Determination of the high-pressure phase equilibria of Polystyrene/p-Cymene in presence of CO2

• Effect of density and Polystyrene concentration was studied on the solubility of p-Cymene in CO2 and on the solubility of CO2 into solutions.
• Solubility of p-Cymene increases when density increases and concentration decreases.
• Solubility of CO2 increases when density and concentration decreases.
• Theoretical prediction allows the selection of the optimum conditions to precipitate the polymer.

An environmentally friendly technology to recycle Polystyrene (PS) wastes from a solution of p-Cymene using CO2 as antisolvent was proposed. In this process, the study of equilibrium of the ternary mixtures CO2/p-Cymene/Polystyrene is crucial, and particularly, the solubility of p-Cymene in CO2 and the sorption of CO2 in the solution are the key factors since the recovered polymer should be precipitated while the solvent should be fully solubilized in CO2. In this work, the effect of pressure (50–100–150 bar), temperature (25–30–40 °C) and polymer concentration (0.05–0.80 g PS/ml p-Cymene) on the solubility of p-Cymene and CO2 were studied to determine the most suitable conditions to perform the precipitation of Polystyrene. The experimental data were correlated as a function of density and polymer concentration according to modifications of well-known semi-empirical expressions (Chrastil's equation and Dual-Mode model). The optimum conditions to carry out the precipitation process of Polystyrene were calculated from the application of the fitted parameters obtained from the previous proposal. The most suitable conditions to precipitate Polystyrene from its solution in p-Cymene were reached at high values of density, it means, high pressure, low temperature and moderated concentration.

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