Mechanistic Approach to Unravel Asphaltene–Wax Interactions: Thermal, Rheological, and Morphological Investigation

• Published in: Energy & fuels Vol. 38; no. 14; pp. 12595 - 12611
• Main Authors: Addepalli, Teja Sree, Kumar, Lalit
• Format: Journal Article
• Language: English
• Published: American Chemical Society 18.07.2024
• Subjects: Traditional Fossil Fuels
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.4c01555

With the growing global consumption of crude oils rich in wax and asphaltene content, comprehending the intricate interactions between wax and asphaltenes in oil is vital for optimizing oil transportation systems. The present study investigates the influence of asphaltenes on the morphology, rheology, and thermal behavior of waxy oils. In this work, model oils containing 10 wt % macrocrystalline wax/microcrystalline wax/their combination (8 wt % macrocrystalline + 2 wt % microcrystalline) and varying asphaltene concentrations (0–2 wt %) were formulated in a toluene-dodecane solvent mixture. Differential scanning calorimetric analysis shows that asphlatene addition resulted in significant changes in wax appearance temperature for model oils containing microcrystalline and macrocrystalline + microcrystalline wax, possibly attributed to the structural similarity between asphaltenes and microcrystalline wax. Across all the model oils, an “optimal asphaltene concentration” was noted in the gelation temperature. In the case of model oils with 10 wt % macrocrystalline wax, it was observed using microscopy that asphaltene introduction caused a transformation in the wax crystal morphology, shifting from needle-like structures to spherulites, resulting in decreased gelation temperature and gel strength. Similarly, weaker gels are formed in microcrystalline waxy oils and macrocrystalline + microcrystalline waxy oils due to asphaltenes acting as “connected growth centers,” resulting in unique “caterpillar-like” structures. Additionally, asphaltene introduction to macrocrystalline + microcrystalline waxy model oils led to the formation of asphaltene-wax islands, resulting in improved rheological behavior. Overall, this study underscores the complex interplay of asphaltene concentrations, wax types, and resulting gel characteristics. Furthermore, it elucidates the mechanisms of asphaltene interaction with waxy oils using micrographs. The findings presented in this work, particularly the morphological observations, reveal novel insights that have not been documented in the existing literature. This knowledge holds significant potential to optimize flow assurance strategies for wax and asphaltene-rich crude oils.