CTS-9987627 Brennecke, Joan University of Notre Dame
Ionic liquids (ILs) are organic salts that in their pure state are liquids at ambient temperature. The typical IL is based on a bulky pyridinium or imidazolium cation paired with a variety of anions. The bulkiness and asymmetry of the molecule prevents the easy packing that promotes crystallization, and hence these materials exhibit low melting points. Although ILs are organic solvents, they exhibit vanishing small vapor pressures, and thus the most prevalent route for escape to the atmosphere and also exposure to workers -- evaporation -- is absent. Low vapor pressure also renders these solvents safer, as flash points will be much higher than for traditional organic solvents. Research has shown that ILs are excellent solvents for a variety of industrially relevant reactions. However, the use of ILs is limited by the paucity of literature data on their physical properties and phase behavior. The number of permutations on the structure of even simple ILs based on 1-methyl imidazolium is extremely large and correlations between structure and properties do not currently exist.
The immediate goal is to explore the relationship between the chemical structure of an IL and its physical properties, including its phase behavior with CO2, other small molecules, water, and organic solutes. The methodology is to use molecular simulations in concert with experimental measurements to develop structure/property relationships that could be used to guide the design, desired properties. In particular, we propose to synthesis a variety of imidazolium-based ionic liquids and measure their pure component melting points and densities. It is proposed to develop molecular forcefields for Monte Carlo simulations that adequately reproduce the pure component data. It is proposed to measure the phase behavior of some of these ionic liquids with organics, water, CO2 and O2 or H2 using several different high pressure vapor/liquid equilibrium apparatuses, gravimetric techniques, and chromatography. To complement these experimental efforts, it is proposed to use Gibbs ensemble Monte Carlo to simulate the phase behavior of an ionic liquid with small molecules such as CO2 or H2. Base upon the measurements and modeling, we propose to develop relationships between the IL structure and its physical properties and phase behavior. This information will be vital to the evaluation of ILs for a variety of important industrial applications (to be developed in future projects. Some examples include the use of Ils as environmentally benign solvents for reactions and separations, as a medium for efficient hydrogenation, oxidation and hydroformylation chemistry, with CO2 as a safe adsorption refrigeration system to replace CFCs and HFCs, as a hydrogen storage medium, and as a solvent for the gel-spinning of polymers.
