Dimethylcyclohexylamine Switchable Solvent Interactions with Asphaltenes toward Viscosity Reduction and in Situ Upgrading of Heavy Oils

Because of the ever-increasing depletion rate of conventional oil resources, it is essential to design processes for heavy oil recovery from petroleum reservoirs. Heavy oils contain high quantities of large molecules, such as asphaltenes, giving rise to high viscosities during production. Solvent extraction processes are capable candidates for heavy oil recovery; however, the separation of conventional solvents is energy-intensive. Therefore, a solvent with not only a high capacity for heavy oil dissolution but also an easy and environmentally friendly separation is in demand. In this work, the N,N-dimethylcyclohexylamine switchable hydrophilicity solvent (SHS) was employed for viscosity reduction and upgrading of heavy oils. Optimum weight ratios of the SHS were added to three different dead heavy oil samples with 11.33 to 17.54 degrees API and a corresponding room-temperature viscosity of more than 4287.0 to 3365.4 cp. To shed light on the interactions of the SHS with asphaltenes, the solvent was also added to heavy oil model solutions of asphaltenes in toluene. The solutions containing the solvent and the recovered oil were exposed to pressurized CO2 in the presence of deionized water to switch the hydrophilicity of the solvent to water-miscible and separate the recovered oil. The thus-obtained aqueous solution was then warmed up to 65 degrees C in the presence of N-2 gas bubbling through the liquid to switch the solvent hydrophilicity to water-immiscible form and recover the SHS. Results indicate that more than 52 wt % of the oils are recovered at the optimum solvent-to-oil ratio (SOR). The heavier the oil, the higher the optimum SOR is, resulting in the viscosity reductions of more than 70%. Dynamic light scattering shows that the size of asphaltene aggregates becomes smaller and considerably uniform by the SHS, indicating weakening of the asphaltene self-association interactions. Dynamic interfacial tension measurements calibrate the amount of impurity in the recovered SHS.