Showing papers in "Separation Science and Technology in 1980"

Analysis and Prediction of Sieving Curves for Ultrafiltration Membranes: A Universal Correlation?

Abstract: Sieving curves [variations in sieving coefficient (θ) with Einstein-Stokes radius (α) of the permeating macromolecule] of a number of synthetic ultrafiltration membranes, and of a variety of mammalian glomerular membranes studied in vivo, conform surprisingly closely to a log-normal-probability relationship between θ and α which allows determination of the complete sieving curve from experimental measurement of only two sieving coefficients for two macrosolutes of differing ESR. Even more striking is the finding that, for all membranes examined, the value of α corresponding to θ = 0.5 (the inflection point in the sieving curve) varies only between 17 and 34 A, and geometric standard deviation about the mean macrosolute radius ([sgrave]α), which is inversely related to the “sharpness” of the sieving curve, lies between 1.2 and 1.7. It is concluded that not only is the log-probability correlation a reasonable and convenient means for interpreting and predicting membrane sieving data, but that most ...

A Novel Approach to Gas Separations Using Composite Hollow Fiber Membranes

Abstract: A method has been developed by which a porous hollow fiber which cannot separate gases to a significant extent can be made to exhibit its intrinsic separation properties by coating with an appropriate material. A unique feature of this composited fiber is that the separation properties are determined by the porous support polymer rather than by the coating polymer. The hollow fibers produced by this method have extraordinarily high rates compared to earlier hollow fibers used for gas separations. In addition, they can function under extremely high pressure gradients. Gases such as He, H2, and CO2 can be separated from gases like CH4, CO, and N2, and the system is chemically and physically stable to a wide range of typical industrial contaminants. As a result, systems based on these fibers should be useful in a variety of processes, some of which include stream splitting, gas composition control, H2 upgrading, and purge gas recovery.

Application of N, N-Dialkyl Aliphatic amides in the Separation of Some Actinides

Abstract: N, N-dialkyl substituted alkyl amides are known to be good extractants of some actinides such as U, Pu, and Th. Their stability is comparable to that of TBP, and their degradation products do not interfere as do the degradation products of TBP. On the other hand, the principal disadvantage of the amides is their tendency to form poorly soluble U adducts in organic diluents. A systematic investigation has been carried out on the extractive behavior of two typical alkyl amides of different structures with respect to the actinide ions UO2 2+, Th4+, Np+4, Pu+4, NpO4+ 2, PuO2+ 2, Pu3+, and Am3+, as well as with respect to the most significant fission products. The results obtained have been compared with those obtained using TBP in the same experimental conditions, verifying the applicability of amides in the separation of U from Th.

Selective Removal of Heavy Metal Ions from Aqueous Solutions by Diafiltration of Macromolecular Complexes

Abstract: A process for the selective removal of heavy metal ions with macromolecular chelating agents or emulsified liquid ion exchange materials in combination with ultrafiltration is described. The theoretical limitations of the procedure are discussed, and several practical applications are presented.

Sulfonic Acids: Catalysts for the Liquid-Liquid Extraction of Metals

Abstract: Three sulfonic acid extractants, dinonylnaphthalene sulfonic acid (HDNNS), didodecylnaphthalene sulfonic acid (HDDNS) and di-(2-ethyl-hexyl) sodium sulfosuccinate (Aerosol OT, AOT) are compared as to their effects on the extraction of nickel with LIX63. The acidic extractants interact synergistically with the oxime. Interfacial tension results are presented which demonstrate that the sulfonates form reversed micelles in non-polar organic solvents. It is proposed that the reversed micelles catalyze the extraction by specific solubilization of both the metal and the extractant, resulting in an increase in the interfacial concentration of the reacting species. The ability of LIX63 to chelate with nickel without deprotonating permits the synergism to occur at low pH.

Magnetic Field-Flow Fractionation: Theoretical Basis

Abstract: The application of high gradient magnetic fields to field-flow fractionation (FFF) is quite attractive based on the preliminary calculations presented here. The theoretical basis has defined the parameters of force on the individual particles and normal FFF parameters to evaluate the separation capability. The possible application of magnetic FFF to dynamic systems as well as a tool for separation of nominally paramagnetic and magnetically tagged molecules provides an impetus for further development.

