Study On Depolymerization Of Wasted PET Bottle By Glycolysis And Alkaline Hydrolysis Method

The consumption of polyethylene terephthalate (PET) is increasing quickly with extensive using of PET products in daily life. The recovery processing of waste polyester has become the key issue for the sustainable development of polyester industry. By chemical recovery, waste PET can be decomposed into monomers or raw chemicals that can be reused for the production of plastics or other advanced materials. In this way, the recycling value of waste PET is maximized.Wasted PET bottles were degraded into terephthalic acid sodium and other by-products with adding ethylene glycol in a weakly alkaline environment. The desired product, terephthalic acid, was obtained and ethylene glycol was recovered from the filtrate by rotary evaporation through decoloration, acidification, crystallization and drying. The effects of reaction temperature, reaction time, dosages of sodium bicarbonate, amount of ethylene glycol, amount of distilled water and agitating rate on the degradation rate of PET and yield of terephthalic acid (TPA) were investigated. The results showed that the reaction temperature was one of the key processing conditions. The degradation rate of PET is more than98%under the reaction temperature of170-180℃, reaction time of30～60min, m(PET):m(NaHCO3):m(H2O):m(EG)=3:3.3:30～40:10. TPA is the predominant degradation product and was characterized by IR spectrum, elemental analysis and thermal analysis. The purity and yield of terephthalic acid are more than97% and94%, respectively. Under the condition of recyclable ethylene glycol instead of fresh ethylene glycol to react, the degradation rate of PET and the yield of TPA are more than95% and82%, respectively.The processing of decoloration and acidification for the depolymerization products and the recycling of ethylene glycol were investigated. The optimal processing conditions were the following:the ratio of activated carbon to decolorizing liquid of0.2%(m/v), temperature of50℃, time of30min for decolorization; temperature of55℃, vacuum degree of0.09MPa for rotary evaporation with ethylene glycol’s recycling rate above89%.