Study on extraction of cobalt(II) by sodium laurate/pentan-1-ol/heptane/NaCl microemulsion system

A microemulsion consisting of sodium laurate, n-pentanol, n-heptane and NaCl solution was investigated for Co(II) extraction. The dilution method and conductivity method were used for the determination of structural parameters of sodium laurate/pentan-1-ol/heptane/NaCl microemulsion system. Co(II) was found to be extracted into the microemulsion phase due to the compound formation of [CoCl]⁺[R₁₁COO]^?, which was confirmed by the continuous variation of R₁₁COONa concentration. Moreover, the effects of cosurfactant, the contact time, the phase ratios, PH and the NaCl concentration in feed solutions on the cobalt extraction yield were investigated. Under the optimum conditions, the extraction percentage of Co(II) could reach 98.9%.     

Enzymatic esterification and phase behavior in ionic microemulsions with different alcohols

The esterification of hexanoic acid and 1-pentanol catalyzed by the lipase fromChromobacterium viscosum was studied at 298.2 K using different Winsor systems as reaction medium. The microemulsion systems consisted of brine and alkane stabilized by the anionic surfactant sodium dodecylsulphate and a short-chained alcohol. The alcohol acts both as a reactant and as a part of the reaction medium. Therefore, it is of great fundamental interest to know the phase behavior of the used microemulsion systems. Partial phase diagrams were determined and the efficiency of different alcohols on the transition from a Winsor I system to a Winsor III or a Winsor IV system with bicontinuous structure and further to a Winsor II system was investigated. The investigated alcohols were 2-methyl-1-propanol, 1-butanol, 2-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, and 1-hexanol. The aqueous medium consisted of 0.5 m NaCl(aq) or a phosphate buffer (pH=7) and the organic medium of octane or 2,2,4-trimethyl pentane. A long alkyl chain of the alcohol or a branching far from the hydroxyl group gives a more efficient cosurfactant and a transition from Winsor I to Winsor III or Winsor IV at lower alcohol contents. In the Winsor III system the yield of 1-pentyl hexanoate is twice as high as the yield in the bicontinuous Winsor IV system.     

Studies of cyclohexane/TX 100 + ethylpropionate/water system: effect of ethylpropionate as cosurfactant

 Pseudoternary phase diagram of cyclohexane/TX 100-ethylpropionate/water system was determined at 30 ^°C. One phase microemulsion was obtained over a small area. The surfactant/cosurfactant ratio was both kept at 1:1 and 1:2 w/w. Viscosity, conductance, adiabatic compressibility values at various temperatures show the expected trend. The addition of NaCl changes one phase microemulsion to Winsor II system and no Winsor III system was obtained. Contact angle data, conductance, etc., show oil continuous system at a constant surfactant weight fraction. The microstructure of Winsor IV microemulsion seems to be W/O. Received: 14 May 1996 Accepted: 23 October 1996     

Synthesis of Ag2S quantum dots in water-in-CO2 microemulsions

Ag2S nanocrystals with a mean diameter of 5.9 nm (sigma= 1.65 nm) and characteristic surface plasmon resonance absorption at 330 nm have been synthesized in water-in-supercritical CO2 reverse microemulsion using the commonly used AOT surfactant with 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (F-pentanol) as cosurfactant.     

The phase behavior of microemulsion systems containing kerosene

The phase behavior of microemulsion systems containing an anionic surfactant (SDS) as well as a nonionic surfactant (Triton X-100) along with cosurfactant (1-pentanol) and using kerosene as an oil phase is reported. The unusual features observed are explained.     

Studies on the Middle-phase Microemulsion of Lauric-N-methylglucamide

The phase behaviour of the middle-phase microemulsion for the quaternary system lauric-N-methylglucamide （MEGA-12）/n-butanollalkane/water has been studied with Winsor type, δ-γ, fishlike and novel ε-β fishlike phase diagrams. A series of phase inversions Winsor I （2）→Ⅲ（3）→Ⅱ （ 2 ） were observed for the three kinds of phase diagrams. The phase types, the phase volumes and the range of alcohol concentrations from the beginning to the end of the middle-phase microemulsion were obtained from Winsor phase diagram. From δ-γ, fishlike phase diagram, the physicochemical parameters, such as the mass fraction of n-butanol in the hydrophile-lipophile balanced inteffacial layer, A^s, the coordinates of the start and end points of the middle-phase microemulsion, and the solubilities of MEGA-12 and n-butanol in alkane phase were calculated. The novel ε-β fishlike phase diagram was also presented. From this kind of diagram, the above experimental phenomena were observed and the physicochemical parameters were calculated precisely. The novel fishlike phase diagram has advantages over the Winsor and δ-γ fishlike phase diagrams in the evaluation of the solubilization power of the microemulsion and calculation of the related physicochemical parameters.     

