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Fabrication and characterization of poly(phenylene oxide)/SBA15/carbon molecule sieve multilayer mixed matrix membrane for gas separation

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Abstract

A novel multilayer mixed matrix membrane (MMM), consisting of poly(phenylene oxide) (PPO), large-pore mesoporous silica molecular sieve zeolite SBA-15, and a carbon molecular sieve (CMS)/Al2O3 substrate, was successfully fabricated using the procedure outlined in this paper. The membranes were cast by spin coating and exposed to different gases for the purpose of determining and comparing the permeability and selectivity of PPO/SBA-15 membranes to H2, CO2, N2, and CH4. PPO/SBA-15/CMS/Al2O3 MMMs with different loading weights of zeolite SBA-15 were also studied. This new class of PPO/SBA-15/CMS/Al2O3 multilayer MMMs showed higher levels of gas permeability compared to PPO/SBA-15 membranes. The permselectivity of H2/N2 and H2/CH4 combinations increased remarkably, with values at 38.9 and 50.9, respectively, at 10 wt% zeolite loading. Field emission scanning electron microscopy results showed that the interface between the polymer and the zeolite in MMMs was better at a 10 wt% loading than other loading levels. The increments of the glass transition temperature of MMMs with zeolite confirm that zeolite causes polymer chains to become rigid.

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... The performance of the MMMs is based on the combination characteristics of the inorganic and organic materials, such as (1) the aggregation of fillers in matrix [22,23] and (2) The adhesion between filler and polymer matrix [24e27]. The gas permeability was limited at low filler loadings; however, the fillers aggregation early occurred when the filler loadings were increased [22]. ...
... The performance of the MMMs is based on the combination characteristics of the inorganic and organic materials, such as (1) the aggregation of fillers in matrix [22,23] and (2) The adhesion between filler and polymer matrix [24e27]. The gas permeability was limited at low filler loadings; however, the fillers aggregation early occurred when the filler loadings were increased [22]. The fillers aggregation causes defects between the two phases or inter-filler void, which have a strong influence on gas performance [11,12]. ...
... Incorporation of inorganic mesoporous SBA-15 silica as a filler into MMMs has been evaluated in our previous studies, and it showed higher gas permselectivity than other microporous silica [22,36]. The SBA-15 silica has a large pore volume, high surface area and better thermal stability than the MCM-41 [37,38]. ...
Article
The composite mixed matrix membranes (MMMs) were prepared by incorporating mesopore SBA-15 as a filler to discuss the effects of its particle shape, particle size, and loadings on the organic–inorganic interfacial morphology. The SBA-15 was synthesized by template method and it's particle shape and size was adjusted by adding electrolyte. The results indicated that the spherical SBA-15 can improve the dispersion and have better adhesion with organic phase, which showed better permselectivity than the rod-like one. The SBA-15 filler also could increase the diffusion selectivity of MMMs by the addition of different particle sizes. The permeabilities of H2 and CO2 were 1207.9 and 552.86 Barrer, respectively, with selectivities of H2/CH4 and CO2/CH4 reached 247.0 and 112.8, respectively, when 1.6 μm spherical SBA-15 was added at 3 wt. %. The dissimilarity occurring in the perm-selectivity values with changes made in the particle shape and size are much more pronounced at the lower SBA-15 loading, which exceeded the 2008 Robeson's upper bound limited.
... For solid/polymer MMMs, the solid fillers embedded in the polymer matrix consist of conventional fillers (zeolites, carbon molecular sieves (CMSs), silicas, metal oxides) and alternative fillers (carbon nanotubes (CNTs), metal organic frameworks (MOFs), graphenes, spherical materials, layered and delaminated materials). In recent years, a large number of studies have focused on incorporation of silica [54], CMSs [55][56][57], zeolites [58,59] and CNTs [60][61][62] into polymers [63][64][65][66][67][68][69][70][71][72][73][74][75][76][77]. Moreover, the critical reviews on zeolite-based MMMs and the use of other conventional fillers were made [40,51,78]. ...
... SBA has numerous excellent properties including narrow pore size distribution, large surface area, large pore volume, high mechanical strength, and long pore diameter; hence, it is an appropriate filler for pore structure modification. Weng et al. [56] prepared multilayer MMMs comprising of poly(phenylene oxide) (PPO) and SBA-15 on an alumina substrate with CMS intermediate layers via the spin coating method. The permeability of H 2 , CO 2 , N 2 , and CH 4 through the PPO/SBA-15/CMS/Al 2 O 3 multilayer MMM was higher than the gas permeability of PPO/SBA-15 MMM. ...
... Recent research has focused on hybrid matrix membranes, and different combinations of matrix materials and filler compositions have been investigated [28,29]. Thus far, MCM-41 has been applied to prepare hybrid matrix membranes based only on conventional polymers, such as polysulfone membranes [30][31][32], polyethylene membranes [33,34] or copolyimide membranes based on 6FDA [35]. ...
Article
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The ability of membranes to separate oil vapour is affected by their permeance and selectivity. This study modifies polyether block amide (PEBA) composite membranes with a microporous zeolite, Silicalite-1, or a mesoporous zeolite, MCM-41. The results show that when PEBA composite membranes are modified with these zeolites, the selective layer of the composite membrane is coated more thinly, resulting in a higher flux of organic gas. Silicalite-1 increases the hydrophobicity of the membrane, which facilitates the adsorption of organic vapour on the membrane surface, thus improving the membrane selectivity. In the separation of oil vapour, both modified membranes can effectively increase the gas permeabilities and selectivities. The main mechanism governing gas transport in the MCM-41-modified membrane is Knudsen diffusion, so the selectivity for small molecules is improved more significantly. By contrast, the dissolution–diffusion mechanism is dominant in the Silicalite-1-modified membranes, which considerably increases the selectivity for large molecules.
... PPO is known as the basis for structural and membrane materials due to its good film-forming ability [28,29]. Modification of PPO membranes by silica, zeolites, fullerenes, titanate nanotubes, carbon nanotubes, and other nanoparticles improved the mechanical strength and permeability of membranes, but the effect of modifiers on selectivity was poor [30][31][32][33]. ...
Article
Membranes and Membrane Technologies, 2019, Vol. 1, No. 2, pp. 99–106. Ethyl tert-butyl ether (ETBE) is one of the most promising oxygenates used as high-octane components of fuels. A method to purify ETBE from an ethanol/ETBE azeotropic mixture formed during industrial synthesis is pervaporation. In this study, hybrid membranes containing nanodiamond particles incorporated into the P84 copolyimide matrix have been synthesized for the pervaporation purification of ETBE. The membrane structure has been studied by scanning electron microscopy and via determining the experimental and theoretical density and free volume. The transport properties of the membranes have been determined in sorption and pervaporation experiments. It has been shown that the introduction of up to 1 wt % of nanodiamonds in the P84 matrix leads to an increase in the main mass transfer parameters, namely, the flux and the separation factor of the azeotropic mixture.
... The PPO/SBA-15/CMS/Al 2 O 3 multilayer membrane composition is formed using a CMS membrane and a PPO/SBA-15 membrane. Details of the CMS and PPO/SBA-15 preparation are described in literature [9]. The membranes were stored in a desiccator until use. ...
Article
Full-text available
Multilayer composite membranes were composed using large-pore mesoporous silica molecular sieve SBA-15, PPO polymer, and CMS/Al2O3 substrate. The SBA-15 was used at different aging temperatures to transform into different crystal sizes. Membranes were characterized by field emission scanning electron microscopy (FESEM) to observe the morphology and cross-sectional images. FESEM images of these composite membranes indicate the existence of voids between the PPO/SBA-15 layer and CMS/Al2O3 if 110°C SBA-15 is added. The permeability and selectivity of PPO/SBA-15/CMS/Al2O3 membranes with different aging temperatures of SBA-15 were also investigated. The selectivity for O2/N2 separation increased remarkably from 6.2 to 8.8, which corresponded to the increase in aging temperature of SBA-15 for the PPO/SBA-15/CMS/Al2O3 composite membrane from 90 to 110°C, respectively. This phenomenon confirms that blockage and reduced mobility of polymer chains as a result of mixing the aging temperature of SBA-15 at 110°C with a PPO matrix may significantly improve the gas separation performance of composite membranes.
... 1−3 Nonetheless, most of the conventional polymer membranes are restricted to the limit of trade-off between permeability and selectivity, 4,5 for instance, high selectivity is always achieved at the cost of low permeability. One effective treatment is to introduce inorganic fillers such as zeolites, 6,7 carbon nanotubes, 8,9 carbon molecular sieves, 10,11 and mesoporous silica 12 into a polymer matrix to obtain mixed matrix membranes (MMMs). The selection of inorganic fillers is commensurate with the importance of the polymer matrix, which depends not only on the separation performance of inorganic particles but also on the compatibility with the polymer matrix. ...
Article
Full-text available
MOFs-based mixed matrix membranes (MMMs) have attracted extensive attention in recent years due to their potential high separation performance, the low cost and good mechanical properties. However, it is still very challenging to achieve defect-free interface between micron-sized MOFs and polymer matrix. In this study, [Cd2L(H2O)]2•5H2O (Cd-6F) synthesized using 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) as organic ligand was introduced into the 6FDA-ODA polyimide matrix to achieve novel MOF MMMs. A specific interfacial interaction between MOF crystals and polymer chains was innovatively targeted and achieved through in-situ polymerization procedure. The enhanced adhesion between MOF particles and polymer phase was observed, and the improved interfacial interaction between Cd-6F and 6FDA-ODA polyimide matrix was confirmed by detailed characterisations including FTIR and NMR. In the meantime, the gas permeance and selectivity of the MMMs are strongly dependent on their morphology. The MMM derived from in-situ polymerization presents excellent interfaces between micron-sized MOF crystals and polymer matrix, resulting in increased permeability and selectivity. The strategy shown here can be further utilized to select MOF/polymer pair, eliminate interfacial voids and improve membrane separation performance of MOFs-based MMMs.
