A comparison of Raman and IR spectroscopies for the monitoring and evaluation of absorbent composition during CO2 absorption processes

The separation of CO2 from flue gases by reactive chemical absorption using aqueous amines is likely to be a critical technology in the mitigation of global CO2 emissions. The operation of large-scale CO2 capture plants requires close monitoring of the absorbent composition to maintain the plant water balance and efficient CO2 removal, and avoid excessive amine loss. Traditionally monitoring of composition is done offline by analytical methods that are manually intensive, with turn-around times of hours to days. This can lead to costly delays in changes to process operation. In this work the use of Raman and infrared (IR) spectroscopies coupled with Partial Least-Squares Regression are compared for the determination of absorbent composition in a binary amine mixture. These methods can be used online, or offline with an analysis time of minutes. Both laboratory and pilot plant samples were assessed. Both Raman and IR spectroscopies were found capable of determining the individual amine and CO2 concentration of laboratory samples. However, only IR proved successful with pilot plant samples as Raman spectroscopy induced fluorescence that made the Raman technique (as used here) impractical.