Multi-component Adsorption Characteristics of Hydrogen Isotopes on Synthetic Zeolite 5A-type at 77.4K

The pressure swing adsorption (PSA) method, operating rapid desorption, has become applied to medium-massive air-component separation. In this study, with the aim of applying the PSA method to a hydrogen isotope separation process, the multi-component adsorption characteristics of H₂-D₂ or H₂-HD-D₂ on a synthetic zeolite at the liquid nitrogen temperature 77.4 K are investigated by using a volumetric apparatus, where the system effects of thermal transpiration and diffusion are taken into account. The adsorption isotherms for pure H₂ and D₂ are shown in a wide pressure range between 10^-2 and 10⁵Pa. The isotherms are closely approximated by an error functional expression proposed here. The separation factors resulting in adsorption are measured in a wide range of amount adsorbed. The separation factors of D₂/H₂ are estimated in accordance with the ideal adsorbed solution theory using the adsorption isotherms for H₂ and D₂. The behavior of the estimated factors agrees with that of the experimental ones. The result suggests that values around 3 are expectable for the factors of D₂/H₂ at amounts adsorbed roughly between 0.01 and 1 mol/kg.     

Numerical Calculation of H2-HT Separative Performances up to −0.3 MPa of Thermal Diffusion Column with Fairly Higher Hot-Wire Temperature

By using the two-dimensional rigorous numerical solution of flow and convection-diffusion equations, the H₂-HT separative performances of thermal diffusion column with 15 mm-radius and 288.15K cold-wall was analyzed up to ?0.3 MPa for higher hot-wire temperature (up to ?1,700K). Flow analysis has revealed: (1) The magnitude of the free convection is almost proportional to the pressure, and laminar solution of free convection could not be obtained at the pressure more than ?0.32 MPa. (2) The magnitude of the free convection increases gradually with ΔT (the temperature difference between hot and cold surfaces), when ΔT<–800 K. In the range of larger ΔT, the magnitude is almost constant or rather decreases gradually with ΔT. As a result, the laminar solution could always be obtained at the pressure less than ?0.32 MPa, no matter how large ΔT may be. Separative analysis for H₂-HT isotope separation has made clear that the thermal diffusion column with 288.15 K cold-wall should be operated at (1) 0.15–0.2 MPa, (2) ΔT that is as large as technically possible, and (3) the feed rate F of 50–100 cm³ (288.15 K, 0.1 MPa)/min.     

Enrichment of Low Level Tritium from Hydrogen Using Potassium-Graphite Intercalation Compound (KC24)

A sorption-desorption process using potassium-graphite intercalation compound (K-GIC) was studied to verify its applicability to hydrogen isotope separation. Lowly concentrated tritium (7.55 MBq/mol-H₂) contained in about 1 l of H₂ gas was successfully enriched using 1 g of KC₂₄. Three cycles of the sorption-desorption process applied to the H₂)-HT gas mixture proved to enhance the tritium concentration by a factor of 3.9, with a concomitant reduction of volume to 1/14. The positive result obtained in this study promises for this type of sorption-desorption process using K-GIC very good prospects of useful application to hydrogen isotope separation. The experimental process was simulated by calculation based on the material balance of the two components, using data of equilibrium in single stage. The calculated values agreed very well with experimentally determined data, thus attesting the applicability of the above simulation procedure to designing K-GIC hydrogen isotopes separators.     

Hydrogen Isotope Separation by Plasma-Chemical Method

Deuterium transfer (exchange) reaction as shown in HDO+H₂=H₂O+HD was studied as a case similar to the tritium transfer reaction as shown in DTO+D₂=D₂O+DT, the first step in tritium isotope separation of the tritiated heavy water DTO. The transfer reaction was plasma-chemically catalyzed by allowing a gas mixture such as H₂O/D₂, D₂O/H₂, H₂O/HDO/H₂ or H₂O/D₂O/HDO/H₂ to flow through an atmospheric pressure discharge zone formed in a reaction chamber, the inner temperature of which was maintained just above 100°C. The plasma-chemical reactions diagnosed by infrared and emission spectroscopy revealed that the mixture underwent instantaneous deuterium transfer reactions as it passed the zone. The effectiveness of the method was demonstrated by high deuterium transfer rate, high separation factor of the transfer and a possibility of miniaturizing the separation facility.     

