An interfacially active cobalt complex, cobalt dodecylbenzenesulfonate, was synthesized. Elemental analysis, atomic absorption spectroscopy, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis, and surface/interfacial tension determination were performed to investigate the properties of the catalyst. Results showed that the synthesized catalyst showed active interfacial behavior, decreasing the surface tension and interfacial tension between heavy oil and liquid phase to below 30 and 1.5 mN/m, respectively. The catalyst was not thermally degraded at a temperature of 400 °C, indicating its high thermal stability. Catalytic performance of the catalyst was evaluated by carrying out aquathermolysis. The viscosity determination showed that the viscosity of the heavy oil decreased by 38 %. The average molecular weight, group compositions, and average molecular structure of various samples were analyzed using elemental analysis, FT-IR, electrospray ionization Fourier transform ion cyclotron resonance (ESI FT-ICR MS), and ¹H nuclear magnetic resonance. Results indicated that the catalyst could attack the sulfur- and O₂-type heteroatomic compounds in asphaltene and resin, especially the compounds with aromatic structure, leading to a decrease in the molecular weight and then the reduction in the viscosity of heavy oil. Therefore, the synthesized catalyst might find an application in catalytic aquathermolysis of heavy oil, especially for the high-aromaticity heavy oil with high oxygen content.

The catastrophic phase inversion process of model emulsions (water/Span 80-Tween 80/heptane) from oil-in-water to water-in-oil emulsion was investigated. During this process, the phase inversion of the emulsion was monitored through Fourier transform infrared spectroscopy (FT-IR). In emulsions without NaCl, oil-in-water gel emulsions are formed prior to phase inversion. As the HLB value increases, the oil volume fraction required for phase inversion becomes higher. Polydisperse distribution of the gel emulsion is observed from microscope optical images. The Turbiscan Lab stability analyzer indicates that O/W gel emulsions before the phase inversion has good stability at 50 degrees C. Rheological measurements reveal that emulsions exhibit non-Newtonian behavior. The viscosity of the gel emulsions increases significantly prior to phase inversion. As the oil volume fraction increases, the storage modulus and loss modulus of the gel emulsion increase to a maximum, at which catastrophic phase inversion occurs. In emulsions with NaCl, there is no oil-in-water gel emulsion formed before phase inversion. The physicochemical properties of the emulsion play a crucial role in whether gel emulsions are produced during catastrophic phase inversion. These gel emulsions have the potential to diversify the applications in crude oil extraction, drug delivery systems, packaging materials, and other fields.

During the production of crude oil, asphaltenes are prone to precipitate due to the changes of external conditions (temperature, pressure, etc.). Therefore, a series of research studies were designed to investigate the effect of temperature on asphaltene precipitation for two Xinjiang crude oils (S1, S2) so as to reveal the mechanism of asphaltene dissolution. First, the changes of asphaltene precipitation were intuitively observed by using a microscope. The results demonstrated that the asphaltene solubility increased with the increase of temperature and the dispersion rate of asphaltene particles increased with the decrease of particle size. Second, the variation of asphaltene precipitation with temperature was quantified by a gravimetric method. The results suggested that the different asphaltenes showed different sensitivity to temperature within the temperature range 25-120 °C. Third, a hypothesis was proposed to explain these results and proved that the asphaltene aggregate structure was an important factor for asphaltene stability. The crystallite parameters of asphaltenes were obtained by X-ray diffraction (XRD) to describe the structural characteristics. The results revealed that the layer distance between aromatic sheets (d _m ) of asphaltenes derived from S1 oil and S2 oil were 0.378 and 0.408 nm, respectively, which implied that the asphaltene aggregates derived from S2 oil were looser than those of S1 oil. Therefore, high temperature could facilitate the penetration of resins into asphaltene aggregates and ultimately improve the dispersion of asphaltenes. Finally, molecular dynamics (MD) simulation was used to verify the conclusions. Based on the molecular dynamics method, asphaltene aggregate models were developed. The compactness and internal energy of each model were calculated. The results showed that the asphaltene dispersion capability was proportional to the porosity and internal energy.