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1.
Mesoporous silica membranes were prepared on porous alumina substrates by a vapor infiltration of tetraethoxysilane (TEOS) into a non-ionic poly(oxyethylene) (Brij56) surfactant film. Periodic mesostructured silica membranes were formed on both α- and γ-alumina substrates pre-treated with polystyrene. The polystyrene polymer plugged the pores of the alumina substrates and inhibited the deposition of silica in the alumina pores, resulting in the formation of a very thin silica membrane without a silica/alumina composite layer at the interface between mesoporous silica and the alumina substrates. The calcined mesoporous silica membrane showed very high nitrogen permeance (>10−6 mol m−2 s−1 Pa−1). The single gas permeation was governed by the Knudsen diffusion mechanism. The durability of the mesoporous silica membrane against moisture in air was improved by a silylation with trimethylethoxysiliane.  相似文献   

2.
We present a new processing scheme for the deposition of microporous, sol–gel derived silica membranes on inexpensive, commercially available anodic alumina (Anodisk™) supports. In a first step, a surfactant-templated mesoporous silica sublayer (pore size 2–6 nm) is deposited on the Anodisk support by dip-coating, in order to provide a smooth transition from the pore size of the support (20 or 100 nm) to that of the membrane (3–4 Å). Subsequently, the microporous gas separation membrane layer is deposited by spin-coating, resulting in a defect-free dual-layer micro-/mesoporous silica membrane exhibiting high permeance and high selectivity for size selective gas separations. For example, in the case of CO2:N2 separation, the CO2 permeance reached 3.0 MPU (1 MPU = 10−7 mol m−2 s−1 Pa−1) coupled with a CO2:N2 separation factor in excess of 80 at 25 °C. This processing scheme can be utilized for laboratory-scale development of other types of microporous or dense inorganic membranes, taking advantage of the availability, low cost and low permeation resistance of anodic alumina (or other metal oxide) meso- and macroporous supports.  相似文献   

3.
In this work we investigate the performance of high flux chemical vapour deposition (CVD) silica membranes for the separation of gas mixtures containing H2 and CO2 at various temperatures. The membranes were prepared by a counter diffusion CVD method where tetraethyl orthosilicate (TEOS) and O2 were used as reactants. Single gas permeation resulted in activated transport for the smaller kinetic diameter gases (H2 and He) whilst the larger kinetic diameter gases (CO2 and N2) showed negative activation energy. The single gas permeation of H2 increased from 5.1 × 10−7 to 7.0 × 10−7 mol m−2 s−1 Pa−1 in the temperature range 100–400 °C, and H2/CO2 and H2/N2 selectivities reached 36 and 57 at 400 °C, respectively. The H2 purity in the permeate stream also increased with temperature for H2:CO2 binary gas mixture, thus being beneficial for H2 diffusion. H2 competitively permeated through the membrane at a several range of gas mixtures, and a saturation level was achieved at H2:CO2 60:40 feed concentration, where the diffusion of CO2 molecules became negligible delivering ∼99% H2 purity in the permeate stream. These results substantiate that the counter diffusion CVD method produced thin silica film membranes with a very precise pore size control, in particular suggesting a narrow pore distribution with average pore radius of about 3.1 Å.  相似文献   

4.
NaA zeolite membranes were synthesized on an asymmetric porous alumina support with a lower mass-flow resistance for development of more economically feasible membranes with higher permeation performance. The support influence on permeation fluxes through the membrane using asymmetric support was investigated by vapor permeation at 100–145 °C in a mixture of water (10 wt.%)/ethanol (90 wt.%) in which the higher permeation fluxes up to 37 kg m−2 h−1 or water permeances up to 3.2 × 10−6 mol m−2 s−1 Pa−1at 145 °C were observed. The performance was higher than those in the previously reported NaA membrane on a monolayer porous alumina support of 31 kg m−2 h−1 or water permeances of 2.5 × 10−6 mol m−2 s−1 Pa−1at 145 °C. These results are experimental evidence to show the effect of asymmetric support utilization in membrane preparation on the higher membrane performance. The estimate of the pressure drop over the both types of support indicates that the improvement of higher permeation fluxes in the asymmetric type membrane could be attributed to the suppression of pressure drop in the support layer due to lower mass-flow resistance there.  相似文献   

