Boosting Ethylene/Ethane Separation within Copper(I)‐Chelated Metal–Organic Frameworks through Tailor‐Made Aperture and Specific π‐Complexation

Abstract

separations. [1] Ethylene (C 2 H 4 ), as the most important olefins, is the mainstay of petrochemical industry, with a global annual production of exceeding 170 million tonnes per year. "Polymer-grade" specification of ethylene is required for the manufacture of polyethylene plastic. The industrial separation of ethylene from ethylene/ethane (C 2 H 4 /C 2 H 6 ) mixtures highly relies on the repeated distillation-compression cycling at the temperature as low as −160 °C. [1,2] Such heat-driven separation involving in the phase change of isolated fractions, is highly energy-and capital-intensive. Finding energy-efficient alternatives to distillation would widely lower global energy consumption, carbon emissions, and pollution. It is feasible in principle to separate C 2 H 4 /C 2 H 6 mixtures based on porous solid materials via the energy-efficient and environmentally friendly adsorption technology. In this context, development of suitable porous adsorbents for ethylene/ ethane separation is of highly commercial significance.A number of porous materials including zeolites, [3] carbon molecular sieves, [4] and alumina, [5] have been explored for the separation of ethylene and ethane. However, the limits on deliberately designing the structure of such purely inorganic materials make them hardly meet the requirement of industrial implement. As an emerging class of microporous The development of new materials for separating ethylene (C 2 H 4 ) from ethane (C 2 H 6 ) by adsorption is of great importance in the petrochemical industry, but remains very challenging owing to their close molecular sizes and physical properties. Using isoreticular chemistry in metal-organic frameworks (MOFs) enables the precise design and construction of target materials with suitable aperture sizes and functional sites for gas separations. Herein, it is described that fine-tuning of pore size and π-complexation simultaneously in microporous copper(I)-chelated MOFs can remarkably boost the C 2 H 4 /C 2 H 6 adsorption selectivity. The judicious choice of organic linkers with a different number of carboxyl groups in the UiO-66 framework not only allows the fine tuning of the pore size but also immobilizes copper(I) ions onto the framework. The tailor-made adsorbent, Cu I @UiO-66-(COOH) 2 , thus possesses the optimal pore window size and chelated Cu(I) ions to form π-complexation with C 2 H 4 molecules. It can rapidly adsorb C 2 H 4 driven by the strong π-complexation interactions, while effectively reducing C 2 H 6 uptake due to the selective size-sieving. Therefore, this material exhibits an ultrahigh C 2 H 4 /C 2 H 6 selectivity (80.8), outperforming most previously described benchmark materials. The exceptional separation performance of Cu I @UiO-66-(COOH) 2 is validated by breakthrough experiments for 50/50 v/v C 2 H 4 /C 2 H 6 mixtures under ambient conditions.

Enhancing the gas adsorption capacities of UiO-66 by nanographite addition

“…The latter happened despite the smaller surface area of UiO-66-(COOH) 2 (622 m 2 /g compared to 713 m 2 /g for UiO-66-COOH). [24]. The effect of UiO-66 topology on the adsorption of ethane and ethylene was also studied by Li and coworkers [25].…”

“…The synthesis of this MOF is relatively easy and enables the tunability of its structural defects [4][5][6][7][8][9][10]. These defects, besides being known to increase pore volumes and surface areas, also change pores' morphology/distribution and affect the adsorption of gases such as CO 2 [14][15][16][17][18], H 2 O [19,20], H 2 [15,[21][22][23], C 2 H 6 [24][25][26][27] or C 2 H 4 [25].…”

“…Although the separation of alkanes from alkenes is an industrially important process, UiO-66 has rather rarely been used in this application, likely owing to the lack of unsaturated metal sites, which would provide the specific interactions/-complexation, as in the case of Cu-BTC (benzenetricarboxylate) [24]. Nevertheless, Qian at al.…”

“…Nevertheless, Qian at al. [24] reported that the number of carboxyl groups in the linkers of UiO-66 affected the C 2 H 6 /C 2 H 4 separation. When 1, 2, 4 BTC (in UiO-66-COOH) was used as a linker, there was no difference between the amount adsorbed of both species at 25°C, and about 1.3 mmol/g were reported.…”

Tuning Atomically Dispersed Fe Sites in Metal–Organic Frameworks Boosts Peroxidase-Like Activity for Sensitive Biosensing

“…Metal-organic frameworks (MOFs) have received widespread applications in various fields because of their attractive features including large surface area, high porosity, structural diversity and functional tunability [23][24][25][26]. Significantly by virtue of the versatile organic linkers and atomically dispersed metal structural building units, the microstructure and the electronic structure of MOFs could be well regulated via various strategies [27][28][29][30][31].…”