Article

Adsorption, Permeation and Diffusion of Gases in Microporous Membranes. II - Permeation of Gases in Microporous Glass Membranes

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Abstract

The gas permeability properties of He, H2, CO2 O2, N2 and CH4 in microporous silica membranes were studied as a function of temperature and pressure. A mathetical model of compressible flow in a hollow fiber tube with permeable walls was developed and solved to describe gas transfer in the membranes. The permeation rate of He in the microporous membrane was comparable to that in industrially produced polymeric membranes. Selectivity factors in the membrane were found to be a function of differences in the gas kinetic diameters. The ideal selectivity factor for He/CH4 was more than 10,000 at 30°C. Selectivity factors decreased with increasing temperature.

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... It has been found that microporous glass can provide high H 2 permeability (Shelekhin et al., 1992), and in particular excellent thermal and chemical stability (Shelekhin et al., 1992(Shelekhin et al., , 1995. The major disadvantage of these membranes is their fragility and, in addition, it is difficult to develop cheap modules with a high production capacity for densely packed glass fibres. ...
... It has been found that microporous glass can provide high H 2 permeability (Shelekhin et al., 1992), and in particular excellent thermal and chemical stability (Shelekhin et al., 1992(Shelekhin et al., , 1995. The major disadvantage of these membranes is their fragility and, in addition, it is difficult to develop cheap modules with a high production capacity for densely packed glass fibres. ...
Chapter
Both polymeric and inorganic membranes are used for CO2 gas separation in CO2 capture by membranes. In the last few decades, considerable effort has been directed towards the development of inorganic membranes at the scientific level because of their applicability at higher operating temperatures than polymeric membranes. For CO2 and hydrogen separation, active transport systems are also under development and both porous and dense inorganic membranes are being developed. In this context, dense Pd or Pd-alloy membranes on ceramic or metallic supports are the most-developed membrane types. Furthermore, water-gas shift (WGS) or methane steam reforming (MSR) reactions may be performed using inorganic membrane reactor technology. Indeed, these reactions can be incorporated in both integrated gasification combined cycle (IGCC) and natural gas combined cycle (NGCC) for electricity production with CO2 capture. Hydrogen selective membrane reactors are capable of concentrating CO2 at both relatively lower costs and energy consumption than conventional pre-combustion CO2 capture, although inorganic membrane technology has not yet been developed on the industrial scale.
... Among them, only a few have foucsed on the helium separation. For instance, Shelekhin et al. [33] studied preparation and assessment of microporous silica membranes with special attention toward helium permeation. Pure gas permeation tests revealed that by increasing the kinetic diameter of gases, the membrane permeability decreased (Fig. 3); indicating that the kinetic diameter of a gas playing an essential role in the performance of microporous membranes. ...
... These membranes have desirable features such as high selectivity and permeability as well as durability in corrosive environments and are capable of operating at . Permeability dependence to gas kinetic diameter in microporous silica membranes [33]. ...
Article
Helium is a valuable gas with unique properties and applications and still the prominent industrial source of helium is natural gas. Because of several advantages of membrane-based separation processes over conventional methods as well as the lack of a comprehensive scientific report, the present study aims to investigate the advances in design and modification of organic and inorganic membranes and materials including pure polymers, mixed matrix membranes, polymer blends, copolymers, ceramics as well as carbon molecular sieves for separation and recovery of helium from methane and nitrogen. In overall, inorganic membranes such as silica have shown good performance in helium separation, but production of such membranes has not yet become viable on the commercial scale. On the other hand, polymeric membranes are low-priced, but their performance is relatively low with much room for improvements. One of the most effective methods to enhance the performance of these membranes is synthesizing copolymer membranes consisting of alternatively flat and bulky segments. Also, alternations in the membrane configurations as well as hybridization of membranes with cryogenic and pressure swing adsorption processes are among the valuable options for optimizing techno-economical viability of helium separation and purifcation.
... The gas permeation rate of the pottery wall is equal to that of a microperforated or microporous film, being much higher than that of the most polymeric films and sheets (18,19), and thus would be expected to confer unique properties on the earthenware containers from the aspect of food storage and preservation. Many fresh produces and some fermented food products require highly permeable packaging materials to preserve their quality and package integrity (7,8,(20)(21)(22). ...
... which is very different from those of most plastic films (typically, in the range of =4-7) (18,25). The onggi permeability ratios are similar to those of air or perforations (15,19), and thus suggest that gas permeation through the pottery wall is achieved mainly through the micropores. The uniqueness of the permeability ratio and high gas transmission rate of the onggi containers can provide an opportunity to obtain optimum packaging conditions for some foodstuffs such as fresh produce, which would be difficult to obtain using plastic packaging. ...
Article
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Ethnic Korean onggi earthenwares were fabricated using different clay formulations and glazing treatments. Their permeability properties against oxygen, carbon dioxide, and moisture were measured at 20 o C and examined from the aspect of food preservation. Onggi walls consisted of micropores that offered higher gas and moisture permeation rates when compared with other food packaging materials. Earthenware walls were unique in having CO 2 /O 2 permeability ratios of 0.60-1.00. Gas and moisture permeabilities were lower, with wall structure having lower porosity and surface glazing. Results revealed onggi jar packages of grape fruits could attain wide range of O 2 and CO 2 concentrations. Onggi containers present good opportunity to obtain optimum packaging conditions for respiring or ripening products, depending on commodity type.
... Unlike polymeric membranes, inorganic membranes can be operated at high temperature, pressure, and corrosive environment. Inorganic membranes like carbon molecular sieves (CMS), porous silica, porous aluminum and MOFs show high He permeance along with significant He/N2 and He/CH4 selectivities [19][20][21][22]. ...
... Interaction of diffusing gases with pore walls might have added to increase the separation performance of the membrane. The selectivity was also found to decrease with increase in temperature [19]. These silica membranes have poor mechanical stability and the surface is susceptible to all kind of reactions at elevated temperature with feed components, hence, surface modification is required [32]. ...
Article
Full-text available
Natural gas produced at high pressure (50-70 bar) is the only industrial source of helium (He). A membrane separation process may offer a more efficient production system with smaller footprint and lower operational cost than the conventional cryogenic system. Inorganic membranes with high mechanical strength are known to exhibit good stability at high pressure. In this work, two inorganic membranes, porous silica and carbon molecular sieve (CMS) were studied by simulation for their applicability in the He recovery process and compared against a Matrimid polymeric membrane. An in-house developed membrane simulation model (Chembrane) interfaced with Aspen HYSYS was used to simulate the membrane area and energy requirement for the He separation process. He was separated directly from a mixture containing methane (CH4) and 1-5 mole% He in the feed stream, and natural gas containing 1-5 mole% of He in a mixture of CH4 and N2. These streams were considered at 70 bar pressure and 25°C. Single and two-stage membrane separation processes with and without recycle stream were simulated to achieve 97 mole % purity and 90% recovery of He. The simulation results showed that all three membranes can achieve required purity and recovery in a two-stage separation process. However, a recycle is required while using Matrimid membrane which adds cost and complexity to the system. The highest net present value (NPV) for silica, CMS, and Matrimid membrane was US$M 2.5, 2, and 1.75, respectively, when 5% He is present in feed gas and 15 years of plant life is considered.
... shown good performance for helium separation (Shelekhin et al., 1992), though the fabrication of such membranes is costly and complicated. ...
Article
In this study, novel membranes are designed and fabricated using CTA as the main matrix with contributions of PEG and as-synthesized ZIF-8 nanoparticles. Gas permeation properties of blend membranes containing 25–45 wt.% PEG and MMMs containing 2–20 wt.% ZIF-8 crystals are evaluated for the separation of He from N2 and CH4 at various temperatures and pressures. The properties of synthesized ZIF-8 nanoparticles as well as membranes are well characterized. Among all the prepared membranes, the MMMs membrane with composition of CTA/PEG/ZIF-8 (60/20/20 wt.%) exhibits the best performance (PH2 = 73.25 Barrer) for He/N2 (α = 43) and He/CH4 (α = 40) separations. In addition, various predictive permeation models are investigated in order to gain more insights about the systems and for validation of the experimental results. The %AAREs of the models are high, while the best value is obtained by applying the Maxwell model (5.98). Also, by choosing Lewis–Nielsen model and taking into account some of the non-ideal effects such as particle pore blockage, polymer chains rigidification as well as the effect of particles size on the rigidified layer thickness, a new while accurate model is proposed. Finally, the accuracy of the newly developed model is examined utilizing several experimental data.
