Influence Factors Of Polycarbonate Depolymerization In Sub-Critical Water

The characteristics of depolymerization of polycarbonate(PC) in sub-critical water were investigated by using a high-pressure batch autoclave reactor. The products were qualitative and quantitative analyzed by Fourier-transform Infrared Spectroscopy (FT-IR), scanning electron microscope (SEM), Gas Chromatography/Mass Spectrometry (GC/MS) and Gas Chromatography (GC), respectively.Depolymerization of PC in sub-critical water was studied under the conditions of temperature (260³40℃), pressure (4.8¹4.8 MPa), reaction time(15⁶0min) and ratio of water/PC (8.0). It was found that PC can be effectively depolymerized in sub-critical water. The temperature and reaction time were main factors in the process of depolymerizaition. As the temperature and reaction time rised, the yield of bisphenol A increased at first and then reduced,while the yield of phenol increased throughout the process. The result showed that at reaction temperature 300℃, reaction pressure 8.7 MPa and reaction time 45 min, the PC could be depolymerized completely with the yield of BPA and phenol were 36.88% and 31.16%, respectively. Based on the qualitative and quantitative analyses of the products, the reaction mechanism, i.e. hydrolytic reaction and side reaction occurred simultaneously during the process of depolymerizaition of PC was proposed. The results of kinetic analysis indicated that the depolymerization followed a pseudo-first-order kinetics and the activation energy of PC depolymerizaition in sub-critical water obtained from Arrhenius equation was 125.7 kJ·mol^-1.Depolymerization of PC which added plastic additives was studied under the conditions of temperature (280³40℃), pressure (6.4¹5.2 MPa), reaction time (15⁶0min) and ratio of water/PC (8.0). The plastic additives were flame retardants (Decabromodiphenyl ether , DBDPO) and plasticizer (Di-n-octyl Phthalate,DnOP). It was found that the flame retardants (DBDPO) would accelerate the hydrolysis of PC,while plasticizer (DnOP) has opposite effect. Both the additives would reduce the yield of BPA obviously, while the temperature and reaction time were still the main factors in this process. The result showed that the PC could be depolymerized completely and the yield of BPA was 30.9% with reaction temperature 300℃and reaction time 45 min when flame retardants had been added. The PC could be depolymerized completely and the yield of BPA was 19.85% with reaction temperature 320℃, reaction time 35 min or temperature 300℃, reaction time 60 min when plasticizer had been added.According to the distribution of depolymerization products and the energy of carbon chain, the main mechanism of depolymerization of PC with plastic additives in sub-critical water was proposed. The result of kinetic analysis showed that the activation energy of PC depolymerized in sub-critical water was 116.48 kJ·mol^-1 when flame retardants had been added, and the activation energy was 147.17 kJ·mol^-1 when plasticizer had been added.