Supercritical Fluid Technology Solution Poly Waste Pet Study

The paper represents the basic characteristic of supercritical fluids and its application of chemical recycling of waste plastic. Meanwhile it reviews the state of chemical recycling of PET and introduces several methods for chemical recycling such as hydrolysis, methanolysis, glycolysis and so on. At the same time, the advantages and disadvantages of each method on technical process are also compared.The depolymerization of waste PET in supercritical methanol is studied using a stainless stirred aotuclave at temperature of 240 ~~ 350 ℃ ,pressure of 8 ~ 15MPa,reaction time of 15~60min and methanol/PET weight ratio of 3 ~ 12. The reaction products were examined by gas chromatography-mass spectrometry and FTIR spectrometry. The main products of the reaction are dimethyl terephthalate and ethylene glycol. There are still some small amounts of byproducts, such as methy-(2-hydroxyethyl) terephthalate, bis(hydroxyethyl) terephthalate, dimers and oligomers. Reversed-phase high performance liquid chromatography and gas chromatography are used to analyze solid products and liquid products respectively. At the range of operation condition, the relationships between the yield of DMT, the degree of PET depolymerization and the operation parameters such as reaction time, pressure and temperature were investigated. The results of depolymerization show that the yield of DMT arid the degree of PET ' depolymerization are dependent on the reaction temperature, time, pressure and weight ratio of methanol to PET. Waste PET can be depolymerized into the monomers in supercritical phase. It is found out that the optimized conditions of the reaction are at temperature of 350 癈 ,pressure of 13MPa,reaction time of 45min and methanol/PET weight ratio of 8. Thedepolymerization of PET in SC methanol is first-order kinetics, then the activation energy of 52.32kJ/mol, close to a literature value (55.7kJ/mol) .What's more, the depolymerization of waste PET in supercritical ethanol is studied using a stainless stirred aotuclave at temperature of 240~3 50℃, pressure of 6 -15MPa,reaction time of 15~60min and ethanol/PET weight ratio of 3~15. The reaction products were examined by gas chromatography-mass spectrometry and FTIR spectrometry. The main products of the reaction are 1,4-benzenedicarboxylic acid diethyl ester and ethylene glycol. There are still some small amounts of byproducts, such as benzoic acid ethyl ester, 1,1-diethoxy ethane. At the range of operation condition, the relationships between the yield of 1,4-benzenedicarboxylic acid diethyl ester, the degree of PET depolymerization and the operation parameters such as reaction time, pressure, temperature and ethanol/PET weight ratio were investigated. The results of depolymerization show that the yield of 1,4-benzenedicarboxylic acid diethyl ester and the degree of PET depolymerization are dependent on the reaction temperature, time, pressure and weight ratio of methanol to PET. It is found out that the optimized conditions of the reaction are at temperature of 350C,pressure of 12MPa,reaction time of 60min and ethanol/PET weight ratio of 10.