... Dans ce cas, la quantité sorbée est exprimée en termes surfaciques, plutôt que volumiques, mais la structure générale de l'équation IV.7 reste inchangée (raisonnement dans le plan à la place du volume). Nous présentons quelques résultats obtenus avec l'équation (IV.7) dans le cas de l'adsorption d'hexane sur des zéolites [103]; pour ce système, l'équation (IV.7) permet un ajustement supérieur aux autres modèles couramment employés (Polyani-Dubinin en particulier [34]). Par contre, les isothermes de sorption dans des strucutres de type gel de silice sont ajustés de manière médiocre et très ~nférieure au modèle de Langmuir; ce résultat pourrait provenir de l'existence de différents sites de sorption sur la surface minérale [103]. ...
Thesis
Le but de ce travail est d'étudier l'extraction de composés organiques de solutions aqueuses par pervaporation sous l'angle du transfert de matière dans la membrane; l'équilibre de sorption et la diffusion de l'eau et d'une série d'alcanols (éthanol à pentanols) dans le polydimethylsiloxane (PDMS) ont été étudiés. La théorie de Flory-Huggins classique ne permet pas de décrire correctement les isothermes de sorption obtenus; une analyse des données d'équilibre, basée sur un critère thermodynamique (Zimm & Lundberg), montre que les molécules d'alcanols ont une tendance à l'autoassociation dans le PDMS (formation de clusters). Les résultats sont correctement décrits par une nouvelle approche mécanistique, postulant l'existence d'affinités élémentaires entre les molécules de solvant et la matrice polymère d'une part, les molécules congénères d'autre part; le modèle conduit à une équation d'équilibre contenant deux paramètres ajustables qui permet la description correcte de nombreux systèmes binaires dans les polymères. La diffusion d'un perméant unique dans le PDMS a été étudiée par la technique de perméation de vapeur; la tendance à la décroissance des coefficients de diffusion avec la fraction volumique en pénétrant correspond qualitativement à l'ordre de tendance à la formation de clusters, dégagé de l'étude de sorption. Dans le dernier chapitre, l'influence de la concentration en alcool et de la température de la charge sur les flux partiels de pervaporation est présentée
... The development of ceramic microporous membranes with good gas separation properties have been described in many recent articles [1] [2] [3] [4]. Some of these membranes consisted of a porous support modified with a silica microporous component by either the CVD or sol-gel technique. ...
Article
Microporous silica membranes are known to exhibit molecular sieving effects. However, separation of nearly equal sized molecules is difficult to carry out by size exclusion. Introducing sorption selectivity and keeping the kinetics favourable to facilitate a good contribution of permeation from sorption is a possible solution to enhance selectivity of adsorbing molecules. Results are presented in this paper on the synthesis of a microporous silica membrane with commendable permselectivity between helium and propylene. Modifications are performed on the membrane to improve its almost non-selective nature to propylene/propane mixtures to give practical separation values. Gas separation results on the modified membranes are presented. Surface selectivity on the newly added alumina surface layer is identified as the helping mechanism in realising this separation.
... Meizner and Dyer (1993) studied the transport properties of microporous inorganic membranes and discussed theoretical basis for describing gas transport through both monolithic and multilayer porous systems. Bhandarkar et al. (1992) and Shelekhin et al. (1992) studied gas permeability properties of various gases in microporous silica membranes mathematically as well as theoretically in terms of selectivity factors by considering diffusion as well as adsorption. Jeong et al. (2003 a & b) reported the synthesis of a FAU type zeolite membrane on a porous α-Al 2 O 3 support tube using a hydrothermal process. ...
Article
Full-text available
Catalytic membrane reactors are multifunctional reactors, which provide improved performance over conventional reactors. These are used mainly for conducting hydrogenation/ dehydrogenation reactions, and synthesis of oxyorganic compounds by using inorganic membranes. In this paper, comprehensive model has been developed for a tubular membrane reactor, which is applicable to Pd or Pd alloys membrane, porous inorganic membranes. The model accounts for the reaction on either side, tube or shell, isothermal and adiabatic conditions, reactive and non reactive sweep gas, multicomponent diffusion through gas films on both sides of membrane, and pressure variations. Equations governing the diffusion of gaseous components through stagnant gas film, and membranes have been identified and described. The model has been validated with the experimental results available in literature. By using the developed model catalytic dehydrogenation of ethylbenzene to produce styrene in a tubular membrane reactor have been simulated. Four catalysts available for this reaction have been evaluated for their performance. It is our view that the model may be used to develop general purpose software for the analysis and design of tubular catalytic membrane reactors through numerical simulation.
... On e of t h e prom isin g direction s of m em bran e m at erials d evelopm ent for gas separation application s is design of m icroporous in organic m aterials, for exam ple, zeolites [1][2][3][4], carbon based m olecu lar sieves [1,[5][6][7][8], glassy m em branes [9][10][11] and others. Such m aterials can be effectively used as for separation processes w h ere preferable perm eabilit y of ligh t m olecu les, su ch as h ydrogen , h eliu m , n itrogen is requ ired an d can be provided du e to sievin g effect [1][2][3][4][5][6] as for processes w h ere preferable perm eability of t h e stron gly adsorptive m olecu les (e.g., low er h ydrocarbon s) is requ ired an d can be provided due to stron g surface Àow contribution as in adsorption selective m em branes [11,12]. ...
Article
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Gas permeability parameters of microporous foils based on exfoliated graphite prepared by controlled pressing as membrane material for gas separation are reported. Permeability of H2, N2, CH4, CO2 and C1-C4 lower hydrocarbons for pressed graphite foil (GF) samples with various densities (240-1500 kg/m³) within the temperature range 20-90 °C was studied. It was found that GF samples with density around 1000 kg/m³ demonstrate high H2/CO2 ideal selectivity (α = 14 - 22) which significantly exceeds Knudsen selectivity. The influence of anisotropy structure features of GF membranes, physical foil density, transport pore distribution and gas flow direction on gas transport and separation properties was investigated as well. The evaluation of the surface flow contribution to the overall gas flow was carried out by approximation method using temperature dependences of gas permeance. It is concluded that the presence of noticeable surface flow can lead as to a decrease of gas permeance in comparison with Knudsen flow (for example, for CO2) as to an increase of gas permeance (for example, for lower hydrocarbons). Development of separation process for particular gas mixture compositions needs to take into account obtained tendency. Future potential applications of GF membranes are discussed as well.
... Permeability of different gaseous penetrants in silica hollow fine fibers with average pore size of 20 m[19]. ...
... Among various membranes that have been used for separation of He, pure dense silica membranes have demonstrated the best performance (see Table 6). Silica membranes are inflexible and the preparation approach is more intricate and expensive than polymeric membranes and these have hampered their commercialization [86,87]. PMMA (Poly (methyl methacrylate)) as an engineering plastic has offered the highest selectivity for separation of He from CH 4 and N 2 with values up to 700-3800, but He permeability not exceeded 10 Barrer [88]. ...
Article
Incompatibility between particles and polymers has the adverse consequence on the performance of mixed matrix membranes (MMMs). To overcome this problem, MMMs containing Cu-BDC nanosheets with two various polyimides (6FDA-DAM and Matrimid) were fabricated and tested for He separation. High aspect ratio of nanosheets (more than 100) was confirmed by TEM and AFM Analyses. FESEM images of MMMs showed that the nanosheets were uniformly distributed all over the matrices and there was no symptom of micro scale polymer-filler phase void up to 15 wt. %. Also due to the interface interaction established between two phases, rigidification of chains happened and resulted in increasing Tg and decreasing FFV of polymers. Addition of particles to matrices led to the permeability of He increased slightly until 9 wt. % loading, but it was reduced at 12 and 15 wt. %. Actually, the oriented stacking of nanosheets caused the permeability of CH4 and N2 reduced significantly and gave rise to developed ideal selectivities. The best MMMs for both polymers was observed at loading of 15 wt.%, so that for 6FDA-DAM based MMM, He/CH4 and He/N2 ideal selectivities enhanced by 2570 and 2320 % compared to pure 6FDA-DAM and surpassed the 2008 Robeson upper bound.
... The table clearly shows that the permselectivities begin trending towards a value of 0.80. However, despite the trend that indicates a transition towards Knudsen diffusion, the authors concluded that better methods to seal the 59 membranes at high temperatures were required in order to obtain reliable data at such temperatures.Way and Roberts[Way and Roberts, 1992] and Ma and co-workers[Shelekhin et al., 1992] studied CO 2 permeation and separation through microporous silica hollow fiber membranes prepared by PPG (commercially purchased). The membranes consisted of hollow fibers that had inner and outer diameters of 22 and 32 m, resulting in a wall thickness of 10 m. ...
