Zeolite Imidazolate Framework–Ionic Liquid Hybrid Membranes for Highly Selective CO₂ Separation

Abstract

Zeolitic imidazolate framework ZIF-69 membranes were grown on porous α-alumina substrates via seeded secondary growth and further functionalized by a CO 2 -selective tricyanomethanide anion/alkylmethylimidazolium cation-based ionic liquid (IL) to plug the gaps between the ZIF crystals yet leave the framework pores open for gas diffusion. In this configuration, ZIF intergrain boundaries and defects were repaired by a medium that exhibits high selectivity for CO 2 . As a result, the selectivity of the hybrid membrane was significantly higher than that of as-grown ZIF membranes and, because of the existence of the ZIF channels, the permeability was higher than that corresponding to bulk IL. Specifically, CO 2 permeated 20 times faster than N 2 through the intact ZIF pores and 65 times faster than through the bulk IL phase. The developed membranes at room temperature and under a 2 bar transmembrane pressure exhibited CO 2 permeance of 5.6 × 10 −11 and 3.7 × 10 −11 mol m −2 s −1 Pa −1 and real CO 2 /N 2 selectivities of 44 and 64 for CO 2 /N 2 mixtures consisting of 44% and 75% (v/v) CO 2 , respectively. In addition, on the basis of the experimental evidence from the hybrid membranes, predictions were made on the expected performance of an ideal, crack-free, and homogeneous ZIF-69 membrane. This work provides a promising solution to the challenges associated with defect formation experienced during growth not only of ZIFs but also of other zeolite and inorganic membranes used for CO 2 separation.

Ionic Liquid/Metal–Organic Framework Composites: From Synthesis to Applications

“…Robeson demonstrated empirical upper bounds for different gas pairs for polymer membranesi n1 991 [92] and updated them in 2008. [96] ILs have been directly incorporated into the MOF membranes [97] or MOF membranes were coveredb yI L-functionalized CNTs. Several porousf illers such as silica, carbon molecular sieves (CMSs), zeolites, and carbon nanotubes (CNTs) have been confined into polymers to prepareM MMs.…”

On the molecular mechanisms for the H2/CO2 separation performance of zeolite imidazolate framework two-layered membranes

“…Liu et al grew a CO 2 -selective preferentially oriented ZIF-69 membrane (CO 2 /N 2 selectivity of 6.3), 9 while Tzialla et al subsequently functionalized this ZIF-69 with a cation based ionic liquid. 10 Zhao et al achieved a CO 2 /N 2 selectivity of 60 at 298 K with a 14 μm thick MOF-5 membrane and studied the influence of the feed pressure and composition. 11 In addition, mixed matrix membranes (MMMs) using MOFs as fillers have also been used for the separation of this mixture.…”

Ionic Liquid/Metal–Organic Framework Composites for H2S Removal from Natural Gas: A Computational Exploration

“…[34][35][36][37][38] Some experimental and theoretical studies have shown that MOFs could be used as potential porous supporter for ILs. [39][40][41][42][43][44][45][46] Jiang and co-workers 42 first investigated the IL/IRMOF-1 composites for CO 2 /N 2 separation by molecule simulation, showing that the selectivity can be enhanced when introducing ILs into the pores of IRMOF-1. Later, this group further computationally explored the capabilities of MOF-supported IL membranes for CO 2 /N 2 separation in which the effect of 5 anions of ILs and the role of hydrophobic/hydrophilic framework were examined.…”