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Abstract
A new precipitation and fractionation procedure was established where asphaltenes were precipitated successively by stepwise addition of pentane. The first fraction was obtained by mixing 3∶1 volumes of n‐pentane/crude oil followed by filtration. The following fractions were obtained by addition of more pentane to the crude oil with filtration between each step. Four fractions were precipitated with this procedure giving fractions based on a pentane‐to‐crude oil ratio of 3∶1, 10∶1, 15∶1, and 20∶1. Near infrared light at 1,600 nm was used to detect precipitation of asphaltenes in solutions of heptane and toluene. The asphaltenes precipitated showed an increasing solubility in heptane/toluene mixtures from the first precipitate to the last one. Interfacial tension was determined using the pendant drop technique. These measurements showed that the 10∶1 intermediate fraction exhibited a considerable reduction of the interfacial tension between toluene and water compared to the other fractions. Obviously the surface activity varies very much (almost by a factor of 2) between the different solubility classes within the asphaltene family. This may have large technical consequences within crude oil production and processing.
The authors would like to thank the following partners for the financial support: Statoil R&D Centre and the members of the Joint Industrial Project on “Particle‐Stabilized Emulsions/Heavy Crude Oils,” including Statoil ASA, Vetco Aibel AS, Shell Global Solutions, Aker Kvaerner, BP, Champion Technologies, Chevron Texaco, Norsk Hydro, Petrobras, Total, ENI Technology, and Maersk Oil & Gas.