Real-time monitoring of polyester esterification rate
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The esterification reaction typically involves 4 substances; for example, terephthalic acid (PTA) and ethylene glycol (EG) undergo an esterification reaction under certain conditions to produce bis(2-ethylhexyl) terephthalate (BHET) and water. There are significant differences in the density (specific gravity) of these 4 substances: the reactant PTA has a density of 1.55, EG has 1.1155, the product BHET has 1.089, and water has a density of 1.000. It is obvious that, with a constant (known) feed ratio, the density of the entire reactant system (i.e., the material system comprising the four substances mentioned above) will vary depending on the degree of reaction progression (i.e., the esterification rate). Therefore, by monitoring the density of the system in real time and combining this data with the feed ratio, it is possible to calculate the esterification rate of the esterification reaction using a model. Given the complexity of the esterification reaction, building on the aforementioned density method and taking into account other characteristics of the esterification process, multiple approaches are utilized to estimate the esterification rate, thereby forming what is known as \"multi-sensor information fusion\" in order to improve the accuracy and reliability of detecting the esterification rate. For example, the heat cross-method, the boiling point elevation method, etc. Through the aforementioned methods, parameters such as the esterification rate of the esterification reaction are calculated using models, and these values are displayed in real time on the DCS to guide production.
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In the later stage of the esterification reaction, oligomers with a molecular weight of around 1000 are primarily formed. Therefore, the density of the entire system is constantly changing. If density is to be used as a measure of the progress of the esterification reaction, it is necessary to take into account the impact of the formation process of oligomers with different molecular weights on the monitoring model. If the problem of density measurement can be solved, then your idea is indeed highly feasible. We generally use the water level line in the esterification effluent tank to determine the degree of esterification, which is not very precise. Because some of the ethylene glycol will be discharged along with the water. Some water will also remain in the process tower.