Effect of Asphaltene Structural Characteristics on Low-temperature Rheology of Waxy model Oils

Abstract Asphaltenes are generally considered as natural pour point depressants, capable of interacting with wax molecules and influencing the flow and gelation behavior of waxy crude oils. The study selected two types of asphaltenes from different regions and two commercial paraffin waxes to investigate the impact of distinct asphaltenes and waxes on the rheological properties of waxy oil systems at low temperature. By combining the structural characterization of asphaltenes and waxes, the mechanism of the interaction between asphaltenes and waxes was further revealed. The results indicated that the role of asphaltenes in modifying the properties of waxy oils is closely related to their structure. Asphaltenes with stronger aliphaticity are more likely to engage in interactions with wax, disrupt wax crystallization process, delay the formation of gel structures, thus exhibit more significant effects in reducing the pour point, gel point, and yield stress of wax oils. However, when the system contains an excessive amount of high carbon number wax, the modifying capabilities of both types of asphaltenes are markedly diminished, exerting negligible impact on the rheological properties at low temperature. The results of the wax crystal micrographs are also consistent with the aforementioned findings. Therefore, it is speculated that that the co-crystallization capacity of asphaltene and wax determines the modification effect of asphaltene, which is directly coupled with the length of asphaltene alkyl substituents and the paraffin carbon number distribution. The outcomes of this investigation provide valuable insights into the interactions between asphaltenes and waxes in oils and provide guidance for the structural design of pour point depressants.