Rheology of unstable mineral emulsions

Abstract

In this paper, the rheology of mineral oils and their unstable water emulsions were investigated. The oil samples were domestic crude oil UA, its fractions UA1, UA4 and blend semi-product UP1, while the concentration of oil in water emulsions was in the range from 1 up to 30%. The results were analyzed based on shear stress. The oil samples UA, UA1 and UP1 are Newtonian fluids, while UA4 is a pseudoplastic fluid. The samples UA and UA4 showed higher values of shear stress (83.75 and 297 Pa) than the other two samples UA1 and UP1 (18.41 and 17.52 Pa). The rheology of the investigated oils, due to their complex chemical composition, should be analyzed as a simultaneous effect of all their components. Therefore, the structural composition of the oils was determined, namely the content of paraffins, naphthenes, aromatics and asphaltenes. All the samples contain paraffins, naphthenes and aromatics but only oils UA and UA4 contain asphaltenes as well. All the investigated emulsions except 30% EUA4 are Newtonian fluids. The EUA4 30% emulsion showed pseudoplastic behaviour, and it is the only 30% emulsion among investigated ones that achieved lower shear stress than its oil. The characteristics of oil samples that could have an influence on their properties and their emulsion rheology were determined. These characteristics are: neutralization number, interfacial tension, dielectric constant, and emulsivity. Oil samples UA and UA4 have significantly higher values of neutralization number, dielectric constants, and emulsivity. The sample UA has the lowest value of interface tension and the greatest emulsivity, indicating that this oil, among all investigated, has the highest preference for building an emulsion. This could be the reason why 20 and 30% emulsions of the oil UA achieved the highest shear stress among all investigated emulsions.