Adsorption separation of carbon dioxide,methane,and nitrogen on Hβand Na-exchangedβ-zeolite

Adsorption isotherms of carbon dioxide （CO2）, methane （CH4）, and nitrogen （N2） on Hβand sodium exchanged β-zeolite （Naβ） were volumetrically measured at 273 and 303 K. The results show that all isotherms were of Brunauer type I and well correlated with Langmuir-Freundlich model. After sodium ions exchange, the adsorption amounts of three adsorbates increased, while the increase magnitude of CO2 adsorption capacity was much higher than that of CH4 and N2. The selectivities of CO2 over CH4 and CO2 over N2 enhanced after sodium exchange. Also, the initial heat of adsorption data implied a stronger interaction of CO2 molecules with Na＋ ions in Naβ . These results can be attributed to the larger electrostatic interaction of CO2 with extraframework cations in zeolites. However, Naβ showed a decrease in the selectivity of CH4 over N2, which can be ascribed to the moderate affinity of N2 with Naβ. The variation of isosteric heats of adsorption as a function of loading indicates that the adsorption of CO2 in Naβ presents an energetically heterogeneous profile. On the contrary, the adsorption of CH4 was found to be essentially homogeneous, which suggests the dispersion interaction between CH4 and lattice oxygen atoms, and such interaction does not depend on the exchangeable cations of zeolite.

Preparation of hybridizing zeolitic imidazolate frameworks with carboxymethylcellulose for adsorption separation of n-hexane/3-methylpentane

A novel ZIF-8-CMC hybrid material was fabricated from the hybridization of ZIF-8 and carboxymethylcellulose(CMC) by impregnation method for n-hexane/3-methylpentane separation.The surface properties of ZIF-8 were tailored by introducing CMC into ZIF-8 nanoparticles.In this work,adsorption separation of n-hexane(nHEX) and 3-methylpentane(3 MP) on ZIF-8-CMC were investigated by batch vapor-phase adsorption and liquid-phase breakthrough adsorption.The adsorption selectivity of nHEX/3 MP reversed from preferable adsorption of nHEX to preferable adsorption of 3 MP upon the increasing of CMC containing in the hybrid materials.As the temperature increases,the adsorption amounts of nHEX and 3 MP decrease.With the increasing of CMC contents,the nHEX uptake decreased,the uptake capacity of 3 MP increased gradually.For liquid-phase breakthrough adsorption,the dynamic adsorption capacity of nHEX also decreased with the increasing of temperature.

4-Pyrazolecarboxylic Acid-based MOF-5 Analogs Framework with High Adsorption and Separation of Light Hydrocarbons

One porous framework [Zn4（μ4-O）（μ4-4-pca）3]·2（DEF）·2（H2O）（1, 4-H2Pca = 4-pyrazolecarboxylic acid, DEF = N,N-diethylformamide） with MOF-5 type topology has been synthesized solvothermally. Significantly, this compound exhibits high capacity of C2 hydrocarbons. C2H2 capacity could compare with the highest value of the reported MOFs, far exceeding that of MOF-5, as well as the high selectivity adsorption of C2s over C1.

Comparison on Adsorptive Separation of n-Paraffins Based on Binderless and Binder-containing Zeolite 5A Pellets

Binderless zeolite is considered to be a potential alternative for binder-containing zeolite in the industrial applications of adsorptive separation process. Synthesized binderless zeolite and commercial binder-containing product were used in adsorptive separation of n-paraffins from a model oil, with their performance compared. It is indicated that the binderless zeolite exhibits by 25%-35% higher in saturated adsorption capacity and by 115%-130% more adsorption amount at the breakthrough point with much shorter length of mass-transfer zone. Adsorptive separation of n-paraffins from naphtha was carried out in a fixed-bed adsorber containing the synthesized binderless zeolite 5 A under the operating conditions covering a feed space velocity of 90 h-1 and an adsorption temperature of 573 K. As compared to original naphtha, the raffinate shows by 34 units more in research octane number and by around 10% more of potential aromatic content, while the desorption oil exhibits by 13.3% more ethylene yield and by 11.7% higher in total olefins yield.

