A Chemically Robust Microporous Zn-MOF for C2H2 Separation from CO2 and Industrially Relevant Four Component Gas Mixtures

Abstract

The separation and purification of acetylene from the light hydrocarbon gas mixtures is considered as one of the most industrially challenging task for the production of fine chemicals. Though metal-organic frameworks (MOFs) are promising candidates for such separation and offer a cost and energy-efficient pathway, achieving the trade-off between sorption capacity and separation selectivity along with framework robustness is a daunting task and demands effective design. Herein, a new 3D chemically stable MOF, IITKGP-24 (stable over a wide range of aqueous pH solution, pH = 2-12) is developed, displaying excellent separation selectivity of 13.9 for C₂H₂/CO₂ (50:50) even at ambient conditions and maintained a trade-off between sorption capacity and separation selectivity. Most importantly, the breakthrough performance analysis under the industrially relevant gas mixture composition revealed that the developed framework possesses excellent separation of acetylene from not only C₂H₂/CO₂ (50:50) gas mixtures but also from the quaternary C₂H₂/C₂H₄/C₂H₆/CO₂ (25:25:25:25) feed gas streams. Separation of C₂H₂ from such a four component gas mixture by MOFs is unexplored. The exceptional framework robustness, high C₂H₂/CO₂ uptake ratio, low heat of adsorption, and excellent recyclability with easy regenerability made the developed framework promising candidate toward this challenging separation.

Keywords: acetylene purification; multi‐component separation; pH‐stable MOF; physisorbent materials; surface functionalization.

Scheme 1

Schematic representation of developed robust IITKGP‐24 framework.

Figure 1

a) Coordination environment of IITKGP‐24 and the SBU displaying paddle‐wheel structure (Color codes: Zn, Cyan; N, blue; O, red; C, gray; H, white); b) 3D packing diagram of IITKGP‐24 displaying two different types of porous channels while viewing along the crystallographic b‐axis; c) Packing diagram of IITKGP‐24 along a‐axis (yellow color indicates how spacer units connected 2D layers to construct a 3D network); d,e) PXRD comparison plots of IITKGP‐24 displaying framework robustness after several treatments (open‐air, humidity, water, aqueous pH medium, CHCl₃ exchange, activation and after sorption experiment).

Figure 2

a) 195 K CO₂ sorption isotherm of IITKGP‐24a for the BET surface area analysis; b,c) Single component gas sorption isotherms of C₂H₂, C₂H₄, C₂H₆, CO₂ at 295 and 273 K, respectively (closed and open circles represent sorption and desorption, respectively); d) Cyclic adsorption test for C₂H₂ gas at ambient temperature; e) IAST selectivity of IITKGP‐24 for C₂H₂/CO₂ (50:50) gas mixtures at 295 K and 1 bar; f) Comparison plot of CO₂ uptake and C₂H₂/CO₂ (50:50) selectivity of IITKGP‐24a with well‐known reported MOFs at 295 K and 1 bar.

Figure 3

a) Isosteric heat of adsorption (Q _st) for C₂H₂ and CO₂ gases. b) Comparison of C₂H₂/CO₂ (50:50) IAST selectivity and C₂H₂/CO₂ uptake ratio at 295 K and 1 bar of IITKGP‐24a; c) Comparison plot of isosteric heat of adsorption (Q _st) of C₂H₂ and C₂H₂/CO₂ (50:50) selectivity of IITKGP‐24a at 295 K and 1 bar; Transient breakthrough performance analysis of IITKGP‐24 at 100 kPa for d,e) C₂H₂/CO₂ (50:50) gas mixtures at 295 K and 273 K temperature, respectively; f) C₂H₂/C₂H₄/C₂H₆/CO₂ (25:25:25:25) gas mixtures at 273 K.