澄清溶液中NaA型分子筛膜的合成及气体渗透性能

The use of zeolite membranes in separation or combined reaction and separation processes is very attractive. Advantages of using such a type of membranes include their ability to discriminate molecules based on the molecular size and their stability[1]. In the past ten years, most efforts were involved in the synthesis and permeation studies of MFI zeolite membrane[2, 3]. Recently, NaA zeolite membrane has attracted much attention because of its high potential in the dehydration of organic liquids[4]. However, few gas permeation results were reported[5]. Furthermore, most of the NaA zeolite membrane was synthesized from gel[4]. In this letter, the synthesis of NaA zeolite membrane from clear solution and its gas permeation properties are reported.     

气体分离分子筛膜

本文简述了气体分离分子筛膜的研究进展,总结了气体分离分子筛膜的制备方法、分子筛膜类型、气体分离性能及催化应用,分析了气体渗透测定方法和分离机理,对分子筛膜的发展提出一些建议。     

Zeolite‐Type Metal Oxalate Frameworks

While many metal oxalate salts are known, few are known to form zeolite‐type topologies. The construction of zeolite types, especially those with low framework density such as RHO, from linear ligands is generally perceived as less likely, because the 180° metal‐ligand‐metal geometry deviates too much from the established strategy of using ligands with bent coordination geometry (centered around 145°) to mimic the geometry in natural zeolites. We show the general feasibility of using linear ligands for the synthesis of zeolite types by reporting a family of indium oxalate salts with multiple zeolite topologies, including RHO, GIS, and ABW. Of particular interest is the synthesis of a zeolite RHO net with double 8‐rings and large alpha cages, which are highly desirable zeolite features.     

Layered Zeolite for Assembly of Two-Dimensional Separation Membranes for Hydrogen Purification

Membrane separation is an energy-efficient and environmentally friendly process. Two-dimensional (2D) molecular sieving membranes featuring unique nanopores and low transport resistance have the potential to achieve highly permeable and selective mixture separation with low energy consumption. High-aspect-ratio zeolite nanosheets with intrinsic molecular-sieving pores perpendicular to the layers are desirable building blocks for fabricating high-performance 2D zeolite membrane. However, a wider application of 2D zeolitic membranes is restricted by the limited number of recognized zeolite nanosheets. Herein, we report a swollen layered zeolite, ECNU-28, with SZR topology and eight-member ring (8-MR, 3.0 Å×4.8 Å) pores normal to the nanosheets. It can be easily exfoliated to construct 2D membrane, which shows a high hydrogen selectivity up to 130 from natural gas and is promising for hydrogen purification and greenhouse gas capture.     

In situ evaluation of defect size distribution for supported zeolite membranes

The permporometry measurements are performed with respect to a series of zeolite membranes with different defect sizes, which can be further applied for in situ measurement of the defect size distribution in zeolite membranes. Gas permeation experiments are conducted for CO₂/N₂ gas mixture to test the separation performance of the studied zeolite membranes. By taking into account the “t-layer” on defect walls, a mathematical model and the corresponding procedure are developed so that the defect size distribution in zeolite membranes can be calculated by using the results of permporometry measurements. The defect size distribution and the maximal defect size show a good correlation with the separation performance of CO₂/N₂ gas mixture for zeolite membranes. It is demonstrated that the separation performance of zeolite membranes is mainly determined by large defects. It has been shown that the permporometry-based methodology proposed in this contribution is an effective way for the quality evaluation of zeolite membranes.     

Beryllosilicate frameworks and zeolites

Using inspiration derived from studying naturally occurring minerals, a series of framework beryllosilicates have been synthesized under hydrothermal conditions. These include two new zeolite topologies, a unique layered beryllosilicate, and beryllosilicate analogues of numerous aluminosilicate zeolites. Materials with the structure of the rare zeolite mineral nabesite have been synthesized for the first time, including both sodium and potassium derivatives. The structural chemistry of these beryllosilicates frameworks is discussed with reference to the networks of linked tetrahedra, which include the first instance of pentagonal, two-dimensional Cairo-tiling of silicate tetrahedra in one of the new zeolite topologies, their porosity, and their thermal stability.     

