Patent ID: 7674877

Claim:
A process for thermally crystallizing a polyester polymer comprising: a) introducing solid amorphous pellets comprising the polyester polymer into a liquid medium having a liquid medium temperature of at least 140° C. within a liquid medium zone within a crystallization vessel and crystallizing the solid amorphous pellets, to obtain crystalline pellets having a degree of crystallinity of 20% or more, in the liquid medium at a liquid medium zone pressure at or above the vapor pressure of the liquid medium at the liquid medium temperature without increasing the molecular weight of the crystalline pellets, wherein the liquid medium zone pressure at least 25 psia; and b) separating at least a portion of the crystalline pellets and at least a portion of the liquid medium from each other, while a separation pressure on at least a portion of the crystalline pellets prior to the separating is equal to or greater than the vapor pressure of the liquid medium and wherein the separation pressure is at least 70% of the liquid medium zone pressure.