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High performance mordenite membranes were successfully prepared in a short synthesis time from fluoride-containing dilute solution without organic template under microwave-assisted heating. The effects of crystallization temperature, fluoride ion and aluminum source on the membrane morphology and separation performance for dehydration of acetic acid by pervaporation were systematically investigated. High performance mordenite membranes with a thickness about 5 µm could be prepared from dilute solution with composition of SiO 2 : 0.06Al 2 O 3 :0.24Na 2 O:0.3NaF:120H 2 O at 165 °C for 4 h using various aluminum sources. These mordenite membranes exhibited high fluxes of 0.87±0.06 kg m −2 h −1 and excellent selectivities, that is only pure water was detected in the permeate side for dehydration of 90 wt% acetic acid aqueous mixtures at 75 °C. The reproducibility of mordenite membranes was high, using the fluoride-containing dilute solution under microwave-assisted heating, which forebodes a promising prospect for industrial applications in preferential separation of water from acetic acid aqueous solutions. [ABSTRACT FROM AUTHOR]

Here we report a modified “two in one” strategy through depositing of ZnO particles onto the macroporous α-alumina tubes with average pore size of 2–3 μm for synthesis of ZIF-8 membranes. The LTA or Al 2 O 3 particles as fillers were firstly deposited to patch the large defects in the support then the ZnO particles were deposited. The ZnO particles reduce the pore size and simultaneously act as “metal source” to create a high supersaturation degree to promote high heterogeneous nucleation sites. Through such strategy, continuous and crack-free ZIF-8 membranes were successfully obtained, exhibiting H 2 permeance of 3.4 × 10 −7 mol m −2 s −1 Pa −1 at 150 °C, with ideal selectivities for H 2 /CO 2 , H 2 /N 2 , H 2 /CH 4 and H 2 /C 3 H 8 system of 7.4, 8.8, 8.2 and 37.8, respectively. When the supports deposited with ZnO particles were treated by pre-reacting with the ligand of 2-methylimidazole, big cracks/gaps occurred at the interface between the ZIF-8 membranes and the supports. This modified “two in one” strategy can be extended for synthesis of large variety of MOFs membranes on large-pore supports through the rational selection of metal oxides. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effects of salts on PV dehydration performance of zeolite membranes were studied. [•] Effects of five salt species on the membrane performance were studied. [•] Different salts had different impact on the membrane flux. [•] Membrane regeneration was performed. [•] An irreversible flux drop was obtained. [ABSTRACT FROM AUTHOR]

Abstract: Thin zeolite T/carbon composite membranes (thickness about 3–4μm) with the favorable CO2 separation performances were successfully synthesized on the porous alumina tubes by dispersing zeolite T particles (particle size about 300nm) into polymeric precursor (polyfurfuryl alcohol (PFA)). The composite membrane is carbonized under the condition of 873K with a dwell time of 2h and ultra-high purity N2 flowing. The CO2 separation performance is influenced by the zeolite contents and dip-coating cycles of the composite membranes. The zeolite T/carbon composite membrane synthesized with zeolite contents of 2wt.% and two coating cycles displayed the best CO2 separation performance. The single and mixed gases permeation properties of the composite membrane were investigated in detail. Due to the competitive permeation effect between adsorbable gas (CO2) and non-adsorbable gas (N2 and CH4) in the membrane, the CO2/CH4 and CO2/N2 permselectivities (143 and 67.1) in the equimolar mixed gas system were higher than the results from single gas permeation test (97.3 and 51.6) at temperature of 298K. The effects of permeation temperature and pressure difference on CO2 separation performances of the composite membranes were also studied. The CO2/CH4 and CO2/N2 selectivities decreased with increasing the permeation temperature or increasing the pressure difference. The zeolite T/carbon composite membrane introduced in this paper can be a novel membrane candidate for industrial CO2 separation. [Copyright &y& Elsevier]

