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Title:Applications of supercritical fluid processing to environmental control
Author(s):Eckert, Charles A.; Leman, Gregory W.; Tomasko, David L.
Contributor(s):University of Illinois at Urbana-Champaign. Advanced Environmental Control Technology Research Center
Subject(s):Supercritical fluid extraction
Environmental engineering -- Technological innovations
Waste minimization -- Technological innovations
Waste reduction -- Technological innovations
Abstract:Environmental control and waste remediation are of immediate technological and political interest. One technology which has great potential is contaminant removal and separation with supercritical fluids (SCF's) or supercritical fluid extraction (SFE). In order to take advantage of this technology, both a fundamental understanding of phase equilibria and applicable engineering design data are required. This report documents an extensive study into both aspects culminating in the design and economic evaluation of a SCF regeneration process for granular activated carbon (GAC). We determined solubilities of relatively non-volatile solid compounds in supercritical fluid solvents, exploring effects of solvent properties, solute properties, and the nature of the critical region. Cosolvents added to an SCF were shown to enhance solubilities and increase selectivities through specific intermolecular interactions. Vapor pressure measurements and spectroscopic investigations also aided the understanding of solubility enhancement. The data were used to test and develop equations of state for calculating phase equilibria in systems containing a supercritical fluid. The ability of supercritical CO2 to remove model contaminant compounds from GAC and subsequently drop out most of the contaminant in a liquid phase has been investigated in a pilot scale apparatus. Typical desorption profiles indicate approximately 85% removal of contaminants 2-chlorophenol and toluene from the carbon. The presence of water on the GAC was shown to inhibit slightly the efficiency of the desorption. The desorption results have been interpreted with a generalized desorption-mass transfer model. The results of the pilot scale studies have been applied to the design of a fixed-site GAC regeneration unit consisting of a three element desorber with two stage flash separation. Optimization of the process centers around minimizing the cost of recycling the SCF through an efficient recompression scheme and regeneration cycle configuration in the desorber unit. An economic evaluation shows a processing cost of lO.6e/lb GAC which compares favorably with thermal regeneration and incineration. This non-destructive process allows re-use of the GAC while maintaining a high adsorbate capacity, which reduces carbon replacement costs and significantly decreases the need for carbon disposal by landfill or incineration.
Issue Date:1991
Publisher:Hazardous Waste Research and Information Center (HWRIC)
Series/Report:TR Series (Hazardous Waste Research and Information Center) ; 006
Genre:Technical Report
Sponsor:EPA Cooperative Agreement EPA CR 812582
Date Available in IDEALS:2007-09-08

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