Poly(trimethylene therephthalate) continuous manufacturing process
View Patent ↗This invention relates to a continuous process for production of poly(trimethylene terephthalate), wherein gaseous 1,3-propanediol by product resulting from the process is condensed in a condenser, and a portion of the condensed by-product is recycled to the condenser while anther portion is recycled back into the process.
1. A continuous process for the production of poly(trimethylene terephthalate) comprising the steps of:
(a) continuously producing poly(trimethylene terephthalate) oligomers comprising 1,3-trimethylene and terephthalate repeating units and having a degree of polymerization of from about 1.9 to about 3.5 by (i) ester exchange reaction of dimethyl terephthalate with excess 1,3-propanediol at an elevated temperature or (ii) direct esterification reaction of terephthalic acid with excess 1,3-propanediol at an elevated temperature;
(b) continuously precondensing the poly(trimethylene terephthalate) oligomers to form a poly(trimethylene terephthalate) prepolymer having an intrinsic viscosity of at least about 0.23 and gaseous by-products comprising volatilized by-product 1,3-propanediol; and
(c) continuously polymerizing the poly(trimethylene terephthalate) prepolymer to form higher molecular weight poly(trimethylene terephthalate) having an intrinsic viscosity of at least about 0.55 dl/g and additional gaseous by-products comprising volatilized by-product 1,3-propanediol,
wherein:
(i) the gaseous by-products are condensed in at least one spray condenser to form condensed by-product 1,3-propanediol, which is then collected in at least one hotwell under conditions such that the temperature of the condensed by-product 1,3-propanediol entering the at least one hotwell is at about 50° C. or lower;
(ii) a portion of the condensed by-product 1,3-propanediol from the hotwell is cooled in at least one heat exchanger and then sprayed in the at least one spray condenser to condense the gaseous by-products; and
(iii) a portion of the condensed by-product 1,3-propanediol from the hotwell, without purification, is fed back into the ester exchange or direct esterification reactions at one or more locations where the temperature is about 150° C. or higher.
2. The process of claim 1 , wherein the condensed by-product 1,3-propanediol entering the at least one hotwell is at about 30° C. to about 45° C.
3. The process of claim 1 , wherein the additional gaseous by-products are condensed in at least one spray condenser to form at least one stream of condensed by-product 1,3-propanediol which is then collected in at least one hotwell and cooled under conditions such that the temperature of the condensed additional by-product 1,3-propanediol entering the at least one hotwell is about 50° C. or lower; and (ii) a portion of the condensed additional by-product 1,3-propanediol from the hotwell is cooled in at least one heat exchanger and then sprayed in the at least one spray condenser to condense the gaseous by-products.
4. The process of claim 3 , wherein the condensed by-product 1,3-propanediol from the additional gaseous by-products entering the at least one hotwell is at about 35° C. to about 45° C.
5. The process of claim 3 , wherein a portion of the condensed additional by-product 1,3-propanediol from the hotwell, without purification, is fed back into the ester exchange or direct esterification reactions at one or more locations where the temperature is about 150° C. or higher.
6. The process of claim 1 , wherein the condensed by-product 1,3-propanediol comprises 1,3-propanediol and solid by-product comprising a mixture of trimethylene terephthalate cyclic dimer and poly(trimethylene terephthalate) oligomers.
7. The process of claim 1 , wherein (i) the gaseous by-products and the additional gaseous by-products are condensed in at least one spray condenser for the precondensing stage (b) to form a condensed by-product 1,3-propanediol, and at least one spray condenser for the polycondensation stage (c) to form a condensed additional by-product 1,3-propanediol, which is then collected in at least one hotwell under conditions such that the temperature of the condensed by-product 1,3-propanediol and the condensed additional by-product 1,3-propanediol entering the at least one hotwell is about 50° C. or lower; (ii) wherein a portion of the condensed by-product 1,3-propanediol and the condensed additional by-product 1,3-propanediol is cooled in at least two heat exchangers and then sprayed in the at least two spray condensers to condense the gaseous by-products and additional gaseous by-products; and (iii) a portion of the condensed by-product 1,3-propanediol and the condensed additional by-product 1,3-propanediol from the hotwell, without purification, is fed back into the ester exchange or direct esterification reactions at one or more locations where the temperature is about 150° C. or higher.
8. The process of claim 1 , wherein a direct esterification reaction is used in step (a).
9. The process of claim 1 , wherein an ester exchange reaction is used in step (a).
10. The process of claim 3 , wherein a direct esterification reaction is used in step (a).
11. The process of claim 3 , wherein an ester exchange reaction is used in step (a).
12. The process of claim 5 , wherein a direct esterification reaction is used in step (a).
13. The process of claim 5 , wherein an ester exchange reaction is used in step (a).
14. The process of claim 7 , wherein a direct esterification reaction is used in step (a).
15. The process of claim 7 , wherein an ester exchange reaction is used in step (a).