Solutions immiscible solvents

Other solubilization and partitioning phenomena are important, both within the context of microemulsions and in the absence of added immiscible solvent. In regular micellar solutions, micelles promote the solubility of many compounds otherwise insoluble in water. The amount of chemical component solubilized in a micellar solution will, typically, be much smaller than can be accommodated in microemulsion fonnation, such as when only a few molecules per micelle are solubilized. Such limited solubilization is nevertheless quite useful. The incoriDoration of minor quantities of pyrene and related optical probes into micelles are a key to the use of fluorescence depolarization in quantifying micellar aggregation numbers and micellar microviscosities [48]. Micellar solubilization makes it possible to measure acid-base or electrochemical properties of compounds otherwise insoluble in aqueous solution. Micellar solubilization facilitates micellar catalysis (see section C2.3.10) and emulsion polymerization (see section C2.3.12). On the other hand, there are untoward effects of micellar solubilization in practical applications of surfactants. Wlren one has a multiphase... 

The theory of the process can best be illustrated by considering the operation, frequently carried out in the laboratory, of extracting an orgaiuc compound from its aqueous solution with an immiscible solvent. We are concerned here with the distribution law or partition law which, states that if to a system of two liquid layers, made up of two immiscible or slightly miscible components, is added a quantity of a third substance soluble in both layers, then the substance distributes itself between the two layers so that the ratio of the concentration in one solvent to the concentration in the second solvent remains constant at constant temperature. It is assumed that the molecular state of the substance is the same in both solvents. If and Cg are the concentrations in the layers A and B, then, at constant temperature ... 

Interfdci l Composite Membra.nes, A method of making asymmetric membranes involving interfacial polymerization was developed in the 1960s. This technique was used to produce reverse osmosis membranes with dramatically improved salt rejections and water fluxes compared to those prepared by the Loeb-Sourirajan process (28). In the interfacial polymerization method, an aqueous solution of a reactive prepolymer, such as polyamine, is first deposited in the pores of a microporous support membrane, typically a polysulfone ultrafUtration membrane. The amine-loaded support is then immersed in a water-immiscible solvent solution containing a reactant, for example, a diacid chloride in hexane. The amine and acid chloride then react at the interface of the two solutions to form a densely cross-linked, extremely thin membrane layer. This preparation method is shown schematically in Figure 15. The first membrane made was based on polyethylenimine cross-linked with toluene-2,4-diisocyanate (28). The process was later refined at FilmTec Corporation (29,30) and at UOP (31) in the United States, and at Nitto (32) in Japan. 

Because almost any diacid can be leaddy converted to the acid chloride, this reaction is quite versatile and several variations have been developed. In the interfacial polymerization method the reaction occurs at the boundary of two phases one contains a solution of the acid chloride in a water-immiscible solvent and the other is a solution of the diamine in water with an inorganic base and a surfactant (48). In the solution method, only one phase is present, which contains a solution of the diamine and diacid chloride. An organic base is added as an acceptor for the hydrogen chloride produced in the reaction (49). Following any of these methods of preparation, the polymer is exposed to water and the acid chloride end is converted to a carboxyhc acid end. However, it is very difficult to remove all traces of chloride from the polymer, even with repeated washings with a strong base. 

The extraction of metal ions depends on the chelating ability of 8-hydroxyquinoline. Modification of the stmcture can improve its properties, eg, higher solubility in organic solvents (91). The extraction of nickel, cobalt, copper, and zinc from acid sulfates has been accompHshed using 8-hydroxyquinohne in an immiscible solvent (92). In the presence of oximes, halo-substituted 8-hydroxyquinolines have been used to recover copper and zinc from aqueous solutions (93). Dilute solutions of heavy metals such as mercury, ca dmium, copper, lead, and zinc can be purified using quinoline-8-carboxyhc acid adsorbed on various substrates (94). 

An equihbrium, or theoretical, stage in liquid-liquid extraction as defined earlier is routinely utilized in laboratory procedures. A feed solution is contacted with an immiscible solvent to remove one or more of the solutes from the feed. This can be carried out in a separating funnel, or, preferably, in an agitated vessel that can produce droplets of about 1 mm in diameter. After agitation has stopped and the phases separate, the two clear liquid layers are isolated by decantation. 