Abstract: A specific synthesis mode, based on precursor diffusion through the support channels, the restricting growth method (RGM) with ultra-dilute precursor has been designed to prepare silicalite-1 zeolite membranes on seeded macroporous α-Al2O3 tubular supports. Several parameters were systematically investigated to evaluate their influence on performance of the membranes, including the H2O/SiO2 ratio, template type and crystallization temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and single-gas permeation tests were used to characterize the as-prepared membranes. Results showed the membrane prepared under optimum parameters (H2O/SiO2 ratio of 800, TPAOH as template and crystallization at 443K) was continuous, dense and with a controllable section thickness almost the same as that of the seed layer. It displayed preferable hydrogen permeance (1.2×10−6 molm−2 s−1 Pa−1) and permselectivity (αH2/SF6 =134) at 298K under 0.1MPa pressure drop. Moreover, due to the utilization of ultra-dilute precursor, this technique has the advantage of reduced chemical consumption. On the contrary, the uncompacted membranes with poor permeation behavior were obtained by the conventional secondary growth method under the same synthesis parameters. [Copyright &y& Elsevier]

Abstract: A novel hydrophilic poly(1-vinylimidazole)/mordenite (PVI/MOR) grafting membrane was prepared by free-radical graft polymerization of 1-vinylimidazole (VI) onto the as-synthesized mordenite zeolite membrane. The surface property and the morphology of the membranes were analyzed by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), diffuse reflectance FT-IR spectroscopy (DRIFTS) and thermogravimetric analysis (TGA). The effects of VI concentrations in the grafting medium, separation temperature, feed concentration on selectivity and flux of the obtained membranes for pervaporation dehydration of acetic acid were examined. The PVI/MOR grafting membrane with the VI solution of 15wt.% astonishingly exhibited the ideal selectivity with water contents in permeates reaching 100.00wt.% over acetic acid feed concentrations from 71 to 94wt.% at 80°C. Both the total fluxes and selectivity for this membrane increased with temperature ranging from 40 to 80°C. It was suggested that an in situ formed complex between the poly(1-vinylimidazole) (PVI) moiety of the membrane and the acetic acid in the feed played an important role in the separation performance. It not only blocked the permeation of acetic acid through the grain boundary defects but also facilitated the transport of the water molecules, resulting in an ideal selectivity of water over acetic acid. [Copyright &y& Elsevier]

Abstract: High performance silicalite-1 membranes on outer surface of macroprous α-Al2O3 supports were synthesized by counter-diffusion secondary growth (CDSG). Different from the conventional synthesis methods by which the silica source (tetraethyl orthosilicate) and the template agent (tetra-propyl ammonium bromide) were mixed together to form the synthesis solution, this method introduced silica source and template agent from the opposite direction of a support wall, resulting in good membrane structures and properties as well as reduced chemical consumption. The correlation between particle size of seeds and the pore size of supports was optimized, and its influence on the morphology and permeation property of the as-prepared membranes was also investigated. Results showed the as-prepared membranes were typical silicalite-1 membranes without any other phase. The membranes were dense, continuous without obvious defects, displaying good permeation property. The H2 permeance and H2/SF6 ideal permselectivity for the membrane prepared under optimized parameters were up to 7.5×10−7 molm−2 s−1 Pa−1 and 103 at 298K under 0.1MPa pressure drop, respectively. Moreover, by the CDSG method the consumption of the template can be greatly reduced. [Copyright &y& Elsevier]

