A Robust Hydrogen-Bonded Metal–Organic Framework with Enhanced Ethane Uptake and Selectivity

Abstract

Selective adsorption of trace C2H6 over C2H4 is important for the industrial purification of polymer-grade C2H4 (>99.95% purity). For practical applications, potential adsorbents show high structural stability while maintaining elevated C2H6 adsorption even at low pressures. Herein, we report a C2H6-selective metal–organic framework (MOF), viz., Co­(AIN)2 (HAIN = 3-aminoisonicotinic acid), with a twofold interpenetrated dia structure. Compared to an isoreticular and unstable Co­(IN)2 (HIN = isonicotinic acid) without internal hydrogen bonding, this framework exhibits exceptional structural robustness even under humid conditions because of the presence of intra- and inter-net hydrogen bonds between carboxylate oxygens and amino groups of AIN–. Decoration of the internal polar pore surfaces with groups that form extensive hydrogen bonds offers a more favorable environment for selective C2H6 adsorption. According to the ideal adsorbed solution theory, the predicted selectivity for C2H6/C2H4 was found to be 2.98 in C2H6/C2H4 (1:15, v/v) mixtures, which surpasses even the best-performing MOFs. The C2H6 uptake at 62.5 mbar partial pressure in the single-component isotherm, in C2H6/C2H4 (1:15, v/v) mixtures, was the highest (63.16 cm3 g–1) among MOF adsorbents, along with a nearly top-tier separation potential (116.03 cm3 g–1). Molecular modeling illustrates that the C–H···π interactions of C2H6 with the pore walls are more significant than those of C2H4, accounting for the improved selectivity for C2H6 over C2H4 in Co­(AIN)2 . The separation performance under dynamic dry and humid conditions was confirmed by breakthrough experiments. Co­(AIN)2 was shown to be synthesized on a gram scale and was easily regenerated by inert gas purging. Thus, we demonstrated that coating of internal pore surfaces with groups that form hydrogen bonds provides more favorable environments for enhanced structural stability and C2H6 affinity and selectivity.

Improving Ethane/Ethylene Separation Performance of Isoreticular Metal–Organic Frameworks via Substituent Engineering

“…Remarkably, each one of them displayed an evidently higher uptake capacity toward C 2 H 6 than toward C 2 H 4 at the low-pressure region, despite comparable amounts being adsorbed at atmospheric pressure. A similar adsorption situation was also observed for the reported MOFs such as MAF-49, 29 Co(AIN) 2 , 30 and Ni(IN) 2 . 31 At 298 K and the partial pressure of 0.1 atm typically encountered in actual mixed gas, the gravimetric uptake capacities of C 2 H 6 reach 51 cm 3 (STP) g −1 for NJU-Bai7, 53 cm 3 (STP) g −1 for ZJNU-21, 40 cm 3 (STP) g −1 for ZJNU-22, and 49 cm 3 (STP) g −1 for ZJNU-23, which surpass those of most C 2 H 6 -selective MOFs documented so far under identical conditions such as Ni(bdc)(ted) 0.5 [10.9 cm 3 (STP) g −1 ], 32 DUT-52(Hf) [17.2 cm 3 (STP) g −1 ], 33 Dia-4-Ni [25.6 cm 3 (STP) g −1 ], 34 and Fe 2 (BDP) 3 [26.2 cm 3 (STP) g −1 ], 35 indicating their excellent performance for trapping lowconcentration C 2 H 6 (Figure 3h).…”

