C2H2 Uptake Research Articles

Structural Regulation and Light Hydrocarbon Adsorption/Separation of Three Zirconium-Organic Frameworks Based on Different V-Shaped Ligands.

On the basis of different V-shaped ligands, three zirconium-organic frameworks (JLU-Liu45, Zr-SDBA, and Zr-OBBA) have been successfully constructed. By regulating spatial configuration and functional groups of organic ligands, these as-synthesized Zr-MOFs (MOF = metal-organic framework) display distinct structures and different light hydrocarbon adsorption/separation capabilities. JLU-Liu45, with a double-walled interpenetrated 3D primitive cubic (pcu) framework, exhibits good gas-adsorption capacity but not prominent selective separation ability. Through regulating sizes and torsion angles of the organic ligands, Zr-SDBA possesses a 2D square lattice (sql) network, while Zr-OBBA displays a non-interpenetrated 3D pcu framework. Furthermore, by regulating functional groups on the ligands, Zr-SDBA shows prominent C2H2 uptake (101.2 cm3·g-1) and the best C2H2/CH4 selectivity (230.5, 1:1) among the three Zr-MOFs, and Zr-OBBA shows a significant C3H8/CH4 selectivity (105.6, 1:1). This work demonstrates the feasibility of structural regulation for MOF materials in the light hydrocarbon adsorption/separation field.

Photoinduced Electron-Transfer (PIET) Strategy for Selective Adsorption of CO2 over C2 H2 in a MOF.

Similarities in sizes, shapes, and physical properties between carbon dioxide (CO2 ) and acetylene (C2 H2 ) make it a great challenge to separate the major impurity CO2 from products in C2 H2 production. The use of porous materials is an appealing path to replace current very costly and energy-consuming technologies, such as solvent extraction and cryogenic distillation; however, high CO2 /C2 H2 uptake ratio with minor adsorption of C2 H2 at standard pressure was only unexpectedly observed in scarce examples in recent years although the related research started early at 1950s, and general design strategies to realize this aim are still absent. This work has successfully developed an efficient PIET strategy and obtained the second highest CO2 /C2 H2 adsorption ratio for porous materials in a proof-of-concept MOF with a photochromism-active bipyridinium zwitterion. An unprecedented photocontrollable gate effect, owing to change of interannular dihedral after photoinduced generation of radical species, was also observed for the first time. These findings will inspire design and synthesis of porous materials for high efficient gas adsorption and separation.

Modulation of Topological Structures and Adsorption Properties of Copper-Tricarboxylate Frameworks Enabled by the Effect of the Functional Group and Its Position

To push forward the structural development and fully explore the potential utility, it is highly desired but challenging to regulate in a controllable manner the structures and properties of MOFs. In this work, we reported the structural and functional modulation of Cu(II)-tricarboxylate frameworks by employing a strategy of engineering the functionalities and their positions. Two pairs of unsymmetrical biaryl tricarboxylate ligands modified with a methyl group and a pyridinic-N atom at distinct positions were logically designed and synthesized, and their corresponding Cu(II)-based MOFs were solvothermally constructed. Diffraction analyses revealed that the variation of functionalities and their positions furnished three different types of topological structures, which we ascribed to the steric effect exerted by the methyl group and the chelating effect involving the pyridinic-N atom. Furthermore, gas adsorption studies showed that three of them are potential candidates as solid separation media for acetylene (C2H2) purification, with the separation potential tailorable by altering functionalities and their locations. At 106.7 kPa and 298 K, the C2H2 uptake capacity varies from 64.1 to 132.4 cm3 (STP) g-1, while the adsorption selectivities of C2H2 over its coexisting components of CO2 and CH4 fall in the ranges of 3.28-4.60 and 14.1-21.9, respectively.

