Continuous process for producing poly(trimethylene terephthalate)

Abstract

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reaction product having a mole ratio of propylene groups to terephthalate groups of less than about 1.5 is continuously withdrawn from the flasher.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 Poly(trimethylene terephthalate) prepolymer having a relative viscosity of at least about 5 is continuously withdrawn from the prepolymerizer and continuously fed to a final polymerizer, where it is continuously polymerized to form a higher molecular weight poly(trimethylene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molecular weight poly(trimethylene terephthalate) having a relative viscosity of at least about 17 is continuously withdrawn from the final polymerizer.

1 . A continuous process for the production of poly(trimethylene terephthalate) comprising the steps of: 
 (a) continuously feeding a liquid feed mixture to a flasher, the liquid feed mixture comprising a catalyst and at least one of bis-3-hydroxypropyl terephthalate and low molecular weight polyesters of 1,3-propanediol and terephthalic acid, and the liquid feed mixture having a mole ratio of propylene groups to terephthalate groups of 1.1 to 2.2;    (b) continuously vaporizing and removing a first stream of gaseous by-products from the flasher, and continuously withdrawing a liquid flasher reaction product having a mole ratio of propylene groups to terephthalate groups of less than about 1.5 from the flasher;    (c) continuously feeding the liquid flasher reaction product to a prepolymerizer, and continuously polymerizing the flasher reaction product in the prepolymerizer to form a poly(trimethylene terephthalate) prepolymer and a second stream of gaseous by-products;    (d) continuously withdrawing the poly(trimethylene terephthalate) prepolymer from the prepolymerizer, the prepolymer having a relative viscosity of at least about 5;    (e) continuously feeding the poly(trimethylene terephthalate) prepolymer to a final polymerizer, and continuously polymerizing the poly(trimethylene terephthalate) prepolymer to form a higher molecular weight poly(trimethylene terephthalate) and a third stream of gaseous by-products; and    (f) continuously withdrawing the higher molecular weight poly(trimethylene terephthalate) from the final polymerizer, the higher molecular weight poly(trimethylene terephthalate) having a relative viscosity of at least about 17.    
     
     
         2 . The process according to  claim 1 , wherein the temperature of liquid reactants in the flasher is maintained at about 235° to about 250° C.  
     
     
         3 . The process according to  claim 1 , wherein the pressure in the flasher is maintained at about 40 to about 80 mm of Hg.  
     
     
         4 . The process according to  claim 1 , wherein the temperature of liquid reactants in the prepolymerizer is maintained at about 240° to about 255° C.  
     
     
         5 . The process according to  claim 1 , wherein the pressure in the prepolymerizer is maintained at about 5 to about 30 mm of Hg.  
     
     
         6 . The process according to  claim 1 , wherein the temperature of liquid reactants in the final polymerizer is maintained at about 245° to about 265° C.  
     
     
         7 . The process according to  claim 1 , wherein the pressure in the final polymerizer is maintained at about 0.5 to about 3.0 mm Hg.  
     
     
         8 . The process according to  claim 1 , wherein the poly(trimethylene terephthalate) that is withdrawn from the final polymerizer has a relative viscosity of at least about 35.  
     
     
         9 . The process according to  claim 1 , wherein the poly(trimethylene terephthalate) that is withdrawn from the final polymerizer has a relative viscosity of at least about 40.  
     
     
         10 . The process according to  claim 1 , wherein the poly(trimethylene terephthalate) that is withdrawn from the final polymerizer has a relative viscosity of at least about 45.  
     
     
         11 . The process according to  claim 1 , wherein the poly(trimethylene terephthalate) that is withdrawn from the final polymerizer has a relative viscosity of at least about 50.  
     
     
         12 . The process according to  claim 1 , wherein the first stream of gaseous by-products is continuously removed from the flasher and condensed, the second stream of gaseous by-products is continuously removed from the prepolymerizer and condensed, and the combined first and second streams of condensed by-products contain not more than 100 ppm by weight of acrolein and not more than 600 ppm of allyl alcohol.  
     
     
         13 . The process according to  claim 12 , wherein the combined first and second streams of condensed by-products contain not more than 60 ppm by weight of acrolein and not more than 400 ppm of allyl alcohol.  
     
     
         14 . The process according to  claim 12 , wherein the combined first and second streams of condensed by-products contain not more than 40 ppm by weight of acrolein and not more than 250 ppm of allyl alcohol.  
     
