aaaaaIonic liquids (ILs) are molten salts with a melting temperature below 100 °C, but are typically liquid around room temperature. They are composed of bulky, organic cations and inorganic or organic, polyatomic anions. ILs have many unique properties that make them attractive for a range of applications. ILs have immeasurable vapor pressure and are thus non-flammable and non-volatile, largely decreasing the chance for fugitive emissions. They are able to solvate a variety of compounds, both polar and nonpolar. In addition, ILs have a large liquidus range, typically from room temperature to their decomposition temperatures around 300-500°C. These attributes, along with the fact that IL properties can be tailored by judicious choice of anion and cation, contribute to the increasing interest in IL applications.
aaaaaApplications for ILs include use as solvents for synthesis, electrolytes/fuel cells, heat-transfer fluids, and lubricants (Brennecke and Maginn 2001). ILs also have potential as separation media, and are being investigated for gas separations (Anthony et al. 2002; Scovazzo et al. 2004), as solvents for extractions (Huddleston et al. 1998; Visser et al. 2000; Visser et al. 2002; Zhao et al. 2005), and for extractive distillation (Lei et al. 2003).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

aaaaaSupercritical fluid extraction (SCE), extractions using supercritical fluids as solvents, has several advantages over traditional extraction processes. Extracts from SCE using carbon dioxide are pure and intact since they are solvent free and can be carried out at the critical temperature of carbon dioxide (31°C), avoiding degradation of thermally sensitive organic compounds. The extract produced from SCE is contaminant-free, as there is no residual solvent. Additionally, because the SCE process is oxygen free, oxidation of extract is less likely than by traditional liquid solvent methods.

 

aaaaaPreliminary research of pomegranate juice has unveiled the anti-cancer capabilities of compounds found in pomegranates. Dr. Brennecke of the University of Notre Dame is collaborating with Dr. Robert A. Newman at M. D. Anderson Cancer Center in Houston, TX and Dr. Ephraim P. Lansky in Haifa, Israel to further research pomegranates' anti-cancer compounds.
aaaaaFor the summer of 2006 in Dr. Brennecke's lab, Caitlin Lambert will be performing series of extractions of fermented pomegranate juice (supplied by Dr. Lansky) utilizing supercritical carbon dioxide at various state points. State points are defined as a particular temperature, pressure and co-solvent composition used in supercritical fluid extractions. The state points currently being tested are at one temperature 40 °C, three pressures (1500, 2000, and 2500 pounds per square inch), and with three co-solvents (ethanol, acetic acid, ethyl acetate), as well as pure carbon dioxide. Sufficient extracts will be sent to Dr. Newman of M.D. Anderson Cancer Center for efficacy analysis of the extracts' anti-cancer capabilities.
aaaaaThere are two particular advantages to using supercritical carbon dioxide extraction instead of normal extraction using ethyl acetate. The first advantage is replacing the volatile organic solvent ethyl acetate with supercritical carbon dioxide, a nontoxic, nonflammable solvent. The second advantage is the increased anti-cancer compound extract concentrations achieved with supercritical fluid extraction.
aaaaaChoosing or evaluating an IL for a particular application requires knowledge of thermophysical properties. We have a variety of instruments for measuring such properties as melting points and glass transition temperatures, thermal decomposition temperatures, heat capacities, densities, and viscosities of pure ILs and mixtures. Such measurements are vital for design and evaluation. Melting points and glass transition temperature values determine the lower end of the useful operating range where the fluid is a liquid. Since ILs do not evaporate, their potential operating range could extend up to the point where they thermally decompose. Thus, thermal decomposition temperatures give an idea of the upper operating range of the fluids. Heat capacities are important for evaluating ILs for thermal storage and heat transfer applications. However, they are also important in evaluating ILs as solvents in any application where heat has to be added or removed. Density as a function of temperature is central to deciding equipment size. Valuable information concerning areas ranging from lubrication properties to reaction conditions is gained from measuring the density as a function of pressure. In general, ILs are quite viscous compared to conventional organic solvents. Viscosity may be a limiting factor in industrial application of ILs if pumping costs become prohibitive. Of course, in many real systems the IL would be mixed with other liquid components (e.g., reactants), which would cause the viscosity of the mixture to be much lower. Nonetheless, viscosity of the pure ILs is an important property that can be used in screening and evaluation of ILs.
aaaaaUsing ILs as reaction solvents can be problematic due to separation issues. Our group has previously shown that it is possible to use supercritical carbon dioxide (SCCO 2) to extract even non-volatile organic compounds with no IL contamination in the recovered products (Blanchard et al. 1999; Blanchard and Brennecke 2001). Carbon dioxide is nontoxic, nonflammable, and readily available, and SCCO 2 is able to dissolve a wide range of compounds. Thus, CO 2 offers an environmentally benign and easily recyclable method for product separation. Since ILs can be used as solvents for both reactions and separations there are many interesting combinations for recyclable processes. An example is IL/SCCO 2 continuous systems, in which the reagents are dissolved in the SCCO 2 and then transported through the reactor, with the products removed in the effluent (Bosmann et al. 2001; Sellin et al. 2001; Webb et al. 2003). Catalysts are chosen so that they are not soluble in the SCCO 2 to allow easy separation of the products from the IL/catalyst mixture. However, problems arise when the products do not dissolve in SCCO 2 or when it is desired to remove the catalyst from the IL.
aaaaaFor solutes that do not dissolve in a supercritical fluid, there are other methods of separation. A dissolved gas antisolvent can create supersaturation of a dissolved liquid or solid solute in a liquid. CO 2 has proven to act as an antisolvent in IL/organic and IL/aqueous mixtures (Scurto et al. 2002; Scurto et al. 2003). The phase split occurs because the CO 2 reduces the solvent strength of the two solvents to a different extent. Recently, our group has used as an CO 2 as an antisolvent to precipitate ammonium salts and zinc acetate solutes from [hmim][Tf 2N]/organic cosolvent mixtures; it was not possible to precipitate the solutes in pure IL (Saurer et al. 2006). It is possible to use CO 2 as an antisolvent for different types of compounds, and the precipitation of ionic compounds and zinc acetate lend credence to the idea of using CO 2 to remove deactivated catalysts and other nonvolatile compounds from ILs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

