No abstract

No abstract

Abstract⎯The structural and rheological properties of resin-free model petroleum mixtures (MPM) with an asphaltene content of 0 to 6 wt % and the same mixtures with added 3.85 wt % petroleum resins have been investigated. The composition of the mixtures simulates the amount of the main hydrocarbon-group components and distillate fractions in light paraffin-base oils ( = 747.7-789.1 kg/m 3 ). Temperature-dynamic viscosity relationships for cooling the MPM have been obtained, most of which displayed abnormalities in the temperature range of ~40-60°C. Calculations of the viscous-flow activation energy (E μ ) have shown that there are abrupt changes in E μ in this abnormality region, which are an indication of structuring processes. By means of Fourier-transform laser diffractomery of MPM solutions in kerosene, it has been found that the particle size of the petroleum mixtures is qualitatively related to the revealed abrupt changes in E μ . It has been shown that these abnormalities correspond to the formation of paraffin-asphaltene associates and their existence is determined by the critical concentration of resins and asphaltenes in the mixtures.

No abstract

A Brookfield DV-II + Pro rotational viscometer was used to study the viscosity of 7 samples of concentrated nanodispersed systems (nanofluids) with a similar viscosity (6-22 mPa ∙ s), the particles of the dispersed phase in which are nanosized surfactant micelles and conglomerates from them. It was found that for 5 out of 7 studied reagents, there is a decrease in viscosity typical for dispersed systems with an increase in the shear rate, and their flow curves, that is, the dependence of the shear stress on the shear rate, correspond to the ideal plastic flow of non-Newtonian fluids. Moreover, with high reliability, R2 ≥ 0.999 is described by the Bingham equation with a small value of the limiting shear stress (less than 0.2 Pa). It is shown that all the studied reagents are also characterized by an increase in the activation energy of a viscous flow Е with an increase in the shear rate. As a result, a decrease in viscosity with an increase in shear rate, typical for disperse systems, including nanofluids, is provided by a more significant increase in entropy changes ΔS compared to Е. It has been substantiated that, depending on the ratio between the activation energy of viscous flow Е and the change in entropy ΔS, the viscosity of concentrated micellar dispersed systems with an increase in the shear rate can decrease, remain unchanged, and increase. The last two cases, not typical for disperse systems and nanofluids, were identified and studied using the example of two demulsifiers, RIK-1 and RIK-2, with a maximum of a very narrow particle size distribution at 160 ± 5 nm, corresponding to the size of a special type of very stable micelles Surfactant — vesicle.