A study of phase behavior, structural development and application of sodium di-2-ethylhexyl phosphate (NADEHP) systems

Fundamental and applied research of sodium di-2-ethylhexyl phosphate (NaDEHP) microemulsions have been conducted. We have systematically investigated the effects of cosurfactant, salinity and solvent structure on phase behavior and structural development of NaDEHP systems, and applied a NaDEHP reverse micellar system to protein and aminoglycoside antibiotic extraction.;With increasing cosurfactant (long chain alcohols and tri-butyl phosphate) or salt concentration, the NaDEHP microemulsion progresses through a transition of Winsor I- Winsor III-Winsor II system. Phase diagrams of NaDEHP microemulsions have been constructed in the NaDEHP-cosurfactant plane for NaDEHP/cosurfactant/solvent/NaCl brine systems with different type of cosurfactant and solvent.;The microemulsion droplet size of NaDEHP/oil/water system is strongly influenced by the variation of cosurfactant and salt concentration. In the Winsor I region, the droplet size increases with cosurfactant or salt concentration, and rises sharply in the region close to WI/WIII phase boundary. In Winsor II region, with increasing cosurfactant or salt concentration, the droplet size decreases sharply near the WIII/WII boundary, and levels off at high cosurfactant or salt concentration. The curvature of the interfacial monolayer decreases continuously with cosurfactant and salt concentration. Based on the concept of M-N-I packing theory, we developed a simple phenomenological model relating droplet size and the packing ratio, and a set of simple equations were developed which directly related droplet size (or the surface curvature) with cosurfactant and salt concentration. The results of these equation are in excellent agreement with our experimental data.;We have successfully used NaDEHP reverse micelle system for protein and aminoglycoside extraction. The extraction efficiency of proteins and aminoglycosides is investigated by varying pH and NaCl concentration in the aqueous phase. The transfer efficiency decreases with increasing pH because the electrostatic interaction become less favorable. With increasing NaCl concentration, the transfer efficiency also declines due to the Debye screening effect. A effective and simple method for the recovery of biomolecules from reverse micelle phase was developed.