Papers by Keyword: Hydrogen Separation

Abstract: Gas permeation of hydrogen (H₂) and nitrogen (N₂) were obtained from 30 and 6000 nm pore diameter tubular commercial alumina ceramic membranes at 0.05 to 1.00 bar and 298 K. Flow rates of up to 3.279 and 2.296 l/min were obtained for H₂ and N₂ respectively. The ratio of H₂/N₂ flow rates were used to calculate H₂/N₂ selectivity. The experimental H₂/N₂ selectivities obtained were 1.85 and 1.43 for the 30 and 6000 nm respectively.

Abstract: Silica sol-gel membranes have been developed for moderate temperature (300 °C) separation of hydrogen (H₂) from nitrogen (N₂), methane (CH₄) and argon (Ar) gas molecules. Tubular ceramic support with 15 nm nominal pore diameter and 45% porosity was modified by dip-coating method. Gas permeation characteristics were evaluated. Defect free silica layer over the substrate for hydrogen gas separation was obtained. Hydrogen gas permeate flux of 4.82x10^-1 mol/sec m² at 1.0 barg feed pressure was obtained. Selectivities of H₂ over N₂, CH₄ and Ar of 3.07, 2.23 and 3.75 at 300 °C, 200 °C and 300 °C and 0.9 barg were obtained with the silica membranes. The gas permeation and the selectivity performance of the membrane were evaluated.

Abstract: Pd composite membranes were prepared on macroporous α-Al₂O₃ tubes modified by silicalite-1 zeolite. Permeation tests of the Pd composite membranes were performed at 773 K to observe the H₂ permeance and H₂/N₂ selectivity. The H₂ flux and ideal selectivity for Pd composite membrane was 0.120 mol m⁻² s⁻¹ and 450 under 0.1 MPa, respectively. The variation of the membrane surface after elevating temperature in N₂ and air atmosphere was characterized in scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS) analyses. As a result, it can be concluded that the formation of pinholes and defects on the membrane surface can be attributed to the oxidation of the Pd membrane.

Abstract: Palladium composite membranes have been prepared by improved electroless plating on macroporous α-Al₂O₃ tubes. TS-1 zeolite layer was introduced in the palladium composite membrane to modify macroporous α-Al₂O₃ tubes and prevent the diffusion between Pd and alumina. The detailed microstructure and morphology of the Pd-TS-1 composite membrane were examined by SEM and XRD. Moreover, gas permeation performance was tested at the temperature range of 623~773K. Results showed that the H₂ permeance and H₂/N₂ ideal selectivity for Pd-TS-1 composite membrane could be up to 3.7×10^-7 mol·m^-2·s^-1·Pa^-1 and 310 at 773K, respectively.

Abstract: . In this paper, thin palladium (Pd) membranes, which are supported on alumina nanofiber nonwoven produced by electrospinning method, were prepared by electroless plating method. The influence of different pretreatment methods (iron wire activation) and reducing agent (sodium hypophosphite and hydrazine hydrate) on the structure of Pd membrane were studied. The morphology, surface element and crystal structure of the Pd membrane were investigated by SEM, EDS and XRD. The results showed that the compact Pd membrane was formed on the alumina nanofiber nonwoven when the pretreatment method of iron wire activation was adopted and the reducing agent of sodium hypophosphite was used, which will be applied widely in hydrogen separation area.

