Improving CH₄/N₂ selectivity within isomeric Al‐based MOFs for the highly selective capture of coal‐mine methane

Abstract

Selectively separating CH4 from N2 in coal‐mine methane is significantly important in the chemical industry, but challenging and energy‐intensive. Using porous materials as adsorbents can separate CH4/N2 mixtures with low energy consumption, but most adsorbents encounter the problem of poor separation selectivity. Here, we propose a strategy for improving CH4/N2 selectivity by controlling pore wall environment in two isomeric Al‐based metal–organic frameworks (MOFs) with four highly symmetric polar sites for strengthened adsorption affinity toward CH4 over N2. At 298 K and 100 kPa, CAU‐21‐BPDC with four highly symmetric polar sites in the pore walls exhibits 2.4 times higher CH4/N2 selectivity than CAU‐8‐BPDC without four highly symmetric polar sites. Gas adsorption isotherms, CH4/N2 selectivity calculations, Qst of CH4, interaction energy calculations, adsorption density distributions of CH4 and N2, and breakthrough curves reveal that CAU‐21‐BPDC is a potential candidate for selective capture coal‐mine methane.

Effect of axial molecules and linker length on CO2 adsorption and selectivity of CAU-8: a combined DFT and GCMC simulation study

“…06Å, and c ¼ 52.57Å 29,60. These lattice constants in PBE-D3(BJ) are, respectively, 0.69% and 1.46% smaller than the experimental values.…”

Enrichment of low concentration methane: an overview of ventilation air methane

“…29,36 The significant difference in the polarizability between CH 4 and N 2 could be exploited to separate CH 4 from N 2 , which has been demonstrated by some MOFs. 38–40…”

“…8,61,62 It is worth mentioning that a lot of new and advanced adsorbents with high CH 4 adsorption capacities (up to 2.90 mmol g −1 ) and high CH 4 /N 2 selectivity (up to 12.5) have been prepared and studied since the trial. 38,63–71 Studies on the performance of concentrators with these newly developed adsorbents are highly desirable, which could lead to high performance and cost-effective concentrators.…”

“…Meanwhile, as discussed in the following part, many adsorbents with high CH 4 adsorption capacities (up to 2.90 mmol g −1 ) and high CH 4 /N 2 selectivity (up to 12.5) have been reported recently. 38,63–71 The use of some of these highly efficient adsorbents in PSA and/or TSA processes is expected to lead to improved VAM enrichment performance.…”

“…As listed in Table 4, for those frequently studied MOFs, so far the highest CH 4 /N 2 selectivity of 12.5 has been reported by Li et al 69 for an ultramicroporous squarate-based MOF, [Co 3 (C 4 O 4 ) 2 (OH) 2 ] (C 4 O 4 2− = squarate); however, the CH 4 adsorption capacity is low (0.40 mmol g −1 ). In addition, a number of MOFs with very high CH 4 /N 2 selectivity (6–12.5) have been reported in recent years, 38,40,68–71,146–152 with some of them also showing decent or extremely high CH 4 adsorption capacity (up to 2.9 mmol g −1 ), making them very promising candidates for VAM or low grade CH 4 enrichment. Further studies on VAM enrichment using these MOFs with high CH 4 /N 2 selectivity and decent or high CH 4 adsorption capacity are very much demanded.…”