Uranium Isotope Separation by Cation Exchange Chromatography Using Uranous Sulfate Complexes

A nearly ideal displacement chromatography has been realized with an eluent of MgS0₄ and H₂SO₄ in the study of uranium isotope separation by means of cation exchange chromatography using uranous sulfate complexes. Uranium-235 was enriched at the end of the chromatogram and ²³⁸U was enriched at the front. Two long distance displacement experiments have been carried out, keeping an isotopic plateau region on the chromatogram. Consequently, good accumulation of the isotopic fractionation based on uranous-sulfate complex formation reactions obtained. The separation coefficient ε of this system was estimated to be about 5×10^?5.     

The theoretical study of the deuterium enrichment of H-D gas mixture in continuous-type thermal-diffusion columns

The separation equations for enrichment of deuterium in H-D (Hydrogen-Deuterium) gas mixture by continuous-type thermal diffusion columns were developed theoretically. The transport equation modeling treats the enriching and stripping sections separately for each component of H₂-HD-D₂ system to estimate the concentration between the bottom and top ends of the thermal diffusion column. The empirical expressions of the transport coefficients were determined with the previous experimental data (Arita et al., 1998) correlating in the exponential form in terms of operating pressure. The theoretical predictions of the degree of separation and separation factor for recovery of deuterium from H-D gas mixture are in good agreement with the experimental results.     

1993 National Symposium on Atomic Energy,Tokyo, Japan

A steady-state simulation model of the gas separation system using a hollow-filament type membrane has been proposed. The mass transfer coefficients in the non-porous thin layer, in the porous support layer of the membrane and in the boundary layer of the membrane surface are estimated in the model. The four types of flow patterns: cross flow, mixing flow, concurrent flow and counter current flow, are also considered in the model. The mass transfer through the non-porous thin layer of the membrane controls the overall mass transfer by ~99%. The experimental observations of TPL (Tritium Process Laboratory in JAERI) for N₂–H₂ and Air—H₂ systems agreed with the calculated results of the cross flow under a set of typical conditions (disposal volume of 2.78×10^?3 Nm³/s, feed-side pressure of 3.44×10⁵Pa, and permeated-side pressure of 1.07×10⁴ Pa). The validity of the simulation method was thus proved. For Air-H₂-H₂O system also, the recovery ratios calculated for H₂ are in good agreement with the experimental observations. However, the calculated recovery ratios of water vapor were slightly smaller than the experimental observations. This discrepancy may result from the difference in separation mechanism between H₂ and water vapor, or the construction change of membrane caused by the existence of water vapor.     

Reduced partition function ratios of hydrogen species adsorbed on platinum cluster Pt19 studied by density functional theory

Geometry optimization and estimation of H/D reduced partition function ratios (RPFRs) of Pt₁₉–H, Pt₁₉–H⁺, Pt₁₉–H₂, and Pt₁₉–H₂⁺ models of hydrogen species adsorbed on surfaces of metallic platinum particles, were carried out based on the density functional theory. Two types of optimized structures were obtained for Pt₁₉–H and Pt₁₉–H⁺, and three for Pt₁₉–H₂ and Pt₁₉–H₂⁺. Stabilization energy consideration suggested that the most probable structure for Pt₁₉–H and Pt₁₉–H⁺ is the one in which H/H⁺ is bonded to a Pt atom, and that for Pt₁₉–H₂ and Pt₁₉–H₂⁺ is the one in which two H/H⁺s are bonded to two adjacent Pt atoms with no direct bonding between the two H/H⁺s. The value of RPFR obtained for those structures ranged from 3.9303 to 4.4014 at 25 °C. Interaction between two adjacent H–Pt bonds seems to slightly enhance the mutual RPFR values.     

Effects of Partition Wall within Packings on Separative Performances of Water Distillation for H2O-HTO Isotope Separation

For the performance assessment of H₂O-HTO isotope separation by distillation, three-dimensional internal vapor flow and concentration profiles were obtained numerically for two types of packing of 6 mm of inner diameter and 6 mm of height: One is a simple cylindrical tube (packing I) and the other diametrically partitioned with an internal wall (packing II). The results of the concentration profiles were used to estimate separative performances of the packings. The total mass transfer rate of HTO from vapor to liquid per unit area of vapor-liquid interface per unit vapor flow rate decreased with an increase in the vapor flow rate, and the value for the packing II is smaller than that for the packing I in the range of relatively small vapor flow rate. Each separative power for the packing I and II has a maximum value of 1.4×10^–7 g/s at the Reynolds number of the vapor Re_v of 54 and 3.7×10^–7 g/s at Re_v =160, respectively.     

