Fast-current-driven synthesis of ultrathin ZIF-8 membrane on ceramic tube for propene/propane separation

MOF membranes are very promising in molecular separation, but it is still a challenge for industrial applications due to the complex and time-consuming synthesis. We use the fast current-driven synthesis (FCDS) method to achieve controlled growth of ZIF-8 membranes on porous graphite-coated ceramic tubes by controlling the growth time and current density. Grown for 30 min at a current density of 0.74 mA/cm², the ZIF-8 membrane exhibits selectivity for C₃H₆/C₃H₈ up to 63 with C₃H₆ permeance of 6 × 10⁻⁹ mol/(m² s Pa). Furthermore, the ZIF-8 membrane exhibits a pressure resistance of up to 3 bar and good stability of ~96 h. This work realizes the breakthrough of the MOF membrane synthesis via FCDS method from the frequently-used expensive and fragile anodic aluminum oxide (AAO) disc substrate to the tough ceramic tubular substrate, which broadens the road for the industrialization of MOF membranes in gas separation fields.     

丙烯/丙烷分离的ZIF-8膜研究进展

同碳数烯烃/烷烃的分离是目前石油化工行业中最耗能的过程之一,开发新型的、低能耗的丙烯/丙烷分离过程被认为是改变世界的七项化工分离技术之一。气体膜分离技术因其高效、节能和环境友好等优点被认为是一种可取代传统低温精馏分离丙烯/丙烷混合气体的新型技术。金属有机骨架材料ZIF-8的有效孔径介于丙烯和丙烷的分子动力学直径之间,可对丙烯/丙烷实现高效分离,是目前分离丙烯/丙烷性能最好的膜材料。本文系统总结了ZIF-8膜的制备方法及用于丙烯/丙烷高效分离的发展历程;探讨了ZIF-8膜微结构的调控,尤其是膜缺陷的修复及ZIF-8骨架柔性的控制;总结了ZIF-8膜在分离丙烯/丙烷时,过程参数对于分离性能的影响规律;并提出ZIF-8膜规模化制备及潜在工业分离丙烯/丙烷研究中存在的问题和未来发展方向。     

Large-area vacuum-treated ZIF-8 mixed-matrix membrane for highly efficient methane/nitrogen separation

Development of materials with excellent separation performances remains an ongoing challenge in methane/nitrogen (CH₄/N₂) separation science. Herein, a facile and effective method for enhancing CH₄ uptake, binding, and CH₄/N₂ selectivity using the surface-carbonized and stiffened zeolitic imidazolate framework-8 (CSZ) via high-vacuum-resistance calcination (HVRC) was demonstrated. Such vacuum-treated CSZ nanoparticles, with carbonized structures that contain Zn-rich sites, high stability, and satisfactory compatibility with polymers, were then uniformly mixed with the strong basic polymer polyvinylamine (PVAm) to obtain large-area mixed-matrix membranes (1120 cm², which is ca. 2 pieces of A4-size paper). Owing to the presence of Zn-rich sites and amino groups, CH₄ molecules were bound more readily to CSZ and PVAm than N₂, as confirmed by gas adsorption isotherms and DFT calculations. The obtained MMM modules (ca. 2000 cm²) exhibited outstanding CH₄ separation performances at 85 wt% CSZ loading, achieving a CH₄ permeance of 7600 GPU and CH₄/N₂ selectivity of 4.35.     

用于CO2/CH4分离的cPIM-1/ZIF-8混合基质膜的制备

自聚微孔聚合物（PIM-1）虽具有良好的CO₂渗透性能,但其气体选择性普遍较差,限制其在CO₂/CH₄分离领域的应用。本文以N,N-二甲基甲酰胺（DMF）为溶剂制备ZIF-8纳米粒子,将其引入到羧基化的PIM-1基质中,制备了cPIM-1/ZIF-8混合基质膜,用于CO₂/CH₄分离。结果表明：由于合成ZIF-8的溶剂也是cPIM-1的良溶剂,使得两者之间具有良好的界面相容性,从而使ZIF-8添加量高达质量分数45%。随着ZIF-8添加量的增加,膜的CO₂渗透速率持续增加,CO₂/CH₄选择性呈现先上升后下降的趋势。当ZIF-8添加量为质量分数25%时,膜的CO₂/CH₄分离性能最好,即CO₂渗透系数为3942 Barrer,CO₂/CH₄选择性为18.7,较cPIM-1纯膜分别提高了 84%和43%,成功地超越了Robeson分离上限。     

