(391k) Asphaltene-Stabilized Model Emulsion Studies: Organic Phase Composition and Aqueous Phase pH Effects

The asphaltenes and their aggregates have an important role in water-in-crude oil emulsion stabilization: under favorable solvent conditions and due to their surface-activity, they exhibit a colloidal behavior, accumulating at water/oil interface and forming a rigid film, they surround the water droplets, hinder the coalescence and hence the phase separation process. Therefore, the formation of emulsions with different stabilities represents the main technological challenge faced by oil producers during the primary processing stage of heavy oils, with their high content of asphaltenes. Our goal in this study is to evaluate the impact of changes in organic phase composition and aqueous phase pH on stability of model emulsion systems. Model emulsion stability was estimated by the percentage of water determined at the bottom of the bottle and it was performed by using a water separability tester, following the ASTM D1401 standard method. All tests were made at room pressure and T = 303.15 K, at 1700 rpm, and were executed by mixing 21 mL of synthetic organic phase, added to 500 ppm of asphaltenes, and 9 mL of synthetic formation water. The organic phase H/C molar ratio (a measure of aromaticity) varied between 1.4 and 2.0, being adjusted by different mixes of toluene and n-heptane. We measured a pH range of synthetic formation water was comprised between 3.0 and 11.0, when adding HCl or NaOH. Asphaltenes used in this work were extracted from a Brazilian crude oil, according to the IP 143 standard method. The results show, as expected, that the more stable emulsions under gravity setting are those where the H/C molar ratio of synthetic organic phase is greater (low aromatic content). We presented data of pH effects on emulsion stability from a range of synthetic organic phase formulated with the same asphaltenes, scarce in the literature.