Supercritical extraction of volatile organic components from polyethylene pellets

This paper evaluates the feasibility of extracting volatile organic compounds (VOCs) from polyethylene pellets via contact with supercritical fluids. Stagnant carbon dioxide (CO2) or stagnant ethane above their critical points contacted stagnant pellets. Then, a quick depressurization step vented the gases, and the pellets were analyzed for volatiles content. Moderately high temperatures (60 °C) appear to be necessary for an effective devolatilization. At 36 °C, diffusion limitations dominate, and the extraction performance is insensitive to the pressure and to the chemical nature of the supercritical fluid. At 60 °C, ethane could extract more volatiles than CO2, indicating that the mutual solubility of VOCs and extraction fluids is an important factor. Up to a 90% reduction of the initial volatile content resulted after a 3-h contact with CO2 in multiple extractions in which pure CO2 periodically replaced VOC-laden CO2. A similar VOC reduction level resulted using ethane in a single extraction (i.e., without replacing the used ethane).