Imidazole-Based Solvents and Membranes for CO 2 Capture Applications
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Imidazole-Based Solvents and Membranes for CO2 Capture Applications Jason E. Bara,1, 3 Matthew S. Shannon,1 W. Jeffrey Horne,1 John W. Whitley,1 Haining Liu,1 David A. Wallace,1 Heath Turner,1 Sergey P. Verevkin,2 Nathan Brown,3 Greg Staab,3 Rene Kupfer3 1
University of Alabama, Department of Chemical & Biological Engineering, Tuscaloosa, AL 35487-0203 USA 2
Department of Physical Chemistry, University of Rostock, Dr-Lorenz-Weg 1, 18059 Rostock, Germany 3
ION Engineering, Boulder, CO 80301 USA
ABSTRACT Imidazoles present a tunable, versatile and economical platform for the development of novel liquid solvents and polymer membranes for CO2 capture. An overview of our studies in this area is presented, with emphasis on characterization of structure-property relationships in imidazole-based materials through both experimental and computational studies. To this end, a growing library of systematically varied imidazole compounds has been synthesized using only commercial available starting materials and straightforward reactions. Using this library of compounds, we have sought to understand and develop predictive models for thermophysical properties relating to process design, including: density, viscosity, vapor pressure, pKa and CO2 absorption capacity. Furthermore, we have discovered that imidazoles are stable in the presence of SO2 and can form reversible 1:1 adducts, which can be beneficial as SO2 is typically present at ppm levels alongside CO2 in flue gas from coal-fired power plants. INTRODUCTION Solvent-based processes are the most commonly employed method by which CO2 is scrubbed from industrial gas streams and are employed under a variety of conditions.[1] Aqueous amine processes have been in use for 85+ years for the removal of CO2 from natural gas. The reversible chemical reaction(s) between amines and CO2 in the presence of water can be used to remove CO2 down to very low levels in gas streams.[2] Typically, primary, secondary or tertiary amines are selected for low, moderate and high pressure streams, respectively.[3] Post-combustion CO2 capture from coal- or natural gas-fired power plants, which are certain to be the primary emissions sources where capture technologies are deployed at full-scale,[4] is a low pressure application and thus necessitates the use of 1o amines or other similarly reactive solvents. When CO2 is present at high concentration and/or high partial pressure, an alternative option is to employ non-reactive “physical” solvent.[5, 6] Common examples of physical solvents industrially used for this purpose include dimethyl ethers of oligo(ethylene glycols) and chilled MeOH.[7] At high partial pressures of CO2, polymer gas separation membranes are also a competitive process technology.[8, 9] A large and growing body of research conducted over the past 10+ years has focused on the use of ionic liquids (ILs) as solvents for CO2 capture applications.[10-12] Much of the
interest in ILs for CO2 capture applications stems from their negligible volatility, which would prevent vaporization of
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