... In recent years, new types of inorganic fillers structure with improved properties have been tailored in order to produce ideal MMM with desired separation performance. Spherical-shape particles such as Santa Barbara amorphous (SBAs), mesoporous silica spheres (MSSs) and hollow zeolite spheres (HZSs) were investigated for the improvement of filler's distribution and minimizing the agglomeration of particles in the polymer phase, especially when incorporating micron-sized particles in polymer matrix (123)(124)(125). The SEM images of spherical-shape particles reported in the literature are shown in Figure 3. ...
Article
In the early stage of membrane technology development in gas separation, utilization of polymeric membranes has gained attention due to their robustness and ease of fabrication. However, the performance of polymeric membranes is limited by the trade-off between permeability and selectivity. Meanwhile, inorganic membrane is capable to exhibit great enhancement in separation performance but unfortunately its fabrication process is hard and costly. Thus, development of mixed matrix membranes (MMMs) by incorporating inorganic fillers into the polymer matrix has become a potential alternative to overcome the limitations of polymeric and inorganic membranes in gas separation. Nevertheless, fabrication of defect-free MMMs with improved separation performance and without compromising the mechanical and thermal stability is extremely difficult and challenging. In the current review paper, various types of inorganic fillers for MMMs fabrication and recent reported efforts to tailor the underlying problems on MMMs fabrication were discussed. The future outlook to advance the performance of MMMs in gas separation especially for CO2/CH4 separation was highlighted.
... Mesoporous silica incorporated in polymer blends has been considered in several studies as well, for example the use of mesoporous silica SBA-15 in membrane synthesis [20,21], and the use of MCM-41 [22]. In addition, functionalized silica is also widely employed in membrane synthesis [23][24][25]. ...
Article
A novel method to incorporate silica on a polyethersulfone (PES) membrane surface was successfully developed. An in situ hydrolysis/condensation of tetraethylorthosilicate (TEOS) precursor was carried out, followed by coating as thin film composite (TFC) via interfacial polymerization. PES membranes casted from 20 and 23 wt.% PES in N-methyl-pyrrolidone (NMP) solutions were prepared by phase inversion. The membrane surfaces were modified by TEOS silica precursors, dispersed in ethanol at different concentrations (0.1, 0.3 and 0.5 w/v%) and catalyzed by a NH3/H2O mixture. Immobilization of the prepared silica on the membrane surface was obtained by adding a polyamide coating. The modified membranes were characterized by FTIR, SEM, AFM, and TGA, which confirmed the successful embedding of silica particles by the in situ sol gel process. In the best conditions, rejection of MgSO4 and Na2SO4 reached 85 and 94.2% respectively. This was consolidated by a proportionally high water flux of 62.2 and 64.15 L m⁻² h⁻¹ for MgSO4 and Na2SO4 salt solutions, respectively, at an operational pressure of 5 bar.
... Some of the unconventional fillers used in the development MMMs are metal organic framework, zeolite imidazolate framework, mesoporous silica, hollow zeolite spheres, layered silicate and more [15][16][17][18]. Amongst them, POSS possesses the most unique feature. ...
Article
The main obstacle encountered during the development of polyhedral oligomeric silsesquioxane (POSS) mixed matrix membrane (MMM) via physical blending is the combination of compatible inorganic filler and polymeric matrix. In this work, mono-functional POSS of different amine functionalised substituent chain lengths namely aminopropylisobutyl POSS (AMPOSS-a) and aminoethylaminopropylisobutyl POSS (AMPOSS-b) were incorporated into Polysulfone (PSf) membrane at 1wt%, 2wt% and 3wt% loadings. The effect of amine substituent chain lengths on its compatibility and dispersion properties as well as the glass transition temperature of the MMMs were studied using scanning electron microscope (SEM), energy dispersive X-ray (EDX) and differential scanning calorimeter (DSC). Particle agglomerations were observed to increase with the loadings of both fillers although more prominent in AMPOSS-b/PSf membranes. This was attributed to the interparticle forces such as van der Waals and electrostatic forces. Distribution of both fillers were concentrated at the upper region of the membranes at 1wt% and 2wt% as a consequence of their density difference. The glass transition temperature (Tg) for pristine PSf at 197ºC showed an overall decrement between 40.3ºC to 47.1ºC when AMPOSS-a and AMPOSS-b were incorporated. The decrement was due to AMPOSS particle loadings, surface chemistry and particle-polymer chain topology. Hence, mono-substituted POSS with varying amine substituent chain lengths did not improve the glass transition temperature nor contribute to homogeneous MMM morphology. This had been identified to be the consequence of POSS surface energy, which might be caused by the association of hydrocarbon chains saturated on the particle surface due to the presence of isobutyl group.
... However, from 0.9 to 1, each stabilization temperature exhibited a different value where all of them made an abrupt increase in the high pressure region. This type of isotherm illustrated the existence of the multi-layered formation [35]. It was also revealed that there was no flattish portion in the curve which indicated that monolayer formation was missing from the carbon membrane sample (Mangindaan et al., 2014). ...
Article
Membranes offer remarkable attributes such as possessing small equipment footprints, having high efficiency and are environmentally friendly, with carbon membranes progressively investigated for gas separation applications. In this study, carbon tubular membranes for CO2 separation are prepared via dip-coating method with P84 co-polyimide as carbon precursor. The prepared membranes were characterized using Thermogravimetric Analysis (TGA), pore structure analysis Brunauer-Emmett-Teller (BET), Fourier Transform Infrared Spectroscopy (FTIR) and pure gas permeation system. The permeation properties of the carbon membranes are measured and analyzed using CO2, CH4 and N2 gases. The P84-based carbon tubular membrane stabilized at 300°C and featured excellent permeation properties with permeance range of 2.97±2.18, 3.12±4.32 and 206.09±3.24 GPU for CH4, N2 and CO2 gases, respectively. This membrane exhibited the highest CO2/CH4 and CO2/N2 selectivity of 69.48±1.83 and 65.97±2.87, respectively.
... Membran düzeneğinin üst kısmından besleme yapılarak basınç dönüştürücü yardımıyla alta geçen gazın zamana karşılık basınç değişimi ölçüldü ve toplanan veriler dijital olarak kaydedildi. Geçirgenlik değerleri aşağıdaki eşitlik [15] Saf polimimit ve karışık matriksli membran karşılaştırıldığında, 100 kPa basıncında NiCoMOF-5/PI membranın H 2 geçirgenliği PI membrana göre %41,7, 200 kPa basıncında, %61,47, 300 kPa basıncında %70,52, 400 kPa basıncında %77,36, 500 kPa basıncında %98,60 artmıştır. H 2 geçirgenlik değerinin karışık matriksli membranda yüksek olmasının nedeni, metal ilave edilmiş MOF-5'in gözenekli yapısı sayesinde gaz taşınımını kolaylaştırmasıdır. ...
... Single gas permeabilities of the prepared membranes were determined for H2 gas. The gas permeability (P) was calculated by the slope of curve of permeate pressure vs. time (dp/dt) using the Daynes-Barrier time lag equation as follows (Weng et al., 2010): ...
... PPO is known as the basis for structural and membrane materials due to its good film-forming ability [28,29]. Modification of PPO membranes by silica, zeolites, fullerenes, titanate nanotubes, carbon nanotubes, and other nanoparticles improved the mechanical strength and permeability of membranes, but the effect of modifiers on selectivity was poor [30][31][32][33]. ...
Article
Poly(phenylene oxide) was incorporated by small amounts (1, 3, and 5 wt%) of hybrid macromolecular stars with fullerene С 60 core and polymer arms of different nature (six nonpolar arms polystyrene and six polar arms of diblock copolymer poly(2-vinyl pyridine)-b-poly(tert-butylmethacrylate). The properties of composite materials were studied in solutions (dynamic light scattering, сapillary viscometry) and in the solid phase (TGA, X-ray diffraction analysis, and dielectric spectroscopy). To characterize physical properties, density and contact angles were determined. Transport properties were studied by measuring the permeability of H 2 , O 2 , N 2, and CH 4 through films containing 0, 1, 3 and 5 wt% hybrid macromolecular stars. An increase of the modifier content in the composite leads to a certain decrease in the permeability coefficients for all gases, but the ideal selectivity in the separation of the O 2 /N 2 and H 2 /CH 4 gas pairs increases.
... The analyses were performed under nitrogen gas with a ramp of 10 • C min −1 at temperatures ranging from 100 to 700 • C. The flow rate of N 2 was controlled at 50 mL min −1 . The membrane surface morphology was characterized using atomic force microscopy (AFM) (Dualscope/Rasterscope C26, DME, Denmark) in noncontact mode [25]. The pore size distribution of original and modified CMS membrane (with Al 2 O 3 support) was carried out using a N 2 adsorption analyzer (BET-201AEL) under the liquid N 2 temperature −77 • C. Finally, the surface morphologies of the prepared CMS membranes were investigated using a field-emission scanning electron microscope (FE-SEM) (JSM 5600 device). ...
... Therefore, it is very important to combine two compatible phases. Various fillers including zeolites (Shen and Lua, 2012;Rostamizadeh et al., 2013;Barquin et al., 2016), silica (Merkel et al., 2002;Jomekian et al., 2011;Zanoletti et al., 2018), carbon molecular sieves (Anson et al., 2004;Rafizah and Ismail, 2008;Weng et al., 2010), carbon nanotubes (Majeed et al., 2012;Khan et al., 2013;Nour et al., 2013;Ahnmad et al., 2014), and metal organic frameworks (Basu et al., 2011;Shahid and Nijmeijer, 2017) were used for the fabrication of mixed matrix membranes by their embedding into different polymers, such as cellulose acetate, polysulfone, polyimide, polyamide, polyphenylene oxide, polycarbonate, and polydimethylsiloxane. Not all of these materials proved to be a good option. ...