Zeolites for separation:Fundamental and application

Material based emerging separation techniques are attracting more and more attention as alternatives to the traditional ones such as distillation and extraction,aiming to reduce energy consumption and pollutant emissions.Due to their structure characteristics,zeolites can act as versatile sieves and adsorbents for molecules and have been successfully applied in some very important separation processes.Herein,two major catalogues of zeolite separations,namely membrane separation and adsorptive separation,are discussed and their underlying mechanisms are focused.In the part of membrane separation,the synthesis strategies toward zeolite membranes are introduced and the uniformly-oriented zeolite membranes are emphasized.In the part of the adsorptive separation,the industrial and popular adsorptive separations with the corresponding zeolite adsorbents are summarized.Generally,membrane separation relies on the molecular diffusion behavior within zeolites while adsorptive separation relies on the guest–host interaction in principle.The key challenges and misconceptions in zeolite separations are highlighted throughout the article.

Cascade adsorptive separation of light hydrocarbons by commercial zeolites

Adsorptive separation of light hydrocarbons by porous solids provides an energy-efficient alternative to state-of-the-art cryogenic distillation.However,an optimal balance between the cost,performance and stability of the sorbent material is yet to be achieved for industrial applications.Here,we report the efficient separation of C2 and C3 hydrocarbons by a faujasite zeolite(Na-X,Si/Al=1.23).A tandem configuration of two fixed-beds packed with Na-X affords complete dynamic separation of the ternary mixture of C_(2)H_(2)/C_(2)H_(4)/C_(2)H_(6)(1/49.5/49.5;v/v/v)under ambient conditions.Pressure-swing desorption on the latter fixed-bed gives ethylene(>99.50%,1.80 mmol g^(-1))and ethane(>99.99%,1.41 mmol g^(-1)).In situ synchrotron X-ray powder diffraction revealed the binding sites for C_(2)H_(2)and C_(2)H_(4)in Na-X.This study highlights the potential application of commercial zeolites for challenging industrial separations.

Efficient separation of C_(4) olefins using tantalum pentafluor oxide anion-pillared hybrid microporous material

With the increasing demand for synthetic rubber,the purification of 1,3-butadiene(C_(4)H_(6))is of great industrial significance.Herein,the successful removal of n-butene(n-C_(4)H_(8))and iso-butene(iso-C_(4)H_(8))from 1,3-butadiene(C_(4)H_(6))was realized by synthesizing a novel TaOF_(5)^(2-) anion-pillared ultramicroporous material TaOFFIVE-3-Ni(also referred to as ZU-96,TaOFFIVE=TaOF_(5)^(2-),3=pyrazine).Single-component adsorption isotherms show that TaOFFIVE-3-Ni can achieve the exclusion of n-C_(4)H_(8) and iso-C_(4)H_(8) in the low pressure region(0–30 kPa),and uptake C_(4)H_(6) with a high capacity of 92.78 cm^(3)·cm^(-3)(298 K and 100 kPa).The uptake ratio of C_(4)H_(6)/iso-C_(4)H_(8) on TaOFFIVE-3-Ni was 20.83(298 K and 100 kPa),which was the highest among the state-of-the-art adsorbents reported so far.With the rotation of anion and pyrazine ring,the pore size changes continuously,which makes smaller-size C_(4)H_(6) enter the channel while larger-size n-C_(4)H_(8) and iso-C_(4)H_(8) are completely blocked.The excellent breakthrough performance of TaOFFIVE-3-Ni shows great potential in industrial separation of C4 olefins.The specific adsorption binding sites within ZU-96 was further revealed through the modeling calculation.