A Microporous Titanate‐Based Metal‐Organic Framework for Efficient Separation of Acetylene from Carbon Dioxide

AbstractSeparation of acetylene (C2H2) and carbon dioxide (CO2) is of prime importance in the petrochemical industry, but their similarities in molecular size and volatility make it particularly difficult. A desired adsorbent for highly efficient C2H2/CO2 separation should have high selectivity and C2H2 uptake simultaneously, and the introduction of functional groups into MOFs is an effective strategy to achieve this purpose. Herein, we report a titanium‐based MOF material (MIL‐125‐NH2), featuring the suitable pore sizes and amino‐functionalized pore surfaces to show the preferential adsorption of C2H2 over CO2 with both high C2H2 uptake and C2H2/CO2 selectivity. Theoretical simulation results indicate that the preferential C2H2 adsorption is mainly attributed to multiple hydrogen bonding interactions between C2H2 molecule and amino functional groups.

High Working Capacity Acetylene Storage at Ambient Temperature Enabled by a Switching Adsorbent Layered Material.

Unlike most gases, acetylene storage is a challenge because of its inherent pressure sensitivity. Herein, a square lattice (sql) coordination network [Cu(4,4′-bipyridine)2(BF4)2]n (sql-1-Cu-BF4) is investigated with respect to its C2H2 sorption behavior from 189 to 298 K. The C2H2 sorption studies revealed that sql-1-Cu-BF4 exhibits multistep isotherms that are temperature-dependent and consistent with the transformation from “closed” (nonporous) to four “open” (porous) phases induced by the C2H2 uptake. The Clausius–Clapeyron equation was used to calculate the performance of sql-1-Cu-BF4 for C2H2 storage at pressures >1 bar, which revealed that its volumetric working capacity at 288 K is slightly superior to acetone (174 vs 170 cm3 cm–3) over a safer pressure range (1–3.5 vs 1–15 bar). Molecular simulations provided insights into the observed switching phenomena, revealing that the layer expansion of sql-1-Cu-BF4 occurs via intercalation and inclusion of C2H2. These results indicate that switching adsorbent layered materials offer promise for utility in the context of C2H2 storage and delivery.

Cage-Like Porous Materials with Simultaneous High C2 H2 Storage and Excellent C2 H2 /CO2 Separation Performance.

Adsorption-based separation is an important technology for C2 H2 purification due to the environmentally friendly and energy-efficient advantage. In addition to the high selectivity of C2 H2 /CO2 , the high uptake of C2 H2 also plays an important role in the separation progress. However, the trade-off between adsorption capacity and separation performance is still in a dilemma. Herein, we report a series of cage-like porous materials named FJI-H8-R (R=Me, Et, n Pr and i Pr) which all have high C2 H2 uptakes at 1 bar and 298 K. Dynamic breakthrough studies show that they all exhibit excellent C2 H2 /CO2 separation performance. Particularly, FJI-H8-Me possesses a long breakthrough time up to 90 min g-1 . Additionally, Grand Canonical Monte Carlo (GCMC) simulation reveals that the suitable pore space and geometry contribute much to the excellent separation performance.

Precise Pore Space Partitions Combined with High‐Density Hydrogen‐Bonding Acceptors within Metal–Organic Frameworks for Highly Efficient Acetylene Storage and Separation

AbstractThe high storage capacity versus high selectivity trade‐off barrier presents a daunting challenge to practical application as an acetylene (C2H2) adsorbent. A structure–performance relationship screening for sixty‐two high‐performance metal–organic framework adsorbents reveals that a moderate pore size distribution around 5.0–7.5 Å is critical to fulfill this task. A precise pore space partition approach was involved to partition 1D hexagonal channels of typical MIL‐88 architecture into finite segments with pore sizes varying from 4.5 Å (SNNU‐26) to 6.4 Å (SNNU‐27), 7.1 Å (SNNU‐28), and 8.1 Å (SNNU‐29). Coupled with bare tetrazole N sites (6 or 12 bare N sites within one cage) as high‐density H‐bonding acceptors for C2H2, the target MOFs offer a good combination of high C2H2/CO2 adsorption selectivity and high C2H2 uptake capacity in addition to good stability. The optimized SNNU‐27‐Fe material demonstrates a C2H2 uptake of 182.4 cm3 g−1 and an extraordinary C2H2/CO2 dynamic breakthrough time up to 91 min g−1 under ambient conditions.

Electrostatically Driven Selective Adsorption of Carbon Dioxide over Acetylene in an Ultramicroporous Material.

