Role of Asphaltene Origin in the Sol-Gel Transition and Deposition of Waxy Model Oil

Summary The potential of asphaltenes as pour point depressants and wax inhibitors in wax oils has been widely recognized; however, the specific influence of asphaltene structure on their performance remains insufficiently understood. In this study, we investigate the effects of asphaltene structural characteristics on the low-temperature rheology and wax deposition behavior in wax oil, utilizing asphaltenes derived from diverse regions. Comprehensive structural characterization provides deeper insights into the mechanisms underlying wax-asphaltene interactions. Our findings reveal that asphaltenes with longer alkyl side chains, lower aromaticity, and reduced heteroatom content exhibit superior co-crystallization capabilities with wax molecules. This interaction induces a morphological transformation of wax crystals from needle-like to compact cluster-like structures, significantly improving the low-temperature rheological properties of wax oils. Furthermore, such asphaltenes substantially influence wax deposition dynamics, achieving the lowest wax deposition rate and the most rapid aging process. These effects are attributed to the weakening of the gel-like structure and the enhanced diffusivity of wax molecules. In addition, the inclusion of asphaltenes creates distinct radial nonhomogeneities within the deposition layers. Only asphaltene particles below a critical size diffuse into the deeper layers, with the asphaltene concentration gradually increasing from the bottom to the surface. However, the wax distribution within the deposition layers depends on asphaltene structure: Asphaltenes with higher aromaticity and heteroatom content increase wax content at the bottom, whereas those with longer alkyl chains reverse this trend. These findings are ascribed to the differential co-crystallization capacities of asphaltenes with wax molecules, highlighting the critical role of molecular structure in modifying waxy oils.