Article
Full-text available
The development of membrane technology for gas separation processes evolved with the fabrication of so-called mixed matrix membranes (MMMs) as an alternative to neat polymers, in order to improve the overall membrane effectiveness. Once the mixed matrix membranes are used, the gas separation properties of the porous materials used as fillers are combined with the economical processability and desirable mechanical properties of polymer matrix. Mixed mesoporous silica/polymer membranes with high CO2 and O2 permeability and selectivity were designed and prepared by incorporating MCM-41 particles into a polymer matrix. Ordered mesoporous silica MCM-41 with high surface confirmed by BET analysis were obtained and functionalized with amino groups. In order to obtain the mixed membranes, the mesoporous silica was embedded into the polysulfone matrix (PSF). Flat mixed matrix membranes with 5, 10, and 20 wt% MCM-41 and MCM-41-NH2 loadings have been prepared via the polymer solution casting method. The phase's interactions were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry (TGA), while the gas separation performances were evaluated using pure gases (CO2, O2, N2). The MCM-41/PSF and MCM-41-NH2/PSF membranes exhibited increased permeabilities for O2 (between 1.2 and 1.7 Barrer) and CO2 (between 4.2 and 8.1 Barrer) compared to the neat membrane (0.8 Barrer). The loss of selectivity for the O2/N2 (between 6 and 8%) and CO2/N2 (between 25 and 41%) gas pairs was not significant compared with the pure membrane (8 and 39%, respectively). The MCM-41/PSF membranes were more selective for CO2/N2 than the O2/N2 pair, due to the size difference between CO2 and N2 molecules and to the condensability of CO2, leading to an increase of solubility. Stronger interactions have been noticed for MCM-41-NH2/PSF membranes due to the amino groups, with the selectivity increasing for both gas pairs compared with the MCM-41/PSF membranes.
... 15.2 and 15.3) as a metric to monitor the technical performances of separation using membranes [6,7]. To overcome the negative effect of the permeability-selectivity trade-off, one accepted approach is to introduce inorganic fillers such as mesoporous silica [8], carbon nanotubes [9], zeolites [10], carbon molecular sieves [11], and metal-organic frameworks (MOFs) [12] into the polymeric matrix to fabricate mixed matrix membranes (MMMs) (Fig. 15.2). ...
... In the last decades the mixed matrix membranes (MMMs) attracted special attention, being studied with different matrix materials and fillers in various compositions [1][2][3][4]. MMMs combine the properties of easy processability of the polymers with the superior selectivity of the inorganic materials [5]. Obtaining MMMs can surpass the difficult and expensive fabrication of inorganic membranes, by using polymers as the continuous matrix and inorganic particles as filler. ...
Article
Full-text available
In order to obtained high selective membrane for industrial applications (such as natural gas purification), mixed matrix membranes (MMMs) were developed based on polysulfone as matrix and MCM-41-type silica material (obtained from coal fly ash) as filler. As a consequence, various quantities of filler were used to determine the membranes efficiency on CO2/CH4 separation. The coal fly ash derived silica nanomaterial and the membranes were characterized in terms of thermal stability, homogeneity, and pore size distribution. There were observed similar properties of the obtained nanomaterial with a typical MCM-41 (obtained from commercial silicates), such as high surface area and pore size distribution. The permeability tests highlighted that the synthesized membranes can be applicable for CO2 removal from CH4, due to unnoticeable differences between real and ideal selectivity. Additionally, the membranes showed high resistance to CO2 plasticization, due to permeability decrease even at high feed pressure, up to 16 bar.
... New structures of inorganic fillers have been designed to fabricate looked-for MMMs with improved gas transport properties. Of these, hollow zeolite spheres (HZSs) were designed for minimized agglomeration and enhanced distribution of filler particles in the polymer network, especially when using microparticles [210][211][212]. This behavior can be attributed to the spherical shape of the filler particles, which enhances the polymer/filler contact, and microparticles can be used to minimize agglomerate formation [154]. ...
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Anthropogenic emissions have developed the environmental demands for proficient carbon dioxide (CO2) separation technologies. Adsorption and membrane technologies are widely used to separate CO2 from other light gases due to their multiple technological benefits, including but not limited to factors such as energy efficiency and low environmental footprint. In this context, zeolites are often used due to their intrinsic molecular sieving capacity. This review initially addresses recent technological advances to enhance the gas separation performance of zeolite materials. Current trends directed toward improving CO2 adsorption capacity of zeolites include amine, silica, and ion-exchange modifications. Other promising efforts to improve the adsorption performance of zeolites involve processing zeolite nanoparticles, nanofibers, and zeolite-based foams. The second part of the review deals with pristine and modified zeolites beneficial properties for designing polymer-based mixed matrix membranes (MMMs), which enable to adapt a desirable gas separation performance. The gas transport mechanisms and morphological properties of MMMs are essential. This review addresses the most current strategies used to improve interfacial adhesions between zeolite particulates and polymer matrices to overcome the trade-off between gas selectivity and permeability faced by pure polymeric membranes. Filler shape and size play vital roles in determining the filler and polymer matrix's interfacial adhesions. New structures of inorganic fillers have been designed to fabricate MMMs with excellent gas transport properties. Hollow zeolite spheres (HZSs) are particularly interesting as they effectively minimize agglomeration and improve filler dispersion in the polymer matrix. Furthermore, approaches that employ nanoporous layered fillers, including AMH-3 and Jilin-Davy-Faraday, layered solid No. 1 (JDF-L1), have been reviewed to overcome the limitation of incorporating high contents of zeolites, which are required to improve the gas transport properties of MMMs. Furthermore, this review explores implementing zeolitic imidazolate frameworks (ZIFs) in MMMs because of their tunable pore structure and remarkably high adsorption capacity and surface area as well as excellent chemical and thermal properties. Lastly, we address the prospects and future developments in gas separation applications.
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Ternary component mixed matrix membrane was prepared from PES, SAPO-34 and 2-hydroxy 5-methyl aniline on a macroporous alumina disk by the solvent evaporation method in order to investigate the effect of existence of an inorganic support. The membrane and its pure PES/Alumina counterpart were characterized by single gas permeability measurements of H2, CH4, C2H6 and C3H8. The corresponding H2/CH4 selectivities of membranes were 71.3 and 41. The membranes were also used to separate equimolar mixtures of H2 with CH4, C2H6 and C3H8 over a temperature range of 35–90 °C. The separation selectivities of ternary component membrane were 73.4 for H2/CH4, 242.9 for H2/C2H6 and >1000 for H2/C3H8 at 35 °C, which are comparable to the separation selectivities of pure PES on alumina. The permeances of all gases through PES/SAPO-34/HMA/Alumina membrane were, however, higher than those through PES/Alumina membrane at 90 °C. Despite its very complex morphology, the PES/SAPO-34/HMA/Alumina membrane preserved its structure and quality during the separation of different gas mixtures over temperature cycles between 35 and 90 °C. The CO2 and CH4 adsorption isotherms of PES-SAPO-34-HMA system were also obtained at 25 °C. The adsorption capacity of ternary component system was 1.55 mmol CO2/g and 0.45 mmol CH4/g, which is appreciably higher than the adsorption capacity of pure PES.
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Novel modified mesoporous silica nanoparticles (mMSN)/polyamide (PA) thin film nanocomposite (TFN) membranes were prepared via interfacial polymerization of trimesoyl chloride (TMC) and piperazine (PIP). Mesoporous silica nanoparticles were functionalized with amino groups and introduced into PIP aqueous phase. Therefore, reaction between mMSN and TMC would occur during interfacial polymerization, giving rise to a covalent bonding between silica nanoparticles and active layer of TFN membrane. By adding an appropriate concentration of mMSN into aqueous phase (0.03 wt%), the pure water flux of the mMSN/PA TFN membrane reaches to a maximum of 32.4 L/m2 h which is almost 1.5 times as high as that of TFC membrane, while the rejection to Na2SO4 of TFN membrane keeps at a relative high level (>80%). Two unique properties of mMSN were favorable for the membrane performance: mesoporous structure for water transport and functional groups for better interaction with polymer matrix. The obtained membrane exhibited a promoted anti-fouling ability as well as a good long-term stability. The effect of the mesopore structures of silica nanoparticles on the membrane performance was also investigated. Modified mesoporous silica nanopraticles with proper pore size was more suitable for the optimization of PA TFN membrane.
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The technology of the membrane has garnered significant interest and attention in the separation processes of modern industries. This is because of efficient high energy, environmental compatibility, continuous operation process, and minimal investment capital. The polymeric membrane-based gas separation has widely been applied industrially in areas such as carbon capture, recovery of hydrogen gas, sweetening of natural gas, and the enrichment of oxygen. Among the various kinds of membranes studied, the mixed matrix membranes (MMMs) integrating the advantages of the polymer matrix and organic/inorganic fillers, have been broadly studied. Over time, research efforts have been invested to improve the performance of gas separation of the mixed matrix membranes (MMMs) alongside their general properties such as thermal stability and mechanical strength. This perspective explains the potential of using mixed matrix membranes (MMMs) in different industrial areas, especially in gas separation. Therefore, in this paper, we reviewed critically the choice of advanced materials for the fabrication of mixed matrix membranes (MMMs), the trendy novelties in MMMs, and their application in the separation of gases with more emphasis on H2/CO2. Lastly, we examined the future outlook of this area of research as technologies unfold.
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Polymeric membrane technology has received extensive attention in the field of gas separation, recently. However, the tradeoff between permeability and selectivity is one of the biggest problems faced by pure polymer membranes, which greatly limits their further application in the chemical and petrochemical industries. To enhance gas separation performances, recent works have focused on improving polymeric membranes selectivity and permeability by fabricating mixed matrix membranes (MMMs). Inorganic zeolite materials distributed in the organic polymer matrix enhance the separation performance of the membranes well beyond the intrinsic properties of the polymer matrix. This concept combines the advantages of both components: high selectivity of zeolite molecular sieve, and mechanical integrity as well as economical processability of the polymeric materials. In this paper gas permeation mechanism through polymeric and zeolitic membranes, material selection for MMMs and their interaction with each other were reviewed. Also, interfacial morphology between zeolite and polymer in MMMs and modification methods of this interfacial region were discussed. In addition, the effect of different parameters such as zeolite loading, zeolite pore size, zeolite particle size, etc. on gas permeation tests through MMMs was critically reviewed.
