SUPERCRITICAL ADSORPTION AND DESORPTION BEHAVIOR OF DDT ON ACTIVATED CARBON USING CARBON-DIOXIDE

Supercritical adsorption isotherms were measured for the priority pollutant DDT on activated carbon at 313.1 and 318.1 K at a fixed carbon dioxide density of 0.658 g/cm(3). Equilibrium loadings, measured at saturation DDT solubilities, ranged from 0.5 to 0.7 g/g of carbon, and the adsorption isotherms are well described by the Freundlich model. The desorption of DDT from activated carbon using supercritical carbon dioxide was examined to assess the influence of temperature, density, and flow rate. Concentration-time desorption profiles were measured using a supercritical extraction apparatus that incorporated a high-pressure UV cell. The desorption efficiency for this system increases with both temperature and density, and the data indicate that the desorption process is limited by the adsorption equilibrium at low CO2 flow rate. Overall the desorption of DDT from activated carbon using supercritical CO2 is unfavorable with less than 60% removal and the bulk of the desorption occurring at very low relative DDT concentrations. A local equilibrium model combined with experimental adsorption data was able to predict the desorption profiles.