Completely water-miscible organic

Figure 5.6 Illustration of the effect of a completely water-miscible solvent (CMOS, i.e., methanol) on the activity coefficient of organic compounds in water-organic solvent mixtures decadic logarithm of the activity coefficient as a function of the volume fraction of methanol. Note that the data for naphthalene (Dickhut et al., 1989 Fan and Jafvert, 1997) and for the two PCBs (Li and Andren, 1994) have been derived from solubility measurements whereas for the anilins (Jayasinghe etal., 1992), air-water partition constants determined under dilute conditions have been used to calculate y,f.

Sometimes the mutual solubility of a solvent pair of interest can easily be decreased by adding a third component. For example, it is common practice to add water to a solvent system containing a water-miscible organic solvent (the polar phase) and a hydrophobic organic solvent (the nonpolar phase). A typical example is the solvent system (methanol + water) + dichloromethane. An anhydrous mixture of methanol and dichloromethane is completely miscible, but adding water causes phase splitting. Adjusting the amount of water added to the polar phase also may be used to alter the K values for the extraction, density difference, and interfacial tension. Table 15-5 lists some common examples of solvent systems of this type. These systems are common candidates for fractional extractions. 

A second liquid is sometimes added to a solution to reduce the solubility of the solute, cause its precipitation/crystallization and maximize the yield of product. It is necessary, of course, for the two liquids (the original solvent and the added precipitant) to be completely miscible with one another in all proportions. The process is commonly encountered, for instance, in the crystallization of organic substances from water-miscible organic solvents by the controlled addition of water. The term watering-out is often used in this connection. This approach is also used to reduce the solubility of an inorganic salt in aqueous solution by the addition of a water-miscible organic solvent in salting-out precipitation processes (section 7.2.5). 

Partially water-miscible organic solvents (PMOSs) may act as either cosolvents or cosolutes, and the research in the past has shown flic complexity of their effects. " It was demonstrated that in order to exert effects on solubility or sorption of HOCs, PMOSs must exist as a component of the solvent mixture in an appreciable amount Munz and Roberts suggested a mole fi action of greater than 0.005 and Rao and coworkers proposed a volume percent of 1% or a concentration above lO mg/L. Cosolvents with relatively high water solubility are likely to demonstrate observable effects on the solubilities of solutes, up to their solubility limits, in a similar manner to cosolvents of complete miscibility with water. A few experimental examples of the effects of PMOSs include 1 -butanol and... 

To determine the efficiency of extraction, it is imperative that the pollutant is bound to the matrix in a similar configuration to that which exists in the environment. The extraction efficiency can then be measured for that analyte in a specific matrix configuration. At present, water is the only matrix where this can be achieved in a relatively straightforward way. The analytes are added below the surface of the sample in a small volume of water miscible solvent. The water must be completely mixed and allowed to stand at least overnight prior to extraction to allow the pollutants to come into equilibrium with the other organic materials, particularly humic matter. The spiked water sample must be analyzed... 

Foster Wheeler Development Corporation (FWDC) has designed a transportable transpiring wall supercritical water oxidation (SCWO) reactor to treat hazardous wastes. As water is subjected to temperatures and pressures above its critical point (374.2°C, 22.1 MPa), it exhibits properties that differ from both liquid water and steam. At the critical point, the liquid and vapor phases of water have the same density. When the critical point is exceeded, hydrogen bonding between water molecules is essentially stopped. Some organic compounds that are normally insoluble in liquid water become completely soluble (miscible in all proportions) in supercritical water. Some water-soluble inorganic compounds, such as salts, become insoluble in supercritical water. 

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