Equilibrium Aqueous Phase Research Articles

Laboratory measurements of the aqueous solubility of mixtures of chlorinated solvents

AbstractThis article describes the results of laboratory batch solubility experiments with five chlorinated solvents (chloroform, carbon tetrachloride, 1,1,1‐trichloroethane, trichloroethylene, and tetrachloroethylene) present alone or in binary or ternary mixtures. The measured aqueous solubility values of the pure compounds revealed significant deviation from the widely used literature values for trichloroethylene and tetrachloroethylene. The experiments with binary and ternary solvent mixtures showed that the chlorinated solvents used in this study exhibited close to ideal behaviour. That means the concentration of an organic compound in the aqueous phase in equilibrium with an organic phase can be described as the mole fraction in the organic phase times the aqueous solubility of the pure compound. The UNIFAC (universal quasi chemical functional group activity coefficients) method was used in this study to estimate the appropriate activity coefficients for the experiments with binary mixtures. The UNIFAC method predicted nonideal behaviour for some of the mixtures. However, the deviation was only significant at relatively low mole fractions. Experiments indicated that the assumption of ideal behaviour for the chlorinated solvents used in this study is a reasonable one. The assumption of ideal behaviour simplifies the use of models to simulate the dissolution of chlorinated solvent mixtures in ground water.

Mercury removal from aqueous streams utilizing microemulsion liquid membranes

AbstractThe goal of this work is the removal of mercury ion from wastewater using thermodynamically stable microemulsions as liquid membranes. The research focuses on identification and modeling of the appropriate aqueous and organic phase equilibrium reactions for mercury extraction and stripping, comparison of extraction kinetics between coarse emulsions and microemulsions, and demulsification and recovery of the emulsion components. An oleic acid microemulsion liquid membrane (water‐in‐oil) containing sulfuric acid as the internal phase reduces the feed phase mercury concentration from 460 mg/l to 0.84 mg/l in a single contacting. This compares favorably with a control extraction (oleic acid/no internal phase) which results in a final concentration of 20 mg/l Hg+2. Microemulsions can be demulsified using butanol as an additive. The demulsification kinetics are proportional to butanol concentration and temperature and inversely proportional to surfactant concentration. The demulsification rate is second order with respect to water concentration which implies that the rate‐limiting step in the process is the rate of internal phase droplet encounters. Proof‐of‐principle experiments demonstrate the ability to extract mercury ion using microemulsions formulated with recycled organic phase, albeit at a somewhat reduced efficiency. The reduced efficiency is attributed to increased internal phase leakage due to residual butanol in the oil phase. Finally, the cycle is brought around full circle by recovering metallic mercury from the internal phase by electroplating.

Extraction of cytochrome c in sodium dodecylbenzenesulfonate microemulsions.

The partition of cytochrome c between an aqueous phase in equilibrium with a microemulsion composed of sodium dodecylbenzenesulfonate, butanol, and decane was studied. By adjusting the pH and the ionic strength in the aqueous phase, cytochrome c can be quantitatively extracted in the microemulsion as long as the protein concentration in the organic phase is less than the initial concentration of micelles. Above this limit, an intermediate phase, containing part surfactant and part cytochrome c, is located between the aqueous and microemulsion phases. The role of electrostatic interactions in the protein partitioning is shown by varying the composition of the phases (pH, salinity, surfactant, and cosurfactant concentrations) and then discussed. Extraction depends on the relative values of the pH of the aqueous phase and the pI of cytochrome c, the size of the micelles, and the protonation of acidic residues. Cytochrome c can be recovered in an aqueous phase by adding butanol in the microemulsion phase. In such conditions, cytochrome c retains 90% of its initial activity, as measured before the extraction step.

The octanol/water distribution coefficients of methylmercuric species: The role of aqueous‐phase chemical speciation

AbstractA model is proposed that quantitatively describes the 1‐octanol/water distribution coefficients of methylmercuric species in terms of the 1‐octanol/water partition coefficients of each individual methylmercuric species (i.e., CH3HgCl0, CH3HgOH0, and CH3Hg+) and the aqueousphase equilibrium speciation of the methylmercuric species CH3HgCl0, CH3HgOH0, and CH3Hg+.

