Isotope Separation Factor Research Articles

Quantum sieving in organic frameworks

The isotopic separation factors for T 2/H 2 and D 2/H 2 mixtures adsorbed in various organic frameworks have been calculated using path integral Monte Carlo simulations. The results are in fair agreement with the available experimental data, and show a very strong dependence on temperature. The selectivity shows a less pronounced dependence on the external pressure, but different behaviours are found for different materials. They are analyzed from the point of view of the solid–fluid potential energy surface.

Effect of Cation on HTO/H2O Separation and Dehydration Characteristics of Y-Type Zeolite Adsorbent

Several types of adsorbers have been studied as they are considered for the first stage of water detritiation systems processing more than 100kg/h of high-level tritiated water generated in a future fusion plant. Zeolite is a suitable adsorbent since it is an inorganic material having a large water capacity. Rapid dehydration characteristics as well as a large HTO/H2O separation factor is necessary for the adsorber to minimize its size. Present experiments were focused on the effect of cations on HTO / H2O separation and dehydration characteristics of Y-type zeolites. The selected cations are Na, K and Ca. The flamework SiO2/Al2O3 ratio of the zeolites is fixed to 5.0 in the present experiments. It was found that the isotope separation factors are around 1.1-1.2 under static conditions. As for dehydration, operating temperature fixes the capacity of movable water from the zeolites. The capacity at room temperature is NaY > CaY > KY. HTO dehydration characteristics depend on the accumulated purge gas amount, while the purge gas rate is less influential. Effect of temperature on HTO dehydration is also less influential especially in the early stage of dehydration. Pressure swing is an effective method for HTO dehydration.

Hydrogen Isotope Separation Using Molecular Sieve of Synthetic Zeolite 3A

It is known that hydrogen isotope molecules can be adsorbed easily onto synthetic zeolite 4A, 5A, and 13X at the liquid-nitrogen temperature of 77.4 K. We show here that hydrogen and deuterium are not adsorptive onto zeolite 3A at the same temperature. This phenomenon is explained by assuming the molecular sieve function in zeolite-3A-crystalline lattice structure. From a series of pseudo-isobaric experiments, it is also shown that the sieving phenomenon appears in a range above 77.4 K. This behavior is interpreted as resulting on the dependence of sieve’s mesh size on temperature, where the sieving effect is considered to appear at a certain temperature. In this interpretation, an isotopic difference between hydrogen and deuterium is suggested to exist in the sieving effect appearance temperatures. This is endorsed in the result of pseudo-isobaric experiments. This temperature deference is very significant because that indicates the possibility of an effective method of hydrogen isotope separation. This possibility is verified through an experimental series of adsorption-desorption with a mixture of H2 and D2, where the gas samples adsorbed through the sieve operated at intentionally selected temperatures are isolated and then analyzed. The result demonstrates remarkable values of isotope separation factor.

Influence of Framework Silica-to-Alumina Ratio on the Tritiated Water Adsorption and Desorption Characteristics of NaX and NaY Zeolites

The fixed-bed adsorption process has been studied as one of the promising processes for the recovery of tritiated water in the field of nuclear fusion. The influence of the framework SiO2/Al2O3 ratio ranging from 2.0 to 10.0 on the tritiated water adsorption and desorption characteristics in the H2O-HTO binary systems was systematically examined using NaX and NaY zeolites. A large difference in isotherm was observed by changing the SiO2/Al2O3 ratio from 7.0to 10.0. The framework SiO2-to-Al2O3 ratio has a slight effect on the isotope separation factor. The capacity of removable water from NaY10.0 around room temperature is approximately four times larger than that from NaA2.0 even though both zeolites have nearly the same capacity for absorbable H2O at nearly P=P0= 1:0. The weaker interaction generates the isotope effect on desorption. The HTO dehydration ratio has a strong interrelation with the accumulative amount of purge gas. Dehydration is independent of the flow rate of the purge gas. On the design side of the water adsorption process with multi-absorber systems, the size of the water absorber such as a dryer or dehumidifier can be downscaled with NaY10.0 as the adsorbent since the consideration of the heating and cooling periods necessary for the temperature swing desorption process is not required in the NaY10.0 column.