C2H6/C3H8影响CH4爆炸极限参数及动力学特性研究

为研究C₂H₆/C₃H₈对甲烷爆炸极限参数及动力学特性的影响,采用标准的可燃气体爆炸极限测定装置测定了不同配比的C₂H₆/C₃H₈混合气体对甲烷爆炸极限的影响规律,同时得出了氮气惰化条件下甲烷爆炸临界参数的变化规律。此外,利用Chemkin软件模拟了C₂H₆/C₃H₈混合气体对甲烷爆炸过程中中间产物浓度的影响情况,并进行了敏感性分析。结果表明,C₂H₆/C₃H₈的存在降低了甲烷的爆炸上下限,增大了甲烷的爆炸危险度;在氮气惰化过程中甲烷的爆炸上限下降,爆炸下限上升,最终爆炸上下限重合,重合点处甲烷浓度和氮气临界浓度均随C₂H₆/C₃H₈的添加而逐渐减小;此外,C₂H₆/C₃H₈混合气体使甲烷爆炸过程中CO和·H的生成量逐渐增大,而CO₂、·O和·OH的生成量则有下降趋势,通过对爆炸过程中甲烷体积的敏感性分析,发现C₂H₆/C₃H₈的存在在某种程度上促进了甲烷爆炸。对比不同配比的C₂H₆/C₃H₈混合气体,发现C₃H₈含量越高,其对甲烷爆炸过程中相关参数的影响越大,这可为工矿企业的安全生产提供一定的理论依据。     

Microwave synthesis of tubular zeolitic imidazolate framework ZIF-8 membranes for CO2/CH4 separation

The separation of CO₂/CH₄ is reported in detail by using zeolitic imidazolate framework (ZIF-8) membrane which was prepared on 3-aminopropyltriethoxysilane modified Al₂O₃ tube through microwave heating synthesis. Attributed to the preferential adsorption affinity of CO₂ over CH₄ and a narrow pore window of 0.34 nm, the ZIF-8 membrane shows high separation performances for the separation of CO₂/CH₄ mixtures. For the separation of equimolar CO₂/CH₄ mixture at 100°C and 2 bar feed (1 bar permeate) pressure, a CO₂ permeance of 1.02 × 10^?8 mol/m²· s· Pa and a CO₂/CH₄ selectivity of 6.8 are obtained, which is promising for CO₂ separation.     

High gas permselectivity in ZIF-302/polyimide self-consistent mixed-matrix membrane

Zeolitic imidazolate framework-302 (ZIF-302) was incorporated within a polyimide (PI) matrix in order to develop a highly selective and permeable mixed-matrix membrane (MMM) for gas separation processes. On the basis of varying fabrication procedures, two different MMMs were formed: a dense MMM (ZIF-302/d-PI) and a spongy, self-consistent MMM (ZIF-302/s-PI). The spongy membrane was shown to have self-consistent and disconnected pores with a reduction in overall membrane density. For ZIF-302/d-PI, a 1.2–1.5-fold increase in the permeability of H₂, O₂, N₂, CO₂, and CH₄ was observed when compared with the pure d-PI membrane. For ZIF-302/s-PI, even better improvements (up to 19-fold higher) in permeance were achieved with negligible effects on selectivity. The gas transport mechanism was then analyzed and showed a considerable enhancement of diffusion coefficients for ZIF-302/s-PI, while ideal gas pair selectivities for CO₂/N₂, H₂/CH₄, and H₂/N₂ were found to be 24.8, 42.3, and 62.6, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48513.     

