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

Abstract

Rhamnolipids (RLs) are biosurfactants produced by Pseudomonas. The biodegradability and the variety of their functionality make them suitable for environmental remediation and oil recovery. We use dissipative particle dynamics simulations to investigate the aggregation behaviors of ionic RL congeners with nonane in various operating conditions. Under zero-salinity conditions, all RL congeners studied here form small ellipsoidal clusters with detectable free surfactants. When salt ions are present, the electrostatic repulsion between the ionized heads is overcome, resulting in the formation of larger aggregates of unique structures. RLs with C10-alkyl tails tend to form elongated wormlike micelles, while RLs with C16-alkyl tails tend to form clusters in spherical symmetry, including vesicles. Di-rhamnolipids (dRLs) require stronger solvation than monorhamnolipids (mRLs) to form clusters, and the resulting size of micelles is decreased. The morphology of the mixed dRL/mRL/oil systems is controlled based on the type of the congeners and the oil contents. In addition, the divalent calcium ions are found to be influential to the structure of the micelles through different mechanisms. For 5 wt % salinity, the ionic RLs can form oil-swollen micelles up to a 1:1 surfactant-to-oil ratio, suggesting that ionic RLs are superb to act as cleaning agents for petroleum hydrocarbons in the marine area. These key findings may guide the design for RL-based washing techniques in enhanced oil recovery.

New Trends in Biosurfactants: From Renewable Origin to Green Enhanced Oil Recovery Applications

“…Lipopeptides exhibit strong surface activity, foam-forming capability, and suitable stability. Surfactin, produced by Bacillus subtilis , is a well-known lipopeptide used in EOR due to its emulsification properties and ability to reduce interfacial tension [ 92 ]. Lichenysin produced by Bacillus licheniformis is also another example of this class of microbial biosurfactant [ 54 ].…”

Microbe cultivation guidelines to optimize rhamnolipid applications

“…Moreover, integrating such meta-analysis data with application-specific data could potentially serve as a tool for producing surfactants with tailored properties. While there are examples of applying chemometric tools in RL research, they mainly focus on optimizing BS production efficiency 26 – 28 , aggregation behavior 29 , solubilization and biodegradation of PAHs 30 , treatment of oily sludges 31 , 32 , coal recovery 33 , and selected adsorption characteristics 34 . To our knowledge, attempts of developing guidelines for the biosynthesis of BSs with specified and targeted properties have not been reported in the scientific literature so far.…”

Classical Molecular Dynamics Simulation of Glyonic Liquids: Structural Insights and Relation to Conductive Properties

“…Rhamnolipids are a type of glycolipid that can be biologically produced by Pseudomonas species . As a well-known biosurfactant, rhamnolipids are biodegradable and relatively nontoxic , and therefore have been studied and applied to a variety of industrial and environmental uses. ,− Also, numerous studies have been carried out to investigate the structures and morphologies of rhamnolipids, − especially computationally, at both vacuum–water ,, and oil–water interfaces, and in rhamnolipid mixtures and solutions. − It was found that the conformations, interactions, and self-assembly structures can be greatly affected by salinity, ionization, and alkyl chain lengths.…”