Chemical Recycling And Downstream Product Development Of Waste Coloured Polyethylene Terephthalate

The weight of waste PET is increasing quickly with the rapid development of polyester industry.The polyester waste recycling and reuse have great significance for alleviating the world oil crisis and reducing waste pollution to the environment.Although many reports have been done about the recycling of colorless/white PET,seldom reports have been done about that of colored PET.Furthermore,pure PET was usually used in experimental study as raw material at present;the adoption of more practical significance polyester waste was scarce.In order to reduce the pollution produced by polyethylene terephthalate(PET) wastes and promote resource recycling,the PET was depolymerized though the developed supercritical methanol method,decolorizated and purified.The degradation of PET in supercritical methanol was studied and its decolorization methods were selected,also the decoloriztion effect was characteried.The differences of depolymerization conditions of different grades of PET were investigated.The composition and content of the decomposition product were characterized by many analysis techniques,such as IR,gas chromatography(GC) and high performance liquid chromatography(HPLC).It was found that,at 265℃,11 MPa,fiber-grade PET depolymerized though supercritical methanol for about 30 min,decolorizated and purified,the yield of dimethyl terephthalate (DMT) was nearly 85%.Process for decolodzing kinds of colored materials showed a good decolorization effect.Monomer purity was the same to fiber-grade PET,but it needed more time to obtain the same depolymerization rate than fiber-grade PET.In order to increase value-added products,a new type of plasticizer- Terephthalic acid bis (2-ethyl) hexyl(DOTP) was preparated through ester-exchange reaction with complex catalyst, using the obtained dimethyl terephthalate.The influences of synthesis conditions such as amount of catalyst,temperature,reaction time and the ratio of raw materials on ester-exchange reaction and product performance were studied and determined the optimum.IR and ¹H-NMR spectroscopy were used to identify the fight products,and high performance liquid chromatography(HPLC) was used to determine the composition of the products under different reaction conditions.The best technology was:under the protection of N₂,at 170℃,selecting the zinc acetate and tetrabutyl titanate as a mixture catalyst with the dosage of 0.125%,the molar ratio of octanol with DMT was 2.5:1,reaction time was 4.5 h.Acid value of the product was under 0.01 mgKOH/g and colority was under 50,consistent with product quality standards.