5.
This paper presents structural and mechanical characterizations of microporous silica membranes for gas separation. The membrane separative layer is made of microporous silica–B2O3 produced via a sol–gel process. This layer of about 200 nm of thickness is deposited on the internal surface of a tubular asymmetric γ-alumina/α-alumina support. FTIR and Raman analyses indicate the presence of the boron in the silica net and the above methods in conjunction with 11B MAS NMR analyses of the samples indicate that boron is located mainly in the tetrahedral framework position. Such membranes present interesting gas separation properties at temperatures up to 500 °C and transmembrane pressures lower than 8 bar. He permeance values close to 10−10 kmol m−2 s−1 Pa−1 are obtained, associated with ideal selectivity α(He/CO2) which can reach 55. Mechanical properties of separative silica-modified layers are measured by nanoindentation and the coefficient of thermal expansion is obtained from pure material.  相似文献   

6.
For the first time a fluorinated polyoxadiazole doped with phosphoric acid as a proton-conducting membrane for operation at temperatures above 100 °C and low humidities for fuel cells has been reported. Fluorinated polyoxadiazole with remarkable chemical stability was synthesized. No changes in the molecular weight (about 200,000 g mol−1) can be observed when the polymer is exposed for 19 days to mixtures of sulfuric acid and oleum. Protonated membranes with low doping level (0.34 mol of phosphoric acid per polyoxadiazole unit, 11.6 wt.% H3PO4) had proton conductivity at 120 °C and RH = 100% in the order of magnitude of 10−2 S cm−1. When experiments are conducted at lower external humidity, proton conductivity values drop an order of magnitude. However still a high value of proton conductivity (6 × 10−3 S cm−1) was obtained at 150 °C and with relative humidity of 1%. In an effort to increase polymer doping, nanocomposite with sulfonated silica containing oligomeric fluorinated-based oxadiazole segments has also been prepared. With the addition of functionalized silica not only doping level but also water uptake increased. For the nanocomposite membranes prepared with the functionalized silica higher proton conductivity in all range of temperature up to 120 °C and RH = 100% (in the order of magnitude of 10−3 S cm−1) was observed when compared to the plain membrane (in the order of magnitude of 10−5 S cm−1).  相似文献   

7.
The line shape parameters of water vapour rovibrational transition at 12145.444 cm−1 belonging to the (2ν1 + ν2 + ν3) overtone band in the presence of three buffer gases He, N2 and CO2 are studied by high resolution near infrared (NIR) diode laser spectrometer. The wavelength modulation spectroscopy (WMS) is adopted to probe buffer gas broadened first derivative (1f) signal of water vapour transition. The simulation of the experimental signals based on Voigt profile provides the collisional broadening coefficients and line strength parameters. The comparison is made between the broadening effects on water vapour transition induced by He, N2 and CO2.  相似文献   

8.
The effect of silica nanoparticles on the gas separation properties of ethylene vinyl acetate (EVA) copolymer containing 28% vinyl acetate has been investigated. The EVA and hybrid EVA–silica membranes were prepared via thermal phase inversion method. Silica nanoparticles prepared by hydrolysis of tetraethylorthosilicate (TEOS), through the sol–gel mechanism. The prepared membranes were characterized using FT-IR, SEM, DSC and XRD methods. FT-IR and SEM results indicated the nanoscale dispersion of silica particles in polymer matrix. As confirmed by XRD and DSC analyses, increasing the silica content enhances the amorphous regions significantly. Gas permeation of EVA–silica nanocomposite membranes with silica contents of 5, 6 and 10 wt.% was studied for N2, O2, CO2 and CH4 single gases at pressures of 4, 6 and 8 bar. The obtained results suggest a significant increase in permeability of all gases and an increase in CO2/N2 and CO2/CH4 gases selectivities upon increasing the silica content. The possible reasons for such behavior were stated and discussed. The pressure dependence of the gas permeabilities of the membranes was also investigated.  相似文献   

9.
Poly(dimethylsiloxane) (PDMS)-HTiNbO5 nanocomposite membranes with various HTiNbO5 nanofiller content were prepared by melt intercalation. WAXS diffraction measurements and TEM observations have suggested that the HTiNbO5 mineral was exfoliated in the PDMS matrix. The influence of the filler in the membrane was evaluated by water diffusion, gas permeation (CO2, N2, O2, ethane and ethylene), toluene pervaporation and by CO2 sorption measurements.A filler content of only 2 wt.% in PDMS-HTiNbO5 nanocomposite membranes slows down the water diffusion significantly, and a filler content of 5 wt.% reduces also the permeability of the films for toluene. The addition of a filler content up to 10 wt.% do not significantly influences the gas permeability (P) except for CO2. The PDMS matrix appears to be highly permeable and, therefore, a decreasing effect on P is only marked for a very high HTiNbO5 content. This effect is more pronounced for CO2, the P value of which decreases by 80% when the amount of nanofiller is 40 wt.%. The sorption measurements show that the interaction between CO2 and PDMS is weak (isotherms agree with Henry’s law). The filler decreases the solubility of CO2 in the films (S = 7.94 × 10−3 and S = 5.44 × 10−3 cm3 STPcm−3 film cmHg−1 for PDMS and PDMS-HTiNbO5 40 wt.%, respectively).  相似文献   

