SEPARATION OF THERMOPLASTICS BY DENSITY USING NEAR-CRITICAL AND SUPERCRITICAL CARBON-DIOXIDE AND SULFUR-HEXAFLUORIDE

Near-critical and supercritical fluids composed of carbon dioxide and/or sulfur hexafluoride have been used to sort thermoplastic waste mixtures according to density. For example, PVC can be readily removed from waste PET, and tinted or filled materials can be separated from their clear and unfilled counterparts. Carbon dioxide alone can be used to separate polyolefins, while pure sulfur hexafluoride, an extremely dense fluid, can be used to separate the non-olefin thermoplastics. Sulfur hexafluoride-rich CO2/SF6 mixtures can be used to separate all of the thermoplastics. The brief exposure of the thermoplastics to the mild temperature, high-pressure environment did not chemically or physically alter them. ne densities of the supercritical or near-critical fluid mixtures have been accurately correlated to temperature, pressure and fluid composition using a cubic equation of state.