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• Simulate He/CH 4 passing MXene nanopores with NEMD, Non-Equilibrium Molecular Dynamics. • MXene nanopores exhibit excellent P He (permeance) & S He/CH4 , even for He/CH 4 mixture. • Gas passes through nanopores with various mechanisms, depending on the pore diameter. • Applied transition state theory to predict S He/CH4 (selectivity) for small nanopores. • Relate density profiles of Equilibrium Molecular Dynamics simulations to P from NEMD. Natural gas is currently the main industrial source of helium, thus He/CH 4 separation has become increasing important. Nanopores based on two-dimensional materials have been considered as very promising for He/CH 4 separation, but the transport mechanism through them is yet unclear. Here, both non-equilibrium molecular dynamics (NEMD) and equilibrium MD (EMD) were employed to study the transport of He/CH 4 through nanopores of different MXenes with various pore diameters (d), pore density and functional groups, which showed two main transport mechanisms, molecular sieving and Knudsen diffusion. Small d was found to be crucial for the molecular sieving and consequently, high He/CH 4 selectivity (S He/CH4). The density profiles of gas molecules in EMD simulations were used to predict S He/CH4 and the permeance for gas passing through different nanopores, yielding results well agreeing with NEMD simulations. This work provides theoretical insights for gas transport through MXene nanopore and may help designing nanopores in the future. [ABSTRACT FROM AUTHOR]

Methane (CH 4) purification using energy-efficient separation technology is important for the economic and safety of natural gas refining. Meanwhile, the common impurity acetylene (C 2 H 2) was also served as raw material to produce various organic products, therefore the highly efficient purification of CH 4 and C 2 H 2 are very important and challenging. Herein, we demonstrate the separation ability of HOF-16 for C 2 H 2 /CH 4 and CO 2 /CH 4 mixtures in detail. HOF-16 has a potential affinity for C 2 H 2 capture, resulting from the exposed free –COOH sites in the suitable pore channel. Gas sorption isotherms reveal that HOF-16a creates a high C 2 H 2 /CH 4 uptake ratio of 7.9 at 298 K and 1 bar, resulting in a C 2 H 2 /CH 4 separation selectivity of 107 (50/50, v/v) under ambient conditions, which is a record value among HOFs and even exceeds many MOFs. Theoretical calculations confirm that the free –COOH sites in the HOF-16a channel provide additional interactions for the C 2 H 2 molecules. Dynamic breakthrough experiments indicate that C 2 H 2 could be highly selective removed from C 2 H 2 /CH 4 (1/99, v/v) mixture. Combined with the low isosteric heat of adsorption (Q st), HOF-16a can efficiently extract C 2 H 2 from the adsorption bed and purify CH 4 into high purity (>99.9%) with low energy consumption. HOF-16 for separating C 2 H 2 /CH 4 gas mixture into high purity gas. [Display omitted] • HOF-16 was synthesized and has free –COOH after activation. • Activated phase HOF-16a has a suitable pore size and a polar pore environment. • HOF-16a exhibits C 2 H 2 /CH 4 selectivity of 107 and C 2 H 2 /CH 4 uptake ratio of 6.9. • HOF-16a can efficiently separate C 2 H 2 /CH 4 mixture in one sorption-desorption cycle. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu(BDC)(DMF) using BDC as a cheap ligand was prepared using a simple and easy-to-scale up method. • Cu(BDC) simultaneously meets the requirements of high C 2 H 6 uptake and excellent ethane/ethylene separation selectivity. • Cu(BDC) exhibits excellent thermal stability and could be stored at room temperature for>1 year. • Cu(BDC) shows excellent separation ability with superior regeneration capability. Separating ethane (C 2 H 6) from ethylene (C 2 H 4) using ethane-selective adsorbents to replace energy-intensive cryogenic distillation technology is an important energy-saving method in the petrochemical industry to obtain high purity C 2 H 4. Limited to the low separation efficiency in current commercial materials, it is very urgent and promising to fabricate such alkane selective adsorbents using cheap ligands and simple synthesis methods, which have characteristics such as stable structure, high C 2 H 6 uptake, and adsorption selectivity. In this work, we have used one of the cheapest ligands (terephthalic acid, H 2 BDC) to prepare Cu(BDC)(DMF) via a simple and easy-to-scale up solvothermal method. The activated Cu(BDC) exposed diamond-shaped one-dimensional pores form a stronger affinity with C 2 H 6 than C 2 H 4 through the double function of C-H∙∙∙π interactions and C-H∙∙∙O hydrogen bonds. Benefiting from the difference in these interactions, Cu(BDC) exhibited a higher adsorption capacity of C 2 H 6 (51.5 cm3/g) compared to C 2 H 4 (45.1 cm3/g) at 1 bar and 298 K, which resulted in high adsorption selectivity (2.0) for the C 2 H 6 /C 2 H 4 mixture (50/50, v/v). Breakthrough experiments indicated that Cu(BDC) successfully achieved the removal of C 2 H 6 from C 2 H 6 /C 2 H 4 (50/50 and 10/90, v/v) mixtures to obtain high purity C 2 H 4 (> 99.99%) using a one-step separation process. When compared with the benchmark materials, Fe 2 (O 2)(dobdc) and NIIC-20, Cu(BDC) had the advantages of much lower preparation cost and enhanced structural stability. These comprehensive properties indicated that Cu(BDC) with a commercially viable price and synthesis process, could be potentially used for the C 2 H 6 removal step during the production of high purity C 2 H 4. [ABSTRACT FROM AUTHOR]

