Production of polyethylene terephthalate from waste PET

摘要

A process for the production of polyethylene terephthalate(PET) from waste PET by cleavage with ethylene glycol (EG), isolation of bis-(hydroxyethylene) terephthalate (BHET), and esterification/polycondensation with terephthalic acid (TPA). The process comprises (a) boiling waste PET with 7-15 mols EG (per mol PET) for 3-8 hrs. in presence of a glycolysis catalyst and then filtering the mixture through a 1-50 micron filter at 70-100 deg C, (b) cooling the hot filtrate to 30-40 deg C (T1) in less than 10 mins. by adding 0.5-2 times its wt. of EG at 10-25 deg C (with heat exchange as required) and keeping the mixture at T1 for 2-15 mins., (c) heating at at least 2-10 deg C/min. to a temperature at least 5 deg C higher in the range 35-40 deg C (T2) and keeping for 30-120 mins. at T2, (d) cooling to 15-25 deg C (T3) at 0.02-2 deg C/min. and separating the crystallised BHET from the liquid by centrifuging with at least 1000 G, (e) dissolving the BHET in 2-15 times its wt. of water at 50-100 deg C, treating th e solution for 5-120 mins. at this temperature with 0.1-10 wt% (based on BHET) of an adsorbent such as active carbon or kieselguhr, and then removing the adsorbent by filtration or centrifuging at 40-100 deg C, (f) crystallising out the BHET at 0-25 deg C, separating by filtration or centrifuging, washing with 0.2-15 times its wt. of water at 0-25 deg C and optionally drying to a moisture content of down to 0.001-1.0 wt%, and (g) mixing the BHET with 0.2-1 mol TPA, reacting at 250-290 deg C and 0.5-2.0 bar in presence of conventional catalysts and with separation of EG and reaction water, and then completing polycondensation to PET at 250-300 deg C by gradually reducing the pressure to about 1 mbar.