Scale-up for a process of supercritical extraction with adsorption of solute onto active carbon. Application to soil remediation

A pilot plant for soil remediation with supercritical CO2 extraction and subsequent adsorption of pollutants on activated carbon has being used to study scale-up procedure for supercritical extraction process. Experimental data were obtained for decontamination of soil polluted with hydrocarbons and operational parameters, such as extraction temperature, solid size particles and solvent ratio, were optimised. These data have been used to obtain the mass transfer coefficient (kga) and the equilibrium parameter (H) using a desorption bed model. A flow diagram of scale-up procedure is presented. From the results obtained in pilot plant, the design of a mobile full-scale plant has been developed and the following data were obtained. Soil treatment capacity: 250 kg/h. Extraction conditions: 26.0 MPa, 40 °C. Adsorption conditions: 26.0 MPa, 50 °C. Gasoil concentration: 14 500 ppm. Carbon dioxide flow: 452 kg/h. Extraction volume: 270 l (three extractors in series of 90 l per extractor and one extractor more for semi-continuous operation). Extraction time: 84 min per shift.