Interaction Forces between Asphaltene Surfaces in Organic Solvents

The colloidal interactions between asphaltene surfaces in heptol, a mixture of n-heptane and toluene, were studied for the first time by colloidal force measurements using an atomic force microscope (AFM). Asphaltenes were deposited on silica wafers and silica spheres using the Langmuir−Blodgett ups...

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Bibliographic Details
Published inLangmuir Vol. 26; no. 1; pp. 183 - 190
Main Authors Wang, Shengqun, Liu, Jianjun, Zhang, Liyan, Masliyah, Jacob, Xu, Zhenghe
Format Journal Article
LanguageEnglish
Published Washington, DC American Chemical Society 05.01.2010
Subjects
Chemistry
Colloidal state and disperse state
Exact sciences and technology
General and physical chemistry
Interfaces: Adsorption, Reactions, Films, Forces
Langmuir blodgett films
Surface physical chemistry
Asphaltene
Attraction
Atomic force microscopy
Binary compound
Force measurement
Hydrocarbon
Volume fraction
Force
Theory
Toluene
Polymer
Heptane
Silica
Aggregation
Organic solvent
Precipitation
Crude oil
Benzenic compound
Langmuir Blodgett layer
Wafer
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Summary:The colloidal interactions between asphaltene surfaces in heptol, a mixture of n-heptane and toluene, were studied for the first time by colloidal force measurements using an atomic force microscope (AFM). Asphaltenes were deposited on silica wafers and silica spheres using the Langmuir−Blodgett upstroke technique. The results showed that the ratio of toluene to heptane can significantly change solvent quality in terms of the ability to solubilize asphaltenes and hence the nature and the magnitude of the interaction forces between asphaltene surfaces. In pure toluene, there is a steric long-range repulsion which can be well fitted by the scaling theory of polymer brushes. As toluene volume fraction in heptol (ΦT) is gradually decreased from ΦT = 1 (pure toluene) to ΦT = 0 (pure n-heptane), the steric repulsion reduced and changed to weak attraction when ΦT < 0.2. The attraction in heptane can be fitted by van der Waals forces alone which are thus believed to promote asphaltene aggregation, leading to asphaltene precipitation. The results obtained in this study provide an insight into interactions that determine asphaltene behavior in an organic medium and hence in crude oils.
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ISSN:0743-7463
1520-5827
DOI:10.1021/la9020004