Influence of pH on Oil-Water Interfacial Tension and Mass Transfer for Asphaltenes Model Oils. Comparison with Crude Oil Behavior

Abstract

-Asphaltenes are shown to be amphoteric, containing acidic and basic species that can ionize at low and high pH respectively when they come in contact with water. We have used a mass transfer model in order to determine the partition coefficients of asphaltenes between oil and water. We have compared the influence of type of asphaltenes on interfacial tension and on mass transfer between oil and water and analysed the influence of an added surfactant. We have also compared the behavior of asphaltenes dissolved in model solvents with that of diluted heavy crude oils. Although asphaltenes qualitatively reproduce the behavior of crude oil components at the oil-water interface, differences were observed, either in interfacial tensions at low pH, or in partition coefficients at high pH. These differences are due to other molecules present in crude oil, which are either more interfacially active or more soluble in water.Résumé -Influence du pH sur la tension interfaciale et les transferts de masse pour des huiles modèles d'asphaltènes. Comparaison avec le comportement du brut -Nous avons mis en évidence le comportement amphotère des asphaltènes, qui contiennent des espèces acides et basiques pouvant s'ioniser lorsqu'ils entrent en contact avec l'eau. Nous avons utilisé un modèle de transfert de masse afin de déterminer les coefficients de partage des asphaltènes entre l'huile et l'eau. Nous avons comparé l'influence du type d'asphaltènes sur la tension interfaciale et le transfert de masse entre l'eau et l'huile, et analysé l'influence d'un tensio-actif ajouté. Nous avons également comparé le comportement des asphaltènes dissous dans des solvants modèle avec celui d'un brut lourd dilué. Bien que les asphaltènes reproduisent qualitativement le comportement du brut dilué à l'interface huile-eau, des différences sont observées entre les tensions interfaciales à bas pH bas, et dans les coefficients de partage à pH élevé. Ces différences sont dues à d'autres molécules présentes dans le brut, qui sont soit plus interfacialement actives, soit plus solubles dans l'eau.

Interfacial Activity of Bitumen Components

“…It should be mentioned that the initial value of pH (reported in this work) might not be the most important variable, but the final pH of the system and the residual naphthenic acid in the oil after contacting with the alkaline solution are Hutin et al () showed that, in acid crude oils and asphaltene solutions, the initial pH of the aqueous phase needs to be greater than 10.5 in order to have a final pH in the emulsion of greater than 8. This is an important finding because it shows that one needs to clarify under what condition is the pH reported (before or after contacting the oil) and because the observation in asphaltene solutions suggests that there is an acidic fraction of asphaltenes that could be interfacially active at high pH values.…”

Evaluating physicochemical properties of crude oil as indicators of low-salinity–induced wettability alteration in carbonate minerals

“…8. The asphaltene/resin ratio evaluates the asphaltene instability because resin stabilizes asphaltene in crude oil [57][58][59][60][61] . A high asphaltene/resin ratio typically indicates asphaltene being unstable.…”

Influence of the Crude Oil and Water Compositions on the Quality of Synthetic Produced Water

“…Once in contact with an aqueous phase, water-soluble hydrocarbons in the crude oil will partition into the water phase [22][23][24] , adsorb at the gas-water interfaces and influence the oil removal efficiency by gas flotation [25][26] . The characteristics of the produced water also depends on the properties, like pH [27][28] , ionic strength 29 and the presence of divalent ions 30 .…”