Comparison of Raman, NIR, and ATR FTIR spectroscopy as analytical tools for in-line monitoring of CO2 concentration in an amine gas treating process

Chemical absorption of CO2 using aqueous amine-based solvents is one of the common approaches to control acidic gases emissions to the atmosphere. Improvement in the efficiency of industrial processes requires precise monitoring tools that fit with the specific application. Process monitoring using in-line multivariate measurement methods provides access to time resolved data of the reaction progress and the composition of the reaction mixture. Fast acquisition of valuable information about the process on site can be used for automated monitoring and process control, saving operational costs and reducing waste products. Therefore, different analytical techniques are being explored for the purpose of their practical application in process analysis. This work compares three vibrational spectroscopy techniques for monitoring CO2 absorption by aqueous monoethanolamine (MEA) solutions: Raman spectroscopy, near infra-red (NIR) spectroscopy, and attenuated total reflectance Fourier transform infra-red (ATR FTIR) spectroscopy. The spectroscopic information has been used to estimate the concentration of CO2 captured by the chemical solvent. The study aims to determine the potential applicability of the spectroscopic methods to the in-line and real time monitoring of a post-combustion capture process. Partial least squares (PLS) regression models were built based on the spectroscopic data before and after spectra pretreatment procedures. All three spectroscopic methods are shown to be well suited. The estimation model constructed using NIR data provides the highest accuracy for estimation of the CO2 loading, with an average deviation of about 0.01 molCO2CO2/molMEA. The models based on Raman and ATR FTIR measurements show deviations of around 0.02 molCO2CO2/molMEA.