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1999 Progress Report: Sub-Critical Water Extraction of Organic Pollutants
EPA Grant Number: R825394Title: Sub-Critical Water Extraction of Organic Pollutants
Investigators: Hawthorne, Steven B.
Current Investigators: Hawthorne, Steven B. , Kubatova, Alena , Lagadec, Arnaud J. , Miller, David J.
Institution: University of North Dakota
EPA Project Officer: Rosenthal, Sheila
Project Period: December 24, 1996 through December 23, 1999
Project Period Covered by this Report: December 24, 1998 through December 23, 1999
Project Amount: $374,925
RFA: Exploratory Research - Water Chemistry and Physics (1996)
Research Category: Engineering and Environmental Chemistry
Description:
Objective:The objectives of the proposed investigations are to: (1) develop the use of subcritical water as an extraction solvent for polar and nonpolar organic pollutants from contaminated solids; (2) measure and model fundamental solubility behavior of polar and nonpolar organics in subcritical 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 subcritical water conditions; and (5) determine the extraction selectivity that can be obtained by controlling water's polarity with temperature. Progress Summary:
Solubility Determinations. A dynamic (flowing) system for determining the solubility of organic solids in subcritical water was developed in Year 1, and initial modifications to allow its use were performed in Year 2. In Year 3, the new system was used to determine the solubility of several liquid solutes including environmental pollutants (e.g., benzene, chlorinated solvents) and flavor and fragrance compounds. These results have been presented in peer-reviewed publications.
Subcritical Water Extraction Mechanisms. Determining extraction mechanisms requires an analytical system that allows the collection of extracted organics every few minutes during an extraction so that extraction rate curves (e.g., mass extracted per minute) can be generated. The system was developed and validated for its ability to give quantitative data suitable for kinetic studies in Year 1.
Two types of pollutants are now being studied for the effects of subcritical water flow rate on extraction rates. These results will allow the relative contributions of two rate-limiting steps (initial desorption of the pollutants from the active soil binding sites, and chromatographic elution) to be determined and modeled. Four environmentally aged soils were collected for these studies including two soils contaminated with polycyclic aromatic hydrocarbons (PAHs) (one soil with high, and one with lower contamination levels) and two soils contaminated with multiple pesticides (one with high, and one with lower contamination levels - both soils include the pesticides metolachlor and pendimethalin). The kinetic extraction data have been completed for the pesticide-contaminated soils, and are nearly complete for the PAH-contaminated soils. We have found that these mechanisms are not as expected based on earlier studies on supercritical carbon dioxide extraction. Therefore, we currently are comparing the extraction behavior of organic pollutants using supercritical carbon dioxide (which does not significantly modify the soil matrix) with subcritical water (which causes soils to swell and expose pollutants in soil micropores, as well as extracting humic material that may contain sequestered organics). We hope that the comparison of supercritical carbon dioxide extraction behavior with subcritical water extraction behavior will provide a powerful tool to understand how pollutant molecules interact and bind to soil matrices. Initial comparison of the characteristics of these two fluids are the subject of a publication in the Journal of Chromatography.
Reactions in Subcritical Water. In Year 1, initial observations of pesticide degradation during subcritical water extraction were conducted. These results were potentially important, because they indicated that subcritical water (with NO additives) could be used to degrade toxic organic compounds. During Year 2, several additional compound classes were tested, and shown to undergo degradation reactions in subcritical water at relatively mild temperatures (e.g., <250°C). Degradation has been demonstrated for several aromatic and aliphatic organics (including chlorinated and nonchlorinated), but at present, we have little understanding of the mechanism(s) and reaction products. Additional studies on selected organics were conducted, with emphasis on chlorinated organics. To date, we have demonstrated two dechlorination mechanisms: dehydrohalogenation for aliphatic chlorinated hydrocarbons such as the pesticide lindane (where HCl is removed from the molecule to yield a double bond), and hydride/chloride exchange for chlorinated aromatics (where Cl atoms on the aromatic ring are replaced by H). These observations lead to attempts to destroy chlorinated dioxins on municipal incinerator fly ash. Initial work was successful and will be continued in collaboration with our colleagues in Belgium's leading dioxin laboratory.