aaaaaCharacterization of liquid-liquid equilibrium (LLE) of ionic liquid (IL) containing systems is important for evaluating ILs as candidates for replacing traditional extraction solvents. Experimentally determined ternary diagrams of IL/alcohol/water systems by direct analysis of phases in equilibrium with our HPLC are sought. Our experimental goals are to determine general trends with respect to tunability of the cation and anion such that IL design for specific separations may be aided.
aaaaaModeling of liquid-liquid equilibrium (LLE) has an extensive thermodynamic background; however, the macroscopic modeling of IL systems is still in its infancy. The modeling of phase behavior for any liquid system is comprised of two problems: parameter estimation and phase equilibrium. The phase equilibrium problem requires the alternation between phase stability and phase split calculations. A model is sought to accurately predict liquid phase behavior of multi-component systems containing ILs. Reliable modeling of IL LLE will allow the prediction of environmentally important partition coefficients, separation limitations, and phase behavior. Thus there are two main research objectives for the modeling: determine model parameters for IL/solvent (alcohol and other organics) and IL/water binary systems and predict the phase behavior for IL/solvent/water systems using IN/GB as a tool. This will allow for the prediction of K ow’s at small IL concentrations. Ultimately, a model that accurately represents imidazolium and pyridinium-based IL/solvent/water systems is desired.

