Acetylene Storage Research Articles

Flexible-Rigid Aluminum-Organic frameworks with Ultra-Fine Pore-Environment regulation for benchmark acetylene storage and purification

Rational regulation of functional groups on the pore surface of robust aluminum metal–organic framework (CAU-10-H) from amino (–NH2), hydrazino (–N2H3), to azido (–N3) continuously control their framework rigidity-flexibility together with ultra-fine pore-size change in the scale of 0.1–0.5 Å. Benefited from the rigid architecture and suitable pore environments, CAU-10-NH2 exhibits a supreme acetylene (C2H2) storage density (473 g/L) exceeding the values of liquid C2H2 (393 g/L) and all reported MOF adsorbents under ambient conditions. Different from CAU-10-H/NH2/N2H3, CAU-10-N3 exhibited temperature-dependent flexible stepwise adsorption behaviors for C2H2 with azido groups as the guest-sensitive gate, having highest storage capacity (106 cm3 cm−3) and second-high storage density (405 g/L) among these materials. Notably, compared with other C2-hydrocarbon and CO2 molecules, only C2H2 can open the azido door at 298 K, and thus effectively enhancing their separation selectivity with top-level uptake ratios for C2H2/C2H4 (2.65) and C2H2/CO2 (2.93), which are further supported by the practical fixed-bed breakthrough curves and theoretical simulations. Such a rational combination of rigidity and flexibility breaks new ground in MOF chemistry and sets a benchmark for acetylene storage and purification.

A Solid-State Transformation of Hydrogen-Bonded Organic Frameworks for Efficient Acetylene Storage and Gas Separation

A Solid-State Transformation of Hydrogen-Bonded Organic Frameworks for Efficient Acetylene Storage and Gas Separation

Molecular Mechanisms behind Acetylene Adsorption and Selectivity in Functional Porous Materials.

Since its first industrial production in 1890s, acetylene has played a vital role in manufacturing a wide spectrum of materials. Although current methods and infrastructures for various segments of acetylene industries are well-established, with emerging functional porous materials that enabled desired selectivity toward target molecules, it is of timely interest to develop new efficient technologies to promote safer acetylene processes with a higher energy efficiency and lower carbon footprint. In this Minireview, we, from the perspective of materials chemistry, review state-of-the-art examples of advanced porous materials, namely metal-organic frameworks and decorated zeolites, that have been applied to the purification and storage of acetylene. We also discuss the challenges on the roadmap of translational research in the development of new solid sorbent-based separation technologies and highlight areas which require future research efforts.

Molecular Mechanisms behind Acetylene Adsorption and Selectivity in Functional Porous Materials

AbstractSince its first industrial production in 1890s, acetylene has played a vital role in manufacturing a wide spectrum of materials. Although current methods and infrastructures for various segments of acetylene industries are well‐established, with emerging functional porous materials that enabled desired selectivity toward target molecules, it is of timely interest to develop new efficient technologies to promote safer acetylene processes with a higher energy efficiency and lower carbon footprint. In this Minireview, we, from the perspective of materials chemistry, review state‐of‐the‐art examples of advanced porous materials, namely metal–organic frameworks and decorated zeolites, that have been applied to the purification and storage of acetylene. We also discuss the challenges on the roadmap of translational research in the development of new solid sorbent‐based separation technologies and highlight areas which require future research efforts.

Commensurate stacking within confined ultramicropores boosting acetylene storage capacity and separation efficiency