Annular Centrifugal Contactors for Solvent Extraction

Abstract: Annular centrifugal contactors suitable for laboratory use in solvent extraction work have been designed and tested for both hydraulic performance and mass-transfer efficiency. The 2-cm contactors have nominal flow rates of 80 mL/min and mass-transfer efficiencies of at least 85% as measured by the extraction of uranium. These contactors work well for organic-to-aqueous (O/A) flow ratios greater than 0.8. Multistage units allow proposed flow sheets to be tested on a continuous basis in the laboratory. Scale-up to larger plant-size units is straightforward.

Studies of the Size-Selective Extraction of Alkali Metal Ions by the Synergistic Extraction System, Crown Ether-DI(2-Ethylhexyl) Phosphoric Acid-Benzene

Abstract: In order to take practical advantage of the size-selective cation-coordinating ability of the cyclic polyethers (crown ethers), experiments seeking a means of avoiding the problem of solubilizing a mineral-acid anion in a nonpolar organic diluent were performed. Mixtures of several known extractants and crown ethers were tried. Results presented indicate that organic soluble cation exchangers mixed in solution with crown ethers produce a synergistic extractant mixture that largely exhibits the size-selective properties expected of the crown ether. Data are presented for the extraction of macro concentrations of alkali metals by di(2-ethylhexyl) phosphoric acid—dicyclohexyl-18-crown-6 mixtures at a single pH, and at nonloading condition(σ metal cone < 0.04 M) as a function of pH, 2 to 6. In both cases potassium is synergized most strongly presumably because of its best fit to the crown ether cavity. Other data indicate, however, that the size-fit principle is not as consistent for all alkali metal...

Mixed ligand chelate extraction of lanthanides I. 8-quinolinol systems

Abstract: A detailed study of the equilibrium extraction behavior of a series of representative tervalent lanthanide ions, La, Pr, Eu, Ho, and Yb, into chloroform solutions containing either 8-quinolinol (HQ) alone or mixed with 1,10-phenanthroline (phen), was carried out. The results demonstrated that, except for La which extracted as a simple chelate, LaQ/sub 3/, the lanthanides extract as self-adduct chelates, LnQ/sub 3/.2HQ, and at higher HQ concentrations, LnQ/sub 3/.3HQ. In the presence of phen, mixed ligand chelates of all the lanthanides but La of the formula LnQ/sub 3/.2HQ.phen are formed. The use of the experimental parameters, pH, concentration of both HQ and phen to optimize the separation of the lanthanides is discussed. It is concluded that chelate extraction systems in which adduct and mixed ligand complexes are formed enhance separation capability.

Solvent Extraction Chemistry and Kinetics of Zirconium

Abstract: The solvent extraction behavior of zirconium in the HN03-tributyl phosphate (TBP) system can be explained based on the existence of four principal aqueous species, Zr4+, ZrOH3+, Zr3(OH)8+ 4, and oxo-polymers. The Zr4+ and ZrOH3+ species are extractable and are in equilibrium with inextractable Zr3(OH)8+ 4. The oxo-polymers are formed by heat, are-inextractable, and are not: in equilibrium with the other species. The aqueous equilibria and their equilibrium quotients have been previously determined. In the present study, these equilibria were used along with both tracer and macro zirconium concentrations (oxo-polymers excluded by extraction and back scrubbing) to determine the distribution equilibrium constants for both the Zr4+ and ZrOH3+ ions. The four equilibrium constants give excellent fits to both tracer and macro-zirconium distribution data. The concentrations of the extractable zirconium species which are calculated from the equilibria have been used to begin examining the extraction kinet...

Pressurized Continuous Chromatography

Abstract: A pressurized continuous annular chromatograph has been developed for preparative separations. This device utilizes a slowly rotating annular bed of sorbent material, fixed multiple feed points, and fixed withdrawal locations. Most of our investigations have been performed with a 28-cm-diam column, but a larger model is being designed and constructed. The separation of copper, nickel, and cobalt components from a carbonate solution has been studied in detail. This solution simulates the leach liquor from the Caron process for recovering nickel and cobalt from laterite ores. Use of continuous gradient elution has been demonstrated. Recent studies have investigated several separations, including that of zirconium and hafnium (necessary for the production of zirconium for use in nuclear reactors), on a preparative scale. This system, because of its continuous feed and product withdrawal, its adaptability to large-scale operations, and its ability to separate many components, is expected to make chro...