10.
NaA zeolite microfiltration (MF) membranes were prepared on α-Al2O3 tube by in situ hydrothermal synthesis method and investigated for water separation and recovery from oily water. NaA/α-Al2O3 MF membranes with average inter-particle pore sizes of 1.2 μm, 0.4 μm and 0.2 μm were prepared. The membranes were characterized by scanning electron microscope (SEM) and the inter-particle pore size distribution (PSD) was determined by gas bubble pressure method. Membranes with pore sizes of 1.2 μm (NaA1) and 0.4 μm (NaA2) were used to treat an oil-in-water emulsion containing 100 mg/L oil. Better than 99% oil rejection was obtained and water containing less than 1 mg/L oil was produced at 85 L m−2 h−1 by NaA1 at a membrane pressure of 50 kPa. Consistent membrane performance was maintained by a regeneration regime consisting of frequent backwash with hot water and alkali solution.  相似文献   

11.
An on-line system with vapour generation (VG) and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of free ammonium and organic nitrogen in agrochemical formulations containing hydrolyzed proteins. Commercial samples were digested, in batch mode, with sulphuric acid and the obtained solution was alkalinized on-line to transform the NH4+ to NH3 that was continuously monitored by FTIR. Free ammonium was determined in the same system after simple dilution of undigested samples with water. Different gas phase separators were assayed in order to introduce gaseous NH3 into a home made IR gas cell of 10 cm pathlength, where the corresponding FTIR spectra were acquired by accumulating 10 scans per spectrum. The 967.0 cm−1 band was used for the quantification of ammonia. The figures of merit of the proposed method involve a linear range up to 100 mg L−1, a limit of detection (3σ) of 1.4 mg L−1 of N, a limit of quantification (10σ) of 4.8 mg L−1 of N, a precision (R.S.D.) of 3.0% for 10 replicate determinations of a 10.0 mg L−1 of N and a sample measurement frequency of 60 h−1. The method was successfully applied to the determination of free ammonium and total N in commercial amino acid formulations and results compare well with those obtained by the Kjeldhal method.  相似文献   

12.
In this paper a novel solid phase extraction method to determine Co(II) and Ni(II) using silica gel-polyethylene glycol (Silica-PEG) as a new adsorbent is described. The method is based on the adsorption of cobalt and nickel ions in alkaline media on polyethylene glycol-silica gel in a mini-column, elution with nitric acid and determination by flame atomic absorption spectrometry. The adsorption conditions such as NaOH concentration, sample volume and amount of adsorbent were optimized in order to achieve highest sensitivity. The calibration graph was linear in the range of 0.5-200.0 ng mL−1 for Co(II) and 2.0-100.0 ng mL−1 for Ni(II) in the initial solution. The limit of detection based on 3Sb was 0.37 ng mL−1 for Co(II) and 0.71 ng mL−1 for Ni(II). The relative standard deviations (R.S.D.) for ten replicate measurements of 40 ng mL−1 of Co(II), and Ni(II) were 3.24 and 3.13%, respectively. The method was applied to determine Co(II) and Ni(II) in black tea, rice flour, sesame seeds, tap water and river water samples.  相似文献   

13.
SrCo1−yNbyO3−δ (y = 0.025–0.4) were synthesized for oxygen separation application. The crystal structure, phase stability, oxygen nonstoichiometry, electrical conductivity, and oxygen permeability of the oxides were systematically investigated. Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y = 0.025–0.2. However, the further increase in niobium concentration led to the formation of impurity phase. The niobium doping concentration also had a significant effect on electrical conductivity and oxygen permeability of the membranes. SrCo0.9Nb0.1O3−δ exhibited the highest electrical conductivity and oxygen permeability among the others. It reached a permeation flux of ∼2.80 × 10−6 mol cm−2 s−1 at 900 °C for a 1.0-mm membrane under an air/helium oxygen gradient. The further investigation demonstrated the oxygen permeation process was mainly rate-limited by the oxygen bulk diffusion process.  相似文献   

