Tubular Alumina Support Research Articles

Exfoliation of lamellar SAPO-34 zeolite to nanosheets and synthesis of thin SAPO-34 membranes by a nanosheet-seeded secondary growth approach

High-aspect-ratio SAPO-34 nanosheets were fabricated by exfoliation of lamellar SAPO-34 zeolite using a solvent-mediated freeze-thaw method for the first time. A novel biomass-based organic structural directing agent (OSDA) together with triethylamine was used to induce the formation of lamellar SAPO-34 zeolite. These nanosheets had a thickness of several nanometers and aspect ratio as high as 230–560. A thin nanosheet layer with thickness less than 100 nm was deposited on the surface of tubular alumina support. High-quality SAPO-34 thin membranes were reproducibly synthesized after nanosheet-seeded secondary growth. Four SAPO-34 membranes prepared under the optimized synthesis conditions displayed average CO2 permeance of (2.5 ± 0.40) × 10-6 mol/(m2 s Pa) [equals to 7500 ± 1200 GPU, 1 GPU = 3.34×10-10 mol/(m2 s Pa)] with average CO2/CH4 selectivity of 102 ± 12.6 in an equimolar CO2/CH4 mixture at room temperature and 0.2 MPa feed pressure.

ZIF-8 tubular membrane for propylene purification: Effect of surface curvature and zinc salts on separation performance

A continuous and defect-free ZIF-8 membrane was successfully grown on a positive surface curvature of a porous tubular alumina support that was prepared from zinc nitrate precursor solution at 120 °C for 4 h of synthesis time. The membrane produced the highest propylene permeation of 198 × 10−10 mol⋅m−2⋅s−1⋅Pa−1 and moderate separation factor of 48. Despite its modest level of separation factor, the membrane was able to enrich propylene from 50 vol%. to 98 vol% from a binary feed mixture containing equal flowrate of propylene and propane. The high purity however came with low propylene recovery of merely 5% because there was a trade-off between the separation factor and permeance as a result of an inversed relationship between the two.

High-performance SAPO-34 membranes for CO2 separations from simulated flue gas

Abstract High-quality SAPO-34 membranes were fabricated by the secondary growth method on outside asymmetric tubular alumina supports. The effects of temperature, pressure and feed flow rate on the separation performance of SAPO-34 membranes were investigated for CO2 separations from simulated flue gas. Single CO2, N2 and CH4 permeances were predicted by Maxwell-Stefan diffusion model, and the predictions were fit well with experimental data. The unexpected high CO2/N2 selectivities were 170 and 110 with high CO2 permeances of ~1.38 × 10−6 mol/(m2 s Pa) (=4120 GPU) through our SAPO-34 membrane for equimolar and 15/85 (vol/vol) CO2/N2 mixtures at 243 K and 0.1 MPa pressure drop, respectively. The membrane also displayed a CO2 permeance of 4.67 × 10−7 mol/(m2 s Pa) (=1390 GPU) and a CO2/N2 selectivity of 10.3 in a dry 15/85 (vol/vol) CO2/N2 mixture at 423 K. The moister in feed gas (0.68 mol% water vapor) decreased CO2 permeance and CO2/N2 selectivity by only 19.3% and 14.9% in a wet 15/85 (vol/vol) CO2/N2 mixture at 423 K, respectively, compared to those in the dry mixture. The separation performance could be recovered to the original values after drying. The current SAPO-34 membranes were far beyond the upper bound of zeolite membranes in CO2/N2 plots and showed potential applications in CO2 separations from power-plant flue gas.

Preparation of CHA zeolite (chabazite) crystals and membranes without organic structural directing agents for CO2 separation

CHA zeolite (chabazite) crystals and membranes were prepared from organic structural directing agents-free (OSDA-free) gels. Chabazite membranes were grown on the tubular alumina supports. The effect of cesium and fluoride salts on the crystallization of chabazite crystals and membranes were investigated. Highly crystalline chabazite and uniform chabazite membranes were only obtained from the gel containing the cesium and fluoride salts. Single CO2, N2 and CH4 permeances and mixed gas separations in CO2/N2 and CO2/CH4 binary mixtures through chabazite membranes were measured. Temperature and pressure affected the permeances and separation selectivities in two mixtures. The best membrane showed CO2/N2 and CO2/CH4 separation selectivities as high as 16 and 46 together with CO2 permeances of ~ 1.0 × 10-7 mol/(m2 s Pa) at a high temperature of 473 K in equimolar dry CO2/N2 and CO2/CH4 binary mixtures, respectively. The CO2/N2 and CO2/CH4 selectivities lost only 11% and 15%, and CO2 permeances lost only 18% and 20% in equimolar wet CO2/N2 and CO2/CH4 mixtures (8% in mole of water vapor) at 473 K compared to these values in dry mixtures, respectively. The OSDA-free chabazite membranes were hydrothermally stable in the presence of vapor water for 4 d at 378 K.

