Abstract
This paper presents a model, which we have designed to get insight into the development of electro-induced instability of a thin toluene emulsion film in contact with the saline aqueous phase. Molecular dynamics (MD) simulations demonstrate the role of charge accumulation in the toluene-film rupture induced by a DC electric field. Two ensembles-NVT and NPT-are used to determine the critical value of the external field at which the film ruptures, the charge distribution and capacitance of the thin film, number densities, and the film structure. The rupture mechanism as seen from this model is the following: in both NVT and NPT ensembles, condenser plates, where the charge density is maximal, are situated at the very border between the bulk aqueous (water) phase and the mixed layer. No ion penetration is observed within the toluene core, thus leaving all the distribution of charges within the mixed zone and the bulk phase that could be attributed to the formation of hydration shells. When the critical electric field is reached within a certain time after the field application, electric discharge occurs indicating the beginning of the rupturing process. The MD simulations indicate that the NPT ensemble predicts a value of the critical field that is closer to the experimental finding.
Highlights
Water-in-oil emulsions are commonly formed during petroleum production and pose serious threats to installations and quality of the final product
Molecular dynamics (MD) simulations demonstrate the role of charge accumulation in the toluene-film rupture induced by a DC electric field
No ion penetration is observed within the toluene core, leaving all the distribution of charges within the mixed zone and the bulk phase that could be attributed to the formation of hydration shells
Summary
Water-in-oil emulsions are commonly formed during petroleum production and pose serious threats to installations and quality of the final product. Panchev et al. developed a method allowing simultaneous investigation of a single water-in-oil emulsion film by both microinterferometry and electrical measurements This method allows in a single experiment to measure the critical voltage of film rupture, the film thickness, the drainage rate, and the disjoining pressure laying the groundwork for computational studies. A comparison of the computed results can be made with the critical voltage values found in the experiment having in mind the limitations—the computational results are for very thin films with no stabilizer in the emulsion This model can be considered as a useful starting basis for a further study of the stability and the structure of thick emulsion films that are stabilized by indigenous crude oil surfactants, namely, asphaltenes, resins, and naphthenic acids
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