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The knowledge of how to control the pore size and morphology of separated mesoporous silica particles is crucial for optimizing their performance in applications, such as molecular sieves and drug delivery systems. In this work, we have systematically studied the effects of various synthesis parameters to gain a deeper understanding of how particle morphologies can be altered. It was found that the morphology for isolated particles of SBA-15 type, with unusually short and wide pores, could be altered from rods to platelets by variations in the NH4F concentration. The pore length is nearly constant (~300 nm) for the different morphologies, but the particle width is increasing from 200 nm to >3 µm when decreasing the amount of NH4F, and the pore size can be tuned between 10 and 13 nm. Furthermore, other synthesis parameters such as heptane concentration, pH, silica precursor, and additions of ions have also been studied. The trend regarding particle width is independent of heptane concentration, at the same time as heptane increases the particle length up to a plateau value of ~500 nm. In all, parameters controlling particle width, length and pore size have been separated in order to evaluate their function in the particle formation. Additionally, it was found that the formation time of the particles is strongly affected by the fluoride ion concentration, and a mechanism for particle formation for this system, where micelles transforms from a foam, to multilamellar vesicles, and finally to cylindrical micelles, is suggested.
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A thin amine-functionalized MIL-53 membrane with high permeability of hydrogen was successfully prepared on a porous alpha-Al2O3 support by using the secondary growth method. Seeded alpha-Al2O3 supports were prepared by a dip-coating technique. In contrast, a discontinuous membrane was obtained by using unseeded support under the same synthesis conditions, implying that the seeds play the key role in the formation of compact membranes. The resulting compact membranes were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeation testing. Results showed that the thickness of the as-prepared membrane was around 2 similar to 4 mu m. Hydrogen permeance of the as-prepared membrane reached a remarkable value of 1.5 x 10(-5) mol m(-2) s(-1).Pa-1 at room temperature under a 0.1 MPa pressure drop. The ideal H-2/CO2 selectivity was found to be 4.4. In addition, the influence of seeding solution on the membrane performance was investigated. We found that the membrane permeance decreased and the ideal selectivity increased when the seeding solution content was increased. Copyright
Article
An ordered mesoporous material, such as SBA-15 was considered as a promising reinforcement agent for polymeric materials due to its large surface area and uniform pore structure. In this paper, poly(methyl methacrylate) (PMMA)/SBA-15 composites were prepared by in situ free-radical solution polymerization of MMA in the presence of SBA-15. The effects of SBA-15 content on solution polymerization and the properties of the final polymer composite were investigated. The PMMA molecular weight and its distribution in PMMA/SBA-15 composites were determined by gel permeation chromatography. Fourier-transform infrared spectra, X-ray diffraction, thermal gravimetric analysis (TGA), differential scanning calorimeter and dynamic mechanical analysis were used to characterize the structure and properties of the composites. The morphology of the composites was observed by scanning electric microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the monomer conversion dropped off, but the polymer average molecular weight increased upon the introduction of SBA-15 into solution polymerization process. When compared with pure PMMA, the storage modulus of the composites was improved and the highest improvement was acquired at 1 wt% of SBA-15, based on the monomer feed content. The glass transition temperatures of the composites were increased slightly. TGA results confirmed that the thermal stability of the composite was not influenced much and a higher degree of terminal vinyl groups was formed in the product of polymerization. SEM and TEM images indicated that SBA-15 particles were incorporated into the polymer matrix.
Article
Different types of fillers of inorganic (titanosilicate ETS-10 and mesoporous silica type MCM-41) and organic-inorganic nature (ZIF-8 and NH2-MIL-53), with different pore size (micro- and mesoporosity) and structure, diverse particle shape, and particle sizes in the 85–400 nm range were embedded in a polysulfone matrix via spin coating. Spin coating technology, widely used in the production of thin and uniform layers on porous substrates was used here to fabricate in one coating step symmetric mixed matrix membranes (MMMs) by adjusting the spinning disk velocity, rotational time, and solid concentration and volume of solution. By selecting the optimal parameters, homogeneous MMMs containing 8 wt% of the various fillers were obtained and tested for H2/CH4 and O2/N2 mixed-gas separations, achieving significant improvements over the neat polymer. While NH2-MIL-53 MMMs revealed the highest separation performance (a rise in selectivity higher than 60 % compared to the pure polymer for H2/CH4 and O2/N2 separations), ZIF-8 MMMs showed a substantial increase in permeability (from 12.7 to 51.4 Barrer for H2, and from 2.0 to 6.1 Barrer for O2). Besides, the spin coating process enhanced solvent evaporation and reduced coat production time compared to the traditional by-hand casting.
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New nanostructured hybrid membranes for gas separation have been prepared and characterized for the first time in the literature by using a block copolymer, poly(styrene-b-butadiene-b-styrene) (SBS), and aminated SBA-15. Short mesopore channels, platelet SBA-15 particles with a high surface density of 3-aminopropyl grafts (3.8 nm�2) and modest surface area reduction (45%) were prepared, characterized and used as a filler. The gas transport characterization of the hybrid membranes indicates that with a 10 wt% content of aminated filler, outstanding performances in terms of selectivity and permeability for the CH4/N2 and the CO2/N2 gas pairs can be obtained. In particular, the CH4/N2 ideal selectivity of 7.3 is higher than the values of the existing block co-polymers used for this separation and of mixed matrix membranes described to date in the literature. Membranes with such a high separation factor may enable the exploitation of natural gas with high N2 content and increase the amount of methane that can be economically recovered. The combination of the CO2/N2 ideal selectivity of 53 with a CO2 permeability of 173 Barrer demonstrates that the new hybrid membranes prepared in this study deserve further attention as a practical commercial solution also for the post-combustion capture of carbon dioxide. Finally, the small and flat particles dispersed in the polymer lend themselves to the fabrication of thin industrial membranes with enhanced productivity.
Chapter
Membrane-based separation is a subject of great interest, owing to features such as environmental friendliness, energy conservation, and ease of operation. Among various membranes, carbon membranes came to prominence as a result of their bimodal pore size distribution and good thermal and chemical stability. These appealing properties enable carbon membranes to display outstanding size exclusion performance at harsh environment, unlike polymeric membranes. In this chapter, the issues affecting the microstructure in terms of the synthesis step are intensively reported, and the desirable microstructure could be obtained by single or integrated pore-tuning technique for the intended application. The commonly used characterization methods are also introduced to specify insight into the microstructure. Further, the shift in pore size of carbon membrane determines the dominating gas transport mechanism through carbon membrane and exhibits different separation performance. The separation capabilities of carbon membrane toward target gas pairs are also assessed. For future perspectives, the emerging application of carbon membrane should be explored to accelerate the commercially feasible processes.
Article
Polymeric materials with polyethylene glycol (PEG) which contains ether oxygen groups are utilized as CO2 separation membranes due to the high selectivity, while suffered from low gas permeability owing to small free volume. The 2-D MOFs nanosheets showed excellent gas molecules permeance because of the unique pore structure and ultra-high specific surface with nanoscale thickness. In this work, the PES-g-PEG copolymer were prepared by thiol-ene click chemistry, the 2-D MOFs nanosheets were then introduced to fabricate MMMs. Benefitting from the effective transfer of MOFs nanosheets for CO2, the obtained MMMs exhibited greatly enhanced CO2 permeability (4 times higher than original PES-g-PEG membrane) and separation performance (71.7% increase of selectivity for CO2/N2 and 72.6% increase of selectivity for CO2/CH4). In addition, the introduction of 2-D MOFs nanosheets also improved the anti-plasticization capability and operation stability of the original PES-G-PEG membranes, the MMMs exhibited excellent stability for CO2 separation.
Article
A novel hybrid ultrafiltration membrane was prepared by incorporating hollow mesoporous silica spheres (HMSS) into a polymer matrix of brominated polyphenylene oxide (BPPO) using triethanolamine as the amination agent. The hybrid membrane exhibits improved water permeability, thermal stability, and water content, while the rejection to egg albumin maintaining at a high level (>90%). Especially when the addition of HMSS is 1.0 wt %, the water flux of the hybrid membrane reaches a maximum that is almost two times that of the BPPO membrane. The unique properties of HMSS and good interaction between HMSS and polymer contribute to the improvement of membrane performance. The effect of the structures of silica particles on the membrane performance was also investigated, and the results suggest that HMSS with moderate wall thickness is more suitable for the optimization of hybrid membrane properties.
Article
The demand for cost-efficient separations requires membranes with high gas flux and high selectivity which opens the path for further improvements. Mixed matrix membranes (MMMs) made from 33.3 wt % ZIF-8 in 6FDA-durene were tested at 35 °C and 3.5 atm. At 33.3 wt % loading of ZIF-8, H2, N2, O2, and CH4 gas permeabilities increased approximately 400%. Cross-linking the surface of this MMM, by reacting with ethylenediamine vapor, yielded a 10-fold increase in H2/CO2, H2/N2, and H2/CH4 selectivities with respect to 6FDA-durene, preserving 55% of the H2 permeability of 6FDA-durene. The permselective properties of the cross-linked skin of the MMM fall above the most recent permeability–selectivity trade-off lines (2008 Robeson upper bounds) for H2/CO2, H2/N2, and H2/CH4 separations. To the best of our knowledge, this is the first example of a cross-linked ZIF/polymer MMM for gas separation.
