Depolymerization Of Polycarbonate In Supercritical And Sub-Critical Water, Methanol, Water/Methanol Mixture

Depolymerization of polycarbonate was studied in supercritical and sub-critical water,methanol,and water/methanol mixture in a batch autoclave under different conditions.The depolymerization products were analyzed by Gas Chromatography,Mass Spectrometry(GC-MS)and Gas Chromatography(GC),Fourier-transform Infrared Spectroscopy(FT-IR), respectively.Depolymerization of PC in supercritical and sub-critical water and methanol was studied under the conditions of temperature(473～673 K), pressure(3.60～28.43 MPa),reaction time(5～60min),ratio of medium/PC (8.0).PC could be degraded completely in supercritical methanol but could not be degraded completely in sub-critical water when the temperature was low.The yield of main products bisphenol A(BPA)and phenol depended on the temperature and time,and has little relationship with pressure.The yield of BPA was first increased and then decreased while the yield of phenol was increased with the temperature and time increasing.The maximal yield of BPA in supercritical and sub-critical water was 38.19% when the temperature was 653 K and the time was 35 min.The maximal yield of BPA in supercritical and sub-critical methanol was 78.58%when the temperature was 533 K and the time was 25 min.Depolymerization of PC in water/methanol mixture was studied under the conditions of temperature(473～573 K),pressure(3.44～13.29 MPa), reaction time(5～45min),ratio of mixture/PC(8.0).It was found that the conversion of PC was increased with temperature and time increasing.The yield of BPA and phenol were varied evidently with temperature and time. The depolymerization of PC in the three supercritical medium were compared with one another.It was found that the mixture has the advantage in depolymerization of PC and the recycling of BPA.According to the distribution of depolymerization products and the energy of carbon chain,the main mechanism of depolymerization of PC in supercritical and sub-critical water was stochastic.The result of kinetic analysis showed that the depolymerization reaction was first order to the polycarbonate concentration in supercritical and sub-critical water and water/methanol mixture.The activation energy was 99.77 kJ·mol^-1in supercritical and sub-critical water and 91.45 kJ·mol^-1in water/methanol mixture.