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.

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.

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.

π-Complexation Mesoporous Adsorbents Cu-MCM-48 for Ethylene-Ethane Separation

Copper incorporated MCM-48 molecular sieve adsorbents with different Cu content have been hydrothermally synthesized. The samples have been characterized by various physicochemical methods, including X-ray diffraction （XRD）, nitrogen adsorption （N2） and X-ray photoelectron spectroscopy （XPS）. The results reveal that Cu-MCM-48 with mass fraction of copper up to 10 % can still retain the uniform mesoporous framework of MCM-48. The copper in the framework of MCM-48 was easily auto-reduced to Cu（I） in N2 at high temperature, which did not alter the mesoporous structure of MCM-48. The adsorption equilibrium isotherms of ethylene and ethane on these molecular sieve adsorbents have been measured at 30℃. At 100 kPa, the adsorption capacities of ethylene on 5Cu-MCM-48 and 10Cu-MCM-48 are higher than those on MCM-48. The 10Cu-MCM-48 molecular sieve adsorbent has a higher selective adsorption ratio of ethylene to ethane, the separation factor is 3.8, and the amount of ethylene adsorbed is 11.1 ml·g ^-1.

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.

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.

CO_2/CH_4 and CH_4/N_2 separation on isomeric metal organic frameworks

Two isomeric metal-organic frameworks(MOFs) with 2-dimensional(2D) and 3-dimensional(3D) topologies both comprised of Cu(Ⅱ) and OTf(OTf = trifluoromethanesulfonate) ions were synthesized and characterized.The CO_2,CH_4 and N_2 adsorption properties of the two isomeric MOFs were investigated from 263 K to 298 K at0.1 MPa.The results showed that the 2D MOF exhibited a higher selectivity for CO_2 from CO_2/CH_4 and CH_4from CH_4/N_2 compared to the 3D MOF,even though it possessed a lower surface area and pore volume.The higher adsorption heats of gases on the 2D MOF inferred the strong adsorption potential energy in the layered MOFs.Dynamic separation experiments using CO_2/CH_4 and CH_4/N_2 mixtures on the two MOFs proved that the2 D MOF had a longer elution time than the 3D MOF as well as better separation abilities.

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.

Synthesis of high-crystallinity MIL-125 with outstanding xylene isomer separation performance

MIL-125 is a metal-organic framework with great potential for the adsorption and separation of xylene isomers.However,MIL-125 is usually synthesized under anhydrous and anaerobic conditions.In this study,homogeneously shaped and highly crystalline MIL-125 was synthesized by introducing water-resistant titanium-containing oligomers into the synthesis process.With the assistance of the novel oligomers,MIL-125 can be synthesized in the presence of water,which meets batch-production requirements.The adsorption separation performance of the obtained highly crystalline MIL-125 was also significantly enhanced.The para-xylene/meta-xylene selectivity can reach 13.5 in mesitylene,which is higher than the selectivity values of most previously reported para-selective adsorbents.The MIL-125 xylene separation performance was verified using both batch adsorption and breakthrough experiments in the liquid phase.In addition,the influence of the solvent effect was evaluated through microcalorimetric experiments,liquid-phase adsorption experiments,and theoretical calculations.

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.

Direct Ethylene Purification from Cracking Gas via a Metal–Organic Framework Through Pore Geometry Fitting

The direct one-step separation of polymer-grade C_(2)H_(4) from complex light hydrocarbon mixtures has high industrial significance but is very challenging.Herein,an ethylene-adsorption-weakening strategy is applied for precise regulation of the pore geometry of four tailor-made metal–organic frameworks(MOFs)with pillar-layered structures,dubbed TYUT-10/11/12/13.Based on its pore geometry design and functional group regulation,TYUT-12 exhibits exceptional selective adsorption selectivity toward C_(3)H_(8),C_(3)H_(6),C_(2)H_(6),C_(2)H_(2),and CO_(2) over C_(2)H_(4);its C_(2)H_(6)/C_(2)H_(4) adsorption selectivity reaches 4.56,surpassing the record value of 4.4 by Fe_(2)(O_(2))(dobdc)(dobdc^(4-)=2,5-dioxido-1,4-benzenedicarboxylate).The weak p–p stacking binding affinity toward C_(2)H_(4) in TYUT-12 is clearly demonstrated through a combination of neutron powder diffraction measurements and theoretical calculations.Breakthrough experiments demonstrate that C_(2)H_(4) can be directly obtained from binary,ternary,quaternary,and six-component light hydrocarbon mixtures with over 99.95%purity.

Commercial Applications of Paraxylene Adsorbents RAX-2000A and RAX-3000

The RAX series paraxylene （PX） adsorbents RAX-2000A and RAX-3000, are developed by the Sinopec Re- search Institute of Petroleum Processing （RIPP） and manufactured by the Sinopec Catalyst Company. Performance test of RAX-2000A showed that the average purity of the PX product reached 99.81%, with an average PX yield of 98.6% per pass. The new generation of PX adsorbents, RAX-3000 not only retains most advantages of the adsorbent RAX-2000A, but also has higher selective adsorption capacity by at least 8%. The actual unit production capability of the adsorbent RAX- 3000 was increased by about 18%. The RAX series PX adsorbents exhibited good adaptability to unfavorable feedstock containing high ethyl benzene （EB） fraction besides their better mechanical strength. Preliminary test results indicated that compared to the adsorbent RAX-2000A, the A/Fa and D/F relating to the adsorbent RAX-3000 were notably decreased due to the hi^her selective adsorotion canacitv of the adsorbent RAX-3000.

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。

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.

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.

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.

Organic-free,Ultrafast Synthesis of K-CHA Nano-aggregates with Various Morphologies and Their Adsorption Performances

K-Chabazite(K-CHA)zeolites were synthesized with an ultrafast procedure through an eco-friendly and cost-effective“one-pot”method.By solely employing colloidal silica and aluminum hydroxide in the K^(+)/Sr^(2+)system without the assistance of seeds,fluorides or organic structure as directing agents,the K-CHA nano-aggregates were successfully synthesized in a few hours.The crystallization behavior of the gels with different SiO_(2)/Al_(2)O_(3) molar ratios(SARs)was investigated using X-ray diffraction(XRD);scanning electron microscope(SEM);X-ray fluorescence(XRF);27Al and 29Si magic angle spinning nuclear magnetic resonance(MAS NMR);Fourier-transform infrared spectra(FTIR);UV-Raman characterizations.As the nucleation rates were changed with the SARs,three kinds of K-CHA nano-aggregates,namely,hamburger-,disk-and walnut-shaped,were obtained.A possible formation mechanism of the K-CHA nano-aggregates was proposed.Additionally,the walnut-shaped sample with an SAR of 7 possessed the largest pore volume and specific surface area,resulting in the highest methane adsorption capacity.Furthermore,it exhibited a CH_(4)/N_(2) selectivity of more than 3 under relative pressures ranging from 0 to 0.6.This work offers guidance for modifying the stacking modes of other nano-sized zeolites.