Probing the Interaction of Ionic Liquids with CO2: A Raman Spectroscopy and Ab Initio Study
Abstract
This research project involves an investigation of the interaction of carbon dioxide (CO2) with selected ionic liquids (ILs). Raman spectroscopy and first principle quantum mechanical calculations were performed on selected IL solvents in contact with CO2 in the effort to discover how the solvents interact with the gas. ILs are salts (mixtures of cations and anions) that are liquid at room-temperature. Recent work has shown that gas solubilities in ILs vary dramatically depending on the cation and anion that comprise the IL. Tailoring the ion structures may therefore optimize the IL's ability to dissolve CO2. Further, the CO2 solubility, negligible vapor pressure, and high thermal stability of ILs point to their potential application as CO2 scrubbing chemicals in harsh operating environments. A combined experimental and computational effort was aimed at investigating the factors which govern the CO2 solubility mechanism. Studies focused on six ILs formed by the permutations of three anions: hexafluorophosphate, tetrafluoroborate, bis(trifluoromethylsulfonyl)imide; and two cations: 1-ethyl-3- methylimidazolium, 1-butyl-3- methylimidazolium. In situ variable-temperature Raman spectroscopy was performed on the selected ILs in equilibrium with atmospheres of different CO2 and nitrogen (N2) partial pressures. Raman spectroscopy is an optical technique capable of resolving molecular vibrations characteristic to inter-molecular interactions. The vibrational frequency bands attributed to the IL molecules shifted in response to the externally varied temperature and partial pressure of CO2. The 2 observed IL band shifts were reversible with respect to changes in atmosphere.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 05, 2008
- Accession Number
- ADA486726
Entities
People
- William Eucker Iv
Organizations
- United States Naval Academy