... However, polymeric membranes generally suffer from plasticization (swelling and deformation) when placed in contact with highly pressurized CO 2 [17,18]. As a result, processes for CO 2 separation using organic membranes are usually performed at relatively low temperatures [19]. Inorganic membranes have high chemical and thermal stability and do not swell. ...
Article
Mixed matrix membranes (MMMs) are hybrid materials prepared by dispersing inorganic particles in a polymeric matrix and are attracting increasing attention for the separation of CO2/CH4 mixtures. The zeolite SAPO-34 and polyetherimide were selected as the inorganic filler and the polymeric matrix for the synthesis of the supported MMMs. Two polymer solvents, dichloroethane (DCE) and N-methyl-2-pyrrolidone (NMP), were investigated for the preparation, and the DCE solvent resulted in a membrane with better CO2/CH4 selectivity. Various SAPO-34 amounts from 0 to 10 wt% were dispersed in the polymer precursor which was dissolved in DCE. The membrane with 5 wt% SAPO-34 content presented the highest performance with a CO2 permeance of 4 × 10−10 mol m−2 s−1 Pa−1 and a CO2/CH4 ideal selectivity of 60. Based on mixed gas permeances and time-lag measurements, the separation of CO2 and CH4 was found to be dominated by the difference in the gas solubilities. The SAPO-34 decreased CH4 transport by increasing its diffusion pathway. Particle agglomeration was observed at 10 wt% zeolite loading in the polymeric matrix.
... Polymeric membranes have low selectivity and stability at high temperatures and plasticize easily in contact with highly pressurized CO 2 [8]. As a result, processes for CO 2 separation using organic membranes are usually performed at relatively low temperatures [9]. Inorganic membranes for CO 2 separation are mainly zeolite membranes [10][11][12][13][14][15], silicate based membranes [16,17], and silica membranes [18][19][20]. ...
Article
Hybrid membranes are promising materials for the purification of natural gas from carbon dioxide. The present paper investigates the effect of the incorporation of primary and secondary amine functional groups on the performance of an organic–inorganic hybrid silica membrane for CO2/CH4 separation. Hybrid membranes were synthesized by chemical vapor deposition using 3-aminopropyltrimethoxysilane and (3-methylaminopropyl)trimethoxysilane as primary and secondary alkylamine–silica precursors, respectively. The amino functionalized membranes were compared to an amine-free membrane prepared using propyltrimethoxysilane as precusor. The amine-free membrane had a pore size of 0.37 nm, and at 393 K a CO2 permeance of 2.1×10−8 mol m−2 s−1 Pa−1 and a CO2/CH4 selectivity of 4. The primary amine membrane had a pore size of 0.36 nm, and at 393 K displayed a CO2 permeance of 2.1×10−8 mol m−2 s−1 Pa−1 and a CO2/CH4 selectivity of 70. The secondary amine hmembrane had a pore size of 0.43 nm and achieved a CO2 permeance of 1.3×10−7 mol m−2 s−1 Pa−1 and a CO2/CH4 selectivity of 140. The pore sizes were estimated by Tsuru׳s method. The transport mechanism of CO2 throughout the amino-silica hybrid membranes was surface diffusion. The secondary amino-silica hybrid membrane was stable for 60 h under a relative humidity of 20%.
... When the Knudsen number is greater than 10, on the other hand, Knudsen diffusion is predominant [44,45]. Li-Zhi Zhang [46] proposed a fractal gas diffusion model for Shelekhin et al [47] studied the gas permeability properties of He, H, CO 2 , 0 2 , N 2 , and CH 4 in micro porous silica membranes as a function of temperatureand pressure. They concluded that the permeation rate of Helium in the micro porous membrane was comparable to that in industrially produced polymeric membranes.Sawly et al [48] presented a numerical method for the simulation of flow in porous. ...
Thesis
Full-text available
Almost all the fossil fuels, on combustion, emit CO2 which is considered to be a greenhouse gas. Developing new power generation cycles that enables carbon-dioxide capture and sequestration are the limelight of current research. Present absorption technologies for carbon capture are energy-intensive and expensive. An alternative to these absorption technologies would be to combust fossil fuels in pure oxygen, whereinthe flue gas stream will have a much higher concentration of CO2, reducing or eliminating the need for costly CO2 capture. Oxy-fuel combustion is considered to be one of the new emerging technologiescapable of capturing and sequestrating CO2. In oxy-fuel combustion, the fossil fuel is burned in an environment of pure oxygen instead of air and the flue gas mainly consists of CO2 and H2O that can be easily separated through condensation processes. Ion Transport Membranes (ITMs) offer promising oxygen production technology with high purity (upto 99%) without adversely affecting the efficiency of the oxy-fired plants. The separation rate of such ITMs can be increased by replacing the conventional inert sweep gas with a reactant/diluent mixture (e.g. CO2, CH4) as this reduces the permeate partial pressure on the permeate side of the membrane, which, along with the temperature, governs the permeation flux. The significant limitation of this approach is that an uncontrolled, exothermic consumption of the permeated specie, can lead to membrane damage, and thus limits the potential of ITMs using reactive sweep gases (i.e. ITM reactors). By using a multichannel ITM reactor, it is proposed to operate the ITM reactor at, or near to isothermal conditions (i.e. a spatially uniform temperature). This may be achieved by introducing a reactantinto the permeate stream uniformly across the entire ITM reactor length from an adjacent channel with porous walls. The present work is aimed at predicting the oxy-combustion characteristics in an oxygen transport reactor with the objective of developing a nearly isothermal reactor. This is achieved by separation of oxygen from air through Ion Transport Membranes (ITM’s) and by using a porous membrane, to achieve uniform stoichiometric ratio of fuel/O2 in order to have uniform combustion all along the length of the membrane. A twodimensional, computational fluid dynamics (CFD) model is solved to study the combustion characteristics. The simulations are based on the numerical solution of the conservation of mass, momentum, energy and species transport equations of two dimensional flows. For the CFD calculations, the commercial solver FLUENT has been used. The mass transfer of oxygen through the membrane is modeled by user defined functions (UDF’s) and the mass transfer of fuel through the porous layer is modeled using a 1D porous jump model. The membrane (ITM) is modeled as a selective layer, which allows the permeation of oxygen as a function of temperature and the difference of partial pressures of oxygen in the feed side and the permeate side. The flux through the porous layer is a function of permeability and thickness of the medium in addition to the pressure difference. The models used have been validated against the experimental results found in the literature and are found to be in good agreement. Influence on the performance of oxygen separation through the ITM has been studied by varying the flow conditions at the permeate side. Results show that for a constant mass flow rate of fuel mixture, the permeation rate of oxygen through ITM increases with increase in CH4/CO2 ratio. It was found that the oxygen permeation rate increased by approximately 3 times with reaction taking place on the permeate side compared to the separation only case. An improved uniform temperature distribution along the membrane was obtained by the combined ITM-porous oxygen transport reactor.
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"... the best handbook on membrane technology, which is currently on the market... " -Membrane News (on the previous edition). Building on the success of the previous edition, Membrane Technology and Applications Third Edition provides a comprehensive overview of separation membranes, their manufacture and their applications. Beginning with a series of general chapters on membrane preparation, transport theory and concentration polarization, the book then surveys several major areas of membrane application in separate chapters. Written in a readily accessible style, each chapter covers its membrane subject thoroughly, from historical and theoretical backgrounds through to current and potential applications. Topics include reverse osmosis, ultrafiltration, pervaporation, microfiltration, gas separation and coupled and facilitated transport; chapters on electrodialysis and medical applications round out the coverage.
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The gas permeability of polymer hybrid membranes has been investigated. The membranes were prepared by dip-coating a methanol solution of poly(N-vinylpyrrolidone) (PVP) and methyltrimethoxysilane (MTMOS) on porous glass tubes. The permeance was measured by using N 2 , CO 2 and He separately at a pressure of 1 kg cm –2 . It was found that the permeance of these gases all increased with temperature in the PVP hybrid membranes. In particular, the permeance of He increased at a much greater rate with temperature, resulting in high selectivity against N 2 . For instance, the permeance of He is 150 times greater than that of N 2 at 100°C. The results indicate the dense structure of PVP hybrid membranes as confirmed by SEM observations. The hybrid membranes also exhibited high selectivity of CO 2 against N 2 . This could be attributed to the high polarity of amide groups in PVP chains which would facilitate the sorption of CO 2 . These polymer hybrid membranes were also found to have high thermal stability compared to organic polymer membranes.
