Role of naphthenic acids in emulsion tightness for a low total acid number (TAN) / high asphaltene oil

V. Pauchard , J. Sjöblom , S. Kokal , Patrick Bouriat (1) , Christophe Dicharry (1) , H. Muller , A. Al-Hajji

1 TEFC - Thermodynamique et Energétique des fluides complexes

The emulsion stabilizing properties of a low-total-acid-number (TAN) crude oil, which had initially been attributed to asphaltenes and calcite precipitation, were re-analyzed with regard to the role of organic acids. Despite high asphaltenes content, this crude oil exhibits features classically observed with acidic oils, such as the increase in emulsion stability upon pressure decrease/pH increase or the poor efficiency of demulsifiers. The potential for a significant role of organic acids was confirmed by the high interfacial activity of indigenous acids, as extracted from the crude oil by means of an ion-exchange resin. This was further addressed analyzing the molecular chemistry of the interfacial layer and its rheology. The interfacial material was found to be composed of a mixture of asphaltenes and organic acids. These acids exhibit a wide range of structures (monoversus dicarboxylic, fatty versus naphthenic and benzoic) and molecular weights (from 200 to 700 g/mol), contrary to the medium molecular weight fatty monocarboxylic acids that are generally believed to cause "soap emulsions". The interfacial rheology is indicative of a 2D gel, with an assumed glass transition temperature of approximately 40 °C. In conclusion, this study shows that a co-precipitation of asphaltenes and organic acids can promote the build up of a very cohesive interface. The disruption of this interface not only requires the drainage of individual molecules but also a collective yield of the gel. This paper is part one of two: it confronts physical and chemical data, the latter being further detailed in an associated paper.

Mots clés: Calcite precipitations; Chemical datum; Co precipitations; Cohesive interfaces; Crude oil; Demulsifiers; Emulsion stabilities; Glass transition temperatures; Interfacial activities; Interfacial layers; Interfacial rheologies; Ion-exchange resins; Molecular chemistries; Monocarboxylic acids; Naphthenic acids; Stabilizing properties Engineering controlled terms: Asphaltenes; Calcite; Carbonate minerals; Crude petroleum; Elasticity; Emulsification; Gelation; Gels; Ion exchange; Molecular weight; Organic acids; Plasticity; Resins; Rheology; Tanning; Viscosity Engineering main heading: Glass transition

Domaines: Chimie-Physique [physics.chem-ph]

V. Pauchard, J. Sjöblom, S. Kokal, Patrick Bouriat, Christophe Dicharry, et al.. Role of naphthenic acids in emulsion tightness for a low total acid number (TAN) / high asphaltene oil. Energy & Fuels, 2009, 23 (3), pp.1269-1279. ⟨hal-00610566⟩