Solubilization Equilibrium Constant Research Articles

Potential of Palm Kernel Alkanolamide Surfactant for Enhancing Oil Recovery from Sandstone Reservoir Rocks

The interest in using benign surfactants has been steadily increasing in the context of enhanced oil recovery (EOR). Palm kernel alkanolamide surfactant (PKA), a nonionic surfactant synthesized from palm kernel oil, was preliminarily assessed for EOR from sandstone reservoir rocks. The performance factors determined were silica adsorption for surfactant loss and crude oil solubilization for oil solubilizing efficiency. The performance of PKA was compared to two commercial ionic surfactants, SDS (anionic surfactant) and CTAB (cationic surfactant). The results show that PKA was less absorbed on silica than CTAB or SDS. The adsorption kinetics were well fit with a pseudo-second order model for all three surfactants. The adsorption equilibrium data for CTAB and PKA were fitted with Langmuir isotherm, while for SDS Freundlich isotherm fit well, indicating multilayer SDS adsorption on silica surfaces. The adsorption of PKA was not significantly affected by added salt or increased temperature. In addition, the solubilization equilibrium constant (Ks) had the rank order PKA > CTAB > SDS, and proportionally increased with added salt. PKA performance was also compared to two commercial nonionic surfactants, Tergitol 15-S-9 and Tergitol TMN-6, and the results indicate that PKA was the least adsorbed, and had the highest Ks among the tested nonionic surfactants.

Predicting organic compound recovery efficiency of cloud point extraction with its quantitative structure–solubilization relationship

Recovery efficiency is an important parameter for cloud point extraction of organic compound, especially in preconcentration and recovery of organic pollutants for further chemical analysis. In this article, based on the solubilization equilibrium constant of organic compounds in aqueous nonionic surfactant micelles solution, a model about the recovery efficiency of cloud point extraction has been set up. A linear correlation between solubilization equilibrium constant and the quantitative structure of organic compounds log P value has been developed, which demonstrates that recovery efficiency can be estimated from the log P value of an organic compound. This prediction fits very well with an experimental result of cloud point extraction of phenolic compounds.

Effect of nonionic surfactant molecular structure on cloud point extraction of phenol from wastewater

Above a temperature known as the cloud point, aqueous solutions of nonionic ethoxylated surfactants separate into two phases: a coacervate phase concentrated in surfactant and a dilute phase with low surfactant concentration. The coacervate phase contains surfactant aggregates which are micelles or micelle-like and will solubilize any organic solutes originally present in the water, resulting in a liquid–liquid extraction known as a cloud point extraction (CPE). Removal of pollutants from water is an important potential application of CPE and we use phenol as a model organic pollutant in this work. In this study, we investigate the effect of surfactant structure on important equilibrium CPE parameters like cloud point, fractional coacervate volume, and phenol and surfactant partition ratios for alcohol ethoxylates (AEs), a major class of nonionic surfactants. Pure, homogeneous surfactants with linear hydrophobes are studied as well as commercial heterogeneous AEs with both linear and branched hydrophobes. The effects of degree of polymerization in the polyethoxylate group (EO number) as well as hydrophobe size (alkyl carbon number) are systematically investigated as well as the effect of hydrophobe branching. The solubilization equilibrium constant is shown to increase linearly with EO number and is unaffected by alkyl carbon number or hydrophobe branching from which we deduce that the phenol is solubilized with the benzene ring at the surface of the micelle core and the hydroxyl group having attractive interactions with the polyethoxylate chains in the palisade layer of the micelle. The effects of surfactant structural features on net intermicellar attractive forces, micellar excluded volume, and solubilization capacity are discussed. A model is developed which can predict the phenol partition ratio at a given temperature for any AE surfactant dependent on only one simple measured parameter: fractional coacervate volume. This universal model is somewhat unique to phenolics or short chain alcohols because of their solubilization loci in the micelle and mechanism of solubilization. Guidelines for surfactant selection for CPE of phenol or similar solutes are outlined.

Colloid-Enhanced Ultrafiltration of Chlorophenols in Wastewater: Part III. Effect of Added Salt on Solubilization in Surfactant Solutions and Surfactant–Polymer Mixtures

ABSTRACTThe solubilization of three phenolic solutes in micellar solutions and surfactant–polymer mixtures is studied: 2-monochlorophenol (MCP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP). The equilibrium dialysis (ED) technique is used to determine the solubilization equilibrium constant as a function of added NaCl concentration. The added salt enhances the solubilization ability of surfactant micelles, but it only slightly affects the solubilization constant of surfactant–polymer aggregates. The solubilization constant for the surfactant–only systems is greater than that for the surfactant–polymer systems. In the micellar solution, the solute with a low water solubility shows a greater solubilization constant than the solute with a higher water solubility; the solubilization constants increase in the order MCP < DCP < TCP. However, in the surfactant–polymer mixtures, the solubilization constant of DCP can exceed that of TCP due to two opposing effects: ion-dipole interaction, and water solubility or hydrophobicity. Understanding and quantifying this solubilization phenomenon is crucial to optimization of the performance of colloid-enhanced ultrafiltration separation processes.

