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The separation of ethane from ethylene using cryogenic distillation is an energy-intensive process in the industry. With lower energetic consumption, the adsorption technology provides the opportunities for developing the industry with economic sustainability. We report an iron-based metal-organic framework PCN-245 with interpenetrated structures as an ethane-selective adsorbent for ethylene/ethane separation. The material maintains stability up to 625 K, even after exposure to 80% humid atmosphere for 20 days. Adsorptive separation experiments on PCN-245 at 100 kPa and 298 K indicated that ethane and ethylene uptakes of PCN-245 were 3.27 and 2.39 mmol, respectively, and the selectivity of ethane over ethylene was up to 1.9. Metropolis Monte Carlo calculations suggested that the interpenetrated structure of PCN-245 created greater interaction affinity for ethane than ethylene through the crossing organic linkers, which is consistent with the experimental results. This work highlights the potential application of adsorbents with the interpenetrated structure for ethane separation from ethylene.

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In the petrochemical industry, ethane/ethylene (C2H6/C2H4) separation is one of the most important processes. Herein, we reported an iron-based metal–organic framework MIL-142A for efficiently trapping C2H6 from C2H6/C2H4 mixture, exhibiting preferential adsorption of C2H6 over C2H4. After various characterization techniques to confirm the successful preparation of MIL-142A, the C2H6 and C2H4 adsorptive separation performance was systematically investigated. Results showed that MIL-142A had remarkably higher C2H6 adsorption capacities than that of C2H4 at 298, 288, and 278 K, such as C2H6 and C2H4 adsorption capacities of 3.8 and 2.9 mmol/g at 298 K and 100 kPa, respectively. In addition, the C2H6 and C2H4 adsorption heats were relatively low and in the corresponding ranges 27.3–25.1 and 26.2–23.8 kJ/mol, which is a favorable property for the regeneration of MIL-142A with less energy penalty. Furthermore, it was inferred that the difference between the adsorption heat for C2H6 and C2H4 with the MIL-142A framework governed the selective adsorption of C2H6 over C2H4. The ideal adsorbed solution theory (IAST) selectivity of C2H6/C2H4 was high up to 5.8 in the initial low pressure and then decreased to 1.5 at 298 K and 100 kPa. Besides, breakthrough experiments also corroborated its efficient separation of C2H6/C2H4 mixture. Additionally, MIL-142A had excellent moisture stability, and its framework remained still intact after being exposed to humid conditions (80% RH) for 15 days. These comprehensive properties demonstrated that this unique material MIL-142A, as a high-performance C2H6-selective adsorbent, can be potentially used for highly adsorptive separation of the C2H6/C2H4 mixture.

Developing metal–organic frameworks (MOFs) with moisture-resistant feature or moisture-enhanced adsorption is challenging for the practical CO2 capture under humid conditions. In this work, under humid conditions, the CO2 adsorption behaviors of two iron-based MOF materials, PCN-250­(Fe3) and PCN-250­(Fe2Co), were investigated. An interesting phenomenon is observed that the two materials demonstrate an unusual moisture-enhanced adsorption of CO2. For PCN-250 frameworks, H2O molecule induces a remarkable increase in the CO2 uptake for the dynamic CO2 capture from CO2/N2 (15:85) mixture. For PCN-250­(Fe3), its CO2 adsorption capacity increases by 54.2% under the 50% RH humid condition, compared with that under dry conditions (from 1.18 to 1.82 mmol/g). Similarly, the CO2 adsorption uptake of PCN-250­(Fe2Co) increases from 1.32 to 2.23 mmol/g, exhibiting a 68.9% increase. Even up to 90% RH, for PCN-250­(Fe3) and PCN-250­(Fe2Co), obvious increases of 43.7 and 70.2% in the CO2 adsorption capacities are observed in comparison with those under dry conditions, respectively. Molecular simulations indicate that the hydroxo functional groups (μ3-O) within the framework play a crucial role in improving CO2 uptake in the presence of water vapor. Besides, partial substitution of Fe3+ by Co2+ ions in the PCN-250 framework gives rise to a great improvement in CO2 adsorption capacity and selectivity. The excellent moisture stability (stable even after exposure to 90% RH humid air for 30 days), superior recyclability, as well as moisture-enhanced feature make PCN-250 as an excellent MOF adsorbent for CO2 capture under humid conditions. This study provides a new paradigm that PCN-250 frameworks can not only be moisture resistant but can also subtly convert the common negative effect of moisture to a positive impact on improving CO2 capture performance.