14.
Polyelectrolytes were incorporated into porous reinforcing materials to study the properties of ionomers in confined spaces and to determine the effect of the porous material on the behaviour of the membranes. Nafion® was imbibed into porous polypropylene (Celgard®), ultra-high-molecular weight polyethylene (Daramic®), and polytetrafluoroethylene (PTFE) films. Through the use of reinforcing materials, it is possible to prepare membranes that are thinner, but stronger than pure ionomer membranes. Thin reinforced membranes have advantages such as lower areal resistance (as low as 0.14 Ω cm2 for 57 μm CG3501 + Nafion® compared to 0.34 Ω cm2 for 89 μm cast Nafion®) and lower dimensional changes due to swelling (as low as a 4% change in length and width for WDM + Nafion® compared to 13% for cast Nafion®). Using reinforcing materials results in a reduction in important membrane properties compared to bulk Nafion®, such as proton conductivity (as low as 0.016 S cm−1 for CG3401 + Nafion® compared to 0.076 S cm−1 for cast Nafion®), effective proton mobility (as low as 3.2 × 10−4 cm2 V−1 s−1 CG3401 + Nafion® compared to 7.6 × 10−4 cm2 V−1 s−1 for cast Nafion®), and water vapour permeance (as low as 0.036 g h−1 Pa−1 m−2 for WDM + Nafion® compared to 0.056 g h−1 Pa−1 m−2 for cast Nafion®). By normalizing the membrane properties with respect to ionomer content, it was possible to examine the properties of the Nafion® inside the pores of the membranes. The proton conductivity (as low as 0.032 S cm−1 for CG3401 + Nafion®), effective proton mobility (as low as 3.6 × 10−4 cm2 V−1 s−1 for CG3401 + Nafion®), and water vapour permeability (as low as 2.7 × 10−6 g h−1 Pa−1 m−1 for PTFE MP 0.1 + Nafion®) of the ionomer in the membrane are also diminished compared to bulk Nafion® due to decreased connectivity of the ionomer and a restriction in macromolecular motions caused by the pore walls. A series of porous materials with increasing pore were also examined. As the pore size of the PTFE MP materials increased from 0.1 μm to 10 μm, the proton conductivity (0.022 S cm−1 to 0.041 S cm−1), effective proton mobility ((4.1 to 5.6) × 10−4 cm2 V−1 s−1), and water vapour permeability ((2.4 to 4.3) × 10−6 g h−1 Pa−1 m−1) of the reinforced membranes improved with increasing pore size and the properties of the ionomer inside the membranes approached the value of bulk Nafion®.  相似文献   

15.
A SAPO-34 membrane separated CO2/H2 and H2/CH4 mixtures at feed pressures up to 1.7 MPa. Strong CO2 adsorption inhibited H2 adsorption and decreased H2 permeances significantly, especially at low temperatures, so that CO2 preferentially permeated and CO2/H2 selectivities were higher at low temperatures. At 253 K, CO2/H2 separation selectivities were greater than 100 with CO2 permeances of 3 × 10−8 mol m−2 s−1 Pa−1. The CO2/H2 separation exceeded the upper bounds (selectivity–permeability plot) for polymer membranes. The SAPO-34 membrane separated H2 from CH4 because CH4 is close to the SAPO-34 pore size and has a lower diffusivity than H2. The H2/CH4 separation selectivity had a small maximum with temperature, and decreased slightly with feed pressure and CH4 feed concentration.  相似文献   

16.
Novel organic–inorganic hybrid membranes were prepared through sol–gel reaction of poly(vinyl alcohol) (PVA) with γ-aminopropyl-triethoxysilane (APTEOS) for pervaporation (PV) separation of ethanol/water mixtures. The membranes were characterized by FTIR, EDX, WXRD and PALS. The amorphous region of the hybrid membranes increased with increasing APTEOS content, and both the free volume and the hydrophilicity of the hybrid membranes increased when APTEOS content was less than 5 wt%. The swelling degree of the hybrid membranes has been restrained in an aqueous solution owing to the formation of hydrogen and covalent bonds in the membrane matrix. Permeation flux increased remarkably with APTEOS content increasing, and water permselectivity increased at the same time, the trade-off between the permeation flux and water permselectivity of the hybrid membranes was broken. The sorption selectivity increased with increasing temperature, and decreased with increasing water content. In addition, the diffusion selectivity and diffusion coefficient of the permeants through the hybrid membranes were investigated. The hybrid membrane containing 5 wt% APTEOS has highest separation factor of 536.7 at 50 °C and permeation flux of 0.0355 kg m−2 h−1 in PV separation of 5 wt% water in the feed.  相似文献   

