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SUPERCRITICAL FLUID EXTRACTION OF POLYCYCLIC AROMATIC HYDROCARBON MIXTURES FROM CONTAMINATED SOILS
Becnel, J. M. AND K. M. Dooley. SUPERCRITICAL FLUID EXTRACTION OF POLYCYCLIC AROMATIC HYDROCARBON MIXTURES FROM CONTAMINATED SOILS. DOI: 10.1021/ie97041, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH. American Chemical Society, Washington, DC, 37(2):584-594, (1998).
Highly contaminated (with PAHs) topsoils were extracted with supercritical CO2 to determine the feasibility and mechanism of supercritical fluid extraction (SFE). Effect of SCF density, temperature, cosolvent type and amount, and of slurrying the soil with water were investigated. Experiments were conducted at 308-343 K and 450-850 kg/m3 and CO2 density. Water and methanol were used as cosolvents in some experiments, at 0.3-6 wt%. For extractions at ˜1000 phase ratio (wt CO2 /wt soil), near complete contaminant removal was achieved. For ˜ 200 phase ratio at 323 K and 13.8 MPa, >95% of two-ring PAHs and >80% of three-ring and heavier PAHs were extracted. Using soil slurries had little effect on the total recoveries. Changes in SCF density also had little influence on SFE, while temperature increases improved both initial rates of extraction and total recoveries. Addition of cosolvents generally hindered extraction of the contaminants. These results are used to show that, at typical conditions for CO2 -based soil extractions, the solubility of the contaminant in the SCF does not limit SFE. Other internal resistances are important, such as desorption from and diffusion within the polymeric soil organic matter.