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Depolymerization Of Polybutylene Terephthalate In Subcritical Water With And Without Catalyst

Posted on:2011-05-11Degree:MasterType:Thesis
Country:ChinaCandidate:J J DaiFull Text:PDF
GTID:2121330338477759Subject:Environmental Engineering
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Depolymerization of Polybutylene Terephthalate(PBT) was studied in sub-critical water with and without catalyst in a batch autoclave. Reaction products were terephthalic acid (TPA) and tetrahydrofuran (THF) that were analyzed by Fourier-transform Infrared Spectroscopy (FT-IR), Gas Chromatography and Mass Spectrometry(GC-MS), High Performance Liquid Chromatography(HPLC) and Gas Chromatography (GC). The influence of depolymerization temperature and time on PBT hydrolysis and products yield was studied. Depolymerization of PBT in sub-critical water was carried out in fused silica capillary reactor for visual observation of phase behavior changes under a microscope.Depolymerization of PBT in sub-critical water was studied under the conditions of temperature (220360℃), pressure (2.218.6MPa), reaction time (560min), ratio of water/PBT (4.012.0). The result showed that PBT could be degraded to monomer completely, TPA was the only solid product and THF was the only liquid product. Compared to the result of Goje.et al., GC-MS analyses did not show the presence of 1,4-butanediol(1,4-BD) in the liquid phase. It was proved by further studies that 1,4-BD could be completely transformed into THF by cyclodehydration at the experimental conditions. The solid product of terephthalic acid played a catalyst role in cyclodehydration of 1,4-BD, there is no publicly reported about the result at home and abroad until now. It was found that the PBT conversion increased with the reaction temperature and time, and had little relationship with ratio of water/PBT. The optimal conditions of the reaction were temperature 320℃, reaction time 15 min, reaction pressure 11.2MPa, ratio of 8:1 (24g H2O/3g PBT), and PBT could be totally depolymerized and the yield of TPA could attain 96.5%.Catalytic depolymerization of PBT sub-critical water was studied under the conditions of temperature (220300℃), pressure (2.28.6 MPa), reaction time (560min), ratio of water/PBT (8.0) and in the presence of sodium hydroxide and zinc acetate as catalysts, respectively. It was found that the conversion of PBT was increased with temperature and time increasing. The yield of TPA and THF were varied evidently with temperature and time. The depolymerizations of PBT in the three systems (no catalysts, NaOH, Zn(Ac)2) were compared. It was found that the system in the presence of zinc acetate as catalysts had the advantage in depolymerization of PBT and the recycling of TPA. The optimal conditions of the reaction were temperature 260℃, pressure 4.7MPa, reaction time 45 min, ratio of 8:1 (24 g H2O/3 g PBT), the mass of catalyst(Zn(Ac)2) 0.05g, and PBT could be totally depolymerized and the yield of TPA could attain 98.8%.Depolymerization of PBT in sub-critical water at elevated pressure and temperature conditions was carried out in fused silica capillary reactor for visual observation under a microscope. The video images showed phase changes of PBT in water during heating, reacting and cooling. At room temperature the system consists of PBT solid, water, steam phase composition. PBT melted at 220℃and formed liquid spherules of PBT, which coexist with aqueous fluid and vapor phases. The liquid PBT spherule shrank and hydrolyzed gradually at 300℃and the depolymerization was completed at 8 min before disappearance, and then the reaction system was composed of aqueous fluid and vapor phases. During the cooling process, phase separation occurred at 225℃and snow-white crystal were observed. The amount of crystal increased substantially at 200℃.The results of kinetic show that the depolymerization is a pseudo-first-order kinetics in sub-critical water with an activation energy of 91.37 kJ·mol-1.
Keywords/Search Tags:Polybutylene Terephthalate, sub-critical water, terephthalic acid, depolymerization, 1,4-butanediol, tetrahydrofuran
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