Modelling the extraction of soil contaminants with supercritical carbon dioxide.

Extractions of volatile organic compounds (VOC's) in contaminated soil from petroleum site were performed with supercritical carbon dioxide at different temperatures, pressures, extraction times, solvent flow rates, soil moisture contents and soil acidity. Three soil systems were investigated in order to compare the best parameters for extraction. A central composite rotatable design has been used to evaluate the influence of operation conditions on the extraction efficiency to generate model equations representing the types of soil. The results indicate that at least 70-80% of the initial amount of VOC's can be removed at moderate temperatures even at very high moisture content. Supercritical extraction is best suited to silt type soils which have a low adsorption capacity. VOC's recoveries from the artificial contaminated soil samples were higher in comparison with real contaminated soils. At moderate temperatures, the extraction efficiency for real soils is low because pollutants bind strongly to the soil.

The influence of silica on pore diameter and distribution in PLA scaffolds produced using supercritical CO2.

Macroporous polylactide (PLA) scaffolds were fabricated using a supercritical CO2 foaming process. The addition of silica particles to the polymer matrix resulted in a significant modification in the pore size distribution exhibited by the scaffold. In the absence of silica, the scaffolds contained pores between 88 microm and 980 microm in diameter as determined using X-ray computed microtomography. The addition of silica at only 2 wt% resulted in the elimination of pores of >620 microm, with no significant influence on the total porosity of the material. This effect was attributed to the silica nucleating the formation of gas bubbles in the polymeric material. Although the addition of further silica to the scaffold resulted in a further reduction in modal pore diameter, when more than 20 wt% was added to the matrix little additional effect was noted. In addition to enabling some control over pore diameter, mineral deposition was shown to occur considerably more rapidly on the silica-modified scaffolds than on those containing no silica.