title: Mixed redox catalytic destruction of chlorinated solvents in soils and groundwater.
abstract: A new thermocatalytic method to destroy chlorinated solvents has been developed in the laboratory and tested in a pilot field study. The method employs a conventional Pt/Rh catalyst on a ceramic honeycomb. Reactions proceed at moderate temperatures in the simultaneous presence of oxygen and a reductant (mixed redox conditions) to minimize catalyst deactivation. In the laboratory, stable operation with high conversions (above 90% at residence times shorter than 1 s) for perchloroethylene (PCE) is achieved using hydrogen as the reductant. A molar ratio of H(2)/O(2)= 2 yields maximum conversions; the temperature required to produce maximum conversions is sensitive to influent PCE concentration. When a homologous series of aliphatic alkanes is used to replace hydrogen as the reductant, the resultant mixed redox conditions also produce high PCE conversions. It appears that the dissociation energy of the C-H bond in the respective alkane molecule is a strong determinant of the activation energy, and therefore the reaction rate, for PCE conversion. This new method was employed in a pilot field study in Tucson, Arizona. The mixed redox system was operated semicontinuously for 240 days with no degradation of catalyst performance and complete destruction of PCE and trichloroethylene in a soil vapor extraction gas stream. Use of propane as the reductant significantly reduced operating costs. Mixed redox destruction of chlorinated solvents provides a potentially viable alternative to current soil and groundwater remediation technologies.
authors.affiliation: Department of Atmospheric Sciences, The University of Arizona, Tucson, Arizona, USA. song.gao@arizona.edu
authors.forename: Song
authors.initials: S
authors.lastname: Gao
authors.forename: Erik
authors.initials: E
authors.lastname: Rupp
authors.forename: Suzanne
authors.initials: S
authors.lastname: Bell
authors.forename: Martin
authors.initials: M
authors.lastname: Willinger
authors.forename: Theresa
authors.initials: T
authors.lastname: Foley
authors.forename: Brian
authors.initials: B
authors.lastname: Barbaris
authors.forename: A Eduardo
authors.initials: AE
authors.lastname: Sáez
authors.forename: Robert G
authors.initials: RG
authors.lastname: Arnold
authors.forename: Eric
authors.initials: E
authors.lastname: Betterton
mesh_terms: D000473:Alkanes; D001673:Biodegradation, Environmental; D002384:Catalysis; D002621:Chemistry / Q000379:methods*; D002623:Chemistry Techniques, Analytical / Q000295:instrumentation / Q000379:methods; D002713:Chlorine / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods; D004787:Environmental Pollution; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D012997:Solvents / Q000737:chemistry*; D013696:Temperature; D014874:Water Pollutants, Chemical / Q000378:metabolism
chemical_list: D000473:Alkanes; D012989:Soil Pollutants; D012997:Solvents; D014874:Water Pollutants, Chemical; D002713:Chlorine; D010100:Oxygen