Supercritical fluid extraction of organic compounds from solids and aqueous solutions: Dissertation

In this thesis, the extraction of organic compounds from solid and liquid matrices using supercritical carbon dioxide as a solvent was studied. Dense carbon dioxide is a very good solvent for the cyclic amide, 6-caprolactam. 6-caprolactam exhibits relatively high solubilities, i.e. up to around 17 wt% at ambient temperatures, and at pressures below 220 bar. Carbon dioxide can be used to dissolve and extract 6-caprolactam from solid and liquid matrices. The remediation of contaminated soil by carbon dioxide extraction was studied. The effect of extraction pressure, temperature, soil moisture content, pH, carbon dioxide mass flow rate, and extraction time on the residual pollutant concentration in the soil after extraction was systematically studied. The selected pollutants were phenanthrene, 2,3,4,6-tetrachlorophenol and pentachlorophenol. The results indicate that at least 80-90 % of the initial amount of pollutant can be removed at moderate temperatures even in the most difficult cases, and in many cases over 99 % of the initial amount of pollutant can be removed from the soil. Supercritical extraction is best suited to sand or silt type soils, which have a low adsorption capacity. The extraction results are found to be case-dependent, and soil remediation at moderate temperatures is observed to be difficult if the pollutant binds strongly to the soil or if the acceptable level of residual concentration is very low. A novel mechanically agitated countercurrent continuous extraction column was introduced by extracting ethanol and 1-butanol from aqueous solutions in the rotating disk column and in the Oldshue-Rushton column. Column efficiencies were measured as a function of solvent-to-feed ratio and rotor speed. Generally, the values of the height equivalent to a theoretical stage HETS were in the range of 0.4-0.8 m. Mechanical agitation enhanced the extraction only at relatively high solvent-to-feed ratios. Column capacities for both types of column were measured, and the total throughput calculated as the feed plus solvent flow rate divided by the smallest cross-sectional area was 50-80 m3h-1m-2. A mechanically agitated column successfully combines the high capacity of supercritical spray columns and the high efficiency of supercritical packed columns.