Supercritical Fluid Extraction of Some Chlorinated Benzenes and Cyclohexanes from Soil: Optimization with Fractional Factorial Design and Simplex

Abstract

The optimization of supercritical fluid extraction (SFE) conditions for chlorinated benzenes (CBs) and hexachlorocyclohexanes (HCHs) from contaminated soil has been investigated. Addition of modifier (toluene, dichloromethane, or tert-butyl methyl ether) enhanced recovery and collection efficiency significantly as compared to pure CO2, with toluene being the most effective modifier for the extraction step. A statistical approach was used to find suitable conditions for the SF extraction of CBs and HCHs for native contaminated soil. A half-replicate of a 24 design revealed that a higher extraction time (45 min instead of 15 min) and an extraction temperature of 60 °C instead of 150 °C contributed more than pressure (200 vs 450 atm) or modifier concentration (1 or 6 mol %) to improve overall extraction efficiency. The factors with a large influence on the recovery (temperature and time) as well as the less important factor pressure were optimized with a modifier simplex procedure. Significances of the data were evaluated by the F-test. The simplex procedure was terminated when 95% overall recovery, based on Soxhlet extraction with toluene, was achieved. For the soil under study, this occurred at 384 atm extraction pressure, 78 min extraction time, and 92 °C extraction temperature.