Impact of aqueous phase in emulsified form on distribution and instability of asphaltene molecules

Asphaltene extracted from a crude oil covers a wide range of molecules that would similarly act in terms of solubility in general but they may differ in terms of precipitation behavior due to different molecular structures. For this reason, they are commonly represented as a solubility class, not a particular molecule though each sub-fraction of asphaltene may have its own precipitation tendency. In recent years, the impact of water presence on the precipitation of these molecules has attracted attention due to increased production of water, although the reported results are somewhat inconsistent. In this study, a systematic experimental study was performed to investigate the impact of aqueous phase, which composed of deionized water and ions of single, double, and three valence with net positive and negative charges on asphaltene precipitation from a synthetic oil composed of toluene and asphaltene. The aqueous phase was emulsified within this synthetic oil phase using ultrasonic mixer. Then, the oil phase was divided into three fractions named oil 1, 2, and 3, respectively depending on the degree of their desire to remain in the emulsion. The results showed that oils 1, 2, and 3 have different precipitation curves. The precipitation became more intensified even up to four fold from oil 1 to 3. Moreover, the presence of ions with higher valence in the aqueous phase drew extra asphaltene molecules from oil 1 to oil 2 and then oil 3 (i.e. from bulk to the interface) which, in turn, changed the precipitation curve. The experimental results also showed that the relative concentration of asphaltene sub-fractions in oils 1, 2 and 3 determines the shape of the final precipitation curve and the onset point of precipitation.