Process for manufacturing polyester resins

Abstract

A method of making a non-solid state polyester that includes: a) reacting terephthalic acid and ethylene glycol; b) removing the water continuously; c) polymerizing the monomers and oligomers in vacuum conditions at a temperature to form molten polyester having an IV (intrinsic viscosity) of about 0.7 to 0.85 dl/g; d) extruding the molten polyester through a die; e) cutting and quenching the molten polyester, forming polyester pellets; f) drying the polyester pellets and transferring the polyester pellets to a storage vessel; g) transferring the polyester pellets to the upper end of a conditioning vessel while a countercurrent flow of air is circulated through the polyester pellets; and h) transferring the polyester pellets to the top of a crystallizer vessel to form a bed of polyester pellets flowing by gravity towards the bottom of the vessel while a countercurrent flow of nitrogen is circulated through the bed, and heating the polyester pellets, wherein increase of the IV of the polyester pellets is less than about 0.01 to 0.015 dl/g and the polyester pellets have a crystallinity greater than about 52%.