The effect of different polymer length on water droplets of reverse AOT microemulsion

We study the effect of polyethylene glycol (PEG) on the dynamic and structure of water droplets at the reverse sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) microemulsion. The mixture of water and oil with anionic surfactant AOT can form microemulsion. The dynamic of microemulsion in the presence of PEG is investigated by photon correlation spectroscopy technique. We mainly focus on the variation of the translational diffusion behaviour as a function of the polymer concentration and polymer length scale. By increasing the content of the lowest PEG length scale (M_n = 285), the dynamic of microemulsion slows down. In addition, one relaxation process is distinguished for all polymer concentration. However, for the two higher polymer length scale (M_n = 2200 and 6000), two relaxations are observed and the dynamic of microemulsion speeds up. We used the small angle X-ray scattering technique to monitor the size and the polydispersity of the mixture system (AOT microemulsion/PEG).     

Solvent extraction of thorium(IV) using W/O microemulsion

The extraction of thorium(IV) was investigated using two types of W/O microemulsion,one of which was formed by a surface-active saponified extractant sodium bis(2-ethylhexyl) phosphate(NaDEHP) and the other was formed by a mixture of an anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate(AOT) and an extractant bis(2-ethylhexyl)phosphoric acid(HDEHP) as the cosurfactant.The extraction capacities of the above two systems were higher than that of the HDEHP extraction system.High concentration of NaNO 3 showed no influence on the extraction in the NaDEHP based W/O microemulsion system,whilst reduced the extractability in the AOT-HDEHP W/O microemulsion system.The mechanism in acidic condition was demonstrated by the log-log plot method.The structure of the aggregations and the water content in the organic phase after extraction were measured by dynamic light scattering and Karl Fischer water titration,respectively.It was found that NaDEHP based W/O microemulsion broke up after extraction,while AOT-HDEHP W/O microemulsion was reserved.     

Extraction of europium by sodium oleate/pentanol/heptane/NaCl microemulsion system

The extraction of europium to a W/O microemulsion with an anionic surfactant was studied. In the sodium oleate (NaOL)/pentanol/heptane/NaCl system, the influence of aqueous-microemulsion ratio, concentration of NaOL, extraction temperature, concentration of cosurfactant, pH and salting-out agent on the extraction yield were investigated. Europium was probably extracted into the microemulsion phase in the form of Eu(OL)₂Cl, and the extraction yield (E%) was above 99% when R = 8. The enthalpy and entropy of Eu(III) extraction were calculated to be −12.18 kJ/mol and −61.41 J/(mol K), respectively. The back-extraction is conducted by hydrochloric acid (0.8 mol/L), which provided better back-extraction yields (95.15%).     

Middle-phase microemulsions of green surfactant alkyl polyglucosides

Microemulsions are important organized molecular assembles in surfactant solutions and are used in various fields such as tertiary oil recovery, pharmaceutics, cosmetics, nanoparticle synthe-sis and chemical engineering. The more commonly used nonionic surfactants to produce micro- emulsions are the ethylene oxide-based compounds (CiEj). In recent years alkyl polyglucosides have been received considerable attention in producing microemulsions[17]. Alkyl polyglucosides (APG), which are widely…     

Physicochemical investigations of microemulsification of eucalyptus oil and water using mixed surfactants (AOT+Brij-35) and butanol

Microemulsification of a vegetable oil (eucalyptus) with single and mixed surfactants (AOT and Brij-35), cosurfactant of different lipophilicities (isomers of butanol), and water were studied at different surfactant and cosurfactant mixing ratios. The phase diagrams of the quaternary systems were constructed using unfolded and folded tetrahedron, wherein the phase characteristics of different ternary systems can be underlined. The microemulsion zone was found to be dependent upon the mixing ratios of surfactant and cosurfactant; the largest microemulsion zone was formed with 1:1 (w/w) S:CS. The effects of temperature and additives (NaCl, urea, glucose, and bile salts of different concentrations) on the phase behavior were examined. The mixed microemulsion system showed temperature insensitivity, whereas the Brij-35 (single) stabilized system exhibited a smaller microemulsion zone at elevated temperature. NaCl and glucose increased the microemulsion zone up to a certain concentration, beyond which the microemulsion zones were decreased. These additives decreased the microemulsion zones as temperature was increased. The effect of urea on microemulsion zone was found to be insignificant even at the concentration 3.0 mol dm(-3). Little effect on microemulsion zone was shown by NaC (sodium cholate) at 0.25 and 0.5 mol dm(-3) at different temperatures. The conductance of the single (AOT) and mixed microemulsion system (AOT+Brij-35) depends upon the water content and mixing ratios of the surfactants, and a steep rise in conductance was observed at equal weight percentages of oil and water. Viscosities for both single (AOT) and mixed (AOT+Brij-35) surfactant systems passed through maxima at equal oil and water regions showing structural transition. The viscosities for microemulsion systems increased with increasing Brij-35 content in the AOT+Brij-35 blend. Conductances and viscosities of different monophasic compositions in the absence and presence of additives (NaCl and NaC) were measured at different temperatures. The activation energy of conduction (DeltaE(cond)( *)) and the activation enthalpy for viscous flow (DeltaH(vis)( *)) were evaluated. It was found that both DeltaE(cond)( *) and DeltaH(vis)( *) were a function of the nature of the dispersion medium. Considering the phase separation point of maximum solubility, the free energy of dissolution of water or oil (DeltaG(s)(0)) at the microdispersed state in amphiphile medium was estimated and found to be a function of surfactant composition.     