Abstract: Silicalite-1 membranes supported on macroporous alumina tubes for hydrogen separation were successfully prepared by a specific synthesis protocol called counter-diffusion hydrothermal crystallization (CDHC). This method introduced silica source (tetraethyl orthosilicate, TEOS) and template agent (tetra-propyl ammonium bromide, TPABr) from opposite directions of the support wall, overwhelming the conventional in situ hydrothermal crystallization (ISHC). After an optimization process, the optimum molar composition of silicon precursor was 1SiO2:0.135Na2O:100H2O:2EtOH and that of template precursor was 1.5TPABr:100H2O. XRD and SEM analysis showed the as-prepared membranes were typical silicalite-1 membranes with high internal crystalline order as well as dense and continuous surface morphology. Single-gas permeation tests indicated the membrane prepared with optimized recipe combined high H2 permeance (1.24×10−6 molm−2 s−1 Pa−1) and good H2 selectivity () at room temperature, 0.1MPa pressure drop. Moreover, the consumption of template in this novel method was about one third of that used in conventional hydrothermal synthesis. This concept can also be extended to other many types of zeolite membranes. [Copyright &y& Elsevier]

Abstract: Due to their improved performance and excellent chemical resistance, there is a growing interest in applying inorganic membranes not only for gas separation, but also in combination with heterogeneous-catalysts in membrane reactors. Obviously, a thorough understanding and a quantification of the mass transfer processes are essential for optimal application. The objective of this work is to study the mass transfer through a Vycor glass membrane, which might be applied successfully in membrane reactors. Transient diffusion experiments were carried out and the exchange of two different gases via the membrane was investigated. The observed pressure responses reveal the complicated nature of the transport through Vycor glass. If adsorbable gases are involved there is a strong asymmetry between corresponding exchange experiments. Very complex responses were observed for the exchange experiments with C4H10 and C3H8. To understand the observed behavior, the adsorption capacity of Vycor glass was measured for several gases at ambient temperature. In order to analyze the transient diffusion experiments, a transport model was applied, which is based on the Dusty Gas Model for the quantification of gas phase transport and on the generalized Maxwell–Stefan theory for the description of the transport of adsorbed species. The model describes relatively well the exchange experiments performed with the pairs H2/N2 and He/CO2. It was found that the quality of the theoretical results for experiments with adsorbable gases depends strongly on the reliability of the model applied to quantify the adsorption isotherms. [Copyright &y& Elsevier]

A novel Pd/silicalite-1 composite membrane supported on the macroporous tubular stainless steel substrate was successfully fabricated by electroless plating at 303 K. The structure, morphology and gaseous permeability of the membrane were detected by X-ray diffractiometry (XRD), scanning electron microscopy (SEM) and single-gas permeation test, respectively. Results confirm the formation of a thin, smooth, and continuous Pdlsilicalite-1 composite membrane. The obtained composite membrane shows a high H2 permeance of 1.15x10-6 mol · m-2 · s-1 · Pa-1 with moderate H2 selectivity of 250 for H2/N2 at 773 K, at 0.1 MPa pressure drop, suggesting the potential application for H2 separation. [ABSTRACT FROM AUTHOR]

Abstract: In this work, beta zeolite membranes were prepared on seeded α-Al2O3 substrate tubes using zeolite structure-directing agent (ZSDA), instead of directly using organic agent as templates. This ZSDA method consists of two steps: preparation of beta ZSDA and growth of beta zeolite membranes with ZSDA by the secondary hydrothermal synthesis. The molar compositions of the synthesis solution of ZSDA and zeolite membrane are of 1SiO2/0.012Al2O3/0.167(TEA)2O/0.031Na2O/9.4H2O and 1SiO2/0.03Al2O3/0.027(TEA)2O/0.27Na2O/25H2O, respectively. Preparing the membranes only needed a little ZSDA, which was used to substitute for conventional templates in the secondary growth process of the membrane. The membranes were characterized by SEM, XRD and nitrogen permeance. It was found that the prepared membranes are continuous and defect-free. The mechanism of membrane growth with ZSDA was discussed simply. [Copyright &y& Elsevier]

