Fabian Jutz

Ionic liquids and dense carbon dioxide: a beneficial biphasic system for catalysis.

2.1. Solubility Phenomena and Swelling 323 2.1.1. CO2 Solubility in ILs 324 2.1.2. Henry’s Law Constants of Gases in ILs 325 2.1.3. Swelling (Volume Changes) 326 2.1.4. Solubility in Ternary Systems 326 2.2. Melting Point Depression 328 2.3. Viscosity 329 2.4. Diffusion Coefficient 329 2.5. Molecular Interactions between CO2 and ILs 330 2.6. Acid-Base Properties 331 3. Applications in Catalysis 332 3.1. Extractions from ILs Using CO2 332 3.2. Multiphase Catalysis 333 3.2.1. Biphasic (IL/CO2) Batch Reactions 333 3.2.2. Biphasic (IL/CO2) Continuous Reactions 335 3.2.3. Supported Ionic Liquid Phase (SILP) Catalysis 336

Supercritical CO2/ionic liquid systems: what can we extract from infrared and Raman spectra?

Infrared (IR) spectroscopy has been successfully applied to study the solubility of supercritical (sc) CO2 in an ionic liquid (IL), the swelling of the IL under scCO2, the diffusion of CO2 in the IL, and the molecular interaction between the IL and scCO2 using a single defined experimental setup. The study has been performed using 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] and scCO2 with a pressure of up to 150 bar at 313 K. The solubility of scCO2 in the IL was calculated via the intensity of the CO2 antisymmetric stretching mode, which was measured using the attenuated total reflection (ATR) method. This approach allowed to determine also the swelling of the IL under scCO2 using several IL bands. The knowledge gained about the solubility and swelling allowed the calculation of the molar fraction of CO2 in the IL and the attainment of similar data as previously determined by other methods. The kinetic measurement of the infrared spectra also offered the opportunity to observe the evolution of the concentration of CO2 in the IL and allowed an estimation of the diffusion coefficient of CO2 in IL under high pressure. Finally, information about the molecular interactions between the IL and scCO2 could also be gained in situ using both infrared and Raman spectroscopy.

Investigation of Binary and Ternary Systems of Ionic Liquids with Water and/or Supercritical CO2 by in Situ Attenuated Total Reflection Infrared Spectroscopy

Two commonly used ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]), as well as binary and ternary mixtures of them with water and/or supercritical CO(2) (scCO(2)) were investigated by means of infrared spectroscopy at high pressure. The experiments were performed using attenuated total reflection (ATR) infrared spectroscopy on dry and wet ILs at 40 degrees C and pressures up to 150 bar of scCO(2). The studies indicate that the content of water does not change significantly the solubility of CO(2) in the ionic liquids tested. Furthermore, the presence of water does not change significantly the interaction between the IL anion and CO(2), which explains why the presence of water in IL does not modify the solubility of CO(2) in the system, even in the case of an initial molar ratio of approximately 50/50 of water in [bmim][BF(4)]. We show that despite the limited solubility of water in supercritical CO(2) an ionic liquid can be efficiently dried using scCO(2) extraction even in the case of a hydrophilic ionic liquid (e.g., [bmim][BF(4)]). During the scCO(2) extraction, the concentration of water was followed in situ using attenuated total reflection (ATR) infrared spectroscopy. After extraction, no residual water could be detected by this technique, which corresponds approximately to a water concentration of below 320 ppm.

Simple in Situ Monitoring of a Complex Catalytic Reaction Network at High Pressure by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy

Attenuated total reflection (ATR) Fourier transform infrared (FT-IR) in situ measurements were performed during the catalytic hydrogenation of acetophenone under high pressure (5.0 MPa). The catalyst used was a suspension of rhodium nanoparticles in an ionic liquid. At the highest temperature used (80 °C), the selectivity of the hydrogenation to 1-phenylethanol dropped from 80% in the beginning of the reaction, when acetylcyclohexane was the main side product, to less than 50% after a few hours of experiment because of the consecutive hydrogenation of 1-phenylethanol to ethylcyclohexane. The evolution of the concentrations of reactant and products was quantified using flawless spectra of pure components with a classical least squares (CLS) multivariate method applied to several ranges of the mid-infrared spectra. The only variable parameters of the analysis are the concentrations of each component themselves and the baseline shift of the spectrum during the reaction. The advantage of using multivariate analysis over the analysis of a single vibrational band, as well as the limitations of this type of spectral analysis, are discussed.

Tracing the acetalization of cyclohexanone in CO2-expanded alcohols by attenuated total reflection infrared spectroscopy.

The CO2-catalyzed acetalization is regarded as a promising alternative to the conventional acid-catalyzed method from a viewpoint of green chemistry (C. A. Eckert et al., Ind. Eng. Chem. Res. 43, 2605 (2004)). We have applied in situ attenuated total reflection infrared (ATR-IR) spectroscopy for elucidating and monitoring the acetalization of cyclohexanone in CO2-expanded ethylene glycol and methanol at 50 °C and 3 MPa. The ATR-IR spectra of the reaction mixtures periodically recorded with a ZnSe crystal demonstrate that ATR-IR spectroscopy is a practical tool for tracing the kinetics of acetalizations in situ. In addition, the rate of CO2 dissolution as well as CO2 solubility into the cyclohexanone–alcohol mixtures could be evaluated from the CO2-v3-antisymmetric stretching band. The ZnSe ATR crystal, however, was corroded during longer use under the acidic conditions realized by the dissolution of CO2 in the alcohols. In contrast, the corrosion did not occur when a Ge crystal was used instead of a ZnSe crystal, and therefore the application of a Ge ATR crystal is recommended for continuous long-term experiments with these media.