Perturbed hydrogen permeation of a hydrogen mixture—New phenomena in hydrogen permeation by Pd membrane (original) (raw)

Hydrogen transport in palladium membranes

Desalination, 2002

The hydrogen flux in palladium membranes acquired from different vendors has been measured as a function of membrane thickness, temperature and feed (pure H2) pressure p~, with permeate (pure H2) pressure P2 fLxed at 1 atm. Palladium foils 12.5, 25 and 47 pm thick were studied at 75-500°C andp~ values of 3.4-6.8 atm. Arrhenius plots of flux, measured withpl fLxed, include a peak within an intermediate temperature range, and different activation energies in the low and high temperature ranges. The peak may be explained by palladium hydride's tx-~ phase transition, which, at intermediate temperatures, takes place at hydrogen activities between those at the respective membrane surfaces. The two activation energies apparently refect different rate-controlling processes: bulk diffusion at high temperatures and surface phenomena at low temperatures.

Studying permeation of hydrogen (H and D) through Palladium membrane dynamically with ERDA method

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007

Permeation of H and D through palladium membrane was studied in real-time with Elastic Recoil Detection Analysis (ERDA). Concentration depth profile of hydrogen at the low pressure side of the membrane was followed by successive recording of ERDA spectra. Bulk concentration of hydrogen was high at low temperatures (below 380 K and 420 K for D and H, respectively) indicating that permeation is desorption limited. At higher temperatures concentration in the low pressure side of membrane diminished and hydrogen flux through the membrane increased as indicated by pressure rise in the vacuum chamber. Permeation of hydrogen therefore becomes diffusion limited.

Hydrogen transport through thin layer Pd alloy membranes: kinetics and gas permeation studies

Separating hydrogen with high selectivity from a gas mixture needs a dense membrane through which only hydrogen can penetrate. Transport of hydrogen from one side of a dense membrane to the other side of the membrane is a sequence of different processes, such as adsorption and dissociation of hydrogen, absorption and diffusion of protons, recombination and desorption of hydrogen. Probably the most important step in this transport is the dissociation of hydrogen molecules in atoms at the membrane surface. This dissociation is necessary for absorption and diffusion to occur and can be realised with a catalytic metal such as palladium. Furthermore, both the solubility and the diffusivity of hydrogen in palladium are relatively very high, which makes palladium a good candidate material for hydrogen selective membrane films. However, palladium suffers from embrittlement by hydrogen that leads to deterioration of metal films. This phenomenon is caused by the formation of palladium hydride that can exist in an alpha and beta phase that co-exist at temperatures lower than about 310°C. To increase the lifespan of membranes made of this material the co-existence of alpha and beta palladium hydride has to be suppressed. One way of doing this is to alloy palladium with e.g. silver or copper that will hardly effect the migration of hydrogen through the membrane.

Model development and validation of hydrogen transport through supported palladium membranes

Journal of Membrane Science, 2010

Porous matrices are often used to provide structural support to thin Pd-based metallic membranes in H 2 separation applications. Optimizing such composite membranes requires detailed understanding of all possible rate-controlling processes including surface and bulk processes in the metal and diffusion of gases through the porous media. In the work described in this paper, we fabricate a composite membrane by depositing a thin (∼5-6 m) Pd film on a porous ␣-Al 2 O 3 tube and then measure the H 2 permeance of this composite membrane over a range of operating conditions. The rate-controlling processes for the H 2 permeation are evaluated with a computational model which combines a detailed thermo-kinetic Pd-H 2 interaction model and a porous media transport model. The Pd-H 2 thermo-kinetic model is validated against literature data, and the porous media transport model is independently calibrated using experimental measurements. The combined composite membrane model gives good agreement with experiments over a large range of temperatures (250-450 • C) and H 2 partial pressures (100-385 kPa). This validated model is then used to analyze the importance of design parameters such as Pd thickness and support micro-structure on H 2 flux through the membrane. These parametric studies will also aid in assessing trade-offs between membrane structural robustness and overall performance.

