Molecular Product Design for Ionic Liquids with Refrigerant Gases
Samantha E. McLeese, John C. Eslick, Aaron M. Scurto, and Kyle V. Camarda*
The University of Kansas, Dept. of Chemical and Petroleum Engineering, 4132 Learned
Hall, 1530 West 15th Street, Lawrence, KS 66045-7609
*Corresponding Author. Email: camarda@ku.edu
Ionic liquids (ILs) are currently being considered for novel uses in
hydrofluorocarbon (refrigerant) gas separations and as solvents in absorption
refrigeration systems. Due to the low to immeasurable volatility of ILs, these compounds
may be well-suited for such applications, and could potentially be considered as
environmentally-benign solvents.
Their molecularly-tunable nature yields an
extraordinary number of possible cation and anion combinations, the majority of which
have never been synthesized. This project applies newly developed quantitative
structure-property relations (QSPRs) along with an optimization framework to design
novel ionic liquids possessing targeted values of such important properties as solubility in
a given refrigerant, diffusivity, viscosity, toxicity, molar volume, and melting and
decomposition temperatures. The electronic structure of ionic liquids is quantified using
modified connectivity indices, which describe bonding environments, charge distribution,
orbital hybridization and other interactions within and between ions, and between the
ions and the refrigerant molecules present. The resulting expressions are integrated
within a computational molecular design framework, which combines the QSPRs with
structural feasibility constraints in a combinatorial optimization problem. The problem is
solved using Tabu Search, a stochastic optimization algorithm which generates many
near-optimal solutions, which are candidate structures for use as environmentally benign
solvents with refrigerant gases. The examples provided show the efficacy of the
approach in terms of computational efficiency.