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Title: Photocatalytic and chemical oxidation of organic compounds in supercritical carbon dioxide. 1998 annual progress report

Abstract

'This report summarizes the results of work done during the first 1.3 years of a three year project. During the first nine months effort focussed on the design, construction and testing of a closed recirculating system that can be used to study photochemistry in supercritical carbon dioxide at pressures up to 5,000 psi and temperatures up to about 50 C. This was followed by a period of work in which the photocatalytic oxidation of benzene and acetone in supercritical, liquid, and gaseous carbon dioxide containing dissolved oxygen was demonstrated. The photocatalyst was titanium dioxide supported on glass spheres. This was the first time it was possible to observe photocatalytic oxidation in a supercritical fluid and to compare reaction in the three fluid phases of a solvent. This also demonstrated that it is possible to purify supercritical and liquid carbon dioxide using photochemical oxidation with no chemical additions other than oxygen. The oxidation of benzene produced no intermediates detectable using on line spectroscopic analysis or by gas chromatographic analysis of samples taken from the flow system. The catalyst surface did darken as the reaction proceeded indicating that oxidation products were accumulating on the surface. This is analogous to the behavior ofmore » aromatic compounds in air phase photocatalytic oxidation. The reaction of acetone under similar conditions resulted in the formation of low levels of by-products. Two were identified as products of the reaction of acetone with itself (4-methyl-3-penten-2-one and 4-hydroxy-4-methyl-2-pentanone) using gas chromatography with a mass spectrometer detector. Two other by-products also appear to be from the self-reaction of acetone. By-products of this type had not been observed in prior studies of the gas-phase photocatalytic oxidation of acetone. The by-products that have been observed can also be oxidized under the treatment conditions. The above results establish that photocatalytic oxidation of organic compounds in supercritical carbon dioxide can be achieved. Until recently it was not possible for us to obtain high quality, quantitative kinetic data. The original flow cell used to obtain UV-Visible spectra on the recirculating fluid did not provide quantitative concentration data because the sapphire windows did not have adequate transmission characteristics below about 240 nm. A pair of windows with better transmission properties arrived as this report was being prepared. While waiting for the replacement windows for the flow cell, the concentration of reactants was monitored by withdrawing samples of the fluid stream for gas chromatographic analysis. This allowed progress to be made in determining some of the factors that affected the rates of reaction in a qualitative sense but the results had large error bars due to the difficulty in obtaining reproducible samples from the pressurized system using gas tight syringes. This problem was recently solved by incorporating a gas chromatograph with automatic sampling valves into the flow system. The two on line analytical methods will now result in reliable analytical data that can be used to follow the reaction kinetics and detect and identify reaction intermediates and by-products, if any are formed.'« less

Authors:
Publication Date:
Research Org.:
National Renewable Energy Lab., Golden, CO (US)
Sponsoring Org.:
USDOE Office of Environmental Management (EM), Office of Science and Risk Policy
OSTI Identifier:
13734
Report Number(s):
EMSP-54847-98
ON: DE00013734
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
40; 05; 54; Progress Report; Catalysts; Chemical Reactions; Waste Processing; Radioactive Wastes; Chemical Wastes; Decontamination; Decommissioning; High-Level Radioactive Wastes; Remedial Action; PROGRESS REPORT; CATALYSTS; CHEMICAL REACTIONS; WASTE PROCESSING; RADIOACTIVE WASTES; CHEMICAL WASTES; DECONTAMINATION; DECOMMISSIONING; HIGH-LEVEL RADIOACTIVE WASTES; REMEDIAL ACTION

