NEAR-CRITICAL AND SUPERCRITICAL-FLUID EXTRACTION OF POLYCYCLIC AROMATIC-HYDROCARBONS FROM TOWN GAS SOIL

The contamination of soil by hazardous and toxic organic pollutants is an ever-growing problem facing the global community. One particular f amily of contaminants that are of major importance are polycyclic arom atic hydrocarbons (PAHs). PAHs are the result of coal gassification an d high-temperature processes. Sludges from these town gas operations w ere generally disposed of into unlined pits and left there for eventua l biodegradation. However, the high levels of PAH contained in the pit s prevented the occurrence of biodegradation. PAH contaminated soil is now considered hazardous and must be cleaned to environmentally accep table standards. One method for the remediation is extraction with sup ercritical water Water in or about its critical region exhibits enhanc ed solvating power toward most organic compounds. Contaminated soil co ntaining 4% by mass of hydrocarbons was ultra-cleaned in a 300-cm(3) s emicontinuous system to an environmentally acceptable standard of less than 200 ppm residual hydrocarbon concentration. The effects of subcr itical or supercritical extraction, solvent temperature, pressure, and density have been studied, and the discerning characteristics of this type of fluid have been identified. The efficiencies of subcritical a nd supercritical extraction have been discussed from a process enginee ring standpoint.