Corrosion behavior analyses of metallic membranes in hydrogen iodide environment for iodine-sulfur thermochemical cycle of hydrogen production

HI decomposition in Iodine-Sulfur (IS) thermochemical process for hydrogen production is one of the critical steps, which suffers from low equilibrium conversion as well as highly corrosive environment. Corrosion-resistant metal membrane reactor is proposed to be a process intensification tool, which can enable efficient HI decomposition by enhancing the equilibrium conversion value. Here we report corrosion resistance studies on tantalum, niobium and palladium membranes, along with their comparative evaluation. Thin layer each of tantalum, palladium and niobium was coated on tubular alumina support of length 250 mm and 10 mm OD using DC sputter deposition technique. Small pieces of the coated tubes were subject to immersion coupon tests in HI-water environment (57 wt% HI in water) at a temperature of 125–130 °C under reflux environment, and simulated HI decomposition environment at 450 °C. The unexposed and exposed cut pieces were analyzed using scanning electron microscope (SEM), energy dispersive X-ray (EDX) and secondary ion mass spectrometer (SIMS). The extent of leaching of metal into liquid HI was quantified using inductively coupled plasma-mass spectrometer (ICP-MS). Findings confirmed that tantalum is the most resistant membrane material in HI environment (liquid and gas) followed by niobium and palladium.

Controlling the size and shape of Mg-MOF-74 crystals to optimise film synthesis on alumina substrates

Mg-MOF-74 is a metal organic framework with the highest CO2 adsorption capacity of any porous material. Therefore, it has been suggested for CO2 separations as both an adsorbent and incorporated into membranes. Design of the Mg-MOF-74 crystal morphology is important to expand the applicability of the material. In this paper one step synthesis of Mg-MOF-74 films has been achieved by controlling the Mg-MOF-74 crystal morphology. Results show that increasing the fraction of ethanol and water in the reaction solution relative to dimethyl formamide (DMF) increases the size of the crystals produced, while resulting in a subsequent drop in yield. By using solvent composition to control the Mg-MOF-74 crystal size and shape the synthesis of Mg-MOF-74 thin films was achieved in one step, without the need for seeding. Films could be produced as thin as 1 μm, ten times thinner than any other previous membranes in the M-MOF-74 series, in a fraction of the time (only 2.5 h). Thicker films (up to 14 μm) could also be produced by increasing the fraction of ethanol and water in reaction solution, offering a methodology by which the thickness of Mg-MOF-74 membranes can be controlled. Films were produced on porous tubular alumina supports, and single gas measurements were conducted resulting in a CO2 permeance of 7.4 × 10−7 mol m−2 s−1 Pa−1 and an ideal CO2/CH4 selectivity of 0.5.

CO2/N2 separation using alumina supported membranes based on new functionalized ionic liquids

Abstract In the present work, supported liquid membranes based on three ionic liquids (ILs) (1-(2-aminoethyl)-3-methylimidazolium trifluoromethanesulfonate ([AEMIm]Tf), 1-(2-aminoethyl)-3-methylimidazolium tetrafluoroborate ([AEMIm]BF4) and trioctylmethylammonium anthranilate ([TOMA])), used as mobile phases, were studied in the separation of carbon dioxide from nitrogen. The IL chemical structures and thermal properties were confirmed by spectroscopic techniques and thermogravimetric analysis (TGA), respectively. The IL homogeneous distribution of the impregnation on alumina tubular supports was determined by scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). Permeation tests were carried out using pure gases at 30 °C and 1 bar. The amino-functionalized ILs, two of them in the cation, [AEMIm]BF4 and [AEMIm]Tf, and the other one in the anion, [TOMA]An, reacted with CO2, leading to the formation of carbamates. [TOMA]An, which has the amine group at the anionic part, showed the best permselectivity, reaching a selectivity of 70.

