Catalytic Depolymerization Of Polycarbonate In Subcritical Water Combined With Raman Spectroscopy

Depolymerization of polycarbonate (PC) with catalyst manganese acetate (Mn(Ac)2) was studied in subcritical water by using a stainless batch autoclave reactor or a fused silica capillary reactor (FSCR), respectively. The solid residue was qualitative analysised by using a Fourier-transform infrared (FT-IR) spectrometer, and the main liquid products bisphenol A (BPA) and phenol were identified and quantified by gas chromatography mass spectrometry (GC-MS) and gas chromatography (GC). The main gaseous product CO2in FSCR was analysed by a Raman spectroscopic qualitatively and quantitatively.The phase behavior of PC in water with or without catalyst Mn(Ac)2during heating, reaction and cooling processes was observed by a microscope, and recorded with a digital camera. Images in two FSCR showed that PC swelled and softened at150℃and generally shank into liquid spherule at200℃, and the spherule gradually became smaller and totally dissolved in subcritical water and formed an aqueous solution coexisted with a vapor phase finally at260℃for a reaction time of45min with Mn(Ac)2and124min without Mn(Ac)2, respectively. Which indicated that adding Mn(Ac)2as catalyst could effectively reduce the reaction time for total depolymerization.To investigate the effect of reaction time on the gaseous product CO2, experiments were performed in a fused quartz glass reactor at temperature ranging from250to280℃, with a reaction time of15min to120min. Raman spectroscopic analysis showed that the volume of CO2increased with the reaction time prolonged, and it leveled off at280℃,270℃,260℃and250℃with reaction time of30min,75min,105min and120min, respectively.Catalytic depolymerization of PC in a batch-type autoclave reactor was conducted on the basis of the results in FSCR. The influences of operating parameters such as catalyst concentration (ratio of Mn(Ac)2to PC)(0%-2.5%), temperature (250～280℃) and reaction time (5min-60min) on depolymerization were investigated. Both yields of BPA and phenol were increased with increasing Mn(Ac)2/PC ratio. The depolymerization yield of PC increased with increasing reaction temperature and time, the BPA yield increased noticeably with time prolonging at first and then decreased for the reason of further decomposition, the yield of phenol increased with increasing depolymerization time. Within experimental conditions, temperature of280℃, reaction time of20min with the ratio (Mn(Ac)2/PC) of2.0%was considered to be relatively optimal conditions, and the yields of BPA and phenol reached55.25%and18.63%, respectively.A reaction pathway for PC catalytic depolymerization in subcritical water was presumed. The present of Mn(Ac)2could accelerate the depolymerization of PC for the hydrogen ions produced. The results of kinetic analysis indicated that the reaction followed a pseudo-first-order kinetics, and the activation energy obtained from Arrhenius equation was144kJ/mol.