Preparation and purification of Semi-Methylthymol Blue

A direct extractive method has been developed for preparation of pure Semi-Methylthymol Blue (SMTB) from a synthetic mixture containing ca. 30% of SMTB in presence of Thymol Blue (TB, ca. 45%), Methylthymol Blue (MTB, ca. 10%) and other components such as acetic acid and iminodiacetic acid (IDA). The method is based on the dependence of the extraction coefficients of the individual components on the pH of an aqueous phase in equilibrium with butanol phase. The separation of TB from the mixture is best at pH 9.5–10.5 and the separation of SMTB is best at pH 2.9–4.5. At pH 10.2 the ratio of the extraction coefficient of TB to that of SMTB is 213 and to that of MTB is 776. At pH 2.9 the ratio of the extraction coefficient of SMTB to that of MTB is ca. 20 and at pH 4.5 is ca. 100, but the absolute values of the extraction coefficient for SMTB are only 3.4 at pH 4.5 and ca. 10 at pH 2.9. This means the quantitative transfer of SMTB to the butanol phase is much easier at pH 2.9. Then a more complete separation of SMTB from the mixture with MTB can be achieved by stripping of the latter into a pH 4.5 aqueous medium. The method for obtaining of anhydrous SMTB is also given. About 70% of the original amount SMTB present can be obtained as the dry product (containing over 99% SMTB).

Desorption and Unavailability of Aged Simazine Residues in Soil from a Continuous Corn Field

AbstractThe sorption/desorption behavior of field weathered (aged) simazine (2‐chloro‐4,6‐bis(ethylamino)‐s‐triazine) residues from a 20‐year continuous corn (Zea mays L.) field was compared to that of 14C‐simazine recently added to the same soil. The apparent sorption coefficients of the aged residues determined from 24‐h and 48‐h desorption experiments were approximately 15 times higher than the sorption coefficients of added simazine. Aged simazine residues were also shown to be biologically unavailable to sugarbeet (Beta vulgaris L.) and to microbial degraders, whereas recently added simazine showed herbicidal damage to sugarbeet and was substantially (ca. 48%) degraded during a 34‐d incubation in soil. Apparently, the process of pesticide aging results in simazine residues that are less bioavailable, as shown by their resistance to plant uptake and microbial degradation, and that desorb slowly into soil solution. The concentration of simazine in water from field soil‐samples (C) was monitored throughout a growing season, and compared to the equilibrium aqueous phase concentration (Cc) predicted from the laboratory determined sorption coefficient (Koc of added 14C‐simazine. The fractional equilibrium values (C/Ce.) were approximately 1 at the time of simazine application in May but fell to 0.05 during July and August. These results show that the concentration of simazine in water contacting field soil is likely to be substantially lower than that predicted from laboratory determined sorption coefficients, except immediately following application.

Bile salt micelle can sustain more cholesterol in the intermicellar aqueous phase than the maximal aqueous solubility

The intermicellar aqueous phase in equilibrium with micelle plays an important role in the uptake of sterol. To test the hypothesis whether cholesterol concentration in the intermicellar aqueous phase of a micellar solution is similar to its maximal aqueous solubility, cholesterol concentration in the intermicellar aqueous phase of a bile salt-cholesterol solution and maximal aqueous cholesterol solubility were quantitatively determined by capillary gas-liquid chromatography after filtration. Cholesterol concentration in the intermicellar aqueous phase increased linearly with cholesterol concentration in the micellar solution and reached 1.3 μ m at its micellar solubility limit, while the maximal aqueous solubility of cholesterol was (1.2–1.4) × 10 −8 m. The intermicellar monomer concentration of taurocholate was 5.8 m m in which 26 × 10 −8 m cholesterol was solubilized. The results indicate the presence of a cholesterol concentration in the intermicellar aqueous phase that is significantly higher than its maximal aqueous solubility, which can be ascribed primarily to the presence of an intermicellar concentration of bile salt.