Abstract: Our recent communication focuses on small scale and nanoscale type engineering applications of alumina inorganic membrane reactors and reactor-permeator systems for the conversion of renewable and non-renewable hydrocarbons and methane rich streams into hydrogen rich gas for direct inner application and operation of fuel cell systems. This study elaborates on new nanomembrane reactors for the steam-methane/hydrocarbon reforming and water gas shift reactions, including work in the synthesis, manufacturing, modeling and operation of such microreaction systems. The projected small scale reactors, separators and overall reaction systems are of current significance in the area of multifunctional microreactor and nanoreactor design and operation in connection with the operation of fuel cells for transportation, stationary, and portable power generation applications. An added advantage of such systems is the reactive and separative operations of the fuel cell membrane-processor which are combined to convert the hydrocarbon with steam to valuable fuel gas for continuous fuel cell operation. Moreover, the nanomembrane systems under development have the unique characteristics to perform multiple operations per unit volume, such as to utilize beneficial equilibrium shift principles in reactant conversion and product yield through the removal of permselective species (i.e., hydrogen) via the inorganic membrane out of the conversion/reaction zone. In this way, improved hydrogen and product yields can be achieved which exceed the equilibrium calculated yields. Simultaneously, the reaction products, such as synthesis gas (i.e., H2, CO and CO2) at the reactor exit can be used as fuel in mostly solid oxide and molten carbonate fuel cells. The role of the alumina nanomembrane is also in the main conversion and upgrading sections of these feedstocks in order to overcome existing heat and mass transfer limitations and increase the overall efficiency of the microreactor-fuel cell system.

Abstract: In our previous studies, 10-40wt%Ni/Al2O3 membrane was prepared by uniaxial pressing and sintered at 900 to 1400°C for 2 h. It was found that 10wt%Ni/Al2O3 membrane sintered at 1400°C showed the highest physical and mechanical properties. Thus, this work we focused on the effect of different pressing processes on the properties of Ni/Al2O3 membrane with longer soaking time. Firstly, 10-40wt%Ni and Al2O3 powders were mixed by dried ball-milling. Then, the mixture powder was pressed to form a bar shape by two different processes; uniaxially pressing (No CIP) and uniaxially pressing followed by cold isostatic pressing (CIP) at 250 MPa for 5 min. All Ni/Al2O3 specimens from two pressing routes were sintered at 1400°C for 4h under air atmosphere and reduced at 900 °C under H2 (99.99%). From the results, it was found that the densification process affected to physical and mechanical properties of Ni/Al2O3. The CIPed - 10wt%Ni/Al2O3 membrane sintered at 1400°C for 4 h showed the highest relative density and flexural strength of 76% and 106 MPa with the lowest pore size (78 nm) and 17% porosity. The addition of nickel content gradually decreased physical and mechanical properties of Ni/Al2O3.

Abstract: This work aimed to investigate the effect of different sintering routes on properties of Ni-Al2O3 membrane. Alumina powder was mixed with 10 wt% nickel powder by dried ball-milling. Then, the mixture powder was uniaxially pressed to a bar shape and sintered via different sintering conditions. First route, the Ni-Al2O3 specimen was sintered at 1300°C for 2 h under air and then reduced at 900°C for 2 h under H2 atmosphere. Second route, the specimen was sintered at 1300°C for 2 h under argon. After sintering process, the physical and mechanical properties of membrane obtained from two routes were compared and discussed.

Abstract: The palladium membrane has been developed for high temperature separation of hydrogen from other syngas molecules. In this study, tubular α-alumina substrate was used as a support for increase mechanical strength for thin palladium membrane. Prior depositing of palladium film, a dip-coating of palladium nuclei was performed to cover the substrate. Afterward, surface of activated support was modified with a thin intermediate layer for improving adhesion between support and Pd membrane. Electroless plating of dense palladium membrane was achieved from the plating bath containing EDTA stabilized palladium complex and hydrazine. The microstructural characteristics of palladium membranes were analyzed.

Abstract: Ni-BaCe0.9Y0.1O3-δ mixed protonic-electronic conductor can be used to separate hydrogen from syngas. Considering that water exists in syngas, it is necessary to evaluate the effect of moisture on chemical stability and hydrogen permeability of the cermet. In this paper, hydrogen permeation rates of Ni- BaCe0.9Y0.1O3-δ (40:60 in volume ratio) in different water partial pressures were measured at intermediate temperatures (600-750°C). It is found that hydrogen permeation rate of the cermet is highest at an appropriate water partial pressure. Samples after experiment were analyzed by XRD, ICP and pH value measurement, in which Ba(OH)2 and doped CeO2 were found. The reaction of water with samples resulting in insulating Ba(OH)2 and doped CeO2 is contributed to the decrease of hydrogen permeation in excessive water partial pressure.