Fuel Gas Purification with Permselective Membranes

Abstract: Production of fuel gas from biomass and recovery of flared gas from landfills, oil fields, coal mines, is hampered by the high cost of gas purification for the removal of C02 and H2S. Membranes offer a potentially simple and attractive technique for on-site gas purification. Two membrane approaches have been considered for fuel gas purification-polymer films and facilitated transport-each with its own unique advantages. Polymer films can be made extremely thin (<500A), and thus have high gas throughput and a very low membrane area requirement. Ultrathin polymer membranes have been found to be extremely attractive for purification of gas produced from waste or in remote site applications. Of particular interest is biogas produced from anaerobic digestion of sewage, municipal waste, agricultural waste, and landfills. Membrane purification is expected to cost less than half of that for conventional scrubbing processes. Additionally, the gas is purified and dried at the same time. Laboratory tests co...

High Temperature Ultrafiltration With Kynar® Poly(Vinylidene Fluoride) Membranes

Abstract: Ultrafiltration membranes prepared from KYNAR® poly(vinyli-dene fluoride) have excellent stability to high temperature and to harsh chemicals such as acids, strong oxidants, and many organic solvents. These membranes can be dried and revetted without degradation of their properties, and they can be autoclaved. Spiral-wound modules with reproducible performance have been fabricated from these membranes and used in pilot plant studies on a simulated textile sizing waste. Flux rates up to 15 gal/ft2 day and retentions of 97% of the poly(vinyl alcohol) have been achieved routinely. No degradation in performance has been observed during continuous operation at 186°F and 20 to 25 psi for 7 months.

Hydrogen Isotope Separation by Catalyzed Exchange Between Hydrogen and Liquid Water

Abstract: The discovery, at Chalk River Nuclear Laboratories, of a simple method of wetproofing platinum catalysts so that they retain their activity in liquid water stimulated a concentrated research program for the development of catalysts for the hydrogen-water isotopic exchange reaction This paper reviews 10 years of study which have resulted in the development of highly active platinum catalysts which remain effective in water for periods greater than a year The most efficient way to use these catalysts for the separation of hydrogen isotopes is in a trickle bed reactor which effects a continuous separation The catalyst is packed in a column with hydrogen and water flowing countercurrently through the bed The overall isotope transfer rate measured for the exchange reaction is influenced by various parameters, such as hydrogen and water flow rates, temperature, hydrogen pressure, and platinum metal loading The effect of these parameters as well as the improved performance obtained by diluting the

Coupling Electrophoresis with Ultrafiltration for Improved Processing of Plasma Proteins

Abstract: The feasibility of coupling electrophoresis with ultrafiltration (electroultrafil-tration) in order to increase the flux and improve the selectivity of the ultrafiltration process was demonstrated experimentally for protein solutions. An electric field controlled the build-up of retained proteins at the membrane surface. Electroultrafiltration fluxes were 3 to 5 times greater than normal ultrafiltration fluxes. Retention and separation factors were also higher. The effects of important process variables were studied.

Isotope Separation by Distillation: Design of a Carbon-13 Plant

Abstract: This isotope separating plant has a great height with many long columns in parallel, low process flows compared with its boil-up, and a long time response. All these features result from dealing with a mixture whose separation factor is near unity, the carbon monoxide system. Considering that there are three isotopes of oxygen involved, six molecular species are being separated. Although CO molecules are unreacting within the columns, an exchange reactor is used when the separation is partially complete to assist in obtaining high quality product. These considerations have been formulated in a good theoretical design procedure along with excellent mechanical design, fabrication and assembly to yield a plant of high performance for carbon-13 production.

Gas Separation by a Continuous Membrane Column

Abstract: The continuous membrane column provides a revolutionary new separation technique. In gaseous diffusion the continuous membrane column is used to separate as highly concentrated products both the most permeable and least permeable gases from a feed mixture of any composition. The main features of the column are countercurrent enrichment, high reflux and minimal backmixing. The new method eliminates the need for numerous interstage compressors and extensive product stream recycling found in conventional gaseous diffusion cascades. Experiments are carried out for systems of C02-O2, O22-N2 (air), and CO2-N2 mixtures using continuous membrane columns made out of silicone rubber membrane. Also, a theoretical model is developed to interpret the experimental data. The agreement between theory and experiment is excellent. The maximum degree of separation can be achieved at total reflux. It is experimentally verified that the maximum degree of enrichment attainable by a conventional method can easily be ex...

