Kinetic Study of an Effective Pb(II) Transport through a Bulk Liquid Membrane Containing Calix[6]arene Hexaester Derivative as a Carrier

The article describes transport of Pb(II) through bulk liquid membrane (BLM) containing calix[6]arene hexaester derivative (1) as a carrier. The effect of various parameters such as temperature, carrier concentration, stirring speed and type of solvent on the Pb(II) transport efficiency of the carrier through BLM was evaluated. The activation energy values for the extraction and re-extraction were found as 56.33 kJ mol^?1 and 14.79 kJ mol^?1, respectively. These values demonstrate that the process is diffusionally controlled by Pb(II). Observations indicate that the membrane entrance and exit rate constants (k₁, k₂) increase with increasing stirring speed as well as carrier concentration and decrease with increasing temperature. The effect of solvent on k₁ and k₂ was found to be in the order of CH₂Cl₂ > CHCl₃ > CCl₄.     

Application of poly (amide-<Emphasis Type="Italic">b</Emphasis>-ethylene oxide)/zeolitic imidazolate framework nanocomposite membrane in gas separation

Mixed matrix membranes (MMMs) are gaining increasing interest in academic and industrial research due to their combined, desirable properties of both polymers and organic/inorganic filler as important materials. In this work, synthesized zeolitic imidazolate framework (ZIF-8) suspension (10–50 wt%) was directly incorporated into a [poly (amide-b-ethylene oxide) Pebax^® 1657] matrix in order to improve the gas separation performance of the membrane. Dynamic light scattering (DLS) analysis showed an average diameter of 77.4 nm for the prepared nanoparticles. The transparent membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffractometry (XRD). These indicated excellent dispersion of nanoparticles, which was achieved by ultrasonication before casting the solution. Incorporation of ZIF-8 as filler in the polymer matrix led to improved thermal and mechanical stability of the membranes. This was confirmed by TGA and tensile analyses, indicating good contacts provided at the polymer/filler interfaces. The effect of ZIF-8 loading (up to 50 wt%) on membrane performance was investigated and it showed an optimum loading of 30 %. Single gas (CO₂, N₂ and CH₄) permeation tests revealed rapid, enhanced permeability of the nanocomposite membranes without significant changes in selectivity (compared to those of the pristine polymeric membrane). The permeability increases for CO₂, CH₄ and N₂ in the optimum Pebax^® 1657/ZIF-8 (30 wt%) membrane were found in the stated order as 111, 88 and 99 %. The study revealed that Pebax^® 1657/ZIF-8 membranes displayed better gas permeation properties compared to those of Pebax^® 1657.     

Effects of Synthesis Temperature and Support Material on CO2 and CH4 Permeation through SAPO-34 Membranes

In this research, continuous SAPO-34 membranes were synthesized via secondary growth method onto both α-Al₂O₃ and mullite supports at three levels of synthesis temperature: 185, 195, and 220°C for 24 h. The synthesized membranes were characterized using XRD and SEM analysis and single gas permeation experiments. It was found out that support material and synthesis temperature both have significant effects on the membrane performance. At higher synthesis temperature, SAPO-34 crystals grown over the mullite support become more uniform and smaller in size but those grown on the α-Al₂O₃ support become larger. Effect of synthesis temperature on single gas permeation properties of the synthesized SAPO-34 membranes was also studied. For the mullite supported membranes, the CH₄ and CO₂ permeances decrease as synthesis temperature increases; but in the case of the alumina supported membranes, by increasing synthesis temperature, CH₄ and CO₂ permeances first decrease up to 195°C and then increase up to 220°C. Even in equal membrane thicknesses, the mullite supported membrane shows lower gas permenaces. Increasing synthesis temperature decreases CO₂/CH₄ ideal selectivity for the α-Al₂O₃ supported membranes, while increases for the mullite supported membranes. Under optimum synthesis conditions, at room temperature and 2 bar feed pressure, the CO₂ permeance through the α-Al₂O₃ and the mullite supported SAPO-34 membranes are 8.2 × 10^?7 and 8.5 × 10^?8 (mol/m² · s · Pa), respectively, and CO₂/CH₄ ideal selectivities are 51 and 61, respectively.     

