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

Abstract

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.

Mechanistic Study on the Effect of Molecular Structure Characteristics of Asphaltene on the Synergistic Modification with EVA on Model Waxy Oil

“…In addition, Ruwoldt et al 22 found that both PPD and asphaltene had similar abilities to reduce WAT, but there was no direct correspondence between them. In contrast, scholars such as D'Avila et al 23 concluded that there is a synergistic modification effect between asphaltenes and EVA PPDs with the function of reducing the WAT. Nevertheless, a substantial body of research posits that asphaltenes can elevate the WAT.…”

“…This alters the size and morphology of precipitated wax crystals, effectively enhancing the oil's fluidity at low temperatures. D'Avila et al 23 suggested that when asphaltenes are dispersed individually in the oil phase, there is no alteration in the oil's WAT, and viscosity remains unaffected. However, coexistence with EVA significantly lowers the oil's WAT and dramatically reduces the viscosity of the model waxy oil.…”

“…In addition, Ruwoldt et al found that both PPD and asphaltene had similar abilities to reduce WAT, but there was no direct correspondence between them. In contrast, scholars such as D’Avila et al concluded that there is a synergistic modification effect between asphaltenes and EVA PPDs with the function of reducing the WAT. Nevertheless, a substantial body of research posits that asphaltenes can elevate the WAT. ,− Kriz hypothesized that the ability of asphaltenes to raise the WAT depends on asphaltene concentration, suggesting the existence of a “critical concentration” of asphaltenes in the oil phase.…”

Evaluation of the Different Compatibility Indices to Model and Predict Oil Colloidal Stability and Its Relation to Crude Oil Desalting

“…Sediment decreasing during the n-heptane dilution process of Kuwait M crude oil might be a result of the mutual dissolving of waxes and asphaltenes. Waxes can improve dissolution of asphaltenes because of the interaction between side alkyl chains in asphaltenes and waxes [55,[58][59][60][61][62]. The dissolution of the solids is accelerated because of increasing volume of alkyl layers surrounding the asphaltenes polyaromatic cores [60].…”

Design of Crystal Growth Dimensionality in Synthetic Wax: The Kinetics of Nonisothermal Crystallization Processes

“…On the other hand, wax crystallization is desired in the development of novel materials for energy storage in the energetics, electronics, and automotive industries. − Moreover, waxes exhibit a strong hydrophobic nature and are commonly used as water repellents, protective layers, and surface modifiers . Controlling wax crystallization is crucial in industrial processes of casting, injection molding, 3D printing, sensor materials design, and pharmaceutical applications. − For the reasons above, the exploration and modification of the crystallization behavior of waxes through various approaches become essential. − …”