Effect of Zeolite 5A Particle Size on Its Performance for Adsorptive Separation of Ethylene/Ethane

The adsorptive separation of ethylene from ethane exhibits a less energy-intensive-alternative technique with development potential among all processes for separation of ethylene/ethane currently. In this approach, zeolite 5 A with different particle sizes ranging from 3 340 nm to 440 nm was prepared by hydrothermal synthesis. The effect of particle size on the adsorptive separation performance of zeolite 5 A was investigated. The results show that the particle size has a significant effect on the ethylene IAST(Ideal Adsorbed Solution Theory) selectivity of zeolite 5 A. The zeolite 5 A with a particle size of 710 nm demonstrated the highest ethylene selectivity(5.6). The relatively high crystallinity of zeolite 5 A is in favor of massive adsorption capacities of ethylene and ethane.

天然气提质过程中可有效回收丙烷和乙烷的高工业应用潜力金属有机框架材料

开发高吸附量和选择性的高效吸附剂,用于天然气中C_(2)H_(6)和C_(3)H_(8)的分离和回收,是一项重要且具有挑战性的任务。在本研究中,我们证明高表面极性和合适的孔径直径是协同增强分离性能的两个关键因素,以金属-有机框架(MOF)-303和Matériaux de l'Institut Lavoisier(MIL)-160为例,它们都具有高杂原子密度和所需孔径大小(5~7Å)的一维开放通道。值得注意的是,MOF-303对C_(3)H_(8)的吸附量在298 K和5 kPa时达到了3.38 mmol·g^(−1),与所有已报道的MOFs相比,C_(3)H_(8)/CH4(5:85,v/v)的理想吸附溶液理论(IAST)选择性达到了创纪录的5114。此外,MOF-303还显示出高C_(2)H_(6)吸附量(在10 kPa时)和C_(2)H_(6)/CH4(10:85,v/v)选择性,分别达到1.59 mmol·g^(−1)和26。由于其一维通道内较大的孔径直径和较低的杂原子密度,与MOF-303相比,MIL-160的吸附量和选择性显然更低,尽管这些值超过了大多数报道的MOFs。密度泛函理论(DFT)计算验证了高表面极性和合适的孔径直径协同增强了框架对C_(3)H_(8)和C_(2)H_(6)的亲和力,导致了对C_(3)H_(8)和C_(2)H_(6)的高负载能力和选择性。两种MOFs都具有显著的湿度稳定性,在暴露于95%相对湿度(RH)一个月后没有结构变化。此外,通过一锅反应可以轻松地扩大合成这两种化合物,以获得高结晶度的约5 g样品。最后,通过三元突破实验、再生测试和循环评估,展示了MOF-303和MIL-160作为高级吸附剂,用于高效分离C_(3)H_(8)/C_(2)H_(6)/CH4的巨大潜力。优异的分离性能、高稳定性、低成本和良好的可扩展性,使得这两种MOFs成为天然气净化及C_(2)H_(6)和C_(3)H_(8)回收的有前途的吸附剂。

Ethylene purification in a metal–organic framework over a wide temperature range via pore confinement

The separation of C2H4from C_(2)H_(6)/C_(2)H_(4)mixture is of great importance but difficult and energy intensive. Adsorptive separation provides an alternative approach to ameliorate this situation. Here, we report a microporous metal–organic framework(MOF) BUT-315-a as a C_(2)H_(6)-selective adsorbent for the separation of C2H6/C2H4gas mixture. BUT-315-a combines good IAST selectivity of 2.35 with high C_(2)H_(6)uptake of 97.5 cm^(3)g^(-1), giving superior high separation potential ΔQ(2226 mmol L^(-1)) for equimolar C_(2)H_(6)/C_(2)H_(4) at 298 K. Impressively, such excellent performance can be preserved at higher temperatures of 313 and 323 K to accommodate industrial conditions. Efficient dynamic separation performance of BUT-315-a has been demonstrated by column breakthrough experiments under varied temperatures and gas ratios. Theoretical calculations further reveal multiple synergistic interactions between C_(2)H_(6) and the framework. This work highlights a new benchmark material for C_(2)H_(6)/C_(2)H_(4)separation and provides guidance for designing adsorbent for separation applications.

