METHOD FOR PRODUCING COPOLYESTER

PROBLEM TO BE SOLVED: To provide a method for continuously producing a copolyester in the presence of a phosphorus compound, wherein a glycol distilled in the production process of the copolyester can be recovered, circulated and reused by an economically advantageous method without degrading the quality of the obtained copolyester. SOLUTION: The method for continuously producing the copolyester in the presence of a phosphorus compound from an aromatic dicarboxylic acid and two or more kinds of glycols as source materials includes circulating and reusing a distillation residue having a water content of not more than 5 mass% as a recovered glycol obtained by distilling off a low boiling fraction mainly comprising water in a distillation column from a distillate distilled from the process. In this method, the supply amount of a new phosphorus compound solution to the production process of the copolyester is controlled to maintain a constant supply amount of the total phosphorus atoms of phosphorus atoms supplied as the recovered glycol to the production process of the copolyester and the phosphorus atoms supplied as a new phosphorus compound solution to the production process of the copolyester. COPYRIGHT: (C)2009,JPO&INPIT