| A new approach for polymer recycling is to depolymerize polymers into monomers, dimers, and useful hydrocarbon materials or liquid fuels in supercritical fluids. The paper introduces the basal characteristics of supercritical fluids and its application on chemical recycling of waste plastics. Recent studies progress on recycling of polycarbonate (PC), especially on chemical recycling, are summarized.Depolymerization of polycarbonate (PC) in supercritical toluene was carried out in a stirred batch autoclave at different conditions such as reaction temperature, resistant time,reactor pressure and the weight ratio of toluene to PC and so on. The depolymerization products were examined by GC-MS, GC, FT-IR, respectively. The main reaction products were bisphenol A(BPA), PC Conversion and content of bisphenol A in the liquid products increases with the increase of temperature and the reaction time. The results of kinetic analysis showed that the depolymerization reaction rate was first order to the polycarbonate concentration. The dependence of the rate constant on the reaction temperature was correlated by the Arrhenius relation, which shows the activation energy of 61.41kJ·mol-1 in supercritical toluene.Depolymerization of PC in supercritical toluene/alcohol co-solvent was also carried out at different tenperature range and at reaction time respectively. The main reaction products were bisphenol A by gas chromatography-mass spectrometry and gas chromatography respectively. Reaction temperature, resident time play a role on component contents of the liquid products. It is found out that the optimized conditions of thereaction are at temperature of 300℃, reaction time of 45min.By discussing mechanisms of depolymerization, Random scission is themain depolymerization path in supercritical fluids. Studies show depolymerization path in supercritical fluid is a typical free radical reaction, which includes random scission, carbon-hydrogen bond fission, propagation H abstraction, intramolecular H abstraction and recombination, disproportionation reactions are the relevant reaction classes.Excellent solubility and mass transfer of supercritical fluids improve greatly molecular fluidity, and enhance hydrogen transfer and engaging in free radical reaction. |
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