Stability of asphaltene-mircoparticles co-stabilized emulsions by oxygen-enriched nonionic demulsifier

The fine mineral particles often coexist in oil-water emulsions, enhancing the stability of oil-water emulsions. Herein, the micro SiO2 was used to investigate its synergistic effects with the interfacially-active asphaltenes (IAA) on forming the strong interfacial film at the oil–water interface. This IAA-particle film showed high rigidity, allowing the emulsion droplets (4 μm − 20 μm) to be much more stable than the traditional asphaltene-stabilized emulsions. With the addition of the oxygen containing demulsifier (MJTJU-2, an alternated aliphatic alcohol nonionic polyether), this kind of emulsion could be broken significantly (over 99 % at the demulsifier concentration > 600 ppm and settling time > 45 min) with almost all of the microparticles transferring from oil phase to the water phase as particle net-like film. The optimal concentration (1000 ppm) of demulsifier were obtained. Further mechanistic study by QCM-D suggested that the desorption process of asphaltenes from solid surface could be divided into three main stages: the demulsifier molecules adsorbed and penetrated into the IAA adsorption film on solid surface; the simultaneous desorption of the adsorbed IAA and pre-adsorbed demulsifiers; the IAA film became loose and was destructed by the demulsifiers. AFM tests found that after addition of demulsifiers, the surface force between IAA and silica (0.0589 mN/m) decreased about 37 %. The MD simulation results showed that the demulsifier molecules would adsorb on the IAA film firstly by van der Waals and hydrogen bond, making the film much looser. The demulsifier could interact with the IAA molecule, resulting in desorption of IAA. Simultaneously, the demulsifier could compete for the adsorption sites on the IAA molecules by forming new hydrogen bonds, which destroyed the IAA adsorption layer. As a result, the stable IAA-solid film at oil–water interface could be broken. These findings would provide fundamental understanding to the stability and instability of IAA-solids co-stabilized oil–water emulsions, oil-sludge treatments.