Ammonia, addition supercritical

Certain free bases of alkaloids were found to be quite soluble in pure supercritical C02 even under mild supercritical conditions. However, the alkaloids were not extracted as much as expected from their solubilities [37]. This discrepancy was assumed to be due to the fact that most alkaloids exist in the form of salts in the plant. Alkaloids have been extracted from plant materials traditionally by extraction processes with the addition of ammonia or calcium hydroxide. Accordingly, the use of basified modifiers in SFE, rather than simple polar modifiers was investigated, in the hope that the extraction efficiencies of alkaloids from their plant of origin would be enhanced. 

Carbon dioxide, water, ethane, ethylene, propane, ammonia, xenon, nitrous oxide, and fluoroform have been considered useful solvents for SEE. Carbon dioxide has so far been the most widely used as a supercritical solvent because of its convenient critical temperature, 304°K, low cost, chemical stability, nonflammability, and nontoxicity. Its polar character as a solvent is intermediate between a truly nonpolar solvent such as hexane and a weakly polar solvent. Moreover, COj also has a large molecular quadrupole. Therefore, it has some limited affinity with polar solutes. To improve its affinity, additional species are often introduced into the solvent as modifiers. For instance, methanol increases C02 s polarity, aliphatic hydrocarbons decrease it, toluene imparts aromaticity, R-2-butanol adds chirality, and tributyl phosphate enhances the solvation of metal complexes. 

In addition to the investigation of numerous model compounds, real wastes from chemical, pharmaceutical and food industry, from municipal sewage treatment plants, and from military and nuclear power facilities were tested in bench and pilot scale plants [110]. For a better understanding of supercritical water oxidation, single components like 2,4-dinitrotoluene, acetic acid, ammonia, aniline, cyanide, dichloromethane, ethanol, formic add, hexachlorocydohexane, hydrogen, phenol, PVC, DDT, pyridine, thiophene, toluene, trichloroethylene, and 1,1,1-trichloroethane were studied. From these experiments, kinetic data were obtained. The destruction efficiency, which is the ratio between the residual total organic carbon content (TOC) and the initial TOC achieved for these compounds is up to 99.999 % [83]. Also flames in supercritical water, e.g. by oxidation of methane with oxygen, have been studied [111, 112]. 

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