(442a) Sustainable Applications Through the Use of Reversible Ionic Liquids

Reversible ionic liquids (RevILs) are a novel class of switchable solvents that are being investigated for use in a wide variety of applications.  Switchable solvents make use of an external physical stimulus to induce a chemical change which causes a drastic, abrupt change in the properties of the solvent.  The RevILs discussed herein are formed when CO₂ is introduced to a silylamine (e.g., 3-(aminopropyl) triethylsilane) to form an ammonium-carbamate ion pair.  These RevILs can be returned to their original molecular (i.e., non-ionic) form when heated or sparged with an inert gas.  Through adjustments in the structure of the silylamine and the degree of conversion of the molecular form to the ionic form the properties (e.g., viscosity, density, polarity, etc.) of the solvent medium can be drastically tuned.  This tuning ability makes these RevILs ideal solvent systems for a number of applications.   

Two applications of particular interest where RevILs have made a significant impact in terms of reducing emissions and waste are carbon capture of CO₂-rich gas streams and nanoparticle synthesis.  These RevILs provide several advantages over traditional CO₂ capture solvents (e.g., monoethanolamine) for recovery of CO₂ from, for example, coal fired power plant flue gas.  The primary advantage involves a dual capture mechanism: (1) chemical absorption and (2) physical absorption which provides for the opportunity to reach similar recoveries as traditional solvents with lower energy requirements.  Traditional synthesis routes for catalytically active nanoparticles can make use of harsh reactants and produce significant amounts of waste.   Nanoparticles with relatively narrow size distribution and an average size less than 10 nm can be produced using these RevILs in a process akin to a reverse-micelle synthesis with the ability to recycle the RevIL  These two applications offer a focus on waste reduction and the environmental sustainability of the processes.