Separating acetylene from carbon dioxide is important but highly challenging owing to their similar physical properties and molecular dimensions. Herein, we report highly efficient electrostatically driven CO2 /C2 H2 separation in an ultramicroporous cadmium nitroprusside (Cd-NP) with compact pore space and complementary electrostatic potential well fitting for CO2 , thus enabling molecular quadrupole moment recognition of CO2 over C2 H2 . This material shows a high CO2 /C2 H2 uptake ratio of 6.0 as well as remarkable CO2 /C2 H2 selectivity of 85 under ambient conditions with modest CO2 heat of adsorption. Neutron powder diffraction experiments and molecular simulations revealed that the electrostatic potential compatibility between pore structure and CO2 allows it to be trapped in a head-on orientation towards the Cd center, whereas the diffusion of C2 H2 is electrostatically forbidden. Dynamic breakthrough experiments have validated the separation performance of this compound for CO2 /C2 H2 separation.

A stable metal–organic framework with well‐matched pore cavity for efficient acetylene separation

AbstractAcetylene, an important petrochemical feedstock, is the starting chemical to produce many polymer products. Separating C2H2 from its by‐product mixtures is still an energy‐consuming process and remains challenging. Here, we present a metal–organic framework[Zn2(bpy)(btec)], with a desirable pore geometry and stable framework, which demonstrated a high separation performance of C2H2 from simulated mixtures. With the desirable pore dimension and hydrogen bonding sites, Zn2(bpy)(btec) shows by far the both highest C2H2/C2H4 and C2H2/CO2 uptake ratios, very high adsorption selectivities and moderately C2H2 uptake of 93.5 cm3/cm3 under 298 K and 1 atm. Not only straightforwardly produced high purity of C2H4, but also recovered high purity of C2H2 (>98%) in the regeneration process (>92% recovery). More notably, Zn2(bpy)(btec) can be straightforwardly synthesized at a large scale under environmentally friendly conditions, and its good water/chemical stability, thermostability, and cyclic stability highlight the promise of this molecular sieving material for industrial C2H2 separation.

An Unprecedented Pillar‐Cage Fluorinated Hybrid Porous Framework with Highly Efficient Acetylene Storage and Separation

AbstractDespite much intense investigation on the C2H2/CO2separation, the trade‐off between the adsorption capacity and separation selectivity is still tricky. To overcome the dilemma, we have rationally synthesized an ultra‐stable fluorinated hybrid porous material SIFSIX‐Cu‐TPA with theith‐dtopology. Completely differing from the famous pillar‐layer fluorinated materials, SIFSIX‐Cu‐TPA possesses a unique pillar‐cage structure, in which the SiF62−anions cross‐link two adjacent metal nodes as pillars to stabilize the three‐dimensional framework constructed by icosahedral and tetrahedral cages. As anticipated, SIFSIX‐Cu‐TPA has high BET surface area (1330 m2 g−1) as well as high C2H2uptake (185 cm3 g−1at 298 K and 1 bar). At the same time, due to the obvious difference in the adsorption performance of CO2and C2H2especially in the low pressure area, SIFSIX‐Cu‐TPA also exhibits an excellent C2H2/CO2separation performance (breakthrough time up to 68 min g−1at 298 K and 1 bar).

A MOF‐based Ultra‐Strong Acetylene Nano‐trap for Highly Efficient C2H2/CO2 Separation

AbstractPorous materials with open metal sites have been investigated to separate various gas mixtures. However, open metal sites show the limitation in the separation of some challenging gas mixtures, such as C2H2/CO2. Herein, we propose a new type of ultra‐strong C2H2 nano‐trap based on multiple binding interactions to efficiently capture C2H2 molecules and separate C2H2/CO2 mixture. The ultra‐strong acetylene nano‐trap shows a benchmark Qst of 79.1 kJ mol−1 for C2H2, a record high pure C2H2 uptake of 2.54 mmol g−1 at 1×10−2 bar, and the highest C2H2/CO2 selectivity (53.6), making it as a new benchmark material for the capture of C2H2 and the separation of C2H2/CO2. The locations of C2H2 molecules within the MOF‐based nanotrap have been visualized by the in situ single‐crystal X‐ray diffraction studies, which also identify the multiple binding sites accountable for the strong interactions with C2H2.

