Negative Rejection of Group Ib Metal Cyanide Complexes in the Hyperfiltration by Cellulose Acetate Membranes. Donnan Membrane Effect

Abstract

Anionic cyanide complexes of Group Ib family metal ions, Cu^ICN)^? ₂, Ag^ICN)^? ₂ and Au^ICN)^? ₂, showed negative rejection in hyperfiltration through cellulose acetate membranes when the feed solution contained such polyvalent anions as succinate, tartrate, aspartate, ethylenediaminetetraacetate, polyacrylate, polyvinylsulfonate, phosphate, and sulfate in a substantial concentration. The dicyanometal complex anions are essentially membrane permeable, while the polyvalent anions are essentially membrane impermeable. Both types of anions combined with the membrane permeable countercations form an ionic ternary system in which the Donnan membrane effect operates to enhance the diffusion of the permeable salt through the membrane, resulting in its enrichment in the permeate solution. By taking advantage of this phenomenon, a selective enrichment of dicyanoargentite in the permeate and its separation from the coexisting transition metals were achieved. Based on this principle, a new hyperfiltration-ultrafiltration technique was proposed for the ion-selective separation of salts.     

The Enrichment of Heavy Water in a Continuous-Type Inclined Thermal Diffusion Column

Abstract

Equations of the best angle of inclination and the maximum separation for the enrichment of heavy water in a continuous-type inclined thermal diffusion column have been derived. Considerable improvement in separation was obtained by employing the inclined column instead of using the Clusius-Dickel column.     

A Novel Procedure of Hydrogen Isotope Separation Based on Chemical Exchange and a Selective Permeable Membrane

Abstract

It is shown theoretically that a novel process of hydrogen isotope separation can be obtained by combining bithermal isotopic exchange with transport through a selective permeable membrane. The theory of the process predicts that a small column with high separation and very small inventory can be realized. The method is attractive especially for small and medium scale processes, such as tritium enrichment, heavy water upgrading, and final deuterium concentration.     

Study of Nonsteady-State Continuous Membrane Column for Gas Separation

Abstract

The permeation and transport processes occurring in a continuous membrane column (CMC) are quite complex, and the system will exhibit inverse response behavior in a certain operating regime. To understand the complex interaction of system variables, this work developed a mathematical model for the CMC and solved the model equations. Dynamic responses of a CMC for the separation of N₂-CO₂, CO₂-O₂, and O₂-N₂ gas mixtures with capillary silicone rubber membranes are presented. The effect of the membrane permeabilities on the CMC dynamics is examined. Responses of system variables to various disturbances, together with the start-up transient of the system, are discussed. The knowledge of the unsteady-state behavior of the CMC will enable us to predict the performance of the CMC and to control the CMC in a dynamic environment.     

The Simplified Equation of Separation for the Enrichment of Heavy Water in a Batch-Type Thermal Diffusion Column

Abstract

A simple but precise equation of separation for the enrichment of heavy water in a batch-type thermal diffusion column has been derived with the consideration of a pseudobinary mixture. The experiment has also been conducted for various initial concentrations of D₂O and the results are in agreement with the prediction of the theory.     

The Extent of Separation in Continuous Multistage Binary Distillation

Abstract

Rony's extent of seapration has been applied to binary distillation, analyzing both single equilibrium stages and the cumulative separation obtained in a multistage column both at finite and total reflux. Both separation indices depend on relative volatility, reflux ratio, and composition. The cumulative extent of separation clearly shows the influence of reflux ratio on the separation obtained in a continuous distillation column. Small variations in the single-stage extent of separation appear to have a pronounced effect on the cumulation extent of separation and the number of stages required to make a given separation.     

Foam Fractionation of Mercury(ll) Nitro Complexes

Abstract

Using a recycle foam separation apparatus, the foam fractionation distribution factor, γ/C, of the anionic metal nitro complexes of mercury(II) with the cationic surfactant, hexadecyltrimethylammonium bromide, was determined. The distribution factor was measured as a function of nitric acid concentration. The maximum occurred at 0.1 N nitric acid, which is in agreement with the anionic ion-exchange column distribution coefficient. Total reflux foam fractionation experiments yielded a 150-fold increase in the enrichment factor with a 20% recovery of the mercury(II) ion.     