Boosting C2H6/C2H4 separation in scalable metal-organic frameworks through pore engineering

The development of ethane (C₂H₆)-selective adsorbents for ethylene (C₂H₄) purification, although challenging, is of prime industrial importance. Pillared-layer metal-organic frameworks (MOFs) possess facilely tunable pore structure and functionality, which means they have excellent potential for high-performance C₂H₆/C₂H₄ separation applications. Herein, we report a family of isostructural pillared-layer MOFs with various metal centers M and co-ligands L, M₂(D-cam)₄L₂ (denoted M-cam-L; M = Cu, Co, Ni; L = pyz, apyz, dabco), with a variety of pore surface properties. All of the M-cam-L materials exhibit preferential adsorption for C₂H₆ over C₂H₄. In particular, Ni-cam-pyz exhibits the highest C₂H₆ capture capacity (68.75 cm³ g⁻¹ at 1 bar and 298 K), Cu-cam-dabco possesses the greatest C₂H₆/C₂H₄ adsorption selectivity (2.3), and the lowest isosteric heat of adsorption is demonstrated for Cu-cam-pyz (20.1 kJ mol⁻¹). Dynamic column breakthrough experiments also confirmed the excellent separation performance of M-cam-pyz and M-cam-dabco materials. The synthesis route of the M-cam-L materials is easily scaled-up under laboratory conditions, and hence this class of MOFs is promising for practical C₂H₄ purification.     

PA/ZIF-8/PVDF复合纳滤膜的制备及其性能

采用反向扩散法在聚偏氟乙烯(PVDF)基膜表面原位生长一层均匀、致密的金属有机骨架材料ZIF-8纳米晶体层,并进一步优化界面聚合反应,制备高性能聚酰胺(PA)/ZIF-8/PVDF复合纳滤膜.采用SEM、XRD、FTIR、AFM、XPS、水接触角测定仪以及固体表面Zeta电位仪对ZIF-8/PVDF复合膜及PA/ZIF-8/PVDF复合纳滤膜的组成、结构和形貌进行了表征,考察了ZIF-8亚层的生长对界面聚合反应、复合纳滤膜结构及性能的影响.结果表明,ZIF-8晶体亚层在PVDF膜表面的均匀连续生长改善了PA分离层与PVDF基膜的界面相容性,提高复合纳滤膜PA分离层的交联度.在0.6 MPa下,复合纳滤膜纯水通量可达24.05 L/(m2·h),对MgSO4、Na2SO4、NaCl和MgCl24种盐的截留率分别达到97.34％、93.57％、89.31％和85.16％,具有优异的抗污染性能.     

Fe/C杂化炭膜的制备及其气体分离性能

将二茂铁作为有机添加剂引入炭膜前驱体聚酰亚胺,经高温热解制备了Fe/C杂化炭膜。考察了二茂铁的添加量对杂化炭膜气体渗透性能的影响。采用热重、红外、X射线衍射和透射电镜等分析方法对所制备的杂化炭膜进行了表征。结果表明,在前驱体中添加二茂铁能显著提高炭膜的气体渗透性能,随着添加量的增加,膜的气体渗透系数明显增加而分离系数则减小,当二茂铁添加量为15%时,对H₂、O₂、N₂、CO₂、CH₄等纯气体的渗透系数分别为2806、1039、266、31、8 barrer,对O₂/N₂、CO₂/N₂、CO₂/CH₄的分离系数分别为8.6、33.5、129.5。Fe/C杂化炭膜是基于“分子筛分”机理分离气体分子。     

Enhanced compatibility and selectivity in mixed matrix membranes for propylene/propane separation

Mixed matrix membranes (MMMs) based on metal–organic framework (MOF) have great promising application in separation of gas mixtures. However, achieving a good interfacial compatibility between polymer and MOF is not straightforward. In this work, focusing on one of the most challenging olefin/paraffin separations: propylene/propane (C₃H₆/C₃H₈), we demonstrate that modification of the MOF filler via dopamine polymerization using a double solvent approach strongly improves interfacial compatibility. The resulting membranes show an outstanding separation performance and long-term stability with propylene permeability nearly 90 Barrer and propylene/propane selectivity close to 75. We anticipate that similar MOF modification strategies may help solve the problem of interface defects in the manufacture of MMMs and be extended to other porous fillers.     

