Modeling of Askarel solubility in supercritical CO2 aiming solid residue treatment

• Development of an efficient thermodynamic approach and tool to calculate solubility of polychlorinated biphenyls and other solutes in supercritical CO2.
• Selection and analysis of a systematic series of solubility data of aromatic and polychlorinated biphenyls in supercritical CO2.
• Environmental importance of the supercritical extraction of Askarel oil from contaminated solid matrices.
• Complex behavior of the solubilities in supercritical CO2 described by vdW2 mixing rule and sublimation pressure expression parameters.

Polychlorinated biphenyls (PCB) are chlorinated organic substances which are highly toxic and also considered persistent organic pollutants (POP). It should be emphasized the environmental importance for treating wastes with PCB. For instance, Stockholm convention on POP established the elimination of the use of PCB in equipments, e.g., electrical transformers and capacitors, by 2025. The decontamination of materials containing PCB may be performed by supercritical extraction technology using carbon dioxide (CO2) as solvent. The first objective of this work was the formulation of a computational tool to correlate solubility data of aromatic compounds in supercritical CO2, using Peng–Robinson equation of state. In a second step, a description of Askarel oil, like Araclor 1254, solubility in supercritical CO2 was provided for simulation purposes of the extraction process. PCB mixture has predominance of congeners: tetra, penta, hexa, heptachloro biphenyl, tri and tetrachlorobenzene. The calculation procedure was initially applied for a series of aromatic compounds (naphthalene, biphenyl, anthracene and phenanthrene) in order to validate the approach. Experimental solubility data collection has been elaborated from the literature, providing a systematic series of the studied aromatic compounds with CO2. The binary parameters for the classical van der Waals quadratic mixing rule (vdW2) were systematically estimated, together with a new set of Clausius–Clapeyron solute vapor pressure in order to describe the temperature dependence and achieve experimental solubility uncertainties. Finally, the estimated parameters were used to simulate solubility values of Askarel oil as function of the operational conditions of extraction by a simultaneous solution of the equilibrium equations for each compound. The thermodynamic modeling demonstrated to be feasible for process analysis and design.

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