Scanning Aggregation Phenomena in Crude Oils with Density Measurements

Abstract

Aggregation phenomena involved in asphaltene precipitation under ambient conditions are studied in an effort to correlate them with the asphaltene deposition. The effects of compositional changes on the aggregation and the flocculation onset of asphaltene have been investigated for different crude oils. Density measurements of the system fcrude oil þ toluene þ n-heptaneg were used to assess changes of aggregation occurring in a crude oil under influence of the chemical or physical factors. Obtained results made it possible to determine the asphaltene flocculation onset of several crude oils. Density changes of mixtures were used to quantify the changes of the molecular packing of the oil components. It was found that n-heptane increase the molecular packing of crude oils but also of deasphalted crude oils. Toluene increases the molecular packing also. Therefore, aggregation phenomena occurring in crude oils concern not only asphaltenes but also other components of the oil.

Incompatibility Determination of Crude Oil Blends from Experimental Viscosity and Density Data

“…To assess the onset of asphaltene precipitation in crude oils from viscosity information, we measured dynamic viscosities of the system crude oil containing asphaltenes and toluene + n -heptane by following the changes of aggregation occurring in the crude oil, according to the procedure by Escobedo and Mansoori . Although toluene is considered to be a “good solvent” for asphaltenes because the aggregates of asphaltene remain stable in the solution and do not grow, it is observed that there exists a strong tendency of the asphaltenes to self-aggregate even in diluted solutions. ,− Therefore, to guarantee the detection of aggregate asphaltenes via this technique, toluene was added in excess (about 48.1 wt %) to a light crude oil (32.1° API gravity at 298.2 K). The SARA analysis for this crude oil is 23.64 wt % saturates, 9.21 wt % aromatics, 64.38 wt % resins, and 2.77 wt % asphaltene.…”

“…The incompatibility region, therefore, corresponds to the n-alkane concentration, leading to the precipitation of asphaltene aggregates. 29 Because the incompatibility region determined from density measurements is in good agreement with that found from viscosity measurements, then the density technique is another possibility to determine the incompatibility region in crude oil blends mixed with liquid hydrocarbons. These results are in accordance with Evdokimov's 35 measurements, who point out that native crude oils of different sources exhibit sharp viscosity and density peaking at phase boundaries, defined by specific asphaltene contents.…”

Characterization of Aggregation Processes in Crude Oils Using Differential Scanning Calorimetry

“…[20][21][22][23][24][25] Accordingly, the value of the solubility parameter depending on the m toluene /m n-heptane ratio is an essential parameter in determining the flocculation process. 24 We determined thermal curves of mixtures of crude oils F1 and F2 with n-heptane and with n-heptane and toluene in the temperature range between 20 and 200 °C. Tending toward elucidating the role of solvent in the aggregation process, different ratios of toluene and n-heptane were used.…”

“…n -Alkanes are considered as “antisolvents” of asphaltenes that induce the growth of asphaltene aggregates and their flocculation. It was shown that the onset of flocculation can be described using Hildebrand's theory of nonelectrolyte solubility. − Accordingly, the value of the solubility parameter depending on the m toluene / m n - heptane ratio is an essential parameter in determining the flocculation process . We determined thermal curves of mixtures of crude oils F1 and F2 with n -heptane and with n -heptane and toluene in the temperature range between 20 and 200 °C.…”

Critical review of asphaltene properties and factors impacting its stability in crude oil

“…• Density measurement: When asphaltene precipitates from the crude oil, the oil density will change. This density change can be used as an indication of the asphaltene onset pressure (Ekulu et al 2004). • Light scattering method: This relates light absorbance of different phases to the asphaltene onset pressure.…”