Counterion effects on the isotopic properties of the Cl− and Li+ ions in aqueous solutions

The reduced partition function ratios between isotopic forms (β-factors) were calculated by the ab initio RHF/6-311++G**(3df, 3p) and MP2/6-311++G**(3df, 3p) quantum-chemical methods for hydrated chloride ion and ion pair hydrates NaCl·nH2O and LiOH · nH2O. The influence of the Na+ cation on the β-factor value and the chlorine isotope separation factor in the precipitation of NaCl from concentrated aqueous solutions was found to be substantial. At the same time, the presence of OH− counterions had no noticeable effect on the β-factor of the hydrated Li+ cation.

Lithium isotope effect accompanying electrochemical insertion of lithium into gallium

Lithium has been electrochemically inserted from a 1:2 (v/v) mixed solution of ethylene carbonate (EC) and methylethyl carbonate (MEC) containing 1 M LiClO 4 or from dimethyl sulfoxide (DMSO) containing 1 M LiCl into gallium, and the lithium isotope fractionation accompanying the insertion has been observed. The lighter isotope was preferentially fractionated into gallium, which was in accordance with the theory of the equilibrium isotope fractionation arising from molecular vibrational quantum effects. The single-stage lithium isotope separation factor ranged from 1.015 to 1.025 at 25 °C. It was independent both of the kind of electrolyte solution and of the chemical composition of the Li–Ga alloys formed within the experimental range studied and within experimental uncertainty.

Electrolytic D/H isotope separation efficiency and electrocatalytic activity of Mo–Pt intermetallic phases

The aim of this work was to investigate efficiency of the electrolytic separation of hydrogen isotopes (D/H), from alkaline 6 M KOH solution as standard electrolyte, on the Mo–Pt intermetallic phases as cathode materials. We measured the isotope separation factor ( α) of the single-stage process, as a basic parameter determining the isotope separation efficiency. Furthermore, we have found that some combinations of activating compounds (ionic activators added directly into the electrolyte, assuming in situ activation) can reduce energy needs per mass unit of hydrogen produced, as well as the isotope separation efficiency, compared to those of the standard electrolyte. Also, the electrocatalytic ability of Mo–Pt intermetallic phases for the hydrogen evolution was investigated and evaluated at fixed overpotential (energy input) trough measured current density. Such investigations offer a possibility to optimize the electrolytic process, based on a significant upgrade of the efficiency regarding two needs: hydrogen production and isotope separation.

Enrichment of slightly concentrated tritiated water by electrolysis using a palladium cathode coated on ionic solid polymer membrane—Design and results

In nuclear installations, tritiated water is generally produced in the process of detritiation of air circulating in the glove boxes. The goal of this work concerns enrichment of this tritiated water at low concentration by electrolysis. The choice of this electrolyzer was dictated by the passivity of selected materials to the radiolysis in low-level tritiated water and the selectivity of the method avoiding further elimination of tritiated water and moisture before release in environment. According to the results, it is feasible to treat non-negligible volume of low-level tritiated water using a cathodic palladium membrane coated on an ionic solid polymer membrane. Presence of a palladium black deposit on the palladium membrane improves effectiveness. Enrichment in tritiated water depends on the isotopic separation factor, thereby the current and the permeability values.

Anion-exchange chromatographic study of the chlorine isotope effect accompanying hydration

The single-stage separation factor for chlorine isotopes ( 35Cl and 37Cl) was determined to be 1.00034 by anion exchange chromatography on a 4.5-m column operated in reverse breakthrough manner at 25 °C. This value is in good agreement with those obtained in our previous works. It was confirmed that the lighter isotope ( 35Cl) was preferentially fractionated into the resin phase, whereas the heavier isotope ( 37Cl) partitioned into the aqueous phase. This observation, however, contradicts the experimental results for Cl isotope fractionation during NaCl precipitation and the recent theoretical results on Cl isotope fractionation: the 37Cl isotope selectively enriched into the solid phase and not into the aqueous phase. This discrepancy is discussed based on the theory of isotope distribution between two phases. It is suggested that the chromatographic results reflect an isotope effect accompanying hydration rather than an isotope effect due to a phase change, whereas the reverse is the case for the results in the NaCl precipitation study.

Transient Behavior of Enrichment of Tritium Water in Adsorption-Distillation Column

Enrichment of tritium in an adsorption-distillation column was experimentally investigated under the two processes of simple distillation and total-reflux distillation. Adsorption of water on silica-gel pellets enhanced the total isotope separation factor in the water distillation column. The transient behavior of tritium enrichment was analyzed using material balance equations of tritium and water in each cell with a height corresponding to HETP. The experimental transient behavior was well simulated by the material balance equations with additional assumptions on vapor and liquid flow rates regardless of the different processes of simple distillation and total-reflux distillation.