Article
Recent development in microporous inorganic membranes represents a significant advance in materials for separation and chemical reaction applications. This paper provides an in-depth review of synthesis and properties of two groups (amorphous and crystalline) of microporous inorganic membranes. Amorphous microporous silica membranes can be prepared by the sol-gel and phase separation methods. Flat sheet, tubular and hollow fiber amorphous carbon membranes have been fabricated by various pyrolysis methods from polymer precursors. A large number of synthesis methods have been developed to prepare good quality polycrystalline zeolite membranes. Several techniques, including vapor and liquid approaches, are reviewed for pore structure modification to prepare microporous inorganic membranes from mesoporous inorganic membranes. Chemical, microstructural and permeation properties of these microporous membranes are summarized and compared among the several microporous membranes discussed in this paper. Theory for gas permeation through microporous membranes is also reviewed, with emphasis on comparison of theoretical with the experimental data. These inorganic microporous membranes offer excellent separation properties by the mechanisms of preferential adsorption, selective configurational diffusion or molecular sieving.
Article
This article is intended to describe recent progress in the synthesis of zeolitic membranes and their permeation properties. While hydrothermal synthesis has been widely employed for zeolitic-membrane synthesis, the development of a new technique for zeolite synthesis, vapor-phase transport (VPT), has enabled us to prepare pinhole-free, zeolite-porous support composite membranes. This article consists of three sections that describe: a survey of the hydrothermal synthesis of zeolitic membranes, our synthesis results and the formation mechanism of zeolitic membranes by the VPT method as well as some permeation results to show the prospects of zeolitic membranes.
Chapter
This chapter presents an overview of transport phenomena in 2D materials‐based membranes from classical theories to modern knowledge based on experimental evidence and simulation results. Fundamentals of mass transport through membranes are first summarized, which hold a general concept to explain the structure‐property‐performance relationships in various membrane materials. Next, nanofluidic transport in confined dimensions is reviewed to highlight the emerging new paradigm of transport mechanism toward next‐generation membranes, such as 2D membranes. Finally, unique transport properties in 2D membranes are explored depending on the membrane configuration, such as nanoporous atomically thin membranes, laminar membranes, and mixed‐matrix membranes.
Article
The gas separation characteristics of ultramicroporous glass capillary membranes were investigated. Glass capillary membranes which had ultramicropores (pore diameter less than 1 nm) were prepared by elution of alkali metal ions from glass capillaries. It was found from elution treatment that alkali metal ions of 3 Na(composition: 778 SiO2, 22 Na2O mol%) and 3 K (composition: 77 SiO2, 22 K2O mol%) glass capillaries were completely eluted after 90 and 10 minutes with 3 mol/L HNO3, 240 and 10 minutes with 3 mol/L CHM3COOH and 3 mol/L H3PO4, respectively. Permeations of N2, He, and CO2 were measured at 298, 373, and 473 K. Permeation rates of the 3 Na and 3 K glass capillary membranes were 1 (cm(STP).cm-s.cmHg). The ratios of permeation rates, CO2/N2 and He/N2, were similar to the theoretical Knudsen values.
Article
In a previous paper [P. Molyneux, “Transition-site” model for the permeation of gases and vapors through compact films of polymers, J. Appl. Polym. Sci. 79 (2001) 981–1024] a transition-site model (TSM) for the activated permeation of gases through compact amorphous solids was developed and applied to organic polymers; the present paper examines the applicability of the TSM to permeation through microporous silica. The basis of the TSM theory for amorphous solids in general is outlined; the present extension to inorganic glasses has revealed that the transition sites (TS) of this theory, which are the three-dimensional saddle-points critical in the molecular sieving action, equate to the doorways long recognized in permeation through amorphous silica and other inorganic glasses. The TSM, which views permeation as a primary process, is contrasted with the conventional sorption–diffusion model (SDM) for permeation. It is pointed out that in the SDM, the widely accepted analysis into two apparently distinct factors – sorption (equilibrium) and diffusion (kinetic) – has the fundamental flaw that these factors are not independent, since both involve the sorbed state. By contrast, the TSM focuses on the permeant molecule in only two states: as the free gas, and as inserted in a doorway D; hence the characteristics of these doorways – (unperturbed) diameter σD, spacing λ, and the thermodynamic parameters θ (force constant) and ν (entropy increment) for the insertion process – can be evaluated. The theory is applied to literature data [J.D. Way, D.L. Roberts, Hollow fiber inorganic membranes for gas separations, Sep. Sci. Technol. 27 (1992) 29–41; J.D. Way, A mechanistic study of molecular sieving inorganic membranes for gas separations, Final Report submitted to U.S. Department of Energy under contract DE-FG06-92-ER14290, Colorado School of Mines, Golden, CO, 1993, www.osti.gov/bridge/servlets/purl/10118702-ZAx4Au/native/1011872.pdf; M.H. Hassan, J.D. Way, P.M. Thoen, A.C. Dillon, Single component and mixed gas transport in silica hollow fiber membrane, J. Membr. Sci. 104 (1995) 27–42] on the permeation through microporous silica hollow-fiber membranes (developed by PPG Industries Inc.) of the nine gases: Ar, He, H2, N2, O2, CO, CO2, CH4 and C2H4, over the temperature range 25–200°C. The derived Arrhenius parameters for the permeation of these gases (excepting He) lead to estimates of the four doorway-parameters: σD, 125 pm; λ, ca. 30nm; θ, 0.43nN; ν, 1.7pNK−1; these values lie within the ranges of those obtained with the glassy organic polymers. Some “secondary effects”, shown particularly by CO and CO2, are interpreted as host–guest interactions at the doorway. The behavior of He is anomalous, the permeation rising linearly with temperature. This study confirms that the TSM may be applied to gas permeation by activated molecular sieving for this type of inorganic membrane.
Article
Porous glasses in shape of beads and flat membranes with controlled mesoporosity in the range between 2 and 20 nm were used as model system to study the correlation between the texture properties and the transport characteristics in the primary pore system of catalyst supports. The beads and membranes were distinguished by comparable texture parameters. The tortuosity factors of the pore structure were obtained from measurements of the permeability of nitrogen of the porous glass membranes. The tortuosity factors vary in the range between 1.5 and 40 depending on the pore diameter and the porosity of the membranes. The hydrogenation of benzene over nickel catalysts based on the porous glass beads was used as test reaction. Here, the effective mesopore diffusivities were obtained from the Arrhenius plots. Furthermore, the pore diffusion coefficients of benzene were determined. The values are in the range between 1 × 10−6 and 2 × 10−5 cm2 s−1. A systematic correlation between the texture properties (mean pore size) and transport characteristics (pore diffusion coefficient) was observed.
Article
Applying molecular dynamics simulation and computer graphics methods we have investigated the dynamic behavior of the separation process of CO2 from the CO2/N2 gas mixture in inorganic membranes at high temperatures. We have demonstrated that the permeation dynamics follows the Knudsen diffusion mechanism in our model system that has a slit-like pore of 6.3 Å. We have analyzed the effect of affinities of gas molecules for the membrane wall on the permeation to predict the optimal affinity strength for high selectivity of CO2. Our results indicate that in the model with the 600 K and 200 K affinities for CO2 and N2, respectively, we can obtain a high selectivity of CO2 even if the temperature is 1073 K. It is also shown that there is an optimal range for the CO2 affinity for the membrane wall to achieve good separation, which was estimated as the range of 400–600 K in our system, if the affinity of N2 is always weaker than that of CO2.
Article
The outer surface of an α-alumina tube was coated with a γ-alumina film formed by a sol-gel process. Then the tube was coated with polycarbosilane (PC), which was cured at 473 K and pyrolyzed at 623–823 K. The composite membrane prepared was ca. 1–1.4 μm in thickness and had no pinholes larger than several nm. For the composite membrane pyrolyzed at 623 K, the permeation of H2 and N2 at 283–673 K was controlled by the activated diffusion mechanism, and for the membrane pyrolyzed at 823 K by the Knudsen diffusion mechanism. The permeation of CO2 was facilitated by the surface diffusion mechanism for all membranes prepared. The optimum pyrolysis temperature was 723 K from the viewpoints of the permeance of H2 and the separation factor of H2 to N2, which were respectively 5.5 × 10−7 mol m−2 s−1 Pa−1 and 7.2 at 673 K.
