Energy & Fuels, Vol.27, No.5, 2399-2412, 2013
Effect of Fumed Silica Particles on Water-in-Crude Oil Emulsion: Emulsion Stability, Interfacial Properties, and Contribution of Crude Oil Fractions
The effect of fumed silica particles on water-in-crude oil emulsions was analyzed by stability tests, interfacial tension measurements, dilatational rheology of the interface, rheology of the particles dispersions, and Cryo-SEM analysis. The crude oil studied is a paraffinic one and was separated by distillation in three fractions containing mainly saturate, aromatic, and resin compounds. The stability of emulsions formed from these oil fractions was also studied with or without silica particles. Experiments without particles performed with oil or its fractions underline that the most stable emulsion is formed with the heavy fraction which corresponds to the highest elastic modulus of the interface. Different mechanisms of emulsion stability in the presence of particles were discussed according to the particle wettability. Whatever the oil phase composition, it is obviously noticed that hydrophilic particles destabilize water-in-oil emulsions, whereas hydrophobic particles stabilize them. For hydrophilic particles, the "solid-like" behavior of the interfacial film revealed by the high value of the elastic modulus, IFT measurements and the observations by Cryo-SEM, supports the presence of A200 particles at the oil/water interface. The highest stability of the emulsions in the presence of hydrophobic particles results from the addition of several effects: the tendency to form a structured organization in the oil continuous phase and the influence of the attached particles at the interface. This study underlined that no direct relation is observed between the stability of water-in-oil petroleum emulsions and the interfacial tension measurements particularly in the presence of particles. Otherwise the viscoelastic measurements by the dilatational drop technique corroborate the relation between a high emulsion stability and a high viscoelastic modulus in the case of emulsions without particles. In the presence of particles, the elastic behavior of the interface is less affected by the hydrophobic than by the hydrophilic particles.