Oxidation of Polychlorinated Biphenyls (PCBs) in Supercritical Water

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ABSTRACTPI: Lawrence L. Tavlarides Institution: Syracuse UniversityProposal Number: 0115650The goal of this project is to advance the existing technology of the supercritical water oxidation (SCWO) process by developing fundamental knowledge which can be used to define an efficient and environmentally safe way to destroy toxic polychlorinated biphenyls (PCBs) extracted from contaminated soil/sediments or from disposal sites. PCBs are highly toxic organic pollutants (POPs) included by 122 nations on a recently banned list of chemicals known as the "dirty dozen." The 209 PCB congeners are approximately twice the number of the elements in the Periodic Table and 17 times the number of chlorobenzenes, offering chess0like possibilities of investigations. Systematically selected congeners and the most used industrial PCB mixtures will be oxidized in SCW both neat and methanolic solutions. Emphasis will be on the methanolic solutions due to observed rate-enhancing quality of MeOH on PCB dechlorination. Several solutions obtained by SC-CO2/MeOH extraction from PCB polluted real world sediments will also be studied to couple the extraction and oxidation steps of a soil remediation technology being developed by the PI. This approach will permit one to design and optimally operate competitive SCWO large-scale units for PCBs and other related pollutants under less severe conditions than those proposed without kinetic studies and without reaction rate enhancers. Based on experimental results, reaction kinetics and pathways and structure-reactivity relationships will be developed.PCB oxidation experiments in supercritical water will be conducted in a high-pressure, isothermal plug-flow tubular reactor capable of continuous operation at temperatures up to 873 K and pressures up to 60 MPa. The approach is to select thermodynamic, kinetic and process parameters in order to find the optimum conditions for achieving the strategic goal of safe and efficient PCB destruction under the least aggressive conditions. The main parameters considered are temperature (673 - 874 K), pressure (25 - 35 MPa), residence time (1-240 s), and solute concentration (0.1 - 10 g/L in MeOH, and 10-3 - 10 mmol/L in SCW). This knowledge will be disseminated to the research community through publications and presentations and will provide a model training/education to students, including Native Americans living on PCB contaminated lands.