Electrochemical Control of Vesicle Formation with a Double-Tailed Cationic Surfactant Bearing Ferrocenyl Moieties

We already reported spontaneous vesicle formation in aqueous solutions of bis(11-ferrocenyl(undecyl))dimethylammonium bromide (11-BFDMA), a newly synthesized ferrocene-modified double-chain-type cationic surfactant (Kakizawa, Y.; Sakai, H.; Nishiyama, K.; Abe, M. Langmuir 1996, 12, 921.). We have examined in this study electrochemical control of vesicle formation of 11-BFDMA using the redox reaction of ferrocenyl groups in their molecules. Static light scattering, conductivity, and cyclic voltammogram measurements on the solution revealed that vesicles made of the reduced form of 11-BFDMA disintegrate and change into smaller molecular aggregates including micelles through oxidation of ferrocenyl groups. Oxidation of ferrocenyl groups also caused a remarkable decrease in the solubilization equilibrium constant for benzene in 11-BFDMA solution and release into the bulk phase of benzene solubilized in bimolecular layers of 11-BFDMA vesicles. In addition, glucose entrapped in the inner aqueous phase of the ve...

Flux and retention analysis during micellar enhanced ultrafiltration for the removal of phenol and aniline

Studies were done for the removal of organic solutes under aqueous medium through micellar enhanced ultrafiltration (MEUF). The organic solutes selected for experiments consisted of an ionic compound (phenol) and a non-ionic compound (aniline); whereas cetyl pyridinium chloride (CPC), a counter-ionic surfactant was used for the formation of micelles under aqueous medium. UF was carried out under both stirred and unstirred conditions using batch cells. The effect of important operating parameters (applied pressure, solutes and surfactant bulk concentrations) on the extent of separation of the organic solutes were observed and studied. Solubilization of these solutes in CPC micelles were also experimentally ascertained. A mathematical model developed in this study was used to describe the separation of organic solutes by MEUF and predict permeate solute concentrations under varying operating conditions. The effect of pressure and feed CPC concentration on the behaviour of permeate flux was explained as a consequence of the formation of concentration polarized layer of CPC, upstream of the membrane surface. The removal of organic solutes (phenol and aniline) were observed to increase with increase in feed CPC concentration; however, upto about 150 mM, beyond which it was more or less constant. Solubilization equilibrium constant of phenol in CPC micelles was estimated to be around four times that of aniline.

Electrochemical control of solubilization using a ferrocene-modified nonionic surfactant

An investigation was conducted on the control of solubilization making use of changes in the surface properties caused by the electrochemical redox reaction of 11-ferrocenylundecyl polyoxyethylene ether (FPEG), a ferrocene-modified nonionic surfactant, in aqueous solutions. Examinations through surface tension measurement of the effect of the redox reaction of the ferrocenyl group on the critical micelle concentration (cmc) of FPEG showed that the oxidation produces an increase in the cmc from 6×10 −6 to 5×10 −5 mol l −1 and the re-reduction causes the cmc to decrease from 5×10 −5 to 9×10 −6 mol l −1. The effect of the redox reaction of the ferrocenyl group was then examined on the solubilization equilibrium constant, K, for solubilization of benzene, ethylbenzene and 2-phenylethylalcohol in FPEG micelles. The equilibrium constant was found for all solubilizates to decrease when the ferrocenyl group is oxidized and increase again if the group is re-reduced, indicating that oxidation of the ferrocenyl group releases portions of the solubilizate from the micelles into the bulk and the re-reduction gives rise to re-solubilization of the released solubilizate.

Use of a Surfactant Coacervate Phase To Extract Chlorinated Aliphatic Compounds from Water: Extraction of Chlorinated Ethanes and Quantitative Comparison to Solubilization in Micelles

At temperatures above the cloud point, aqueous solutions of nonionic surfactants separate into a coacervate phase and a dilute phase. The distribution of di-, tri-, and tetrachloroethanes between these phases was shown to increasingly favor the coacervate phase as the hydrophobicity (degree of chlorination) of the solute increases. The solute solubilization equilibrium constant was shown to be very similar for solubilization into coacervate surfactant aggregates compared to micellar solubilization per aggregated surfactant molecule for octylphenol polyethoxylate surfactants and to increase with increasing temperature and increasing solute hydrophobicity. As temperature increases above the cloud point, the partition ratio increases primarily because the concentration of surfactant in the coacervate increases, second because the solubilization equilibrium constant in the coacervate surfactant aggregate increases, and third because the concentration of micellized surfactant (and solubilization therein) in th...

