Three-component isotope separation

Stream Percent J3Su Flow rate relative to top product  

For close isotope separation processes that depend on differences in molecular weight, such as gaseous diffusion or the Becker nozzle process. 

We wish to find a value function V, a generalization of the separation potential for a two-component mixture, now a function of Xf and x, which can be used to evaluate the separative capacity, and from it, the total flow rate. The difference equation (12.313) for Fis obtained by writing a V balance for the stage, in which the difference between the separation potential carried by the stage effluents and the stage feed is equated to the separative capacity of the stage, given by Eq. (12.174) asAfi/ /4  

When Eq. (12.313) is expanded in a Taylor series about Xs and x, the following differential equation is obtained  

Terms in F, dV/bXs, and bV/bXf, have dropped out because of material-balance relations. Substitution of ys —Xs from (12.311) and —Xe from (12.312) into (12.315) leads to 

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Three-component mixing models. Some isotope hydrograph separation studies have shown that the stream values fall outside of the mixing line defined by the two end-members (DeWalle et al., 1988). Other studies have shown that stream 3 values fall off the mixing line when both and are used for fingerprinting... 

The classical methods for detection and quantitation of racemization require analysis of the chiral purity of the product of a peptide-bond-forming reaction. For example, the Anderson test is used to explore a variety of reaction conditions for the coupling of Z-Gly-Phe-OH to H-Gly-OEt (Scheme 6). 9 The two possible enantiomeric tripeptides are separable by fractional crystallization, so that gravimetric analysis furnishes the racemization data. This procedure has a detection limit of 1-2% of the epimerized tripeptide. A modification by Kemp,1"1 utilizing 14C-labeled carboxy components, extends the detection limit by two to three orders of magnitude by an isotopic dilution procedure. The Young test 11 addresses the coupling of Bz-Leu-OH to H-Gly-OEt, and the extent of epimerization is determined by measurement of the specific rotation of the dipeptide product. 

Mass spectrometers are used primarily as tools for measuring isotopic compositions, although some kinds can also be used to determine elemental abundances. Mass spectrometers have three basic components (1) a means of ionizing the sample (2) a mass analyzer that separates atoms based on their masses and (3) a detector. Most of the time, the mass spectrometer is identified by its source, although the mass analyzer can also be identified. In the next few paragraphs, we will describe the various sources, the different mass analyzers, and the detectors, and then describe the most common configurations used in cosmochem-istry. For more details, see Gross (2008). 

Differences between the bulk compositions of chondrites, planets and asteroids can be attributed to accretion from different batches of CAIs, chondrules and other components, which are spread along variation lines on the standard three-isotope plot. The preservation of oxygen isotopic anomalies shows that there were numerous oxygen reservoirs for the manufacture of chondrules and CAIs that were quite separate. 

All of the processes for separating isotopes of hydrogen or other light elements dealt with in this chapter involve distribution between a liquid and a vapor phase. To remain consistent with standard chemical engineering usage, component fractions in the vapor phase are denoted by y and the liquid phase by x. For a two-component mixture, the symbol y or x wiD denote the fraction of desired component (e.g., atom fraction deuterium in a mixture of HjO, HDO, and DjO) in the vapor or liquid phase. For a mixture containing three or more components, a subscript will be used to designate the component. For example, hd denotes mole fraction HD in a vapor mixture of H2, HD, and Dj. However, in mixtures of Hj, HD, and D2 whose deuterium content is so low that the fraction of D2 can be ne ected, the mole fraction of HD will be denoted by > or x without subscript. 

Marti 2001), also make the analyses prone to atmospheric contamination. Nevertheless, the indigenous component can be separated by a stepwise gas extraction protocol in suitable samples, and three studies all find the isotopic composition of indigenous lunar nitrogen to be enriched in the heavy isotope by 13-17%o relative to the composition of the terrestrial atmosphere (Kerridge et al. 1991a Murty and Goswami 1992 Mathew and Marti 2001). Mathew and Marti (2001) note the approximate consistency of this composition with values reported for the terrestrial mantle but caution that fractionation effects during the formation of the moon are difficult to assess. 

Cylinders of the flashed gas were analysed for hydrocarbon gas composition on a Carle gas chromatograph (GC) system equipped with both a thermal conductivity detector (TCD) and a flame ionization detector (FID). An offline preparation system and dual inlet mass spectrometer (MS) were used to analyse the carbon and hydrogen isotopic values of hydrocarbon components. A customized Gow Mac GC was interfaced with a vacuum/combustion system to separate hydrocarbons from other components and combust to CO2 and water that were purified and sealed into Pyrex tubes for isotopic analysis. The CO2 was analysed directly on one of three dual inlet mass spectrometers Finnigan Delta S, Finnigan Delta + XL or VG SIRA II. The water was reacted with zinc turnings and converted to hydrogen gas, which was analysed on either the Delta S or Delta + XL MS. 

Numerical Modeling of Transient Isotope Responses On the first step, the authors analyzed in detail five possible heterogeneous methanation models based on two gas phase (CO, CH4) and three surface components (COads, Ca,ads, and Cp,ads) that follow from qualitative analysis of CO labeling data [19,21]. These models contained either a buffer step or parallel routes of methane formation. The homogeneous model having one type of methane intermediate was also considered. A methanation reaction was modeled separately from the entire set of reactions included in the Fischer-Tropsch ... 

The difference between the dissociation constants of HX and DX in the same solvent is termed a primary isotope effect, since isotopic substitution takes place at the bond which is being broken. The kind of comparison discussed in the last three paragraphs really involves both a primary effect and a solvent isotope effect, though the latter term is often used to describe the gross effect observed, since it cannot readily be separated into its components. In addition we may have secondary isotope effects, where isotopic substitution takes place in a part of the molecule not directly concerned in the reaction for example, the dissociation constants of CD3CO2H and CH3CO2H are not identical. These effects are much smaller than the primary ones, typical values being... 

The weak van der Waals potential between He atoms and the bosonic nature of He also are basic for understanding why He is the only bulk superfluid below Tc = 2.18 if at 0.05 bar. The rare isotope He, a fermion, on the other hand, only becomes superfluid at a three orders of magnitude lower temperature. There are many well known macroscopic manifestations of superfluidity such as (i) flow without resistance (ii) a vanishing viscosity (iii) the ability to creep out of vessels against the forces of gravity (iv) the fountain effect which is driven by a type of Maxwell demon which separates the superfluid from the normal fluid components and (v) an enormous thermal conductivity which is 30 times greater than that of copper. Table 7.1 compares some properties of liquid argon (also a cry-omatrix) with those of helium in the normal and in the superfluid state. 

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