     
         15 . The process according to  claim 1 , wherein the third stream of gaseous by-products is continuously removed from the final polymerizer and condensed, and the third stream of condensed by-products contains not more than 200 ppm of acrolein and not more than 3000 ppm of allyl alcohol.  
     
     
         16 . The process according to  claim 15 , wherein the third stream of condensed by-products contains not more than 100 ppm of acrolein and not more than 2500 ppm of allyl alcohol.  
     
     
         17 . The process according to  claim 15 , wherein the third stream of condensed by-products contains not more than 70 ppm of acrolein and not more than 1000 ppm of allyl alcohol.  
     
     
         18 . The process according to  claim 1 , wherein the temperature of liquid reactants in the flasher is maintained at about 235° to about 250° C.; the pressure in the flasher is maintained at about 40 to about 80 mm of Hg; the temperature of liquid reactants in the prepolymerizer is maintained at about 245° to about 255° C.; the pressure in the prepolymerizer is maintained at about 5 to about 30 mm of Hg; the temperature of liquid reactants in the final polymerizer is maintained at about 245° to about 265° C.; and the pressure in the final polymerizer is maintained at about 0.5 to about 3.0 mm Hg.  
     
     
         19 . The process according to  claim 1 , wherein the temperature of liquid reactants in the flasher is maintained at about 240° to about 245° C.; the pressure in the flasher is maintained at about 50 to about 70 mm of Hg; the temperature of liquid reactants in the prepolymerizer is maintained at about 245° to about 250° C.; the pressure in the prepolymerizer is maintained at about 10 to about 20 mm of Hg; the temperature of liquid reactants in the final polymerizer is maintained at about 250° to about 260° C.; and the pressure in the final polymerizer is maintained at about 0.5 to about 3.0 mm Hg.  
     
     
         20 . A continuous process for the production of poly(trimethylene terephthalate) comprising the steps of: 
 (a) continuously feeding a liquid feed mixture to a flasher, the liquid feed mixture comprising a catalyst and at least one of bis-3-hydroxypropyl terephthalate and low molecular weight polyesters of 1,3-propanediol and terephthalic acid having an average degree of polymerization of not greater than 15, and the liquid feed mixture having a mole ratio of propylene groups to terephthalate groups of 1.1 to 2.2;    (b) continuously vaporizing, removing and condensing a first stream of gaseous by-products from the flasher;    (c) continuously withdrawing a liquid flasher reaction product having a mole ratio of propylene groups to terephthalate groups of less than about 1.5 from the flasher, wherein the temperature of liquid reactants in the flasher is maintained at about 235° to about 250° C., and the pressure in the flasher is maintained at about 40 to about 80 mm of Hg;    (d) continuously feeding the liquid flasher reaction product to a prepolymerizer, and continuously polymerizing the flasher reaction product in the prepolymerizer to form a poly(trimethylene terephthalate) prepolymer and a second stream of gaseous by-products, wherein the temperature of liquid reactants in the prepolymerizer is maintained at about 245° to about 255° C., and the pressure in the prepolymerizer is maintained at about 5 to about 30 mm of Hg;    (e) continuously removing and condensing the second stream of gaseous by-products from the prepolymerizer, whereby said first and second streams of condensed by-products, when combined, contain not more than 100 ppm by weight of acrolein and not more than 600 ppm of allyl alcohol;    (f) continuously withdrawing the poly(trimethylene terephthalate) prepolymer from the prepolymerizer, the prepolymer having a relative viscosity of at least about 5;    (g) continuously feeding the poly(trimethylene terephthalate) prepolymer to a final polymerizer where the poly(trimethylene terephthalate) prepolymer is continuously polymerized to form a higher molecular weight poly(trimethylene terephthalate) and a third stream of gaseous by-products, wherein the temperature of liquid reactants in the final polymerizer is maintained at 245° to 265° C., and the pressure in the final polymerizer is maintained at 0.5 to 3.0 mm Hg; and    (h) continuously withdrawing the higher molecular weight poly(trimethylene terephthalate) from the final polymerizer, the higher molecular weight poly(trimethylene terephthalate) having a relative viscosity of at least about 40; and    (i) continuously removing and condensing the third stream of gaseous by-products from the final polymerizer, whereby the resulting condensate contains not more than 200 ppm by weight of acrolein and not more than 3000 ppm of allyl alcohol.