Satoshi Fukada

Isotope separation factor and isotopic exchange rate between hydrogen and deuterium of palladium

An isotopic exchange experiment was performed using a Pd particle bed for a fundamental study of hydrogen isotope separation. The isotope separation factor and the rate constant of the isotopic exchange reaction between gaseous deuterium and hydride were determined from fitting numerical calculations to experimental effluent curves of the Pd bed. The separation factors under the condition of a dilute deuterium concentration were correlated with the relation of αH − D =exp(−0.121 + 228/T) and were independent of the total hydrogen pressure. The rate-determining step of the overall isotopic exchange reaction at T > 300K was diffusion in the pore of Pd particles. The step at T < 300K was estimated to be diffusion in the β-phase Pd, although there is a little possibility of isotopic exchange reaction based on Bonhoeffer-Farcus mechanism. The height equivalent to a theoretical plate, HETP, was correlated as a function of the interstitial fluid velocity in the bed.

Comparison of chromatographic methods for hydrogen isotope separation by Pd beds

Comparison among three chromatographic separation methods, i.e. hydrogen-displacement chromatography, self-displacement chromatography and frontal chromatography, is made in an experimental way using several gas mixtures of hydrogen and deuterium. There is small difference in the height equivalent to a theoretical plate (HETP) based on the plate theory among the three chromatographic techniques. The HETP value for the self-displacement chromatography is 3.9 cm, and that for the frontal or H2-displacement chromatography is 3.0 cm at the same flow-rate. The self-displacement chromatography is more useful for the separation of a small amount of deuterium or tritium from other hydrogen isotopes under a moderate recovery ratio. Since the frontal chromatography uses no other gas than the sample, it is more convenient for the separation of deuterium from natural hydrogen even though a lower recovery ratio.

Hydrogen Isotope Separation by Displacement Chromatography with Palladium

In order to establish a lab-scale hydrogen isotope separation system, experimental and numerical studies were performed by means of displacement chromatography of protium and deuterium using a bed of spongy palladium particles. The inlet deuterium concentration of 5.0% D or 54.9% D was prepared for the experiment. The equations of the material balance of deuterium in the bed and the isotopic exchange rate between protium and deuterium were simultaneously solved. The contributions of isotopic exchange reaction on Pd surfaces, diffusion in the solid and axial dispersion in the interstitial of the Pd bed to overall mass transfer were taken into consideration in the equations. The numerical calculation results fitted to the experimental data. They predicted well the maximum deuterium concentration in the effluent and the shape of the displacement band. In the calculations, we used the values of the concentration-dependent isotope separation factor and the isotopic exchange rate constant determined in our prev...

Possibility of Separation of Deuterium from Natural Hydrogen by a Palladium Particle Bed

Deuterium in natural hydrogen can be successfully concentrated by means of frontal chromatography using a Pd particle bed at room temperature. The deuterium concentration at the outlet reaches a maximum immediately after hydrogen breaks through the bed. The outlet concentration curve is correlated to a unified profile based on the plate model regardless of the gaseous flow rate and the inlet deuterium concentration. The height equivalent to a theoretical plate, HETP, decreases from 7.6 to 4.7 mm with an increase of the flow rate from 15 to 87 mL(NTP)/min.

Hydrogen isotope separation by self-displacement chromatography using palladium particles

We here propose a new system for hydrogen isotope separation using columns packed with Pd particles. The present system is a modified one to adopt self-gas purge different from hydrogen displacement chromatographic techniques previously reported<1l-(5). The selfdisplacement chromatography uses no carrier gas in a similar way to Hoys method<6l. Hydrogen isotopes gas mixture is easily transferred by pressure difference without any external pump through twin columns maintained at different temperatures. Each hydrogen isotope is separated at different elution times.

Hydrogen isotope separation with palladium particle bed

Abstract Calculations and experiments of the isotopic exchange from a hydride to a deuteride and from a deuteride to a hydride are comparatively conducted for a basic study of the hydrogen isotope separation using a metal particle bed. The numerical calculations reveal in terms of the dimensionless parameters of Peh, Stg, Sts and Str how much effect longitudinal dispersion in the bed, diffusion in the gaseous phase and the solid phase, and the intrinsic isotopic exchange process, have on an effluent curve. The H–D isotopic exchange experiment using a Pd bed shows that the effluent curves under the condition of the comparatively high D concentration agree with those of the local equilibrium model regardless of the H to D and D to H exchanges.

Effect of nitrogen on hydrogen absorption in titanium particle beds

Abstract In order to develop a method for the separation of hydrogen and nitrogen as impurities in inert gas, a study was performed using titanium particle beds. Experiment was focused on effects of nitrogen on the amount and the rate of hydrogen absorption in case of both pre-exposure and co-flow conditions. Although nitrogen in case of the pre-exposure decreased only hydrogen capacities, co-flow nitrogen affected mainly hydrogenating rates. Variations of nitrogen toxicity with temperature and the concentrations of hydrogen and nitrogen were correlated by using an overall mass-transfer capacity coefficient. A qualitative explanation for the differences in the nitrogen toxicity was given based on the formation of a nitride film on the surfaces. In addition, removal rates of nitrogen were quantitatively evaluated. It was desirable to operate the titanium bed at 600°C for hydrogen recovery and at above 900°C for nitrogen removal.

Hydrogen isotope separation based on isotopic exchange in palladium bed

A continuous hydrogen isotope separation system using twin beds of metals or alloys is here proposed. The isotope separation system called a twin-bed periodically counter-current flow (TB-PCCF) is analytically and experimentally investigated. Palladium and LaNi 4.7 Al 0.3 were selected based on experimental data of the isotope separation factor and the isotopic exchange rate. Numerical calculations by a plate model revealed effectiveness of the TB-PCCF method which is composed of an enriching column packed with Pd particles and a stripping column packed with LaNi 4.7 Al 0.3 particles. A preliminary experiment was performed at the condition where absorption and desorption cycles are repeated between room temperature and 473K for Pd and 363K for LaNi 4.7 Al 0.3 at the total reflux, and it showed possibility of the hydrogen isotope separation.

A STUDY OF A NEW HYDROGEN ISOTOPE SEPARATION SYSTEM USING A SIMULATED MOVING BED

A new hydrogen isotope separation system has been experimentally studied to concentrate deuterium from natural hydrogen. The present system comprises four columns packed with Pd particles and is operated in such a way that Pd particles and a hydrogen isotope gas flow simulated countercurrently. Deuterium is concentrated at the top end of the column at room temperature and atmospheric pressure. The deuterium concentration increases with an increase in the number of passages through the columns. When a 0.00996 in molar fraction D2 + 0.994 H2 mixture or natural hydrogen with 0.00015 D in atomic molar fraction was passed through 16 columns, the maximum atomic molar fraction of deuterium at the column top end were 0.728 or 0.0508, respectively.

Analysis of oxygen reduction rate in a proton exchange membrane fuel cell

The rates of oxygen reduction and generation of water vapor in a gas diffusion electrode and an active catalyst layer of a proton exchange membrane fuel cell were analytically studied. In particular, the analytical model accounts for the diffusion of oxygen and water vapor, the reaction of oxygen and hydrogen ion in the liquid and the effectiveness factor of a porous Pt catalyst on the cathode side. Calculations of cell polarization behavior are compared with existing experimental data. There is a great possibility that the rate limiting process is transport of oxygen and hydrogen ion in the Pt catalyst particle when the effective diameter of the Pt catalyst particle is greater than 2 μm.