Developing advanced porous materials possessing both a high storage capacity and selectivity for acetylene (C2H2) remains challenging but a sought-after endeavor. Herein we show a strategy involving synergic combination of spatial confinement and commensurate stacking for enhanced C2H2 storage and capture via maximizing the host—guest and guest—guest interactions. Two ultramicroporous metal-organic frameworks (MOFs), MIL-160 and MOF-303 are elaborately constructed to exhibit ultrahigh C2H2 uptakes of 235 and 195 cm3·g−1, respectively, due to the confinement effect of the suitable pore sizes and periodically dispersed molecular recognition sites. Specially, C2H2 capacity of MIL-160 sets a new benchmark for C2H2 storage. The exceptional separation performances of two materials for C2H2 over both CO2 and ethylene (C2H4), which is rarely observed, outperform most of the benchmark materials for C2H2 capture. We scrutinized the origins of ultrahigh C2H2 loading in the confined channels via theoretical investigations. The superior separation efficiency for C2H2/CO2 and C2H2/C2H4 mixtures with unprecedented C2H2 trapping capacity (> 200 L·kg−1) was further demonstrated by dynamic breakthrough experiments.

Nitrogen-rich porous organic cages with high acetylene storage and separation performance

Two nitrogen-rich porous organic cages (POCs) have been investigated for acetylene (C2H2) storage and separation applications, achieving a high C2H2 uptake value of up to 146 cm3 g−1 at 298 K and 1 atm and effective separation of C2H2/CO2 mixtures.

Dative B←N bonds based crystalline organic framework with permanent porosity for acetylene storage and separation.

The utilization of dative B←N bonds for the creation of crystalline organic framework (BNOF) has increasingly received intensive interest; however, the shortage of permanent porosity is an obstacle that must be overcome to guarantee their application as porous materials. Here, we report the first microporous crystalline framework, BNOF-1, that is assembled through sole monomers, which can be scalably synthesized by the cheap 4-pyridine boronic acid. The 2D networks of BNOF-1 were stacked in parallel to generate a highly porous supramolecular open framework, which possessed not only the highest BET surface area of 1345 m2 g-1 amongst all of the BNOFs but also features a record-high uptake of C2H2 and CO2 in covalent organic framework (COF) materials to date. Dynamic breakthrough experiments demonstrated that BNOF-1 material can efficiently separate C2H2/CO2 mixtures. In addition, the network can be regenerated in organic solvents with no loss in performance, making its solution processable. We believe that BNOF-1 would greatly diversify the reticular chemistry and open new avenues for the application of BNOFs.

Partial Linker Substitution Strategy to Construct a Quaternary HKUST-like MOF for Efficient Acetylene Storage and Separation.

Multicomponent metal-organic frameworks (MOFs) have received much attention as emerging materials capable of precisely programing exquisite structures and specific functions. Here, we applied a partial linker substitution strategy to compile an HKUST-1-like quaternary MOF by introducing a bifunctional ligand into the well-known HKUST-1 structure. FUT-1, a new HKUST-like tbo topology MOF, was assembled with paddlewheel [Cu2(COO)4], triangular metallocycle pyrazole cluster Cu3(μ3-OH) (NN)3 building blocks, and two distinct linkers. FUT-1 exhibited good mechanical stability, water stability, and chemical stability (pH = 3-12) in aqueous solutions. Moreover, the porous environments created by this multicomponent primitive endow FUT-1 with high C2H2 storage and significantly selective separation performance of C2H2/CO2. Dynamic breakthrough experiments and ideal adsorbed solution theory calculations further demonstrate that FUT-1 can selectively capture C2H2 from C2H2/CO2 mixtures under ambient conditions. Based on grand canonical Monte Carlo simulations, the high C2H2 separation performance of FUT-1 is attributed to the π-complex formed between the C2H2 molecule and the trinuclear metallocycle clusters on the wall, which provides stronger affinity for C2H2 recognition than the CO2 molecule.

Tunable acetylene sorption by flexible catenated metal-organic frameworks.

The safe storage of flammable gases, such as acetylene, is essential for current industrial purposes. However, the narrow pressure (P) and temperature range required for the industrial use of pure acetylene (100 < P < 200 kPa at 298 K) and its explosive behaviour at higher pressures make its storage and release challenging. Flexible metal-organic frameworks that exhibit a gated adsorption/desorption behaviour-in which guest uptake and release occur above threshold pressures, usually accompanied by framework deformations-have shown promise as storage adsorbents. Herein, the pressures for gas uptake and release of a series of zinc-based mixed-ligand catenated metal-organic frameworks were controlled by decorating its ligands with two different functional groups and changing their ratio. This affects the deformation energy of the framework, which in turn controls the gated behaviour. The materials offer good performances for acetylene storage with a usable capacity of ~90 v/v (77% of the overall amount) at 298 K and under a practical pressure range (100-150 kPa).

