Paramagnetic Ionic Liquid/Metal Organic Framework Composites for CO2/CH4 and CO2/N2 Separations

Abstract

Global warming is arguably the biggest scientific challenge of the twenty-first century and its environmental consequences are already noticeable. To mitigate the emissions of greenhouse gases, particularly of CO 2 , there is an urgent need to design materials with improved adsorbent properties. Five different magnetic ionic liquids were impregnated into the metal–organic framework ZIF-8. The composites were produced by a direct-contact method, and their performance as sorbents for gas separation applications was studied. The impact of the ionic liquid anion on the sorption capacity and ideal CO 2 /CH 4 and CO 2 /N 2 selectivities were studied, focusing on understanding the influence of metal atom and ligand on the adsorbent properties. Reproducible methodology, along with rigorous characterization, were established to assess the impact of the ionic liquid on the performance of the composite materials. Results show that the ionic liquid was well-impregnated, and the ZIF-8 structure was maintained after ionic liquid impregnation. The produced composites were of microporous nature and were thermally stable. CO 2 , CH 4 , and N 2 adsorption–desorption isotherms were obtained at 303 K and between 0 and 16 bar. The adsorption-desorption data of the composites were compared with that obtained for original ZIF-8. The general trend in composites is that the increased gas uptake per available pore volume compensates the pore volume loss. Adsorption data per unit mass showed that composites have reversible sorption, but inferior gas uptake at all pressure ranges. This is due to the observed total pore volume loss by the ionic liquid pore occupation/blockage. In most cases, composites showed superior selectivity performance at all pressure range. In particular, the composite [C 4 MIM] 2 [MnCl 4 ]@ZIF-8 shows a different low-pressure selectivity trend from the original MOF, with a 33% increase in the CO 2 /N 2 selectivity at 1 bar and 19% increase in the CO 2 /CH 4 selectivity at 10 bar. This material shows potential for use in a post-combustion CO 2 capture application that can contribute to greenhouse gas mitigation.

Adsorption of Carbon Dioxide, Methane, and Nitrogen on Zn(dcpa) Metal-Organic Framework

“…Although the reported equilibrium selectivity did not take into account the influence of adsorption kinetics or the impact of a real gas mixture, these results serve as a first evaluation of the good potential of Zn(dcpa) for CO2 separation from CO2/N2 and CO2/CH4 mixtures. Comparing the selectivity of Zn(dcpa) for CO2/N2 with those of the commercial MOFs MIL-53(Al) [31], ZIF-8, [44], and Fe-BTC [45] (Figure 10b,c), it is concluded that the former outperformed the others at a lower pressure. For example, at 1 bar, the order of selectivities was 12.8 (Zn(dcpa)) > 10.5 (Fe-BTC) > 9.6 (MIL-53(Al)) > 5.9 (ZIF-8).…”

“…Figure 10. (a) Adsorption equilibrium isotherms of CO 2 ( ), CH 4 ( ), and N 2 (•) on Zn(dcpa) at 303 K. Filled and empty symbols represent adsorption and desorption data, respectively; (b) CO 2 /N 2 and (c) CO 2 /CH 4 equilibrium selectivity at 303 K as a function of pressure for Zn(dcpa) and commercial MOFs MIL-53(Al)[31], ZIF-8[44], and Fe-BTC[45].…”

Unveiling the Temperature Influence on the Sorptive Behaviour of ZIF-8 Composite Materials Impregnated with [CnMIM][B(CN)4] Ionic Liquids

“…In this work, replicate measurements were done to check data reproducibility. Further details concerning the gravimetric apparatus and methodology employed in the measurements can be found elsewhere [13,[22][23][24].…”

Impact of Ionic Liquid Structure and Loading on Gas Sorption and Permeation for ZIF-8-Based Composites and Mixed Matrix Membranes

“…The other potential location of the IL consists of its successful encapsulation inside the cavity of the MOF. This strategy originated from attempts to improve MOF sorption properties [12,13,31,32]. Target molecules for separation from CO 2 (with a kinetic diameter of 3.3 A) include nitrogen (N 2 ; 3.64 A) and methane (CH 4 ; 3.8 A), and the functionalization of MOFs through ILs has allowed the preparation of more selective materials in terms of preferential sorption towards CO 2 [33,34].…”