Aprotic heterocyclic anion ionic liquids (AHAs) have been shown to have promise for CO2 capture applications due to their ability to react stoichiometrically with CO2 and because of their vast tunability. The reaction of an amine group of the AHA IL with CO2 is a very fast acid-base type reaction. We have recently shown that in addition to the amine functionalized anion reacting with CO2 to form a carbamate product as expected, phosphonium based AHA ILs form a phosphonium ylide that can react CO2 with the a-carbon of the tetra-alkyl phosphonium cation at relatively moderate conditions. The cation-CO2 complex is temperature dependent and begins to form around 40�C and less than 1 bar of CO2. The phosphonium cation-CO2 reaction is more exothermic than the anion-CO2 reaction and is thus a more stable product.In this work we examine the effect of temperature, pressure, and basicity of the anion on the thermodynamic equilibrium of the two reaction pathways. The carbamate formation is normally the dominant product in the presence of CO2; however results show that the corresponding anion impacts the final reaction pathway. Utilizing 1H and 31P NMR we quantify each of the two competing reactions and determine a relationship between anion pKa and the formation of the phosphonium ylide in phosphonium based AHAs. The reaction is traced in-situ using a stirred cell reactor equipped with an ATR-FTIR to aid in determining the reaction mechanism. By increasing temperature (22 - 100�C), pressure (0 � 5 bar), and basicity of the anion we get a better understanding of the cation-CO2 reaction and can possibly find a way to use the chemistry as an advantage in the CO2 capture process.

Understanding the equilibrium of ylide formation in azole ionic liquids used for CO<sub>2</sub> capture

247th National Meeting (2014)

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Understanding the equilibrium of ylide formation in azole ionic liquids used for CO2 capture

Understanding the equilibrium of ylide formation in azole ionic liquids used for CO₂ capture