Article
The development of compact hydrogen separator based on membrane technology is of key importance for hydrogen energy utilization, and the Pd-modified carbon membranes with enhanced hydrogen permeability were investigated in this work. The C/Al2O3 membranes were prepared by coating and carbonization of polyfurfuryl alcohol, then the palladium was introduced through impregnation-precipitation and colloid impregnation methods with a PdCl2/HCl solution and a Pd(OH)(2) colloid as the palladium resources, and the reduction was carried out with a N2H4 solution. The resulting Pd/C/Al2O3 membranes were characterized by means of SEM, EDX, XRD, XPS and TEM, and their permeation performances were tested with H-2, CO2, N-2 and CH4 at 25 degrees C. Compared with the colloid impregnation method, the impregnation-precipitation is more effective in deposition of palladium clusters inside of the carbon layer, and this kind of Pd/C/Al2O3 membranes exhibits excellent hydrogen permeability and permselectivity. Best hydrogen permeance, 1.9 x 10(-7) mol/m(2) s Pa, is observed at Pd/C = 0.1 wt/wt, and the corresponding H-2/N-2, H-2/CO2 and H-2/CH4 permselectivities are 275, 15 and 317, respectively. Copyright
Article
A TiO2 sol was prepared from tetrabutyltitanate using polyethylene glycol as a stabilizer, and this was homogeneously mixed with polyfurfuryl alcohol, dip-coated on a porous Al2O3 substrate and carbonized at 700°C for 4 h to produce TiO2-doped carbon membranes. SEM, TEM, XRD and granulometry were used to characterize the membranes, and their permeation performance for CO2, N2 and CH4 were tested. It was found that polyethylene glycol is effective in controlling the hydroxylation of the tetrabutyltitanate. This not only favored the formation of spherical TiO2 nanoparticles with a small size and narrow size distribution but also improved the homogeneity of the dispersion of the TiO2 nanoparticles in polyfurfuryl alcohol. The doping of the membranes with TiO2 nanoparticles greatly improved the CO2 permeance and permselectivity. The TiO2 doping helps to create diffusion paths, but it may also block the pores in the carbon matrix. Therefore, the CO2 permeance reached a maximum of 7.0×10-8 mol·m-2 · s-1 · Pa-1 with a mass ratio of TiO2 sol to polyfurfuryl alcohol of 2, where the CO2/N2 and the CO2/CH4 selectivities were 34 and 64, respectively.
Article
The development of carbon membranes for the separation of various gases has gained interest among researchers due to their superior performance in gas separation. The preparation of carbon membranes by blending materials has many advantages including time and cost effectiveness for tuning the properties of the membranes. Here we review the recent research progress that has been made in the context of breakthroughs and challenges in the development of carbon membrane materials. In addition, we provide information regarding carbon membrane fabrication in terms of the selection of precursors and additives, carbon membrane process conditions, and coating conditions that influence the performance of gas separation of the resulting carbon membranes. The perspectives and future research directions for carbon membranes are also presented.
Chapter
Ionic liquids have attracted the attention of the scientific community, especially in the last few years, owing to their fascinating structures, nonvolatility, thermal stability, good CO2 affinity, and tunable properties, which makes them a suitable candidate for gas separation. The combination of membranes with ionic liquids offers great potential to improve the current membrane technologies. This chapter critically reviews the development of ionic liquid-based membranes, including supported ionic liquid membranes, poly(ionic liquid) membranes, polymer ionic liquid composite membranes, and ionic liquid composite mixed matrix membranes. The chapter also summarizes the membrane material selection, fabrication methods, gas transport, separation performances, and membrane stability. Further, the future perspectives and research directions of ionic liquid-based membranes for CO2 separation are identified and briefly described.
Chapter
Over the past two decades, membrane technology has attracted tremendous attention at CO2 separation from other gases, which has shown great potential to significantly improve energy efficiency and reduce cost associated with processes. The membrane structures and chemistry properties greatly affect their CO2 separation performances, including selectivity and permeability. In recent years, there has been significant progress in the development of CO2-selective membranes. This chapter reviewed the recent activities relating to the fabrication and separation performances of polymeric, inorganic and mixed-matrix membranes for CO2 separation purposes.
Article
We unveil a unique kinetic driven separation material for selectively removing linear paraffins from iso-paraffins via a molecular sieving mechanism. Subsequent carbonization and thermal treatment of CD-MOF-2, the cyclodextrin metal-organic framework, afforded a carbon molecular sieve with a uniform and reduced pore size of ca. 5.0 Å, and it exhibited highly selective kinetic separation of n-butane and n-pentane from iso-butane and iso-pentane, respectively.
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The increased demand for a reliable and sustainable renewable energy source encourages the hydrogen-based economy. For the same, membrane separation approaches were reviewed as an advantageous process over contemporary techniques due to the environmentally friendly nature, economically viable pathway, and easily adaptable technology. A comprehensive assessment for the advancements in the type of membranes namely, polymeric and mixed matrix membranes (MMMs) has been delineated in the present article with the fabrication methodologies and associated mechanism for hydrogen separation. In hydrogen separation mechanism of the membrane, depends on the morphology of the membrane (dense or porous). The existence of pores in membranes offers various gas transport mechanisms such as Knudsen diffusion, surface diffusion, capillary condensation, molecular sieving mechanisms were observed, depending on the pore size of membranes and in dense membrane gas transport through the solution-diffusion mechanism. In polymer membrane, hydrogen separation occurs mainly due to solubility and diffusivity of gases. The hydrogen separation mechanism in MMMs is very complex due to the combining effect of polymer and inorganic fillers. So, the gas separation performance of MMMs was evaluated using the modified Maxwell model. Moreover, adequate polymeric material and inorganic fillers have been summarised for MMMs synthesis and highlighting the mechanism for gas transport phenomena in the process. Several types of materials implemented with polymeric matrix examined in the literature, amongst these functionally aligned CNTs with Pd-nanoparticles dispersed in polymer matrix were observed to reveal the best outcome for the hydrogen separation membrane due to the uniform distribution of inorganic material in the matrix. Henceforth, the agglomeration gets reduced promoting hydrogen separation.
Article
Harnessing the full potential of polymers to the formation of supported thin films in other materials has been important for application in the membrane fabrication area. However, it faces the effects on the differences in properties between materials, such as chemical affinity and structure type. This paper describes a new approach for obtaining a thin polymeric film on porous supports. For this, the dip-coating/phase inversion technique was adapted. The called wet-dry process consisted of immersing a porous ceramic tube in a polymer solution (dip-coating), followed by immersion in a non-solvent bath (wet phase inversion), and finally, allowing the set to dry in a controlled atmosphere (dry phase inversion). The morphology was investigated by scanning electron microscopy to verify the efficacy of the method. The new technique proved to be effective in the formation of a thin polymer film supported on macroporous ceramic support minimizing intrusion into the support pores.
Article
Carbon membranes have emerged in the 70's and have been presenting promising results for application in processes involving gas separation because of their sieving effects. The carbon membranes are obtained by pyrolysis of a precursor polymer beyond its initial decomposition temperature under essentially inert conditions. Supported and unsupported carbon membranes can be produced, but the former are distinguished for the industrial separation of gases due to the improved mechanical strength and high chemical and thermal stability. In this context, different types of support, coating methods and pyrolysis conditions for supported carbon membranes have been reported in the literature, in order to improve the separation capability of gas mixtures in respect to permeability and selectivity. The aim of this review article is to report and discuss the evolution of supported carbon membrane in the last 10 years in respect to configuration, transport mechanisms, manufacturing processes and its main applications, highlighting the main challenges still to be overcome for this technology to be applied industrially.
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The carbon dioxide (CO2) separation can be enhanced by using modified materials like a deep eutectic solvent (DES) modified mesoporous silica SBA-15 in polymeric support i.e polysulfone via mixed matrix membranes (MMMs). The pure SBA-15 and DES are potential candidates for the CO2 capturing and their combination has not been reported yet. In this work, a fresh DES was synthesized by combining equal concentrations of Decanoic acid and choline chloride by mass. MMMs were fabricated by DES functionalized SBA-15 (DES-SBA) filler. The DES-SBA-based polymeric MMMs of different compositions, from 5% to 20% with the difference of five each, were developed and subjected to the gas permeation analysis to evaluate relative selectivities and permeabilities of membranes. The DES-SBA-based MMMs were characterized by SEM and FTIR to obtain distribution analysis of filler in the polymer matrix as well as the cross-sectional and surface morphology and the structural analysis of membranes, respectively. The gas permeation evaluations have been utilized to mixed and pure gas samples and the findings of selectivities for CO2/N2 and CO2/CH4 and permeabilities of synthesized MMMs are being reported. The performance of the MMMs has been enhanced via functionalization of SBA-15 by DES as compared to the neat polysulfone (PSF) based simple membrane.
Article
A physicochemical study of novel hybrid polymer membranes based on polyphenylene oxide with a star-shaped modifier incorporated into the matrix has been conducted, and the transport properties of the membranes in the gas separation process have been studied. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been selected as the polymer matrix because of the low cost and high mechanical strength of this material. Star-shaped macromolecules (up to 5 wt %) containing six polystyrene arms grafted onto a fullerene(C60) central core have been used as the filler. The structure and physical properties of the resulting membranes have been characterized by scanning electron microscopy, membrane density measurements, differential scanning calorimetry, and thermogravimetric analysis. Film surface has been studied by contact angle measurements. The gas separation properties of the membranes have been studied by the barometric method for the following individual gases: H2, O2, N2, and CH4. Data on the separation properties have been plotted as a Robeson diagram to compare with published data. It has been shown that the incorporation of star-shaped polystyrene into the PPO matrix leads to an improvement of the separation efficiency for selected gas pairs and an increase in selectivity compared with that of the unmodified membrane.
Article
Using thin film nanocomposite (TFN) membranes is an effective method to obtain high CO2/CH4 separation performance compared to traditional mixed matrix membranes (MMMs). In this study, high CO2 permeable TFN membranes comprising the coated Pebax as a CO2-philic layer filled with Zr-MOFs over the high permeable polymethylpentyne (PMP) support with substantial free volume and desired thermal stability were fabricated to achieve the efficient CO2/CH4 separation. A series of pure CO2 and CH4 gases permeation tests were carried out to evaluate the influence of Zr-MOFs on the gas transport properties of synthesized TFN membranes. Using the amine functionalized UiO-66 was intensified the interaction between the polymer phase and embedded MOF particles that led to improve the CO2/CH4 selectivity. The obtained results from FESEM and TGA/DSC analysis confirmed that the TFN membranes showed a superior compatibility between polymer and filler without non-selective voids at polymer/filler interface. Moreover, the pure gas separation performance of TFN membranes was examined under various feed pressure with the range of 2 – 7 bar. The CO2/CH4 separation was improved as the feed pressure increased so that the CO2 permeability of 393.8 Barrer and CO2/CH4 selectivity of 39.8 were achieved for TFN membranes containing 1.5 wt% of UiO-66-NH2 at feed pressure of 7 bar. Also, the mixed gas separation experiments revealed the reasonable CO2 permeability and CO2/CH4 selectivity for TFN membranes in both dry and humid conditions.