The effects of polymer chain rigidification, zeolite pore size and pore blockage on polyethersulfone (PES)-zeolite A mixed matrix membranes

The polyethersulfone (PES)-zeolite 3A, 4A and 5A mixed matrix membranes (MMMs) were fabricated with a modified solution-casting procedure at high temperatures close to the glass transition temperatures (T_g) of polymer materials. The effects of membrane preparation methodology, zeolite loading and pore size of zeolite on the gas separation performance of these mixed matrix membranes were studied. SEM results show the interface between polymer and zeolite in MMMs experiencing natural cooling is better (i.e., less defective) than that in MMMs experiencing immediate quenching. The increment of glass transition temperature (T_g) of MMMs with zeolite loading confirms the polymer chain rigidification induced by zeolite. The experimental results indicate that a higher zeolite loading results in a decrease in gas permeability and an increase in gas pair selectivity. The unmodified Maxwell model fails to correctly predict the permeability decrease induced by polymer chain rigidification near the zeolite surface and the partial pore blockage of zeolites by the polymer chains. A new modified Maxwell model is therefore proposed. It takes the combined effects of chain rigidification and partial pore blockage of zeolites into calculation. The new model shows much consistent permeability and selectivity predication with experimental data. Surprisingly, an increase in zeolite pore size from 3 to 5 Å generally not only increase gas permeability, but also gas pair selectivity. The O₂/N₂ selectivity of PES-zeolite 3A and PES-zeolite 4A membranes is very similar, while the O₂/N₂ selectivity of PES-zeolite 5A membranes is much higher. This implies the blockage may narrow a part of zeolite 5A pores to approximately 4 Å, which can discriminate the gas pair of O₂ and N₂, and narrow a part of zeolites 3A and 4A pores to smaller sizes. It is concluded that the partial pore blockage of zeolites by the polymer chains has equivalent or more influence on the separation properties of mixed matrix membranes compared with that of the polymer chain rigidification.     

原位合成分子筛气-液改性毛细管柱的制备与评价

 用原位合成方法成功地制备了一类新型NaA分子筛毛细管柱 ,与传统柱型相比 ,原位合成柱的分子筛层更加均匀与致密、分离效果更佳。在此柱上涂敷不同极性的固定液制备了一类新型气 液分子筛改性SCOT柱 ,测试表明该柱型分离效果较佳、热稳定性好 ,其中超短柱及大口径柱的成功应用更显示该柱型具有很高的实际应用价值 ,值得推广。     

Nanocomposite MFI-alumina membranes via pore-plugging synthesis: Genesis of the zeolite material

This paper presents a study of MFI-type zeolite crystal growth during hydrothermal synthesis of nanocomposite MFI-alumina membranes by the pore-plugging method, using the standard protocol described in a previous study [S. Miachon, E. Landrivon, M. Aouine, Y. Sun, I. Kumakiri, Y. Li, O. Pachtová Prokopová, N. Guilhaume, A. Giroir-Fendler, H. Mozzanega, J.-A. Dalmon, Nanocomposite MFI-alumina membranes via pore-plugging synthesis: specific transport and separation properties, J. Membr. Sci. 281 (2006) 228]. To this aim, the materials have been characterized by SEM, EDX, pure H2 gas permeance and n-butane/H2 mixture separation at different stages of the synthesis. The effect of synthesis time in the range of 4–89 h and the effect of a 9-h interruption after a 8-h hydrothermal synthesis have been surveyed, as well as the mean pore size and the alumina phase of the support inner layer. Our results suggest that an interruption during the synthesis is necessary to allow the zeolite precursor to diffuse into the support pores. This diffusion leads to a further growth of zeolite crystals into the support matrix without formation of a continuous zeolite film on top of the support, as is usually reported in the literature. The zeolite crystals are fully embedded into the support top layer after at least 53-h synthesis time, leading to high quality membranes in only one synthesis run. The nanocomposite MFI-alumina architecture at the nanoscale has important consequences in improving the gas separation performance of this kind of materials when compared to more conventional film-like structures. A method based on gas transport measurements has been used to determine the effective thickness of the separating material.     

Improving the Gas-Separation Properties of PVAc-Zeolite 4A Mixed-Matrix Membranes through Nano-Sizing and Silanation of the Zeolite

Mixed-matrix membranes containing synthesised nano-sized zeolite 4A and PVAc were fabricated to investigate the effect of zeolite loading on membrane morphology, polymer-filler interaction, thermal stability and gas separation properties. SEM studies revealed that, although the membranes with 40 wt % nano-sized zeolite particles were distributed uniformly through the polymer matrix without voids, the membranes with 15 wt % zeolite loading showed agglomeration. With increasing zeolite content, the thermal stability improved, the permeability decreased and the selectivity increased. The effect of silanation on dispersion of 15 wt % zeolite 4A nanoparticles through PVAc was investigated by post-synthesis modification of the zeolite with 3-Aminopropyl(diethoxy)methylsilane. Modification of the nanoparticles improved their dispersion in PVAc, resulting in higher thermal stability than the corresponding unmodified zeolite membrane. Modification also decreased the rigidity of the membrane. Partial pore blockage of the modified zeolite nanoparticles after silanation caused a further decrease in permeability, compared to the 15 wt % unmodified zeolite membrane.     