Citation Formats

Blake, D.M.. Photocatalytic and chemical oxidation of organic compounds in supercritical carbon dioxide. 1998 annual progress report. United States: N. p., 1998. Web. doi:10.2172/13734.
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Blake, D.M.. Photocatalytic and chemical oxidation of organic compounds in supercritical carbon dioxide. 1998 annual progress report. United States. doi:10.2172/13734.
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Blake, D.M.. Mon . "Photocatalytic and chemical oxidation of organic compounds in supercritical carbon dioxide. 1998 annual progress report". United States. doi:10.2172/13734. https://www.osti.gov/servlets/purl/13734.
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@article{osti_13734,
title = {Photocatalytic and chemical oxidation of organic compounds in supercritical carbon dioxide. 1998 annual progress report},
author = {Blake, D.M.},
abstractNote = {'This report summarizes the results of work done during the first 1.3 years of a three year project. During the first nine months effort focussed on the design, construction and testing of a closed recirculating system that can be used to study photochemistry in supercritical carbon dioxide at pressures up to 5,000 psi and temperatures up to about 50 C. This was followed by a period of work in which the photocatalytic oxidation of benzene and acetone in supercritical, liquid, and gaseous carbon dioxide containing dissolved oxygen was demonstrated. The photocatalyst was titanium dioxide supported on glass spheres. This was the first time it was possible to observe photocatalytic oxidation in a supercritical fluid and to compare reaction in the three fluid phases of a solvent. This also demonstrated that it is possible to purify supercritical and liquid carbon dioxide using photochemical oxidation with no chemical additions other than oxygen. The oxidation of benzene produced no intermediates detectable using on line spectroscopic analysis or by gas chromatographic analysis of samples taken from the flow system. The catalyst surface did darken as the reaction proceeded indicating that oxidation products were accumulating on the surface. This is analogous to the behavior of aromatic compounds in air phase photocatalytic oxidation. The reaction of acetone under similar conditions resulted in the formation of low levels of by-products. Two were identified as products of the reaction of acetone with itself (4-methyl-3-penten-2-one and 4-hydroxy-4-methyl-2-pentanone) using gas chromatography with a mass spectrometer detector. Two other by-products also appear to be from the self-reaction of acetone. By-products of this type had not been observed in prior studies of the gas-phase photocatalytic oxidation of acetone. The by-products that have been observed can also be oxidized under the treatment conditions. The above results establish that photocatalytic oxidation of organic compounds in supercritical carbon dioxide can be achieved. Until recently it was not possible for us to obtain high quality, quantitative kinetic data. The original flow cell used to obtain UV-Visible spectra on the recirculating fluid did not provide quantitative concentration data because the sapphire windows did not have adequate transmission characteristics below about 240 nm. A pair of windows with better transmission properties arrived as this report was being prepared. While waiting for the replacement windows for the flow cell, the concentration of reactants was monitored by withdrawing samples of the fluid stream for gas chromatographic analysis. This allowed progress to be made in determining some of the factors that affected the rates of reaction in a qualitative sense but the results had large error bars due to the difficulty in obtaining reproducible samples from the pressurized system using gas tight syringes. This problem was recently solved by incorporating a gas chromatograph with automatic sampling valves into the flow system. The two on line analytical methods will now result in reliable analytical data that can be used to follow the reaction kinetics and detect and identify reaction intermediates and by-products, if any are formed.'},
doi = {10.2172/13734},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jun 01 00:00:00 EDT 1998},
month = {Mon Jun 01 00:00:00 EDT 1998}
}
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DOI:  10.2172/13734
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  • ; ;
    'The background for the project is briefly reviewed and the work done during the nine months since funding was received is documented. Work began in January, 1997. A post doctoral fellow joined the team in April. The major activities completed this fiscal year were: staffing the project, design of the experimental system, procurement of components, assembly of the system. preparation of the Safe Operating Procedure and ES and H compliance, pressure testing, establishing data collection and storage methodology, and catalyst preparation. Objective The objective of the project is to develop new chemistry for the removal of organic contaminants from supercriticalmore » carbon dioxide. This has application in processes used for continuous cleaning and extraction of parts and waste materials. A secondary objective is to increase the fundamental understanding of photocatalytic chemistry. Cleaning and extraction using supercritical carbon dioxide (scCO{sub 2}) can be applied to the solution of a wide range of environmental and pollution prevention problems in the DOE complex. Work is being done that explores scCO{sub 2} in applications ranging from cleaning contaminated soil to cleaning components constructed from plutonium. The rationale for use of scCO{sub 2} are based on the benign nature, availability and low cost, attractive solvent properties, and energy efficient separation of the extracted solute from the solvent by moderate temperature or pressure changes. To date, R and D has focussed on the methods and applications of the extraction steps of the process. Little has been done that addresses methods to polish the scCO{sub 2} for recycle in the cleaning or extraction operations. In many applications it will be desirable to reduce the level of contamination from that which would occur at steady state operation of a process. This proposal addresses chemistry to achieve that. This would be an alternative to removing a fraction of the contaminated scCO{sub 2} for disposal and using makeup scCO{sub 2}. A chemical polishing operation can reduce the release of CO{sub 2} from the process. It can also reduce the consumption of reagents that may be used in the process to enhance extraction and cleaning. A polishing operation will also reduce or avoid formation of an additional waste stream. Photocatalytic and other photochemical oxidation chemistry have not been investigated in scCO{sub 2}. The large base of information for these reactions in water, organic solvents, or air suggest that the chemistry will work in carbon dioxide. There are compelling reasons to believe that the properties of scCO{sub 2} should increase the performance of photocatalytic chemistry over that found in more conventional fluid phases.'« less

