Patent ID: 7732556

Claim:
A process of producing polyesters having a stable intrinsic viscosity by using a polycondensation reaction apparatus having one or more polycondensation reaction vessels provided with one or more sets of an ejector, an upstream condenser placed between the polycondensation reaction vessel and the ejector, a condenser placed in the downstream portion of the ejector, a barometric leg, and one or more hot well tanks connected to the condenser via the barometric leg, wherein the upstream condenser is equipped with a collection tank for collecting a condensate obtained from condensing a vaporous composition obtained from the polycondensation reaction vessel, and including driving the ejector by a vapor composed mainly of 1,4-butanediol, condensing the vapor composed mainly of 1,4-butanediol as discharged from the ejector in the condenser placed in the downstream portion of the ejector, and making the reactor in a reduced pressure state to undergo polycondensation reaction, the process being characterized in that: water contained in a sealing liquid in at least one hot well tank is maintained at a concentration of not more than 3% by weight; and tetrahydrofuran contained in a sealing liquid in at least one hot well tank is maintained at a concentration of not more than 4% by weight to thereby produce polyesters having a stable intrinsic viscosity.