Subcritical Water as a "Green" Solvent. Our better understanding of organic solubility behavior in subcritical water (discussed above) has lead to investigations into using subcritical water as a replacement for organic solvents used in industrial processing. To date, we have used subcritical water to remediate soils that were highly contaminated with PAHs and pesticides (co-funded by the Department of Energy) as described in an article accepted for publication in Environmental Science and Technology. Additional preliminary experiments have shown that extractions of valuable organics from plant tissue can be performed (e.g., lactones from Kava Kava, flavor compounds from herbs), and we plan to pursue these studies in Year 4. These investigations are really quite interesting, because dealing with extracts that smell good (instead of our normal organic pollutant extracts) is a pleasant change! A final area in which initial experiments are promising is the extraction of potentially toxic monomers and reaction products from food- and medical-packaging polymers. For example, subcritical water extracted several contaminants from a polyethylene bread bag including benzene, larger aromatics, and aliphatic aldehydes. Because the bag material was physically the same after extraction, these results indicate that it may be possible to remove potentially harmful contaminants from plastics before their use for food and medical product packaging.
Future Activities:soil, sediments, PAHs, PCBs, dioxins, organics, green chemistry, clean technologies, remediation, environmental chemistry, analytical.
Journal Articles on this Report: 6 Displayed | Download in RIS Format
| Other project views: | All 10 publications | 9 publications in selected types | All 9 journal articles |
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Hawthorne SB, Grabanski CB, Martin E, Miller DJ. Comparisons of Soxhlet extraction, pressurized liquid extraction, supercritical fluid extraction, and subcritical water extraction for environmental solids: recovery, selectivity, and effects on sample matrix. Journal of Chromatography A, September 2000;892(1-2):421-433. |
R825394 (1999) R825394 (Final) |
not available |
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Lagadec AJM, Miller DJ, Lilke AV, Hawthorne SB. Pilot-scale subcritical water remediation of polycyclic aromatic hydrocarbon- and pesticide-contaminated soil. Environmental Science & Technology 2000;34(8):1542-1548. |
R825394 (1999) R825394 (Final) |
not available |
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Miller DJ, Hawthorne SB. Method for determining the solubilities of hydrophobic organics in subcritical water. Analytical Chemistry 1998;70(8):1618-1621. |
R825394 (1999) R825394 (Final) |
not available |
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Miller DJ, Hawthorne SB, Gizir AM, Clifford AA. Solubility of polycyclic aromatic hydrocarbons in subcritical water from 298K to 498K. Journal of Chemical and Engineering Data 1998;43(6):1043-1047. |
R825394 (1999) R825394 (Final) |
not available |
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Miller DJ, Hawthorne SB. Solubility of liquid organic flavor and fragrance compounds in subcritical (hot/liquid) water from 298K to 473K. Journal of Chemical and Engineering Data 2000;45(2):315-318. |
R825394 (1999) R825394 (Final) |
not available |
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Yang Y, Belghazi M, Lagadec A, Miller DJ, Hawthorne SB. Elution of organic solutes from different polarity sorbents using subcritical water. Journal of Chromatography A, June 1998;810(1-2):149-159. |
R825394 (1999) R825394 (Final) |
not available |
Toxics, Geographic Area, Scientific Discipline, Waste, Remediation, HAPS, Physics, Environmental Chemistry, Engineering, State, organic pollutants, clean technologies, North Dakota (ND), solvents, hydrocarbon, PCBs, process scale equipment, corrosivity, PAH, PCB, sub critical water extraction
Progress and Final Reports:
Original Abstract
Final Report