Immobilization of the Polar Group into an Ultramicroporous Metal–Organic Framework Enabling Benchmark Inverse Selective CO₂/C₂H₂ Separation with Record C₂H₂ Production

Abstract

One-step harvest of high-purity light hydrocarbons without the desorption process represents an advanced and highly efficient strategy for the purification of target substances. The separation and purification of acetylene (C2H2) from carbon dioxide (CO2) by CO2-selective adsorbents are urgently demanded yet are very challenging owing to their similar physicochemical properties. Here, we employ the pore chemistry strategy to adjust the pore environment by immobilizing polar groups into an ultramicroporous metal–organic framework (MOF), achieving one-step manufacture of high-purity C2H2 from CO2/C2H2 mixtures. Embedding methyl groups into prototype stable MOF (Zn-ox-trz) not only changes the pore environment but also improves the discrimination of guest molecules. The methyl-functionalized Zn-ox-mtz thus exhibits the benchmark reverse CO2/C2H2 uptake ratio of 12.6 (123.32/9.79 cm3 cm–3) and an exceptionally high equimolar CO2/C2H2 selectivity of 1064.9 at ambient conditions. Molecular simulations reveal that the synergetic effect of pore confinement and surfaces decorated with methyl groups provides high recognition of CO2 molecules through multiple van der Waals interactions. The column breakthrough experiments suggest that Zn-ox-mtz dramatically achieved the one-step purification capacity of C2H2 from the CO2/C2H2 mixture with a record C2H2 productivity of 2091 mmol kg–1, surpassing all of the CO2-selective adsorbents reported so far. In addition, Zn-ox-mtz exhibits excellent chemical stability under different pH values of aqueous solutions (pH = 1–12). Moreover, the highly stable framework and excellent inverse selective CO2/C2H2 separation performance showcase its promising application as a C2H2 splitter for industrial manufacture. This work paves the way to developing reverse-selective adsorbents for the challenging gas separation process.

Pore engineering of metal–organic frameworks for boosting low-pressure CO2 capture

“…This method was also applicable to other MOF systems containing different polar functional groups such as sulfonate, sulfone, nitryl, etc. 122–127,157,158 Hu et al applied a pore chemistry strategy to immobilize the polar methyl group into Zn-ox-trz (ox = oxalate; trz = 1,2,4-triazole). 125 The synergistic effect of the pore environment change and additional binding sites toward CO 2 contributes to the significantly enhanced CO 2 /CH 4 selectivity of the resultant MOF, Zn-ox-mtz (mtz = 3-methyl-1,2,4-triazole) (Fig.…”

Cucurbituril-Shaped Cd18(triazolate)12 Unit-Based Metal–Organic Framework Exhibiting an C2H2/CO2 Separation Ability

“…In the typical C 2 H 2 production processes, the impurity of CO 2 in the C 2 H 2 product should be removed. 27,28 The MOF has been utilized for mixed C 2 H 2 /CO 2 separation. 29,30 As a crystalline porous material, the MOF possesses the advantages of adjustable pore chemistry and designable pore sizes.…”

“…Acetylene (C 2 H 2 ) is an important chemical raw material in the industry. In the typical C 2 H 2 production processes, the impurity of CO 2 in the C 2 H 2 product should be removed. , The MOF has been utilized for mixed C 2 H 2 /CO 2 separation. , As a crystalline porous material, the MOF possesses the advantages of adjustable pore chemistry and designable pore sizes. The introduction of the large electronegative fluorine or/and oxygen groups into the MOF is a useful strategy for improvement of the C 2 H 2 /CO 2 separation performance. − The modulation of the pore surface chemistry is another approach to enhancing the C 2 H 2 /CO 2 separation ability. , However, the development of a MOF possessing a high-performance C 2 H 2 /CO 2 separation ability is still a challenge because of the similar linear molecular sizes (C 2 H 2 : 3.32 × 3.34 × 5.7 Å 3 ; CO 2 : 3.18 × 3.33 × 5.36 Å 3 ) and the same kinetic diameter of 3.3 Å for C 2 H 2 and CO 2 .…”

Cation exchange in an anionic metal–organic framework enhancing propylene/propane separation

“…Metal–organic frameworks (MOFs) have gradually become one of the most promising porous materials 3–19 owing to their excellent designability and long-range ordered porous structures. 20–29 Among numerous synthesis strategies, post-synthetic modification of known MOF structures to achieve specific functions breaks the barrier of introducing functional sites through direct synthesis.…”