Methane (CH4) and nitrous oxide (N2O) emissions from the system of rice intensification (SRI) under a rain-fed lowland rice ecosystem in Cambodia

The present field study investigated the effects of the system of rice intensification (SRI) on greenhouse gas emissions and rice yield, in the first field trial of its kind in Cambodia. The study was a 2 × 4 factorial design, including SRI and conventional management practices (CMP) with the following treatments: control, composted farmyard manure (FYM), mineral fertiliser (MF) and FYM + MF. The results indicated large seasonal variations of CH₄ patterns during the growing season with a peak emission of about 1,300 mg CH₄ m^?2 day^?1 under both production systems 2 weeks after rice transplanting. There was large temporal variability of CH₄ fluxes from morning to midday. Emission of N₂O was below the detection limit in both systems. Under each production system, the highest seasonal emission of CH₄ was under the FYM + MF treatment, namely 282 kg ha^?1 under CMP and 213 kg ha^?1 under SRI. Total CH₄ emission under SRI practices was reduced by 22 % in the FYM treatment, 17 % in the MF treatment and 24 % in the FYM + MF treatment compared to CMP. There was no effect of water management on CH₄ emission in the non-fertilized treatment. Grain yields were not significantly affected by the production system. Thus the yield-scaled global warming potential (GWP) was lower under SRI than CMP, namely 21 % in FYM and FYM + MF treatments, and 8 % in MF treatment. The application of mineral fertilisers moderately increased CH₄ emission but significantly increased rice yields, resulting in a significantly lower yield-scaled-GWP compared to farmyard manure.     

The effect of membrane pores wettability on CO2 removal from CO2/CH4 gaseous mixture using NaOH,MEA and TEA liquid absorbents in hollow fiber membrane contactor

The present paper renders a modeling and a 2D numerical simulation for the removal of CO₂ from CO₂/CH₄ gaseous stream utilizing sodium hydroxide (NaOH), monoethanolamine (MEA) and triethanolamine (TEA) liquid absorbents inside the hollow fiber membrane contactor. Counter-current arrangement of absorbing agents and CO₂/CH₄ gaseous mixture flows are implemented in the modeling and numerical simulation. Non-wetting and partial wetting modes of operation are considered where in the partial wetting mode, CO₂/CH₄ gaseous mixture and liquid absorbents fill the membrane pores. The deteriorated removal of CO₂ in the partial wetting mode of operation is mainly due to the mass transfer resistance imposed by the liquid in the pores of membrane. The validation of numerical simulation is done based on the comparison of simulation results of CO₂ removal using NaOH and experimental data under non-wetting mode of operation. The comparison illustrates a desirable agreement with an average deviation of less than 5%. According to the results, MEA provides higher efficiency for CO₂ removal in comparison with the other liquid absorbents. The order for CO₂ removal performance is MEA > NaOH > TEA. The influence of non-wetting and partial wetting modes of operation on CO₂ removal are evaluated in this article as one of the novelties. Besides, the percentage of CO₂ sequestration as a function of gas velocity for various percentages of membrane pores wetting ranging from 0 (non-wetting mode of operation) to 100% (complete wetting mode of operation) is studied in this research paper, which can be proposed as the other novelty. The results indicate that increase in some operational parameters such as module length, membrane porosity and absorbents concentration encourage the removal percentage of CO₂ from CO₂/CH₄ gaseous mixture while increasing in membrane tortuosity, gas velocity and initial CO₂ concentration has unfavorable influence on the separation efficiency of CO₂.     

Highly Efficient and Selective Transport of Cu(II) with a Cooperative Carrier Composed of Tetraaza-14-Crown-4 and Oleic Acid through a Bulk Liquid Membrane

Tetraaza-14-crown-4 and oleic acid was successfully applied for transport of Cu(II) in chloroform bulk liquid membrane. The uphill moving of Cu(II) during the liquid membrane transport process has occurred. The main effective variable such as the type of the metal ion acceptor in the receiving phase and its concentration, tetraaza-14-crown-4 and oleic acid concentration in the organic phase on the efficiency of the ion-transport system were examined. By using L-cysteine as a metal ion acceptor in the receiving phase, the maximum amount of copper (II) transported across the liquid membrane was achieved to 96 ± 1.5% after 140 minutes. The selectivity of copper ion transport from the aqueous solutions containing Pb²⁺, Tl⁺, Ag⁺, Co²⁺, Ni²⁺, Mg²⁺, Zn²⁺, Hg²⁺, Cd²⁺ and Ca²⁺ ions were investigated. In the presence of CH₃COONH₄ and Na₄P₂O₇ as suitable masking agents in the source phase, the interfering effects of Pb⁺² and Cd²⁺ were diminished drastically.     

