Isotopes distillation

It is instructive to use the case of enriched deuterium production to describe distillation and exchange distillation isotope separation. To begin, the historical background of the need for... 

Although isotopes have similar chemical properties, their slight difference in mass causes slight differences in physical properties. Use of this is made in isotopic separation pro cesses using techniques such as fractional distillation, exchange reactions, diffusion, electrolysis and electromagnetic methods. 

Examination of possible systems for boron isotope separation resulted in the selection of the multistage exchange-distillation of boron trifluoride—dimethyl ether complex, BF3 -0(CH3 )2, as a method for B production (21,22). Isotope fractionation in this process is achieved by the distillation of the complex at reduced pressure, ie, 20 kPa (150 torr), in a tapered cascade of multiplate columns. Although the process involves reflux by evaporation and condensation, the isotope separation is a result of exchange between the Hquid and gaseous phases. 

Off-Gas Treatment. Before the advent of the shear, the gases released from the spent fuel were mixed with the entire dissolver off-gas flow. Newer shear designs contain the fission gases and provide the opportunity for more efficient treatment. The gaseous fission products krypton and xenon are chemically inert and are released into the off-gas system as soon as the fuel cladding is breached. Efficient recovery of these isotopes requires capture at the point of release, before dilution with large quantities of air. Two processes have been developed, a cryogenic distillation and a Freon absorption. 

In nature, oxygen occurs in three stable isotopic species oxygen-16 [14797-70-7] O, 99.76% oxygen-17 [13968-48-4], 0.038% and oxygen-18 [14797-71-8], 0.20% (7). Commercial fractional distillation of water produces concentrations of as high as 99.98% concentrations up to 55% are also produced. The isotope has been used to trace mechanisms of organic reactions. 

British Columbia, and three at the U.S. Army Ordinance Works operated by the DuPont Company at Morgantown, West Virginia Cluldersburg, Alabama and Dana, Indiana. The plant at Trail used chemical exchange between hydrogen gas and steam for the initial isotope separation followed by electrolysis for final concentration. The three plants in the United States used vacuum distillation of water for the initial separation followed by electrolysis. Details of these plants and their operations may be found in the Hterature (10). 

J. R. Bardet, W. H. Denton, and R. H. Sherman, "Hydrogen Isotope Distillation for the Tritium Systems Test Assembly," American Nuclear Sodef... 

Irreversible processes are mainly appHed for the separation of heavy stable isotopes, where the separation factors of the more reversible methods, eg, distillation, absorption, or chemical exchange, are so low that the diffusion separation methods become economically more attractive. Although appHcation of these processes is presented in terms of isotope separation, the results are equally vaUd for the description of separation processes for any ideal mixture of very similar constituents such as close-cut petroleum fractions, members of a homologous series of organic compounds, isomeric chemical compounds, or biological materials. 

The isotopic purity of the products from a lithium aluminum deuteride reduction is usually equivalent to that of the reagent. The presence of moisture has little effect on the isotope composition of the products, causing only the decomposition of some of the reagent. For the best results, however, it is advisable to distill the solvent— usually ether, tetrahydrofuran or dioxane depending on the desired reaction temperature—from lithium aluminum hydride directly into the reaction flask. In this manner the reduction of 3-keto-5a-steroids (60), for example, gives the corresponding 3a-di alcohols (61) in 98% isotopic purity. ... 

Dimethyl sulfate (16 g) is added to a mixture of dimethyl carbonate (400 g) and deuterium oxide (1(X) g) in a 1 liter flask. Two reflux condensers and a drying tube are attached in series (initial rapid evolution of carbon dioxide may entrain some liquid), and the reaction mixture is heated under reflux for 72 hr. The methanol-OD is distilled directly from the reaction flask through a 30 cm Vigreux column. Redistillation from a small amount of sodium yields 275 g of pure methanol-OD bp 66-66.5° isotopic purity, 98.6%. ... 

