Chlorinated solvents properties/recovery

Utilization of a processing plant, it would be necessary to be able to process multiple varieties such as cherry, plum, peach, apple, etc. It is essential that the cost of by-product remain reasonable once a successful recovery operation has been established. Most of the data reported here are for oil samples prepared under laboratory conditions. The extracting solvent used for the oil recovery was usually n-hexane, which is acceptable for edible purposes. Chlorinated solvents are unacceptable for the recovery of edible oils because they may contain chlorinated components such as tetrachloroethane which is not removable by heat treatment and which if present would make the oil too toxic to be consumed. Often oils that are recovered from by-products have properties that make them desirable in cosmetics and in medical preparations. Such specialized application may command a premium price. 

Solubility — the amount of a given substance (the solute) that dissolves in a unit volume of a liquid (the solvent). This property is of importance in the handling and recovery of spilled hazardous materials. Water-insoluble chemicals are much easier to recover from water than spills of water-soluble chemicals. Acetone, which is miscible/soluble in water in all proportions, is not readily recoverable from water. In contrast, benzene, which is lighter than water and insoluble as well, can be readily trapped with a skimmer. For organic compounds, solubility tends to decrease with increasing molecular weight and chlorine content. 

Microemulsions became well known from about 1975 to 1980 because of their use in "micellar-polymer" enhanced oil recovery (EOR) (35). This technology exploits the ultralow interfacial tensions that exist among top, microemulsion, and bottom phases to remove large amounts of petroleum from porous rocks, that would be unrecoverable by conventional technologies (36,37). Since about 1990, interest in the use of this property of microemulsions has shifted to the recovery of chlorinated compounds and other industrial solvents from shallow aquifers. The latter application (15) is sometimes called surfactant-enhanced aquifer remediation (SEAR). 

The use of supercritical fluid extraction (SEE) as an extraction technique is related to the unique properties of the supercritical fluid. These fluids have a low viscosity, high diffusion coefficients, low toxicity, and low flammability, all clearly superior to the organic solvents used in SPE extraction. The most common fluid used is carbon dioxide. SEE extractions of sediment samples have shown recoveries of >95% for all the individual PCBs. The separation of PCDDs from PCBs and chlorinated benzenes is difficult because of their similar solubility. An interesting development is the use of fat retainers. Samples, mixed in different weight ratios with, e.g., silica/silver nitrate 10% or basic alumina, can be placed in 7 ml extraction cells. The analytes are recovered by elution with 1.5-1.8 ml of hexane. With the correct fat-silica ratios and SEE conditions, no additional cleanup procedure is necessary for GC with an electron-capture detector (ECD). One drawback of SEE may be that the methods developed are valid for a specific matrix, but as soon as, e.g., the fat content of a biota sample or the type of lipids changes, the method has to be adapted. SEE is relatively complicated compared to other extraction techniques. In addition, the cell volumes are small, which limits the sample intake, and, with that, the detection limits. Einally, some reliable types of SEE equipment have recently been withdrawn from the market. This will have a substantial negative effect on the use of SEE in the near future. 

Selective adsorption properties are obtained from the structure, controlled distribution of pore sizes, high surface areas and chemical nature of the matrix. Applications include the recovery of a wide range of solutes from the aqueous phase, including phenol, benzene, toluene, chlorinated organics, PCBs, pesticides, antibiotics, acetone, ethanol, detergents, emulsifiers, dyes, steroids, amino acids, etc. Regeneration may be effected by a variety of methods which include steam desorption, solvent elution, pH change and chemical extraction. 

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