Article

The Effect of Hydrotalcite Content in Microporous Composite Membrane on Gas Permeability and Permselectivity

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Abstract

Microporous silica membrane containing hydrotalcite (HT) was prepared successfully without losing the former’s molecular sieving property. The microporous HT-silica membrane (200 nm in thickness) was formed on the surface of mesoporous γ-alumina layer (9 μm in thickness) and supported by macroporous α-alumina substrate (ca. 2 mm in thickness). The pore size of the microporous HT-silica membrane was 8.5Å, slightly larger than the pristine silica membrane (5Å). The composite membrane was found to enhance the permeability of gases and permselectivity of carbon dioxide from gas mixture comprising methane, hydrogen or nitrogen. Microporous HT-silica membrane with 15 vol.% HT displayed the highest permselectivities in the order of CO2/CH4 > CO2/N2 > CO2/H2 and the permselectivities decreased with increasing HT content.

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... Recently, capturing of CO 2 has increased attention by researchers work due to release high amount of CO 2 to the atmospheric compared to other greenhouse gases [3]. There are a several of separation processes that can be applied successfully to separate CO 2 from gas streams include physical and chemical absorption [1,4], permeation through organic and inorganic membranes [5,6], adsorption [7] and cryogenic distillation [8]. Currently, chemical absorption of CO 2 into alkanolamines solutions has been favored method of the purification processes in the commercial industry [9]. ...
... In this research the fabrication of novel membrane from HT material modified microporous silica membranes to increase the separation selectivity of CO2 from synthesis gas is a subject of this study. Modification of the internal pore surface of silica membrane with HT increases the amount of adsorbed CO2 resulting in increase of the CO2 diffusion and separation selectivity [11][12]. The composite membrane of HT-silica is expected to provide high CO2 permeance due to the surface affinity of HT to CO2 gas and adequate separation factor. ...
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A novel thin microporous composite membrane of a dual-element hydrotalcite-silica was prepared on porous alumina support by sol-gel method. Strong CO2 adsorption on hydrotalcite material inhibited the diffusion of H2 through the membrane and decreased H2 permeances significantly so that CO2 preferentially permeated. The effects of pressure difference across the membrane, operating temperature and CO2 feed concentration on the CO2 separation performance of the membrane were investigated using synthetically mixed gas. The CO2 permeance and CO2/H2 separation selectivity decreased with increasing the temperature due to the loss of the membrane ability for CO2 adsorption with temperature. Further increase of the pressure difference across the membrane decreased both CO2 permeance and CO2/H2 separation selectivity. The CO2 feed concentration with 40% showed the best performance with a CO2/H2 separation selectivity of 10.59.
... Although bulk and Knudsen diffusions are particularly useful for mass transport in macro and meso-porous materials, the surface affinity mechanism is reportedly predominant and substantially influential in microporous materials with pore size smaller than 1 nm [22][23][24][25]. The experimental permeability of H 2 gas across mesoporous Al 2 O 3 (alumina) was obtained previously [26,27]. The gas flowed across a membrane disc (250 mm diameter, 30 mm thickness). ...
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Colloidal silica particles, grown on a mesoporous silica layer using macroporous alumina substrate as a support, were used to separate hydrogen from carbon dioxide. The particles transformed into rectangular interlocking silicalite-1 structures with size approximately 8 × 4 × 4 μm, oriented epitaxially with film thickness of ca. 22 μm. The silicalite-1 particles grew in size due to the effect of structure directing agent (SDA), Oswald ripening and hydrothermal synthesis that promoted the growth of the colloidal particles into crystals. Permeation experiment using silicalite-1 showed that CO2 flux decreased and H2 flux increased with increase in temperature. The separability of H2 that was unity at the lower temperature became increased in value as the temperature was raised.
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Intercalated materials containing iron and carbonate species were synthesized in this work to study their hydrolysis and condensation from sol to gel transition. The former material was designated as PV (perovskite) and the latter HT (hydrotalcite). Another sample containing neither of the indicated ions was designated as AlMg(OH)5 (aluminum magnesium hydroxide). The conversion energy of these materials for the hydrolysis and condensation reaction during the transition was estimated to be≈14cal/mol, much lower than the hydration energy of 10–14kcal/mol computed using molecular dynamic simulation from the previous work. The energy consumed was interpreted as equivalent to the drop of temperature due to the endothermic reaction. PV material exhibited the highest swelling ratio, amounting to 76% from its dried weight, demonstrating its ability to intercalate water readily. HT sample, on the other hand, was completely saturated and did not dilate.
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Yttria-doped zirconia and pure zirconia membranes were prepared with sol-gel method using zirconium oxychloride octahydrate (ZrOCl28H2O) as starting material. Characterization for membranes was performed by means of BET, TG-DTA, SEM, XRD, FT-IR and Raman spectroscopy. Stable tetragonal phase and pore structure in yttria-doped zirconia membranes were observed at 400–700C. And, phase transformation temperature can be retarded to 300C. As a result, yttria doping can be developed as a method to secure the membrane from cracking in preparation process and high temperature applications.
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The hydrothermal stability of microporous (0.6 nm) silica membranes prepared by the sol-gel process was studied at 600 and 800 C in a 50 mol% steam atmosphere. The membranes remained microporous after calcination and hydrothermal treatment at 600 C for 30 h but a substantial reduction in the specific surface area (48%) accompanied by a 77% decline in the micropore volume was observed. Hydrothermal treatment at 800 C for 30 h resulted in complete densification of the membranes. The effect of alumina and magnesia on the hydrothermal stability of the membranes was investigated. Both Al2O3 and MgO were introduced into the membranes by doping the starting silica sol with controlled amounts of the corresponding nitrate salts. Alumina did not change the pore structure of the silica membranes which retained a large part of their microporosity after hydrothermal treatment at 600 C compared to pure silica membranes. Doping with magnesia, however, resulted in lower specific surface areas relative to those of pure and alumina-doped silica membranes after drying and calcination. These effects on the stability of the membranes are explained by assuming structural changes in the membranes catalysed by magnesia.
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Palladium bis(2,2,6,6-tetramethyl-3,5-heptanedionate), a structurally well defined O-containing transition metal complex, is reported to be an efficient catalyst for alkoxycarbonylation and aminocarbonylation reactions under milder operating conditions. The system tolerated the carbonylative coupling of various aryl halides with phenol/alcohol and amines, providing good to excellent yields of desired products under optimized reaction conditions. Copyright
Predominant gas transport in microporous hydrotalcite-silica membrane. Transport Porous Med., DOI:10.1007/s1124201302618. Downloaded by
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Othman, M.R. (2013) Predominant gas transport in microporous hydrotalcite-silica membrane. Transport Porous Med., DOI:10.1007/s1124201302618. Downloaded by [University of Colorado at Boulder Libraries] at 09:50 03 January 2015