Modeling of supercritical CO2 extraction of contaminants from post-consumer polypropylene: Solubilities and diffusion coefficients in swollen polymer at varying pressure and temperature conditions

- Supercritical CO2 extraction mechanism can be simplified to a process controlled by diffusion and solubility.
- Diffusion coefficient and solubility depend strongly on contaminant molecular structure.
- Important role played by the matrix swelling by SCCO2 pressure on the diffusion coefficient enhancement.
- Swelling induced by CO2 pressure decreases the activation energy for diffusion of contaminants in polypropylene.
- Pressure has a positive effect on solubility in supercritical CO2, whereas temperature effect is complex.

The reported work aimed at the modeling of the supercritical CO2 (SCCO2) extraction of contaminants covering a wide range of molecular weights from post-consumer polypropylene. A theoretical model taking into account the combined effects of the two essential phenomena involved in the extraction process (diffusion through the matrix and solubility in SCCO2) is applied to experimental results in order to analyze extraction and disclose relevant kinetics limitations affecting extraction process. From fitting the model to the experimental data obtained at varying pressure and temperature conditions, information on diffusion coefficients of contaminants through polypropylene swollen by SCCO2, activation energies for diffusion and solubilities in the supercritical fluid at temperatures of 50, 70 and 90 °C, and pressures of 100, 200 and 300 bar were obtained. Good agreement between the theoretical model and our experimental measurements was observed. Diffusion coefficients of contaminants through swollen polypropylene have an order of magnitude of 10−11-10−10 m2/s, which are much more important than those through virgin polypropylene due to the swelling effects. Finally, the effects of pressure and temperature on diffusion coefficients and solubilities were examined and discussed in order to understand the effects of these two chief parameters on the SCCO2 extraction rate.

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