Article
MOF-based membranes, which have appropriate MOF dispersion and suitable interaction, have shown high CO2 permeability and significant CO2/CH4 and CO2/N2 selectivity. In this study, a layer of Pebax was coated on polysulfone (PSF), which this layer incorporated by various content of Cu-MOFs to improve the performance (permeability and CO2/CH4 and CO2/N2 selectivity) of all membranes. Characterization techniques such as SEM, TGA, BET, and gas adsorption verified that Cu-BTC was successfully dispersed into the Pebax matrix Pure CO2 and CH4 gases permeation experiments were performed to investigate the impact of Cu-MOFs on the gas permeability of prepared MOF-based membranes. The “Pebax” embedded by 15 wt% CuBTC and 15 wt% of NH2-CuBTC over PSF support exhibited higher gas separation performance compared to the pristine one. They demonstrated a CO2 permeability of 228.6 and 258.3 Barrer, respectively, while the blank membrane had a CO2 permeability of 110.6 Barrer. Embedding the NH2-Cu-BTC intensified the interaction between incorporated MOF particles and the polymer phase that led to increase the CO2/CH4 and CO2/N2 selectivity In addition, the performance of prepared membranes was evaluated at various feed pressures with the range of 2–10 bar. The CO2/CH4 and CO2/N2 separation was enhanced as the feed pressure surged.
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Global warming and environmental degradation have stimulated the drive towards the capture of large point source carbon emissions and reducing high energy intensity of industrial processes. Mixed membranes infused with high porosity silica sodalite are potential useful for pre-combustion CO2 capture. However, development of high quality mixed matrix membranes is a challenge. In this study, silica sodalite (SSOD) infused polysulfone (PSF) membranes were developed and evaluated for pre-combustion CO2 capture. The SSOD was obtained via topotactic conversion of layered silicates; and the membrane was prepared using the phase inversion method. The physicochemical nature of the SSOD and the SSOD/PSF was checked using XRD, SEM, and N2 physisorption at 77 K. Single gas permeation used to check membrane quality. N2 physisorption shows that the SSOD possesses higher surface area of 56.56 m²/g and pore volume of 0.181 cm³/g, when compared to that of the hydrothermally-synthesized hydroxy sodalite (HSOD) crystals (surface area: 27.43 m²/g; pore volume: 0.084 cm³/g). The SSOD/PSF membrane is asymmetric with higher mechanical strength than the ordinary PSF. Loading the PSF with SSOD enhanced its H2 permeance from 4.9 × 10⁻⁷ mol/m²·s·Pa but with a decrease in H2/CO2 separation factor from 2.2 to 0.6. While the enhanced H2 permeance is attributed to the enhanced porosity of the SSOD, the ideal selectivity is low but still within the values reported in literature. Increasing the SSOD loading up to 10 wt% enhanced the quality and performance of the PSF membrane, displaying H2 permeance of 6.5 × 10⁻⁷ mol/m²·s·Pa and a separation factor of 1.1. Though results reported in this study are promising, a robust synthesis protocol that will further enhance both the H2 selectivity and H2 permeance of the membrane is required. Furthermore, more studies are required on the process optimization and techno-economic feasibility for pre-combustion CO2 capture.
Chapter
Advances in separation technology, the continuing development of material science and increased rate of carbon emission have provided an important opportunity to find novel materials for separation of different species from eachother. Membrane-based gas separation technology have been used for capturing CO2 and offered many advantages due to their inherent attributes such as energy-saving and continuous operation compared to traditional methods like absorption and adsorption processes. To fabricate the membranes, various organic and inorganic materials can be utilized. Mixed matrix membranes, a family of the hybrid organic-inorganic membranes, are known as the innovative membranes for separation of CO2 from gas stream. Zeolites, silica, carbon nano tube (CNT), carbon molecular sieve (CMS), metal organic framework (MOF) and graphene are the most popular filler particles which have been utilized for adding into polymer matrix. Each has its own advantages and drawbacks when they are incorporated within the polymer. The performance of the mixed matrix membranes fabricated with different types of filler particles based on existing literature were reviewed with special focus on post- and pre-combustion carbon capture, for separation of CO2/N2 and H2/CO2, respectively. In most of cases, the CO2 permeability and selectivity are increased after embedding of fillers within polymer matrix compared to the neat polymers alone. Mixed matrix membranes preparation methods and formation of interfacial defects were also discussed briefly.
Article
In the current study, multiwall carbon nanotubes (MWCNTs) were functionalized with Tetraethylene Pentamine (TEPA) and added into polyurethane (PU) polymer matrix to prepare PU-MWCNT-TEPA nanocomposite membranes. The prepared membranes were characterized using FT-IR, XRD and SEM analysis. The analysis results showed that MWCNTs were properly functionalized with TEPA and also uniformly dispersed in polymer matrix. The CO2 permeability increased by 99.8% at 10 wt.% loading of MWCNTs-TEPA. The nanocomposite membrane's CO2/CH4 selectivity was also increased by 9.6%. Impacts of operating pressure and temperature on the membranes’ CO2 permeability and CO2/CH4 ideal selectivity were also investigated. Finally, the gaseous penetrants permeabilities through the nanocomposite membranes were predicted using the Maxwell, the KJN, and the modified KJN models by AAREs of 31.4–35.2, 27.8–31.6, and 4.4–5.7%, respectively.
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Mixed-matrix membranes (MMMs) are based on polymeric membranes filled with inorganic particles as a means to improve their gas separation performance. In this study, MMMs were prepared from polysulfone (PSf) containing embedded nonporous fumed silica nanoparticles and the gas permeation properties of the resulting membranes were investigated. Physical properties such as film density, thermal degradation and glass transition temperature of PSf/silica MMMs were characterized. The distribution of the silica nanoparticles in PSf was observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Furthermore, the interface between the polymer and silica agglomerates was studied in relation with the gas transport properties. The gas permeabilities of hydrogen, helium, oxygen, nitrogen, methane, and carbon dioxide were measured as a function of silica volume fraction and diffusion and solubility coefficients were determined by the time-lag method. The effect of silica nanoparticles in PSf membranes on gas permeability is in contrast with predictions based on the Maxwell model. The O2 permeability is approximately four times higher and CH4 permeability is over five times greater than in a pure PSf membrane. However, the performance comprising permeability versus selectivity of PSf/silica MMMs for O2/N2 and CO2/CH4 follows a similar slope to that of the trade-off upper bound with increasing silica content.
Article
Homogeneous polymer–zeolite membranes were fabricated by incorporation of dispersible template-removed zeolite A nanocrystals into polysulfone. SEM, XRD, N2 adsorption–desorption measurements were used to characterize the zeolite A nanocrystals. The uniformity of the polysulfone–zeolite A nanocomposite membranes was examined by SEM. Air separation measurements of the nanocomposite membranes showed enhanced performance in O2/N2 selectivity and O2 permeability. The polysulfone–zeolite nanocomposite membrane with 25 wt% zeolite A loading exhibited an O2/N2 selectivity of 7.7 and O2 permeability of 1.8 Barrers whereas the pure polysulfone membrane had an O2/N2 selectivity of 5.9 and O2 permeability of 1.3 Barrers.
Article
A novel polyetherimide (PEI)/multi-wall carbon nanotubes (MWCNTs) composite carbon membrane was prepared by spin coating method using PEI as a precursor. The PEI precursor was also modified by blending with polyvinylpyrolidone (PVP) and its effect on the gas transport property of the resulting carbon membrane was examined. The characteristics of the carbon structures and the gas permeation properties of the carbon molecular sieve (CMS) membranes pyrolyzed at 500°C were investigated. The best performance was obtained using the PEI/nanotube CMS membrane, where CO2 permeability 1463 Barrer and O2/N2 permselectivity was 24.16 at 26°C. Further the membranes were extensively characterized by field emission scanning electron microscopy (FE-SEM) for surface morphology studies and thermal gravimetric analysis (TGA) for thermal properties. X-ray diffraction was employed to characterize the structures. The results indicated that the MWCNTs improve gas diffusivity by increasing the micropore volume, even the MWCNTs were not well dispersed in CMS membrane.
Article
The research investigated carbon molecular sieve (CMS) membranes through the dry/wet-phase inversion method from the casting polyetherimide (PEI) on alumina support for hydrogen separation. Different coating techniques such as dry method (slide casting followed by drying under vacuum; and spin coating followed by drying under vacuum); and wet method (spin coating and then later kept in an isopropyl alcohol (IPA)/water coagulating bath) at different pyrolysis temperatures of 550, 600, 650 °C min−1 were also investigated.The membranes were extensively characterized by field emission scanning electron microscopy (FE-SEM) for surface morphology studies and thermo gravimetric analysis (TGA) for thermal properties. The best performance was obtained from CMS membranes fabricated with the dry-phase method (slide casting/vacuum) and pyrolysis at 600 °C, where the H2/N2 permselectivity was 16.2. In contrast with the wet-phase, the increase in gas permselectivity by the dry-phase (slide casting/vacuum) was believed to be due to the quick solidification that prevents rearrangement of polymer aggregates and coalescence of the nascent voids formed due to the spinodal or nucleation growth.
Article
Porous aluminum membrane has been prepared by annealing, quenching and acid etching a commercial Al foil. Hydrogen and carbon dioxide permeation and separation properties have been measured under pressure gradient. H2 and CO2 permeability coefficients for porous Al membrane have been found to increase with increasing etching time, whereas H2/CO2 selectivity first increases then decreases. In order to improve H2/CO2 selectivity, composite membrane has been prepared by depositing a thin layer (∼8μm) of polysulfone (PSF) on the highly porous Al membrane. The optical micrographs show that microstructures of Al grain particles and openings of etch pits are of micron order.