Boosting xenon adsorption with record capacity in microporous carbon molecular sieves

Xenon/krypton(Xe/Kr)separation is an important task in industry,yet it remains challenging to develop adsorbents with high Xe/Kr selectivity and adsorption capacity of Xe,especially at low partial pressures.Herein,we report a series of microporous carbon molecular sieves(CMSs)for Xe/Kr separation.Those materials have ideal bimodal pore size distributions that not only provide substantial space for the accommodation of gas molecules,but also allow selective diffusion of gas molecules.Additionally,the carbon frameworks decorated with polar oxygen-containing functional groups afford higher affinity for Xe than Kr,which is proven by density functional theory(DFT)calculations and charge density difference analysis.The optimal CPVDC-700 exhibits a high selectivity of Xe/Kr and,more importantly,a record-high uptake of Xe(2.93 mmol g^(-1))at 0.2 bar and298 K,which is the highest among all the reported carbon adsorbents.Breakthrough experiments confirm the excellent performance of such CMSs for Xe/Kr separation,and the dynamic adsorption uptake of Xe and productivity of high-purity Kr are calculated to be 2.91 mmol g^(-1)and 208 m L g^(-1)(9.29 mmol g^(-1)),respectively,which also set up a new benchmark for Xe/Kr separation of carbon adsorbents.

Functional graphene oxide nanosheets modified with cyclodextrins for removal of Bisphenol A from water

A novel type of functional graphene oxide nanosheets(GNs)modified with b-cyclodextrins(b-CDs)have been developed by coating dopamine-functionalized cyclodextrin(DACD)molecules on GNs for removing Bisphenol A(BPA)molecules from water.The DACD molecules with both b-CD groups for achieving adsorption property and dopamine(DA)groups for achieving adhesion property are synthesized by grafting DA onto carboxymethyl-b-cyclodextrin(CmbCD).The proposed DACD molecules can be firmly coated on the surfaces of various inorganic and organic substrates.Due to the large specific surface area of GNs,DACD-coated GNs(DACD@GNs)are proposed for efficient adsorption separation of BPA molecules from water.Due to the host-gust complexation between the BPA molecules in water and b-CDs on DACD@GNs,the fabricated DACD@GNs exhibit excellent adsorption performances.The adsorption kinetics can be explained via the pseudo-second-order model effectively.The experimental adsorption capacity of DACD@GNs is 11.29 mg·g^(-1) for BPA.Furthermore,after the adsorption process,the DACD@GNs can be easily separated from aqueous solutions via vacuum filtration with porous membranes,and then regenerated by simply washing with ethanol.The proposed strategy in this study can be used for effectively functionalizing the surfaces of various substrates with functional b-CDs,which is highly promising in applications in the field of adsorption separations,especially water treatments.

Efficient Splitting of Trans-/Cis-Olefins Using an Anion-Pillared Ultramicroporous Metal-Organic Framework with Guest-Adaptive Pore Channels

Trans-/cis-olefin isomers play a vital role in the petrochemical industry.The paucity of energy-efficient technologies for their splitting is mainly due to the similarities of their physicochemical properties.Herein,two new tailor-made anion-pillared ultramicroporous metal–organic frameworks(MOFs),ZU-36-Ni and ZU-36-Fe(GeFSIX-3-Ni and GeFSIX-3-Fe)are reported for the first time for the efficient trans-/cis-2-butene(trans-/cis-C_(4)H_(8))mixture splitting by enhanced molecular exclusion.Notably,ZU-36-Ni unexpectedly exhibited smart guest-adaptive pore channels for trapping trans-C_(4)H_(8)with a remarkable adsorption capacity(2.45 mmol∙g^(−1))while effectively rejecting cis-C_(4)H_(8)with a high purity of 99.99%.The dispersion-corrected density functional theory(DFT-D)calculation suggested that the guest-adaptive behavior of ZU-36-Ni in response to trans-C_(4)H_(8)is derived from the organic linker rotation and the optimal pore dimensions,which not only improve the favorable adsorption/diffusion of trans-C_(4)H_(8)with optimal host–guest interactions,but also enhance the size-exclusion of cis-C_(4)H_(8).This work opens a new avenue for pore engineering in advanced smart or adaptive porous materials for specific applications involving guest molecular recognition.