Synthesis and characterization of PbS nanotubes in bicontinuous microemulsion system

PbS nanotubes were successfully synthesized in bicontinuous microemulsion system containing cyclohexane, aqueous solution, n-pentanol and surfactant OP (polyethylene glycol p-octylphenyl ether). The morphology of PbS nanotubes was confirmed by the transmission electron microscopy. The crystallinity and structural features of PbS nanotubes were characterized by powder X-ray diffraction. The effect of key parameters, such as the molar ratio of water to surfactant and the reactant concentration, on the resulting product has also been investigated. The formation mechanism of PbS nanotubes and nanowires synthesized in bicontinuous microemulsion system has been discussed.     

Vortex-assisted surfactant-enhanced-emulsification liquid-liquid microextraction for the determination of triazine herbicides in water samples by microemulsion electrokinetic chromatography

A novel method based on the combination of microemulsion electrokinetic chromatography (MEEKC) and vortex‐assisted surfactant‐enhanced‐emulsification liquid–liquid microextraction (VSLLME) was developed for the determination of five triazine herbicides (simazine, atrazine, ametryn, prometryn, and terbutryn) in water samples. The five triazine herbicides were baseline separated by using the microemulsion buffer containing a 10 mmol/L borate buffer at pH 9.5, 2.5% (w/v) SDS as surfactant, 0.8% (w/v) ethyl acetate as oil phase, and 6.0% (w/v) 1‐butanol as cosurfactant. The optimum extraction conditions of VSLLME were as follows: 100 μL chloroform was used as extraction solvent, 5.0 × 10^?5 mol/L Tween‐20 was chosen as the surfactant to enhance the emulsification, and the extraction process was carried out by vortex mixing for 3 min. Under these optimum experimental conditions, the calibration curve was linear in the range of 2.0–200.0 ng/mL, with the correlation coefficients (r²) varying from 0.9927 to 0.9958. The detection limits of the method varied from 0.41 to 0.62 ng/mL. The purposed method was applied to the determination of five triazine herbicides in real water samples, and the recoveries were between 80.6 and 107.3%.     

A Closed Concept of Extractive Whole Cell Microbial Transformation of Benzaldehyde into l-Phenylacetylcarbinol by Saccharomyces cerevisiae in Novel Polyethylene-Glycol-Induced Cloud-Point System

Extractive microbial transformation of benzaldehyde into l-phenylacetylcarbinol (l-PAC) by Saccharomyces cerevisiae (Baker’s yeast) has been carried out in a novel polyethylene-glycol-induced cloud-point system (PEG-CPS). The extractive microbial transformation in the PEG-CPS and a downstream process for stripping of the product from the microbial transformation broth with microemulsion extraction are demonstrated. The results indicate that the PEG-CPS maintains the advantage of CPS for in situ extraction of polar product in the microbial transformation. At the same time, the utilization of hydrophilic nonionic surfactant in the PEG-CPS is favorable for stripping of product from the nonionic surfactant in the microbial transformation broth by Winsor I microemulsion extraction. Thus, a closed concept of in situ extraction of polar product in microbial transformation and its downstream process of product recovery are fulfilled at the same time.     

W/O microemulsions of styrene monomer and dimer

The reason for the lower water solubility in W/O microemulsions of the styrene dimer, trans, trans-1,4-diphenyl-1,3-butadiene, in comparison with the monomer was investigated by determining the phase equilibria in the microemulsion system with pentanol as the cosurfactant and sodium dodecyl sulfate as the surfactant. The main factor for the low tolerance for water in the system was the incompatibility of the dimer with the cosurfactant and surfactant.     

