Evaluation of the Chemical Additive Effect on Asphaltene Aggregation in Dead Oils: A Comparative Study between Ultraviolet-Visible and Near-Infrared-Laser Light Scattering Techniques

Asphaltenes flocculate as a consequence of changes in the temperature, pressure, or composition. This flocculation can result in several oil production problems. The application of chemical additives (inhibitors or dispersants) is a well-known way to control asphaltene flocculation. Ultraviolet-visible (UV-vis) spectroscopy is the most common analytical technique that has been applied to study the effectiveness of chemical additives in keeping asphaltene particles dispersed into crude oils. However, this technique requires being performed in diluted solutions, which can interfere significantly in the aggregation phenomena. The objective of this work was to evaluate the effect of three chemical additives, 4-dodecyl benzenesulfonic acid (DBSA) and two commercial products (CO and C1), on the asphaltene aggregation behavior of two Brazilian crude oils, using near-infrared (NIR)-laser (lambda = 1550 nm) scattering measurements. This is a new methodology developed to study the aggregation kinetics and settling of asphaltenes around its n-heptane flocculation onset. The NIR-laser scattering method offers the possibility to work with samples at a higher crude oil concentration, being more representative of real systems. The results obtained were compared to those determined with the traditional UV-vis method (lambda = 850 nm) and showed qualitatively similar trends. Settling measurements suggest that the stabilization provided by the additives can occur by slowing both formation and growing of asphaltene particles and delaying the phase separation process. DBSA was more effective in keeping the asphaltene particles dispersed in solution and prevented them from settling at lower concentrations when compared to commercial products, for both crude oils studied. It was demonstrated that the methodology developed using NIR-laser scattering was more accurate and sensitive.