Achieving a stable COF with the combination of“flat”and“twist”large-size rigid synthons for selective gas adsorption and separation

A new type of covalent organic framework(COF)was achieved using combination of structrally rigid and conformationally othorganal building blocks.The N-2-aryl-substituted triazole derivative(NAT-CHO)was prepared with co-planar conformation among the three aromatic rings as the“flat”building block.The 4,4,4,4-(ethene-1,1,2,2-tetrayl)tetraaniline)(ETTA)was applied as the“twist”building block.A 2 D sheet of network was obtained through imine formation.The resulting NAT-COF gave excellent thermal and chemical stability,survived aqueous solutions from p H 5 to 13.With large-size building blocks,the porous framework NAT-COF gave efficient gas adsorption with excellent selectivity of C3 propane over C1 me-thane,suggesting its potential application for selective gas capture and separation.

Adsorption and separation of methane/hydrogen in octaphenylsilsesquioxane based covalently-linked organic-inorganic hybrid framework

The adsorption and separation of CH4/H2 in two covalently-linked organic-inorganic hybrid frame- works polyoctaphenylsilsesquioxane （JUC-Z1） were computationally studied using the Grand Canon- ical Monte Carlo （GCMC） simulations. The results show that JUC-Z1 with Linde type A （LTA） and polycubane （zeolite code ACO） net topologies can adsorb up to 20.32, 18.57 mmol/g of CH4 and 19.04, 17.89 mmol/g of H2 at 298 K and 10 MPa, respectively. For the adsorption of binary mixture, the selectivity of CH4 over H2 in LTA-JUC-Zl decrease gradually with the increase of the pressure or the CH4 mole fraction of the mixture. As to ACO-JUC-Z1, the selectivity first increases at low pressure or CH4 mole fraction, and then begins to decrease with the further increase of the corresponding amount. Anyhow, the two materials both exhibit excellent adsorption and separation capacities of CH4/H2.

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(C_(2)H_(2))remains challenging but a sought-after endeavor.Herein we show a strategy involving synergic combination of spatial confinement and commensurate stacking for enhanced C_(2)H_(2)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 C_(2)H_(2)uptakes of 235 and 195 cm^(3)·g^(−1),respectively,due to the confinement effect of the suitable pore sizes and periodically dispersed molecular recognition sites.Specially,C_(2)H_(2)capacity of MIL-160 sets a new benchmark for C_(2)H_(2)storage.The exceptional separation performances of two materials for C_(2)H_(2)over both CO_(2)and ethylene(C_(2)H_(4)),which is rarely observed,outperform most of the benchmark materials for C_(2)H_(2)capture.We scrutinized the origins of ultrahigh C_(2)H_(2)loading in the confined channels via theoretical investigations.The superior separation efficiency for C_(2)H_(2)/CO_(2)and C_(2)H_(2)/C_(2)H_(4)mixtures with unprecedented C_(2)H_(2)trapping capacity(>200 L·kg^(−1))was further demonstrated by dynamic breakthrough experiments.

Robust microporous metal-organic framework with high moisture tolerance for efficient separation of propylene from propane

Adsorptive separation of propylene(C_(3)H_(6))from propylene/propane(C_(3)H_(8))is desired to replace energy-intensive cryogenic distillation for its energy efficiency,economical viability,and environment friendship.In this work,we report a cupper-based robust microporous metal-organic framework,Cu-Hmpba,constructed by the hard soft acid-base principle using the bifunctional pyridylcarboxylate ligand featuring methyl group,for high-efficient separation of the propylene/propane mixture.Under the synergistic effect of the protective group and hard soft acid base principle,Cu-Hmpba possesses good solvents stability,especially water stability.Cu-Hmpba exhibits the adsorption capacity of C_(3)H_(6)with 2.10 mmol g^(-1)and good equimolar C_(3)H_(6)/C_(3)H_(8)selectivity with 2.24 at ambient conditions.The gas adsorption experiments,IAST selectivity calculations and theoretical calculations comprehensively support the selective adsorption toward C_(3)H_(6)among C_(3)H_(6)/C_(3)H_(8)mixture.Furthermore,it could maintain stable under moisture environment,suggesting its potential for the industrial separation of C_(3)H_(6)/C_(3)H_(8)mixture.The results of experiments and simulations demonstrate that the Cu-Hmpba would be a candidate adsorbent for the separation and purification of light hydrocarbons,and this work provides the insight of syn-thesizing stable MOF materials for separating high-value chemicals.