“…At the temperature of 298 K, the K H values of C 2 H 6 and C 2 H 4 are 0.344 and 0.239 mmol g −1 kPa −1 for NJU-Bai7 (Figure S18), 0.503 and 0.338 mmol g −1 kPa −1 for ZJNU-21 (Figure S19), 0.322 and 0.254 mmol g −1 kPa −1 for ZJNU-22 (Figure S20), and 0.467 and 0.403 mmol g −1 kPa −1 for ZJNU-23 (Figure S21), respectively. 4g), such as MUF-15 (1.95), 38 DUT-52(Hf) (1.9), 33 PCN-250 (1.9), 39 NUM-7 (1.764), 40 Dia-4-Ni (1.76), 34 Ca(H 2 tcpb) (1.67), 41 CPM-233 (1.64), 42 NUM-9 (1.61), 43 JNU-2 (1.6), 44 SNNU-40 (1.58), 45 LIFM-63 (1.56), 46 JXNU-9 (1.53), 47 MIL-53-NDCA (1.53), 48 Sc-BPDC (1.5), 49 MIL-142A (1.5), 50 Azole-Th-1 (1.44), 51 UPC-612 (1.41), 52 In-soc-MOF-1 (1.4), 53 NPU-1 (1.32), 54 MOF-545 (1.31), 55 and CPOC-301 (1.3), 56 but is inferior to that of a few high-performance C 2 H 6 -selective coordination framework compounds like Fe 2 O 2 (dobdc) (4.4), 36 Cu(Qc) 2 (3.4), 57 Co(AIN) 2 (2.96), 30 ZJU-120 (2.74), 58 MAF-49 (2.7), 29 and NKMOF-8-Br (2.65). 59 As shown in Figures S26−S29, the adsorption selectivity of C 2 H 6 over C 2 H 4 increases with the decreasing measurement temperatures.…”

“…Under the conditions of 298 K and 109 kPa, the adsorption selectivity of C 2 H 6 over C 2 H 4 , respectively, reaches 1.7, 1.4, 1.3, and 1.2 for ZJNU-21 , NJU-Bai7 , ZJNU-22 , and ZJNU-23 . The selectivity value of ZJNU-21 is similar to and even surpasses that of many coordination framework compounds reported for C 2 H 6 /C 2 H 4 separation (Figure g), such as MUF-15 (1.95), DUT-52­(Hf) (1.9), PCN-250 (1.9), NUM-7 (1.764), Dia-4-Ni (1.76), Ca­(H 2 tcpb) (1.67), CPM-233 (1.64), NUM-9 (1.61), JNU-2 (1.6), SNNU-40 (1.58), LIFM-63 (1.56), JXNU-9 (1.53), MIL-53-NDCA (1.53), Sc-BPDC (1.5), MIL-142A (1.5), Azole-Th-1 (1.44), UPC-612 (1.41), In- soc -MOF-1 (1.4), NPU-1 (1.32), MOF-545 (1.31), and CPOC-301 (1.3), but is inferior to that of a few high-performance C 2 H 6 -selective coordination framework compounds like Fe 2 O 2 (dobdc) (4.4), Cu­(Qc) 2 (3.4), Co­(AIN) 2 (2.96), ZJU-120 (2.74), MAF-49 (2.7), and NKMOF-8-Br (2.65) . As shown in Figures S26–S29, the adsorption selectivity of C 2 H 6 over C 2 H 4 increases with the decreasing measurement temperatures.…”

A robust ethane-selective hypercrosslinked porous organic adsorbent with high ethane capacity

“…14,15 Indeed, as a result of the successful implementation of nonpolar pore properties by sophisticated design, C 2 H 6 -selective adsorbents based on MOFs, COFs, HOFs, and porous organic cages have been developed in recent years. 5–8,11,13,16–20 However, because they exhibit poor structural stability and problems with large-scale synthesis, it is necessary to develop a suitable porous material that lacks the shortcomings of existing materials.…”

A Microporous Metal‐Organic Framework with Channels Constructed from Nonpolar Aromatic Rings for the Selective Separation of Ethane/Ethylene Mixtures

“…A notable one is the iron-peroxo sites in Fe 2 O 2 (dobdc) showed a strong affinity toward C 2 H 6 with an uptake capacity of 3.3 mmol/g and high C 2 H 6 /C 2 H 4 IAST selectivity of 4.4 at 1 bar and 298 K. [31] Besides the polar functional sites, nonpolar moieties (e. g., featuring aromatic or aliphatic moieties) in the pore walls of a MOF can endow stronger coupling with ethane through Van der Waals force. [32,33] Although the above methods are conducive to obtaining C 2 H 6 -selective MOFs, the performance of these materials is still suffers from poor selectivity(1.3-3.0) and low ethane uptake. [34][35][36][37][38] Therefore, effort should also be devoted to seeking C 2 H 6 -selective adsorbents with superior separation performance, stability, and low cost.…”