Carbon Di-Oxide Removal with Mesoporous Adsorbents in a Single Column Pressure Swing Adsorber

Abstract

A five-step PSA cycle was studied for CO₂ separation from CO₂-N₂ gas mixture in a single column at elevated temperatures using Poly-ethyleneimine (PEI) impregnated mesoporous silica SBA-15 as adsorbent. The PSA cycle study included a strong adsorptive rinse step in which the strongly adsorbed component, i.e., CO₂ was used for rinsing the adsorbent bed in order to increase the purity of CO₂ product. The study indicates that the adsorbent is regenerable under typical PSA conditions. The productivity of the adsorbent studied for CO₂ separation was found to be comparable with commercial zeolite adsorbents as reported in literature.     

Experimental Studies on the Separation of Deuterium Oxide in Continuous Thermal Diffusion Column for Low Concentration Range

Abstract

Separation equations for the enrichment of heavy water in a continuous-flow thermal diffusion column have been derived for low-concentration operations. Experimentals on two feed concentrations of the H₂O-HDO-D₂O system have also been conducted, and the results quantitatively confirm the predictions of theory.     

Optimum Plate-Spacing for the Best Performance of the Enrichment of Heavy Water in Flat-Plate Thermal-Diffusion Columns of the Frazier Scheme

Abstract

The effect of plate spacing on the degree of separation and production rate for the enrichment of heavy water in flat-plate thermal diffusion columns of the Frazier scheme with fixed operating expense has been investigated. The equations for estimating optimum plate-spacing for maximum separation and for maximum production rate have been developed. Considerable improvement in performance is obtainable when thermal diffusion columns with optimum plate-spacing are employed for operation.     

Concentration Maxima in Ternary Distillation at Total Reflux

Abstract

For a ternary fractionation system at total reflux, a procedure has been developed which predicts whether or not the component of intermediate volatility will achieve a concentration maximum at an intermediate location in the column rather than in the top or bottom product stream. Further, the value and location of any such maxima are analytically defined for a fixed feed and separation. Finally, the maximum value of the concentration maximum and its location are given for a fixed feed and column.     

Effect of Changes in Operating Variables on Stage-wise and Cumulative Separation in Binary Multistage Distillation

Abstract

The progressive separation that occurs stage-wise within a multistage distillation column is characterized by the cumulative extent of separation, ζ _N ; while the contribution of individual stages, δ _N , to the overall separation is given by the difference between ζ _N for successive stages. These indexes permit the “goodness” of separation for individual stages and for the entire column to be compared on an equivalent basis. This paper examines the effects of changing operating variables of reflux ratio, feed rate, feed composition, and feed stage location on the separation obtained in a distillation column containing a fixed number of ideal stages, and how the single-stage contribution changes when these variables are altered from the design value. The calculations show that the reflux ratio (R) is probably the most important variable in determining how well a column makes a separation. Separation declines rapidly as R is reduced below the design value, as the feed rate is increased at constant boil-up rate, and as the feed concentration drops below the design value. Changing the feed stage location of ±5 stages in a 50-stage column has a minimal effect on separation at all feed compositions. δ _N clearly shows how the contribution of individual stages changes when operating variables are varied from the design values.     

The Optimum Plate Aspect Ratio for the Best Performance in a Flat-Plate Thermal Diffusion Column with Transverse Sampling Streams

ABSTRACT

The effects of plate aspect ratio on the degree of separation, production rate, and plate surface area in a flat-plate thermal diffusion column with transverse sampling streams have been investigated. Theoretical considerations show that when a thermal diffusion column is constructed with the best plate aspect ratio, either maximum separation or maximum production rate or minimum plate surface area can be obtained. The optimum plate aspect ratio for maximum separation is obtained with a given production rate and plate surface area, while that for the maximum production rate is determined with the degree of separation and plate surface area fixed, and that for the minimum plate surface area is estimated with a known degree of separation and the production rate. It is interesting that the optimum plate aspect ratio for maximum separation is exactly the same as that for minimum plate surface area. The maximum separation and maximum production rate are achieved without changing the total expenditure, while the design with minimum plate surface area results in minimizing the total expenditure.     