17.
Cardo polyetherketone (PEK-C) composite membranes were prepared by casting glutaraldehyde (GA) cross-linked sulfonated cardo polyetherketone (SPEK-C) or silicotungstic acid (STA) filled SPEK-C and poly(vinyl alcohol) (PVA) blending onto a PEK-C substrate. The compatibility between the active layer and PEK-C substrate is improved by immersing the PEK-C substrate in a GA cross-linked sodium alginate (NaAlg) solution and using water–dimethyl sulfoxide (DMSO) as a co-solvent for preparing the STA-PVA-SPEK-C/GA active layer. The pervaporation (PV) dehydration of acetic acid shows that permeation flux decreased and separation factor increased with increasing GA content in the homogeneous membranes. The permeation flux achieved a minimum and the separation factor a maximum when the GA content increased to a certain amount. Thereafter the permeation flux increased and the separation factor decreased with further increasing the GA content. The PV performance of the composite membranes is superior to that of the homogeneous membranes when the feed water content is below 25 wt%. The permeation activation energy of the composite membranes is lower than that of the homogeneous membranes in the PV dehydration of 10 wt% water in acetic acid. The STA-PVA-SPEK-C-GA/PEK-C composite membrane using water–DMSO as co-solvent has an excellent separation performance with a flux of 592 g m−2 h−1 and a separation factor of 91.2 at a feed water content of 10 wt% at 50 °C.  相似文献   

18.
We carried out the partial substitution of the B-site in BaFeO3−δ perovskite with divalent cations to develop novel oxygen-permeable materials. We demonstrated that the partial substitution of Cu or Ni by more than 10% resulted in the stabilization of the cubic perovskite structure even at room temperature in a highly oxygen-permeable phase, as revealed by the X-ray diffraction (XRD) analysis. The Cu substitution was more effective for the stabilization, because the introduction of Cu in the lattice more effectively made the Goldschmidt tolerance factor (t) close to 1.0. Ni- and Cu-substituted BaFeO3−δ membranes showed higher oxygen permeabilities than their parent BaFeO3−δ membranes particularly at lower temperatures around 600-700 °C owing to the stabilization of the cubic phase. Among the fabricated membranes, a BaFe0.85Cu0.15O3−δ membrane (1.0 mm thickness) showed the highest oxygen permeation flux (1.8 cm3 min−1 cm−2 at 930 °C) under an air/He gradient. The results indicated that Cu-substituted BaFeO3-δ is promising as a material for Co-free membranes with high oxygen permeabilities.  相似文献   

19.
Wittaya Ngeontae 《Talanta》2009,78(3):1004-630
Chemically modified silica containing amidoamidoxime group was studied as a sorbent for solid-phase extraction (SPE) and preconcentration of Cu(II) prior to determination by flame atomic absorption spectrometry (FAAS). The sorbent showed an extremely high selectivity towards Cu(II) in the pH range of 4-6, while the extraction of Pb(II), Cd(II), Ni(II) and Co(II) was low. The adsorption isotherm followed the Langmuir model and the maximum sorption capacity of 0.0163 mmol Cu(II) g−1 was achieved. In the flow system, Cu(II) was completely retained on a column containing 40 mg of the modified silica at the flow rate of 4.0 mL min−1 and quantitatively eluted by 5 mL of 1% (v/v) HNO3. No interference from Na+, K+, Mg2+, Ca2+, Cl and SO42− at 10, 100 and 1000 mg L−1 was observed. When applied for preconcentration and determination of Cu(II) in tap water, pond water, and seawater, the recoveries were 96, 101, and 95%, respectively, with high precision (% relative standard deviation (R.S.D.) < 4) and low method detection limit (9 μg L−1).  相似文献   

20.
The long-term stability of Pd–23%Ag/stainless steel composite membranes has been examined in H2/N2 mixtures as a function of both temperature and feed pressure. During continuous operation, the membrane shows a good stability at 400 °C while the N2 leakage increases very slowly at a temperature of 450 °C (Pfeed = 10 bar). After 100 days of operation (Pfeed = 5–20 bar, T = 350–450 °C), the N2 permeance equals 7.0 × 10−9 mol m−2 s−1 Pa−1, which indicates that the H2/N2 permselectivity still lies around 500, based on a H2 permeance equal to 3.0 × 10−6 mol m−2 s−1 Pa−1. Despite the generation of small pinholes, a membrane life-time of several (2–3) years (T ≤ 425 °C) is estimated for the experimental conditions employed based on long-term stability tests over 100 days. Post-process characterisation shows a considerable grain growth and micro-strain relaxation in the Pd–23%Ag membrane after the prolonged permeation experiment. Changes in surface area are relatively small. In addition, segregation of Ag to the membrane surfaces is observed. The formation of pinholes is identified as the main source for the increased N2 leakage during testing at higher temperature.  相似文献   

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