Electrochemical Control of Solubilization by Redox-Active Surfactants

The solubilization of organic molecules in surfactant molecular assemblies may be controlled effectively by electrochemical reactions using redox-active surfactants. In this study, several aromatic compounds were solubilized in aqueous micellar solution of ferrocene-modified nonionic surfactant (11-ferrocenylundecyl polyoxyethylene ether : FPEG) and the effects of redox reactions on solubilization were examined. The solubilization equilibrium constant (K) of the solutes in FPEG micelles, which represents the distribution of solubilizates between micelles and bulk solution, was noted to decrease with the oxidation of ferrocenyl moieties of FPEG molecules, but increase with reduction of ferrocenyl moieties. Electrochemical control of vesicle formation and applications for solubilization control were investigated using aqueous mixtures of a ferrocene-modified cationic surfactant (FTMA) and anionic sodium dodecylbenzene sulfonate (SDBS).

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.

Redox Control of the Solubilization of Benzene with a Ferrocene-Modified Nonionic Surfactant

Benzene was solubilized in aqueous micellar solutions of a redox-active nonionic surfactant (11-ferrocenylundecyl polyoxyethylene ether : FPEG) and the effect of the redox reactions on the solubilization is studied. The solubilization equilibrium constant (K) of benzene in FPEG micelles, which represents the distribution of solubilizates between micelle and bulk solution, was found to decrease with the oxidation of ferrocenyl moieties of FPEG molecules, but to increase with reduction in ferrocenyl moieties. Active and reversible control of solubilization is thus shown possible through application of the redox reactions of FPEG micellar solution.

Solubilization by Various Surfactant Solutions and Applications to Separation Technology

Solubilization phenomena of various organic solutes by surfactant solution was reviewed. The interpretation of intramicellar solubilization data obtained from semi-equilibrium dialysis (SED), head-space gas chromatography (HSGC), and solute vapor pressure methods (SVP) are presented for determining equilibrium constants for the solubilization of organic species by aqueous surfactant solutions as well as activity coefficients of both the organic solute and the surfactant within the micelle. The solubilization equilibrium constant of an organic solute in an aqueous micellar solution (K) is defined as the ratio of the mole fraction of organic solute in the micellar 'pseudophase' (X) to the concentration of the unsolubilized monomeric organic solute in the aqueous phase (Cp). The simple empirical expression K=K0 (1-αX+βX2) is used to correlate the solubilization equilibrium constant (K) with the mole fraction of the organic solute in the surfactant aggregates (X). Water-soluble polyelectrolyte/surfactant complexes, involving oppositely charged species, can form at quite low thermodynamic activities of the surfactant. This fact is exploited in colloid-enhanced ultrafiltration separations, where both molecular organic pollutants and toxic ions are to be removed from contaminated aqueous streams.

Effect of Temperature on Solubilization of Aromatic Compounds by Didodecyldimethylammonium Bromide Vesicles.

The solubilization of aromatic compounds (phenol, benzoic acid, benzene, ethylbenzene) in the aqueous solutions of didodecyldimethylammonium bromide (DDAB) vesicles was investigated as a function of temperature by measuring the solubilization equilibrium constants (K vesicle ), the microviscosity of the vesicle bilayer membrane, and the degree of the dissociation (α) of the counter-ion from the vesicle. Benzene and ethylbenzene are only sligthtly solubilized below the temperature of 8°C, and K vesicle between the DDAB vesicle and the bulk aqueous phase shows an abrupt increase at the temperature range 8∼10°C, The fluorescence measurement indicates that the phase transition temperature (Tc) of the DDAB vesicle is about 9.5°C. The solubilization of benzene and ethylbenzene will depend on the microviscosity of the vesicle bilayer membrane. The comparison of K vesicle with the partition coefficient (Kdodecane) of the aromatic solute between the n-dodecane phase and the water phase suggests that the benzene molecule is solubilized at the vesicle surface where the π electron cloud of the benzene interacts with the changed surfactant head groups, and that the ethylbenzene molecule is located inside the bilayer membrane. On the other hand, K vesicle values of phenol and benzoic acid exhibit a maxima at ca. Tc of DDAB, and the α value of the vesicle also has a maximum around Tc. It is thought that the solubilization of phenol and benzoic acid depends on the degree of the DDAB vesicle charge, and these polar solutes are located at the vesicle surface because the polar groups are attracted electrostatically to the charged head groups of DDAB.

