In
order to design ionic liquids as absorbents for gas separation,
a systematic computer-aided ionic liquid design (CAILD) methodology
is applied and demonstrated by three cases of CO2 capture.
Mixed-integer nonlinear programming problems are formulated, where
a mass-based Absorption-Selectivity-Desorption index (ASDI) integrating
the most important thermodynamic properties of ILs (i.e., gas solubility,
selectivity, and desorption capacity) is proposed as the objective
function and calculated by the COSMO-GC-IL inputted COSMO-SAC model.
The physical properties of ionic liquids are implemented as optimization
constraints, which are estimated by semiempirical models. The reliability
of the thermodynamic method for IL-gas systems is validated first
by comparing a large number of experimental and calculated data of
Henry’s law constant of different gases in ILs. Then, comparative
CAILD studies are performed for CO2 separation from flue
gas (CO2/N2) to demonstrate the importance of
ASDI for identifying practically attractive ILs. Afterward, the developed
method is applied to design IL solvents for the separation of CO2 from syngas (CO2/H2) and sour gas (CO2/H2S). The correspondingly designed ILs for each
case ([OAc]− and COOH-functionalized pyridinium
for CO2/H2 and CO2/N2;
[AlCl4]− and long branched alkyl substituted
pyridinium for CO2/H2S) are analyzed from the
σ-profile point of view.