Continuous process for producing poly(trimethylene terephthalate)

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 dl/g 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 and the additional gaseous by-products are condensed in at least two spray condensers to form at least two streams of condensed by-product 1,3-propanediol which are then collected in at least one hotwell, and
• (ii) at least a portion of the condensed by-product 1,3-propanediol 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.