Surfactant partition into phases

Increasing the aqueous phase salinity appeared to increase foam sensitivity to the presence of a hydrocarbon phase. This behavior may be due to increased surfactant partitioning into the oil phase. This can be quantified by determining the ratio of foam volume in the presence of decane to that in the absence of an added hydrocarbon (Table II. Figure 3). With few exceptions, this ratio decreased with increasing aqueous phase salinity. The values of this ratio for AEGS surfactants declined less with increasing aqueous phase salinity than for other surfactants. 

A particularly interesting part of the pilot involved the treating of produced emulsions. Over the life of the pilot, 93% of the injected surfactant was produced at the production wells, and this situation led to serious emulsion problems. Heating the emulsion to a specific, but unreported, temperature caused the surfactant to partition completely into the aqueous phase and leave the crude oil with very low levels of surfactant and brine. The resulting oil was suitable for pipeline transportation. The critical separation temperature had to be controlled to within 1 0. At higher temperatures, surfactant partitioned into the oil, and at lower temperatures, significant quantities of oil remained solubilized in the brine. Recovered surfactant was equivalent to the injected surfactant in terms of phase behavior, and had the potential for reuse. 

Hirasaki (1981) explained why the negative salinity gradient works from the point of phase velocity. He stated that an overoptimum salinity ahead of the surfactant bank is desirable because surfactant that mixes with the high-sahnity water will partition into the oleic phase, and because the phase velocity (fa/S) of the oleic phase is less than unity, the surfactant will be retarded. An underoptimum salinity is not desirable ahead of the surfactant bank because the surfactant partitions into the aqueous phase, which has a phase velocity greater than unity. However, an underoptimum salinity is desirable in the drive to propagate the surfactant. Thus, a system with overoptimum salinity ahead of the surfactant bank and underoptimum salinity in the drive will tend to accumulate the surfactant in the three-phase region where the lowest interfacial tensions generally occur. 

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey... 

In addition to lowering the interfacial tension between a soil and water, a surfactant can play an equally important role by partitioning into the oily phase carrying water with it [232]. This reverse solubilization process aids hydrody-namically controlled removal mechanisms. The partitioning of surface-active agents between oil and water has been the subject of fundamental studies by Grieser and co-workers [197, 233]. 

Guha S, PR Jaffe, CA Peters (1998) Bioavailability of mixtnres of PAHs partitioned into the micellar phase of a nonionic surfactant. Environ Sci Technol 32 2317-2324. 

Guha, S. and Jaffe, P. R. (1996). Biodegradation kinetics of phenanthrene partitioned into the micellar phase of nonionic surfactants, Environ. Sci. Technol., 30, 605 611. 

The phase transfer catalysts are generally not surfactants. But the surfactants (small as well as large) are good phase transfer catalysts. The good phase transfer catalysts are partitioned into the organic phase of a two phase mixture... 

The impact of salt concentration on the formation of micelles has been reported and is in apparent accord with the interfacial tension model discussed in Sect. 4.1, where the CMC is lowered by the addition of simple electrolytes [ 19,65, 280,282]. The existence of a micellar phase in solution is important not only insofar as it describes the behavior of amphipathic organic chemicals in solution, but the existence of a nonpolar pseudophase can enhance the solubility of other hydrophobic chemicals in solution as they partition into the hydrophobic interior of the micelle. A general expression for the solubility enhancement of a solute by surfactants has been given by Kile and Chiou [253] in terms of the concentrations of monomers and micelles and the corresponding solute partition coefficients, giving... 

Properties of surfactant and cosolvent additives affect the rate of apparent solubilization of organic contaminants in aqueous solutions and may serve as a tool in remediation of subsurface water polluted by NAPLs. Cosolvents (synthetic or natural) are organic solutes present in sufficient quantities in the subsurface water to render the aqueous phase more hydrophobic. Surfactants allow NAPLs to partition into the... 

Winsor reported that the phase behavior of SOW systems at equilibrium could exhibit essentially three types, so called Wl, Wll and Will, illustrated by the phase diagrams indicated in Fig. 1. In the Wl (respectively, Wll) case, the surfactant bears a stronger affinity for the water (respectively, oil) phase and most of it partitions into water (respectively, oil). As a consequence, the system exhibits a two-phase behavior in which a microemulsion is in equihb-rium with excess oil (respectively, water). 

The partitioning can be revealed by different patterns that are found in experimental data. The first one is a reduction in solubilization because a part of the surfactant mixture is no longer at interface. For the same amount of surfactant in the system at optimum formulation, the volume of microemul-son middle phase is lower, just because a certain proportion of the surfactant is no longer in the microemulsion, but has partitioned into one of the excess phases. However, it is worth noting that there are other reasons for the solubilization to decrease, hence this is only a hint. 

Experiments suggested a potential cesium-stripping problem in the CSSX process due to the presence of nitrite in the waste stimulant. The true reason for the cesium-stripping problem was, in fact, the presence of surfactant (sodium mono- and dimethyl naphthalene sulfonate) that can partition into the organic phase on extraction and then retain cesium upon stripping. To overcome this drawback, the authors proposed a caustic wash with a moderate concentration of sodium hydroxide sufficient to remove enough of these lipophilic anions to rejuvenate the solvent, therefore,... 