Robbins ( Oquid-Liquid Extraction, in Schweitzer, Handbook of Separation Techniques for Chemical Engineers, McGraw-Hill, New York, 1979, sec. 1.9) reported that most liquid-liquid extrac tion systems can be treated as having either (A) immiscible solvents, (B) partially miscible solvents with a low solute concentration in the extract, or (C) partially miscible solvents with a high solute concentration in the extract. 

Relative Solubility of Immiscible Solvents. Many solid materials in solution can be removed by transferring them to a second solvent it is essential that the solvents be mutually insoluble. 

When the distribution ratio is low, continuous methods of extraction are used. This procedure makes use of a continuous flow of immiscible solvent through the solution if the solvent is volatile, it is recycled by distillation and condensation and is dispersed in the aqueous phase by means of a sintered glass disc or equivalent device. Apparatus is available for effecting such continuous extractions with automatic return of the volatilised solvent (see the Bibliography, Section 9.10). 

The isopiestic method is based upon the equality of the solvent chemical potentials and fugacities when solutions of different solutes, but the same solvent, are allowed to come to equilibrium together. A method in which a solute is allowed to establish an equilibrium distribution between two solvents has also been developed to determine activities of the solute, usually based on the Henry s law standard state. In this case, one brings together two immiscible solvents, A and B, adds a solute, and shakes the mixture to obtain two phases that are in equilibrium, a solution of the solute in A with composition. vA, and a solution of the solute in B with composition, a . 

Immiscible solvents like water and oil can be transformed by addition of solubilizers to single-phase solutions. Amphiphilic substances are known as effective solubilizers. Solubilization depends on the HLB of the components that ought to form a single phase and on the kind of solubilizer used. Phosphorus-containing surfactants with their variety of possible molecular structures are solubilizers that can be tailored to the task demanded. 

In conventional solvent extraction, a solute is partitioned between two immiscible solvents. Here, used as an... 

Studies described in earlier chapters used cellular automata dynamics to model the hydrophobic effect and other solution phenomena such as dissolution, diffusion, micelle formation, and immiscible solvent demixing. In this section we describe several cellular automata models of the influence of the hydropathic state of a surface on water and on solute concentration in an aqueous solution. We first examine the effect of the surface hydropathic state on the accumulation of water near the surface. A second example models the effect of surface hydropathic state on the rate and accumulation of water flowing through a tube. A final example shows the effect of the surface on the concentration of solute molecules within an aqueous solution. 

The steroid-loaded formulations are prepared by a patented solvent evaporation process (45,46). Basically, the wall-forming polymer and the steix>id are added to a volatile, water-immiscible solvent. The dispersion or solution is added to an aqueous solution to form an oil-in-water emulsion. The volatile solvent is then removed to afford solid microparticles. The microparticles are usually subd vided with sieves to isolate fractions of the desired diameters. It is i nper-ative that a reliable and reproducible microencapsulation procedure be used to fabricate long-acting formulations. 

In the framework of the mobile order and disorder (MOD) theory five components contribute most to the Gibbs free energy of partitioning of a solute in a biphasic system of two essentially immiscible solvents [23] ... 

MEEKC is a CE mode similar to MEKC, based on the partitioning of compounds between an aqueous and a microemulsion phase. The buffer solution consists of an aqueous solution containing nanometer-sized oil droplets as a pseudo-stationary phase. The most widely used microemulsion is made up of heptane as a water-immiscible solvent, SDS as a surfactant and 1-butanol as a cosurfactant. Surfactants and cosurfactants act as stabilizers at the surface of the droplet. 

The predominant RO membranes used in water applications include cellulose polymers, thin film oomposites (TFCs) consisting of aromatic polyamides, and crosslinked polyetherurea. Cellulosic membranes are formed by immersion casting of 30 to 40 percent polymer lacquers on a web immersed in water. These lacquers include cellulose acetate, triacetate, and acetate-butyrate. TFCs are formed by interfacial polymerization that involves coating a microporous membrane substrate with an aqueous prepolymer solution and immersing in a water-immiscible solvent containing a reactant [Petersen, J. Memhr. Sol., 83, 81 (1993)]. The Dow FilmTec FT-30 membrane developed by Cadotte uses 1-3 diaminobenzene prepolymer crosslinked with 1-3 and 1-4 benzenedicarboxylic acid chlorides. These membranes have NaCl retention and water permeability claims. 

