Supercritical Fluid Extraction of Polycyclic Aromatic Hydrocarbon Mixtures from Contaminated Soils

Abstract

Highly contaminated (with PAHs) topsoils were extracted with supercritical CO2 to determine the feasibility and mechanism of supercritical fluid extraction (SFE). Effects of supercritical fluid (SCF) density, temperature, and 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 CO2 density. Water and methanol were used as cosolvents in some experiments, at 0.3−6 wt %. For extractions at an ∼1000 phase ratio (wt of CO2/wt of soil), near-complete contaminant removal was achieved. For an ∼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 with water 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.

Effect of supercritical fluid extraction parameters and clay properties on the efficiency of phenanthrene extraction

“…Subsequently the SFE technique could be used for more adequate analyses of contaminated soil, waste and sediments as well for its remediation. In extracting contaminants from soils, SFE would be less energyconsuming than thermal methods applied to an entire soil mass, and it leaves the soil's structure relatively intact [5]. The use of SFE to extract contaminants has been studied for various solid and soil matrices such as sand, clay, slag, and sediment (among others, [5][6][7][8][9][10][11]).…”

“…In extracting contaminants from soils, SFE would be less energyconsuming than thermal methods applied to an entire soil mass, and it leaves the soil's structure relatively intact [5]. The use of SFE to extract contaminants has been studied for various solid and soil matrices such as sand, clay, slag, and sediment (among others, [5][6][7][8][9][10][11]). Other researchers applied a variety of operational parameters, such as fluid pressure, fluid temperature, extraction time, cosolvent type and amount, and modifiers to optimize the recovery of organic compounds.…”

Supercritical CO2 extraction of PAHs on spiked soil

“…Thus, this enhancement has been attributed to an increase in the supercritical phase density if compared to pure supercritical carbon dioxide [8]. Additionally, co-solvent nature can affect the diffusivities within the solid by matrix swelling.…”

“…The positive influence can be attributed to a swelling process due to the presence of the co-solvent. Swelling would eventually increase intraparticle diffusivities facilitating, therefore, the extraction of PAHs [8]. Unfortunately, hydrogen peroxide did exert no significant influence in the process.…”

One-step SFE-plus-C 18 selective extraction of low-polarity compounds, with lipid removal, from smoked fish and bovine milk

“…dichloromethane, benzene). The use of supercritical-fluid extraction (SFE) has received increasing attention as a suitable alternative to classical solvent extraction techniques for environmental sample analyses [11,12,13,14,15]. Among the clear advantages of employing supercritical CO 2 over liquid solvents for extraction are controllable solvent power, ability to handle smaller sample volumes, reduced analysis times, easy automation, and extremely low toxicity [16,17,18].…”