| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to continuously analyze a sample, even in a small amount, at good accuracy within a short time without treating the sample and to thereby permit the stable supply of starting materials, the stabilization of reaction conditions and the stabilization of quality by controlling the composition of the reaction system on the basis of the specified analytical values on the diol concentration, diol condensate concentration, water content and catalyst concentration of the recycle liquid in an esterification reaction. SOLUTION: In producing a polyester by forming a slurry by dispersing a powder of an aromatic dicarboxylic acid such as terephthalic acid or isophthalic acid in a liquid diol such as ethylene glycol, reacting the slurry at 240-270 deg.C at normal pressure or under a pressure of 300,000Pa while removing the formed water from the reaction system, a solution containing unreacted diol from the polycondensation process and a catalyst is recirculated as a recycle liquid, the concentrations of the components in the liquid are analyzed with a near-infrared analyzer having a noise level of 50×10<-6> Abs or below and a wavelength reproducibility of 0.01nm or below and a fluorescent X-ray analyzer, and the composition of the total of the feed materials and the recycle liquid are controlled according to the analytical values.
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