Influence of Asphaltene Aggregation State on the Wax Crystallization Process and the Efficiency of EVA as a Wax Crystal Modifier: A Study Using Model Systems

The precipitation/deposition of waxes poses a major problem for the production and transport of petroleum. Understanding the factors that affect this problem is very important to select preventive actions. The influence of asphaltenes on the behavior of waxes has not been widely explored in the literature and is still controversial. The objective of this work was to assess the influence of the asphaltene aggregation state (by varying the solvent quality) on the behavior of waxes and the performance of a wax deposition inhibitor using model systems. A commercial wax (melting point 53–57 °C), asphaltenes C7I, and poly­(ethylene-co-vinyl acetate) were used in this study. The wax appearance temperature (WAT) was determined by microcalorimetry (μDSC), the flow behavior as a function of temperature was investigated by measuring viscosity, and the morphology of the wax crystals was evaluated by optical microscopy. The presence of asphaltenes C7I in the dispersed state did not affect the WAT, but in the aggregated state, they led to a reduction in the WAT at the asphaltene/wax ratio of 0.1%. The asphaltenes C7I acted to reduce the viscosity of the systems at temperatures below the WAT when compared to the behavior of the respective system free of asphaltenes, but the intensity of the viscosity reduction varied with the aggregation state of the asphaltenes: in the aggregation state immediately before the precipitation onset condition, the asphaltenes caused the lowest viscosities. There was a synergistic effect between the asphaltenes C7I and the wax deposition inhibitor to decrease the viscosity of the model system below the WAT.