Performance of zeolite powder and tubular membrane having different Si/Al ratio for removing As(III) in aqueous phase

AbstractThree different types of zeolite having pore sizes in the range 0.26‐0.74 nm, (NaP, NaA, and NaY) powders and membranes are synthesized with different Si:Al ratio on low cost clay alumina tubular support. The results of the permeation and separation studies showed that the NaP zeolite powder and membrane removes maximum As(III) from the water solution (more than 80%) compared to other zeolites. The removal of As(III) to achieve drinking water standard, by zeolite membrane, in a single step process does not seem to have been reported before the present investigation. These are the novelty achieved.

Separation of Helium from Gases Using the Synthesized Hydroxy Sodalite Membrane

The goals of this work are to synthesize and evaluate the potential of hydroxy sodalite membrane in the separation of helium from natural gas. Sodalite membrane was synthesized via direct hydrothermal method (conventional heating) on tubular alumina support. It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeation using helium and N2. After drying of the membrane, permeances of single gases were found to be of the order Helium > CH4 > N2 > CO2 at low temperatures and the membrane was impermeable to N2, CO2 and CH4 at high temperatures (>85 °C). In the investigated range of temperature 35-180 °C, membrane performance tended to high selectivity. The maximum separation factors (helium/N2 ~ 8.8, helium/CO2 ~ 16.5 and helium/CH4 ~ 5) with acceptable permeance were observed at 85 °C.

Influence of Zeolite Protective Overlayer on the Performances of Pd Thin Film Membrane on Tubular Asymmetric Alumina Supports

The role of zeolite overlayer in the performance of Pd thin film membranes on asymmetric alumina tubular supports is analyzed. These novel multilayer membranes have a ceramic base support (asymmetric α-Al2O3 tubes) on which a crack-free Pd dense thin film was deposited by electroless plating deposition followed by creation of a further zeolite (titanium silicalite, TS-1) membrane compact layer on the top of the Pd thin film. The TS-1 layer was prepared by a two-step procedure: (i) the preseeding with TS-1 nanocrystals by dip-coating, eventually assisted by a polymer (PEI or PDADMAC), followed by (ii) a secondary growth. The composite membranes are crack-free and homogeneous, and show good mechanical properties, in terms of adhesion between metallic film and substrate, and between the zeolitic film and Pd thin film. The composite membranes were evaluated in terms of H2 permeance with respect to bare Pd membrane. The zeolite overlayer induces a change in the rate-limiting step in H2 transport, due to the pa...

Hydrogen permeation through palladium membranes and inhibition by carbon monoxide, carbon dioxide, and steam

Palladium membranes are being developed for the separation of hydrogen from syngas in industrial applications. However, syngas constituents carbon monoxide, carbon dioxide, and steam are known to adsorb at the membrane surface and inhibit the permeation of hydrogen. The current study combines an experimental study and modelling approach in order to investigate and quantify the inhibition effects. Experiments have been performed with a 2.8μm thick palladium membrane (surface area 174cm2) on a tubular alumina support, including systematic variation of the concentrations of carbon monoxide, carbon dioxide, and steam at 22bar total pressure and 350–450°C. Carbon monoxide and steam inhibit hydrogen permeation. No significant effect has been found for carbon dioxide, except indirectly by carbon monoxide produced in situ from carbon dioxide. A constriction resistance model has been derived, explicitly relating the decrease in surface coverage by adsorbed hydrogen to the ensuing decrease in transmembrane flux. Very high surface coverages by inhibiting species θi>0.995 are predicted. The results highlight that inhibition effects are greatly reduced at high hydrogen partial pressures due to competitive adsorption. Due to the lateral diffusion of permeating hydrogen atoms in the metallic membrane, the thickness of the palladium membrane strongly determines the extent to which surface coverage by non-hydrogen species causes a decrease in hydrogen transmembrane flux. Depending on the operating conditions, membranes are predicted to have an optimal minimum thickness below which an increased intrinsic permeance is offset by an increased impact of inhibition.

