Aggregation and solubility behavior of asphaltenes and their subfractions

Area of Science:

• Petroleum Geochemistry
• Materials Science
• Colloid Science

Background:

• Asphaltenes are complex macromolecules found in crude oil.
• Their aggregation behavior significantly influences petroleum production and processing.
• Understanding asphaltene solubility and interactions is crucial for addressing operational challenges.

Purpose of the Study:

• To investigate the chemical characteristics and aggregation behavior of asphaltenes from different crude oils.
• To correlate asphaltene subfraction properties with their solubility and aggregate size.
• To elucidate the role of polar and pi-bonding interactions in asphaltene aggregation.

Main Methods:

• Fractionation of asphaltenes using heptane-toluene mixtures.
• Chemical analysis, including elemental composition (H/C, N, V, Ni, Fe).
• Vapor Pressure Osmometry (VPO) and Small Angle Neutron Scattering (SANS) for aggregate size determination.

Main Results:

• A polar, hydrogen-bonding asphaltene subfraction exhibited strong interactions and formed larger aggregates.
• Aggregate size generally increased with decreasing solvent aromaticity, with exceptions at solubility limits.
• Different crude oil asphaltenes showed distinct aggregation mechanisms (e.g., pi-bonding vs. polar interactions).

Conclusions:

• Less soluble asphaltene subfractions, rich in polar and pi-bonding species, are primarily responsible for aggregation.
• Asphaltene aggregation contributes to significant petroleum production problems, including pipeline deposition and emulsion stabilization.
• The study provides insights into controlling asphaltene-related issues through understanding molecular interactions.