Evaluating the hydrophilic–lipophilic nature of asphaltenic oils and naphthenic amphiphiles using microemulsion models

Asphaltenes and naphthenic acid derivatives, which are polar and surface-active species, are known to interfere with the recovery of heavy crude oil by promoting the formation of stable emulsions. In this study, previously established microemulsion phase behavior models were applied to quantify the hydrophilic–lipophilic nature of asphaltenic oils (bitumen, deasphalted bitumen, asphalt, naphthalene) and surface-active species found in heavy oils (naphthenic compounds and asphaltenes). For the test oils, the equivalent alkane carbon number (EACN) was determined by evaluating the “salinity shifts” of microemulsions formulated with a reference surfactant (sodium dihexyl sulfosuccinate – SDHS) and a reference oil (toluene) as a function of test oil volume fraction. Similarly, the characteristic curvature (CC) of surface-active species was determined by evaluating the salinity shifts as a function of the molar fraction of the surface-active species in mixture with SDHS. As a part of the oil phase, asphaltenes and asphaltene-like species are highly hydrophilic, which lead to low EACN values despite their large molecular weight. As a surface-active material, asphaltenes are hydrophobic species that lead to the formation of water-in-oil emulsions. Naphthenates, particularly sodium naphthenates, are highly hydrophilic compounds that lead to the formation of oil-in-water emulsions. These hydrophilic–lipophilic characterization parameters, and the methods used to determine them, can be used in the future to understand the phase behavior of complex oil–water systems.

Microemulsion phase behaviour transition as a function of the electrolyte concentration for formulations composed of an anionic surfactant, oil, and aqueous phase.Figure optionsDownload as PowerPoint slide