Article
A powder comprised of nickel oxide and proton-conducting Nd- and Zr-doped barium cerate with a particle size on the order of 10nm has been co-synthesized using the glycine–nitrate combustion process. The two compositions are intimately mixed with no significant elemental substitution between them after synthesis. To ensure complete reaction of the cerate components, the synthesized powder must be calcined at 1000∘C. Among the barium cerate compositions investigated, the 30% Zr- and 15% Nd-doped material exhibited the best combination of chemical stability in CO2 and conductivity in hydrogen environments. At least 35vol% Ni is required to achieve percolation in the composites. When sintering is carried out in an atmosphere which promotes reduction of nickel oxide to nickel metal, the result is a mixed electronic- and protonic-conducting composite which has potential use as a hydrogen separation membrane. Composites with a relative density of 99.2% and nanoscale grains have been prepared by hot pressing.
Article
This study investigates the gas separation performance of a mixed matrix membranes flat sheet based on polyethersulfone/polyimide (PES/PI) miscible blend incorporated with zeolite particles. Zeolite 4A was selected and its loading were varied between 10 and 50wt%. Initial attempt of annealing at 150 and 240°C resulted in ideal separation factors far lower than the intrinsic values of the host polymeric membranes. The ideal separation factor was improved by a factor of 5 by increasing the annealing temperature up to 280°C, which is above the glass transition temperature (Tg) of the polymer blend. Only one Tg was observed in DSC analysis, indicating the high miscibility of PES/PI polymer blend and zeolite particles. The ideal separation factors of O2/N2 were higher compared to the value reported for the PES/PI blend membrane and the value increased with increasing zeolite loading. It is concluded that addition of zeolite particles into the matrix of PES/PI polymer blend has significant effect on the membrane structure and properties.
Article
Mixed matrix membranes composed of zeolite L dispersed in a 6FDA-6FpDA-DABA polyimide matrix were fabricated and characterized for gas separation performance. The interfacial contact between the two phases relied on introducing amine functional groups on the zeolite surface and covalently linking them with carboxylic acid groups present along the polyimide backbone. While certain gas permeabilities in the membranes increased with the addition of zeolite L, overall these mixed matrix membranes did not offer substantial selectivity improvements. Separate gravimetric sorption measurements indicated that the sorption capacity of zeolites modified with silane coupling agents is substantially lower than the gas sorption in unmodified zeolites.
Article
The effect of zeolite particle size on the performance of silicalite–PDMS mixed matrix membranes is investigated at two different zeolite loadings. The separation properties of the membranes prepared are characterized by permeability measurements for O2, N2 and CO2 gases. The permeabilities of the silicalite–PDMS mixed matrix membranes are determined to increase with increasing particle size. The variations occurring in the permeability values with changes made in the particle size are much more pronounced at the higher zeolite loading. The ideal selectivity values corresponding to the mixed matrix membranes, on the other hand, generally seem to be less affected by the changes made in the particle size. The permeability values corresponding to the mixed matrix membranes exceed those pertaining to the original polymer membrane only at relatively higher zeolite loadings and/or for relatively larger particle sizes. The variations occurring in the permeabilities and selectivities with changes made in the zeolite particle size may be responsible for the different values of these parameters reported in the literature for the same types of zeolite filled polymeric membranes.
Article
CNT/Polymer nanocomposites have been fabricated by dispersing (0.1%) weight fraction of SWNT and MWNT in polycarbonate matrix separately using benzene as a solvent. Alignment has been performed by inducing DC electric field (500V/cm). X-ray diffraction measurements have been performed to confirmation of SWNT, MWNT and their presence in PC matrix. Gas permeability has been found to be increased in aligned CNT/polymer nanocomposites comparison to random dispersed CNT/polymer nanocomposites. The electrical conductivity in aligned CNT/polymer composite membranes indicates two resistive regions. Experimental results exhibits here that CNT/polymer nanocomposite membranes can be used as good hydrogen separating media. Surface morphology of aligned CNT/polymer nanocomposites was confirmed by optical microscopy.
Article
Treating the glass temperature TG of polymers as an iso‐free volume state allows one to derive the result (αL—αG). TG=K1, a constant; or the approximate result αLTG=K2, another constant. The α's are the coefficients of cubical expansion for 100% amorphous polymer above and below TG. K1 is 0.113 for a wide variety of polymers differing in cohesive energy density, chain stiffness, and geometry. We thus have a general criterion for TG. K2 is 0.164. This latter relation combined with the principle of corresponding states, results in an expression for Tg as a function of cohesive energy density and chain rigidity. The polyalkyl methacrylates which have side‐chain transitions below TG follow the first equation if αG is replaced by αG′, the expansion coefficient below the side‐chain transition. Polymer‐solvent systems are similar to the polyalkylmethacrylates. Two additional products, αL⋅TM and ΔCP⋅TG, where TM is the melting point of the polymer and ΔCP is the jump in specific heat at TG, are approximately constant.
Article
A new morphological model for random ionomers is proposed which incorporates the findings of recent dynamic mechanical and X-ray scattering studies. The model is based on the existence of multiplets, which reduce the mobility of the polymer chains in their vicinity. The thickness of the restricted mobility layer surrounding each multiplet is postulated to be of the order of the persistence length of the polymer. Isolated multiplets act as large cross-links, thus increasing the glass transition temperature of the material. The model is in good agreement with a very wide range of experimentally observed phenomena, especially those based on dynamic mechanical and X-ray scattering techniques.
Article
Prior work has suggested simple guidelines for matching transport characteristics of materials to form high-performance mixed-matrix materials for gas separation. Such materials comprise a dispersion of molecular sieving particles in a properly selected matrix polymer phase. Recent work has shown that these simple criteria are necessary but not sufficient to achieve the desired properties. The analysis presented here shows the need to optimize the transport properties of the interfacial region, i.e., the region between the bulk polymer and dispersed sieve phases. Guided by the need to optimize both the transport properties of the interfacial region and the matrix material selection criteria noted above, a new paradigm is recommended for matrix phase selection. The practicality of the paradigm is validated by the formation of mixed-matrix membranes with an appropriate polymer and sieve. These materials lead to the attractive predicted performances at low loading. For success at higher loading a zeolite “priming” protocol based on polymer-solvent sieve interactions is shown to be necessary. This modified protocol leads to success at intermediate and high dispersed-phase loading.
Article
Mixed matrix materials comprising molecular sieve entities embedded in a polymer matrix can economically increase membrane permselectivity, thereby addressing a key challenge hindering the widespread use of membrane-based gas separations. Prior work has clarified the importance of proper selection of the dispersed sieve phase and the continuous matrix phase based on their intrinsic transport properties. Proper material selection for the two components, while necessary, is not sufficient since the interfacial contact zone appears to be equally important to achieve optimum transport properties. Specifically, it was found that chemical coupling of the sieve to the polymer can lead to better macroscopic adhesion but to even poorer transport properties than in the absence of the adhesion promoter. This counterintuitive behavior may be attributed to a nanometric region of disturbed packing at the polymer sieve interphase. The poor properties are believed to result from “leakage” of gas molecules along this nanometric interface. The Maxwell model was modified to take into account these complexities and to provide a first order quantification of the nanometric interphase. The analysis indicates that optimization of the transport properties of the interfacial region is key to the formation of ideal mixed matrix materials. This approach is used in the second part of this paper to form successful mixed matrix membrane materials.
Article
Surface tension measurements were used to assess the viability of the membrane-casting system for poly(2,6-dimethyl-1,4-phenylene)oxide asymmetric membranes for gas separation. The data was obtained from solvent(chloroform)/nonsolvent additive solutions. The nonsolvent additive was varied consisting of linear, straight and branched alcohols. It is illustrated how surface tension data can be used to elucidate the role of nodules on the surface of the asymmetric membranes.
Article
Interfacial void-free Matrimid polyimide (PI) membranes filled with zeolites were prepared by introducing 2,4,6-triaminopyrimidine (TAP). TAP enhanced the contact of zeolite particles with polyimide chains presumably by forming hydrogen bonding between them. The threshold amount of TAP, needed to depress totally the void formation, varied with zeolite type in the order of zeolite 4A≈13X<NaY<5A<NaSZ390HUA. It was also observed that the threshold amount of TAP could be related with the number of external hydroxyl groups of zeolite particles. The void-free PI/zeolite 13X/TAP membrane showed the higher gas permeability for He, N2, O2, CO2 and CH4 with a little expense of permselectivity compared with the PI/TAP membrane, while the PI/zeolite 4A/TAP membrane showed the lower permeability but higher permselectivity. The facilitation ratios of the zeolite-filled PI membranes were strongly affected by the pore size of zeolites. In addition, the molecular sieving effect of zeolites seemed to take place when the kinetic diameter of gas penetrants approached the pore size of zeolites.
Article
Gas permeabilities of molecular sieve 13X filled polysulfone and unblended polysulfone membranes fabricated by a melt extrusion process were measured by a constant volume technique at room temperature. The relative permeation rates of the industrially important gases were found to be in the order H2⪢He⪢CO2⪢O2⪢CH4≈N2.
Article
By combining organic polymers normally used to make membrane filters with inorganic substances, multi-walled carbon nanotube (MWCNTs), an extraordinary ability to separate H2 from CH4 was developed in this study. A series of MWCNTs/PBNPI nanocomposite membrane with a nominal MWCNTs content between 1 and 15 wt% were prepared by solution casting method, in which the very fine MWCNTs were embedded into glassy polymer membrane. Detailed characterizations, such as morphology, thermal stability and crystalline structure have been conducted to understand the structures, composition and properties of nanocomposite membranes. The results found that this new class of membrane had increased permeability and enhanced selectivity, and a useful ability to filter gases and organic vapours at the molecular level.
Article
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 (Tg) 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 (Tg) 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.
Article
A new class of multi-wall carbon nanotubes (MWCNTs)/carbon nanocomposite thin films was successfully prepared by incorporating (MWCNTs) into polyimide (PI) precursor solution. The carbon films were obtained in only one coating step by spin-coating technique on a macroporous alumina substrate and were pyrolyzed at 773 K. The structure and single gas permeation properties of PI-based carbon membranes incorporated with or without MWCNTs were investigated. From the FE-SEM images, the pure carbon membranes have a thin dense permselective layer with few closed pores while the permselective layer of the MWCNTs/carbon nanocomposite thin films are porous due to the structure of nanotubes. The MWCNTs/carbon nanocomposite thin films exhibited that the ideal carbon dioxide flux was 866.6 Barrer (1 Barrer = 1)/10 (10 cm 3 (STP) cm cm (2 s (1 cm Hg (1) and the separation factor of CO 2 /N 2 was 4.1 at room temperature and 1 atm, which was 2Á4 times of magnitude higher than that of pure carbon membrane prepared by the same procedures and conditions.
