Catalyzed Depolymerization Of Polycarbonate In Subcritical Water

The characteristics of subcritical water and its application in recyclingof polymer were introduced in the paper. Studies of PC depolymerizationand recycling in sup ercritical fluids are summarized.The experiment was carried out in a batch autoclave with magneticallydriving agitator. The depolymerization products were analyzed by GasChromatography and Mass Spectrometry (GC-MS), Gas Chromatography(GC), Fourier-transform Infrared Spectroscopy (FT-IR), respectively.The main product of thermal degradation of PC were carbon dioxide,phenol, 4-Methylphenol, 4-(1-methyl-1-phenylethyl)-Phenol andBisphenol A. Depolymerization of PC in subcritical water wasexperimentally studied under the conditions of temperature 280-320℃,reaction time 15-60min, ratio of water/PC 5.0-10.0 and concentration ofco-solvent 0-30％. The results indicated that the products ofdepolymerization were multiplicity, yield of BPA decreases with theincreasing of temperature and reaction time when the depolymerizationsufficiency, the best concentration of co-solvent was discovered. Themaximal yield of BPA was gained at optimal conditions of temperature 300 ℃, reaction time 15min, ratio of ethanol/PC 8.0 and concentration ofco-solvent 20％, respectively.Catalyzed depolymerization of PC in subcritical water was carded outunder the condition of temperature 180～240℃, reaction time 5～60min,ratio of water/PC 5.0～10.0, concentration of ethanol co-solvent 0-30％andamount of catalyst 0.6-1.8g/(160ml), respectively. The main products werephenol, 1,2,4,5-Tetramethylbenzene and Bisphenol A. It was found that theyield of BPA can reach 76.5％at the optimal reaction conditions oftemperature 200℃, reaction time 5min, ratio of ethanol/PC 8.0,concentration of co-solvent 0％, amount of catalyst 1.4g/(160ml).According to the distribution of depolymerization products and theenergy of carbon chain, the main mechanism of deploymerization andcatalyzed depolymerization of PC in subcritical water was hydrolyzation,the free radicals were gained for the random break of chain, which wereeasily to aggregate with the products. The selectivity of deploymerizationcould be improved for the proper concentration of ethanol, besides, thehydrolyzation would be accelerated and the yield of BPA would beenhanced.