Performance evaluation of a synthesized and characterized Pebax1657/PEG1000/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> membrane for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation using response surface methodology

In this work, the response surface methodology (RSM) based on the central composite design (CCD) was used to examine effects of different gamma alumina (γ-Al₂O₃) loadings (0 to 8 wt.%) and various polyethylene glycol 1000 (PEG1000) contents (0 to 40 wt.%) as parameters on membrane preparation. Accordingly, pure carbon dioxide (CO₂) and methane (CH₄) gasses permeability and ideal CO₂/CH₄ selectivity values were considered as responses. Poly (ether block amide) 1657 (Pebax1657) was used as the base polymer matrix for the membranes fabrication. The neat Pebax1657 membrane was prepared via solution casting-solvent evaporation method and the other membranes were prepared via solution blending technique. Analysis of variance (ANOVA) was used to analyze the experiments statistically and the results indicated that the optimized amounts of γ-Al₂O₃ nanoparticles and PEG1000 in order to enhance both CO₂ permeability and ideal CO₂/CH₄ selectivity were 8 wt.% and 10 wt.%, respectively. Additionally, a comparison between the separation performance of the neat membrane, the nanocomposite membrane with the optimum amount of γ-Al₂O₃ nanoparticles, the blended membrane with optimum amounts of PEG1000, and the blended nanocomposite membrane with optimum amounts of γ-Al₂O₃ nanoparticles and PEG1000 was presented. The obtained gas permeation results showed that the blended nanocomposite membrane exhibits the highest CO₂/CH₄ separation performance compared to the neat Pebax membrane.     

Methane uptake by saline–alkaline soils with varying electrical conductivity in the Hetao Irrigation District of Inner Mongolia,China

Soil salinization adversely affects sustainable land use and limitation of greenhouse gas emission. Methane (CH₄) uptake and the specific activity of methanotrophs in three saline–alkaline soils—S1, electrical conductivity (EC) 4.80?dS?m^?1; S2, EC 2.60?dS?m^?1; and S3, EC 0.74?dS?m^?1—were observed and measured across crop phenological development in the Hetao Irrigation District of Inner Mongolia, China. There were significant differences in CH₄ uptake between the three soil types. The cumulative uptake of CH₄ was 97.97 mg m^?2, 109.49 mg m^?2, and 150.0 mg m^?2 in S1, S2, and S3, respectively. Cumulative CH₄ uptake was 35%, 35%, and 53% lower in S1 than in S3, and was 27%, 28%, and 19% lower in S2 than in S3 in 2014, 2015, and 2016, respectively. Differences in CH₄ uptake were driven by the different specific activities of the methanotrophs in the three soils, of which the key controlling factor was soil EC. The findings demonstrate that saline–alkaline soils with high EC led to low CH₄ uptake and thereby significantly increased the total greenhouse effect of CH₄.     

Synthesis and Characterization of Lauryl Trimethyl Ammonium Surfactants with New Counteranion Types

A new family of lauryl trimethyl ammonium surfactants of the general formula CH₃(CH₂)₁₁ N⁺(CH₃)₃X^? (X = CH₃OCOO, HCOO, CH₃COO, CH₃CHOHCOO) were prepared and characterized both structurally and as aqueous surfactants. Lauryl trimethyl ammonium mono-methyl carbonate was synthesized by using dimethyl carbonate (DMC) as the alkylating agent and lauryl dimethyl amine as the starting material. The latter compound was reacted with formic acid, acetic acid, and lactic acid, respectively, to give the corresponding quaternary ammonium salts with other counteranions. They were structurally characterized by IR, ¹H NMR, MS. Members of this family reduced the surface tension of water to 32–38 mN/m at concentration levels of 10^?2 mol/L.     

Carbon-tolerance effects of Sm0.2Ce0.8O2−δ modified Ni/YSZ anode for solid oxide fuel cells under methane fuel conditions

Samarium-doped ceria (SDC) is coated onto a Ni/yttria-stabilized zirconia (Ni/YSZ) anode for the direct use of methane in solid-oxide fuel cells. Porous SDC thin layer is applied to the anode using the sol–gel coating method. The experiment was performed in H₂ and CH₄ conditions at 800 °C. The cell performance was improved by approximately 20 % in H₂ conditions by the SDC coating, due to the high ionic conductivity, the mixed ionic and electronic conductive property of the SDC, and the increased triple phase boundary area by the SDC coating in the anode. Carbon was hardly deposited in the SDC-coated Ni/YSZ anode. The cell performance of the SDC-coated Ni/YSZ anode did not show any significant degradation for up to 90 h under 0.1 A cm^?2 at 800 °C. The porous thin SDC coating on the Ni/YSZ anode provided the electrochemical oxidation of CH₄ over the whole anode, and minimized the carbon deposition by electrochemical carbon oxidation.     

