Chemical Recycling Development of Poly(ethylene terephthalate) by Glycolysis and Cooling Crystallization with Water

A systematic study was carried out to develop the cooling crystallization of bis-(2-hydroxyethyl) terephthalate (BHET) from 65 to 25 degrees C with various cooling rates (5 and 80 degrees C/h) and volumes of water added (60, 120, and 240 mL) after fixing the glycolysis conditions for 10 g clear poly-(ethylene terephthalate) (PET) in 60 mL of ethylene glycol (EG) (T = 185 degrees C, t = 2 h, and catalyst = 0.111 g Na2CO3). The glycolysis of PET gave the actual conversion, crystal yield, and purity of BHET monomers of 93.0 +/- 0.7, 70.3 +/- 1.5, and 98.5 +/- 0.0%, respectively. The use of water as the solvent medium was found to be advantageous for impurity and catalyst removal. The increase in water volume affected the actual conversion and purity insignificantly but decreased the viscosity of the H2O/EG solution, which gave faster nucleation rates favoring the production of the 180-250 mu m-sized metastable delta-form BHET needle-like crystals with less crystal yield, shorter filtration and drying times, and poor flowability. The concept of carrying out glycolysis on the recycled BHET dimers was also successfully verified.