Lipophilicity is a molecular property expressing the relative affinity of solutes for an aqueous phase and an organic, water-immiscible solvent. As such, lipophilicity encodes most of the intermolecular forces that can take place between a solute and a solvent, and represents the affinity of a molecule for a lipophilic environment. This parameter is commonly measured by its distribution behavior in a biphasic system, described by the partition coefficient of the species X, P. Thermodynamically, is defined as a constant relating the activity of a solute in two immiscible phases at equilibrium [111,112]. By convention, P is given with the organic phase as numerator, so that a positive value for log P reflects a preference for the lipid phase ... 

Some guidelines for predicting the results from distributing a sample between two immiscible solvents are summarized in Table 8.3 [67,68]. The efficiency of an extracting solvent, E, depends primarily on the affinity of the solute for the extracting solvent, Kd) the phase ratio, V, and the number of extractions, n. For simple batchwlse extractions K, should be l u ge, as there is a practical limit to the volume of the extracting solvent and the... 

The effect of the medium (solvent) on the dissolved substance can best be expressed thermodynamically. Consider a solution of a given substance (subscript i) in solvent s and in another solvent r taken as a reference. Water (w) is usually used as a reference solvent. The two solutions are brought to equilibrium (saturated solutions are in equilibrium when each is in equilibrium with the same solid phase—the crystals of the dissolved substance solutions in completely immiscible solvents are simply brought into contact and distribution equilibrium is established). The thermodynamic equilibrium condition is expressed in terms of equality of the chemical potentials of the dissolved substance in both solutions, jU,(w) = jU/(j), whence... 

If two electrolyte solutions in immiscible solvents are in contact and contain a common ion Bz+ and the anions are not soluble in the opposite phase, then the relationship for the Galvani potential difference follows from Eq. (3.1.5) ... 

In emulsion polymerization, a solution of monomer in one solvent forms droplets, suspended in a second, immiscible solvent. We often employ surfactants to stabilize the droplets through the formation of micelles containing pure monomer or a monomer in solution. Micelles assemble when amphiphilic surfactant molecules (containing both a hydrophobic and hydrophilic end) organize at a phase boundary so that their hydrophilic portion interacts with the hydrophilic component of the emulsion, while their hydrophobic part interacts with the hydrophobic portion of the emulsion. Figure 2.14 illustrates a micellized emulsion structure. To start the polymerization reaction, a phase-specific initiator or catalyst diffuses into the core of the droplets, starting the polymerization. 

Consider a batch two-phase extraction system, with a single solute transferring from the feed phase into an immiscible solvent phase. The background to the problem is discussed in Section 3.3.1.1... 

If a substance is soluble in both water and the organic solvent, the result of the extraction depends on the ratio of solubilities if the partition coefficient , e.g. the ratio of the solubility in water to that in ether, is large, correspondingly more ether must be used or the number of extractions must be increased. For this coefficient determines how a substance soluble in two immiscible solvents will distribute itself between them. Whether an aqueous solution should be extracted with a certain amount of ether in one portion or whether it is better to extract several times with smaller portions is... 

The behavioural pattern of two immiscible solvents, say a and ib is essentially nonideal with respect to one another. Now, if a third substance is made to dissolve in a two-phase mixture of the solvents (i.e., a and 3 ), it may behave ideally in either phases provided its concentration in each individual phase is approximately small. Therefore, under these prevailing experimental parameters the ratio of the mole fractions of the solute in the two respective immiscible phases ( a and A) is found to be a constant which is absolutely independent of the quantity of solute present. It is termed as the Nernst Distribution Law or the Partition Law and may be expressed as follows ... 

The partition of a solute between two immiscible liquid phases provides the basis for simple solvent extraction techniques. The polarity of both solute and solvent are important factors in determining the solubility of the solute, and polar solutes will dissolve more readily in polar solvents than in nonpolar solvents. 

If a quantity of a solute A is distributed between two immiscible solvents, for example I2 between carbon tetrachloride and water, then at equUibrium the chemical potentials or escaping tendencies of the solute are the same in both phases thus, for A(in solvent a) = A(in solvent b)... 

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