SCALE-UP AND ECONOMIC-ANALYSIS FOR THE DESIGN OF SUPERCRITICAL-FLUID EXTRACTION EQUIPMENT FOR REMEDIATION OF SOIL

The magnitude of the contaminated site clean-up in the United States i ndicates the need for more effective, less costly remediation technolo gies. Supercritical Fluid Extraction (SFE) using carbon dioxide (CO2) as a supercritical fluid is a possible alternative technology for reme diation of soils contaminated with volatile organic compounds. The fea sibility of this process is mainly dependent on two factors. the exten t and extraction rate of heavy molecular weight organic compounds from soil by supercritical carbon dioxide (SC-CO2). This paper presents re sults of a bench-scale study for remediation of soils contaminated wit h naphthalene and 1,2,4 trimethyl benzene as a function of the flow ra te (Qco(2)) and supercritical fluid density (rho co(2)). These data ar e used to perform a basic economic analysis of the process by using th ese two organics selected as model soil contaminants. An additional ai m of this study was to develop scale-up methodology from laboratory SF E devices to industrially useful equipment. Laboratory scale data, suc h as mass transfer coefficients, have implications for the sizing and control of process units including reactors and separation columns sin ce high mass transfer rates allow smaller reactors. Furthermore, this study included the collection and analysis of the experimental data to support the application of the supercritical fluid extraction technol ogy and to provide the conceptual design and operational processes req uired for the construction of a pilot plant unit. The experimental dat a were presented as an outlet concentration profile of solute (naphtha lene or 1,2,4 trimethyl benzene) desorption at different flow rates. T his qualitative analysis of the desorption experiments suggested that a promising model should include external and intraparticle mass trans fer and be based upon equilibrium at a desorption site. Thus, a simula tion has been performed using an equilibrium desorption model [1] and fitted using MATHEMATICA(R) software (version 2.2.2). Finally, a preli minary economic analysis using these results showed that the proposed process (SFL) is feasible for soils contaminated with two different pu re (naphthalene or 1,2,4 trimethyl benzene) hazardous organics as a mo del system.