Asymmetric Permeators—A Conceptual Study

Abstract: The asymmetric permeator concept of Ohno et. al. utilizing two different membranes for rare gas separation has been explored in general. Various geometrical arrangements and possible applications to gas separations other than rare gas-nitrogen mixtures have been discussed. The utility of an asymmetric permeator for multicomponent gas separations has been investigated. The separation factor of a ternary system in a perfectly mixed asymmetric permeator has been obtained. The amount of separation obtained with a ternary feed in a perfect crossflow stage having no axial mixing has been analytically determined for some limiting cases with an asymmetric permeator. The asymmetric permeator concept has been extended also to a high separation factor liquid solution separation process like reverse osmosis desalination. Preliminary calculations have been carried out to show that an asymmetric desalinator with reverse osmosis (RO) and piezodialysis (PD) membranes has a lower increase in brine concentration a...

Uranium(VI) and Ruthenium Extraction by Dialkyldithio-Phosphoric Acids

Abstract: Oxygen donors like dialkylphosphoric acids are good extractants for actinide ions, but little is known about their sulfur homologs. In this paper investigations of U(VI) and Ru extraction from various aqueous media are reported. This includes extraction of U(VI) from nitric, perchloric, and phosphoric acids by solutions of dialkyldithiophosphoric acids in dodecane or benzene. Extraction of U(VI) by synergistic mixtures, of which at least one of the components is a sulfur donor, has been investigated. The extracted species have been identified, and a comparison with the complexes obtained by extraction with the homologous oxygen donors is made. The sulful-actinide bond is weaker than the oxygen-actinide one, but in some synergistic extractions the dialkyldithlophosphonates are more efficient than the oxygen donors. In addition to size effects, this behavior could be attributed to the weakness of the hydrogen bonds of the SH groups, which allows a greater variety of the ligands to enter the coordin...

Application of extraction chromatography to nuclear fuel reprocessing

Abstract: The potentialities of applying extraction chromatography to the reprocessing of reactor fuels on an industrial scale have been investigated. The stationary phase was undiluted (100%) tri-n-butyl phosphate (TBP) and the mobile phases were nitric acid or nitrate salt solutions with or without reducing agents for plutonium. Several extraction chromatographic processes for the recovery of nuclear grade uranium and plutonium are described. The flowsheets are based on a systematic determination of the distribution coefficients of relevant metal species (particularly those of uranium, neptunium, plutonium, americium, ruthenium, zirconium and niobium) in the chromatographic systems employed. The Purochromex process developed for the recovery of uranium and plutonium from light-water reactor fuels and the Eurochromex process developed for the separation of highly enriched uranium from irradiated U/Al alloy, U/Zr alloy and uranyl sulfate fuels have successfully been hot-tested on a laboratory scale and cold-tested on an industrial scale. Some complementary studies related to the separation processes, such as radiation degradation of the stationary phase and the removal of tributyl phosphate from product and waste streams, are also described.

Numerical Simulation of Solute Dispersion in Laminar Tube Flow

Abstract: The dispersion of a solute slug in laminar tube flow has been simulated by a numerical method (the Flux Corrected Transport Algorithm) for a set of tube lengths embracing the pure convection through Taylor dispersion regimes. The results reveal unexpected double peak breakthrough curves for tubes of intermediate length. Experimental evidence of double peaks which qualitatively confirms the simulations is discussed.

Reducing the long-term hazard of reactor waste through actinide removal and destruction in nuclear reactors

Abstract: Public opposition to nuclear power has focused on the long-term risks from reactor waste. In the Purex process used in Europe, this waste is a concentrated nitric acid solution containing all nonvolatile fission products and the actinides Np, Am, and Cm, plus smaller amounts of U and Pu. Techniques have recently been described which guarantee an absolutely safe containment of this high-active waste (HAW) for about 1000 years. At longer times, the risk to the biosphere is dominated by the actinides. If these actinides are isolated from the rest of the HAW and destroyed through nuclear incineration, the long-term risks of the HAW will be dramatically reduced. This paper presents a detailed scheme for removing the actinides from the Purex-HAW solution. In principle, the process consists of three different solvent extraction cycles, using HDEHP and TBP in three successive steps. The scheme has been tested on a synthetic HAW solution containing all fission products and actinides (except Z ≥96, Cm) usi...