[Display omitted] • UiO-66 functionalized with trifluoromethyl groups exhibits high structural stability. • Optimized pore environment and functionalization enhance C 2 H 2 recognition. • UiO-66-(CF 3) 2 displays improved C 2 H 2 /C 2 H 4 and C 2 H 2 /CO 2 IAST selectivities. • UiO-66-(CF 3) 2 shows remarkable separation performance with good cycling capability. The potential of metal–organic frameworks (MOFs) for application in gas separation processes has been widely recognized. Nonetheless, due to their structural instability and high cost, few MOFs have been utilized in the industry. Among them, UiO-66 is one of the most promising materials which displays good structural stability and its preparation is considered economical. Notably, it also provides a valuable platform for the construction of other robust MOFs for various applications. Herein, trifluoromethyl ligands were introduced into the UiO-66 framework to optimize pore environment also to improve its C 2 H 2 recognition ability. Single component adsorption and the corresponding IAST calculation confirmed that compared to UiO-66, UiO-66-(CF 3) 2 exhibited 2 ~ 3 times higher selectivity for C 2 H 2 /C 2 H 4 and C 2 H 2 /CO 2 separation. Enhanced selectivity resulted in a significantly improved C 2 H 4 separation productivity (56 compared to 36 cm3/cm3) and a reduction in the co-adsorption time. Importantly, the modified UiO-66 framework could be prepared using a simple method and inherited a highly stable structure and good cycling performance of the original material. [ABSTRACT FROM AUTHOR]

• Gate-opening pressure difference is used to separate twin-like gases CO 2 and N 2 O. • The performance of flexible MOFs ELM-11, ELM-12 and MIL-53Al for N 2 O-CO 2 separation is researched systematically. • Efficient separation of CO 2 -N 2 O (50%/50%) in the mixture breakthrough at high pressure is carried. • MIL-53Al has great potential to separate N 2 O and CO 2 at 8 bar. N 2 O and CO 2 are two linear molecules, which have almost the same molecular size and similar physical properties (polarizability and quadrupole moment). Therefore, the separation of CO 2 and N 2 O is extremely challenging. Flexible metal organic frameworks exhibit a gate-opening phenomenon for one type of gas molecule, but not for another, thus enabling excellent selectivity for twin-like molecules. In this study, the separation of CO 2 /N 2 O by flexible metal organic frameworks with different structures was studied systematically using a combination of adsorption and breakthrough tests. The results show that the gate-opening pressure of CO 2 is lower than that of N 2 O on Cu(bpy) 2 (BF 4) 2 (ELM-11) and Cu(bpy) 2 (OTf) 2 (ELM-12), which are two-dimensional layered flexible MOFs, whereas N 2 O has a lower gate-opening pressure than CO 2 on MIL-53Al, a three-dimensional breathing structure with an adsorption capacity of up to 8 mmol/g was observed at 298 K and ~5 bar, indicating its good separation properties for N 2 O from CO 2 under high pressure. Breakthrough experiments for N 2 O/CO 2 mixtures confirmed that MIL-53Al is capable of separating N 2 O and CO 2 under the optimized conditions (8 bar), making it a promising material for industrial application. [ABSTRACT FROM AUTHOR]