Synthesis of mono- and bi-layer MFI zeolite films on macroporous alumina tubular supports: Application to nanofiltration

This work is dedicated to the development of MFI-type structure zeolite films (single-layer or bilayer) on the internal layer of a specific macroporous alumina tubular support for nanofiltration applications. The bottom MFI layer was obtained by direct hydrothermal synthesis while a secondary growth method was used for the top MFI layer. A complete characterization of the obtained MFI membranes (single-layer or bilayer) is proposed using various techniques, such as X-ray diffraction, scanning electron microscopy, mercury porosimetry and nitrogen sorption measurements. Dense and highly crystallized films of MFI-type structure zeolite were obtained for both single-layer and bilayer MFI films. The total film thickness were around 7.1±0.5μm and 14.5±1μm for single-layer and bilayer MFI films respectively. The Si/Al molar ratio of the MFI films varied between 185 and 305 for single-layer and bilayer MFI films respectively. The hydraulic permeability of the tubular MFI membrane was achieved by the filtration of pure water. The hydraulic permeability of the single-layer and bilayer MFI membranes decreased rapidly at the beginning of the conditioning process, and stabilized at 1.08×10–14m3m−2 and 1.02×10–15m3m−2 after 15h and the rejection rates of neutral solute (Vb 12) are 10% and 50% for the single-layer and bilayer MFI films respectively.

Preparation and Characterization of Inorganic Membranes for Hydrocarbon Separation from N2 for Environmental Applications

This paper reports the preparation and characterization of gas transport using tubular alumina support and silica membrane for propylene (C3H6) and nitrogen (N2) separation. Dip-coating technique was employed to deposit silica on the support after which the membrane was heat treated at 65 0C. Nitrogen adsorption measurements reveal that this membrane possesses mesostructure with pore diameter of 3.940 nm and BET surface of 0.484 m2/g. Scanning electron microscopy (SEM) studies show that the layers are defect free and energy diffraction x-ray analysis (EDXA) confirms the compositional element of silica. Propylene and nitrogen permeation tests also confirm that the membrane is defect free with C3H6/N2 selectivity of 1.79 higher than ideal Knudsen selectivity.

One-step coating and characterization of α-Al2O3 microfiltration membrane

An one-step coating α-Al2O3 microfiltration membrane without any intermediate layers was prepared directly on macroporous alumina tubular support by dip-coating. Coating suspension was obtained by dispersing α-Al2O3 powder (d50=100nm) in 1.8wt% boehmite sol followed by addition of PVA in determined weight percentage and 0.8g PVP. The hydrogen bondings of boehmite and PVA absorbed on the surface of α-Al2O3 particles lead to crosslinking acceleration and giant network formation. This impedes particles in the membrane forming suspension to infiltrate into the macroporous support. The morphology, pore size distribution and permeance of membrane were investigated. The crack-free membrane fired at 1300°C for 2h prepared using the suspension with 25vol% α-Al2O3 and 3.01wt% PVA has a permeance of 441Lm−2h−1bar−1 with the resistance of 9.55×1011m−1. The membrane has a narrow pore size distribution centered at around 0.27μm. Its largest pore size is about 0.3μm.

Novel polymeric membrane materials for ethanol/water separation via pervaporation

In this research, novel polybenzoxazine (PBZ) membranes, synthesized from bisphenol-A, formaldehyde and diamines, were coated on a tubular alumina support by dip-coating technique for ethanol purification application via pervaporation. The effects of dipping time and precursor concentration on the membrane preparation and the separation performance showed that both PBZ membranes were remarkably stable, resistant to swelling, and provided an impressively high separation factor of higher than 10,000 for all ethanol concentration ranges, characteristics implying that they could be a good candidate for high purity ethanol production.

A simple approach to uniform PdAg alloy membranes: Comparative study of conventional and silver concentration-controlled co-plating

An Ag-controlled co-plating method was developed for the preparation of palladium/silver alloy membranes on porous tubular alumina supports. By controlling the feed rate of Ag to the Pd bath, the concentration of the silver in the plating bath was restricted during the course of plating. As a result, preferential deposition of silver at the beginning was suppressed and uniform dispersion of silver inside the membrane with silver composition in the desired range was achieved. Ultrathin (∼2.5 μm) PdAg alloy membranes with uniform silver composition of ∼25% were successfully obtained. The membrane showed a hydrogen permeance of 0.88 mol m−2 s−1 and pure-gas H2/N2 selectivity of 2140 at 823 K with ΔP = 100 kPa. Only one hydride phase existed in the studied temperature range from 373 to 823 K with ΔPH2=100kPa. Direct comparisons with the conventional simply-mixed co-plating method showed that membranes made by the novel Ag-controlled co-plating method had much more uniform silver distribution, smoother surface, denser membrane structure, higher utilization rate of metal sources, and shorter alloying time.