Micropore Regulation in Ultrastable [Sc3O]-Organic Frameworks for Acetylene Storage and Purification.

High storage capacity, high separation selectivity, and high structure stability are essential for an idea gas adsorbent. However, it is not easy to achieve all three at the same time, even for the promising metal-organic framework (MOF) adsorbents. We demonstrate herein that robust [Sc3O]-organic frameworks could be regulated by a micropore combination strategy for high-performance acetylene adsorption. Under the same solvent system with formic acid as a modulator, similar tritopic ligands extend [Sc3O(COO)6] trigonal-prismatic clusters to generate SNNU-5-Sc and SNNU-150-Sc adsorbents. Notably, the two Sc-MOFs can keep their architectures over 24 h in water at different pH values (2-12) or at 90 °C. Modulated by the linker symmetry, the final stacking metal-organic polyhedral cages produce open window sizes of about 10 Å for SNNU-5-Sc and 5 Å + 7 Å for SNNU-150-Sc. Due to such micropore combinations, SNNU-5-Sc exhibits a top-level C2H2 uptake of 211.2 cm3 g-1 (1 atm and 273 K) and SNNU-150-Sc shows high C2H2/CH4, C2H2/C2H4, and C2H2/CO2 selectivities of 80.65, 4.03, and 8.19, respectively, under ambient conditions. Dynamic breakthrough curves obtained on a fixed-bed column and grand canonical Monte Carlo (GCMC) simulations further support their prominent acetylene storage and purification performance. High framework stability, storage capacity, and separation selectivity make SNNU-5-Sc and SNNU-150-Sc ideal acetylene adsorbents in practical applications.

Acetylene storage performance of [Ni(4,4′-bipyridine)2(NCS)2]n, a switching square lattice coordination network

The coordination network sql-1-Ni-NCS exhibits benchmark working capacity for acetylene storage at practically relevant conditions of temperature and pressure.

Metal-Organic Framework Based Hydrogen-Bonding Nanotrap for Efficient Acetylene Storage and Separation.

The removal of carbon dioxide (CO2) from acetylene (C2H2) is a critical industrial process for manufacturing high-purity C2H2. However, it remains challenging to address the tradeoff between adsorption capacity and selectivity, on account of their similar physical properties and molecular sizes. To overcome this difficulty, here we report a novel strategy involving the regulation of a hydrogen-bonding nanotrap on the pore surface to promote the separation of C2H2/CO2 mixtures in three isostructural metal-organic frameworks (MOFs, named MIL-160, CAU-10H, and CAU-23, respectively). Among them, MIL-160, which has abundant hydrogen-bonding acceptors as nanotraps, can selectively capture acetylene molecules and demonstrates an ultrahigh C2H2 storage capacity (191 cm3 g-1, or 213 cm3 cm-3) but much less CO2 uptake (90 cm3 g-1) under ambient conditions. The C2H2 adsorption amount of MIL-160 is remarkably higher than those for the other two isostructural MOFs (86 and 119 cm3 g-1 for CAU-10H and CAU-23, respectively) under the same conditions. More importantly, both simulation and experimental breakthrough results show that MIL-160 sets a new benchmark for equimolar C2H2/CO2 separation in terms of the separation potential (Δqbreak = 5.02 mol/kg) and C2H2 productivity (6.8 mol/kg). In addition, in situ FT-IR experiments and computational modeling further reveal that the unique host-guest multiple hydrogen-bonding interaction between the nanotrap and C2H2 is the key factor for achieving the extraordinary acetylene storage capacity and superior C2H2/CO2 selectivity. This work provides a novel and powerful approach to address the tradeoff of this extremely challenging gas separation.