Cation-modified silikalit-2 as a selective adsorbent for gas chromatography columns

A selective adsorbent was proposed on the basis of synthetic zeolite silikalit-2 modified with cadmium, tallium, and silver cations. It is intended for the gas chromatographic separation of some isomeric benzene derivatives. The adsorbent possesses pronounced retention properties to para isomers of aromatic compounds, which is due to the molecular sieve properties of the zeolite and the ability of benzene derivatives to form unstable complexes with cations entering the composition of the zeolite. Low selectivity to ortho and meta isomers is due to only the complexation effect.     

Microporous manganese formate: a simple metal-organic porous material with high framework stability and highly selective gas sorption properties

Novel microporous metal-organic framework material composed of Mn(II) and formate ions displays permanent porosity, high thermal stability, and size-selective gas sorption behavior. The framework is stable enough to maintain single crystallinity after the complete guest removal at 150 degrees C under a reduced pressure. Most importantly, it selectively adsorbs H2 and CO2 but not N2 and other gases with larger kinetic diameters, which appears to be due to the small aperture of the channels. Despite a moderate H2 storage capacity, which is however still higher than that of any zeolite, its H2 surface coverage is one of the highest among the known microporous materials. Thus this new zeolite-like material made of a simple organic building block may find useful applications in gas separation and sensor.     

Separation of gas mixtures using a range of zeolite membranes: a molecular-dynamics study

Gas separation efficiencies of three zeolite membranes (Faujasite, MFI, and Chabazite) have been examined using the method of molecular dynamics. Our investigation has allowed us to study the effects of pore size and structure, state conditions, and compositions on the permeation of two binary gas mixtures, O(2)N(2) and CO(2)N(2). We have found that for the mixture components with similar sizes and adsorption characteristics, such as O(2)N(2), small-pore zeolites are not suited for separations, and this result is explicable at the molecular level. For mixture components with differing adsorption behavior, such as CO(2)N(2), separation is mainly governed by adsorption and small-pore zeolites separate such gases quite efficiently. When selective adsorption takes place, we have found that, for species with low adsorption, the permeation rate is low, even if the diffusion rate is quite high. Our results further indicate that loading (adsorption) dominates the separation of gas mixtures in small-pore zeolites, such as MFI and Chabazite. For larger-pore zeolites such as Faujasite, diffusion rates do have some effect on gas mixture separation, although adsorption continues to be important. Finally, our simulations using existing intermolecular potential models have replicated all known experimental results for these systems. This shows that molecular simulations could serve as a useful screening tool to determine the suitability of a membrane for potential separation applications.     

膜分离天然气脱水蒸汽技术的研究现状

天然气脱水蒸汽是天然气净化过程中的必要环节,选择合适的脱水蒸汽技术和工艺至关重要。本文首先简要概述了新兴的膜分离天然气脱水蒸汽方法的特点,然后介绍了膜分离性能的表征参数及测试、膜组件设计及操作条件的选择,重点介绍了近年来膜分离甲烷脱水蒸汽技术中的聚合物膜材料、沸石分子筛膜材料,最后展望了金属有机骨架材料的应用潜力以及天然气脱水蒸汽技术未来的发展趋势。     

CO2／CH4分离膜及沸石填料影响渗透过程的研究

报导了甲基硅橡胶和纤维素（ＣＡ、ＣＴＡ、ＥＣ）膜对ＣＯ２、ＣＨ４的选择透气性能，并讨论了沸石作为填料所引起的分子筛作用的气体渗透过程。甲基硅橡胶的气体渗透系数最高，而选择性最低，且不受填料沸石的影响。纤维素膜的气体选择性较大，渗透系数可以通过沸石的加人而明显增加。特别是沸石１３Ｘ．沸石３Ａ、４Ａ、５Ａ在ＥＣ膜中对气体分子筛作用，改变了气体原有的渗透过程，提高了选择性。使用Ａｒｒｈｅｎｉｕｓ公式计算出ＥＣ－沸石３Ａ膜的气体渗透活化能。     

