Stage Separation Factor Research Articles

Enrichment of lithium isotopes by a triazacrown trimerrifield peptide resin

A study on the elution chromatographic separation of lithium isotopes was carried out with a triazacrown trimerrifield peptide resin. The capacity of the triazacrown trimerrifield peptide resin has a value of 0.08 meq/g. Upon column chromatography [0.2 cm (I.D)×35 cm (height)] using 4.0M NH4Cl solution as an eluent, the single stage separation factor of 1.028 was obtained by the Glueckauf theory. The heavier isotope, 7Li, was concentrated in the resin phase, while the lighter isotope, 6Li, was enriched in the solution phase.

Chromatographic separation of magnesium isotopes by monoazacrown bonded Merrifield peptide resins

Magnesium isotope separation was investigated by chemical ion exchange with the 1-aza-12-crown-4 (I) and the 1-aza-18-crown-6 (II) bonded Merrifield peptide resin using an elution chromatographic technique. The capacities of each novel monoazacrown ion exchanger were 1.0 meq/g for (I) and 2.3 meq/g for (II) bonded Merrifield peptide resins, respectively. The single stage separation factor was determined according to the method of Glueckauf from the elution curves and isotopic assays. The separation factors of magnesium isotope pairs, 24Mg2+–25Mg2+, 24Mg2+–26Mg2+ and 25Mg2+–26Mg2+ were 1.015, 1.029, and 1.014 for (I) and 1.012, 1.024, and 1.009 for (II) bonded Merrifield peptide resins, respectively.

Separation of lithium and magnesium isotopes by hydrous manganese(IV) oxide

Lithium and magnesium isotopes were separated by chemical ion exchange using hydrous manganese(IV) oxide and elution chromatography. The capacity of manganese(IV) oxide was 0.5 meq/g. The glass ion exchange column used was 35 cm long with an inner diameter of 0.2 cm, and 2.0M CH3COONH4 solution served as eluent. The single stage separation factor was determined from the elution curves and isotopic assays according to the method of Glueckauf. The separation factor of 6Li+-7Li+ was 1.022±0.002, those of 24Mg2+-25Mg2+, 24Mg2+-26Mg2+, and 25Mg2+-26Mg2+ were 1.012±0.001, 1.021±0.002, and 1.011±0.001, respectively.

Separation of Magnesium Isotopes by Chemical Exchange with Manganese (IV) Oxide

Separation of magnesium isotopes was investigated by chemical ion exchange with manganese (IV) oxide using an elution chromatographic technique. The capacity of manganese (IV) oxide ion exchanger was 0.5 meq/g. The heavier isotopes of magnesium were concentrated in the manganese oxide phase, while the lighter isotopes were enriched in the solution phase. The glass ion exchange column used in our experiment was 35 cm long with inner diameter of 0.2 cm, and 1.0 M CH3COONH4 solution was used as an eluent. The single stage separation factor was determined according to the method of Glueckauf from the elution curve and isotopic assays. The separation factors of 24Mg2+-25Mg2+, 24Mg2+-26Mg2+, and 25Mg2+-26Mg2+ were 1.008, 1.014, and 1.006, respectively.

Separation of magnesium isotopes by 1-aza-12-crown-4 bonded Merrifield peptide resin

Magnesium isotope separation was investigated by chemical ion exchange with the 1-aza-12-crown-4 bonded Merrifield peptide resin using elution chromatography. The capacity of the novel azacrown ion exchanger was 1.0 meq/g dry resin. The heavier isotopes of magnesium were enriched in the resin phase, while the lighter isotopes were enriched in the solution phase. The single stage separation factor was determined according to the method of Glueckauf from the elution curve and isotopic assays. The separation factors of24Mg2+-25Mg2+,24Mg2+-26Mg2+, and25Mg2+-26Mg2+ isotope pairs were 1.012, 1.024, and 1.011, respectively.