Magnetic field effects on the hydrogen isotope separation with metal hydrides

Hydrogen isotope separation experiments were conducted under the influence of magnetic field with the ferromagnetic LaCo5 and the paramagnetic LaNi5 compound as working materials. The deuterium concentration in the gas phase after hydrogen-absorbing reactions depended on applied magnetic fields for LaCo5, but not for LaNi5. The isotope separation factor α=(D/H)gas/(D/H)solid increased from 1.54 in zero field to 2.25 at 13 T in the β+γ region for the system LaCo5–(H2+D2). The increase in a is related to the magnetic field effect on the equilibrium pressure in ferromagnetic metal hydrides.

Ion exchange properties and selectivity of lithium isotopes on ion exchangers in the hydrogen form prepared from LiTixZr2−x(PO4)3(0 ≤ x ≤ 2)

LiTixZr2−x(PO4)3 (0 ≤ x ≤ 2) (LiTZP(x)) were synthesized by heating stoichiometric mixtures of lithium carbonate, zirconyl nitrate, titanium oxide and phosphoric acid at 950 °C for 10 hours. Ion exchangers in the hydrogen form (HTZP(x)) were prepared by the acid treatment of LiTZP(x) and their cation exchange properties were investigated with group 1 and group 2 metal ions. While the topotactic ion exchange from LiTZP(x) to HTZP(x) occurred for 0 ≤ x ≤ 1.5, the main phase of HTZP(2.0) was semicrystalline layered Ti2O3(H2PO4)2·2H2O. All the ion exchangers obtained were not very stable and partially decomposed under basic conditions. HTZP(x) (0 ≤ x ≤ 1.5) showed high selectivity towards the lithium ion from among group 1 metal ions, whereas HTZP(2.0) showed no specific affinity towards any group 1 metal ions. The H+/Li+ ion exchange equilibrium in acidic conditions at 25 °C was attained within 7 days for HTZP(0.0), in 1 day for HTZP(0.5), HTZP(1.0) and HTZP(1.3) and within 1 min for HTZP(2.0). The H+/Li+ ion exchange rate thus increased with increasing x. The exceptionally high ion exchange rate on HTZP(2.0) could be ascribed to the layered structure of the main phase of HTZP(2.0). All the ion exchangers synthesized preferentially took up the lighter isotope of lithium (6Li) over the heavier counterpart (7Li). The maximum value of the lithium isotopic separation factor (S) was 1.044 obtained at x = 1.0 to 1.3. This indicated that the size and the nature of ion exchange sites was a determining factor of S, which depended on the differences in the ionic radius and electronegativity of titanium(IV) and zirconium(IV).

Transient Behavior of Enrichment of Tritium Water in Adsorption-Distillation Column

Enrichment of tritium in an adsorption-distillation column was experimentally investigated under the two processes of simple distillation and total-reflux distillation. Adsorption of water on silica-gel pellets enhanced the total isotope separation factor in the water distillation column. The transient behavior of tritium enrichment was analyzed using material balance equations of tritium and water in each cell with a height corresponding to HETP. The experimental transient behavior was well simulated by the material balance equations with additional assumptions on vapor and liquid flow rates regardless of the different processes of simple distillation and total-reflux distillation.

Tritium Isotope Separation Using Adsorption-Distillation Column

In order to miniaturize the height of a distillation tower for the detritiation of waste water from fusion reactors, two experiments were conducted: (1) liquid frontal chromatography of tritium water eluting through an adsorption column and (2) water distillation using a column packed with adsorbent particles. The height of the distillation tower depends on the height equivalent to a theoretical plate, HETP, and the equilibrium isotope separation factor, αH-Tequi. The adsorption action improved not only HETP but also αH-Tequi. Since the adsorption-distillation method proposed here can shorten the tower height with keeping advantages of the distillation, it may bring an excellent way for miniaturizing the distillation tower to detritiate a large amount of waste water from fusion reactors.

An experimental system to investigate kinetics and isotopic properties of the electrolytic metal hydride formation

We present in this paper an experimental set-up based in a mass spectrometer connected to a closed electrolytic cell. Calibrations accomplished with a Pt cathode and H 2O/D 2O mixtures have shown new kinetics in galvanostatic electrolysis. These findings may be relevant in some important processes such as the hydrogen evolution reaction, isotopic separation factors or the electrolytic formation of metal hydrides.

