Flocculation behavior of asphaltenes in solvent/nonsolvent systems

Area of Science:

• Petroleum Chemistry
• Colloid Science
• Physical Chemistry

Background:

• Asphaltenes are complex molecules in crude oil.
• Understanding asphaltene aggregation is crucial for petroleum processing.
• Flocculation behavior influences oil stability and flow.

Purpose of the Study:

• To investigate asphaltene flocculation dynamics.
• To determine the influence of aromatic solvents and alkanes on flocculation.
• To correlate diffusion coefficients with kinetic flocculation studies.

Main Methods:

• Pulsed-field gradient spin echo nuclear magnetic resonance (PFG-SE NMR) for diffusion coefficients.
• UV-VIS spectrophotometry for kinetic flocculation studies (turbidity).
• Measurement of transverse (T2) relaxation times.

Main Results:

• Diffusion coefficients showed small changes with up to 30 wt% alkane addition.
• Stability ratio (W) indicated varying asphaltene stability in different solvent/alkane systems.
• Flocculation dramatically increased above a threshold alkane concentration.
• Flocculation transitioned from reaction-controlled to diffusion-controlled at higher alkane concentrations.
• Two distinct asphaltene transverse relaxation times (0.6 ms and 7 ms) were observed.

Conclusions:

• Asphaltene flocculation is highly dependent on alkane concentration.
• A threshold concentration exists for significant asphaltene aggregation.
• The flocculation process is governed by reaction kinetics initially, then by diffusion.
• PFG-SE NMR and UV-VIS spectrophotometry provide complementary insights into asphaltene stability.