Zeolite LTA/carbon membranes for air separation (original) (raw)
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Synthesis, characterization and single gas permeation properties of NaA zeolite membrane
Journal of Membrane Science, 2005
High quality NaA zeolite membrane was synthesized on an ␣-Al 2 O 3 support with the aid of nucleation seeds from a gel synthesis mixture. The influence of synthesis conditions, such as synthesis times, synthesis stages and nucleation seeds, on the formation and permeation properties of the NaA zeolite membranes was investigated. Nucleation seeds played a critical role on the formation of a continuous NaA zeolite membrane on the support surface. The quality of the NaA zeolite membranes were improved by employing the multi-stage synthesis method. The best NaA zeolite membrane was obtained after a three-stage synthesis with the synthesis time of 24 h and with the aid of nucleation seeds. Single gas permeation properties of the NaA zeolite membranes were studied. The permeance of H 2 , O 2 , N 2 and n-C 4 H 10 decreased as the molecular kinetic diameter of the gases increased. At 298 K and under pressure difference of 0.10 MPa, the permselectivity of H 2 /N 2 , H 2 /n-C 4 H 10 and O 2 /N 2 were 20.1, 106 and 2.61, respectively, which were much higher than those of the corresponding Knudsen diffusion ratios of 3.74, 5.39 and 0.96. With increasing temperature, the gas permeance increased and the permselectivity of H 2 /N 2 , H 2 /n-C 4 H 10 and O 2 /N 2 slightly decreased. All these properties indicated that the gases mainly permeated through the channels of NaA zeolite and the gas permeation was predominantly controlled by the molecular sieving effect of NaA zeolite membrane. However, the permeation of n-C 4 H 10 indicated that the NaA zeolite membranes had certain defects with diameters larger than the pore size of NaA zeolite.
Zeolite A/carbon membranes for H2 purification from a simulated gas reformer mixture
Journal of Membrane Science, 2011
Zeolite LTA membranes supported on macroporous carbon discs have been modified by means of ion exchange and tested for their H 2 purification performance using a simulated reformer mixture as feed stream. As-prepared membranes (i.e. sodium form, Na-LTA/carbon) have been ion-exchanged with CsNO 3 (Cs-LTA/carbon) to tailor the membrane pore size and tested in a Wicke-Kallenbach (WK) cell in order to study their permeation properties. Both membranes have been tested using a simulated reformer mixture in dry conditions (50% H 2 , 1.25% CO and n% CO 2 in He), where the CO 2 concentration has been modified (n% = 0, 2, 5, 10, 15 and 20%), and their permeation properties studied. In addition, these membranes (Naand Cs-forms) have been also tested using a simulated reformer mixture on humid conditions (50% H 2 , 1.25% CO, 20% CO 2 and 5% H 2 O in He). All the experiments using different stream compositions have been carried out at three different temperatures (303, 398 and 423 K). Furthermore, in order to analyze and understand the permeation characteristics of the composite materials, commercial zeolite A in powder form has been used to study the interaction between CO 2 and the zeolite. Therefore, thermogravimetric analysis (TGA), in situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) experiments and CO 2 adsorption isotherms at different temperatures (303 K, 398 K and 423 K) have been used in order to analyze this interaction. The final composite, Cs-LTA/carbon can separate H 2 from CO under all the experimental conditions studied and possesses high permeance and an excellent H 2 /CO separation factor.
Ceramic-zeolite composite membranes and their application for separation of vapor/gas mixtures
Journal of Membrane Science, 1994
Ceramic-zeolite composite membranes were prepared by in-situ synthesis of a thin ( _ 10 pm) polycrystalline silicalite-1 layer on the inner surface of an alumina membrane tube. The inner surface is a y-alumina coating that has 5-nm diameter pores. X-ray diffraction verified the presence of a pure silicalite phase in the layer, and SEM showed that individual silicalite crystals had grown together to form a continuous silicalite-1 layer. The addition of silicalite to the alumina membrane decreased the Nz permeance by a factor of 5, but it decreased the n-C4Hu, permeance by a factor of 190, and n-C.,H10 appeared to adsorb on the membrane. At room temperature, the permeante ratio of n-C4H,,-,/i-C4Hlo was one for the alumina membrane, but it was 3 for the zeolite membrane. Methanol was separated from HZ and from CH4 at 373 K and pressures from 110 to 1100 kPa by preferentially permeating CH30H through the zeolite membrane. For some conditions the CH30H/H2 separation factor was greater than 1000, and the CHsOH/CH4 separation factor was 190. Apparently, CH30H adsorbs and blocks the pores for H2 or CH4 permeation.
