The aqueous solubility of trichloroethene (TCE) and tetrachloroethene (PCE) as a function of temperature

doi:10.1016/S0883-2927(99)00058-X

Applied Geochemistry

Volume 15, Issue 4, 1 May 2000, Pages 501-512

https://doi.org/10.1016/S0883-2927(99)00058-X Get rights and content

Abstract

Using a flexible Au bag autoclave and a precision high-pressure liquid chromatography pump to control pressure, the liquid–liquid aqueous solubilities of TCE and PCE were measured as a function of temperature from 294 to 434 K (at constant pressure). The results were used to calculate the partial molal thermodynamic quantities of the organic liquid aqueous dissolution reactions: ΔḠ_soln, ΔH̄_soln, ΔS̄_soln and ΔC̄_{p soln}. Calculated values for these quantities at 298 K for TCE are: ΔḠ_soln=11.282 (±0.003) kJ/mol, ΔH̄_soln=−3.35 (±0.07) kJ/mol, ΔS̄_soln=−49.07 (±0.24) J/mol K, and ΔC̄_{p soln}=385.2 (±3.4) J/mol K. Calculated values for these quantities at 298 K for PCE are: ΔḠ_soln=15.80 (±0.04) kJ/mol, ΔH̄_soln=−1.79 (±0.58) kJ/mol, ΔS̄_soln=−59.00 (±1.96) J/mol K and ΔC̄_{p soln}=354.6 (±8.6) J/mol K. These thermodynamic quantities may be used to calculate the solubility of TCE and PCE at any temperature of interest. In the absence of direct measurements over this temperature range, the Henry's Law constants for TCE and PCE have been estimated using the measured aqueous solubilities and calculated vapor pressures.

Introduction

Ground water contamination with hydrocarbons and halogenated hydrocarbons remains a perplexing national problem. In particular, contamination with chlorinated alkanes and alkenes (e.g. TCE and PCE) that were widely used as solvents is volumetrically of great significance. Many of these compounds are suspected carcinogens. A number of remedial methods are currently employed, and others are in development, to clean up contaminated sites. In all cases an understanding of the partitioning of the organic phase into the aqueous liquid and vapor phases is essential in designing, monitoring and modeling remedial methods.

Although many measurements have been made of the aqueous solubility of these chlorinated hydrocarbons of environmental interest, most measurements were made at ambient temperature (298±15 K). These data have been tabulated and reviewed (Sorensen et al., 1979, Horvath, 1982). More recent work (Stephenson, 1992, Tse et al., 1992, Turner et al., 1996, Washington, 1996, Sleep and Ma, 1997, Heron et al., 1998a) has clearly indicated the significant dependence of aqueous solubility on temperature, yet measurements made at higher temperatures are rare. Direct measurements of Henry's Law constants at elevated temperatures are similarly rare (Meylan and Howard, 1991, Nirmalakhandan et al., 1997, Brennan et al., 1998).

Recently, the potential beneficial use of high temperature in remedial methods has been recognized, especially with regard to increasing mass transfer (Aines, 1992, Imhoff et al., 1997, Heron et al., 1998b). Application of heat alone or heat plus steam (±O₂) injection has been proposed as the basis for in situ treatment via aqueous oxidation (Knauss et al., 1999). In order to understand the geochemistry and be able to model these systems quantitatively, measurements of the thermodynamic properties of organic aqueous species, e.g. TCE and PCE, need to be made at temperatures above ambient.

In order to address this need, the aqueous solubilities of liquid TCE and PCE were measured as a function of temperature from 294 to 434 K (at constant pressure). The results were used to calculate the partial molal thermodynamic quantities of the aqueous dissolution reactions for these organic liquids: ΔḠ_soln, ΔH̄_soln, ΔS̄_soln and ΔC̄_{p soln}. These thermodynamic quantities may now be used to calculate the solubility of TCE and PCE at any temperature of interest.

Section snippets

Experimental design

The laboratory experiments were performed in pure Au flexible bag reactors, employing a reusable pure Ti closure, contained in a water-filled steel pressure vessel heated inside a large tube furnace (Seyfried et al., 1979, Seyfried et al., 1987). This hydrothermal system is ideal for mutual solubility (organic liquid/aqueous fluid) measurements for liquids with sufficient density contrast at high temperature and pressure. Maximum conditions attainable are up to approximately 723 K in

Results

The results of all TCE and PCE solubility vs. temperature measurements are shown in Fig. 1. In this figure measurements are plotted with an indication of the direction of approach to equilibrium prior to sampling — from either under- or over-saturation. Each symbol in all but three cases represents the mean concentration of two samples taken within the minimum time span dictated by the analytical protocol (20 min).

The variability in measured values for both compounds at high temperature is

Discussion

When calculating the derived thermodynamic quantities the following standard state conventions have been used. The standard state for the solvent (H₂O) and for the separate organic liquid phases (TCE_liq or PCE_liq) is the pure liquid at all temperatures and pressures. The standard state for the organic aqueous species (TCE_aq or PCE_aq) is a hypothetical 1 molal solution referenced to infinite dilution at all temperatures and pressures (Shock and Helgeson, 1990).

Using TCE as an example, the

Conclusions

This work presents the results of TCE and PCE solubility measurements made as a function of temperature over a range of conditions that are significant with respect to both natural processes and to various thermal remedial techniques. The derived thermodynamic quantities for the solution reaction are directly applicable to geochemical/hydrologic modeling of processes occurring at contaminated sites and at sites under active remediation via thermal methods. The thermodynamic quantities

Acknowledgements

The technical support of Leon Newton, Ben Reamed and Natalie Drest is greatly appreciated. The regression analyses were done using DataDesk for the Macintosh (v. 5.0). This work was funded by the Department of Energy, Office of Science and Technology (EM-50) Subsurface Contaminants Focus Area, DNAPLs Remediation Product Line and was performed under the auspices of the US Department of Energy, contract number W-7405-ENG-48.

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The aqueous solubility of trichloroethene (TCE) and tetrachloroethene (PCE) as a function of temperature

Abstract

Introduction

Section snippets

Experimental design

Results

Discussion

Conclusions

Acknowledgements

Water Res.

Geochim. Cosmochim. Acta

Appl. Geochem.

Water Res.

Geochim. Cosmochim. Acta.

Solubility of organic mixtures in water

Environ. Sci. Technol.

Evaluation of thermodynamic functions from equilibrium constants

Trans. Faraday Soc.

Henry's law constant for trichloroethylene between 10 and 95°C

Environ. Sci. Technol.

Soil heating for enhanced remediation of chlorinated solvents: a laboratory study on resistive heating and vapor extraction in a silty, low-permeable soil contaminated with trichloroethylene

Environ. Sci. Technol.

Halogenated Hydrocarbons: Solubility–Miscibility with Water

Evaluation of thermal effects on the dissolution of a nonaqueous phase liquid in porous media

Environ. Sci. Technol.