(Supercritical Extraction/Liquid Phase Oxidation)
The Institute of Gas Technology's (IGT) Supercritical Extraction/Liquid Phase Oxidation (SELPhOx) process (see figure below) removes organic contaminants from soils and sludges and destroys them. SELPhOx combines two processing steps: (1) supercritical extraction (SCE) of organic contaminants in liquids, and (2) wet air oxidation (WAO) destruction of the contaminants. The two-step process, linked by a contaminant collection stage, offers great flexibility for removing and destroying both high and low concentrations of organic contaminants.
Combining SCE and WAO in a single two-step process allows development of a highly efficient and economical process for remediating contaminated soils. Supercritical extraction with carbon dioxide (CO2) removes organic contaminants from the soil and transfers them to an aqueous phase while leaving much of the original soil organic matrix in place. The contaminants are then collected on activated carbon in a contaminant collection vessel. The activated carbon with sorbed contaminants is then transported in an aqueous stream to a WAO reactor for destruction. Concentrating the organic contaminants on activated carbon in water provides a suitable matrix for the WAO feed stream and improves process economics by decreasing WAO reactor size. The activated carbon is regenerated in the WAO reactor with minimal carbon loss and can be recycled to the contaminant collection vessel.
The SELPhOx process requires only water, air, makeup activated carbon, and the extractant (CO2). Primary treatment products include cleaned soil, water, nitrogen (from the air fed to the WAO step), and CO2. Organic sulfur, nitrogen, and chloride compounds that may be present in the original soil or sludge matrix are transformed to relatively innocuous compounds in the product water. These compounds include sulfuric acid and hydrogen chloride, or their salts. The treated soil can be returned to the original site, and the water can be safely discharged after thermal energy recovery and minor secondary treatment. The gas can be depressurized by a turbo expander for energy recovery and then vented through a filter.
The SELPhOx process removes organic contaminants from soils and sludges, including chlorinated and nonchlorinated polynuclear aromatic hydrocarbons (PAH), polychlorinated biphenyls, and other organic contaminants. The process is targeted toward sites that are contaminated with high levels of these organics (hot spots).
The SELPhOx process was accepted into the SITE Emerging Technology Program in July 1994. The primary objectives of the project are to (1) evaluate SCE's contaminant removal efficiency, (2) determine the potential for CO2 recovery and reuse, and (3) determine destruction efficiencies of extracted contaminants in the WAO process. Analytical results from the project will provide the necessary information for the full-scale process design.
Laboratory-scale SCE tests have been completed using soils contaminated with PAHs. Operating conditions for the SCE stage and the activated carbon adsorption stage have been selected. A transportable field test unit has been constructed. Testing of this unit with PAH-contaminated soil is underway.
EPA PROJECT MANAGER:
Brunilda Dávila
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7849
Fax: 513-569-7620
TECHNOLOGY DEVELOPER CONTACT:
Anil Goyal
Institute of Gas Technology
1700 South Mount Prospect Road
Des Plaines, IL 60018-1804
847-768-0605
Fax: 847-768-0671
E-Mail: goyal@igt.org
Michael Mensinger
ENDESCO Services, Inc.
1700 South Mount Prospect Road
Des Plaines, IL 60018-1804
847-768-0602
Fax: 847-768-0516
E-mail: mensing@igt.org