Porous ionic liquids to improve the separation and transformation of gases
Margarida Costa Gomes
CNRS Chemistry Laboratory, Ecole Normale Supérieure de Lyon
46 allée d’Italie, 69634 Lyon, France
E-mail: margarida.costa-gomes@ens-lyon.fr
Among the alternative sorbents potentially capable of outperforming current separation technologies,
in particular gas separations, ionic liquids are promising candidates. Their most attractive feature is the
possibility of tuning their physical and chemical properties through proper pairing of anions and cations,
which can include reactive groups, enabling the selective absorption of different gases, even at low
partial pressures [1].
We will describe ionic liquid-based absorbents which are liquids with permanent porosity [2], designed
to selectively absorb different gases. The absorbents are stable suspensions of metal-organic
frameworks (MOFs) in salts whose ion pairs are too voluminous to enter the solid pores [3]. The
increase in gas absorption, when compared with the pure ionic liquids, is proportional to the amount of
porous solid in suspension. The thermodynamic analysis of the absorption data, as well as molecular
dynamics simulations, show that the driving force for gas absorption by the porous ionic liquids is
energetic as well as structural and thus is controlled by gas-solid affinity or by the porous liquid free
volume [4,5].
We have shown that porous ionic liquids prepared as stable suspensions of ZIF-8 in phosphonium
acetate or levulinate salts can selectively absorb carbon dioxide with a capacity more than 100% higher
than that of the pure MOF at 1 bar and 303 K [6]. Porous ionic liquids can also be designed to promote
the reaction, at mild conditions of temperature and pressure, of the gases absorbed. Carbon dioxide
can be catalytically coupled with epoxides to form cyclic carbonates in porous ionic liquids containing
alkylphosphonium halides and ZIF-8. The high activity and selectivity observed at atmospheric pressure
and room temperature indicate that porous ionic liquids are a promising and sustainable family of
sorbents for both separating and transforming gases [7,8].
References
[1] Bui et al. Energy Environ. Sci. 2018, 11 (5), 1062–1176.
[2] Giri et al. Nature 2015, 527, 216-221.
[3] Costa Gomes et al. Angew. Chem. Int. Ed. 2018, 57, 11909-11912.
[4] Avila et al. Adv. Mater. Interfaces 2021, 8, 2001982.
[5] Avila et al Materials Adv. 2022, 3, 8848-8863.
[6] Avila et al. Angew. Chem. Int. Ed. 2021, 60, 12876-12882.
[7] Zhou et al. Chem. Commun. 2021, 57, 7922-7925.
[8] Clark et al. J. Chem. Phys. B 2023, 127, 3266−3277
