Molecular Origins of Heavy Crude Oil Interfacial Activity Part 2:  Fundamental Interfacial Properties of Model Naphthenic Acids and Naphthenic Acids Separated from Heavy Crude Oils

• Published in: Energy & fuels Vol. 21; no. 1; pp. 199 - 204
• Main Authors: Varadaraj, Ramesh, Brons, Cornelius
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.01.2007
• Subjects: Applied sciences; Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics; Crude oil, natural gas and petroleum products; Energy; Exact sciences and technology; Fuels; Asphaltene; Water oil emulsion; Stability; Hydrocarbon; Molecular structure; Oil water emulsion; Stabilization; Organic acids; Interface properties; Naphthenic acid; Crude oil; Naphthenic oil; Chemical composition; Performance; Molecular mass; Heavy oil
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef060425s

Fundamental interfacial properties were determined at the hydrocarbon−water interface for 5β-cholanic acid, abietic acid, and three crude oil naphthenic acids separated from three naphthenic-acid-containing crude oils. Observed interfacial properties were correlated to the composition and chemical structure of crude oil naphthenic acids. Crude oil naphthenic acids are a mixture of primary, secondary, and tertiary, largely cycloparrafinic, organic acids in the molecular weight range of 250−750 amu. The percentage of primary naphthenic acids and proportion of low molecular weight naphthenic acids influence interfacial activity and emulsion stability of water-in-oil emulsions. Naphthenic acid composition and chemical structure determine the nature of molecular aggregation at the hydrocarbon−water interface and impact interfacial properties and emulsion stabilization performance. Crude oil naphthenic acids containing about 80% primary acids and a higher proportion of 250−425 molecular weight species were the most effective in reducing the interfacial tension and stabilizing water-in-oil emulsions. Medium effects on interfacial properties were investigated using a model hydrocarbon, 5:1:  hexadecane:toluene, and naphthenic-acid-free crude oil as the hydrocarbon phase. Crude oil naphthenic acids reduce the interfacial tension of the naphthenic-acid-free crude oil to 18.5 dyn/cm, whereas they reduce the interfacial tension of the model oil to 28 dyn/cm. The enhanced activity of the naphthenic acids in the crude oil medium is attributed to the interaction between crude oil naphthenic acids and crude oil asphaltenes.