非イオン界面活性剤ミセル水溶液における合成香料の可溶化平衡定数

ポリオキシエチレン (POE) 鎖長 (n) の異なる4種類の非イオン界面活性剤 {ヘキサデシルポリオキシエチレンエーテル (C16POEn;n-10, 20, 30, 40)} を用いた合成香料 {2-フェニルエチルアルコール (PEA), ベンジルアセテート (BA), d-リモネン (LN)} の可溶化を, 可溶化平衡定数およびミセル粒子径の測定から検討した。香料の可溶化平衡定数は, 非イオン界面活性剤のPOE鎖長あるいは香料のHLB値の増加に伴い減少した。ミセル中におけるPEAの活量係数は他の香料よりかなり小さく, 0.1～0.2であった。また, 香料1分子を可溶化するのに必要な界面活性剤の分子数 (2B値) は, LNの場合0.7～1.0, BAの場合0.4～1.0, PEAの場合1.7～2.8であった。さらに, C16POE10ミセルの粒子径はPEAの可溶化量の増加に伴い増大した。これらのことから, PEAはLNやBAに比べ, より強くミセル親水部のPOE鎖 (親水基) に吸着し, POE鎖の脱水和を誘起することが示唆された。

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.

On the interpretation of solubilization results obtained from semi-equilibrium dialysis experiments

The interpretation of intramicellar solubilization data obtained from semi-equilibrium dialysis (SED) experiments is described, and methods are presented for determining equilibrium constants for the solubilization of organic species by aqueous surfactant solutions as well as activity coefficients of both the organic solute and the surfactant within the micelle. The solubilization equilibrium constant of an organic solute in an aqueous micellar solution (K) is defined as the ratio of the mole fraction of organic solute in the micellar “pseudophase” (X) to the concentration of the unsolubilized monomeric organic solute in the aqueous phase (c0). Expressions compatible with the Gibbs-Duhem equation are used to represent the concentration dependence of activity coefficients of both the solubilizate and surfactant in the micellar pseudophase; the analysis leads to calculated values of the concentrations of free and intramicellar surfactant and organic solute in both compartments of the equilibrium dialysis cell. Solubilization equilibrium constants for many amphiphiles are well correlated by the simple expressionK=K0(1-BX)2, whereB is an empirical constant andK0 is the limiting value ofK asX approaches 0.

Solubilization of Perfume Compounds by Pure and Mixtures of Surfactants

The solubilization of two perfume compounds, 2-phenylethanol (PEA) and benzyl acetate (BA), was studied by using an anionic surfactant (sodium dodecyl sulfate, SDS), a nonionic surfactant (hexadecyl polyoxyethylene ether, C 16POE 20), and mixed anionic-nonionic micelles (SDS/C 16POE 20). In order to study the distribution of perfume compounds between the micelle and bulk phases, the solubilization equilibrium constants (distribution constant) were determined as functions of the intramicellar mole fraction of perfume compounds by using the semi-equilibrium dialysis method. The results of the present study show that (1) two or three surfactant molecules may on the average provide a location for the attachment of a PEA molecule in the single surfactant system, (2) BA molecules presumably bind somewhat more weakly to water and other polar groups in the hydrophilic group region of the single surfactant micelle, and (3) the solubilization equilibrium constants for the mixed surfactant system are smaller than predicted by linear or additive mixing rules applied to the single-component surfactant equilibrium constants, indicating that the compactness of the hydrophilic region of the mixed micelle may reduce the number of solubilization sites for the solutes in the micelle as a result of the hydrophilic interaction between the oxygen atoms of anionic surfactant and the ethylene oxide chains of nonionic surfactant.

Solubilization of 2-phenylethanol by dodecyldimethylamine oxide in aqueous solution

The solubilization of 2-phenylethanol (PEA) was measured over a wide range of solute activities and pH values by using dodecyldimethylamine oxide (DDAO) as the surfactant. The DDAO in micellar form is all cationic (protonated) at low pH and all nonionic at high pH. At intermediate pH levels, the DDAO forms mixed micelles containing both the cationic and nonionic forms of surfactant. Thus, measurement of the solubilization of PEA as a function of pH produces solubilization data as a function of mixed micelle composition for this amphoteric surfactant. The solubilization equilibrium constant was found to decrease with increasing mole fraction of PEA in the micelle for all pH values and to be less in the mixed micelles than in either pure cationic or pure nonionic micelles. This latter effect could be due to the hydrophilic region of the mixed micelle being more compact than that of the single-component micelles.

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.

Solubilization of mono-and dichlorophenols by hexadecylpyridinium chloride micelles. Effects of substituent groups

Semiequilibrium dialysis measurements have been made to determine solubilization equilibrium constants and activity coefficients of mono- and dichlorophenols in aqueous solutions of hexadecylpyridinium chloride (CPC) at 25{degree}C. Solubilization equilibrium constants (which relate the concentration of solubilizate in the micelle to the concentration of free organic in the bulk solution) are well correlated by the expression K = K{sub 0}(1 {minus} BX){sup 2}, where B is an empirical constant, K{sub 0} is the limiting value of the solubilization constant, and X is the mole fraction of the phenol present in the surfactant micelles.