Determining the onset of asphaltene precipitation in a model oil system toluene–asphaltene–heptane by ultramicroscopy method

Determining the stability threshold of oils and oil systems is an important task in the oil industry. It is important to be able to detect the precipitation of solid phase from oils at the earliest stages. For the first time, the ultramicroscopy method was used to study the precipitation of asphaltenes from a toluene solution during titration with heptane. The study allowed for the visualization of asphaltene aggregates in the toluene–asphaltene–heptane mixture at the earliest stages of aggregation. The relationship between the numerical concentration of asphaltene aggregates and the heptane concentration was measured. Analysis of this dependence led to the determination of the threshold concentration of heptane, above which asphaltene precipitation and aggregation (referred to as the “Onset point”) occurred. A comparison was made between the capabilities of ultramicroscopy and those of dynamic and static light scattering methods for determining the “Onset point”. It was shown that the ultramicroscopy method has greater sensitivity and can detect the onset of aggregation at lower concentrations of the precipitant.