(7e) Dynamics Study and Gas Solubility in Phase Change Ionic Liquid for CO2 Capture

Phase
change ionic liquids (PCIL) undergo a
solid to liquid phase transition when they react with CO₂. The heat of fusion during the phase change can be utilized to reduce
the energy requirements for CO₂ capture. Here we present the results
of a molecular simulation study in which the water solubility, dynamics and
liquid structure of PCILs are computed and used to gain an understanding of
these liquids.

Water
solubility in PCILs is
important because in the regeneration
step, the separation of water from the IL
solution requires additional thermal energy to vaporize the water. Water
solubility is determined
in molecular simulation by calculating the solvation
free energy. These are
related to the Henry's Law constants, which are
then compared with experimental data. The enthalpy and entropy of solvation are also obtained from the simulations. A hydrogen bond analysis is performed and the structure of the liquid is
studied in an effort to explain the solubility calculations. A trend of
hydrophobicity in a series of PCILs is predicted.

It has also
been found that the viscosity of aprotic
heterocyclic
anion-based
PCILs
does not increase due to CO₂ complexation, unlike conventional
amines. Molecular
dynamics simulations are performed to investigate the relationship between dynamic properties and liquid structure
of PCILs. In this work, a prediction is made on dynamics and by analogy the viscosity of these
ionic liquids by simulation and experiments. It is found that, like the
experimental results, the dynamics are unaffected by reaction with CO₂
when aprotic
heterocyclic
anion-based
PCILs are used.