Phase behavior of water-in-supercritical carbon dioxide microemulsion with sodium salt of bis(2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate

The fluorinated analogues of AOT surfactant, sodium salt of bis(2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate, which has CO₂-philic chains and a hydrophilic head group, was synthesized for forming water-in-CO₂ microemulsion. The cloud point of this surfactant was measured and the supercritical fluid-phase behavior of water-in-CO₂ microemulsion was investigated by using a variable-volume view cell apparatus. It was found that the phase behavior of microemulsion is affected by the concentrations of water and surfactant in CO₂, molar ratio of water to surfactant (W_o = [water]/[surfactant]), and the amount of CO₂. From this experiment, we found out another cloudy point which exists above the homogeneous microemulsion region. We defined this point as “upper cloud point” and general cloud point as “lower cloud point. The region which exists between these two cloud points was defined as “stable region of microemulsion”. Conditions for the formation of water-in-CO₂ microemulsion were obtained at temperatures up to 370.15 K.     

Interfacial and Thermodynamic Properties of Formation of Water‐in‐Oil Microemulsions with Surfactants (SDS and CTAB) and Cosurfactants (n‐Alkanols C5–C9)

The interfacial and thermodynamic properties of water‐in‐oil microemulsion systems consisting of water, isopropyl myristate, n‐alkanol, and surfactant have been investigated using the method of dilution. The surfactants used were hexadecyl trimethylammonium bromide and sodium dodecylsulfate, and the cosurfactants were n‐alkanols with varying chain length from (C₅–C₉). The distribution of cosurfactant (n‐alkanol) between the interface of water and oil regions at the threshold level of stability as well as the energetics of the transfer of the cosurfactant from the oil to the interfacial region have been examined as a function of varying cosurfactant chain length (C₄–C₉) and temperature. The structural parameters (including dimension, population density and effective water pool radius) of the dispersed water droplets in the oil phase have also been evaluated and correlated with alkanol chain length.     

Temperature-induced phase separation in pseudoternary mixtures of Triton X-100–butanol–kerosene–water

The transparent Winsor IV domain in the phase diagram of the mixtures of emulsifier (Triton X-100 and butanol), oil (kerosene), and water is found to be 34% of the total phase diagram in presence of emulsifier with surfactant:cosurfactant::1:1, and is water dominant. Increase in cosurfactant/surfactant ratio inverts the Winsor IV domain to become oil rich. The plot of conductance of the microemulsions prepared by substituting water by brine against water content depicts the existence of three distinct phases like oil-in-water, bicontinuous, and water-in-oil microemulsion in the phase diagram. The phase contrast micrographs of the mixtures of different compositions in these three different phases reveal the existence of microdroplets of oil dispersed in water and water dispersed in oil. Further, the dynamic light scattering studies of these solutions reveal an inhomogeneity in the size distribution of the droplets. A temperature-induced clouding in the microemulsion domain leading to phase separation has been observed. Additives like glucose, sucrose, and sodium chloride decrease the cloud point (CP), while addition of ammonium thiocyanate increases it. A quantitative relationship of the clouding temperature with the composition of the microemulsion has been established. With increase in oil and emulsifier, the cloud point of the microemulsion increases. The separated phases after the clouding have been used for preconcentration of water-soluble metal ions as well as oil-soluble dyes. The turbid systems on heating led to separation into three isotropic phases which are found to be stable at ambient temperature. The stability of these phases is ascribed to the formation of stable microemulsions by mass transfer from one phase to other.     

Structure and phase behaviour of the ternary system water, n-heptane and the nonionic surfactant Igepal® CA520

The phase behavior of the system water, n-heptane and the nonionic surfactant Igepal^® CA520 has been studied by visual inspection, high-performance liquid chromatography, polarizing microscopy and freeze-fracture electron microscopy. The phase diagram at 25?°C contains two large homogeneous microemulsion phases, an extended region of a lamellar liquid crystalline structure and some two- and three-phase regions. The oil-rich part of the phase diagram has been investigated by static and dynamic light scattering in order to examine the behavior of the collective diffusion coefficient and the scattering intensity in the presence of increasing concentrations of water, starting from the binary system of n-heptane and Igepal^® CA520. The results suggested that at a very low water content the aggregates of the microemulsion are small. With the exception of this region the structure is bicontinuous.     

Effect of short-chain alcohols on the oil-in-water microemulsion polymerization of styrene

The influence of short-chain alcohols, 1-butanol (C₄OH), 2-pentanol (C₅OH) and 1-hexanol (C₆OH), on the formation of oil-in-water styrene microemulsions and the subsequent free-radical polymerization was studied. Sodium dodecyl sulfate was used as the surfactant. The overall performance of C₄OH as the cosurfactant is quite different from C₅OH and C₆OH. The range of the microemulsion region in decreasing order is C₄OH > C₅OH > C₆OH. The primary parameters selected for the microemulsion polymerization study were the concentrations of cosurfactant and styrene. Only a small fraction of microemulsion droplets initially present in the reaction system can be successfully transformed into latex particles and the remaining droplets serve as a reservoir to supply the growing particles with monomer. Limited flocculation of latex particles also occurs during polymerization and the degree of flocculation is most significant for the C₄OH system. Received: 24 August 1999/Accepted in revised form: 22 October 1999