Article
A porous α-alumina tube of 2.5 mm O.D. and 1.9 mm I.D. was used as the support of an inorganic membrane and was modified for the purpose of separating small-molecule gases. Macropores of the tube, about 150 nm in size, were plugged with silica formed by thermal decomposition of tetraethylorthosilicate at 600–650°C with no special pretreatment. To improve the step coverage of the deposition, the reactant was evacuated through the porous wall of the support. Silica was decomposed inside the macropores, forming a layer of 500–1000 nm. At a permeation temperature of 600°C, the H2 permeance of the modified membrane was of the order of 10−8 mol·m−2·s−1·Pa−1, while the N2 permeance was below 10−11 mol·m−2 · s−1 · Pa−1. When the membrane was exposed in mixture of nitrogen and steam at 500°C for 24 h, the H2 permeance was decreased to half the initial value but was little reduced by a further exposure of 48 h. The membrane was resistant to cyclic temperature changes.
Article
Glass–alumina composites were developed for possible use as membrane supports. Preparation involved dip-coating of α-Al2O3 tubes with a suspension of borosilicate glass particles (9.1% Na2O–29.7% B2O3–61.2% SiO2), sintering to convert the particle layer into a nonporous layer of phase separated glass, and leaching the glass with a strong acid to remove the soluble phase and obtain the final porous layer of about 10μm thickness. In some preparations a 10% α-Al2O3 powder was added to the initial suspension. The composite supports were characterized by SEM, EDAX and EPMA for elemental composition, XRD for crystalline phase content, nitrogen adsorption for surface area and pore size distribution, and by permeation measurements with single gases and mixtures. After leaching the glass layers had pore size 1–4nm, and contained varying amounts of boron, sodium, and aluminum oxides, in addition to silica. The nitrogen permeance of the composite supports was 10–100 times higher than that of standard porous Vycor tubing.
Article
This chapter discusses methods for the characterization of porous structure in membrane materials. The relationships among the membrane synthesis route, the membrane microstructure or morphological properties, and the permeation properties are described with an emphasis on the porous properties of membranes and their characterization. The origin of porosity in inorganic materials is outlined and a quantitative description of pore structures in idealized model systems is given. In such model systems, the pore geometry can be defined precisely in terms of pore size, shape, and connectivity. This provides the basis for theoretical developments describing diffusion and transport processes in such porous materials. The link between the concept of a model porous structure and the theoretical prediction of diffusivity and mass transport is also crucial in the characterization of porous materials. Thus, each characterization technique yields experimental parameters that are related to the pore structure of a material; these parameters define the porous properties on the basis of an assumed model pore structure.
Article
This chapter discusses the basic adsorption isotherms, presents the fundamental theories of adsorption, and describes the experimental techniques for the measurements of adsorption isotherms and the surface area and pore-size distribution. It discusses the adsorption of gases on microporous membranes and of liquids on mesoporous and macroporous membranes and the inter-relation between adsorption and permeation. Adsorption plays an important role in the separation of gaseous mixtures by microporous membranes and of liquids in ultra- and microfiltration. Adsorption can either enhance or reduce the selectivity coefficient, depending on the affinity of the individual gases. Adsorption can cause membrane fouling in ultra- and microfiltration. Although the potential function techniques give consistent and satisfactory results, caution must be exerted in using these techniques for the calculation of the pore-size distribution, because of the uncertainty involved in the values of the parameters used in the calculation and the simplifying assumptions employed in the derivation of the model equations. A thorough understanding of the interrelation between adsorption and separation in microporous membranes can provide information for the improvement of membrane synthesis.
Article
This chapter discusses the transport and separation properties of membranes with gases and vapors. The transport of mixtures is complicated, especially in membrane systems with a more complex architecture and operated with large pressure gradients. Quantitative solutions for permeation and separation efficiency are not available in an applicable form. Specific solutions have to be obtained by approximations and by combining solutions for limiting cases. The chapter provides an overview of the important theoretical aspects of single gas permeation and of accepted ways to combine several simultaneously operating mechanisms in simple membrane architectures. It discusses the transport properties of mixtures that can be applied in membrane systems and describes the permeation and separation in real but simple porous membrane systems, with a focus on operational applicability. It also discusses the validity of the important approximations of important problems and opportunities, and of some models. The most promising systems to obtain high selectivity in combination with reasonable permeation values are focused.
Article
The permeances of several gaseous species (He, H2, CO2, N2, CH4, and C2H4) were measured through silica hollow fiber membranes over a temperature range of 298 to 473 K at a feed pressure of 20 atm. Permeances ranged from 10 to 2.3 * 105 Barrer/cm at 298 K and were inversely proportional to the kinetic diameter of the penetrant. The permeance of gaseous species were found to decrease with decreasing differential pressure driving force at ΔP <5 bar. No pressure dependency was found at ΔP > 5 bar. Mass transfer through the silica hollow fiber membrane was found to be an activated process. Activation energies for diffusion through the silica membrane calculated from the slopes of Arrhenius plots of the permeation data ranged from 4.61 10 14.0 kcal/mole and correlate well with the kinetic diameter of the penetrants. Large separation factors were obtained for the penetrants. The separation factors decreased with increasing temperature. The CH4/CO2 mixed separation factors were higher than the values calculated from pure gases at temperatures below 373 K. This behavior was observed after the membrane had been heated to at least 398 K and then cooled in an inert gas flow. The differences between the mixture and ideal separation factors is attributed to a competitive adsorption effect in which the more strongly interacting gases saturate the surface and block the transport of the weakly interacting gases.
Article
The ability to monitor free volume formation during space-making treatments is critical for the ultrafine tuning of nanospace for efficient gas separation. Here, investigating the polymer thermal rearrangement using synchrotron in situ small-angle X-ray scattering for the first time and combining this information with transport theory, we elucidate the evolution of nanospace features in polymer-based gas separation membranes. The proposed nanospace monitoring technique encompasses the structure–property relationships, therefore offering a powerful tool for tuning the polymer properties for particular gas-related clean energy applications. These results demonstrate that the fine control of the nanospace dimension and magnitude leads to a drastic improvement in gas separation performance above any material to date.
Article
Optimum conditions for synthesis of lithium zirconate by the solid state reaction were studied experimentally. The monoclinic phase lithium zirconate can be formed from a lithium carbonate, zirconia and potassium carbonate mixture of a certain composition in the temperature range of 850–1200 °C. The equilibrium and kinetics of CO2 sorption on pure lithium zirconate, potassium doped lithium zirconate and potassium doped lithium yttrium-zirconate were studied experimentally by TGA and modeled by gas–solid reaction equilibrium and a simple diffusion model based on the double shell CO2 sorption mechanism. Both experimental results and thermodynamics analysis show a step function for the isotherms of CO2 sorption on these materials. The rate of the CO2 sorption on pure lithium zirconate is controlled by the diffusion of CO2 in the solid lithium carbonate shell. For potassium doped lithium zirconate or lithium yttrium-zirconate the rate limiting step for CO2 sorption is shifted to diffusion of oxygen ions in the zirconia shell.
Article
The asymmetric aluminium oxide flat membranes were prepared by sintering the polymeric precursors which were made of N-methyl-2-pyrrolidone (NMP), polyethersulfone (PESf) and aluminium oxide powder. In the polymeric precursor, N-methyl-2-pyrrolidone (NMP) was used as solvent and polyethersulfone (PESf) was used as polymer binder. The aluminium oxide flat membranes were characterized using simultaneous thermal analysis and SEM. Effects of the content of inorganic powders and the sintering temperature on the structure were studied. The asymmetric structure resulted from the phase inversion technique was preserved after the sintering process. This membrane with a moderate permeation characteristic can serve as a high performance filter material.
Article
Mass spectrometry has been widely used in lander missions to characterize the volatiles in rocks and soils on planetary surfaces. A good vacuum seal is very important for introducing such solid samples to a vacuum chamber and ejecting them. However, multiple measurements require many metal gaskets, leading to extra weight and complexity for the instruments. In this study, we investigate the capability of three kinds of elastomeric O-rings (Viton, Nexus-SLT, and Nexus-FV) as vacuum seals for mass spectrometric measurements, particularly for in situ K–Ar dating on Mars. First, thermal cycle tests revealed that low-temperature-resistant O-rings can maintain pressure <10⁻⁵ Pa at −60°C under 1 bar ambient pressure, whereas Viton O-rings leaked at −25°C. Then, the amount of ⁴⁰Ar due to outgassing from the O-rings and permeation under the ambient pressure of 650 Pa or 3 Pa was measured and compared with the amounts of ⁴⁰Ar that a flight-equivalent laser would liberate from potential target Martian rocks. The measured amounts were <1% of that a target rock with 5000 ppm K2O and an age of 4.2 Ga would yield. These results suggest that a Viton O-ring can maintain the Ar blank low under the Mars atmospheric pressure when temperatures are higher than −25°C. A double O-ring seal using the low-temperature-resistant elastomers would be an alternative approach at lower temperatures. The elastomeric O-rings would be useful for constructing a small and light-weighted mass spectrometric instrument for in situ K–Ar dating on Mars.