Facilitated propylene transport in mixed matrix membranes containing ZIF-8@Agmim core-shell hybrid material

The ZIF-8@Agmim core-shell hybrid material was synthesized via a favorable post-modification method of ion exchange (PMIE). This infrequent ZIF-8@Agmim core-shell structure maintains a well-integrated pore size that is almost the same as ZIF-8. The similar equilibrium isotherms with ZIF-8 and better kinetic separation toward propylene/propane than ZIF-8 render ZIF-8@Agmim to be an interesting candidate for propylene/propane separation. The core-shell hybrid nanomaterial was further used as nanofillers in the polymer of intrinsic microporosity matrix (PIM-1) for propylene/propane separation. The resultant mixed-matrix membranes (MMMs) exhibited a simultaneous increase in C₃H₆ permeability and C₃H₆/C₃H₈ ideal selectivity compared to pure polymer membrane owing to a synergistic effect of molecular sieving from ZIF-8 and π-complexation of Ag⁺ with propylene. The separation performance of the prepared MMM surpasses the upper bound line of polymer membranes. Furthermore, the hybrid materials possess superb photochemical stability and the corresponding MMMs exhibit excellent anti-aging property and long-term stability.     

PDMS/ZIF-8 coating polymeric hollow fiber substrate for alcohol permselective pervaporation membranes

In order to develop high performance composite membranes for alcohol permselective pervaporation (PV), poly (dimethylsiloxane)/ZIF-8 (PDMS/ZIF-8) coated polymeric hollow fiber membranes were studied in this research. First, PDMS was used for the active layer, and Torlon®, PVDF, Ultem®, and Matrimid® with different porosity were used as support layer for fabrication of hollow fiber composite membranes. The performance of the membranes varied with different hollow fiber substrates was investigated. Pure gas permeance of the hollow fiber was tested to investigate the pore size of all fibers. The effect of support layer on the mass transfer in hydrophobic PV composite membrane was investigated. The results show that proper porosity and pore diameter of the support are demanded to minimize the Knudsen effect. Based on the result, ZIF-8 was introduced to prepare more selective separation layer, in order to improve the PV performance. The PDMS/ZIF-8/Torlon® membrane had a separation factor of 8.9 and a total flux of 847 g·m^-2·h^-1. This hollow fiber PDMS/ZIF-8/Torlon® composite membrane has a great potential in the industrial application.     

The effects of spinning conditions on asymmetric 6FDA/6FDAM polyimide hollow fibers for air separation

We have found that the chemistries of inner and external coagulants, gelation bath temperature, and air gap distance have profound effects on 6FDA-polyimde hollow-fiber morphology and performance. This 6FDA-polyimide is made of 50 mol % 2,2′-bis(3,4′-dicarboxyphenyl) hexafluoro propane dianhydride (6FDA) and 50 mol % 2,2′-bis(3-aminophenyl) hexafluoro propane (4,4′ 6F-diamine) (6FDAM). An increase in air gap distance tends to induce three-dimensional open-cell pore formation. Raising bath temperature has a similar effect. Multilayer finger-void structure can be completely eliminated if one properly chooses a bore-fluid flow rate and a gelation bath temperature. Experimental data demonstrate that the location of the dense layer can be shifted from the inner skin to the outer skin based on the chemistry (solubility parameter) of coagulants. The location of finger voids is also dependent on the chemistry of coagulants, and the dense layer location may shift from the inner surface to the external surface or appear in both surfaces dependent on the differences in solubility and coagulation rate. A defect-free 6FDA/6FDAM polyimide fiber with a selectivity of 4.73 and a permeance of 38.1 GPU is produced. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1555–1569, 1997     