 

 

 

 

 

 

aaaaaILs have proven to be successful solvents for many types of reactions, but there is little fundamental understanding of how anions, cations and their substituents, and added cosolvents influence solvent properties. Because ILs can be used as solvents for both reactions and separations, there are many interesting combinations for recyclable processes. Furthermore, methods for separating various types of compounds from ILs using carbon dioxide have been developed. A more complete understanding of the individual solvent effects on the macroscopic properties of ILs and their mixtures will allow the selection and design of IL/CO 2 systems for reactions, product separation, and catalyst separation. Current studies include: measuring the CO 2 antisolvent ability for removing compounds from ILs, understanding the solvent strength of ILs and IL/mixtures using spectroscopic probes, and finally, developing a correlation between the two.
aaaaaA common way to classify solvent strength is the solvatochromic comparison method, which uses the difference in electronic excitation energy of an indicator dye in different solvents to define empirical parameters of solvent strength. Kamlet and Taft have devised a system that breaks down solvent strength into hydrogen bond donating ability, hydrogen bond accepting ability, and general dipolarity/polarizability. This allows a systematic study of IL/organic/CO 2 mixtures to specifically understand the effects of different organics and different IL cations and anions in order to design more effective systems.
aaaaaA supercritical fluid (SCF) is defined as a compound at temperature and pressure above its critical point. SCFs have unique properties, transport properties similar to gases and solvent properties similar to liquids. Also, their properties are tunable in the near critical region. The solvating power of SCFs can be modified isothermally with only a slight change in pressure, or by the addition of a cosolvent. The most common SCF is carbon dioxide, it has low critical temperature and relatively low critical pressure, is inexpensive, non-toxic, abundant, and nonflammable. Supercritical carbon dioxide has been extensively used in multiple applications, such as reactions, separations, extractions, among others.
aaaaaCurrently, there is great interest in CO 2 expanded liquids. CO 2 expanded liquids are currently used in homogenous catalysis since they have the advantages of solubilize conventional homogeneous catalysts, and permanent gases, and they can be engineer from pure solvent to pure CO 2 to meet specific needs. To optimize the use of CO 2 expanded solvents the understanding of the phase behavior is of paramount importance. In Brennecke’s group, we are interested in the investigation of phase behavior of CO 2 expanded solvents. Specifically, we are working on the vapor-liquid equilibrium of CO 2 expanded methanol, acetone, and acetonitrile. Different gases of interest in reactions are currently investigated, such as CO, O 2, H 2, at different conditions of temperature and pressure.
aaaaaUnderstanding gas solubilities in ionic liquids (ILs) is important for several reasons. Many reactions require gases (i.e. H 2, CO, O 2) to react with organic compounds such as hydrogenation, hydrofomulations, and oxidation reactions. The solubility of the gas into the solvent or organic media itself is key to the kinetics and yields of the reactions. The removal of acid gases (i.e. CO 2 and SO 2) from gas streams of natural gas industries, oil refineries, and petrochemical plants is gaining importance as government regulations of these gas becomes more restrictive. By studying the solubility of gases in ILs, structural relationships can be established to tune an IL to be selective towards a particular gas. Thus, allowing ILs to be used in gas separations. ILs are being evaluated for their use as traditional reaction solvents. Understanding the solubility of supercritical fluids in ILs is required to evaluate the effectiveness of using supercritical fluids as an extraction method for the removal of solutes (i.e. reaction products, used catalyst) from the IL phase. It is also important to investigate the gas solubilities in ILs to determine the nature of the interactions between the gas and IL, such as hydrogen-bonding, dipole-dipole, dipole-induced dipole, and dispersion forces. By understanding the interactions valuable information about the underlying solvent behavior of ILs.
aaaaaOur group uses a variety of instruments and techniques to study gas solubilities in ILs. the Kohn apparatus allows us to measure the solubility of a gas in an IL stoichiometrically. A known number moles of gas is added to the IL and the number of moles of the gas can be calculated after equilibrium has been achieved based on the volume of the gas above the liquid. The Intelligent Gravimetric Analyzer (IGA) and Rubotherm are gravimetric microbalances that measure the weight gain of an IL sample at set pressures. A set-volume view cell has been designed in our group for the purpose of measuring mixed gas solubilities in ILs. The composition of the gas mixture added to the IL chamber is measured before and after equilibrium by GC. The solubility of each gas in the mixture is then calculated.
Dr. Brennecke
Phone Number
Phone Number: (574) 631 - 5847
Group Office: A-60
 (574) 631 - 7709
Fax Number:(574) 631 - 5847
Labs: A53
 (574) 631 - 5848
Email
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