Separation of15N by chemical exchange in NO, NO2−HNO3 system under pressure

The basic isotopic exchange reaction is responsible for the separation of15N in the Nitrox system that between gaseous nitrogen oxides and aqueous nitric acid with a single stage separation factor α=1.055 for 10M nitric acid, at 25°C and atmospheric pressure takes place. In order to know what happens in15N separation at higher pressure, when the isotopic transport between two phases is improved, a stainless steel laboratory experimental plant with a 1000 mm long × 18 mm i.d. column, packed with triangular wire springs 1.8×1.8×0.2 mm2, was utilised. At 1.5 atm (absolute), and 2.36 ml·cm−2·min−1 flow rate HETP was 7% smaller than at atmospheric pressure and 1.5 times smaller flow rate. HETP at 3.14 ml·cm−2·min−1 flow rate and 1.8 atm is practically equal with that obtained at atmospheric pressure and 2 times smaller flow rate. The operation of the15N separation plant at 1.8 atm (absolute), instead of atmospheric pressure, will permit doubling of the 10M nitric acid flow rate and of15N production of the given column.

Stage extent of separation in ideal countercurrent recycle membrane cascades

Rony's extent of separation ξ is useful to characterize the quality of separation of a binary feed that occurs in membrane stages, membrane modules and cascades. The stage extent of separation, ξ i , has a maximum value for a specified stage separation factor, α i . The ideal cascade design requires a minimum total interstage flow compressor duty, and membrane area to make a specified overall separation. It is shown that ξ i has the maximum value at each stage in an ideal membrane cascade composed of ideal perfect-mix stages. This is also true in a “properly designed” no-mix cascade composed of crossflow stages. This suggests that ξ is a basic separation index.

Analysis of Parameters for Ion Permeation in Immobilized Liquid Membranes. I. Perfect-Mix Stages and Cascades

This study is concerned with the engineering design and analysis of systems for which the basis for separation is the selective permeation of dissociated salts from aqueous feed to strip solutions through immobilized liquid membranes. Theoretical equations are derived for binary mixtures, assuming Fick's law, to model perfect-mix permeation stages, and separation cascades containing perfect-mix stages. The results should apply both to passive (ordinary) diffusion and macrocycle-mediated transport. Important stage variables include the ratio of total dissociated salt concentrations in the stage feed and strip solutions, the total concentration in the stage strip solution, the stage cut, and the ratio of permeability coefficients for the two species in the separation mixture, i.e., the ideal separation factor. The stage separation factor is a complex function of these variables, and may be much less than the ideal separation factor, depending on values of these variables. Severe stagewise diffusional limitations can exist, particularly if the feed solution must be stripped to very low concentration levels. A conceptual design for an ion permeation cascade is presented which suggests that the overall ion permeation process is quite complex and may be energy intensive. For many separations, cascading is required to achieve desired separations, even with very large ideal separation factors.

No-Mix and Ideal Separation Cascades

Abstract Ideal countercurrent recyle cascades are characterized by two propertie: 1) The compositions of heads and tails streams forming the feed stream to individual stages are the same, and 2) the heads separation factor for each stage is constant. When these two criteria are met, the heads and tails separation factors are constant and equal to the square root of the stage separation factor. The mixing of streams with different compositions within a separation cascade obviously constitutes an inefficiency since it is precisely the reverse of this process that is desired, hence Condition 1, which is often referred to as the no-mix-criterion. Separation cascades for which both criteria are valid are termed ideal. However, the ramifications of Condition 2 are not obvious and it is possible to design no-mix cascades which do not meet the second condition. Mathematical relationships between ideal and no-mix separation cascades are derived to quantify these differences. It is shown that Condition 2 minimizes ...

Improved Donors for the Separation of the Boron Isotopes by Gas-Liquid Exchange Reactions

Abstract Chemical exchange between gaseous boron trifluoride (BF3) and the liquid BF3·dimethyl ether complex has been used extensively for the commercial fractionation of boron isotopes. Several compounds never before studied as donors in the isotope exchange reaction were examined to determine if they were viable replacements for the dimethyl ether system. For the first time, ketones were studied as donors in the boron isotope exchange reaction. The ketones examined were acetone, methyl isobutyl ketone, and diisobutyl ketone. The ideal single stage separation factors, α, measured for these ketones were between 1.038 and 1.043 at 30°C. The observed separation factor for a fourth donor system, nitromethane, was 1.067 at 30°C, well above that predicted by theory or observed for any known BF3/donor system. For each of the systems studied, the separation factors were greater than the value of α = 1.027 reported for the dimethyl ether/BF3 system at 30°C. In view of the experimentally observed separation factor...

