The separation of ethylene (C2H4) from C2 hydrocarbons is considered
as one of the most difficult and
important processes in the petrochemical industry. Heat-driven cryogenic
distillation is still widely used in the C2 hydrocarbons
separation realms, which is an energy intensive process and takes
up immense space. In response to a greener, more energy-efficient
sustainable development, we successfully synthesized a multifunction
microporous Mg-based MOF [Mg2(TCPE)(μ2-OH2)(DMA)2]·solvents (NUM-9) with C2H6/C2H2 selectivity
based on a physical adsorption mechanism, and with outstanding stability;
especially, it is stable up to 500 °C under an air atmosphere. NUM-9a (activated NUM-9) shows good performances
in the separation of C2H6/C2H2 from raw ethylene gases. In addition, its actual separation
potential is also examined by IAST and dynamic column breakthrough
experiments. GCMC calculation results indicate that the unique structure
of NUM-9a is primarily conducive to the selective adsorption
of C2H6 and C2H2. More
importantly, compared with C2H4, NUM-9a prefers to selectively adsorb C2H6 and C2H2 simultaneously, which makes NUM-9a as a sorbent have the capacity to separate C2H4 from C2 hydrocarbon mixtures under mild conditions through
a greener and energy-efficient separation strategy.
As
a new type of porous material, metal–organic frameworks (MOFs)
have been widely studied in gas adsorption and separation, especially
in C2 hydrocarbons. Considering the stronger interaction
between the unsaturated molecules and the metal sites, and the smaller
molecular size of unsaturated molecules, the usual relationship of
affinities and adsorption capacities among C2 hydrocarbons
in most common MOFs is C2H2 > C2H4 > C2H6. Herein, a unique microporous
metal–organic framework, NUM-7a (activated NUM-7), with a completely reversed adsorption relationship
for C2 hydrocarbons (C2H6 > C2H4 > C2H2) has been successfully
synthesized, which breaks the traditional concept of the adsorption
relationship of MOFs for C2 hydrocarbons. Based on this
unique adsorption relationship, a green and simple one-step separation
purification for a large amount of C2H4 can
be expected to be achieved through the selective adsorption of C2H6. In addition, NUM-7a also shows
good selectivities in C2H2/CO2 and
CO2/CH4.
The propane (C 3 H 8 )-trapping adsorption behavior is considered as a potential performance to directly produce highpurity propylene (C 3 H 6 ). Herein, we report an ultramicroporous Mn-based metal−organic framework (NUM-7) with a reverse C 3 H 8 -selective behavior in the low-pressure area. The pore structure of this material possesses more electronegative aromatic benzene rings for the stronger binding affinity to C 3 H 8 , and the material shows outstanding reverse ideal adsorbed solution theory (IAST) selectivity values. Single-component sorption isotherms preliminarily show the reverse adsorption behavior in the lowpressure part, and the moderate heat of adsorption further confirms this performance and exhibits less energy consumption for regeneration. In addition, the purification effect for the C 3 H 8 / C 3 H 6 mixture is evaluated by the IAST selectivity and transient breakthrough curves, and the GCMC calculation results reveal that the fascinating C 3 H 8 -trapping behavior mainly depends on the multiple C−H•••π interactions. Moreover, because C 3 H 6 is the desired target product, the interesting C 3 H 8 -selective adsorption behavior of NUM-7 may provide its potential for one-step purification of C 3 H 6 , and this work can provide the method of developing C 3 H 8 -selective materials for the purification of C 3 H 6 .