Front Cover: New Paradigms in Porous Framework Materials for Acetylene Storage and Separation (Eur. J. Inorg. Chem. 44/2021)

Front Cover: New Paradigms in Porous Framework Materials for Acetylene Storage and Separation (Eur. J. Inorg. Chem. 44/2021)

New Paradigms in Porous Framework Materials for Acetylene Storage and Separation

AbstractAcetylene is an important precursor in the petrochemical, plastics and electronic industries, as well as the prominent fuel for welding and metal cutting. The high flammability and explosive nature of acetylene, however hinder its safe storage and transportation. Porous materials are highly promising for acetylene storage and as they can provide strong binding interactions and an optimal pore environment. Furthermore, high selectivity and separation can be achieved for acetylene over other gases such as CO2and small hydrocarbons. In this review, we divulge into the recent advancements and paradigms in acetylene storage and separation with a focus on porous metal‐organic frameworks (MOFs). An overview of the benchmark materials for acetylene storage and separation, along with some recent developments in the strategies to balance the trade‐off between the uptake capacity and selectivity is provided. The approaches of designing small pores and highly functionalized pore environments for strong binding with the acetylene adsorbate; along with the pore space partition, window space directed assembly and inverse CO2/C2H2adsorption for the separation of acetylene from CO2, CH4, C2H4and other hydrocarbons are reviewed to provide a summary and help further augment the research in this direction.

An Isomeric Copper‐Diisophthalate Framework Platform for Storage and Purification of C2H2and Exploration of the Positional Effect of the Methyl Group

AbstractThree isostructural metal‐organic frameworks (MOFs) based on dicopper paddlewheels and dimethyl‐functionalized linear diisophthalate ligands were solvothermally constructed, with the aim to investigate their performance regarding acetylene (C2H2) storage as well as separation and purification and to further understand the positional effect of the weakly polarized methyl functionality. Isotherm measurements and IAST selectivity analyses revealed that the three compounds exhibited the promising potential for storing C2H2and recovering C2H2from carbon dioxide (CO2) and methane (CH4) at ambient conditions. Furthermore, their C2H2adsorption properties can be tailored and optimized by altering the relative position of the methyl substituents immobilized in the organic linkers. At 298 K and 1 atm, the C2H2uptake capacities vary from 173.0 to 183.6 cm3 (STP) g−1, while the C2H2/CH4and C2H2/CO2adsorption selectivities are in the range of 24.5–26.6 and 4.34–4.70 for the equimolar gas mixtures. Theortho‐dimethyl‐modified MOF outperformed better than the other two MOF isomers. The results indicate that rational arrangement of functional groups can to some extent improve gas adsorption properties. Although the property discrepancy caused by the less‐polar methyl group is not as large as that by Lewis‐basic nitrogen atoms, this is the first experimental demonstration of the positional effect of methyl group on C2H2adsorption.

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.

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.

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

The high storage capacity versus high selectivity trade-off barrier presents a daunting challenge to practical application as an acetylene (C2 H2 ) 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 C2 H2 , the target MOFs offer a good combination of high C2 H2 /CO2 adsorption selectivity and high C2 H2 uptake capacity in addition to good stability. The optimized SNNU-27-Fe material demonstrates a C2 H2 uptake of 182.4 cm3 g-1 and an extraordinary C2 H2 /CO2 dynamic breakthrough time up to 91 min g-1 under ambient conditions.

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).

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

Despite much intense investigation on the C2 H2 /CO2 separation, 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 the ith-d topology. Completely differing from the famous pillar-layer fluorinated materials, SIFSIX-Cu-TPA possesses a unique pillar-cage structure, in which the SiF6 2- 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 C2 H2 uptake (185 cm3 g-1 at 298 K and 1 bar). At the same time, due to the obvious difference in the adsorption performance of CO2 and C2 H2 especially in the low pressure area, SIFSIX-Cu-TPA also exhibits an excellent C2 H2 /CO2 separation performance (breakthrough time up to 68 min g-1 at 298 K and 1 bar).