ZINC ISOTOPE EFFECTS IN COMPLEX FORMATION WITH A CROWN ETHER

Abstract Isotope effects for zinc upon complex formation with dicyclohexano-18-crown-6 were investigated. The single stage separation factor for unit mass difference (α = 1.013) was great compared with that of calcium isotopes. One of the isotopes, 67Zn, showed a larger isotope effect than the other isotopes of even mass number.

Chromatographic Separation of Calcium Isotopes with Polymer-Bound Ligands

Abstract Calcium isotopes were enriched in chromatography columns containing the polymer-bound ligands cryptand [2B22], cryptand [2B21], and 18-Crown-6. The largest equilibrium single stage separation factor, 1.0039 ± 0.0002 for the calcium 40/44 isotope pair, was found in calcium exchange with cryptand [2B22]. The largest separation factor found for 18-Crown-6 was 1.0025 ± 0.0003 for the 40/44 isotope pair. The size of the isotope effect was found to be highly dependent on the solvent composition. An iminodiacetate resin ion exchange column yielded small enrichments of calcium isotopes. Calcium 40/44 exchange with the chelating functional group iminodiacetate yielded a small equilibrium separation factor of 1.00011 ± 0.00003, which was more typical of calcium ion exchange isotope effects. Comparisons of the above chemical systems based on separative power showed crown chemical exchange to be an improvement over cryptand and iminodiacetate exchange. The cryptand system was rendered impractical as a consequence of a slow exchange rate and a resulting large stage residence time contribution to the separative power, on the order of 45 min. The separation factor for the iminodiacetate system was too small for practical applicability.

A Comparative Study of Gel-Type and Macroreticular Cation Exchange Resins for the Separation of Rare Earth Elements

Abstract Owing to the macro- and micro- pores in the matrix, macroreticular resins have larger micro-void volume ratio in the ion exchange column chromatography. It is advantageous in the ion exchange kinetics resulting from the quicker mass transfer. By means of EDTA displacement column chromatography for the Pr-Nd separation study, we have found that macroreticular cation exchange resins have higher separation efficiency in HETP, single stage time, and the pure Pr production rate, e. g. for AG 50W-X8, 200∼400 mesh resin (gel-type) and AG MP-50, 200∼400 mesh resin (macroreticular), the HETP values are 0.40 cm and 0.24 cm; the single stage times are 3.11 min and 1.30 min; the pure Pr production rates are 0.19 and 0.68 m mole/hr, respectively. Because both types of resins contain the same functional group, the single stage separation factors for Pr-Nd separation have the same value of 2.0±0.1 at 92°C. The cation exchange resins which were prepared in our laboratory with higher micro-void volume ratio could...

ChemInform Abstract: Hydrogen Isotope Effects in Ammonium Ion(aq)/Water Exchange and Distillation of Ammonium Chloride Solutions at 373 K.

AbstractThe single stage separation factor (αE) for NH4+/H2O exchange has been determined to be 1.05.

Rubidium Isotope Separation by Constant Current Electromigration in a Cation-exchange Membrane

Separation of rubidium isotopes (85Rb, 87Rb) by electromigration in a cation exchange membrane has successfully been carried out in a band operation manner at 25 °C. The migration velocity has been varied from 2.5 to 12.1 cm/h. There existed a wide non-isotope-fractionated zone between the 85Rb enriched zone at the front and the 85Rb depleted zone at the rear of the band. The single stage separation factor was about 1.0009 and was independent of the migration velocity, migration length and operation technique at a given temperature. The steepness of the 85Rb accumulation curves, increased with increasing migration velocity.