Nanoporous rice husk derived carbon for gas storage and high performance electrochemical energy storage

We report on the gas storage behaviour and electrochemical charge storage properties of high surface area activated nanoporous carbon obtained from rice husk through low temperature chemical activation approach. Rice husk derived porous carbon (RHDPC) exhibits varying porous characteristics upon activation at different temperatures and we observed high gas uptake and efficient energy storage properties for nanoporous carbon materials activated even at a moderate activation temperature of 500 °C. Various experimental techniques including Fourier transform-infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy and pore size analyser are employed to characterise the samples. Detailed studies on gas adsorption behaviour of CO₂, H₂ and CH₄ on RHDPCs have been performed at different temperatures using a volumetric gas analyser. High adsorption capacities of ~9.4 mmol g^?1 (298 K, 20 bar), 1.8 wt% (77 K, 10 bar) and ~5 mmol g^?1 (298 K, 40 bar) were obtained respectively for CO₂, H₂ and CH₄, superior to many other carbon based physical adsorbents reported so far. In addition, these nanoporous carbon materials exhibit good electrochemical performance as supercapacitor electrodes and a maximum specific capacitance of 112 F g^?1 has been obtained using aqueous 1 M Na₂SO₄ as electrolyte. Our studies thus demonstrate that nanoporous carbon with high porosity and surface area, obtained through an efficient approach, can act as effective materials for gas storage and electrochemical energy storage applications.     

Carbon molecular sieve membranes for natural gas purification: Role of surface flow

Carbon molecular sieve membranes (CMSM) were prepared from the pyrolysis of polyimide films within a temperature range of 600°C-800°C under nitrogen stream. The membrane samples were characterized and tested for the permeation of He, CH₄, CO₂, and N₂ at different pressures and temperatures, respectively. The CMSM700 membrane (pyrolyzed at 700°C) showed an ideal selectivity of ~ 11 for N₂/CH₄ with a permeability of 2.18 × 10⁻¹⁵ mol · m/m² · s · Pa for N₂. The separation mechanism for the N₂/CH₄ pair was shown to be largely molecular sieving rather than surface flow. The membrane showed an ideal selectivity of ~ 500 for the CO₂/CH₄ pair with a CO₂ permeability of 9.72 × 10⁻¹⁴ mol · m/m² · s · Pa. The permeability of He was lower than that of CO₂, suggesting that the surface flow played a significant role in the CO₂ permeation. The updated permeability-selectivity tradeoff curves show that this CMSM membrane compared favourably with other membrane materials reported in the literature for the removal of N₂ and CO₂ from CH₄ for natural gas upgrading.     

Hydrophobicity optimization of polypropylene hollow fiber membrane by sol–gel process for CO<Subscript>2</Subscript> absorption in gas–liquid membrane contactor using response surface methodology

In membrane technology, wettability is one of the most crucial points for successful industrial application of membrane contactors. To solve this issue, a non-wetting polypropylene (PP) hollow fiber membrane was prepared by the incorporation of modified silica nanoparticles (CH₃SiO₂) synthesized through sol–gel process on the surface and the cross-section of the membrane. Tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) were used as precursor and hydrophobic agent, respectively, to synthesize CH₃SiO₂ nanoparticles (NPs). In preparation procedure of NPs, the influential parameters including MTES/TEOS and H₂O/TEOS molar ratios and NH₄OH concentration were optimized using central composite design of response surface method (RSM) by considering contact angle (CA) as response variable. The CA of 168° was obtained using analysis of variance (ANOVA) when the MTES/TEOS molar ratio, H₂O/TEOS molar ratio and NH₄OH concentration were, respectively, 3.774, 8.000 and 0.511 M. ATR-FTIR, FE-SEM, mechanical strength and porosity measurements were used to characterize the optimum membrane. The neat and modified membranes were also tested for the CO₂ absorption process in a gas–liquid membrane contactor system. The CO₂ absorption flux of modified membrane almost remained constant within 30 days, while the neat membrane slightly suffered from wetting problem, resulted in a continuous decline in the CO₂ flux.     