Article
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هلیم به دلیل ویژگی‌های منحصربه‌فرد کاربردهای گسترده‌ای به‌ ویژه در حوزه‌های پزشکی، هسته‌ای و فضایی یافته است. در حال حاضر منبع اصلی و صنعتی هلیم گاز طبیعی است که باید حداقل حاوی %0/05 مولی هلیم باشد تا فرایند استخراج که عمدتاً مبتنی بر سرمایش است صرفه‌ی اقتصادی داشته باشد. به دلیل مزایای متعدد فناوری غشایی، استخراج هلیم توسط این فناوری حدود نیم قرن است که مورد مطالعه قرار گرفته است. برخی غشاهای غیرآلی مانند سیلیکا عملکرد مناسبی در جداسازی هلیم از خود نشان داده‌اند اما هزینه‌ و پیچیدگی‌های ساخت و توسعه آن‌ها زیاد است. در مقابل غشاهای پلیمری کم‌هزینه‌ترند و نیاز به ارتقا و بهبود دارند تا عملکردشان به حد مطلوب برسد. درکنار ایجاد آمیزه پلیمری و بکارگیری ترکیبات پرکننده غیر آلی، از جمله مؤثرترین روش‌های بهبود عملکرد این غشاها، سنتز غشاهای کوپلیمر می‌باشد. همچنین سامانه‌ی پیشنهادی استفاده‌ی ترکیبی از فناوری‌های سرمایشی، غشایی و جذب فشار نوسانی می تواند منجر به کاهش مصرف انرژی و هزینه‌ها ‌گردد.
Article
The development of high-temperature processes and tighter environmental regulations requires utilization of efficient gas-separation processes that will provide high fluxes, high selectivity of separation, and the ability to operate at elevated temperatures. Dense inorganic membranes and membrane reactors are especially well suited for high-temperature reactions and separations, due in part to their thermal stability and high separation selectivity (in theory, infinite). Furthermore, membrane reactors offer an inherent advantage of combining reaction, product concentration, and separation in a single-unit operation for the improvement of process economics and waste minimization. The classification of membrane reactors can either be by membrane material and geometry or by the configuration of the reactor. Porous and dense membranes in both tubular and disk forms have been used for membrane reactors. The membrane can either be catalytically active (catalytic membrane reactor [CMR]) or simply act as a separation medium. In the latter case, the catalyst is packed in the reactor, whose walls are formed by the membrane (packed-bed membrane reactor [PBMR]). In addition, if the membrane is also catalytically active, the reactor is called a packed-bed catalytic membrane reactor (PBCMR). The principal materials from which porous inorganic (ceramic) membranes are made are alumina, zirconia, and glass. Alumina and zirconia membranes are usually asymmetric and composite, with a porous support (0.5–2.0 mm thick) for mechanical strength and one or more thin layers for carrying out separations. On the other hand, glass membranes, such as Vycor and microporous glass, have symmetric pores. Materials commonly used as the porous support are alumina, granular carbon, sintered metal, and silicon carbide.
Chapter
The Langmuir equation can be used to describe the experimentally measured CO2 adsorption isotherms on the Vycor glass membrane at nine temperatures ranging from -55 °C to 250 °C with pressures up to 13 atm. The permeation of CO2 through the Vycor membrane is by the Knudsen and surface diffusion while the H2 permeation is by the Knudsen diffusion mechanism. The separation of CO2/H2 mixtures shows CO2 enrichment at -60 °C, due, primarily, to the condensation of CO2 in the membrane pores, thus either partially or totally blocking the pores for the hydrogen permeation.
Chapter
A membrane is a layer of material which serves as a selective barrier between two phases and is impermeable to specific particles, molecules, or substances when exposed to the action of a driving force. Some components are allowed passage by the membrane into a permeate stream, whereas others are retained by it and accumulate in the retentate stream. Membranes can be of various thicknesses, with homogeneous or heterogeneous structures. Membrane can also be classified according to their pore diameter. There are three different types of pore sizes based on the IUPAC (International Union of Pure and Applied Chemistry) classification: microporous (d p < 2 nm), mesoporous (2 nm < d p < 50 nm), and macroporous (d p > 50 nm) [1, 2]. Membranes can be neutral or charged, and the transport through a membrane can be active or passive. The latter can be facilitated by pressure, concentration, chemical or electrical gradients. Membranes can be generally classified into synthetic membranes and biological membranes.
Article
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Supported liquids membranes are very promising products. They have been intensively investigated in last two decades and widely used in many technologies especially in gas separation and purification processes. A key aspect in obtaining satisfying effectiveness and long membrane lifetime is a proper choice of ionic liquid and polymeric or ceramic support. Properties of both affect the processes of obtaining useful supported ionic liquid membranes. In comparison to polymeric membranes, ceramic ones are slightly thicker, however they are thermally and mechanically more stable. Our research was aimed at sintering fine glass particles of 500 to 45 um in size in order to prepare porous membranes which can be used as supports for liquid membranes. Dextrin and borax were used as pore-making agents. The membranes, as disks 35 mm in diameter and 3 mm of thickness, were prepared. The porosity was determined using absorption method. It was found, that the porosity could be controlled by changing the applied pressure from 1 to 5 MPa, particle size distribution, sintering temperature, type and amount of pore-enhancing agents.
Article
The pore diameters in alumina tubular membranes were progressively reduced via SiO2 and TiO2 atomic layer deposition (ALD) using sequential surface reactions. The SiO2 ALD was accomplished using alternating exposures of SiCl4 and H2O. The TiO2 ALD was achieved using alternating exposures of TiCl4 and H2O. The reduction of the pore diameter was observed using in situ N2 conductance measurements. The total conductance, Ct = Q/ΔPt, was measured using a mass flow controller to define a constant gas throughput, Q, and two capacitance manometers to monitor the total pressure drop, ΔPt. These N2 conductance measurements revealed that the SiO2 and TiO2 ALD progressively reduced the pore diameter from an initial diameter of 50 Å to molecular diameters. Using an aperture model for the conductance, the pore diameter was found to decrease at a rate of 1.3 ± 0.1 Å per SiCl4/H2O AB cycle during SiO2 deposition and 3.1 ± 0.9 Å per TiCl4/H2O AB cycle during TiO2 deposition. The N2 conductance measurements were also very sensitive to the functional groups on the surface of the pores. The SiCl4 and TiCl4 exposures leave the pore surface terminated with SiCl* and TiCl* surface species, respectively. Subsequent exposure to H2O converts these surface species to SiOH* or TiOH* species. During SiO2 deposition, the pore diameters are 0.9 ± 0.2 Å larger after the H2O exposure replaces the SiCl* species with the SiOH* species. During TiO2 deposition, the pore diameters are 0.7 ± 0.2 Å larger after the H2O exposure replaces the TiCl* species with the TiOH* species. These pore diameter differences are somewhat smaller than the differences predicted by steric interaction calculations of bond lengths and van der Waals hard sphere radii for these surface functional groups. The N2 conductance measurements illustrate that gas transport through microscopic pores is determined by pore diameters and the effect of the surface species.
Article
Removal of CO2 by membrane technologies is one promising approach as compared to other CO2 capture technologies due to advantages such as simpler operation, higher reliability, lower capital and operating cost, higher energy efficiency, and a cleaner process. In the field of CO2 gas separation, inorganic membranes have been attracting a lot of attention. Three classes of microporous membrane family, i.e. microporous silica membranes, microporous carbon membranes and zeolite membranes, have been widely studied due to their potential in separating CO2 gas molecules, contributed by their distribution of selective micropores which are almost identical to the required molecular sizes for diffusing CO2 gas. This paper review various methods to fabricate the above three types of microporous membranes, at the same time, looking at other researchers employing these methods to fabricate microporous membranes for CO2 separation.
