Dyeing waste plastic pellets with supercritical CO ₂ decolorization and recycling PET

Recycling of waste plastics is an important research direction for realizing resource recycling. Dyed waste plastics have huge reserves, so it is necessary to decolorize them before recycling to avoid poisoning of degradation catalysts or difficulties in the separation and purification of subsequent products. In the past, the decolorization of waste plastics was mostly done by organic solvents reacting at high temperatures, which was costly and put environmental pressure. This paper proposes that supercritical CO2 extraction can decolorize the dyed waste plastic pellets. With trace DMF as cosolvent, the reaction time is 3 hours at 90°C and 15 MPa, and the decolorization rate is as high as 87% and after the experiment, the solvent was recovered and reused. Based on the extraction kinetic curve, the solubility data of dyes in supercritical carbon dioxide were obtained and correlated with the density formula. The experimental results provide a possibility for green, efficient, and low-carbon decolorization of dyed waste plastics, and it is expected to realize large-scale production.