Abstract: The invention relates to a process for making polyethylene terephthalate (PET) from ethylene glycol (EG), purified terephthalic acid (PTA) and optionally up to 6 mol % comonomer, using a mixed metal catalyst system and comprising the steps of a) esterifying EG and PTA to form diethyleneglycol terephthalate and oligomers (DGT), and b) melt-phase polycondensing DGT to form PET and EG, wherein the catalyst system substantially consists of 70-160 ppm of Sb-compound, 20-70 ppm of Zn-compound, and 0.5-20 ppm of Ti-glycolate as active components (ppm metal based on PET). With this process that applies reduced amount of metal catalyst components PET can be obtained with high productivity, which polyester shows favorable color and optical clarity, also if recycling of EG is applied within the process.

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) compounds, comprising the steps of a) esterifying EG and PTA to form diethyleneglycol terephthalate and oligomers (DGT), and b) melt-phase polycondensing DGT to form polyester and EG1 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 favorable color and optical clarity, also if recycling of EG is applied in the process, and a relatively low rate of acetaldehyde regeneration during melt-processing.

Abstract: The invention relates to a process for making polyethylene terephthalate (PET) from ethylene glycol (EG), purified terephthalic acid (PTA) and optionally up to 6 mol % comonomer, using a mixed metal catalyst system and comprising the steps of a) esterifying EG and PTA to form diethyleneglycol terephthalate and oligomers (DGT), and b) melt-phase polycondensing DGT to form PET and EG, wherein the catalyst system substantially consists of 70-160 ppm of Sb-compound, 20-70 ppm of Zn-compound, and 0.5-20 ppm of Ti-glycolate as active components (ppm metal based on PET). With this process that applies reduced amount of metal catalyst components PET can be obtained with high productivity, which polyester shows favourable colour and optical clarity, also if recycling of EG is applied within the process.

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) compounds, comprising the steps of a) esterifying EG and PTA to form diethyleneglycol terephthalate and oligomers (DGT), and b) melt-phase polycondensing DGT to form polyester and EG1 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 re-generation during melt-processing.