Abstract
Establishing new energy-saving systems for gas separation using porous materials is indispensable for ensuring a sustainable future. Herein, we show that ELM-11 ([Cu(BF4)2(4,4′-bipyridine)2]n), a member of flexible metal–organic frameworks (MOFs), exhibits rapid responsiveness to a gas feed and an ‘intrinsic thermal management’ capability originating from a structural deformation upon gas adsorption (gate-opening). These two characteristics are suitable for developing a pressure vacuum swing adsorption (PVSA) system with rapid operations. A combined experimental and theoretical study reveals that ELM-11 enables the high-throughput separation of CO2 from a CO2/CH4 gas mixture through adiabatic operations, which are extreme conditions in rapid pressure vacuum swing adsorption. We also propose an operational solution to the ‘slipping-off’ problem, which is that the flexible MOFs cannot adsorb target molecules when the partial pressure of the target gas decreases below the gate-opening pressure. Furthermore, the superiority of our proposed system over conventional systems is demonstrated.
Highlights
Establishing new energy-saving systems for gas separation using porous materials is indispensable for ensuring a sustainable future
The opposite phenomenon occurs during gate-closing based on the relationship between the endothermic heat of desorption of the guest and the exothermic shrinkage of the host. These effects are not observed for conventional adsorbents with rigid frameworks, but they are desired features for the rapid pressure vacuum swing adsorption (PVSA) process: resulting from the suppressed heating impact owing to the adsorption and cooling from desorption, the CO2 loading and working capacities of flexible metal–organic frameworks (MOFs) during the rapid PVSA cycle can be much larger than those of conventional adsorbents (Fig. 1c)
We show that the issue of the slipping-off phenomenon can be solved by improving the adsorption column from an operational point of view, and we demonstrate that our proposed rapid PVSA process using flexible MOFs is an advanced adsorption system for CO2 separation
Summary
Establishing new energy-saving systems for gas separation using porous materials is indispensable for ensuring a sustainable future. The opposite phenomenon occurs during gate-closing based on the relationship between the endothermic heat of desorption of the guest and the exothermic shrinkage of the host These effects are not observed for conventional adsorbents with rigid frameworks, but they are desired features for the rapid PVSA process: resulting from the suppressed heating impact owing to the adsorption and cooling from desorption, the CO2 loading and working capacities of flexible MOFs during the rapid PVSA cycle can be much larger than those of conventional adsorbents (Fig. 1c). The third issue involves solving the “slipping-off” phenomenon of the flexible MOFs; flexible MOFs cannot adsorb guest molecules when the partial pressure of the guest in a gas mixture flowing in an adsorption column decreases below its specific gate-opening pressure This has not been recognized as a major challenge in the development of gas separation systems using flexible MOFs, as it was first reported by Horike et al.[14]. We show that the issue of the slipping-off phenomenon can be solved by improving the adsorption column from an operational point of view, and we demonstrate that our proposed rapid PVSA process using flexible MOFs is an advanced adsorption system for CO2 separation
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