Numerical model for separation of H-D gas mixture in batch-type concentric-tube thermal diffusion columns

The modeling simulation for the separation of H-D gas mixture in batch-type concentric-tube thermal diffusion columns have been analyzed from the transport equation coupled with the application of mass balance. The most important assumption is that the concentrations of H₂, HD and D₂ are locally equilibrium at every points in the column as H₂ + D₂ ↔ 2HD. The concentration distribution equation was derived and the concentration difference between the bottom and top ends of the column could be estimated. The degree of separation and separation factor for recovery of deuterium from H-D gas mixture in the batch-type cryogenic-wall thermal diffusion column were estimated.     

Molecular-sieving effect of zeolite 3A on adsorption of H2, HD and D2

Synthetic zeolite 3A has the molecular-sieving windows of nominal diameter 0.3 nm in its crystal lattice framework, which obstruct the crystalline adsorption of molecules of diameter larger than 0.3 nm, except water, hydrogen and helium. The window's diameter slightly varies with temperature, however, that is endorsed in experimental results that hydrogen cannot be adsorbed at the liquid-nitrogen temperature. Authors measured the range of temperature where zeolite 3A permits hydrogen adsorption, and revealed the temperature difference of several degrees in appearance of molecular sieving for H₂ and D₂. This difference is important because from a H₂–D₂ mixture one isotope could be isolated by adsorption if operated at a temperature regulated between the molecular-sieving appearance temperatures. We have reported large values of D₂/H₂ separation factor obtained from molecular-sieving experiments. In this study, the effect of sieving for the hybrid-atomic isotope HD is examined using a H₂–HD–D₂ mixture. We here report the experimental HD/H₂ separation factor evaluated between the D₂/H₂ factor and unity. This result is significant because where the effective molecular diameter concerning the sieving mechanism is suggested. From this knowledge, the isotopic effect of sieving for HT and DT can be predicted.     

Inverse Power Series Fittings of Temperature Dependence of Thermal Diffusion Factors between Two Components of Hydrogen Isotope Molecules

Temperature dependence of thermal diffusion factor of binary isotope mixture of hydrogen with one tracer level component α^[A]?1.0 _Tab was numerically fitted as an inverse power series of temperature from 25 to 1,500 K so that relative errors are less than 0.01 to approximations of the rough estimate of thermal diffusion factor which was previously reported. Composition dependence of thermal diffusion factor was expressed as a linear function of the c-th power of the mole fraction.     

Hydrogen and Deuterium Transport through Type 304 Stainless Steel at Elevated Temperatures

The permeation time-lag method have been used to determine the permeabilities, diffusion coefficients and solubilities of hydrogen and deuterium in type 304 stainless steel of three kinds of surface treated specimens; with oxide film, reduced by H₂ gas and Pd coated. For the specimen with a thin oxide film the permeability increased abruptly at the temperature higher than 1,050 K owing to reduction of the oxide film by H₂ gas introduced. The permeability and diffusion coefficient for hydrogen-reduced specimens agreed with those for Pd-coated specimens showing the data of bulk diffusion limited. The isotope effects for permeability Φ_H/Φ_D, diffusion coefficient D _H/D _D and solubility were about 1.4, 1.2 and 1.1, respectively. From these values θ(=hν/k)=1,530±50K and θ′(=hν/k)=2,740±20K were obtained by the quantum effect of a harmonic approximation.     

Metallurgical properties of irradiated cold-worked Zr-2.5 wt% Nb pressure tubes

Three cold-worked pressure tubes of Zr-2.5 wt% Nb were irradiated as components of Chalk River reactor loops, under operating conditions similar to those in the Canadian design of heavy water cooled, heavy water moderated power reactor. A fourth tube, part of which was artificially prehydrided to about 200 ppm H₂, was irradiated unstressed, in air.     