Microporous mixed-ligand metal–organic framework with fluorine-decorated pores for efficient C2H2/C2H4 separation

The selective separation of C2H2 from C2H4 is a very important process for downstream industrial production, and porous metal-organic frameworks (MOFs) have shown great potential for such an application due to their tunable pore surroundings and adjustable building blocks. In this study, a new microporous MOF formulated as {(Et2NH2)[In(TBOT)(2,3-FDA)](DEF)(H2O)2}n (1, H3TBOT ​= ​4,4′,4’’-(((2,4,6-trimethylbenzene-1,3,5-triyl)tris(oxy))tris(methylene))tribenzoic acid, 2,3-HFDA ​= ​2,3-difluorobenzoic acid and DEF ​= ​N,N-diethylformamide) with 2-fold interpenetrated network and 1D fluorine-decorated pores has been prepared via using an acid-acid mixed-ligand strategy. The activated complex 1 (named as 1a) demonstrates apparently higher C2H2 uptake than C2H4 around room temperature, resulting in its relative high C2H2/C2H4 (v:v ​= ​1:99) IAST (Ideal Adsorbed Solution Theory) selectivity of 10.3 ​at 298 ​K and 1 ​bar. Furthermore, the GCMC (grand canonical Monte Carlo) simulation results indicate that the 2,3-FDA moieties serve as preferential binding sites for C2H2 via the multipoint F2⋯H–CC–H⋯F2 interactions, implying the feasibility of the mixed-ligand approach for building porous MOFs with the targeted applications.

Creative Construction of a Series of Chiral 3D Indium-Organic Frameworks with a umy Topology.

Using 2,2'-R2-biphenyl-4,4'-dicarboxylic acid to bind with a cis-[InO4(μ2-OH)2] octahedron, three novel chiral 3D indium-organic frameworks, [In(μ2-OH)L] [1, L1, R = N(CH3)2; 2, L2, R = OCH3; 3, L3, R = CH3], have been hydrothermally synthesized without chiral reagents. Crystal structure analyses reveal that 1-3 show an unprecedented 4-connected umy topology with the Schläfli symbol (42·64). 1 exhibits high water stability and good sorption selectivity of CO2 over N2, while 3 displays high C2H2, C2H4, and C2H6 uptake capacity at 273 K.

Fine-Tuning Pore Dimension in Hybrid Ultramicroporous Materials Boosting Simultaneous Trapping of Trace Alkynes from Alkenes.

Removing trace amounts of alkynes from alkenes is one of the most critical and challenging steps to produce high-purity alkenes, the fundamental raw materials in petrochemical industry. Selective hydrogenation using noble metal catalysts under harsh conditions can convert trace alkynes to alkenes, but suffers from limited selectivity, over-hydrogenation, and energy-intensive consumption. Herein, the simultaneously adsorptive removal of trace propyne (C3 H4 ) and acetylene (C2 H2 ) from quaternary C2 H2 /C2 H4 /C3 H4 /C3 H6 mixture is reported for the first time using an anion-pillared hybrid ultramicroporous material ZU-16-Co (or TIFSIX-3-Co) by finely tuning the pore dimensions and introducing different binding sites to match the shape of alkynes. ZU-16-Co with contracted aperture size and judiciously extended cell dimension simultaneously exhibits superior trapping capacity for propyne under low concentration (2.45mmol g-1 at 5000ppm) and surprisingly high C2 H2 uptake (4.18 and 1.4mmol g-1 at 1.0 and 0.01bar, respectively) through synergistic host-guest and guest-guest interactions. Importantly, the ability of ZU-16-Co to capture trace alkynes (C2 H2 and C3 H4 ) in one step is confirmed by breakthrough experiments for quaternary C3 H4 /C2 H2 /C3 H6 /C2 H4 mixtures, presenting ZU-16-Co as a promising material for alkyne trapping.

Efficient Trapping of Trace Acetylene from Ethylene in an Ultramicroporous Metal-Organic Framework: Synergistic Effect of High-Density Open Metal and Electronegative Sites.