Tetraethyl orthosilicate (104.2 g) and deuterium oxide (40 g) are stirred in a stoppered distillation flask at room temperature until a viscous, miscible solution is obtained (approximately 24 hr). (A small amount of acid catalyst, such as deuteriochloric acid, speeds up the reaction considerably. ) A distillation head and a receiver cooled in a dry ice-acetone bath are attached and the solution is distilled at 2 mm pressure until no further product is obtained. A 90% yield of ethanol-OD is obtained having an isotopic purity equal to that of the deuterium oxide used. ... 

Fractional distillation of NO provides another effective route and, as the heavier isotope of oxygen is simultaneously enriched, the product has a high concentration of Many... 

The authors constructed an 80-well hydrogenator. Fifteen catalysts were screened and the isotopic incorporation assessed by LC/MS. The regiospecificity was determined by VAST Direct Injection NMR [82] in conjunction with SPADEZ [83], a multispectrum analysis tool - this is capable of displaying and quantifying up to 96 spectra. So far it has not been possible to vary the solvents as, under the experimental conditions, the more volatile distil over into the less volatile solvents. 

Isotopic and chemical patterns are given for an ambient sample (downtown Portland) and four sources of carbonaceous particles. The source C contributions (Ct) are expressed as percent of total aerosol mass, and the subscripts refer to Vegetation (slash burning), Road dust, Oil (residual and distillate), and Auto exhaust. Units for the ordinate are also percent of total aerosol mass, except for, 4C which is expressed as dpm/g-aerosol. Abscissa points for each pattern are ordered as l4C, C, Si, Ni, and Pb. 

The onset of testing of hydrogen bombs in the atmosphere led to an understanding of isotope fractionation in the water vapor that distills from the ocean surfaces throughout the world. 

In figure 1, the points at very large isotope depletions (delta 0 -300 ppt and delta 180 -40 ppt) have been measured in very cold ice from the bottom of the Antarctic ice cap, laid down in ice ages. Points at small depletions (delta D O ppt and delta 180 0 ppt) have been measured in tropical precipitation distilled from warm oceans. Points between have been measured in middle latitudes. 

The IAEA monthly measurements show seasonal variations in that the heavy isotopes are depleted in precipitation when water vapor distills off cold oceans in the winters and enriched in precipitation when water vapor distills off warm oceans in the summers. See figure 3 for monthly isotope variations in precipitation, for example in Stuttgart. 

However, the history of the surface temperatures of the temperate oceans should be stored in the rings of trees which grew in the temperate regions of the world and which subsisted on precipitation which distilled from those oceans. Each tree ring should contain some kind of average annual value of the isotope ratios in the precipitation of the year corresponding to the ring. 

Thus in our study of isotope variations in lengthy chronological sequences of tree rings, we are evaluating fluctuations in the sea surface temperatures, from which distilled the precipitation which nourished the trees and the sea surface temperatures, in turn, are affected by variations in the ultraviolet spectrum of the sun. 

A logical explanation for the global nature of these correlations is that they are all related to variations of the sun, which cause variations in the temperature of the sea surface, thus causing variations in the isotopic composition of water vapor which distills off the sea and is stored as wood in trees and also forms the annual layers of the ice cap. The variations of the sun are furthermore related to the flux of solar neutrons in the earth s atmosphere and so cause small variations in the carbon-14 content of the bristle cones. During times of a quiet sun the average carbon-14 production is about 25 percent larger than when solar activity is high [43]. 

Using the above laboratory relations we compute the values of 6D and 618 expected for rain made by a single distillation from the ocean and for rain made by a subsequent distillation for sea rain which fell on the land. These values show that when rain and snow exhibit very large depletions of the heavy isotopes, e.g., 6D of -200 and -300 ppt, two or three distillations have occurred. It is known from measurements of tritium in rain [76] that two or three distillations occur in the U.S. between evaporation from the Pacific Ocean and precipitation in the eastern U.S. The agreement between the number of distillations deduced from stable isotopes and deduced from tritium is gratifying. 

If we are dealing with major elements, partition coefficients Dt may be expected to vary with many parameters, including temperature or liquid chemistry. For some elemental pairs and particularly for isotopes for which activity coefficients are correlated, there is a better chance, however, that the ratio of two partition coefficients Dn and Di2 shows lesser variations. We therefore subtract the distillation equation (1.5.3) for element or isotope il from that for i2 as... 

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