Article
The separation and sequestration of CO2 produced from the combustion of fossil fuels is the need of the day to encounter ‘Greenhouse Effect’ and ‘Global Warming’. Again, it is quite important also for improving the calorific value of natural gas and for reutilization of flue gas. Membrane technology has the potential to play a crucial role in this regard. Compared to other traditional techniques for the separation and sequestering of CO2, membrane technology, particularly ceramic membrane, is still in relatively developing stage. But it has tremendous potential to emerge as a successful technology to meet the requirement in future. This article reviews previous works and recent achievements by different researchers on various CO2 selective ceramic membranes with reference to other type of membranes, like polymeric, hybrid and mixed matrix type. It also discusses various gas transport mechanism in membranes, different features of ceramic membranes, parameters that affect the gas separation in ceramic membranes, new generation ceramic and other types of membranes, industrial applications of membrane based gas separation process and future direction in membrane research.
Chapter
Controlled atmosphere (CA) storage and modified atmosphere packaging (MAP) are two useful technologies to extend the shelf-life of fresh agricultural and horticultural produce. Simply stated, these technologies involve storing a fruit or vegetable in a modified atmosphere usually consisting of reduced O2 and elevated CO2 concentrations compared to air. The modified atmosphere reduces the rates of respiration and ethylene production, which are often associated with the benefits of retardation of physiological, pathological, and physical deteriorative processes occurring in the product. Aerobic respiration is a complicated process that involves a series of enzymatic reactions taking place through the metabolic pathways of glycolysis, the tricarboxylic acid (TCA) cycle, and the associated electron transport system (Kader, 1987).
Article
Inorganic membranes capable of separating carbon dioxide and nitrogen mixture offer potential applications in membrane process for postcombustion carbon dioxide capture. This article provides a concise review of carbon dioxide permeation and separation characteristics and the chemical and thermal stability of microporous carbon, silica, and zeolite membranes. Gas permeation and separation through these microporous membranes generally occur by the solution (adsorption) and diffusion mechanism. All of these membranes are permselective for carbon dioxide over nitrogen because carbon dioxide has a large solubility and mobility in membrane micropores in comparison to nitrogen. These microporous membranes exhibit good carbon dioxide permeance (up to 10(-6) mol m(-2) s(-1) Pa-1) and extremely high carbon dioxide to nitrogen selectivity (up to 500) at around room temperature. The selectivity diminishes above 200 degrees C because the membrane selectivity is controlled by diffusion, and the diffusivity ratio for carbon dioxide to nitrogen is <2. At around room temperature, zeolite (especially Y type) membranes offer attractive properties for use in postcombustion carbon dioxide capture. New membranes such as dense mixed-conducting ceramic-carbonate dual-phase membranes show high carbon dioxide separation performance at high temperatures and may be used in precombustion processes for carbon dioxide capture.
Article
Porous carbon nanotubes, which are single-walled carbon nanotubes having tailored pores in their sidewalls, are proposed as potential membrane materials for separating gas mixtures with high selectivity and high permeance. We present both quantum mechanical calculations and classical statistical mechanical calculations with empirical potentials showing that porous carbon nanotubes having the correct pore size can very effectively separate mixtures of H2/CH4 and also of CO2/CH4. In each of these mixtures, CH4 is effectively prevented from entering the pore due to size exclusion. These porous carbon nanotubes could be used in mixed matrix polymer membranes to increase both the permeance and the selectivity for targeted gas mixtures.
Article
The permeances of gases with kinetic diameters ranging from 2.6 to 3.9 Å were measured through silica hollow fiber membranes over a temperature range of 298 to 473 K at a feed gas pressure of 20 atm. Permeances at 298 K ranged from 10 to 2.3· 105 Barrer/cm for CH4 and He, respectively, and were inversely proportional to the kinetic diameter of the penetrant. From measurements of CO2 adsorption at low relative pressures, the silica hollow fibers are microporous with a mean pore size estimated to be between 5.9 and 8.5 Å. X-ray scattering measurements show that the orientation of the pores is completely random. Mass transfer through the silica hollow fiber membranes is an activated process. Activation energies for diffusion through the membranes were calculated from the slopes of Arrhenius plots of the permeation data. The energies of activation ranged from 4.61 to 14.0 kcal/mol and correlate well with the kinetic diameter of the penetrants. The experimental activation energies fall between literature values for zeolites 3A and 4A. Large separation factors were obtained for O2N2 and CO2CH4 mixtures. The O2N2 mixed gas separation factors decreased from 11.3 at 298 K to 4.8 at 423 K and were up to 20% larger than the values calculated from pure gases at temperatures below 373 K. Similar differences in the separation factors were observed for CO2CH4 mixtures after the membrane had been heated to at least 398 K and then cooled in an inert gas flow. The differences between the mixture and ideal separation factors is attributed to a competitive adsorption effect in which the more strongly interacting gases saturate the surface and block the transport of the weakly interacting gases. Based on Fourier transform infrared (FTIR) spectroscopy results, this unusual behavior is attributed to the removal of physically adsorbed water from the membrane surface.
Article
CO2 capture, transport, and long-term storage or sequestration (CCS) is visualized as a promising strategy for mitigating CO2 emissions at short- and midterms, especially in stationary sources. In the case of precombustion CO2 capture, carbon-templated microporous silica and MFI membranes constitute the most mature materials for membrane design on the basis not only of the reproducibility of their synthesis protocols, but also of their narrow thickness down to the micrometer level. In the case of postcombustion CO2 capture, MFI membranes can find suitable applications for CO2/N2 separations driven by preferential CO2 adsorption. The presence of moderate Si/Al ratios in these materials provides a trade-off for preferential CO2 adsorption and moderate poisoning by moisture below a threshold value. Finally, in the case of CO2/CH4 separations, the SAPO-34 membranes prepared by Noble and Falconer can show potentials with a proven reproducibility of synthesis protocols.
Article
Mesoporous anodic oxidized alumina (MAOA) capillary tubes with and without a barrier layer have been synthesized by applying a pulse-sequential voltage. The single gas permeances at an elevated temperature and the thermal and hydrothermal stabilities of MAOA were investigated. A highly oriented radial mesopore channel with pore sizes from 40 to 4 nm was formed in the MAOA tubes. Micropores with sizes from 0.4 to 0.8 nm were formed in the barrier layer. The H2 permeance of MAOA with a barrier layer (barrier type) was approximately 540 times lower than that of MAOA without a barrier layer (block type) at 773 K. The H2/N2 permselectivity of the barrier type in the temperature range from 333 to 673 K was 3.4; those of the barrier type at 773 and 823 K were 4.4 and 11, respectively. On the other hand, the H2/N2 permselectivities of the block type were from 3.1 to 3.6 in the temperature range from 333 to 773 K. The H2 permeance and the H2/N2 permselectivity of the amorphous silica membrane on the block type were 1.1 × 10 mol/m · s · Pa and 40 at 773 K, respectively. MAOA synthesized by the pulse-sequential voltage method can be applied to the mesoporous support of the gas separation membrane at elevated temperatures.
Article
This paper provides a technical overview of inorganic membranes. Emphasis is placed on porous membranes for pressure-driven applications. Methods of membrane preparation are discussed in relation to resultant microstructures. Commercial as well as developmental inorganic membranes are reviewed with focuses on separation properties and application areas for liquid and gas separations. Finally, potentials and technical challenges for inorganic membranes are addressed. It is shown that porous inorganic membranes are generally superior to organic membranes in thermal, mechanical and structural stability, chemical and microbiological resistance, and ease of cleaning and regenerating. Therefore, these membranes have been used in liquid phase separations and in gaseous diffusion for uranium recovery.
Article
Pure gas permeabilities of He, H2, CO2, N2, and CO were measured for microporous silica hollow fiber membranes as a function of temperature. The transport mechanism for gas permeation is clearly non-knudsen since several heavier gases permeate faster than lighter gases. An excellent correlation is obtained between permeability and kinetic diameter of the penetrant. The proposed mass transfer mechanism is a combination of surface diffusion and molecular sieving. High ideal separation factors (permeability ratios) are observed at 343 K for H2/N2 and H2/ CO of 163 and 62.4, respectively, which compare very favorably with polymeric and molecular sieve gas separation membranes.
Article
The properties, the advantages and drawbacks of hollow fiber carbon molecular sieving membranes as gas separators are discussed. Some mechanistic aspects are surveyed and permeability of methane-hydrogen mixture through the carbon membrane was studied. The presence of methane which is adsorbable and a poor permeant, does not impair the permeability of hydrogen even at temperatures as low as -80°C. This suggests that, because of the large difference in size of the two molecules, they occupy different positions in the membrane material prior to the jump through a critical constriction.
