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

摘要

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.