Emissions of CH4, N2O, NH3 and odorants from pig slurry during winter and summer storage

Manure storage contributes significantly to greenhouse gas (GHG), NH₃ and odour emissions from intensive livestock production. A pilot-scale facility with eight 6.5-m³ slurry storage units was used to quantify emissions of CH₄, N₂O, NH₃, and odorants from pig slurry during winter and summer storage. Pig slurry was stored with or without a straw crust, and with or without interception of precipitation, i.e., four treatments, in two randomized blocks. Emissions of total reduced S (mainly H₂S) and p-cresol, but not skatole, were reduced by the straw crust. Total GHG emissions were 0.01–0.02 kg CO₂ eq m^?3 day^?1 during a 45-day winter storage, and 1.1–1.3 kg CO₂ eq m^?3 day^?1 during a 58-day summer storage period independent of storage conditions; the GHG balance was dominated by CH₄ emissions. Nitrous oxide emissions occurred only during summer storage where, apparently, emissions were related to the water balance of the surface crust. An N₂O emission factor for slurry storage with a straw crust was estimated at 0.002–0.004. There was no evidence for a reduction of CH₄ emissions with a crust. Current Intergovernmental Panel on Climate Change recommendations for N₂O and CH₄ emission factors are discussed.     

Electrolyte type and concentration effects on poly(3-(2- aminoethyl thiophene) electro-coated on glassy carbon electrode via impedimetric study

In this study, 3-(2-Aminoethyl thiophene) (2AET) monomer was electropolymerized on glassy carbon electrode (GCE) using various electrolytes (lithium perchlorate (LiClO₄), sodium perchlorate (NaClO₄), tetrabutyl ammonium tetra fluoroborate (TBABF₄) and tetraethyl ammonium tetra fluoroborate (TEABF₄) in acetonitrile (CH₃CN) as solvent. Poly(3-(2-aminoethyl thiophene) (P(2AET))/GCE was characterized by cyclic voltammetry (CV), Fourier transform infrared reflectance spectrophotometry (FTIR-ATR), scanning electron microscopy, energy dispersive X-ray analysis (EDX), and electrochemical impedance spectroscopy (EIS) techniques. The electrochemical impedance spectroscopic results were given by Nyquist, Bode-magnitude, Bode-phase, capacitance and admittance plots. The highest low frequency capacitance (C _LF) value obtained was 0.65 mF cm^?2 in 0.1 M LiClO₄/CH₃CN for the initial monomer concentration of 1.5 mM. The highest double layer capacitance (C _dl = ~0.63 mF cm^?2) was obtained in 0.1 M LiClO₄/ACN for [2AET]₀ = 0.5, 1.0 and 1.5 mM. The maximum phase angles (θ = 76.1^o at 26.57 Hz) and conductivity (Y″ = 3.5 mS) were obtained in TEABF₄/ACN for [2AET]₀ = 0.5 and 1.0 mM, respectively. An equivalent circuit model of R(Q(R(Q(R(CR))))) was simulated for different electrolytes (LiClO₄, NaClO₄, TBABF₄ and TEABF₄)/P(2AET)/GCE system. A good fitting was obtained for the calculated experimental and theoretical EIS measurement results. The electroactivity of P(2AET)/GCE opens the possibility of using modified coated electrodes for electrochemical micro-capacitor electrodes and biosensor applications.     

Synthesis of 9H-carbazole-9-carbothioic methacrylic thioanhydride,electropolymerization, characterization and supercapacitor applications

A novel organic molecule of 9H-carbazole-9-carbothioic methacrylic thioanhydride (CzCS₂metac) was synthesized by incorporating CS₂ and methacrylate groups into the carbazole monomer structure. CzCS₂metac was characterized by FTIR, ¹H-NMR and ¹³C-NMR spectroscopy. CzCS₂metac was electropolymerized in 0.1 M tetraethylammonium tetrafluoroborate (TEABF₄)/acetonitrile (CH₃CN) on glassy carbon electrode (GCE). The characterization of the electrocoated P(CzCS₂metac)/CFME thin film was studied by various techniques, such as cyclic voltammetry, scanning electron microscopy–energy-dispersive X-ray analysis and electrochemical impedance spectroscopy. The specific capacitance (C _sp) of P(CzCS₂metac)/MWCNT/GCE in the scan rate of 20 mV s^?1 (C _sp = 38.48 F g^?1 from area formula, C _sp = 38.52 F g^?1 from charge formula) was increased ~15.66 and ~15.64 times in area and charge formulas compared to P(CzCS₂metac)/GCE (C _sp = 2.46 F g^?1 from area and charge formulas). The same results were also obtained from Nyquist graphs. The specific capacitance value of composite film (C _sp = 1.09 × 10^?3 F) is ~15.66 times higher than the polymer film (C _sp = 6.92 × 10^?5 F). The composite film may be used as supercapacitor electrode material in energy storage devices.     

