Patent ID: 7504474

Claim:
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.