Hydrogen permeation through Pd–Ag membranes: Surface effects and Sieverts' law

International Journal of Hydrogen Energy, 2013

Metal membranes mainly made of Pd alloys can be applied in membrane reformers for ultrapure hydrogen production from hydrocarbons and alcohols. Knowledge of the hydrogen mass transfer mechanisms through metals is very important to the purpose of properly designing and operating the membrane reactors. With the aim of understanding the deviations from the ideal behavior of the transport mechanisms predicted by the Sieverts' law, a permeation model which takes into account the surface effects has been applied to the permeability measurements that have been carried out on dense PdeAg permeator tubes from 473 to 623 K. The model has been validated by the results of permeation tests in a wide range of pressure (200e800 kPa) and membrane thickness (84e200 mm). The new model modifies the Sieverts' law by introducing the mass transfer resistances due to surface effects. The values of the surface resistance and permeability calculated by the model have been compared with the literature. Finally, the new hydrogen permeation expression has been applied in order to analyze the cost of a separation system which would consist of tubular Pd-based membranes.

Correlations in palladium membranes for hydrogen separation: A review

Journal of Membrane Science, 2011

This review describes palladium and palladium alloy membranes for hydrogen separation prepared by different fabrication methods and using different membrane supports. Several correlations of structure and function for those membranes are provided based on mechanistic considerations of permeance along with structural properties and membrane morphologies. Particular attraction is placed in analysis of the hydrogen permeance and selectivity of membranes reported in recent papers. Composite palladium membranes prepared by the electroless plating technique deposited on alumina substrates are found to be the most promising for practical applications. It is concluded that the prospects for the use of palladium membranes in industrial applications are improving due to extensive research addressing current problems such as durability, hydrogen embrittlement, fouling by hydrocarbons or hydrosulfide compounds, and the high cost of palladium.

Hydrogen permeation in stressed and strained membranes of palladium alloys

International Journal of Hydrogen Energy, 1992

ln experimental studies of hydrogen permeation through a Pd77Ag23 membrane at 25 and 50°C, forms of the time-dependent changes of hydrogen pressure within the membrane have been found to be clearly dependent on the catalytic activities of the membrane surface, initial hydrogen content of the membrane and conditions of lattice strain due to different processes of generation of lattice stress. This strongly supports the appreciation that hydrogen diffusion in metals involves non-Fickian features which are associated with Gorsky Effect phenomena. Correlations have been made between these effects and the forms of isothermal hydrogen pressure(p)-hydrogen content(n) relationships for the Pd77Ag23H, system.

The permeability of hydrogen in bulk palladium at elevated temperatures and pressures

Journal of Membrane Science, 2003

The permeability of hydrogen in bulk palladium membranes (approximately 1-mm thickness) was determined for the first time at conditions of simultaneously elevated temperature (623-1173 K) and hydrogen pressure (0.1 × 10 6 to 2.76 × 10 6 Pa). When the hydrogen partial pressure exponent value was constrained to a value of 0.5, the permeability was described by an Arrhenius-type relation where the pre-exponential constant and activation energy for this correlation were 1.92 × 10 −7 mol/(m s Pa 0.50) and 13.81 kJ/mol, respectively. These Arrhenius values were in good agreement with prior low-pressure correlations. However, the hydrogen flux results of this study were most accurately represented by an Arrhenius permeability expression where 3.21 × 10 −8 mol/(m s Pa 0.62), 13.41 kJ/mol, and 0.62 represent the pre-exponential constant, activation energy of permeation and permeability driving force, respectively. Although the partial pressure exponent value of 0.62 was slightly greater than the commonly accepted value of 0.5 (atmospheric and sub-atmospheric pressure studies), the optimal exponent value in this study decreased as the upper limit of pressure employed in the database was reduced. Therefore, the deviation in the partial pressure exponent with increasing hydrogen pressure may be attributed to variances in the product of the diffusion coefficient and Sieverts constant at elevated pressures. Published by Elsevier Science B.V.