Practical Sulfur Isotope Separation by Distillation

Abstract

Sulfur isotopes were separated in 1.07 and 1.50-m experimental packed distillation columns at cryogenic temperatures under total reflux. The ³²S/³⁴S ratio at column top was as much as 19% different from the bottom ratio. The ³²S/³³S separations were the square root of ³²S/³⁴S separations. Typical relative volatilities of ³²S/³⁴S are 1.0023 for H₂S, 0.9978 for SF₄, 0.9985 for SF₆, 1.0006 for COS, and 1.0011 for CH₃SH. A ¹²C/¹³C volatility of 0.9982 was also seen in COS. Sulfur separations in SF₄ and SF₆ and the carbon separation in COS are reverse isotope effects.

Distillation is a feasible method for sulfur isotope separation. Hydrogen sulfide is the best candidate compound for a practical sulfur isotope separation. Existing distillation columns could economically produce as much as 50 kg/yr of contained ³⁴S at 15% enrichment. Smaller amounts of more highly enriched isotopes could also be produced.     

Separation of Heavy Water by Vapor-Phase Thermal Diffusion Coupled with Distillation and Condensation

Abstract

A study on the enrichment of heavy water in a vapor-phase thermal-diffusion column has been conducted. With the combination of the effects of distillation, vapor-phase thermal diffusion, and partial condensation, considerable improvement in the degree of enrichment has been achieved in a vapor-phase column rather than in a liquid-phase column. It was also found that even the part of enrichment contributed only by vapor-phase thermal-diffusion effect is much higher than that obtained by liquid-phase thermal diffusion.     

A Study on the Separation Efficiencies of Rotating-Tube Wired Thermal-Diffusion Columns under Higher Flow-Rate Operations

Abstract

Even under higher flow-rate operations, σ > 0.42A ², rotating the tubes oppositely in a wired concentric-tube thermal diffusion column still substantially increases the separation efficiency by improving the cascading effect. The equations for estimating the best tube speed of rotation and maximum separation, with the inclination of the wire angles as parameters, have been derived. The maximum separation increases as the inclination of the wire angle decreases; however, this also leads to increasing the best tube speed of rotation and thereby raising the operating cost.     

The Extent of Separation: Applications to Multistage Systems

Abstract

The fundamental equations for calculating the extent of separation are given for countercurrent multistage systems operated at either zero reflux, partial reflux, or total reflux. With the component distribution coefficients assumed constant, simple expressions for the maximum extent of separation are derived. The calculations clearly show how multistaging and reflux influence component separation.     

Energy Consumption of Chemical Uranium Enrichment

Abstract

A quantitative study of chemical separation energy for enriching uranium-235 by the redox chromatography was conducted. Isotope exchange reactions between U⁴⁺-UO₂ ²⁺ ions in the enrichment column are maintained by the redox reactions. The chemical separation energy is ultimately supplied by hydrogen and oxygen gas for regenerating redox agents. The redox energy for the isotope separation is theoretically predicted as a function of the dynamic enrichment factor observed in the chromatographic development of uranium adsorption band. Thermodynamic treatments of the equilibrium reactions implies an “inverse redox reaction” which can be enhanced by the chemical potential of the ion-exchange reaction of oxidant. Experimental results showed 30 to 90% recovery of the redox energy by the inverse reaction. These results will devise a simplified redox chromatography process where a number of columns in one module is reduced.     

The Improvement of Separation Theory in a Continuous Thermal Diffusion Column

Abstract

A more precise equation of separation applicable to the whole concentration range in a continuous thermal diffusion column with the feed introduced from any position has been derived. The results are also represented graphically and compared with those obtained by Powers in which he, as well as almost all previous investigators, considered the concentration at the feed position of the column to be approximately the feed concentration.     

A Diffusion Scrubber for the Collection of Gaseous Nitric Acid

Abstract

A diffusion denuder with a thin anion exchanger membrane tube as the collecting element and with a scrubber solution flowing in a narrow annular gap outside the membrane is described. The use of this device with a dilute sulfate-sulfamic acid solution as scrubber has been exploited for collecting nitric acid. The method is essentially free from interference due to NO₂, and response characteristics are described for a continuous flow application. Direct UV detection, used to demonstrate response characteristics in the continuous monitoring mode, is not sufficiently sensitive for the measurement of low levels of ambient gaseous HNO₃.