Solubility and Aging of Calcium Silicate Hydrates in Alkaline Solutions at 25°C

Calcium silicate hydrate (C‐S‐H) gels are the principal bonding material in portland cement. Their solubility properties have been described, enabling pH and solubilities to be predicted. However, the gels also interact with other components of cements, notably alkalis. C‐S‐H has been prepared from lime and silicic acid in solutions of sodium hydroxide or potassium hydroxide and by the hydration of tricalcium silicate (C3S) in sodium hydroxide solutions. Analyses of aqueous phases in equilibrium with 85 gels show that the aqueous calcium and silicon concentrations fit smooth curves over the range of increasing sodium concentrations. Where anomalous data occur, they correspond to solids with low lime contents: such gels are tentatively assumed to fall into a region where the presence of another gel phase influences the aqueous composition. Dimensional changes have been observed in the hydration products of C3S as a function of alkali content and these may be relevant to the alkali‐silica reaction. The significance of this and other data is discussed with reference to real cement systems.

Quaternary Cation Exchange on Silver Hill Illite

AbstractThe simultaneous exchange of Na, K, Ca, and Mg on Silver Hill illite suspended in 5 mol m−3 perchlorate background at pH 7 was investigated systematically. Composition data for both the exchanger and the equilibrium aqueous solution phase were obtained directly. The data showed that the total adsorbed metal charge was independent of exchanger composition provided that all four cations were considered. Analysis of the composition data with exchange isotherms and calculated Vanselow selectivity coefficients showed that: (i) K+ was preferred over Na+, Ca2+, and Mg2+, and the preference decreased as EK decreased (E = charge fraction on the clay mineral); (ii) bivalent cations were preferred only slightly over Na+ for ENa > 0.01, whereas for ENa ≤ 0.01, the reverse was true; (iii) no preference was shown in Ca‐Mg exchange at ENa values between 0 and 0.13.

The equilibrium composition of hydroxyapatite and fluorapatite—water interfaces

Abstract Chemical models describing the composition of the aqueous phase in equilibrium with hydroxy-apatite and fluorapatite solids have been established. The effect of atmospheric CO 2 contamination on the composition of these interfaces has been demonstrated. From these models, the amount of acid or base needed to maintain a given pH, the potential determining ions, and the points of zero net charge could be determined. Thus, the point of zero net charge for hydroxyapatite in water at equilibrium is at pH 8.65, which shifts to pH 7.05 if the system is allowed to contact atmospheric carbon dioxide. For fluorapatite the point of zero net charge is at pH 6.45 when air is present. Various aspects of apatite dissolution are also discussed.

Distribution and monomer activity of cholesterol in micellar bile salt: effect of cholesterol level.

Despite the fact that uptake of cholesterol by the enterocyte occurs as a monomer from the intermicellar aqueous phase in equilibrium with micelle, the cholesterol monomer concentration in the aqueous phase and the partition coefficient between intermicellar aqueous phase and micellar aggregate have not been clarified. The present study deals with the distribution of cholesterol and monomer activity in constant bile salt-fatty acid micellar solutions with different cholesterol concentrations. In addition, uptake of cholesterol from these micellar solutions into rat jejunum was studied using everted sacs. Cholesterol monomer concentration in the aqueous phase increased linearly with the concentration of cholesterol in the micellar solution. Partition coefficient of cholesterol between the aqueous phase surrounding micelle and micellar aggregate was essentially constant at any cholesterol level (K = 3 X 10(-2)). Cholesterol monomer activities were linearly proportional to the cholesterol concentrations in the micellar solutions and correlated well with the rate of cholesterol uptake. It is concluded from these experiments that a partitioning phenomenon determines cholesterol monomer concentrations in the intermicellar aqueous phase from which the cholesterol is absorbed. After disappearance of the cholesterol monomers from the aqueous phase, these monomers are replaced by a shift of monomers from the intramicelle to intermicellar aqueous phase, under constant partition coefficient between extra- and intramicelle. The bile salt micelle provides a huge reservoir for partitioning of cholesterol monomers.

