Partitioning of Acidic Solutes between Water and Supercritical Carbon Dioxide. Effect of pH and Ionic Strength

Abstract

Partitioning of pentachlorophenol (PCP) between water and CO 2 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 CO 2 phase. Together, these two facts suggest that the aqueous phase hydrolysis equilibrium is shifted toward unhydrolyzed solute as PCP partitions to CO 2 . 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 2,4dichlorophenoxyacetic acid at about 40 °C, between about 100 to 270 bar.

Supercritical extraction of contaminants from soils and sediments

“…These compounds include 2,4-dichlorophenol [14], phenol [55][56][57], p-chlorophenol, m-cresol, and benzene [57], toluene [58], a PAH mixture [15], naphthalene, phenanthrene, hexachlorobenzene, and pentachlorophenol [10,13,16]. Partitioning isotherms are also reported for the solutes pentachlorophenol, 2,3,4,5-tetrachlorophenol and 2,4-dichloro-phenoxyacetic acid between water and SCCD at about 40 • C and 100-270 bar [59].…”

Limiting the risk inherent to geological CO2 storage: The importance of predicting inorganic and organic chemical species behavior under supercritical CO2 fluid conditions

“…Similar to thermodynamic modeling for trace inorganic elements, we cannot currently predict the eff ect of electrolytes in the aqueous phase on the partitioning behavior of organic compounds in sc-CO 2 . Curren and Burk, 46 measuring the partitioning of pentachlorophenol between water and sc-CO 2 as a function of NaCl concentration, found an increase in pentachlorophenol activity when salinity increased consistent with the 'salting out' eff ect. Xie et al 47 showed that the salting out eff ect was greater for organic compounds with a high molar volume.…”

“…The decrease in brine pH facilitates organic acid protonation and partition to sc‐CO 2 . This is consistent with lower water solubility and in agreement with Curren and Burk 2000's estimated K‐factors …”

“…Th is is consistent with lower water solubility and in agreement with Curren and Burk 2000's estimated K-factors. 46…”

Partition Coefficients of Organics between Water and Carbon Dioxide Revisited: Correlation with Solute Molecular Descriptors and Solvent Cohesive Properties

“…The experimental K-factor data were taken from the original sources. 13−26 However, some of the solutes, notably pentachlorophenol, 19 2,3,4,5-tetrachlorophenol, 21 3-methyl-4-chlorophenol, 22 and 2-methyl-4,6-dinitrophenol 22 and propiophenone 23 were omitted because of the lack of vapor pressure data at the required temperatures (see below). Therefore, the most extensive set of experimental Kfactor data comprised 455 data points for 44 solutes of diverse structures and falling within the temperature range of 297−363 K and the pressure range of 2.5−31.5 MPa.…”