Tritium Isotope Separation by Water Distillation Column Packed with Silica-gel Beads

Tritium enrichment or depletion by water distillation was investigated using a glass column of 32 cm in height packed with silica-gel beads of 3.4mm in average diameter. The total separation factor of the silica-gel distillation column, α_H-T—, was compared with those of an open column distillation tower and of a column packed with stainless-steel Dixon rings. Depletion of the tritium activity in the distillate was enhanced by isotopic exchange with water adsorbed on silica-gel beads that have a higher affinity for HTO than for H₂O. The value of alpha_H-T-1 of the silica-gel distillation column was about four times larger than that of a column without any packing and about two times larger than that of the Dixon-ring column. The improvement of α_H-T by the silica-gel adsorbent indicated that the height of the distillation-adsorption column becomes shorter than that of the height of conventional distillation columns.     

Separation Factor of Hydrogen and Deuterium by Suspension Electrolysis Using Mercury Cathode

The electrolytic separation factor between hydrogen and deuterium was examined using mercury or else platinum cathode immersed in IF NH₄Cl in 10v/oD₂O water containing cobalt sulfide powder in suspension. Several other kinds of powdered materials in suspension were also studied. In the case of mercury pool electrode, the materials added in suspension were effective in enhancing the hydrogen/deuterium separation factor, but powder suspension was ineffective on platinum plate electrode. The powdered material added in suspension served as catalyst on the hydrogen evolution reaction at the mercury cathode. The influence of the applied potential on the separation factor was studied over the temperature range of 15°~80°C. The results provided an indication of the rate-determining steps governing the electrolytic hydrogen evolution.

The experimental values obtained for the separation factor and activation energy gave an insight into the mechanism of the rate-determining step of the hydrogen evolution at the working electrode.     

TCAP氢同位素分离装置的小型化及分离性能

根据TCAP氢同位素分离原理及系统小型化要求,设计了一套小型氢同位素分离装置。采用分离柱外室中螺旋型电阻加热器对Pd/K分离柱进行加热,利用低温恒温槽中的低温无水乙醇在外室中循环冷却分离柱。采用西门子PLC模块,根据程序设定对TCAP分离过程进行自动控制。在参数优化的条件下,研究了全回流及生产模式下的分离效率。研究发现,设计的小型氢同位素分离系统实现了稳定的分离柱加热-冷却循环,循环时间为0.25 h。在生产模式下,由氘纯度为80%的原料气可分离出氘纯度99.5%产品气,生产效率可达8.7 mL/h。低氘含量H-D混合气（D%=20%）同样能实现明显的氘浓缩效果（产品气D含量达99.0%）。     

Gas Chromatographic Measurements of Hydrogen Isotopes Mixture by Using Catalytic Oxidation Type Detector

A new type of gas chromatograph for quantitative measurements of hydrogen isotopes mixture has been developed through the adoption of catalytic oxidation type detector. Experiments using He as the carrier gas were successfully performed for the separation of D₂-HD and H₂-HD-D₂ mixtures. The minimum detection limits were 0.4–0.9 μl-STP for these components. The linear calibration curves were obtained in the range of 10 μl-STP–20 ml-STP. The sensitivities for H₂, HD and D₂ were 843, 774 and 654 (μl-STP)^?1, respectively. The maximum time needed for the analysis was about 16 min.     

Numerical Analysis of Pressure Effects on Heavy Water Separation Characteristics for a Pair of Dual Temperature Multistage-Type H2/H2O-Exchange Columns

In order to study how the operating pressure has influence on the heavy water separation characteristics for a pair of dual temperature multistage-type H₂/H₂O-exchange columns, the authors utilized the analytical expressions derived from the finite difference equation describing the material balance in the exchange column. The separation characteristics of the system were studied theoretically under the conditions where the temperature in a hot column t_h=200°C, the pressure in a hot column π≦50atm and the pressure in a cold column π = 5–50atm.

As the results, the optimum modified specific column volume v^*_opt decreases with the increase of π and then keeps the nearly constant value, and is smaller at ≦=50atm than at ≦=30atm in the case where the temperature in a cold column t_c is constant. Other important parameters such as the optimum operating temperature in a cold column t_copt the optimum numbers of stages in a hot column M_opt and in a cold column t_opt, the optimum hydrogen to feed water molar flow ratio γ _opt and the optimum degradation ratio δ_opt were also calculated.