Chromatographic Lithium Isotope Separation Using Cubic Antimonic Acid as Column‐Packing Material

Ion‐exchange chromatographic lithium isotope separation was performed by using granular cubic antimonic acid as column packing material at 50°C. While the single‐stage separation factor for the lithium isotopes was 1.0020, independent of the flow rate, HETP was a monotonously increasing function of flow rate both in breakthrough and reverse breakthrough experiments. After 442 cm chromatographic development, the 6Li atomic fraction increased to 0.256 in the reverse breakthrough experiment and decreased to 0.026 in the breakthrough experiment both from its original value of 0.074. The granular C‐SbA was kindly donated by Toagosei Chemical Industry Co. We acknowledge Professor M. Hosoe, the National Defense Academy, who measured the lithium isotopic ratios reported in this paper.

Isotope effects in: a) Catalytic generation of hydrogen from sodium tetrahydridoborate and b) Oxidation of hydrogen in fuel cells

We have investigated deuterium/hydrogen (D/H) isotope effects a) during catalytic evolution of hydrogen gas from the water solution of sodium tetrahydridoborate (NaBH4), the sodium borohydride fueled hydrogen generator HGen-E, Fractal Carbon, with the carbon monolith supported platinum reactor was used; b) oxidation of hydrogen in a PEM-type fuel cell to produce electrical energy. We used the E-TEK membrane electrode assemblies with an active area of 4 cm2, assembled in a two fuel cell stack. Both processes are important as possible parts of an energy-hydrogen-energy cycle. Any transfer of energy into hydrogen or vice versa induces a change of the D/H isotope ratio, which can be considered from the isotope separation point of view and possible development of a method to produce heavy water as a by-product of the above cycle. In this way, the separation efficiency can contribute to the overall efficiency of the cycle. This work is an initiative to take the isotope effects into account while cycling energy via some specific processes. We measured the isotope separation factor (a) of the single-stage process, as a basic parameter determining the isotope separation efficiency. The results proved that deuterium migrated to the dense (liquid) phase in both systems. Average values of the obtained separation factors are: ?(a) = 5.4 ?(b)>12. The results obtained could serve for a model for optimization purposes rather than to improve the separation efficiency of a particular unit. To do that it would primarily be necessary to play with a variety of catalysts, which was beyond the main aim of this work.

A density functional theory study applied for carbon isotope effects in the non-aqueous [Cu(CO)] +/CO system

DFT calculations were performed on the carbon isotopomers of CO and CO-complexes [Cu(NH 2CH 2CH 2OH) 3(CO)] +, [Cu(CH 3OH) 3(CO)] + and results compared with (Du's) experimental results on the carbon isotope exchange equilibria between CO and CO–copper-complex. The gas-phase model was used even for calculating the isotope effects involving the solutes of solutions. Contributions of the extramolecular motion of the solute molecular to the RPFR are responsible for the steep slope of the ln α-vs. −1/ T plot of Du's data, where α is the isotope separation factor which is identical to K in the present exchange system. The calculated result agrees well with (Du's) experiment data.

Experimental determination of chlorine isotope separation factor by anion-exchange chromatography

Chlorine isotope fractionation factor was determined by strongly basic anion-exchange chromatography with 0.1 mol/l HCl at 25 °C. The magnitude of the factor was calculated as a single-stage separation factor of 1.00030 with analytical precision of 0.00006 (1 σ). The results showed that the lighter isotope ( 35 Cl ) was preferentially fractionated into the resin phase, while the heavier one ( 37 Cl ) enriched into the aqueous phase. This trend suggested that the hydrated Cl − ions in the aqueous phase were slightly more stable than the hydrated Cl − ions electrostatically interacting with the ion-exchange groups of the resin.

Lithium Isotope Effect Accompanying Electrochemical Intercalation of Lithium into Graphite

Lithium has been electrochemically intercalated from a 1:2 (v/v) mixed solution of ethylene carbonate (EC) and methylethyl carbonate (MEC) containing 1 M LiClO4 into graphite, and the lithium isotope fractionation accompanying the intercalation was observed. The lighter isotope was preferentially fractionated into graphite. The single-stage lithium isotope separation factor ranged from 1.007 to 1.025 at 25 °C and depended little on the mole ratio of lithium to carbon of the lithium-graphite intercalation compounds (Li-GIC) formed. The separation factor inceased with the relative content of lithium. This dependence seems consistent with the existence of an equilibrium isotope effect between the solvated lithium ion in the EC/MEC electrolyte solution and the lithium in graphite, and with the formation of a solid electrolyte interfaces on graphite at the early stage of intercalation.