Acetylene (C2 H2 ) removal from ethylene (C2 H4 ) is a crucial step in the production of polymer-grade C2 H4 but remains a daunting challenge because of the similar physicochemical properties of C2 H2 and C2 H4 . Currently energy-intensive cryogenic distillation processes are used to separate the two gases industrially. A robust ultramicroporous metal-organic framework (MOF), Ni3 (pzdc)2 (7 Hade)2 , is reported for efficient C2 H2 /C2 H4 separation. The MOF comprises hydrogen-bonded linked one-dimensional (1D) chains, and features high-density open metal sites (2.7 nm-3 ) and electronegative oxygen and nitrogen sites arranged on the pore surface as cooperative binding sites. Theoretical calculations, in situ powder X-ray diffraction and Fourier-transform infrared spectroscopy revealed a synergistic adsorption mechanism. The MOF possesses S-shaped 1D pore channels that efficiently trap trace C2 H2 at 0.01 bar with a high C2 H2 uptake of 60.6 cm3 cm-3 and C2 H2 /C2 H4 selectivity.

Efficient Trapping of Trace Acetylene from Ethylene in an Ultramicroporous Metal–Organic Framework: Synergistic Effect of High‐Density Open Metal and Electronegative Sites

AbstractAcetylene (C2H2) removal from ethylene (C2H4) is a crucial step in the production of polymer‐grade C2H4but remains a daunting challenge because of the similar physicochemical properties of C2H2and C2H4. Currently energy‐intensive cryogenic distillation processes are used to separate the two gases industrially. A robust ultramicroporous metal–organic framework (MOF), Ni3(pzdc)2(7 Hade)2, is reported for efficient C2H2/C2H4separation. The MOF comprises hydrogen‐bonded linked one‐dimensional (1D) chains, and features high‐density open metal sites (2.7 nm−3) and electronegative oxygen and nitrogen sites arranged on the pore surface as cooperative binding sites. Theoretical calculations, in situ powder X‐ray diffraction and Fourier‐transform infrared spectroscopy revealed a synergistic adsorption mechanism. The MOF possesses S‐shaped 1D pore channels that efficiently trap trace C2H2at 0.01 bar with a high C2H2uptake of 60.6 cm3 cm−3and C2H2/C2H4selectivity.

Acetylene/Ethylene Separation and Solid-State Structural Transformation via [2 + 2] Cycloaddition Reactions in 3D Microporous ZnII Metal-Organic Frameworks.

Purification of ethylene by removing acetylene from an ethylene/acetylene (99/1 v/v) mixture is a challenging task in the petrochemical industry. Our effort toward finding new porous materials that can selectively uptake acetylene resulted in two 3D metal-organic frameworks. Compound 1, {[Zn(p-pda)(bpee)]} (p-pda = p-phenylenediacetate and bpee = 1,2-bis(4-pyridyl)ethylene) turned out to be a nonporous structure due to the presence of a bulky and rigid aromatic ring in the p-pda ligand. Interestingly, replacement of p-pda with succinic acid yields the microporous framework {[Zn2(μ3-OH)(suc)1.5(bpee)]·CH3OH·2H2O} (2; suc = succinate), which offers a 1D channel along the a direction occupied by guest methanol and water molecules. Remarkably, the desolvated framework of 2 shows selective uptake of C2H2 over other gas molecules such as C2H4, C2H6, CO2 and CH4 at 293 K. An ideal absorbed solution theory (IAST) study predicts a high selectivity value for acetylene adsorption over the other gas molecules mentioned above. The efficiency of removal of acetylene from ethylene/acetylene mixtures containing 1% acetylene was established through a column breakthrough experiment performed at room temperature. The performance of our material in the purification of ethylene by removing acetylene is comparable with those reported in the literature. In the frameworks of both 1 and 2, the ethylenic double bonds of adjacent bpee linkers are aligned parallel and readily undergo [2 + 2] cycloaddition reactions upon UV-light irradiation to yield {[Zn2(p-pda)2(rctt-tpcb)]} (1IR) and {[Zn4(μ3-OH)2(suc)3(rctt-tpcb)]·2CH3OH·4H2O} (2IR), respectively (rctt-tpcb = regio-cis,trans,trans-tetrakis(4-pyridyl)cyclobutane). Photochemical structural transformations of 100% were observed in single-crystal to single-crystal fashions, which were also supported by 1H NMR spectroscopy. The structures of both 2 and 2IR underwent temperature-dependent reversible structural transformations, which was confirmed by SCXRD and DSC analysis. Selective C2H2 uptake of the dehydrated framework of 2IR was also examined, which demonstrates results similar to those of 2.