Chemical equilibrium studies on the iron(III)-sulfuric acid/β-alkenyl 8 hydroxy-quinoline-xylene system

A thermodynamic equilibrium model is developed for the distribution of iron(III) between phases of the system ferric sulfate-sulfuric acid/β-alkenyl-8-hydroxyquinoline in xylene. Equilibrium data are obtained in the range [Fe]T (0.01 to 0.20 mol/dm3), pH (0.2 to 2.0), [HR] (0.02 to 0.06 mol/dm3) and temperatureT(298 to 323 K). The best fit of the data from a linear regression results in the following equation: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaO% qaaiGacYgacaGGUbWaaSaaaeaadaWadaqaamaanaaabaGaamOraiaa\(\ln \frac{{\left[ {\overline {FeR{}_3} } \right]\left[ {H^ + } \right]^3 }}{{\left[ {Fe^{ + 3} } \right]\left[ {HR} \right]^3 }} = 8.79 + 2623\left( {\frac{1}{T} - \frac{1}{{298}}} \right) + 0.79 I^{0 5} \) The regression analysis employs the aqueous phase ionic concentration of [Fe+3] and [H+], which are obtained by consideration of pertinent aqueous phase species equilibria. This model includes the effects of ionic strength on the aqueous phase equilibrium concentration. The stoichiometry of the given reaction is established using the method of continuous variation. Presence of only one species in the organic phase is also determined by the method of continuous variation. The results indicate that the enthalpy of the reaction and the entropy change are −21.8 kJ/mole and −0.05 J/mole K, respectively.

Determination of ionic charge by liquid—liquid partition

The possibility of determining the net charge of ionic substances by studying their partition between two liquid aqueous phases in equilibrium has been investigated. The partition has been influenced by including there different salts in the systems; viz., sodium sulphate, sodium chloride perchlorate. In aqueous dextran—polyethylene glycol systems, the difference between the logarithms of partition coefficients determined for systems containing two different salts, is proportional to the net charge of the ionic molecule present at low concentration. This offers a simple way to determine the net charge of the water-solvated ion by liquid—liquid partition. Simple ions and organic acids and bases as well as dyes and proteins have been investigated. Deviations in the net charges, determined by partition, from the expected values are discussed in the light of the known properties of solvated ions.

The influence of hydrophobic ions and dipolar molecules on the electrostatic barrier in biomembranes

To calculate the electric field inside a membrane the aqueous phase can be approximated by a conductor since the dielectric constant of water is much larger than that of the membrane. Then, using the method of image charges, ions adsorbed inside the membrane can be considered as dipoles and dipolar molecules adsorbed inside the membrane may similarly be regarded as sets of two similarly oriented dipoles. The microscopic interactions and, therefore, the spatial correlations of the adsorbed species can then be obtained. Together with the Gouy theory for the diffuse double layer these results allow the determination of the adsorbed phase—aqueous phase equilibrium. From the densities and spatial correlations of the adsorbed ions and dipolar species, their influence upon the electrostatic barrier as experienced by an ion translocating the membrane can be calculated. Changes observed in the relaxation time and initial conductance of translocating hydrophobic ions in voltage-pulse experiments on bilayer membranes are predicted using this model of the electrostatic barrier. In addition, an equation giving the surface tension as a function of the (non-ideal) adsorption of hydrophobic ions and dipoles is derived.

SOLVENT EXTRACTION OF VANADIUM (V) FROM AQUEOUS SOLUTIONS BY PRIMARY AMINES

Vanadium (Ⅴ) can be quantitatively extracted by primary amines from nearly neutralchromium (Ⅵ) containing aqueous solutions Under similar conditions wtth equilibriumaqueous phase pH above 7, no vanadium can practically be extracted by tertiary amines whileextraction by secondary amines is only about 25--30%. The quantitative extraction of vana-dium from aqueous solutions containing no chromium (Ⅵ) can be obtained by adding acidto the extent that the ratio of gram equivalents of H~+ added to the gram atoms of vanadiumin the apueous solution is equal to one or slightly higher. The mechanism of axtraction isbelieved to be solvation with molecular association between primary amines and tetravanadicacids through hydrogen bonding.

