Structure and Dynamics of Neat and CO2-Reacted Ionic Liquid Tetrabutylphosphonium 2-Cyanopyrrolide
H Wu and JK Shah and CM Tenney and TW Rosch and EJ Maginn, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 50, 8983-8993 (2011).
Results of molecular dynamics simulations are reported in which the structure and dynamics of the reacted and unreacted forms of the task- specific ionic liquid (TSIL) tetrabutylphosphonium 2-cyanopyrrolide were computed. This particular ionic liquid is one of several newly discovered TSILs containing aprotic heterocyclic anions designed specifically for CO2 capture. The physical properties, liquid structure, and dynamics of the ionic liquid were computed as a function of extent of reaction with CO2. Translational and rotational dynamics showed little change upon reaction with CO2, in sharp contrast to traditional TSILs and consistent with experimental viscosity measurements. It is shown that this is due to the failure of a hydrogen-bond network to form upon reaction with CO2. The Henry's law constants for the physical solubility of CO2, N-2, O-2, and H2O were computed for the unreacted TSIL and found to be comparable to values observed with other ionic liquids. In the reacted state, the solubility of CO2, N-2, and O-2 remained essentially unchanged, whereas the solubility of H2O increased by over a factor of 10 because of favorable hydrogen-bonding interactions with the carbamate.
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