Probing Interfacial Properties Of Oil Field Pickering Emulsions From Refinery Desalters

"Demulsification of oil-field Pickering emulsions is a major challenge for the oil and gas industry. The most common, naturally occurring emulsifiers in petroleum products are asphaltenes, clay nanoparticles, resins, naphthenates and, inorganic particles. This study focused on two naturally-occurring emulsifiers: asphaltenes and clay nano-particles. Specifically, the effect of asphaltenes in combination with clay nano-particles, such as monmorillonite and kaolinite on model heptol-water interfaces was studied.The combined equilibrium surface excess associated with asphaltenes and clay nano-particles was attempted to be measured using the Langmuir isotherm coupled with the Gibbs surface energy (Langmuir EoS). Interfacial tension was measured using the pendant-drop method.Interfacial tension data showed the effect of asphaltenes on the heptol-water interface was inconsistent. It was likely because in addition to concentration, asphaltenes interfacial activity was also affected by the size of asphaltene aggregates in heptol, which is difficult to control. Furthermore, interfacial tension data showed that asphaltenes did not reach an equilibrium surface excess at the interface. The presence of n-heptane in heptol enhanced the adsorption of asphaltenes onto the heptol-water interfaces, causing continuous adsorption and forming a multilayer (physical barrier). This study suggests that n-heptane in crude oil creates a favourable environment for the formation of the interfacial barriers, and emulsions in general. This interfacial barrier likely prevents coalescence when emulsions are processed in electrostatic desalters.The pendant-drop method could not adequately measure the interfacial tension associated with the presence of clay nano-particles because kaolinite and monmorillonite precipitated in RO water.The combined equilibrium surface excess at the heptol-water interface could not be determined because of asphaltenes continuous adsorption, inconsistent experimental data, and the precipitation of clay nano-particles.Due to enhanced asphaltene adsorption in the presence of n-heptane and asphaltenes’ affinity toward clay nano-particles, asphaltenes and clay nano-particles were hypothesized to form a strong and complex network of aggregates at the heptol-water interface. Thus, asphaltene-clay aggregates at the interface were studied using model oil-in-water Pickering emulsions. The interfacial aggregates were characterized using an optical microscopy and material balances. Results showed that increasing the amount of montmorillonite nano-particles in the system enhanced the strength of the interface. On the other hand, asphaltenes and kaolinite nano-particles did not form any oil-in-water emulsions. This likely occurred because kaolinite acted as an inhibitor in the presence of asphaltenes and prevented emulsification. Future work should further test kaolinite as an inhibitor for emulsification, as it may be used to prevent emulsification in oil-field operations"--