in toluene solutions using a fiber
optic refractometer designed to work with high-viscosity and high optical density samples. The data of the
samples were analyzed using the Lorentz-Lorenz theory and simple mixing rules. The refractive index for
crude oils without dilution for three crude oils with different American Petroleum Institute (API) degree,
asphaltene quantity, and stability were measured. Flocculation onset for crude oils and asphaltene
solutions were measured using n-heptane as the precipitant agent. Results showed that medium crude
oils and maltenes from medium, heavy, and extra-heavy crude oils follow the Lorentz-Lorenz mixing rule.
In the case of Boscan crude oil, a sample without any significant asphaltene precipitation problems, the
refractive index is lower than that obtained for toluene. In contrast, Furrial crude oil, a sample with severe
asphaltene precipitation problems, gave a refractive index higher than toluene. Finally, asphaltene
flocculation onset was clearly followed by refractive index measurement in crude oils and asphaltene in
toluene solutions after n-heptane addition.