Solubilization Isotherms Research Articles

Solubilization and separation of o-toluidine and tricyclazole in sodium dodecyl sulfate micelles in micellar enhanced ultrafiltration.

The solubilization laws of pollutants in micelles and their separation efficiency are very important in the successfully efficient application of micellar enhanced ultrafiltration (MEUF). The solubilization behavior of o-toluidine (OT) and tricyclazole (TC) into sodium dodecyl sulfate (SDS) micelles in MEUF was studied using nonlinear equation sets for concentration analysis, which resolved the issue on the overlap of absorption spectra of multicomponent compounds restricting the application of conventional ultraviolet (UV) spectroscopic method. The solubilization isotherms for both pollutants could be best explained by the Langmuir-Freudlich model (R2>0.99) followed by the modes of Langmuir and Freudlich, inferring the complexity of solubilization mechanism and solubilization advantage of monolayer over multilayer. The calculated thermodynamic parameters (ΔG0, ΔH0 and ΔS0) indicated that this process was endothermic and spontaneous. The solubilization of OT and TC well followed the pseudo second-order and pseudo first-order kinetics, respectively. The separation and recovery of SDS solubilizing these two pollutants were also investigated through lowering solution temperature to 2 °C followed by centrifugation. The best recovery rate of about 66% for SDS was achieved containing 10 and 5% of each initial amount of OT and TC, respectively, at near-neutral solution pH value. The recovery of SDS could decrease to some extent under alkaline and acidic conditions.

Highly efficient micellar extraction of toxic picric acid into novel ionic liquid: Effect of parameters, solubilization isotherm, evaluation of thermodynamics and design parameters

A simple and new approach in cloud point extraction (CPE) method was developed for removal of picric acid (PA) by the addition of N,N,N,N’,N’,N’-hexaethyl-ethane-1,2-diammonium dibromide ionic liquid (IL) in non-ionic surfactant Triton X-114 (TX-114). A significant increase in extraction efficiency was found upon the addition of dicationic ionic liquid (DIL) at both nearly neutral and high acidic pH. The effects of different operating parameters such as pH, temperature, time, concentration of surfactant, PA and DIL on extraction of PA were investigated and optimum conditions were established. The extraction mechanism was also proposed. A developed Langmuir isotherm was used to compute the feed surfactant concentration required for the removal of PA up to an extraction efficiency of 90%. The effects of temperature and concentration of surfactant on various thermodynamic parameters were examined. It was found that the values of ΔG° increased with temperature and decreased with surfactant concentration. The values of ΔH° and ΔS° increased with surfactant concentration. The developed approach for DIL mediated CPE has proved to be an efficient and green route for extraction of PA from water sample.

Enhanced separation of toxic Blue BG dye by cloud point extraction with IL as an additive: Effect of parameters, solubilization isotherm and evaluation of thermodynamics and design parameters

Cloud point extraction (CPE) was adopted for removal of Blue BG dye from aqueous solution using tetraethyl ammonium tetrafluoroborate [TEA(BF4)] ionic liquid (IL) as an additive with non-ionic surfactant Triton X-114 (TX-114). The effect of different operating parameters such as temperature, time, concentration of surfactant; IL and dye on extraction of dye have been studied in detail to find out optimum conditions. The extraction efficiency was found to increase significantly with temperature, time, surfactant concentration and IL concentration. A developed Langmuir isotherm was used to compute the feed surfactant concentration required for the removal of Blue BG dye up to an extraction efficiency of 90%. The effect of temperature and concentration of surfactant on various thermodynamic parameters, like change in Gibbs-free energy (ΔG°), change in enthalpy (ΔH°), and change in entropy (ΔS°) were examined. It was found that ΔG° increased with temperature but decreased with surfactant concentration whereas ΔH° and ΔS° increased with surfactant concentration.

Solubilization of dibutyltin dichloride with surfactant solutions in single and mixed oil systems

The harmful effects of organometallic compounds and their metabolites on the environment and human health require the development of more effective remediation methods. Surfactant enhanced remediation has been considered as a potential method for the removal of organometallic compounds; however, additional understanding is needed about the solubilization processes of these compounds. The surfactant enhanced solubilization of dibutyltin dichloride (DBT), an organometallic compound, was the focus of this research. In addition, the synergistic effects of DBT solubilization in perchloroethylene (PCE) and decane mixtures were evaluated. The results indicate that PCE and decane were solubilized into the core of these surfactant micelles in both single and mixed oil systems. DBT solubilization was limited when DBT alone was present (single oil system), and the nature of the solubilization isotherm suggests that DBT solubilization tended to occur near the micelle surface in a single oil system. DBT solubilization was found to increase when present in the PCE and decane oil mixture. PCE and decane may have facilitated the solubilization of DBT because they were solubilized in the micelle core. From this study, it may be concluded that the DBT behaves like polar oil such as dodecanol, having properties of a polar organic compound.

