Deuterium separation

Rechargeable metal hydrides have a number of potential applications in the "hydrogen economy" concept and in the present industrial sector. Because general surveys of hydride applications have been recently published(1,22,23), we will not try to review all the potential applications, but rather concentrate on a few that might be particularly applicable to the hydrogen industry storage containers, H2 compressors, H2 purification or separation, and deuterium separation. 

Deuterium Separation. Most hydrogen storage alloys show similar absorption/desorption properties for hydrogen and deuterium. Occasionally, however, the hydride and deuteride show... 

Hydrogen-Deuterium Separation.—When an aqueous solution is electrolyzed, the hydrogen gas evolved always contains relatively more of the lighter isotope than does the electrolyte the difference is expressed as the separation factor (s) defined by... 

As a result of experimental studies it appears that the electrolytic hydrogen-deuterium separation factors fall into two distinct classes " in the first 8 has a value of about 6, viz.,... 

Another starting material, fluoroform-d, was reported by Tuccio and Harford. This molecule undergoes multiphoton dissociation when irradiated with a pulsed CO2 laser and dissociates to yield DF. An enrichment factor of greater than 5000 was obtained. Based on these studies. Marling, Herman, and Thomas have proposed a 100 Mg/yr deuterium separation plant using trifluoromethane as the working material. ... 

Marling, J.B. Herman, I.P. Deuterium separation with 1400-fold single-step isotopic enrichment and high yield by C02-laser multiple-photon dissociation of 2,2-dichloro-l,l,l-trifluoroethane. Appl. Phys. Lett. 1979, 34, 439. 

To provide adequate space for the fusion reactor, electric generators, the electrolysis plant and the support equipment, the floating structure will be hundreds of meters in length and width. It will be supported by several hundred flotation-structures. Because of their large number the loss or leakage of one flotation structure, or even several, will not disable the platform. There will be time available for repair or replacement of the floats on a normal maintenance schedule. The volume inside the flotation structures will be available for support equipment such as water pumps, electrolysis units, deuterium separation equipment or simple storage. 

In a two-component mixture, the separation factor a is defmed as the fraction of desired component in the phase in which it concentrates divided by the fraction of desired component in the other phase. Deuterium, the isotope principally discussed in this chapter, almost always concentrates in the liquid phase. For such deuterium separation processes, the deuterium separation factor a is given by... 

Derivation of Eq. (13.3). The following derivation of Eq. (13.3) relating the deuterium separation factor in the distillation of water to the vapor pressure rr of H2O and D2O is similar to that given by Urey [Ul]. It is assumed that ... 

Water contains the three molecular species HjO, HDO, and DjO. In concentrating heavy water by distillation, the deuterium separation factor is defined as the ratio of the atomic ratio of deuterium to hydrogen in the liquid to the corresponding ratio in the vapor. In terms of the mole fractions of individual compounds in the liquid x and vapor y, the separation factor a is... 

Distillation of water. Combs et al. [Cll] have determined the deuterium separation factor in the distillation of water by measuring the H/D ratio in water liquid and vapor in equilibrium. The third and fourth columns of Table 13.4 compare their measured separation factors with values predicted by Eq. (133) from their values for the vapor pressures of pure H2O and DjO. The agreement in the two sets of values of In a is within 6 percent. The agreement with Kirdienbaum s vapor-pressure ratios [K2] is somewhat poorer. Rolston et al. [R8] have proposed the equation In a = 03592 — 803/T -I- 25,490/r to correlate all data to... 

Distillation of ammonia. Petersen and Benedict [P2] have made similar direct measurements of the deuterium separation factor in the distillation of ammonia. Table 13.5 compares their values for ammonia containing 24 percent deuterium with those predicted by Eq. (13.9) from vapor pressures of NH3 and ND3 measured by Kirshenbaum and Urey [K3], Groth et al. [G4], and Taylor and Jimgers [Tl]. 

Table 13.5 Deuterium separation factois in distillation of ammonia...

Process requirements. Distillation of water for deuterium separation differs from all other industrial distillation processes in the extremely small difference in normal boiling point between the key components, O.T C between HjO and HDD. This, coupled with the very low natural abundance of deuterium, leads to an extraordinarily high reboil vapor ratio, so that the heat consumption per unit of DjO product is enormous. 

Separation factors. Deuterium separation factors in the electrolytic plants described above, together with the types of cells used and operating conditions that may have had an effect on separation factor, are listed in Table 13.13. Separation factors of from 6 to 10 have been reported for the secondary plants, and from 3.8 to 7.0 for the primary plants. The lower values for the primary plants are attributed to their higher cell temperatures, their use of diaphragms, and the greater difficulty of keeping large equipment clean. 

In a detailed laboratory investigation of the effect of cell variables on the deuterium separation factor in electrolysis of water, Brun and co-workers [B13] have found that a depends on the cathode material, electrolyte composition, and cell temperature, generally as follows. The separation factor is higher for an alkaline electrolyte than for an add. With KOH, at 15°C, a pure iron cathode gave the highest value reported, 13.2. The separation factor for mild steel, the material used in most commercial electrolyzers, was 12.2. Values as low as S were reported for tin, zinc, and platinized steel. At 2S°C the separation factor with a steel cathode was 10.6, and at 75°C it had dropped to 7.1. 

Discussion of processes for industrial separation of uranium isotopes cannot be as complete as the discussion of deuterium separation in Chap. 13. The detailed technology of the most economical and most promising processes is subject to security classification and to proprietary restrictions. Nevertheless, processes for enriching uranium can be described in sufficient detail to make their principles clear and to illustrate the similarities and differences between them and processes for separating isotopes of light elements. 

If feed is cheap, e.g., natural water fed to a deuterium separation plant, the stripping section might be dispensed with. The countercurrent streams moving from product or waste ends back to the feed point are known as reflux streams. Materials balance requires the sum of product and waste withdrawal rates to equal the feed rate. 

Erdey-Gruz and Volmer and Butler/ to whom we owe a rate expression for charge transfer processes. Later, Frumkin " took into account the potential distribution at the electrode-electrolyte interface and its influence upon the process of discharge of ions. Experimentally observable quantities other than the Tafel constants have also been employed since then in elucidating the mechanism. For example, experimental observations of and attempts of theoretical interpretation of the electrolytic hydrogen-deuterium separation factor were presented by Topley and Eyring, Horiuti, " and others, " as briefly reviewed elsewhere. ... 

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