Description

There are a number of technologies for license for the production of PET resins, both for the esterification and polycondensation sections (known as the melt-phase plant) and for the solid-state polymerization plant to make higher IV resins for bottles, etc. A listing of the known major licensors is shown below: MAJOR PET LICENSORS Melt-Phase Solid-State     Zimmer Zimmer Teijin Bepex Kanebo Hosokawa Ems-Inventa Karl Fischer John Brown Deutsche Sinco DuPont Buehler Sunkyong Sunkyong Potential combinations of melt-phase licensor technology and solid-state licensor technology are limited due to exclusive arrangements between many of the licensors. These alliances allow a company to offer a complete technology package through to the final bottle-grade pellets. The process designs for the production of bottle-grade PET from either DMT or PTA are quite similar; the main difference is in the bis-HET production section. Since the PTA based process is now most frequently chosen for new plants, only this process will be covered. The process design for the production of bottle-grade PET from PTA is divided into the following major processing blocks: Esterification of PTA to bis-HET Polycondensation of bis-HET Solid-state polymerization of PET Ethylene glycol recovery DuPont claims an improvement to polycondensation that eliminates vacuum operation. In this enhanced melt-phase design inert gas is used to lower the partial pressure of ethylene glycol over the polymer melt in the prepolymerizer and finisher. Plant operation is conducted at a slight positive pressure, negating the need for expensive vacuum equipment and vacuum designed process equipment. The patent also claims that it eliminates possible air contamination that can cause product degradation and gel formation. The process features conventional esterification (or transesterification if DMT is used) followed by prepolymerization and finishing. In the patent design, inert gas (nitrogen) preheated to 280 to 320°C is introduced into the finisher to flow countercurrent to the direction of polymer flow in order to remove the reaction byproduct volatiles, principally ethylene glycol. The nitrogen flows through the finisher and then to the prepolymerizer, where it removes ethylene glycol formed at that point. This stream is sent to a column where ethylene glycol is recovered for recycle. The nitrogen stream exiting the column is sent to an adsorption bed to remove organic impurities such as acetaldehyde. Another DuPont development consists of a polyester process that eliminates the final polycondensation section of the plant, replacing it with a mechanical rotoforming step. DuPont claims that their development permits the crystallization of low IV melt resin for subsequent solid state polymerization to high IV polymer, such as for bottle-grade resin. Chem Systems has estimated the potential production cost improvement achieved by use of DuPont's rotoformer as compared to conventional PET production technology.