Supercritical Fluid Extraction of Contaminated Soil

The objective of this preliminary investigation is to determine the ability of supercritical carbon dioxide (SC-CO2) to remove contaminant organic compounds from soil. The focus is to obtain experimental data on the extraction of organic hazardous waste from soils by SC-CO2. The aim of this study is to evaluate this information for its applicability to the design of a supercritical fluid extraction (SFE) process for environmental remediation and waste management. An experimental continuous-flow extraction apparatus that can be operated up to 340 atm has been constructed at Vanderbilt University. With this apparatus the effects of pressure, temperature, flow rate, and soil properties on the equilibrium thermodynamics and mass-transfer coefficient of the SFE process can be studied. For the purposes of this paper, it is assumed that the supercritical solvent flows through a fixed bed extracting organic contaminants from spherical soil particles. To verify the apparatus and our experimental technique, preliminary studies on the equilibrium solubility of naphthalene were conducted. The extraction cell was packed with a single section of one layer of pure cylindrical naphthalene pellets. The results show that naphthalene solubility in supercritical CO2 experimentally determined at constant temperature (55°C) agree over the entire pressure range studied (125-270 atm) with results published by other investigators. Experiments were also conducted with naphthalene and 1,2,4 trimethylbenzene in soil formed into spherical shape. Preliminary results of this investigation has demonstrated that effective extraction (98%) of naphthalene from soil by supercritical CO2 can be achieved in our apparatus.