Determination of design parameters for the cloud point extraction of congo red and eosin dyes using TX-100

A systematic method is outlined to design cloud point extraction process. The aim is to calculate the concentration of non-ionic surfactant required for a desired extraction of dye at various operating conditions (feed dye concentration and temperature). In the course of design calculations, information about the following two characteristics of this system are required: (1) the solubilization isotherm of the dye in the surfactant solution at various operating temperatures and (2) quantification of the variation of the fractional coacervate phase volume with the feed surfactant, dye concentration and the operating temperature. In case of TX-100 and the dye system (congo red and eosin), a Langmuir type solubilization isotherm is fitted using the experimental data. Correlations are developed for the variation of isotherm parameters with temperature. A simple correlation of fractional coacervate phase volume with feed surfactant concentration is proposed in the form of a c s b . From the experimental data, the variations of a and b with feed dye concentration and temperature are evaluated. Using the developed correlations and proposed design method, the concentration of feed surfactant required to achieve 1 ppm dye concentration in the dilute phase is calculated for the two dyes at typical operating temperatures and feed dye concentrations. The developed method will be of immense help for scale up of cloud point extraction process.

Solubilization of Phenols in Anionic Polyelectrolyte Gels with Adsorbed Cationic Surfactant

Solubilization isotherms for various phenols in cetylpyridinium chloride (CPC)-polyelectrolyte gel aggregates have been determined in order to compare solubilization within these aggregates with that in free micelles and to examine the effects of gel chemistry and structure on solubilization. The isotherms describing solubilization are quite similar to those found for free surfactant in solution. Solutes that are more hydrophobic give rise to larger solubilization constants with trends similar to what is seen for hydrophobic effects in adsorption from aqueous solutions onto hydrophobic solids. The solubilization constants decrease as the fraction of solute in the aggregates increases, indicating that the solutes partition into the palisade region of the aggregates. Solubilization is found to be quite insensitive to changes in gel structure (cross-linker varying from 1% to 3%) and chemistry (poly(acrylic acid) versus poly(methacrylic acid) and neutralization from 50% to 100%). However, the switch from poly(acrylic acid) to poly(methacrylic acid) did give rise to a slight decrease in magnitude of the slope of the isotherm. The most significant factors appear to be the initial concentration of surfactant in solution and the ratio of surfactant solution to gel amount. A decrease in surfactant concentration (especially combined with an increase in solution volume) gives rise to a decrease in solubilization constants.

Interfacial solubilization of model amphiphilic molecules in block copolymer micelles.

We investigate the solubilization of 2-nitrodiphenylamine, a hydrophobic but polar dye molecule, in aqueous solutions of polystyrene(310)-b-poly(acrylic acid)(47) micelles. The solubilization capacity of the micelles, which consist of a polystyrene core and poly(acrylic acid) corona, and the micelle-water partition coefficient are evaluated as a function of the solubilizate concentration. The solubilization isotherm shows a nonlinear behavior, and the partition coefficient, instead of being constant, is strongly dependent on the dye concentration. These results are explained by treating solubilization as a binding process, and by fitting the data to a Langmuir adsorption model. In addition, we examine the locus of solubilization of 2-nitrodiphenylamine using its solvatochromic properties and solubility in model solvents, and we identify the micellar interface as the solubilization site. Confirmatory studies, including the dependence of solubilization on the interfacial area of the aggregates, the role of the poly(acrylic acid) corona chains in stabilizing the solubilized molecules, and the effect of the solubilizate structure on the extent of incorporation, were also conducted. The results, consistent with surface localization, show that solubilization is dependent on the interfacial area of the aggregates, and on the affinity of the solubilizate for the micellar interface.

Effect of cation exchange on surfactant-enhanced solubilization of trichloroethene