Optimizing Pore Space for Flexible-Robust Metal-Organic Framework to Boost Trace Acetylene Removal.

Isoreticular principle has been employed to realize a flexible-robust metal-organic framework (MOF) with extended pore structure for the adsorptive removal of trace acetylene from ethylene under ambient conditions. The substitution from zinc(II) to copper(II) of high coordination distortion leads to elongated Cu-F bonds that expand the closed pore cavities in the prototypical MOF from 3.5 × 3.9 × 4.1 to 3.6 × 4.3 × 4.2 Å3. The optimal cavity size together with strong binding sites thus endows the new Cu analogue to possess open pore space accessible for trace C2H2 within a substantial low-pressure range while excluding C2H4 molecules, as validated by gas isotherms and single-crystal structure of its partially C2H2-loading phase. In contrast to the Zn prototype, at 298 K and 1.0 bar, the guest-free Cu analogue shows significant C2H2 uptake increase with a total capacity of 4.57 mmol g-1, and gains an over two orders of magnitude jump in IAST selectivity for C2H2/C2H4 (1/99, v/v). These results are higher than the benchmark MOFs for molecular sieving of C2H2/C2H4, leading a high C2H4 productivity of 14.9 mmol g-1. Crystallography studies, molecular modeling, selectivity evaluation, and breakthrough experiments have comprehensively demonstrated this flexible-robust MOF as an efficient adsorbent for C2H2/C2H4 separation.

A Microporous MOF with Inorganic Nitrate Ions Immobilized on a Porous Surface Displaying Efficient C2H2 Separation and Purification

A microporous MOF based on a heterotopic ligand was successfully synthesized under solvothermal conditions and fully characterized using single‐crystal and powder X‐ray diffraction, TGA, FTIR, and microanalyses. Single‐crystal X‐ray diffraction analyses showed that the title MOF contains rich inorganic nitrate ions decorating the channel surface that can serve as C2H2 recognition sites. Its selective gas adsorption properties towards C2H2 over CO2 and CH4 were evaluated by single‐component equilibrium adsorption measurements and IAST calculations, establishing its promising potential for C2H2 separation and purification. At ambient conditions, the C2H2 uptake capacity reaches 92.2 cm3 (STP) g–1, while the IAST‐predicted adsorption selectivities are up to 30.6 and 4.5 for the equimolar C2H2‐CH4 and C2H2‐CO2 binary gas mixtures, respectively. Furthermore, DFT computation studies revealed that the inorganic nitrate ion plays a very important role for preferential adsorption of C2H2 over CO2 and CH4.

Highly Selective Separation of C3H8 and C2H2 from CH4 within Two Water-Stable Zn5 Cluster-Based Metal–Organic Frameworks

Adopting the mixed ligands approach, two water-stable Zn5 cluster-based MOFs, [Zn10(TZ)12(TADIPA)2(DMF)4]•DMF•6H2O (JLU-MOF66) and [Zn10(TZ)12(TPTA)2(DMA)2]•2DMA•4H2O (JLU-MOF67) have been constructed (H4TADIPA = 5,5'-(1H-1,2,4-triazole-3,5-diyl) diisophthalic acid, H4TPTA = [1,1':3',1"-terphenyl]-3,3",5,5"-tetracarboxylic acid, and HTZ = 1H-[1,2,3]triazole). Both two compounds with [Zn5(TZ)6] clusters exhibit extraordinary stability (pH = 2-11) and selectivity of C3H8/CH4 (308 for JLU-MOF66, and 287 for JLU-MOF67). Compared to JLU-MOF67, JLU-MOF66 with functional groups exhibits higher CO2 and C2H2 uptake capacity and excellent selective separation for C2H2/CH4 (86, 1:1). Such high separation and chemical stability render them the promising materials for industrial applications.