Using of cheap materials for making of zeolite membranes with an innovative method
In this research, two new innovations have been made. The first innovation involves the synthesis of zeolite membranes from the source of kaolin. In the first step, the kaolin was calcined at 700 C to the metakaolinite phase. As a second step, the zeolitisation experiments have been carried out under hydrothermal conditions. The metakaolinite obtained has been reacted with NaOH solutions in autoclaves at 100C. The second innovation to membrane synthesis was based on Self-supported zeolite membranes. Synthesis of nano NaA zeolite membrane from tubular extruded of kaolin was investigated. In the first step, kaolin has been calcined at 500-850 C to the metakaolinite phase. As a second step, the zeolitisation experiments have been carried out under hydrothermal conditions. The metakaolinite obtained has been reacted with NaOH solutions in autoclaves at 100C. X-ray diffraction (XRD) patterns of the membranes exhibited peak corresponding to the zeolite. The morphology of the support and membrane subjected to crystallization was characterized by Scanning electron microscopy (SEM). Separation performance of the NaA membranes was evaluated using pervaporation (PV) of water–organic mixtures. The membranes showed high water selectivity in the water–organic mixtures.
A novel approach to fabricate zeolite membranes for pervaporation processes
2015
The conventional methods used in preparing zeolite membranes, such as the secondary growth and in situ crystallization methods, involve long and complex procedures that require the preparation of the zeolite aluminosilicate gel prior to the fabrication process and often result in membranes which contain pin holes. Here we report a simple, cheap, and less time-consuming technique to fabricate zeolite A and mordenite membranes on a porous stainless steel support. In addition, the technique makes it possible to fabricate types of zeolite membranes that have been previously difficult to synthesise. A clinoptilolite membrane was fabricated to demonstrate the ability to manufacture a zeolite membrane from an existing crystalline zeolite (natural or synthetic). All three membranes were subjected to separation tests, (ethanol dehydration, ethanol-cyclohexane and phenol removal from water) to demonstrate the efficacy of membrane synthesis. The fluxes obtained and separation factors which were achieved are comparable with literature values but as with most zeolite membranes there is a trade-off between high flux and separation. Experimental Membrane preparation The overriding aim of the work is to produce a simple and repeatable method of producing zeolite membranes. The method which has been developed can be summarised as
Journal of the American Ceramic Society, 2013
Zeolite NaA membranes were prepared hydrothermally by secondary crystallization process at different temperatures (55°C-75°C) on porous a-alumina-based support tubes (inner side) precoated with poly(ethyleneimine) (PEI) buffer layer and NaA seed particles. The NaA seed crystals synthesized at 65°C /2 h in the size range 100-200 nm having BET surface area of 71.57 m 2 g À1 were used for secondary crystallization of the membranes. The secondary crystallization at 65°C for (4 + 4) h (double-stage) showed highly dense NaA grains in the microstructure of the membrane with a thickness of 5 lm. It rendered the permeance values of 50.6 3 10 À8 , 2.47 3 10 À8 , and 0.55 3 10 À8 molm À2 s À1 Pa À1 for H 2 , N 2 , and CO 2 , respectively, with their permselectivity of 20.48 (H 2 / N 2 ), 92 (H 2 /CO 2 ), and 4.49 (N 2 /CO 2 ). A tentative mechanism was illustrated for the interaction of PEI with the support substrate and NaA seed crystals.