The objective of this study was to develop the single-well push–pull test as a diagnostic tool for assessing the potential for cation exchange to adversely affect the phase behavior of sodium dihexyl sulfosuccinate surfactant (Aerosol MA 80-I) and its solubilization of trichloroethene (TCE) in the subsurface. Laboratory push–pull tests were conducted on a model natural aquifer sediment collected from a TCE-contaminated field site and a test solution consisting of 36,800 mg/l (3.7 wt.%) sulfosuccinate, 100,000 mg/l (10 wt.%) isopropanol, and 3200 mg/l (0.32 wt.%) KBr. Laboratory experiments were designed to simulate conditions occurring during single-well, “push–pull” tests. In batch experiments conducted in the presence of excess TCE, the test solution gave a Winsor Type I system with an enhanced aqueous TCE solubility of 26,700 mg/l and a solution density of 1.000 g/cm 3. The sulfosuccinate surfactant was transported conservatively in sediment packs containing no TCE. However, increasing concentrations of Ca 2+ and Mg 2+ resulting from cation exchange caused the TCE solubilization potential of the injected surfactant to exceed values predicted from the solubilization isotherm. Sulfosuccinate surfactant transport was strongly retarded in sediment packs containing 5 vol.% residual TCE because cation exchange resulted in the formation of a Winsor Type II system, which resulted in the partitioning of the sulfosuccinate surfactant into the residual TCE phase. Conservative sulfosuccinate transport was observed in a separate sediment pack containing 5 vol.% residual TCE when a 130 meq/l Na + pre-flush was used to reduce quantities of Ca 2+ and Mg 2+ in the sediment pack prior to sulfosuccinate injection. The results of this study emphasize the importance of cation exchange on the performance of surfactant-enhanced TCE solubilization and demonstrate the utility of the push–pull test for predicting the potentially deleterious effects of cation exchange on surfactant phase behavior in the presence of residual TCE.

A Micellar Electrokinetic Chromatographic Method for Determination of Solubilization Isotherms in Surfactant Micelles

We have devised a new micellar electrokinetic chromatographic method for determination of the solubilization equilibrium constants of neutral solutes in surfactant micelles as functions of the intramicellar mole fraction of the solute. In this method, the running solution in a capillary and in electrode vessels contains the neutral solute as well as the surfactant micelles, and the injected solution contains the surfactant micelles and the dilute marker compounds for aqueous and micellar phases but not the solute. The mobility of the solute can be measured from a negative peak recorded on the chromatogram. The solute concentration in the capillary is established, and the mobility of the micellar phase incorporating the solute, which depends on the intramicellar mole fraction of the solute, can be measured from the migration time of the micelle marker. These merits enable precise determination of the solubilization isotherms. This method has been used to study the solubilization equilibria of benzene, phenol, and a series of aliphatic ketones in sodium dodecyl sulfate solution, and the validity and effectiveness of this method for quantifying solubilization have been verified.

Solubilization of Aromatic Solutes in Block Copolymers

Several factors affecting solubilization of aromatic solutes in triblock copolymers (PEO n -PPO m -PEO n or PPO m -PEO n -PPO m ) known to form micelles have been investigated. Solubilization isotherms of toluene, benzene, chlorobenzene, and p-xylene in various aqueous polymeric solutions were determined using head-space gas chromatography. The solute partition coefficient in the polymer, K s , was shown to have a strong dependence on the solute concentration for all polymers. The amount solubilized was at its highest for the high molecular weight, hydrophobic polymers. For the less hydrophobic or lower molecular weight polymers, it was determined that solubilization capacity was a function of the polymer concentration. Comparisons between the different solute solubilization isotherms indicate that PPO-PEO, polymer-water, and polymer-solute interactions have a strong influence on aggregation and solubilization. Finally, the solubilization studies show distinct differences between conventional surfactant micelles and polymeric surfactant micelles, thereby indicating two different solubilization processes. To best understand the mechanism for solubilization in the polymeric surfactant solutions, it was postulated that (1) the addition of apolar solutes promotes aggregation of the polymeric surfactant molecules, (2) the central core of the polymeric micelles contains some water molecules, and (3) solubilization is initially a replacement process in which water molecules are displaced from the micellar core by the solubilizate.

Solubilization Isotherms of Aromatic Solutes in Surfactant Aggregates

Several factors affecting solubilization of aromatic solutes in surfactant micelles have been investigated. Solubilization isotherms of benzene, toluene, and chlorobenzene in various aqueous micellar solutions were determined using head space gas chromatography. Cationic surfactants such as cetylpyridinium chloride or cetyltrimethylammonium bromide present high solubilization capacities. Comparable anionic surfactants exhibit lower solubilization and a greater tendency to precipitate. It was observed that nonionic surfactants show high solubilization on a molar basis. Solubilization in mixed cationic-anionic micelles was also investigated. It also appears that the molecular size of the solute determines the extent of the solubilization. Finally, the shape of the different isotherms indicates that knowing the amount solubilized at saturation of the micellar solution is not sufficient to estimate solubilization at solute concentrations lower than the solute aqueous solubility.