Influence of alkyl chain length compatibility on microemulsion structure and solubilization

The solubilization capacity of water/oil microemulsions formed with fatty acid soaps and alcohols was studied as a function of alkyl chain length of oil (C 8 to C 16), soap (C 14 and C 18), and alcohol (C 4 to C 7). For n-butanol with both soaps, the maximum amount of water solubilized in the microemulsion continuously decreased with increasing oil chain length whereas for n-heptanol the solubilization capacity continuously increased. For pentanol with both soaps and for hexanol with sodium stearate, the solubilization reached a maximum when the oil chain length, l o, plus that of the alcohol, l a, was equal to that of the surfactant, l s, (i.e., l a + l o = l s). When excess water was added to these systems, a birefringent aqueous phase in equilibrium with an isotropic upper phase formed if l a + l o < l s whereas a different phase behavior, namely, the formation of two isotropic phases, was observed if l a + l o ⩾ l s. Both of these observations indicate a chain length compatibility effect similar to that observed in monolayers, foams, emulsions, and lubricants. The solubilization behavior is interpreted in terms of partitioning of alcohol among oil, water, and the interface depending upon the chain length of oil and alcohol, as well as in terms of molecular packing at the interface in relation to the disorder produced by the chain length compatibility effect. It was concluded from the oil-alcohol titration study that the molar ratio of alcohol to soap at the interface increases with oil chain length. We propose that the increase in the alcohol/soap molar ratio leads to increased spacing between carboxyl groups resulting in a greater degree of ionization. Electrical resistance and dielectric constant measurements yielded results consistent with this interpretation. At a given water/oil ratio, the electrical resistance of microemulsions decreases, the dielectric constant increases, and the thickness of ionic atmosphere within the water droplets increases as the oil chain length is increased. These phenomena are consistent with the concept that microemulsions form, and vary their structure, under the influence of surfactant and alcohol partitioning between aqueous and oleic phases and the consequent interfacial activity of both species. Here, the partitioning of alcohol and soap is subtly varied by changing the oil chain length.

A Mathematic Model of Distribution Equilibria in the Extraction of U(VI), U(IV), Pu(IV), Np(VI), Np(IV), and Nitric Acid by 30% Tributyl Phosphate (TBP) in Aliphatic Diluents

AbstractEmpiric equations are suggested for the calculation of the distribution ratios of U(VI) (also in the presence of Pu(IV) or U(IV)), U(IV) (also in the presence of U(VI)), Pu(IV) (also in the presence of U(VI)), Np(IV) and Np(VI) (also in the presence of U(VI)) and HNO3 (also in the presence of U(VI) and Pu(IV)) in the extraction with 30% TBP in an individual or mixed aliphatic diluent from nitric acid solutions. The distribution ratios are calculated from concentrations of HNO3, U(VI), and Pu(IV) (or some of them) in the equilibrium aqueous phase.

