Characterization of Water-in-Oil Emulsion and Upgrading of Asphalt with Supercritical Water Treatment

The products of asphalt upgrading in supercritical water (SCW) forms a mixture of cracked oil, water, and fine coke particles; this mixture tends to be emulsified, which introduces direct challenges to emulsified water removal. In this study, the asphalt upgrading in SCW was performed at 390–450 °C and 22.4–27.2 MPa for 40 min. A differential scanning calorimetry analysis between −60 and 50 °C was conducted to evaluate the water content and size distribution in the water-in-oil emulsions. The mechanical centrifugation and chemical demulsification were performed to test the water removal efficiency and stability of the emulsions. The results of properties and emulsification characteristics of the oil products indicate that the transition temperature of asphalt upgrading was between 400 and 410 °C. At temperatures lower than the transition temperature, the oil products were similar to the feed asphalt in terms of high viscosity, carbon residue, and asphaltene content. In the emulsification process, the contact between water and oil products was limited by the semisolid state of the oil products, which decreased the water content and size of the droplets in the emulsions. At temperatures higher than the transition temperature, the viscosities of the oil products were below 1.2 Pa·s, and a large number of water droplets were observed clearly in the fluid emulsions. The emulsified water was partially removed by centrifugation; however, the content of fine water droplets with diameters less than 5 μm was still greater than 14% in the centrifuged emulsions. Furthermore, the addition of chemical demulsifier was more effective on demulsification than centrifugation. When the temperature was higher than 430 °C, the water content of the demulsified emulsion was less than 2.5%. On the basis of comprehensive consideration of maltene yield, oil property, and water removal of water-in-oil emulsions, the temperature of 430–440 °C is the most beneficial condition for asphalt upgrading.