Rhamnolipid Biosurfactants for Oil Recovery: Salt Effects on the Structural Properties Investigated by Mesoscale...

Area of Science:

• Biochemistry and Environmental Science
• Surfactant Chemistry
• Computational Chemistry

Background:

• Rhamnolipids (RLs) are biodegradable biosurfactants produced by *Pseudomonas* bacteria.
• Their amphipathic nature and functionality make them promising for environmental remediation and oil recovery applications.
• Understanding RL aggregation behavior is crucial for optimizing their use in these fields.

Purpose of the Study:

• To investigate the aggregation behavior of ionic rhamnolipid congeners with nonane using dissipative particle dynamics simulations.
• To explore the influence of operating conditions, such as salinity and ion type, on RL aggregate morphology.
• To assess the potential of RLs as cleaning agents for petroleum hydrocarbons.

Main Methods:

• Dissipative Particle Dynamics (DPD) simulations were employed to model the interactions between RL congeners and nonane.
• Simulations were conducted under varying conditions, including zero and non-zero salinity, and different salt ion concentrations.
• The structural characteristics and morphologies of the resulting aggregates were analyzed.

Main Results:

• In the absence of salt, RLs formed small ellipsoidal clusters with free surfactants.
• The presence of salt ions facilitated the formation of larger aggregates with unique structures by overcoming electrostatic repulsion.
• RLs with C10 tails formed wormlike micelles, while C16 tails formed spherical clusters and vesicles.
• Di-rhamnolipids (dRLs) required stronger solvation and formed smaller micelles compared to mono-rhamnolipids (mRLs).
• Divalent calcium ions significantly influenced micelle structure.
• At 5 wt % salinity, ionic RLs formed oil-swollen micelles up to a 1:1 surfactant-to-oil ratio.

Conclusions:

• The aggregation behavior and morphology of ionic RLs are highly dependent on salinity, congener type, and oil content.
• Ionic RLs demonstrate excellent potential as cleaning agents for petroleum hydrocarbons, particularly in marine environments.
• These findings provide valuable insights for designing effective RL-based washing techniques for enhanced oil recovery.