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The fractal aggregation of asphaltenes
Michael P Hoepfner1, Cláudio Vilas Bôas Fávero, Nasim Haji-Akbari
1Department of Chemical Engineering, The University of Michigan, Ann Arbor, Ann Arbor, Michigan 48109, United States.
Langmuir : the ACS Journal of Surfaces and Colloids
|July 2, 2013
Summary
Asphaltene structure and stability were investigated using time-resolved small-angle neutron scattering. Insoluble asphaltenes form higher fractal dimension clusters, revealing destabilization mechanisms and aiding in understanding crude oil stability.
Area of Science:
- Petroleum Science
- Materials Science
- Physical Chemistry
Background:
- Asphaltenes are complex molecules in crude oil that significantly impact stability.
- Understanding asphaltene aggregation and precipitation is crucial for oil production and processing.
Purpose of the Study:
- To investigate the structure and stability of asphaltenes in crude oil and model oil.
- To differentiate scattering from soluble and insoluble asphaltenes.
- To elucidate the mechanism of asphaltene destabilization and precipitation.
Main Methods:
- Time-resolved small-angle neutron scattering (TR-SANS).
- Novel method to isolate scattering signals from soluble and insoluble asphaltenes.
- Experiments conducted on both crude oil and model oil systems with and without precipitant (heptane).
Main Results:
- Both soluble and insoluble asphaltenes form fractal clusters.
- Insoluble asphaltene clusters exhibit a higher fractal dimension than soluble ones.
- Heptane addition increases soluble asphaltene cluster size but not fractal dimension.
- Heptane-insoluble asphaltenes are the primary source of small-angle scattering.
- Asphaltene solubility at low heptane concentrations was measured.
Conclusions:
- Asphaltene aggregation leads to fractal cluster formation with varying dimensions.
- The polydisperse nature of asphaltenes prevents a defined phase stability envelope.
- Precipitation occurs even at low precipitant concentrations.
- Stable asphaltenes are dispersed at the nanoscale.
- A new asphaltene precipitation mechanism is proposed based on experimental findings.
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