(772g) Vibrational Spectroscopy Characterization of CO2-Ionic Liquid Systems for Pre-Combustion CO2

Ionic liquids are attractive for pre-combustion CO₂ capture applications due to their low volatility, thermal stability, and non-aqueous environment.^1,2  Studies have shown that CO₂ solubility in ionic liquids can be modified through molecular changes in the anion and cation.^3–5  This is promising for the development of new ionic liquids.  However, the larger number of possible cation and anion combinations suggest that a better understanding of molecular structure and CO₂ solubility is necessary guide the development of new ionic liquid CO2 solvents.  Vibrational spectroscopy techniques can provide a picture at the molecular level of CO₂-ionic liquid interactions, aiding in understanding the mechanism of CO₂ capture and relationships of solubility to properties of the ionic liquid.  In this work, we use Raman spectroscopy to study the interaction of CO₂ with a class of imidazolium ionic liquids a high pressure optical cell, we are able to study the vibrational spectra of solvated CO₂ from 1 to 40 bar, pressures relevant to pre-combustion capture condition.  We observe peaks in the CO₂-IL spectra that correspond to the upper and lower band of the fermi-diad split of the CO₂ symmetric stretch vibration, suggesting that solvated CO₂ maintains a linear geometry.  The bands are slightly shifted from the gas phase spectra of CO₂, indicating impact of the solvent environment.  Additionally, we observe a pressure dependence on spectral intensity of the solvated CO₂ peaks that correlate with CO₂concentration.  

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