Lithium Isotope Separation by Liquid-Liquid Extraction Using Benzo-15-Crown-5

The lithium isotope separation in the liquid-liquid extraction system H2O/CHCl3 is investigated using benzo-15-crown-5 as complexing agent. The maximum single stage separation factor αmax for 6Li/7Li obtained in the present study was 1.044±0.003. For the chemical exchange reactions without valence change, this value is the second largest behind one obtained using cryptand (2 B , 2,1) polymer. The lithium salt was extracted into the organic phase with highly concentrated crown ether forming Li+[crown]2 complexes. The chemical and isotopic equilibria were attained rapidly. The separation factors were 1.026, 1.032 and 1.035 at 25°C for I− SCN− and trifluoroacetate (TFA) as counter anions, respectively. In regard to the separation factor, the distribution coefficient and the stability to the change of temperature, lithium iodide would be most suitable for the industrial application. The isotope effects in Li+-crown complex are hindered by the hydration of the complex ion, but the obstraction can be avoided by using the organic solvent with highly concentrated crown ether.

Lithium Isotope Separation by Cryptand (2B, 2, 1) Polymer

Single stage separation factors α have been determined for 7Li and 7Li between lithium ions in methanol and complexed ions with a cryptand (2B, 2,1) polymer. The 6Li was concentrated in the cryptand. The separation factors were compared with the values of other chemical exchange systems. The maximum enrichment factor obtained was ε=0.047±0.002. The figure is one of the greatest in the chemical exchange reactions without valence change and almost 10 times larger than the values of ion exchangers. The variation in α depending on the chemical species was small in the non-aqueous system. High enrichment of lithium isotopes was expected to be achievable by means of the chromatographic application of the cryptand (2B, 2,1).

Observations on flow fields generated by opposed free-jets of gas mixtures

Spatial distributions of velocities in the neighborhood of the interference zone of nondiametrically opposed two-dimensional free-jets of argon–helium mixtures have been investigated using Doppler-shifted fluorescence radiation excited by an electron beam. Macroscopic velocities for each species were measured using a scanning Fabry–Perot interferometer system. Complementary spatial distributions of species mole fractions were determined using a mass flow probe, molecular beam sampling system, and quadrupole mass analyzer. Data were obtained over a wide range of experimental parameters, in particular, the reservoir to test region pressure ratio, 1.9 to 42, the Reynolds number based on reservoir conditions and jet width, 25 to 117, the mixture ratio, from 1% to 10% argon in helium, and the total included angle between jet axes, 120° and 90°. Detailed field plots of velocity and of mole fraction provide the basis for the construction of parameteric correlation functions for velocities and for compositions. Stage separation factors were calculated giving values comparable with those expected from ideal barrier separation processes. Processes of separation are discussed.

Lithium isotope separation by cryptand (2B,2,1) polymer.

Single stage separation factors α have been determined for 7Li and 7Li between lithium ions in methanol and complexed ions with a cryptand (2B, 2,1) polymer. The 6Li was concentrated in the cryptand. The separation factors were compared with the values of other chemical exchange systems. The maximum enrichment factor obtained was ε=0.047±0.002. The figure is one of the greatest in the chemical exchange reactions without valence change and almost 10 times larger than the values of ion exchangers. The variation in α depending on the chemical species was small in the non-aqueous system. High enrichment of lithium isotopes was expected to be achievable by means of the chromatographic application of the cryptand (2B, 2,1).

Lithium isotope separation by liquid-liquid extraction using benzo-15-crown-5.

The lithium isotope separation in the liquid-liquid extraction system H2O/CHCl3 is investigated using benzo-15-crown-5 as complexing agent. The maximum single stage separation factor αmax for 6Li/7Li obtained in the present study was 1.044±0.003. For the chemical exchange reactions without valence change, this value is the second largest behind one obtained using cryptand (2 B , 2,1) polymer. The lithium salt was extracted into the organic phase with highly concentrated crown ether forming Li+[crown]2 complexes. The chemical and isotopic equilibria were attained rapidly. The separation factors were 1.026, 1.032 and 1.035 at 25°C for I− SCN− and trifluoroacetate (TFA) as counter anions, respectively. In regard to the separation factor, the distribution coefficient and the stability to the change of temperature, lithium iodide would be most suitable for the industrial application. The isotope effects in Li+-crown complex are hindered by the hydration of the complex ion, but the obstraction can be avoided by...