Reverse Osmosis Separation of Thiosalts from Mining Effluents

Abstract: Cellulose acetate membranes were characterized in terms of pure water permeability constant, solute transport parameter, and mass transfer coefficient with a reference system of aqueous sodium chloride solution. Reverse osmosis separation behavior of sulfate, thiosulfate, dithionate, trithionate, and tetra-thionate was studied. Plant effluents containing various thiosalts and metal ions were subjected to reverse osmosis at 300 psig, and product water of suitable quality for use in recycle operations was obtained.

The Nonsynchronous Flow-Through Coil Planet Centrifuge without Rotating Seals Applied to Cell Separation

Abstract: A new nonsynchronous flow-through coil planet centrifuge allows continuous elution through a coiled separation column without the use of rotating seals. Rates of rotation and revolution of the column are independently adjustable to meet the requirements for the separation of cell particles. The capability of the present apparatus was demonstrated by the separation of human and sheep erythrocytes using an isotonic saline solution.

A New Continuous Flow Reactor for Simultaneous Reaction and Separation

Abstract: The acid catalysed hydrolysis of methylformate has been investigated in a continuous flow annular reactor packed with activated charcoal, and equipped with a rotating feed injection port. Chromatographic separation of the products, formic acid and methanol, effectively suppressed the reverse reaction, causing conversions to be significantly greater than the thermodynamic equilibrium conversions that would have been obtained in the absence of separation. Comparisons of numerically simulated reactor performance with experimental results showed good agreement, although some differences occurred as experimentation proceeded, most probably due to deactivation of the activated charcoal.

Ternary Ion-Exchange Equilibria

Abstract: The shape of parametric lines in both phases of ternary ion-exchange systems are discussed for both ideal and nonideal systems. It has been shown that deviations of the parametric lines from linearity correspond to nonideality of the system while the converse is not necessarily valid. Conditions of linearity for nonideal systems are derived. Equations for calculating activity coefficients of resinates in ternary mixtures are given. Triangular diagrams and three-dimensional diagrams of the dependence of activity coefficients on composition are illustrated by the systems NH4 +-Na+-H+ and Ba+-Cu2+-Co2+ on sulfostyrene-type exchangers. Methods for prediction of ternary ion-exchange equilibria are discussed. A comparison of these methods for the systems studied shows that consideration of the nonideality of the systems is required for accurate prediction.

Design, Scale-Up, and Applications of the Reciprocating Plate Extraction Column

Abstract: The Reciprocating Plate Extraction Column has been scaled up successfully from small diameter (1′′ and 2′′) test columns to many production units up to 40 inches in diameter. Optimization of the extraction process in the small diameter test column is the key to the economic optimum scale-up. The optimization procedure includes maximizing volumetric efficiency as well as selecting the best plate spacing variation. The latter can be calculated from the physical properties of the system and the throughputs in different sections of the column. Design features, principles of design, and scale-up procedure will be reviewed. Several typical applications will be discussed.

Studies of the separation of hydrogen isotopes by a pressure swing adsorption process

Abstract: A theoretical and experimental study was made of the mechanism of the separation of a mixture of hydrogen isotopes by a two-column pressure swing adsorption process in which vanadium hydride was used as the solid phase. Theoretical predictions of process performance were compared with data from process experiments using hydrogen containing a trace of HT as feed. For process operation wholly within the monohydride phase, a postulated isotope effect in the rates of hydrogen absorption and desorption appeared to control process performance. When process operation involved transitions back and forth between the monohydride and dihydride phases, process performance was determined mainly by an equilibrium isotope effect.

On the Origins of Flow-Rate Dependence of Elution Volume in Gel Permeation Chromatography

Abstract: The peak elution volume of a narrow polystyrene fraction in a porous silica column is a function of the solvent flow rate through the column. The explanation for this effect offered by Gudzinowicz and Alden and others is that the equilibrium assumption, usually made in size exclusion Chromatography, is no longer valid at high flow rates. An alternative explanation based on a flow-rate-dependent equilibrium distribution coefficient (ratio of intrapore polymer concentration to extrapore polymer concentration) is offered here. This view is supported by experimental results for the equilibrium flow-rate-dependent column retention measured previously in these columns.

Problems and Recent Advances in Aerosol Filtration

Abstract: Particles to be collected in fiber filters must be transported to the fiber surface and retained there. The collection efficiency θ can therefore be written as θ = ηh where η is the collision efficiency, which describes the transport of particles to the fibers, and h is adhesion probability. The results of both theoretical and experimental studies of η and h are presented. It is shown that electrostatic effects can have a major influence on collision efficiency.