Sub-Critical Water Extraction of Organic PollutantsEPA Grant Number: R825394
Title: Sub-Critical Water Extraction of Organic Pollutants
Investigators: Hawthorne, Steven B. , Clifford, Anthony
Current Investigators: Hawthorne, Steven B. , Kubatova, Alena , Lagadec, Arnaud J. , Miller, David J.
Institution: University of North Dakota , University of Leeds
Current Institution: University of North Dakota
EPA Project Officer: Hiscock, Michael
Project Period: December 24, 1996 through December 23, 1999
Project Amount: $374,925
RFA: Exploratory Research - Water Chemistry and Physics (1996) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Engineering and Environmental Chemistry
Solvents that are environmentally-friendly are needed for processes ranging from environmental remediation to analytical extractions to process chemistry. Water is normally too polar to be considered useful for the extraction of organic pollutants associated with environmental solids; however, water can be changed from a highly polar to non-polar solvent by simply increasing its temperature. While steam and supercritical water (T>374 oC and P>221 bar) have been studied, hot liquid-phase water ("sub-critical" water) has received virtually no attention as a solvent for organic compounds despite the fact that a much broader range of polarities can be achieved with sub-critical water than either steam or supercritical water. By simply heating water under low pressure, solubilities of polar organics increase dramatically, and even non-polar organics such as PAHs can increase solubilities by >106-fold.
In preliminary studies, we have demonstrated that hot (e.g., 50 to 250°C) water (maintained as a liquid by a few bar pressure) is an excellent extraction solvent for polar organics (e.g., phenols and amines), as well as organics as non-polar as PAHs. Quantitative extractions of organics ranging from phenols to PAHs and PCBs from soils and sludges have been demonstrated. In addition, compound class selectivity can be achieved by simply extracting at sequentially higher temperatures. Potential practical advantages of sub-critical water over supercritical water include much lower corrosivity, much lower pressure and temperature requirements, and much lower engineering costs for process-scale equipment.
The objectives of the proposed investigations are to: 1) develop the use of sub-critical water as an extraction solvent for polar and non-polar organic pollutants from contaminated solids; 2) measure and model fundamental solubility behavior of polar and non-polar organics in sub-critical water; 3) investigate the mechanisms controlling the extraction of organic pollutants from model and real-world solids; 4) determine the reactivity of model organics under different sub-critical conditions; and 5) determine the extraction selectivity that can be obtained by controlling water's polarity with temperature.
The results of this study will provide the fundamental data needed to evaluate the potential for using sub-critical water for environmental remediation of contaminated solids at a large scale and at the analytical scale, as well as providing fundamental background data to allow evaluation of sub-critical water as a replacement for organic solvents for industrial processes and for leaching/biotoxicity assays.