Article
The incorporation of zeolite particles in the micrometer range into polymeric matrices was investigated as a way to improve the gas separation properties of the polymer materials used in the form of membranes. The adhesion between the polymer phase and the external surface of the particles appeared to be a major problem in the preparation of such membranes when the polymer is in the glassy state at room temperature. Various methods were investigated to improve the internal membrane structure, that is, surface modification of the zeolite external surface, preparation above the glass-transition temperature, and heat treatment. Improved structures were obtained as observed by scanning electron microscopy, but the influence on the gas separation properties was not in agreement with the observed structural improvements. © 1994 John Wiley & Sons, Inc.
Article
The time lag permeation technique has proven to bean effective method for characterisation. Because of the simple nature of the permeation experiment, transport parameters can be directly obtained from experimental data hence avoiding the intensive mathematical treatment required by other techniques. The method has historically been applied to diffusion and adsorption in porous membranes and diffusion in polymer membranes. Since its origins in 1920, interest in the time lag method has expanded because of its value in characterising simple permeation processes and also complex systems of diffusion with simultaneous adsorption and surface diffusion. This review focuses on presenting the asymptotic solution of the mass balance diffusion equations and includes applications of time lag analysis, in order to give a critical and broad perspective of this method as a tool for characterisation. It includes much of the previously published literature in order to show that for most cases the asymptotic solution of the transport equations is simple, and for more complex cases that an analytical solution is possible hence avoiding cumbersome numerical techniques.
Article
Gas separation membranes with enhanced performance were developed by the introduction of nanosized magnesium oxide particles followed by treatment with silver ions. Firstly, nanocomposite membranes were fabricated by incorporating nanoscale magnesium oxide particles with different loadings into the Matrimid matrix. The addition of MgO nanoparticles led to an increase in gas permeability of membranes; the highest permeability was observed for the membranes containing 40 wt% MgO loading. However, the selectivity of nanocomposite membranes was less than the neat Matrimid. These changes can be mainly ascribed to the effect of pore dimensions of MgO nanoparticles which are larger than the size range of gas molecules. Heat treatment at temperatures below polymer glass transition temperature resulted in densified structure, while heat treatment above Tg resulted in further increase in gas permeability of membranes through the changes in free volume of membrane. Secondly, nanocomposite membranes with 20 wt% MgO were modified by silver treatment for stipulated periods of time. A dipping procedure was adopted for this process which resulted in the impregnation of silver ions into the nanocomposite membranes. It was found that the major driving force for penetration of silver ions was offered by MgO nanoparticles and polymer played the role of a carrier. The adsorption process was confirmed by different techniques and oxygen sites at the surface of MgO were recognized to be responsible for this process. The longer immersion time led to more silver adsorption into the membrane. All the modified membranes exhibited enhanced gas separation performance for selected gas pairs compared to the neat Matrimid membrane. The best performance was observed for nanocomposite membranes (with 20 wt% MgO) after a 10-day silver treatment in which the CO2/CH4 and H2/N2 selectivity increased by 50% and 35%, respectively.
Article
Polymeric gas separation membrane materials have improved significantly over the past two decades due to systematic optimization in backbone structure. Recent evidence suggests, however, that advantages of a purely polymer-based approach are reaching diminishing returns for important separations such as O2 and N2. Zeolites, carbon molecular sieves (CMS), and rigid rod polymers offer attractive transport properties but are difficult and expensive to process. Mixed matrix composite (MMC) membranes, incorporating molecular sieving materials within polymeric substrates, may provide economical, high performance gas separation membranes if defects at the molecular sieve/polymer interface can be eliminated. In addition, careful matching of the intrinsic permeability and selectivity of the support matrix and the molecular sieve domains is necessary. Theoretical O2 permeability and selectivity predictions are presented for such optimized membranes of zeolite 4A and CMS in Ultem® and Udel® matrices using two idealized expressions based on classical and more recent results. Positive and desirable deviations from these idealized results can be anticipated if a continuous molecular sieving phase is formed, but this special case is not required if a proper selection of the polymer matrix is made.
Article
Composite membranes, consisting of a highly hydrophobic zeolite, silicalite-1, and PDMS polymer were prepared. Distinct gas permeation effects have been found for these membrane types. A new parameter, the facilitation ratio of zeolite, was introduced to characterize the function of silicalite in the membrane. Using this parameter it was confirmed that silicalite played an important role in the molecular transport and that the altered permeabilities and selectivities were a result of the molecular sieving effect of the silicalite.
Article
In this paper, we report multiwall carbon nanotube (MWNT) doped polyaniline (PANI) composite thin films for hydrogen gas sensing applications. PANI was synthesized by in- situ chemical oxidative polymerization of aniline using ammonium persulfate in acidic medium.This emeraldine salt form of PANI was converted into emeraldine PANI base and doped with MWNT (4 wt%) in presence of champhor sulfonic acid (CSA) by solution mixing method. The MWNT/PANI composite films were deposited onto ITO coated glass substrate using spin cast technique. The gas sensitivity of these composite films was evaluated by measuring the change in electrical resistance of composite films in presence of hydrogen gas for different pressures at room tempeature. It is observed that the MWNT/PANI composite film shows a higher sensitivity in comparison to pure PANI and it decreases on increasing hydrogen gas pressure. The composite films have also been characterized by X-ray diffraction (XRD) analysis and Atomic force microscopy (AFM).
Article
Mixed-matrix membranes were prepared from Matrimid® and mesoporous ZSM-5 nanoparticles containing crystalline ZSM-5. The ideal selectivity for H2/N2 separation increased from 79.6 for pure Matrimid® to 143 at 10% loading, while the selectivity of O2/N2 increased from 6.6 for pure Matrimid® to 10.4 at 20% loading. The ideal H2/CH4 separation factor increased from 83.3 to 169 at 20% loading. The results suggest that the mesopores of the ZSM-5 material provide good contact between the nanoparticles and the polymer, since the polymer chains can penetrate into the mesopores. The micropores of ZSM-5 crystals provide size and shape selectivity.
Article
The effect of the introduction of specific adsorbents on the gas separation properties of polymeric membranes has been studied. For this purpose both carbon molecular sieves and zeolites are considered. The results show that zeolites such as silicate-1, 13X and KY improve to a large extent the separation properties of poorly selective rubbery polymers towards a mixture of carbon dioxide/methane. Some of the filled rubbery polymers achieve intrinsic separation properties comparable to cellulose acetate, polysulfone or polyethersulfone. However, zeolite 5A leads to a decrease in permeability and an unchanged selectivity. This is due to the impermeable character of these particles, i.e. carbon dioxide molecules cannot diffuse through the porous structure under the conditions applied. Using silicate-1 also results in an improvement of the oxygen/nitrogen separation properties which is mainly due to a kinetic effect. Carbon molecular sieves do not improve the separation performances or only to a very small extent. This is caused by a mainly dead-end (not interconnected) porous structure which is inherent to their manufacturing process.
Article
Gas separation by selective transport through polymeric membranes is one of the fastest growing branches of membrane technology. However, the existing polymeric membrane materials are inadequate to fully exploit the application opportunities on industrial scale; the improvement in permeability is at the expense of selectivity, and vice versa. A new type of membrane material emerging with the potential for future applications is mixed matrix materials composed of homogeneously interpenetrating polymeric and inorganic particle matrices. Compared to original polymeric membranes, significant improvement in separation properties with trivial loss in membrane flexibility is expected for the resultant mixed matrix membranes (MMMs). This review first gives an outline of the concept and the key advances of MMMs. Subsequently, recent developments are presented, including two immediate challenges: achieving an optimized interface structure, and forming asymmetric or composite membrane with an ultrathin and defect-free mixed matrix skin. Attractive avenues to overcome these challenges are emphasized. The review of the Maxwell model demonstrates how the transport properties of MMMs are related to the polymer matrix, molecular sieves, as well as membrane morphology. Finally, future directions of MMMs’ fabrication and application are suggested.
Article
Mixed matrix membranes of polyethersulfone (PES), a glassy polymer, and hydrophilic zeolites 13X and 4A were prepared by using different membrane preparation procedures. Using selected procedure (c), the permeation rates of N2, O2, Ar, CO2 and H2 were measured with a variety of membranes prepared at different zeolite loadings. Significant differences in measured permeability and calculated selectivity values demonstrated the importance of the type and percentage of zeolite. For both zeolitic additives, permeabilities and selectivities are enhanced at high zeolite loadings.In order to understand the permeation mechanism taking into account the polymer-zeolite interactions, macro-positioning of zeolites and matrix distribution, the heterogeneous membrane morphologies were investigated by scanning electron microscopy (SEM). Significant changes in the membrane morphologies of PE-13X and PES-4A matrices were observed, implying the importance of zeolite type.
Article
A highly ordered large pore mesoporous silica molecular sieve SBA-3, SBA-15, Al-SBA-15, and SBA-1, were developed and characterized by XRD, BET, FTIR, SEM, and NMR-MAS. The catalytic materials were synthesized using different raw materials and operation conditions. These materials contain a regular arrangement of uniform channels with diameters between 1.8 and 10 nm, high specific surface area and high specific pore volume. The designed methods were effective for the synthesis, presenting each mesostructured materials, patterns of XRD and other characteristics corresponding to the reported ones in literature. The new route employed to synthesize Al-SBA-15, generates a catalyst with only aluminum in tetrahedral form, according to the data of (27)Al NMR-MAS. However, several reports indicated that the coordination of the Al atoms changes below the Si/Al ratio of 45, presenting peaks corresponding to penta and hexa-coordinated aluminum, which are absent in our samples (Si/Al = 50 and 33).