Alcoholysis process and swelling pretreatment of high-viscosity poly(ethylene terephthalate)
Ethylene glycol(EG)was used as a depolymerizing agent to alcoholyze polyethylene terephthalate(PET)chips with intrinsic viscosities of 0.670 and 1.014 dL/g,respectively,and their mixtures.The alcoholysis products were characterized.The effects of reaction temperature,EG to PET ratio,reaction time and catalyst addition on the yield of alcoholysis products were in-vestigated by a single factor control method.A swelling pretreatment process was proposed to solve the difficulty in the alcoholysis of high-viscosity PET chips,and the alcoholysis kinetics of PET chip exposed to swelling pretreatment were studied.The results showed that the chemical structure of the alcoholysis products of PET chips with different viscosities was basically the same,and the main product was dihydroxyethyl terephthalate(BHET);the high-viscosity PET chips required the reaction temperature of al-coholysis system higher than that of the low-viscosity PET chips;the yield of BHET product was 48.65％under the suitable alco-holysis process conditions for high-viscosity PET chips as follows:the molar ratio of EG to PET 14:1,0.5％catalyst by mass fraction,reaction time at 240 min and reaction temperature 200℃;the crystallinity of high-viscosity PET chips decreased from 30.95％to 25.25％,and the reaction rate constant increased from 0.1319 min-1 to 0.1719 min-1,the alcoholysis rate was sig-nificantly increased after swelling pretreatment at 130℃,and the rational swelling pretreatment temperature was higher than the glass transition temperature of PET chips and 20-30℃lower than the crystallization temperature.
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