In Situ Raman Spectroscopy Real-Time Monitoring of a Polyester Polymerization Process for Subsequent Process Optimization and Control

Here, in situ Raman spectroscopy is used to develop a method for determining in real time the percentage of esterification denoted as Ester%, a key quality index of polymerization processes in polyester industries. Specifically, Raman spectra of the polymerization (esterification and polyesterification) of terephthalic acid (PTA) and 1,4-butanediol (BDO) to obtain poly(butylene terephthalate) (PBT) are monitored as a function of reaction time. They are processed through a background subtraction algorithm to yield Raman spectra, which allows for the identification and quantification of Raman bands corresponding to the ester and carboxylic groups. The Ester% is calculated by the ratio between the ester and carboxylic groups in terms of the characteristic peak intensities or areas. The ratio based on the Raman peak areas yields more satisfactory results, namely, the calculated values of the Ester% are less noisy and agree better with those obtained by titration. The established in situ Raman spectroscopy method allows for real-time monitoring and quantification of the Ester% during the polymerization process. It will be adopted for process optimization and control at a pilot scale and ultimately at an industrial production scale.