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Title: PARTITIONING OF ACIDIC SOLUTES BETWEEN WATER AND SUPERCRITICAL CARBON DIOXIDE. EFFECT OF PH AND IONIC STRENGTH

Author
item Curren, Meredith
item BURK, ROBERT - CARLETON UNIV, ONTARIO

Submitted to: Journal of Chemical and Engineering Data
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: The determination of pesticides in natural waters is an important problem requiring new methods of analysis and data that describe the partitioning of these compounds from such media. This study was initiated to provide solubility and partitioning data of common environmental contaminants in natural systems where the water acidity and salt content varies. A unique extraction agent was used in these studies to separate the pesticides and pollutants from the water, namely compressed carbon dioxide. Carbon dioxide is environmentally benign, inexpensive, and non-toxic to analysts performing these measurements. The resultant data can be used not only for the design of analytical methods to determine pesticide content in water, but also for the design and optimization of engineering-based extraction processes. Such processes will aid in the removal of these toxicants from our nation's water supply. The use of the described method has the potential to remove the need for using expensive and toxic organic solvent which are commonly employed for this purpose.

Technical Abstract: Partitioning of pentachlorophenol between water and CO2 was investigated to determine the effects of pH and ionic strength on the value of the distribution coefficient, K. Decreasing the pH or increasing the ionic strength increased the value of K. The distribution coefficient was larger than that predicted by considering the extent of hydrolysis of the solute in the aqueous phase. However, impedance measurements suggest that negligible concentrations of ions exist in the CO2 phase. Together, these two facts suggest that the aqueous phase hydrolysis equilibrium is shifted toward unhydrolyzed solute as PCP partitions to CO2. The value of K was smaller than the ratio of solubilities of the solute in the two phases, likely due to the effect of solute composition on the solute activity coefficients in each phase. Partitioning isotherms are also reported for the solutes pentachlorophenol, 2,3,4,5-tetrachlorophenol and 2,4-dichlorophenoxyacetic acid at about 40 deg C, between about 100 to 270 bar.