PREPARATION OF POLYESTER

PURPOSE:To prepare a polyester, smoothly, by adding a Ca or Li compound to the transfer line of the esterified product in the preparation of a polyester composed mainly of terephthalic acid and ethylene glycol, and subjecting the mixture to polycondensation reaction. CONSTITUTION:In the preparation of a polyester using terephthalic acid and ethylene glycol as main starting raw materials, the line for transferring the esterified product obtained in the first esterification reactor 1 and the second esterification reactor 2 to the first preliminary polymerization tank 7 is furnished with a line 4 for adding a Ca and/or Li compound (e.g. calcium acetate, lithium acetate, etc.) to the esterified product, and both components are mixed together in the line. A specified additive is added to the first preliminary polymerizing tank 7, the polycondensation reaction is carried out under slight vacuum, and the reaction product is transferred through the second preliminary polymerizer 8 and the horizontal polymerizer 9 to obtain a polyester having desired degree of polymerization.