# Ionic Liquid-Enhanced Interfaces to Boost Reactive CO2 Capture

## TL;DR

Adding ionic liquids to a CO2 capture solution improves its performance by altering the chemical environment at the gas-liquid interface.

## Contribution

This study introduces a novel approach using ionic liquids to enhance reactive CO2 capture by modifying interfacial properties.

## Key findings

- Ionic liquids affect CO2 solubility, surface tension, and CO2 localization near hydroxide ions.
- The choice of cation, anion, and concentration of ionic liquids significantly impacts CO2 capture performance.
- Experiments confirm that ionic liquid additives improve CO2 capture and are sensitive to their chemical composition.

## Abstract

The addition of ionic liquids (ILs) to a mixture containing
a molecular
solvent and other ionic species can induce the heterogeneous redistribution
of cations and anions at the gas–liquid interface. This nonuniform
redistribution of cations and anions driven by the differences in
the solvophilicity of ions can improve the thermophysical and interfacial
properties of such mixtures, creating a local chemical environment
that is conducive to some reactions. In this work, ILs are added to
a mixture of potassium hydroxide (KOH) and ethylene glycol (EG), used
as a reactive absorbent and electrolyte in the migration-assisted
moisture-gradient (MAMG) process for CO2 capture. Molecular
dynamics (MD) simulations are employed to probe into the effects of
complex ion–ion and ion–solvent interactions and to
examine the chemical composition at the gas–liquid interface.
A total of 12 systems are investigated using molecular simulations
to identify trends in the performance of IL additives based on the
choice of cation, anion, and IL concentration. The cation effects
are studied using IL additives based on 1-ethyl-3-methylimidazolium
([EMIM]+) and 1-butyl-3-methylimidazolium ([BMIM]+), while the impact of anions is examined using additives based on
dicyanamide [DCA]−, triflate [TfO]−, bistriflimide [NTf2]−, and hexafluorophosphate
[PF6]− anions, respectively. The influence
of the IL concentration is also evaluated at molar concentrations
between 1% and 4%. The simulation results indicate that the use of
IL additives can affect the physical CO2 solubility, surface
tension, and the localization of CO2 around the [OH]− ions at the gas–liquid interface. It is also
evident that the choice of cations, anions, and IL concentration determines
the extent to which the IL additives impact the local physicochemical
properties. Physical dissolution, diffusive transport, and interaction
with [OH]− are critical intermediate steps toward
reactive CO2 capture using a liquid absorbent. Hence, the
improvement in one or more of these properties, aided by IL additives,
is expected to improve the overall CO2 capture performance.
Experiments reaffirmed the impact of IL additives on CO2 capture performance and the sensitivity to the choice of the cation,
anion, and concentration of the IL additive.