  • Determine if photocatalytic or other clean oxidation chemistry can be applied to the removal of organic or inorganic contaminants that are introduced into supercritical carbon dioxide during its use as an extraction and cleaning medium in DOE environmental and waste minimization applications. The targets are those contaminants left in solution after the bulk of the solutes have been separated from the fluid phase by changing pressure and/or temperature (but not evaporating the CO2). This is applicable to development of efficient separations of contaminants from the fluid stream and will strengthen pollution prevention strategies that eliminate hazardous solvents and cleaning agents.more » Explore the use of supercritical carbon dioxide as a solvent for the photocatalytic oxidation of organic compounds and compare it to other types of oxidation chemistry. This will add to the fundamental understanding of photocatalytic oxidation chemistry of particulate semiconductors and provide new knowledge about conditions that may have relevance to the chemical fixation of carbon dioxide under photocatalytic conditions.« less

  • The goal of the proposed research is to develop new chemistry for the removal of organic contaminants from supercritical carbon dioxide. This has application in processes used for continuous cleaning and extraction of parts and waste materials. Cleaning and extraction using supercritical carbon dioxide (scCO2) can be applied to the solution of a wide range of environmental and pollution prevention problems in the DOE complex. The objectives at the outset of the project were to: (1) determine if photocatalytic or other clean oxidation chemistry can be applied to the removal of organic or inorganic contaminants that are introduced into supercriticalmore » carbon dioxide during its use as an extraction and cleaning medium. The target will be contaminants left in solution after the bulk of solutes have been separated from the fluid phase by changing pressure and/or temperature (but not evaporating the CO2). This is applicable to development of efficient separations and will strengthen pollution prevention strategies that eliminate hazardous solvents and cleaning agents. (2) explore the use of supercritical carbon dioxide as a solvent for the photocatalytic oxidation of organic compounds and to compare it to other types of oxidation chemistry. This will add to the fundamental understanding of photocatalytic oxidation chemistry of particulate semiconductors and provide new knowledge about conditions that have relevance to the chemical fixation of carbon dioxide.« less

  • Supercritical fluid extraction (SFE) using unmodified carbon dioxide has been explored as an alternative method for the extraction of semivolatile organic compounds from high-efficiency particulate air (HEPA) filters. HEPA filters provide the final stage of containment on many exhaust systems in US Department of Energy (DOE) facilities by preventing the escape of chemical and radioactive materials entrained in the exhausted air. The efficiency of the filters is tested by the manufacturer and DOE using dioctylphthalate (DOP), a substance regulated by the US Environmental Protection Agency under the Resource Conservation and Recovery Act. Therefore, the filters must be analyzed for semivolatilemore » organics before disposal. Ninety-eight acid, base, and neutral semivolatile organics were spiked onto blank HEPA material and extracted using SFE, Soxhlet, automated Soxhlet, and sonication techniques. The SFE conditions were optimized using a Dionex SFE-703 instrument. Average recoveries for the 98 semivolatile compounds are 82.7% for Soxhlet, 74.0% for sonication, 70.2% for SFE, and 62.9% for Soxtec. Supercritical fluid extraction reduces the extraction solvent volume to 10--15 mL, a factor of 20--30 less than Soxhlet and more than 5 times less than Soxtec and sonication. Extraction times of 30--45 min are used compared to 16--18 h for Soxhlet extraction.« less

  • ; ; ; ...
    'This project investigates the in-situ degradation of semivolatile organic compounds (SVOCs) and volatile organic compounds (VOCs) using in-well sonication, in-well vapor stripping, and biodegradation. The project has the primary objectives of developing this integrated system for efficient and economical removal and degradation of SVOCs and VOCs from groundwater. The project has as its goal the partial degradation (softening) of the more recalcitrant organic compounds in order to convert them into compounds that are more amenable to both air sparging and biological treatment. By performing the softening in-well, the treated organics can be reinjected and percolated through the subsurface, thereby enhancingmore » biodegradation by generating organics that are more easily biodegraded. This report summarizes work after nearly 2 years of a 3-year project. Argonne National Laboratory is developing a new technology that combines in-well sonication, in-well vapor stripping, and in-situ biodegradation for removal of SVOCs and VOCs from solution. Bench-scale batch experiments have been performed investigating the separate treatment systems involving stripping and sonication of halogenated organics in groundwater, along with the combined sonication/stripping system. Organic contaminants studied include: trichloroethylene (TCE), carbon tetrachloride (CCl4 ), tetrachloroethylene (PCE), trichloroethane (TCA), and ethylene dibromide (EDB). Initial organic concentrations range from {approximately}10 to {approximately}100 mg/L. Results of the sonication and vapor stripping experiments are available upon request.'« less