Highly selective separation and purification of acetylene
(C2H2) from ethylene (C2H4)
and carbon dioxide (CO2) are daunting challenges in light
of their similar molecule sizes and physical properties. Herein, we
report a two-dimensional (2D) stable metal–organic framework
(MOF), NUM-11 ([Cu(Hmpba)2]·1.5DMF) (H2mpba = 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoic
acid), with sql topology, stacked together through
π–π interactions for efficient separation of C2H2 from C2H4 and CO2. The 2D-MOF material offers high hydrolytic stability and good purification
capacity; especially, it could survive in water for 7 months, even
longer. This stable MOF selectively captures C2H2 from mixtures containing C2H4 and CO2, as determined by adsorption isotherms. The ideal adsorbed solution
theory selectivity calculations and transient breakthrough experiments
were performed to verify the separation capacity. The low isosteric
heat of NUM-11a (desolvated NUM-11) (18.24 kJ mol–1 for C2H2) validates the feasibility of adsorbent regeneration
with low energy footprint consumption. Furthermore, Grand Canonical
Monte Carlo simulations confirmed that the pore surface of the NUM-11 framework enabled preferential binding
of C2H2 over C2H4 and
CO2 via multiple C–H···O, C–H···π,
and C–H···C interactions. This work provides
some insights to prepare stable MOF materials toward the purification
of C2H2, and the water-stable structure, low
isosteric heat, and good cycling stability of NUM-11 make it very promising for practical industrial application.
One-step harvest of high-purity light
hydrocarbons without the
desorption process represents an advanced and highly efficient strategy
for the purification of target substances. The separation and purification
of acetylene (C2H2) from carbon dioxide (CO2) by CO2-selective adsorbents are urgently demanded
yet are very challenging owing to their similar physicochemical properties.
Here, we employ the pore chemistry strategy to adjust the pore environment
by immobilizing polar groups into an ultramicroporous metal–organic
framework (MOF), achieving one-step manufacture of high-purity C2H2 from CO2/C2H2 mixtures. Embedding methyl groups into prototype stable MOF (Zn-ox-trz)
not only changes the pore environment but also improves the discrimination
of guest molecules. The methyl-functionalized Zn-ox-mtz thus exhibits the benchmark reverse CO2/C2H2 uptake ratio of 12.6 (123.32/9.79 cm3 cm–3) and an exceptionally high equimolar CO2/C2H2 selectivity of 1064.9 at ambient conditions.
Molecular simulations reveal that the synergetic effect of pore confinement
and surfaces decorated with methyl groups provides high recognition
of CO2 molecules through multiple van der Waals interactions.
The column breakthrough experiments suggest that Zn-ox-mtz dramatically achieved the one-step purification
capacity of C2H2 from the CO2/C2H2 mixture with a record C2H2 productivity of 2091 mmol kg–1, surpassing all
of the CO2-selective adsorbents reported so far. In addition, Zn-ox-mtz exhibits excellent chemical
stability under different pH values of aqueous solutions (pH = 1–12).
Moreover, the highly stable framework and excellent inverse selective
CO2/C2H2 separation performance showcase
its promising application as a C2H2 splitter
for industrial manufacture. This work paves the way to developing
reverse-selective adsorbents for the challenging gas separation process.
Ethylene (C2H4) is one of the most significant
substances in the petrochemical industry; however, the capture of
acetylene (C2H2) in about 1% from C2H2/C2H4 mixtures is a difficult
task because of the similarity of their physical properties. With
the aggravation of the energy crisis, using metal–organic framework
(MOF) materials to purify C2H4 through adsorptive
separation is a promising way to save energy and reduce emission.
Pore-space partition (PSP) with the aim of enhancing the density of
the binding sites and the strength of the host–guest interactions
is an effective means to promote a solution for the challenging gas
separation problems. Herein, we report a new embedding metal-carboxylate
chain-induced topology upgrade strategy within a MOF to realize PSP
and separation of C2H2/C2H4 mixtures. As a proof of concept, we construct a microporous MOF
(NUM-12) utilizing the in situ insertion of cobalt terephthalic
chains into a pretargeted ant-type framework during synthesis. Because
of the attainment of an elaborately tuned aperture size and a specific
pore environment through this strategy, NUM-12a (activated NUM-12) not only has a remarkable gas sorption capacity and
strong interactions for C2H2 but also possesses
an excellent purification performance for C2H2/C2H4 mixtures. Both experiments and simulation
calculations clearly reveal that NUM-12 is a promising
candidate for the separation of C2H2/C2H4, proving the feasibility of this new strategy for developing
newly fashioned MOFs with adjustable structure and performance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.