Article
The purpose of the current project is to use the technology base available at ORGDP to develop membranes that will be of significant economic value to the nation for the economical use of fossil energy materials. The first part of the project will be directed toward fabricating a membrane to separate hydrogen from the synthetic gas produced by coal gasification processes. Later efforts will be directed toward tailoring membranes to eliminate the acid gases, such as sulfur and nitrogen oxides and hydrogen sulfide, from gasified coal. Project activities during FY 1989 focused primarily on developing small pore size ceramic membranes and developing a model for transport of various gases of interest through such membranes. As membranes having smaller pore size were produced and tested the need to improve the resolution of some of the test systems was recognized and such improvements were implemented. This report summarizes project activities during FY 1989 related to the three main areas of endeavor: development of a transport model for gas separation, development of small pore size ceramic membranes, and improvement of tests used to characterize the membranes. 2 refs., 2 figs., 2 tabs.
Article
A mathematical model of multicomponent permeation systems with high-flux, asymmetric hollow-fiber membranes is presented. The model takes into account the permeate pressure variation inside the fiber. In the special case of negligible permeate pressure drop, the model yields a simple analytical solution for membrane area calculation that eliminates the numerical integration step required in existing methods. Laboratory multicomponent permeation experiments have verified the mathematical model and have demonstrated the technical feasibility of using the high-flux asymmetric cellulose acetate hollow fiber for H2, CO2, and H2S separation. It is shown that the selectivity of the cellulose acetate membrane is ideally suited to the recovery of hydrogen from the purge gas of reactor recycle loops. For the separation of high-concentration CO2 or H2S, the test data show that the permeabilities of the individual components in mixed gas permeation are significantly different from those of pure gases.
Article
Results of single-gas permeation experiments with seven gases at 323-473 K are presented, and the mechanism of permeation through the modified porous glass is estimated. On the basis of the results mentioned above, the permeation mechanism can be estimated. It can be reasonably concluded that the mechanism for the original glass consisted of Knudsen flow and surface flow; it was also pointed out by previous researchers. Pore control or enclosure, however, can be expected after modification. As the pore becomes smaller, the permeation mechanism would change from Knudsen regime to micropore diffusion (molecular sieve) regime. Moreover if the pore is enclosed, a gas molecule dissolves in and diffuses through the membrane.
Article
Permeability, diffusivity and solubility of gases in polymer/inorganic composite membranes are reported. Membranes were prepared by covering a porous Vycor glass tube with polysilastyrene solution followed by pyrolysis at 382 and 470°C. The experimental data indicate that the gas separation properties of such a membrane are a combination of the transport characteristics of the polymer and the molecular-sieve material. Selectivity factor for H2/SF6 increases to 328 for the membrane pyrolyzed at 470°C whereas for the unpyrolyzed polymer it is merely 10.
Article
Adsorption of CO2, H2O, C2H4, CH4, N2, C2H5OH, and CH2Cl2 in microporous silica hollow fiber membranes was studied at temperatures of 30°C and 70°C and at pressures up to 1.3 MPa. The experimental date were fitted with Langmuir, Dubinin-Radushkevic, and Freundlich isotherms. The best fitting model was found to be the Dubinin-Radushkevich isotherm. Based on the fitting results the total under investigation. No capillary condensation of the water and ethanol vapors was observed in the microporous fibers. The limits for the pore diameter, d, of the membrane deduced from the study were 5 < d < 20 Å.
Article
Non-supported microporous silica (amorphous) and titania thin films were made by the polymeric gel route. The titania system consisted of particles smaller than 5 nm. Reproducible modification of supported γ-alumina films with silica demands a strict control of every modification step. Silica films of 30–60 nm thickness on top of and presumably partly inside the γ-alumina film were realised. The permeabilities of helium and hydrogen through this film are activated, while the propylene permeability was below the detection limit. Separation factors of a H2C3H6 mixture are larger than 200 at 200 °C with a flux of the preferentially hydrogen of 1.6 × 10−6 mol/m2-sec-Pa. The pores must be of molecular dimensions to realise this (< 1 nm diameter). Preliminary research shows that changes in the synthesis parameters result in higher activation energies and improved separation properties. The relation between synthesis, resulting microstructure and gas separation properties, however, is not yet fully understood.
Article
Films of amorphous SiO2 were deposited within the walls of porous Vycor tubes by SiH4 oxidation in an opposing-reactants geometry: SiH4 was passed inside the tube while O2 was passed outside the tube. The two reactants diffused opposite to each other and reacted within a narrow front inside the tube wall to form a thin SiO2 film. Once the pores were plugged the reactants could not reach each other and the reaction stopped. At 450°C and 0.1 and 0.33 atm of SiH4 and O2, the reaction was complete within 15 min. The thickness of the SiO2 film was estimated to be about 0.1 μ. Measurements of H2 and N2 permeation rates showed that the SiO2 film was highly selective to H2 permeation. The H2: N2 flux at 450°C varied between 2000 and 3000. Thermal annealing at 600°C reduced somewhat that selectivity. Thermal annealing in the presence of H2O vapor decreased further the flux of H2 and increased the flux of H2. Permeation of H2 is believed to occur through an activated diffusion mechanism. Applications of such H2-permeable films to membrance reactors for equilibrium-limited reactions are discussed.
K. Kammermeyer, Gas and vapor separations by means of membranes The carbon molecular sieve membranes. General properties and the permeability of CH
  • S.-T Hwang
  • K Kammermeyer
References S.-T. Hwang and K. Kammermeyer, Membranes in Separations, R.E. Krieger Publishing Company, Mal-abar, FL, 1984. K. Kammermeyer, Gas and vapor separations by means of membranes, in: E.S. Perry (Ed.), Progress in Separation and Purification, John Wiley & Sons, New York, NY, 1968. J.E. Koresh and A. Sofer, The carbon molecular sieve membranes. General properties and the permeability of CH,/N2 mixture, Sep. Sci. Technol., 22 (1987) 973-982.
Reactive inorganic membranes, The 1988 Sixth Annual Membrane Technology/Planning Con-ference Proceedings
  • Y H Ma
Y.H. Ma, Reactive inorganic membranes, The 1988 Sixth Annual Membrane Technology/Planning Con-ference Proceedings, F. Meumier and M.D. Levan (Eds. ), Lavosier Technique et Documentation, Paris, 1988,111-l-111-12.
Development of ceramic membranes for gas separation, FY Development Activities, Feb Hollow fiber inorganic 1022. C.Y. Pan, Gas separation by high-flux, asymmetric hollow-fiber membrane
  • D E Fain
D.E. Fain, et al., Development of ceramic membranes for gas separation, FY Development Activities, Feb. 1990, K/QT-352, DE 90,008737, U.S. Dept. of Energy. J.D. Way and D.L. Roberts, Hollow fiber inorganic 1022. C.Y. Pan, Gas separation by high-flux, asymmetric hollow-fiber membrane, AIChE J., 32 (1986) 2020.
The Ronald Press Company The Properties of Gases and Liquids, McGraw-Hill Series in Chemical Engi-neering Adsorption, diffusion and permeation of gases in hollow fiber glass mem-branes
  • A H Shapiro
  • . R C Reid
  • T K Sherwood
A.H. Shapiro, The Dynamics and Thermodynamics of Compressible Fluid Flow, Vol. I, The Ronald Press Company, New York, NY, 1953, p. 189. R.C. Reid and T.K. Sherwood, The Properties of Gases and Liquids, McGraw-Hill Series in Chemical Engi-neering, New York, NY, 1966,646 p. M. Bhandarkar and Y.H. Ma, Adsorption, diffusion and permeation of gases in hollow fiber glass mem-branes, Presented at the NSF-CNRS Workshop on Adsorption Processes for Gas Separation, Published in the Proceedings, pp. 83-88, (Sept. 1991).
Development of ceramic membranes for gas separation
  • D E Fain
  • G E Roettger
D.E. Fain and G.E. Roettger, Development of ceramic membranes for gas separation, Proc. of the Fourth Annual Conference on Fossil Energy Materials R.R. Judkins and D.N. Braski (Eds.), DOE Dot ORNL/ FMP90/l, (1990).
Reactive inorganic membranes
  • Ma
Deposition of H2 permselevtice silica films
  • Gavalas
Molecular sieving inorganic membranes
  • Fleming