Determination of Asphaltene Particle Size: Influence of Flocculant, Additive, and Temperature

Abstract

Variations in temperature, pressure and composition during oil production, transport and refining can compromise the stability of asphaltenes. Flocculation occurs when the asphaltenes particles associate and form clusters that precipitate out of the solution. The objective of this work was to evaluate the variation in the size of the asphaltenes macromolecule particles as a function of the concentration of asphaltenes, the thermodynamic quality of the solvent medium, the addition of asphaltenes dispersants, temperature of the dispersion, and exposure time of the asphaltenes to the model solvent, using the photon correlation spectroscopy (PCS) technique with detection by backscattering. The average size of the asphaltenes particles in toluene at low concentrations ranged from 12 to 22 nm. With the successive addition of a flocculant (n-heptane), the particle size increased until their precipitation (>1000 nm). The presence of a dispersant additive in these systems caused a reduction in the size of the asphaltenes aggregates, inhibiting the formation of particles larger than 1000 nm. These results agree with those of the asphaltenes precipitation onset test. The increasing temperature of the asphaltenes dispersions caused a reduction in the sizes of the aggregates, characterizing UCST phase behavior (upper critical solution temperature) for the asphaltenes evaluated. On the other hand, increased contact time of the asphaltenes with the model solvent increased the average size of the asphaltenes particles.