Production and Characterization of Zeolite Membrane
2012
The use of bioethanol as an alternative fuel with a purity of more than 99.5% wt has prompted research on bioethanol purification. One of the promising methods used for bioethanol purification is pervaporation membrane. This research is aimed to prepare and characterize zeolite membranes for pervaporation membrane. The membrane preparation consisted of two stages, namely support preparation and zeolite deposition on the support. In support preparation, α alumina and kaolin with spesific composition (50:30; 40:40; 50:30) was mixed with additives and water. After pugging and aging process, the mixture became paste and extruded into tubular shape. The tube was then calcined at temperature of 1250 °C for 3 hours. After that, zeolite 4A is deposited on the tubes using clear solution made of 10 %wt zeolite and 90 %wt water and heated at temperature of 80 °C for 3 hours. Furthermore, the resulting zeolite membranes was washed with deionized water for 5 minutes and dried in oven at temperature of 100 °C for 24 hours. Characterization of zeolite membranes included mechanical strength test, XRD, and SEM. In the mechanical strength test, the membrane sample with alumina:kaolin = 50:30 (#membrane A#) has the highest mechanical strength of 46.65 N/mm 2. Result of XRD analysis for the membran A indicated that mullite and corundum phases were formed, which mullite phase was more dominant. Meanwhile the result of SEM analysis shows that zeolite crystals have been formed and covered the pores support, but the deposition of zeolite has not been optimal yet. The performance examination for bioethanol purification showed that the membrane could increase the purty of bioethanol from 95% to 98% wt.
Optimization of conditions for the preparation of zeolite HS membrane
Effects of synthesis parameters on the membrane structure and performance have been investigated for Nano pore Hydroxysodalite (HS) zeolite membranes grown onto seeded mullite supports. Molar composition of the starting gel of HS zeolite membranes was SiO2/Al2O3=1.0-5.0, Na2O/Al2O3=15-65, and H2O/Al2O3=500-1500. In addition, Effects of crystallization time and temperature on the membrane performance were studied. X-ray diffraction (XRD) patterns of the membranes exhibited peaks corresponding to the support and the zeolite. The crystal species were characterized by XRD and morphology of the supports subjected to crystallization was characterized by Scanning electron microscopy (SEM). Separation performance of HS zeolite membranes was studied for water-Ethanol mixtures using pervaporation (PV). The membranes showed good selectivity towards water in the water-Ethanol mixtures. Water permeates faster because of its preferential adsorption into the Nano-pores of the hydrophilic zeolite membrane. In PV of water-Ethanol mixtures, the membrane exhibits a hydrophilic behavior, with a high selectivity towards water and a good flux. The best Flux and separation factor of the membranes were 2.05 kg/m 2 .h and 10000, respectively. Effects of operation condition (temperature, rate and pressure) on the membrane performance have been investigated for HS zeolite membranes grown onto seeded mullite supports.
Microporous and Mesoporous Materials, 2011
The hydrothermal synthesis of intermediate-silica CHA-type zeolite membranes from the precursor mixtures containing single K + alkali cations was studied in detail under different conditions, including the influencing factors of silica source, the crystallization temperature, water concentration and gel alkalinity of the initial gels. Additionally, CHA-type zeolite membranes were also prepared tentatively by the interzeolitic transformation method. The pervaporation (PV) measurements on these resulting CHA-type membranes for the dehydration of alcohol aqueous solutions were performed to investigate the quality of these membranes. As a result of these pervaporative studies, the optimal synthetic recipe was formulated with an optimized crystallization temperature spanning from 130 to 150°C. The PV data showed that the separation performances of CHA membranes obtained were strongly dependent on the type of silica source employed with Ludox HS-30 being the optimal silica source. Furthermore, synthetic temperature had a strong influence on the morphology of the resultant CHA membranes. Under the optimized synthetic condition, the total permeation flux and separation factor of a representative membrane were 2.20 kg/m 2 h and 3900, respectively, for the separation of 10 wt.% H 2 O/EtOH mixtures at 75°C. The CHA membranes were characterized by X-ray diffraction, field emission-scanning electron microscopy and energy dispersive X-ray spectroscopy.