Porous silica–zirconia membranes were fabricated by the sol–gel techniques to study their stability against water and the pervaporation performance of aqueous solutions of organic solvents. Zirconia (10–70 mol%) was added to silica to obtain silica–zirconia composite membranes by firing at 400–500 °C for pervaporation tests with organic solvent/water mixtures, such as iso-propyl alcohol (IPA)/water and tetrahydrofuran (THF)/water mixtures at their normal boiling points.The membrane coatings have been done effectively by the hot-coating methods proposed previously. Boiling water treatments introduced in the coating processes have made the membranes quite stable even in the high water concentration region of aqueous organic solutions at their normal boiling points. Zirconia contents larger than about 40 mol% have made the silica–zirconia membranes quite stable. The membranes of zirconia contents less than about 30 mol% were found not stable in a dilute aqueous solution of IPA. The membranes fabricated by the conventional dip-coating methods with slow drying were not stable against water because of the probable segregation of silica and/or silica-rich phases during drying.The membranes fired at lower temperature (400 °C) gave a higher water flux of around 500 mol m−2 h−1 (9 kg m−2 h−1) with a separation factor larger than 1500 at 10 wt.% of water in the boiling feed of IPA/water mixture, for example. [Copyright &y& Elsevier]

Boron-substituted silicalite-2 (B-ZSM-11) membranes were prepared on seeded cheap macroporous α-Al 2 O 3 tubes to separate ethanol from water by pervaporation. The incorporation of boron atom into MEL framework was confirmed by XRD and FTIR. The effects of B/Si ratio in the synthesis solution together with PV operation temperature and feed concentration on separation properties of the membranes were investigated. The B-ZSM-11 membrane prepared with B/Si ratio of 0.06 exhibited the highest separation factor of 35.0 with a total flux of 1.51 kg m −2 h −1 for 5 wt% ethanol/water mixtures at 60 °C. The total flux increased with increasing PV temperature from 30 to 75 °C and the separation factor showed the highest value at 60 °C. The separation factor decreased with feed concentration from 1 to 7 wt% and the total flux also showed the highest value for a 5 wt% mixture. It is demonstrated that the incorporation of boron atom into MEL structure improved separation performance of B-ZSM-11 membrane for ethanol/water solutions. On the other hand, the better hydrophobicity of B-ZSM-11 membranes, evidenced by contact angle measurements, is responsible for pervaporation performance for ethanol/water mixtures. [ABSTRACT FROM AUTHOR]

Abstract: Pilot-scale zeolite NaA membranes with high PV performance supported on cheap coarse macroporous supports were prepared by one single secondary growth using varying temperature hot dip-coating seeding method (VTHD). Through the VTHD method, a thin, dense and pinhole-free asymmetric NaA seed layer composed of large and small NaA seeds could be manipulated onto the surface of a coarse macroporous support. The large NaA seeds mainly acted as fillers to reduce the pore sizes of the support while the small NaA seeds acted as nuclei to provide sites for NaA crystal growth. The effects of the seed suspension concentrations, the seed sizes and coating temperature on the morphology of the seed layer and the separation performance of the resulting NaA membranes were investigated. The reproducibility of the VTHD method was as high as 70%. The zeolite NaA membrane prepared by the VTHD method showed a water flux of 2.85kgm−2 h−1 with a separation factor over 10,000 in dehydrating the 90wt% ethanol/10wt% water mixture at 343K. The use of a cheap macroporous support and the high reproducibility of the VTHD method provide the feasibility for large-scale commercial production of low cost zeolite NaA membranes, promoting the broad application of zeolite NaA membranes. [Copyright &y& Elsevier]

Abstract: The crystallization of defect-free, acid-proof film microstructure is consistently pursued for making hydrophilic pervaperation (PV) membranes popular in process industries. We show that a novel modified secondary growth method can fabricate high-PV-performance, excellent-acid-stability mordenite membranes by eliminating grain boundary defects, dramatically by optimizing film microstructure. This method consists of growing the assembled nanocrystals of an ultrathin seed layer to a well-intergrown film directly on a macroporous support at a relatively low crystallization temperature (150°C) by avoiding events that lead to an acid nonresistant film microstructure, such as the formation of Al-rich film surface and grain boundaries. Fluoride anions are used as mordenite crystal structure modifiers to optimize distribution of aluminum atoms in zeolitic film, so grain boundaries can be kept intact for long-term acidic corrosion. The polycrystalline films are ultrathin (3–4μm), and oriented with different Si/Al ratios (5.6–20.1). Comparison with conventional synthesized membranes shows that these microstructurally optimized membranes have superior PV performance and acid stability for the dehydration of high-concentration acetic acid (AcOH) mixtures. [Copyright &y& Elsevier]

