Extraction with chemically active solvents

Extraction by chemically active solvents. Not infrequently the crude organic product from a reaction may contain a mixture of acidic (phenols and carboxylic acids), basic and neutral components in various combinations. Some of these components may of course be impurities, but none the less, whether as a preliminary purification stage or as a means of separating the mixture, a carefully planned solvent extraction procedure may be adopted using acidic and basic reagents which react chemically with the basic and acidic components of the mixture respectively. The following full account of a typical procedure may be abbreviated in practice according to the complexity of the mixture to be handled. 

The valuable fertile elements are recovered from the acid solution by extraction with an organic solvent. The acid residue, containing the extremely radioaetive fission products, is processed to convert the waste into a stable solid form. The fission product waste, in a very concentrated form, is stored for ultimate disposal. This waste represents a different problem than the waste from current burner reactors. Because of the chemical concentration step there is less total mass of material. The same concentration process that reduced the mass of the waste concentrates the radiation produced into a smaller more intense package. This waste is so radioactive that it gets hot and must be actively cooled or diluted to prevent meltdown. Safe storage and disposal methods are very difficult to design. 

Extractions and Chemical Analyses of Amaranthus palmerl S. Wats (Amaranthaceae). The plant material for the chemical studies was supplied by Dr. R. M. Menges, USDA, Weslaco, TX. The air-dried aerial parts (518 g) were extracted at ambient temperature with petroleum ether (PE), dichloromethane (CI Clj) and methanol (MeOH) and the solvents were evaporated In vacuo providing 4.5 g, 4.7 g and 12.lg crude extracts, respectively. Samples of the crude extracts were tested by Dr. J. M. Bradow for germination regulation activity and the biological data are described in her paper. 

Coal is a complicated material, and more than one simple chemical process takes place during solvent extraction. The activation energy necessary for dissolving coal increases with the extent of the process up to a point at a certain temperature insufficient energy is available for more extraction. When the activation energy necessary for extraction becomes more than maximum energy supplied, additional coal will not dissolve. The rate constants, average heats of activation, and apparent activation entropies predict the dissolution... 

Reid and others(11. 121 have shown that supercritical solvents exhibit varying degrees of specificity towards a particular specie. Furthermore, the small number of SC solvents available limits the potential use SC extraction. The use of entrainers or mixtures of solvents, may remove the limitation imposed by the narrow choice of likely solvents. Moreover, it is possible that through the proper choice of entrainer and solvent the desired chemical activity can be adjusted to improve the selectivity of the solvent. For example, mixtures of solvent gases with entrainers can permit a modification of critical properties as well as chemical properties, so that P and T adjustment can be used to maximize some physical property of the system(2). 

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