Continuous process for producing poly(trimethylene terephthalate)

摘要

A continuous process for the production of poly(trimethylene terephthalate) is disclosed. According to the process, a liquid feed mixture comprising bis-3-hydroxypropyl terephthalate and/or low molecular weight polyesters of 1,3-propanediol and terephthalic acid, the liquid feed mixture-having a mole ratio of propylene groups to terephthalate groups of 1.1 to 2.2 is fed to a flasher. A first stream of gaseous by-products is continuously vaporized and removed from the flasher, and a liquid flasher reaction product having a mole ratio of propylene groups to terephthalate groups of less than about 1.5 is continuously withdrawn from the flasher. The liquid flasher reaction product is continuously fed to a prepolymerizer where it is continuously polymerized to form a poly(trimethylene terephthalate) prepolymer and a second stream of gaseous by-products. Poly(trimethylene terephthalate) prepolymer having a relative viscosity of at least about 5 is continuously withdrawn from the prepolymerizer and continuously fed to a final polymerizer, where it is continuously polymerized to form a higher molecular weight poly(trimethylene terephthalate) and a third stream of gaseous by-products. Higher molecular weight poly(trimethylene terephthalate) having a relative viscosity of at least about 17 is continuously withdrawn from the final polymerizer.