Ultramicroporous MOF with multiple adsorption sites for CH4/N2 separation

doi:10.11949/0438-1157.20241213

Abstract

Abstract:

The development of adsorbents for purifying methane (CH₄) from unconventional natural gas is of great significance for the sustainable development of energy and environment. However, the physical and chemical properties of CH₄ and N₂ are extremely similar, making the design of high-performance adsorbents a daunting challenge. Herein, an ultra-microporous metal-organic framework (Ni-BZZA) was constructed using a low polarity aromatic imidazole ring ligand 1H-benzimidazole-5carboxylic acid for efficient separation of CH₄/N₂ mixtures. The pore surface of Ni-BZZA has dense nitrogen heterocycles and accessible oxygen atoms that can serve as strong binding sites for CH₄. The ultramicroporous of Ni-BZZA provide strong constraints for CH₄. The synergistic effect of pore size and pore surface chemistry results in excellent CH₄ uptake (39.1 cm³·g^-1) and CH₄/N₂ (50/50, vol) selectivity (8.6) of Ni-BZZA at 298 K and 0.1 MPa. Breakthrough experiment conducted under simulated industrial conditions has confirmed that Ni-BZZA can efficiently separate CH₄/N₂ mixture. The excellent CH₄ uptake and CH₄/N₂ selectivity of Ni-BZZA indicate its great potential for enriching CH₄ in unconventional natural gas.

Key words: metal-organic framework, adsorbent, natural gas, selectivity, adsorption, separation

摘要：

开发用于纯化非常规天然气中甲烷（CH₄）的吸附剂，对能源和环境的可持续发展具有重要意义。然而，CH₄和N₂的物理化学性质极为相似，这使得高性能吸附剂的设计成为巨大的挑战。以低极性芳香族咪唑环配体1H-苯并咪唑-5-羧酸构建超微孔金属有机框架材料（Ni-BZZA），有望实现CH₄/N₂混合的高效分离。该材料孔表面具有密集的氮杂环和氧原子，可作为CH₄的强结合位点。Ni-BZZA的超微孔道为CH₄提供了强大的约束性作用，在298 K和0.1 MPa下呈现出优异的CH₄吸附量（39.1 cm³·g^-1）和CH₄/N₂（体积比50/50）选择性（8.6）。在模拟工业条件下进行的穿透实验证实Ni-BZZA可以高效分离CH₄/N₂混合物。Ni-BZZA具有优异的CH₄吸附量和CH₄/N₂选择性，说明其在非常规天然气中富集CH₄方面具有极大的潜力。

关键词: 金属有机框架, 吸附剂, 天然气, 选择性, 吸附, 分离

CLC Number:

TQ 028.1

Pengtao GUO, Ting WANG, Bo XUE, Yunpan YING, Dahuan LIU. Ultramicroporous MOF with multiple adsorption sites for CH₄/N₂ separation[J]. CIESC Journal, 2025, 76(5): 2304-2312.

郭彭涛, 王婷, 薛波, 应允攀, 刘大欢. 用于CH₄/N₂分离的多吸附位点超微孔MOF[J]. 化工学报, 2025, 76(5): 2304-2312.

Figures/Tables 9

Fig.1 (a) Secondary building blocks of Ni-BZZA; (b) Crystal structure of Ni-BZZA viewed along c axis

Fig.2 (a) PXRD patterns of as-synthesized and activated Ni-BZZA; (b) SEM images of Ni-BZZA; (c) Thermogravimetric analysis curves of Ni-BZZA; and (d) CO2 adsorption-desorption isotherms of Ni-BZZA at 195 K (Inset: pore size distribution of Ni-BZZA)

Fig.3 Single-component adsorption isotherms of CH4 and N2 in Ni-BZZA at 298 K and 273 K

Table1 Comparison of CH4 uptake of Ni-BZZA with other adsorbents at 298 K and 1 bar

吸附剂	晶体密度/(g·cm^-3)	吸附量/(cm³·g^-1)	体积吸附量/(cm³·cm^-3)	文献
Ni-BZZA	1.31	39.1	51.20	本研究
Al-CDC	1.27	32.0	40.64	[33]
Co₃(C₄O₄)₂(OH)₂	2.18	9.0	19.81	[29]
STAM-1	1.47	14.2	20.87	[34]
NKMOF-8-Me	1.37	39.5	54.11	[35]
MIL-160	1.12	10.5	11.76	[36]
Al-FUM-Me	1.04	27.2	28.29	[37]
Ni(BTC)(PIZ)	1.04	36.3	38.06	[38]
Co-MA-BPY	1.42	20.6	29.25	[39]
CAU-10	1.16	16.6	19.26	[36]
Ni(OAc)₂L	0.81	25.7	20.82	[22]

Fig.4 (a) Adsorption heat of Ni-BZZA for CH4 and N2; (b) Comparison of adsorption heat Qst of Ni-BZZA with other adsorbents

Table2 Parameters for fitting adsorption isotherms of CH4 and N2 on Ni-BZZA at 298 K using dual-site Langmuir-Freundlich equation

Gas	$N A m a x$ /(cm³·g^-1)	b_A/bar^-1	V_A	$N B m a x$ /(cm³·g^-1)	b_B/bar^-1	V_B	R²
CH₄	30.98924	3.457645	1.025724	34.41176	0.776073	1.055484	0.9999
N₂	15.94589	0.691774	1.888699	8.010242	3.280542	1.146546	0.9999

Table2 Parameters for fitting adsorption isotherms of CH4 and N2 on Ni-BZZA at 298 K using dual-site Langmuir-Freundlich equation

Gas	$N A m a x$ /(cm³·g^-1)	b_A/bar^-1	V_A	$N B m a x$ /(cm³·g^-1)	b_B/bar^-1	V_B	R²
CH₄	30.98924	3.457645	1.025724	34.41176	0.776073	1.055484	0.9999
N₂	15.94589	0.691774	1.888699	8.010242	3.280542	1.146546	0.9999

Fig.5 Dual-site Langmuir-Freundlich equations fit for CH4 (a) and N2 (b) adsorption isotherms of Ni-BZZA

Fig.6 (a) CH4/N2 (50/50, 30/70 and 10/90, vol) IAST selectivity of Ni-BZZA at 298 K; (b) Comparison of IAST selectivity and CH4 uptake of Ni-BZZA with other adsorbents

Fig.7 (a) Breakthrough curves of CH4/N2 (50/50, vol) mixtures of Ni-BZZA at 298 K; (b) Comparison of CH4 breakthrough uptake of Ni-BZZA with those of other adsorbents

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Ultramicroporous MOF with multiple adsorption sites for CH₄/N₂ separation

用于CH₄/N₂分离的多吸附位点超微孔MOF

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