Abstract: An effective seeding method is a mandatory step to have thin and defect-free zeolite membranes prepared by means of secondary growth method on macroporous tubular supports. The permeation properties of the as-prepared membranes depend strongly on the seeding method of zeolite crystals during which the whole support surface should be covered uniformly and sufficiently. In this work a novel and simple seeding method was designed and developed to prepare seed layer on low-cost macroporous Al2O3 support. This seeding technique includes three steps: (a) pre-modify the support surface by hot dip-coating in large seed (1.2μm) suspension; (b) rub off the excess large seeds which stick on the support surface; (c) further modify the support by hot dip-coating in another seed (0.4μm) suspension. After the composite seeding process, silicalite-1 membrane was synthesized by microwave heating (MH) at 423K for 2h using the synthesis solution of 1SiO2:0.3TPAOH:80H2O:4C2H5OH. Results showed the as-prepared zeolite membrane was dense and continuous with a thickness of ∼4μm. Moreover, it exhibited high hydrogen permeance of 3.01×10−6 molm−2 s−1 Pa−1 and permselectivity of 66 for H2/i-C4H10 at room temperature. [Copyright &y& Elsevier]

Abstract: Pervaporation (PV) using zeolite membrane is one of the emerging technologies undergoing a rapid growth in recent years, regarded as an alternative method to distillation for its energy-efficient. However, grain boundary defects, especially for hydrophilic zeolite membranes, inevitably formed due to their polycrystalline structures and strong negative surface charges of Al-containing zeolites during hydrothermal synthesis, degrade their selectivity by providing nonselective transport pathway for permeating species. We show that functional defect-patching (FDP) can improve the PV performances of thin columnar membrane of a certain zeolite (mordenite) by eliminating grain boundary defects, by grafting functional polymer groups onto grain boundaries. This methodology enables the preparation of mordenite zeolite membrane (MZM) with high PV performances for the dehydration of acetic acid (AcOH) and holds promise for realizing high-throughput and scalable production of the membrane with improved energy efficiency. Furthermore, durable tests for acid stability showed that the FDP-treated membrane displayed a reasonably strong acid resistance. Finally, the products fabricated were characterized by a variety of techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), diffuse reflectance FT-IR spectroscopy (DRIFTS) and thermogravimetric analysis (TGA). [Copyright &y& Elsevier]

Abstract: With one step of vacuum coating and pyrolysis, the thin zeolite L/carbon nanocomposite membranes (about 3–4μm) were obtained on the porous alumina tubes by incorporating nano-sized zeolite L (about 100nm) into polymeric precursor (polyfurfuryl alcohol (PFA)). The permeation properties of pure H2, CO2, N2 and CH4, together with CO2/CH4 and CO2/N2 mixtures through the composite membrane were measured and analyzed. A notable increase was observed in the permeances of gas species in comparison with the pure carbon membrane owing to the enhancement of the pore structure properties, including pore volume, surface area, pore size and its distribution. Due to the restricted diffusion of non-adsorbable gas by adsorbable component in the micropores, the CO2/CH4 and CO2/N2 permselectivities in the mixed gas system were higher than the results from pure gas permeation. The effects of permeation temperature, pressure difference and CO2 content in feed gases on separation performances of the composite membranes were also investigated. It was found that the CO2/CH4 and CO2/N2 separation factors decreased with increasing the permeation temperature and pressure difference, and increased with increasing CO2 content in the mixtures. [Copyright &y& Elsevier]