Polysulfone/poly(ether sulfone) blended membranes for CO2 separation

Polymer blending as a modification technique is a useful approach for augmenting the gas‐separation and permeation properties of polymeric membranes. Polysulfone (PSF)/poly(ether sulfone) (PES) blend membranes with different blend ratios were synthesized by conventional solution casting and solvent evaporation technique. The synthesized membranes were characterized for miscibility, morphology, thermal stability, and spectral properties by differential scanning calorimetry (DSC), field emission scanning electron microscopy, thermogravimetric analysis, and Fourier transform infrared (FTIR) spectroscopy, respectively. The permeation of pure CO₂ and CH₄ gases was recorded at a feed pressure of 2–10 bar. The polymer blends were miscible in all of the compositions, as shown by DSC analysis, and molecular interaction between the two polymers was observed by FTIR analysis. The thermal stability of the blend membranes was found to be an additive property and a function of the blend composition. The morphology of the blend membranes was dense and homogeneous with no phase separation. Gas‐permeability studies revealed that the ideal selectivity was improved by 65% with the addition of the PES polymer in the PSF matrix. The synthesized PSF/PES blend membranes provided an optimized performance with a good combination of permeability, selectivity and thermal stability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42946.     

Permeation of H2, N2, CH4, C2H6, and C3H8 through asymmetric polyetherimide hollow‐fiber membranes

Permeation properties of pure H₂, N₂, CH₄, C₂H₆, and C₃H₈ through asymmetric polyetherimide (PEI) hollow‐fiber membranes were studied as a function of pressure and temperature. The PEI asymmetric hollow‐fiber membrane was spun from a N‐methyl‐2‐pyrrolidone/ethanol solvent system via a dry‐wet phase‐inversion method, with water as the external coagulant and 50 wt % ethanol in water as the internal coagulant. The prepared asymmetric membrane exhibited sufficiently high selectivity (H₂/N₂ selectivity >50 at 25°C). H₂ permeation through the PEI hollow fiber was dominated by the solution‐diffusion mechanism in the nonporous part. For CH₄ and N₂, the transport mechanism for gas permeation was a combination of Knudsen flow and viscous flow in the porous part and solution diffusion in the nonporous part. In our analysis, operating pressure had little effect on the permeation of H₂, CH₄, and N₂. For C₂H₆ and C₃H₈, however, capillary condensation may have occurred at higher pressures, resulting in an increase in gas permeability. As far as the effect of operating temperature was concerned, H₂ permeability increased greatly with increasing temperature. Meanwhile, a slight permeability increment with increasing temperature was noted for N₂ and CH₄, whereas the permeability of C₂H₆ and C₃H₈ decreased with increasing temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 698–702, 2002     

C6H11NO/nCF3SO3H型低共熔溶剂氧化脱除模拟油中的二苯并噻吩

通过简单加热并搅拌己内酰胺（C₆H₁₁NO）和三氟甲磺酸（CF₃SO₃H）的混合物合成了C₆H₁₁NO/nCF₃SO₃H（n=0.25,0.5,1）型酸性低共熔溶剂。利用红外光谱（FTIR）和氢谱（¹HNMR）确定了C₆H₁₁NO/nCF₃SO₃H的结构特征。以C₆H₁₁NO/0.5CF₃SO₃H低共熔溶剂和H₂O₂组成萃取-氧化脱硫系统,并将其应用于脱除模拟油中的二苯并噻吩（DBT）。研究n(CF₃SO₃H)∶n(C₆H₁₁NO)、反应温度、O/S、C₆H₁₁NO/0.5CF₃SO₃H的加入量和不同类型的硫化物对脱硫效果的影响。实验结果表明,在模拟油体积为5mL、n(CF₃SO₃H)∶n(C₆H₁₁NO)=0.5、反应温度为60℃、 O/S=6、C₆H₁₁NO/0.5CF₃SO₃H的加入量为1.0mL的最佳反应条件下,C₆H₁₁NO/0.5CF₃SO₃H对DBT、4,6-DMDBT、BT和真实油的脱硫率分别达99.4%、98.6%、83.6%和61.6%。红外表征分析了DBT与DESs之间存在相互作用,这种作用促进了氧化脱硫的进程。催化剂5次循环反应以后,其脱硫率仍高达91.9%,表明C₆H₁₁NO/0.5CF₃SO₃H低共熔溶剂具有较高的脱硫性能和稳定性。     