We began the batch squalane extraction studies by mixing 30 mis of the middle phase from the surfactant system 10% SDBS/17% IPA/12.4% NaCl/dodecane (Figure 6) with 30 mis. of squalane. The solutions were mixed for 10 minutes on a wrist action shaker and allowed to separate. Coalescence was rapid and complete in 5 minutes. The squalane rich phase was separated, and both phases were analyzed for dodecane and SDBS by the methods described previously. These results are summarized in Table V. The batch study was encouraging since 98% of the original solubilized dodecane from Figure 6 (12.4% NaCl ) partitioned into squalane. All the surfactant remained in the aqueous phase, as expected. 

Kibbey, T. C. G. Ramsburg, C. A. Pennell, K. D. Hayes, K. F. Effects of Surfactant Properties on Equilibrium and Non-equilibrium Alcohol Partitioning into Dense Nonaqueous-Phase Liquids (DNAPLs) for In Situ Density Modification Applications, presented at the Fall American Geophysical Union national meeting, San Francisco, California, December, 1998. 

The partitioning of alcohol into the oil, water, and interfacial layer domains of a microemulsion controls whether a two-phase or a three-phase microemulsion system is formed, as well as the microscopic characteristics of the microemulsion phases. F or the typical alcohols used, the amount of alcohol present in the oil domain can be large and comparable to the amount present in the interfacial layer. This is in contrast to the behavior of the surfactant, most of which remains at the interfacial layer and only a negligibly small amount of which are partitioned into the oil and the water domains. Therefore, the accurate accounting of the partitioning of alcohol into the oil domain is a necessary part of any quantitative theory of microemulsions. Such a theory must account for the facts that the alcohol is present in the oil phase as both monomers and aggregates and that the self-association of alcohol in the oil is responsible for its appreciable presence in the oil domain. 

Lif and Holmberg have demonstrated the efficiency of microemulsions as a medium for both organic and bioorganic hydrolysis of a 4-nitrophenyl ester see Scheme 3 of Fig. 3 [7]. The reactions were performed in a Winsor I type microemulsion and took place in the lower phase oil-in-water microemulsion. After the reaction was complete a Winsor I—>111 transition was induced by a rise in temperature. The products formed, 4-nitrophenol and decanoic acid, partitioned into the upper oil phase and could easily be isolated by separation of this phase and evaporation of the solvent. The principle is outlined in Fig. 4. The surfactant and the enzyme (in the case of the lipase-catalysed reaction) resided in the middle-phase microemulsion and could be reused. 

In this system using a polystyrene containing block copolymer, the polystyrene segment should readily partition into the lipophilic polystyrene particle core while the poly(FOA) or PDMS block is solubilized in the CO2 continuous phase to provide steric stabilization and prevent coagulation. In comparison of the polystyrene-b-poly(FOA) diblock copolymers to the polystyrene-b-PDMS diblock copolymers, it was found that the use of a polystyrene-b-PDMS stabilizer gives much more monodisperse particles. This most likely arises from the synthetic technique employed in the surfactant synthesis. The blocks in the polystyrene-b-PDMS block copolymers have a much narrower polydispersity than the blocks in the polystyrene-b-poly(FOA) block copolymers. It was noted that the particles obtained in... 

The results of surfactant-dependency on protein trahsfer indicate that protein extraction reverse micelles not only provide a hydrophilic droplet in a non-aqueous solvent to facilitate protein partition, but also make proteins sufficiently hydrophobic to solubilize into an organic solvent by coating the protein surface. Consequently, we suggest that proteins in the aqueous phase are extracted through the formation of an interfacial complex, a surfactant-coated protein and that the hydrophobic property dominates the extraction efficiency of the proteins, as seen in Figure 14.4. The unsaturated or branched alkyl chain may contribute to the formation of a soluble protein-surfactant complex into a non-aqueous solvent. 

Nearly all of the treatment processes in which fluids are injected into oil wells to increase or restore the levels of production make use of surface-active agents (surfactant) in some of their various applications, e.g., surface tension reduction, formation and stabilization of foam, anti-sludging, prevention of emulsification, and mobility control for gases or steam injection. The question that sometimes arises is whether the level of surfactant added to the injection fluids is sufficient to ensure that enough surfactant reaches the region of treatment. Some of the mechanisms which may reduce the surfactant concentration in the fluid are precipitation with other components of the fluid, thermally induced partition into the various coexisting phases in an oil-well treatment, and adsorption onto the reservoir walls or mineral... 

Many surfactants have been suggested as candidates for CO2 foam. However, at high salinity and temperature in the presence of oil, most surfactants foam poorly due to partitioning and emulsion formation and fail to control mobility during CO2 injection. This behavior is analogous to that observed in chemical (microemulsion) oil recovery (5-1). As the salinity, hardness and temperature increase, surfactants form water/oil emulsions, precipitate surfactant-rich coacervate phases, and partition into the oleic phase. CO2 decreases further the solubility of surfactant in the aqueous phase. 

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