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

Abstract

The phenomenon of synergistic improvement of the low-temperature rheology of waxy oil between asphaltenes and polymer pour point depressants has been widely reported. However, there has been limited systematic investigation into the variations in synergistic effects among different asphaltenes and pour point depressants. In this study, asphaltenes were extracted from crude oils originating from four distinct blocks, and their impacts on the low-temperature rheological and exothermic characteristics of undoped/doped model waxy oils were comprehensively examined. Furthermore, by integrating the results of mesoscopic particle size testing with the asphaltene molecular structure, we have unveiled the underlying mechanisms governing the synergistic modification effect between asphaltene and pour point depressants. The results indicate that the more pronounced the asphaltene's individual modification effect on waxy oil, the weaker its synergistic modification interaction with pour point depressants becomes. Delving into the underlying reasons, we postulate that the modification capability of asphaltene is intricately linked to its capacity to participate in the crystallization of wax components, with the content of methylene and heteroatoms in its molecule directly influencing its cocrystallization capacity with wax. However, simultaneously, the presence of nonpolar units in asphaltene molecules can disrupt the polar adsorption of PPDs on their surfaces, consequently diminishing the synergistic modification effect between asphaltene and PPDs. The discovery of this phenomenon contributes to the refinement of the theoretical framework governing the cooperative modification of waxy oil by PPDs and asphaltenes, offering insights into the subsequent targeted development of highly efficient pour point depressants for waxy crude oil.

Effect of R/A Mass Ratio on the Rheology of Model Waxy Oils Undoped/Doped with EVA Pour Point Depressant

“…Numerous studies have shown that asphaltene is the natural pour point depressant (PPD), − and thermal treating at relatively high temperatures (60–80 °C) is necessary to activate the pour point depressing ability of asphaltene. However, there is still controversy over the mechanism of asphaltene: on the one hand, colloidal asphaltene can provide large amounts of nucleation templates for paraffin wax, thereby enhancing the WAT of waxy crude oil and generating numerous small wax particles; on the other, the cocrystallizing effect between asphaltene and paraffin wax may be more dominant than heterogeneous nucleation, resulting in a reduction in WAT and the generation of large wax aggregates with a small number. , The reason for the difference is related to the molecular structure and the dispersing state of asphaltene. , Research by Xia et al showed that the asphaltene molecules with higher methylene content and lower heteroatom content can fully participate in the cocrystallization process with paraffin, thereby having a stronger effect on improving the rheology of waxy crude oil. In addition, Xia et al altered the dispersing state of asphaltenes by changing the solvent composition and then investigated the effect of asphaltenes’ dispersing state on the rheology of a model waxy oil.…”