Design and Characterization of Aprotic <i>N</i>-Heterocyclic Anion Ionic Liquids for Carbon Capture
Austin N. Keller, Caitlin L. Bentley, Oscar Morales‐Collazo, Joan F. Brennecke
Abstract
The transport properties, thermal properties, and CO2 solubility for several ionic liquids (ILs) with triethyl(octyl)phosphonium cations and a variety of CO2-reactive aprotic N-heterocyclic anions (AHAs) are reported in this work. Eleven new ILs were designed and synthesized. They were characterized in terms of their melting points, glass transition temperatures, decomposition temperatures, viscosities and densities (where possible), as well as their CO2 capacity as a function of pressure. Of the 11, 3 were solid at room temperature, 1 was a room-temperature liquid which remained liquid upon reaction with CO2, and 7 others were liquids that crystallized at room temperature upon reaction with CO2, so experimentation at elevated temperatures was required. The CO2 uptake isotherms for seven of the ILs, at temperatures ranging from 49 to 64 °C and pressures from 0 to 80 kPa, were fit to a Langmuir model. The CO2 solubility for several of these ILs was among the highest reported at these temperatures and pressures for AHA ILs in the literature, but they have lower thermal stability and higher viscosity than other promising AHA ILs.