Thorium removal from aqueous solutions of Mexican erionite and X zeolite

Thorium(IV) removal from aqueous solutions by erionite and X zeolite was investigated. The Th(IV) uptake at different thorium nitrate concentrations (from 0.25 to 25 mM) was evaluated. The thorium content in the aqueous solution was determined by neutron activation analysis. Th(IV) retained by zeolites was 1.7 and 3.7 meq/g for erionite and X zeolite. In order to explain the thorium sorption process in both zeolites, ion exchange mechanism was considered. It was found that thorium sorption behavior is strongly dependent of the type of zeolite, the separation factor for Mexican erionite was α^Th(IV) _Na(I)<1, this zeolite shows preference for Na(I) rather than for Th(IV), however, by X zeolite, α^Th(IV) _Na(I)~1, this value suggested an approximately ideal ion exchange behavior. The effect of pH on thorium sorption was also considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

Decorated Traditional Zeolites with Subunits of Metal–Organic Frameworks for CH4/N2 Separation

Metal–organic frameworks (MOF) materials are promising materials for gas separation, but their application still faces various challenges. A strategy is now reported for introducing subunits of MOFs into traditional zeolite frameworks to obtain applicable adsorbents with advantages of both zeolites and MOFs. The subunits of ZIFs were introduced into zeolite Y and zeolite ZSM‐5 for CH₄/N₂ separation. Both the molecular simulation and experimental results validated that the IAST CH₄/N₂ selectivity of the resulting samples greatly improved (above 8, at 100 kPa and 25 °C) with the incorporation of ZIF subunits into zeolites structure, and the selectivities were obviously higher than that of zeolites and even better than that of ZIFs. This strategy not only gave rise to an efficient adsorbent for CH₄/N₂ separation but also provided ideas for design of other adsorption and separation materials.     

Synthesis Optimization of SSZ-13 Zeolite Membranes by Dual Templates for N2/NO2 Separation

High-silica SSZ-13 zeolite membranes are promising in industrial separations of light gases and continuous membranes are highly demanded for better separation performances. Herein, pure-phase, continuous and thin SSZ-13 zeolite membranes were synthesized using dual templates of N,N,N-trimethtyl-1-adamantammonium hydroxide(TMAdaOH) and tetraethylammonium hydroxide(TEAOH). Systematical investigations of TMAdaOH/TEAOH ratios and their concentrations show that TMAdaOH acts as the main structure-directing agent in the formation of the SSZ-13 zeolite. TMAdaOH cooperatively plays with TEAOH in promoting the SSZ-13 crystal intergrowth to form a continuous polycrystalline membrane. Additionally, appropriate introduction of TEAOH is able to adjust the membrane thickness to the crystal-comparable size of ca. 2.0 μm. The SSZ-13 membranes are further applied for N₂/NO₂separation, which is firstly reported on zeolite membranes. The gas permeation results show that the SSZ-13 membrane synthesized by the dual-template approach exhibits selective separation of N₂ over NO₂ with N₂/NO₂ separation factor of 7.6 and N₂ permeance of 1.66×10^-8 mol·m^-2·s^-1·Pa^-1.     

Single gas permeation through compositionally different zeolite NaA membranes: Observations on the intercrystalline porosity in an unconventional,semicrystalline layer

The successful application of zeolite A membranes in the industrial market has thus far been restricted to the pervaporative dehydration of solvent streams in the pharmaceutical and engineering industries. Their application in gas separation processes remains elusive, largely due to the existence of uncontrollable, intercrystalline diffusion pathways in the boundary regions of neighbouring crystals.     

Preparation of supported Sil-1, TS-1 and VS-1 membranes: Effects of Ti and V metal ions on the membrane synthesis and permeation properties

The incorporation of titanium and vanadium metal ions into the structural framework of MFI zeolite imparts the material with catalytic properties. These zeolites are good candidates for catalytic membranes. The Sil-1, TS-1 and VS-1 membranes were grown on pre-seeded porous stainless steel support using hydrothermal synthesis method. The effects of silica and metal (i.e. Ti and V) contents, template concentration and temperature on the zeolite membrane growth and morphology were investigated. The addition of Ti and V metal ions inhibits the zeolite growth and, thus, restricting the amount of metals (i.e. Ti and V) that can be effectively incorporated into the membrane without compromising its separation performance. Optimum Si and TPAOH concentrations were identified for the synthesis of well-intergrown zeolite membranes. An increase in the synthesis temperature can result in a change in film crystallographic orientation and the appearance of imperfections in the form of imbedded zeolite crystals. Single gas permeation experiments were conducted for noble gases (He and Ar), inorganic gases (H₂, N₂, SF₆) and hydrocarbons (methane, n-C₄, i-C₄) to determine the separation performance of these membranes. The results indicate that the gas transport through Sil-1 and VS-1 membranes is predominantly through the zeolite pores and that the presence of vanadium in VS-1 has significant influence on the permeance of adsorbed gases (e.g. hydrocarbons). Laminar flow is important for the TS-1 membrane that exhibited microscopic cracks.