Mesoporous carbon aerogel membrane for phospholipid removal from Jatropha curcas oil

Mesoporous carbon aerogel was successfully coated on the macroporous alumina tubular support to form the tubular carbon aerogel membrane via a sol gel process. The thickness and average pore size of the carbon aerogel membranes were approximately 10μm and 10nm, respectively. As compared to polymeric and ceramic membranes, the tubular carbon aerogel membrane combines the advantages of low cost, high mechanical strength and reuse. For the first time, the tubular carbon aerogel membrane was further used for the phospholipid removal from Jatropha oil provided for the application of biofuels. Furthermore, the decrease in the viscosity, water, carbon residue and phospholipid contents of Jatropha oil results from the successful removal of the gums and phospholipids during the degumming process; the rejection of the phospholipids was recorded to be around 80%. The as-prepared carbon aerogel membrane provides the possibility of the purification of bio-oil, resulting in its application as biofuels.

TUBULAR MFI ZEOLITE MEMBRANES MADE BY IN-SITU CRYSTALLIZATION

Polycrystalline MFI zeolite membranes were prepared on �-alumina tubular support by hydrothermal treatments at 413 K. The synthesized zeolite membranes were characterized by XRD, SEM and single gas permeation. The influence of hydrothermal treatment steps and the calcination time on the zeolite layer formation were investigated. MFI zeolite membrane prepared by four subsequent hydrothermal treatments and calcined at 673K for 30 h had optimum quality from morphological and crystalline point of view. The grown MFI zeolite layer was uniform with about 20 µm thickness and well-intergrown zeolite crystals.

Highly selective SAPO 34 membrane on surface modified clay–alumina tubular support for H2/CO2 separation

The formation and growth of Silicoaluminophosphate (SAPO 34) zeolite membrane was developed on the low cost indigenous clay–alumina tubular substrate modified by cationic polymer as an intermediate layer. The amino (–NH2) and hydroxyl (–OH) groups on the backbone of polymer are responsible for hydrogen bonding between zeolite surface and support surface. Seeding of the support surface accelerates the zeolite crystallization and enhances the formation of homogenous SAPO 34 membrane layer. The seeds were synthesized by hydrothermal process and used to provide nucleation for the membrane growth. The synthesized membranes along with seed crystals were characterized by XRD, FTIR, FESEM, TEM and EDAX analysis. The performance of the membrane formed was evaluated by single gas as well as mixture gas permeation measurement for H2 and CO2. The H2/CO2 separation selectivity of the membrane increased upto 5.88 at room temperature which is more than reported values and the reproducibility towards gas permeation and selectivity of SAPO 34 membrane shows excellent result.

Long term performance cobalt oxide silica membrane module for high temperature H2 separation

Here we show the long term performance at high temperatures of a multi-tube module containing 8 membranes in 4 parallel lines with a total of 545 cm2 area. The membranes were prepared via thin film dip coating of cobalt oxide silica (CoOxSi) sol–gel on tubular alumina supports. A preliminary study found that the sol–gel containing 20 mol% cobalt oxide formed the best microporous structure with the highest surface area and pore volume. All resulting membranes delivered permeances of ∼1 × 10−7 mol m−2 s−1Pa−1 at 500 °C, indicating a high repeatability for the membrane fabrication process. The permselectivities of helium (He) and hydrogen (H2) over carbon dioxide (CO2) and nitrogen (N2) increased from 10–20 at 100 °C to values close to 1000 at 500 °C. Additionally, the apparent energies of activation (Eact) for the smaller kinetic diameter gases He and H2 at 12.2 and 19.5 kJ mol−1 were high and contrary to the negative values for larger gases N2 and CO2 at −1.8 and −7.4 kJ mol−1. These remarkable results were attributed to the molecular sieving mechanism of the microporous silica which was enhanced by the embedding of cobalt oxide into the matrix, delivering structural control with an average pore size of 3 Å. The Eact for H2 permeance was higher than that of He, indicating that the cobalt oxide played an important role in H2transport. Two membrane lines performed exceptionally well for binary gas mixture processing with H2 purity reaching values close to 100% in the permeate stream for argon (Ar) concentrations of up to 80% in the retentate stream. A major finding here is that the binary gas selectivity was independent of temperature, contrary to the permselectivity observed for single gas permeance. Further, the H2 flow rate was greatly affected by the concentration of Ar in the mixture, while the temperature dependency played only a marginal role. In particular, competitive adsorption in the percolative pathways containing pore constrictions or bottlenecks of the anisotropic CoOxSi matrix allowed Ar to impede H2 diffusion. Finally, the CoOxSi membranes proved thermally stable and robust for 2000 h of testing for various thermal cycles up to 500 °C.