High-pressure phase equilibria of Polystyrene dissolutions in Limonene in presence of CO2

Dissolution with terpenic solvents is presented as an alternative and original route to recycle Polystyrene wastes at room temperature. Limonene was the chosen solvent to carry out the dissolution process because it presents high compatibility with Polystyrene besides being natural, non toxic and relatively low cost. The solvent removal is possible thanks to supercritical CO2 since it provides high solubility of Limonene and complete PS insolubility at moderated pressures and temperature. In order to determine the proper working conditions to conduct the precipitation of the polymer, accurate knowledge of the phase equilibrium for mixtures of carbon dioxide, Limonene and Polystyrene should be known. s work, the solubility of Limonene in the ternary system CO2/Limonene/Polystyrene was determined. The phase equilibrium experiments were conducted in a variable-volume view cell employing the static method. These experiments were carried out in the temperature range of 298.15–313.15 K, at pressures up to 15 MPa and in the concentration range of 0.05–0.80 g PS/ml Limonene. Initially the binary systems were studied by means of equations of state: Peng–Robinson in the case of CO2/Limonene and Sanchez–Lacombe in the case of Limonene/PS and CO2/PS. Predicted data were collected together with the experimental to check the agreement and to determine the limits of the ternary system formed by CO2–Limonene–PS. It is indispensable to determine the behaviour of the ternary system to know completely the fluid phase equilibrium. The results indicate that the solubility of Limonene in the vapour phase is favoured by high pressure and temperature as well as low concentration.