Process for making polyethylene terephthalate

Abstract

The invention relates to 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) compound, comprising the steps of a) esterifying EG and PTA to form diethyleneglycol terephthalate and oligomers (DGT), and b) melt-phase polycondensing DOT to form polyester and EG, wherein the Sb- and P-compounds are added in step a) and the Zn¬compound is added after step a). With this process PET can be obtained that shows favourable colour and optical clarity, also if recycling of EG is applied in the process, and a relatively low rate of acetaldehyde regeneration during melt- processing.