ELECTROCHEMICAL RECOVERY OF CHLORINE AND HYDROGEN FROM HYDROGEN CHLORIDE BY-PRODUCT PRODUCED IN THE PETROCHEMICAL INDUSTRY

Simultaneous production of hydrogen as an energy carrier and chlorine as a valuable chemical from recycled hydrogen chloride was investigated employing a lab-scale membrane electrolysis setup. The effects of various process parameters including current density (1–4 kA m^?2), cell temperature (45°–75°C), flow rate of hydrochloric acid feed (200–500 mL min^?1), and concentration of acid (18–21 wt.%) on the cell voltage and chlorine current efficiency (ChCE) were studied. The Taguchi design of experiments (L₁₆ array) was employed to design the minimum number of experiments necessary to fully study the process. A filter press type cell of 10 cm² surface area comprising a DSA anode, an alloy of predominantly nickel cathode and Nafion 115 membrane, was used. It was observed that increasing anolyte flow rate, anolyte concentration, or cell temperature caused a decrease in cell voltage and an increase in ChCE, while increasing current density linearly increased cell voltage and decreased ChCE.     

Hybrid FSC membrane for CO2 removal from natural gas: Experimental,process simulation,and economic feasibility analysis

The novel fixed‐site‐carrier (FSC) membranes were prepared by coating carbon nanotubes reinforced polyvinylamine/polyvinyl alcohol selective layer on top of ultrafiltration polysulfone support. Small pilot‐scale modules with membrane area of 110–330 cm² were tested with high pressure permeation rig. The prepared hybrid FSC membranes show high CO₂ permeance of 0.084–0.218 m³ (STP)/(m² h bar) with CO₂/CH₄ selectivity of 17.9–34.7 at different feed pressures up to 40 bar for a 10% CO₂ feed gas. Operating parameters of feed pressure, flow rate, and CO₂ concentration were found to significantly influence membrane performance. HYSYS simulation integrated with ChemBrane and cost estimation was conducted to evaluate techno‐economic feasibility of a membrane process for natural gas (NG) sweetening. Simulation results indicated that the developed FSC membranes could be a promising candidate for CO₂ removal from low CO₂ concentration (10%) NGs with a low NG sweetening cost of 5.73E?3 $/Nm³ sweet NG produced. © 2014 American Institute of Chemical Engineers AIChE J 60: 4174–4184, 2014     

Hybrid H2-Selective Silica Membranes Prepared by Chemical Vapor Deposition

Hybrid organic-inorganic H₂-selective membranes consisting of single-layer or dual-layers of silica incorporating aromatic groups are deposited on a porous alumina support by chemical vapor deposition (CVD) in an inert atmosphere at high temperature. The single-layer silica membranes, which are made by the simultaneous decomposition of phenyltriethoxysilane (PTES) and tetraethylorthosilicate (TEOS), have good hydrothermal stability at high temperature and a high permeance for hydrogen in the order of 10^?7 mol m^?2 s^?1 Pa^?1 at 873 K, while preventing the passage of other larger molecular gases such as CH₄ and CO₂. The dual-layer silica membranes, which are obtained from the sequential decomposition of PTES and TEOS, exhibit an extremely high permeance for hydrogen of 3.6 × 10^?6 mol m^?2 s^?1 Pa^?1 at 873 K with a permselectivity of hydrogen over methane of 30. A normalized Knudsen based permeance method is applied to measure the pore size of PTES-derived silica membrane on the dual-layer silica membrane before treatment with TEOS. The method indicates that the pore size of the silica network is approximately in the range of 0.50–0.85 nm, which is higher than the characteristic length of pure silica membranes of 0.3 nm, accounting for the high permeance of the hybrid membranes.