Pebax/a-MoS2/MIP-202混合基质膜的制备及CO2分离性能

为了获得高性能的CO₂/N₂分离膜,把空气中氧刻蚀的二硫化钼（a-MoS₂）和金属有机框架材料MIP-202通过机械力化学反应制备的双功能填料作为分散相,聚醚嵌段酰胺（Pebax-1657）作为连续相,采用溶液浇铸法制备了Pebax/a-MoS₂/MIP-202混合基质膜。采用FT-IR表征了填料的化学结构,借助ATR-FTIR、SEM、TG和力学性能测试表征了混合基质膜的化学结构、微观形貌结构、热稳定性和物理力学性能。研究了水含量、双功能填料配比、含量、膜两侧压差和操作温度对膜气体分离性能的影响,并考察了模拟烟道气（CO₂/N₂体积比15/85）条件下混合基质膜的长时间运行稳定性。结果表明：在温度为25℃、膜两侧压差为0.1 MPa的操作条件下,a-MoS₂与MIP-202质量比为5∶5和双功能填料含量为6%（质量）时,膜的气体分离性能达到最优,CO₂渗透性和CO₂/N₂选择性分别为380 Barrer和124.7,超过了2019年McKeown等提出的上限值。连续测试360 h后,混合基质膜的性能没有明显降低,其平均CO₂渗透性和CO₂/N₂选择性分别为358 Barrer和120.1。这主要是由于a-MoS₂和MIP-202协同提高了膜的气体分离性能。     

Pebax/a-MoS2/MIP-202混合基质膜的制备及CO2分离性能

为了获得高性能的CO₂/N₂分离膜,把空气中氧刻蚀的二硫化钼（a-MoS₂）和金属有机框架材料MIP-202通过机械力化学反应制备的双功能填料作为分散相,聚醚嵌段酰胺（Pebax-1657）作为连续相,采用溶液浇铸法制备了Pebax/a-MoS₂/MIP-202混合基质膜。采用FT-IR表征了填料的化学结构,借助ATR-FTIR、SEM、TG和力学性能测试表征了混合基质膜的化学结构、微观形貌结构、热稳定性和物理力学性能。研究了水含量、双功能填料配比、含量、膜两侧压差和操作温度对膜气体分离性能的影响,并考察了模拟烟道气（CO₂/N₂体积比15/85）条件下混合基质膜的长时间运行稳定性。结果表明：在温度为25℃、膜两侧压差为0.1 MPa的操作条件下,a-MoS₂与MIP-202质量比为5∶5和双功能填料含量为6%（质量）时,膜的气体分离性能达到最优,CO₂渗透性和CO₂/N₂选择性分别为380 Barrer和124.7,超过了2019年McKeown等提出的上限值。连续测试360 h后,混合基质膜的性能没有明显降低,其平均CO₂渗透性和CO₂/N₂选择性分别为358 Barrer和120.1。这主要是由于a-MoS₂和MIP-202协同提高了膜的气体分离性能。     

富氧条件下Rh/Co_3O_4催化剂对C_3H_6还原NO性能的影响

采用液相沉淀法制备Co3O4氧化物,并以其为载体制备负载型Rh催化剂。考察不同焙烧温度制备的载体和催化剂的结构、织构、氧化还原性能及其对C3H6催化还原NO性能的影响。结果发现,经600℃焙烧的载体制备的Rh/Co3O4催化剂中Rh与Co3O4的相互作用较强,促进对N—O键的削弱作用,提高对C3H6还原NO的还原能力。在相同实验条件下,当体系中C3H6为500×10-6、NO为500×10-6和O2体积分数为5%时,NO转化率50%,催化性能优于Rh/Al2O3催化剂。