Solubilization of trichloroethylene by polyelectrolyte/surfactant complexes

AbstractAn automated vapor pressure method is used to obtain solubilization isotherms for trichloroethylene (TCE) in polyelectrolyte/surfactant complexes throughout a wide range of solute activities at 20 and 25°C. The polyelectrolyte chosen is sodium poly (styrenesulfonate), PSS, and the surfactant is cetylpyridinium chloride or N‐hexadecylpyridinium chloride, CPC. Data are fitted to the quadratic equation K = K0 (1 − αX + βX2), which correlates the solubilization equilibrium constant (K) with the mole fraction of TCE (X) in the micelles or complexes at each temperature. Activity coefficients are also obtained for TCE in the PSS/CPC complexes as a function of X. The general solubilization behavior of TCE in PSS/CPC complexes resembles that of TCE in CPC micelles, as well as that of benzene or toluene in CPC micelles, suggesting that TCE solubilizes in ionic micelles both within the hydrocarbon micellar interior and near the micellar surface. The presence of the polyelectrolyte causes a small decrease in the ability of the cationic surfactant to solubilize TCE, while greatly reducing the concentration of the surfactant present in monomeric form. PSS/CPC complexes may be useful in colloid‐enhanced ultrafiltration processes to purify organic‐contaminated water.

Substituent group effects on the solubilization of polar aromatic solutes (phenols, anilines, and benzaldehydes) by N-hexadecylpyridinium chloride

Solubilization isotherms of polar aromatic solutes (phenols, anilines, and benzaldehydes) in N-hexadecylpyridinium chloride micelles have been determined at 25{degree}C by using the semiequilibrium dialysis method. Effects of various substituent groups (H, F, Cl, Br, CH{sub 3}O, NO{sub 2}, CH{sub 3}, Et, i-Pr, and CF{sub 3}) have been studied for the solubilization of phenol, aniline, and benzaldehyde derivatives in aqueous solutions of the surfactant. Both hydrophobic and electrostatic effects are shown to be important in influencing the solubilization behavior. The simple expression, K = K{sub 0}(1 {minus} BX){sup 2}, is used to correlate the solubilization equilibrium constant (K) with the mole fraction of solute in the micelles (X). Linear free energy relationships can be used to correlate the solubilization results for the different classes of compounds.

Calculation of organic solute and surfactant activities from solubilization data

Vapor pressure methods developed in our laboratory have produced highly precise solubilization data relating to the interaction of volatile organic compounds with nonvolatile solutes, including ionic surfactants in aqueous solution. By using a computational method similar to one developed previously we can infer the change in activity of the surfactant from solubilization isotherms. The technique, employing a form of the Gibbs-Duhem equation, yields values of the surfactant activity or monomer concentration, independent of any particular mass action model. Results show that surfactant activities inferred from benzene vapor pressure data for aqueous solutions of sodium n-octylsulfate are nearly equal to those calculated previously with a mass-action model. New activity coefficient results (obtained by vapor pressure and vapor pressure osmometry methods) are reported for both the organic solute and the surfactant in several systems containing organic compounds dissolved in aqueous n-hexadecylpyridinium chloride.

Solubilization and catalysis in reversed micelles

Solubilization of soluble or scarcely soluble substances such as water, methanol, acetic acid, propylamine, imidazole and others in reversed micelles was studied from measurements of solubility, vapor pressure, NMR and other physico-chemical properties. The heat of solubilization was used to estimate the interaction of solubilizates with reversed micelles and secondary solubilization. The partition of solubilizates between reversed micelles and solvents, as well as the interaction, was measured by gas chromatography to clarify solubilization phenomenon. Solubilization isotherms were very useful to estimate the interaction and the partition. The effects of solubilization on the catalysis or reversed micelles or the carrier effect of reversed micelles on catalyzing solubilizates was studied for several reactions. The interaction or the partition of solubilizates studied was to a considerable extent related to both effects.

Classification of solubilization isotherms of water by oil—soluble surfactants in nonaqueous solutions

The solubilization isotherms of water by oil-soluble surfactants in nonaqueous solutions could be classified into four types when the relative vapor pressure of water solubilized by the surfactants was plotted against the molar ratio of water to the surfactant. Type I showed an S-shaped solubilization isotherm. Water in the initial stage of solubilization was more firmly bound than in the later stage, the amount of strongly bound water being about one molecule per surfactant molecule. Type II was the most frequently encountered solubilization isotherm and had a concave shape to the vapor pressure axis in the initial stage of solubilization, whereas the later stage was similar to Type I. Type III was similar to Type II except for the range neighboring the saturated water vapor pressure, i.e., the isotherm did not reach the saturated vapor pressure. The isotherm classified as Type IV reached the saturated vapor pressure at small ratio of water to the surfactants and was encountered for the system of more oleophilic surfactants. The classification of solubilization of polar substances by dinonylnaphthalenesulfonates and phenylstearates in nonaqueous solutions reported by Kaufman and Bascom et al. was also tried in connection with that of solubilization of water.