Online composition analysis of phase separation solvent for carbon dioxide capture using ATR-FT-IR

An amine solvent that undergoes phase change after absorption of CO₂ has been studied to reduce the energy consumed during the CO₂ capture process. Depending on the components of the solvent, the CO₂-rich phase can be separated for the regeneration step or the component in CO₂-lean phase accelerates the regeneration step in the solvent that undergoes liquid-liquid phase change. Since the homogeneous solvent separates into two liquid phases after CO₂ absorption, an analysis method to track the change in chemical species during the absorption process, especially at the phase separation time, is necessary to illuminate the phenomenon. To establish an online method to analyze the components of the solvent, a Fourier-transform infrared (FT-IR) spectrometer equipped with an attenuated total reflection (ATR) probe was used during the CO₂ absorption of phase separation solvent composed of amine, ether, and water. The calibration samples of amines, ethers, and CO₂-loaded solutions were used to develop the partial least square regression model. The consumption of reactants, as well as the formation of products, can be monitored quantitatively using the FT-IR spectra. Utilizing this information, the changes in the chemical species shed light on the phase separation mechanism of this solvent: ether was pushed out of the solvent to form a CO₂-lean phase due to its hydrophobicity, while CO₂ and its products along with amine and water remain in the CO₂-rich phase. Without sampling, this rapid and high-accuracy method is suitable for closed processes, especially for a high-pressure process.