Patent ID: 8859713

Claim:
A process for making polyethylene terephthalate (PET) from ethylene glycol (EG), purified terephthalic acid (PTA) and optionally up to 30 mol % comonomer, using a catalyst system essentially consisting of antimony—(Sb), zinc—(Zn) and phosphorous—(P) compounds, comprising the steps of a) esterifying EG and PTA in the presence of the Sb-compound and the P-compound at a pressure of 0.1 to 10 MPa to form diethyleneglycol terephthalate and oligomers (DGT), and b) reducing the pressure to 50 to 500 Pa and melt-phase polycondensing DGT to form polyester and EG, wherein the Zn-compound is added after reducing the pressure; and wherein the catalyst system consists essentially of 50-200 ppm of Sb, and 20-200 ppm of Zn, and 40-100 ppm of P (elemental contents based on PET).