Cosurfactants in Micellar Systems Used for Tertiary Oil Recovery

Abstract The influence of alcohols used as cosurfactants on several micellar systems was investigated. These alcohols modify phase behavior and control the amount of brine or hydrocarbon that a microemulsion can "solubilize." Also, viscosity can be adjusted using the right cosurfactant for mobility control. Relationships between cosurfactant concentration and electrolyte concentration, hydrocarbon type, or temperature are presented. Introduction Micellar slugs used as oil-displacing agents in extra-oil recovery projects are usually composed of surfactant(s), hydrocarbon, water, electrolyte, and one or more alcohols that serve as cosurfactants. Physicochemical properties of these systems have Physicochemical properties of these systems have been presented by several authors; phase behavior has received special attention. Such emphasis is justified because of displacement-mechanism considerations and micellar-slug deterioration by reservoir rock and fluids. Other work has been concerned with defining the role of particular sulfonates in oil displacement and loss of surfactant to reservoir rock. Healy et al. presented detailed analyses of a single surfactant/cosurfactant combination in micellar systems and laboratory oil recovery experiments. Papers have presented qualitative information on the role of cosurfactants. Gogarty and Tosch found that the amount of 2-propanol (IPA) required to produce phase-stable systems depended on produce phase-stable systems depended on hydrocarbon type. They and others reported that IPA makes a micellar slug more compatible with reservoir brines, whereas oil-soluble alcohols enhance compatibility with crude oils. Cosurfactants have various effects on viscosity; IPA usually causes a reduction. Healy and Reed noted a decrease in viscosity upon addition of tertiary amyl alcohol (TAA). For the system examined, TAA increases the size of the water-external region in the ternary phase diagram. Others have reported that cosurfactants increase water solubility of sulfonates and reduce adsorption on reservoir rock. Although cosurfactants have been shown to perform a variety of functions, no systematic quantitative study of their effect on physicochemical properties of micellar systems has appeared in the petroleum literature. This paper will show how cosurfactants affect phase behavior, control hydrocarbon and brine solubility, interact with electrolyte concentration, and change viscosity and electrical conductivity. Systems examined include a low-water-concentration, oil-external microemulsion; a water-external microemulsion; and "intermediate" systems for which the continuous phase is not clearly defined. Each type of micellar system has been tested in field applications of the Maraflood oil recovery process. process. MATERIALS AND METHODS Compositions of the six micellar systems studied are shown in Table 1, which also indicates the source and equivalent weight of the petroleum sulfonate surfactants used. Table 2 lists information about the alcohols used as cosurfactants. Viscosities were measured at 72 deg. F and at 3 or 6 rpm with a Brookfield Model LVT viscometer equipped with a UL adaptor. Shear rates at this speed are about 5 to 10 sec-1. All phase-behavior experiments were performed at 72 deg. F, with the exception of the relationships shown in Fig. 11. Systems were observed for a minimum of 24 hours. PHASE BEHAVIOR WITH ALCOHOL PHASE BEHAVIOR WITH ALCOHOL Alcohols as cosurfactants modify the phase behavior of a brine-hydrocarbon-surfactant micellar system. For example, Composition A in Table 1, composed of an oleophilic surfactant (470-equivalent-weight petroleum sulfonate), 28-weight-percent water, petroleum sulfonate), 28-weight-percent water, and hydrocarbon (light, straight run gasoline), separates into an aqueous phase in equilibrium with a microemulsion phase. SPEJ P. 161

Effect of Age on Ultracentrifugal Stability of Liquid Petrolatum-Water Emulsions

The effect of aging over 135 days on the rate of separation of oil from 50% liquid petrolatumce:inf>50% water emulsions with both 0.2 and 0.4% sodium dodecyl sulfate (based on the water) was determined in an ultracentrifuge at 25° and 39,460 r.p.m. The concentration of sodium dodecyl sulfate in the equilibrium aqueous phase was also determined. The stability of the emulsion with 0.2% sodium dodecyl sulfate decreased for the first 25 days and thereafter increased with time, with a qualitative change in the mode of loss of oil after 135 days. There was no change in the stability of the emulsion with 0.4% sodium dodecyl sulfate over the same time period. The results with the 0.2% sodium dodecyl sulfate emulsion can be rationalized in terms of an initial increase in drop size with an accompanying desorption of sodium dodecyl sulfate and a decrease in stability, followed by coverage of a greater fraction of the remaining oilce:inf>water interface by adsorbed sodium dodecyl sulfate from the more concentrated solution of sodium dodecyl sulfate resulting from the initial desorption.

A adsorção de boro pelo solo

Amostras de solos procedentes dos horizontes B2 e B3 da Série Guamium (Latosólico Vermelho Escuro-orto) e do horizonte Ap da Série Godinhos (Podzólico Vermelho-Amarelo, var. Piracicaba) do Município de Piracicaba, foram tratadas com carbonato de cálcio a fim de se obter uma variação relativamente ampla do pH. Avaliou-se a capacidade de retenção ou adsorção de boro das amostras de solos, mediante a agitação de dois gramas de material com 5 ml de soluções padrão contendo quantidades crescentes de boro. Após um repouso durante 16 horas, procedeu-se à determinação do teor de boro da solução de equilíbrio. Calculou-se a quantidade de boro adsorvida por diferença entre a originalmente existente e a determinada na solução de equilíbrio após a agitação e repouso. Os dados obtidos evidenciaram que a quantidade de boro adsorvido pelas amostras de solos estudadas aumenta com a concentração de boro da solução de equilíbrio e cresce à medida que se eleva o pH. A equação de Freundich, na sua forma linear, traduziu de um modo adequado a dependência da quantidade de boro adsorvida (log x/m ) da concentração de boro da solução de equilíbrio (log c ) e do pH do solo.