Novel Porous Aromatic Framework with Excellent Separation Capability of CO2 in N2 or CH4

A novel porous aromatic framework, PAF-52, was obtained via the polymerization of tetrahedral mono- mer tetrakis（4-cyanodiphenyl） methane（TCDPM） with the aid of a facile ionothermal method. PAF-52 has a surface area of 1159 m2/g（BET）, and shows a considerable high separation ability of CO2 in N2 or CH4 respectively at room temperature, using gas-chromatography experiments as evidence,

Direct imaging and mechanism study of C_(6)α-olefin adsorption on faujasite and Linde Type A zeolites

Linearα-olefins are important chemical raw materials.To purifyα-olefins from a high-temperature Fischer–Tropsch synthetic oil,it is necessary to separate theα-olefins from the paraffins,which is challenging.Adsorption separation by zeolites is a promising alternative to energy-intensive distillation forα-olefin/paraffin separation.An integrated differential phase-contrast scanning transmission electron microscopy(iDPC-STEM)technique is used in combination with density functional theory(DFT)simulations and batch adsorption experiments to study the adsorption behavior of C_(6)α-olefins and the mechanism of selective adsorption of C_(6)α-olefin/paraffin.Direct electron microscopy real-space imaging of the atomic frameworks of the faujasite(FAU)and Linde Type A(LTA)zeolites and the C_(6)α-olefin-adsorption positions on their lattices is achieved through iDPC-STEM.The images provide direct evidence that C_(6)α-olefins preferentially adsorb at the edges of the FAU and LTA zeolite cavities.DFT calculations further reveal the relationship between host–guest interactions and different molecular orientations.Calculated and experimental results also show that the presence of calcium cations can enhance the selectivity of zeolites forα-olefin/paraffin adsorption.This work provides a means to investigate the behavior of guest molecules and the host–guest interactions in the adsorption or catalytic process of nanoporous materials.

Hydrogen-bonded metal-nucleobase frameworks for highly selective capture of ethane/propane from methane and methane/nitrogen separation

The separation of light hydrocarbons,including C_(2)H_(6)and C_(3)H_(8),is essential to natural gas upgrading.Meanwhile,N_(2)removal from CH_(4)is also crucial to concentrating low-quality coalbed methane,but the adsorption process is challenging because of the close kinetic diameter.This work reports two hydrogen-bonded metal-nucleobase frameworks(HOF-ZJU-201 and HOF-ZJU202)capable of efficiently separating C_(3)H_(8)/CH_(4),C_(2)H_(6)/CH_(4),and CH_(4)/N_(2).Due to strong affinity for C_(3)H_(8)and C_(2)H_(6),the lowpressure capacity for C_(3)H_(8)(5 kPa)and C_(2)H_(6)(10 kPa)of HOF-ZJU-201a exceeds most adsorbents.The ideal adsorbed solution theory(IAST)selectivity of C_(3)H_(8)/CH_(4)and C_(2)H_(6)/CH_(4)is 119 and 45 at ambient conditions.According to density functional theory calculations,surface polarization environments formed by electron-rich anions and electron-deficient purine heterocyclic rings contribute to the selective capture of C_(3)H_(8)and C_(2)H_(6)with greater polarizability.Furthermore,the high CH_(4)adsorption capacity(1.73 mmol/g for HOF-ZJU-201a and 1.50 mmol/g for HOF-ZJU-202a at 298 K and 1.0 bar)and excellent CH_(4)/N_(2)selectivity(6.0 for HOF-ZJU-201 at 298 K),as well as dynamic breakthrough experiments of binary CH_(4)/N_(2)gas mixture implied their efficacy in the concentration of low-quality coalbed methane.