In this paper, recent advances in the separation of metals by liquid surfactant membranes are reviewed, with emphasis placed on development of a suitable surfactant. In establishing a metal recovery process using liquid surfactant membranes, the choice of a suitable surfactant is a key factor. It is important to elucidate the role of the surfactant on the behavior of liquid surfactant membranes, e.g., the break-up rate and the swelling rate of W/O emulsion glubules in a mixer, the demulsirication rate of the emulsions in an electrical coalescer and the extraction rate of metal by liquid surfactant membranes. These problems are discussed. The application of liquid surfactant membranes to the metal separation processes is also described.
A mathematical model has been proposed for describing the coupled gas-solid reactions in a reacting gas atmosphere. Effects of the following five parameters on the conversions of solids B and D have been examined: reaction/diffusion ratio, Sherwood number, reactivity ratio, factors of catalytic activity and reactant amount ratio. The conversion of solid B was found to be able to be increased by reducing the pellet size, increasing the relative initial amount of solid D to solid B, or increasing the velocity of bulk gas.
The formation and stability of the ordered structure LS13, composed of large and small monodispersed spherical particles L and S respectively in aqueous solutions, are investigated, the Brownian motion of particles with interparticle potential being simulated by the Monte Carlo method. The ordered structure is composed of an icosahedron of 12 particles S with a central particle S within a cube of particles L. It is found that formation of the ordered structure LS13 is successfully simulated once 13 particles S are distributed within a cube of particles L, and the conditions within which the ordered structure is stable are clarified.
Density, heat capacity and thermal conductivity were measured for polyacrylamide gel which is used for electrophoresis. Dependence of the density and heat capacity on gel concentration is explained by a model in which the gel is assumed to be a two-component solution of polyacrylamide and water. Dependence of the thermal conductivity on gel concentration is examined by assuming that the gel is composed of multiple thin layers of these components. The specific properties of density, heat capacity and thermal conductivity of polyacrylamide in the gel were obtained from these models and correlated with temperature. These quantities are comparable to those of ordinary plastics. Variations of the thermophysical properties with gel concentration and temperature are well estimated by correlation equations based on the models in this study.
The kinetics of enzyme release from yeast using a bead mill was investigated. The enzymes investigated were invertase, acid phosphatase, alcohol dehydrogenase and alkaline phosphatase. A two-step consecutive process model was proposed to describe the behavior of enzyme release. The model described well the release of both membrane-bound and non membrane-bound enzymes, such as alkaline phosphatase and other enzymes, respectively.
Supercritical fluid extraction was applied to the separation and purification of indole. Indole is important as a feedstock for tryptophan, which is used in the field of biotechnology. Supercritical fluid extraction of coal tar oil including indole was conducted using CO2 and C2H4. Not much indole was extracted, but it was concentrated in the raffinate. To concentrate high-purity indole in the rafflnate, ethylene glycol and mono ethanol amine (MEA) were used as additives for supercritical fluid extraction by C2H4. After distiflation of the raffinate with MEA was conducted, high-purity indole was obtained. On the basis of these results, a newly developed process was proposed that uses combined supercritical fluid extraction to separate high-purity indole from coal tar oil.
A corresponding-states viscosity model using oxygen, octane and water as the reference fluids was developed for a variety of liquids and liquid mixtures. The present model is generally accurate for most pure liquids being tested. A set of quadratic mixing rules is adequate to correlate the viscosity of non-aqueous solutions. Using an augmented asymmetric mixing rule to calculate the pseudo-critical temperature yields a good representation for the binary and ternary aqueous solutions.
A zero-pressure mixing rule for the energy parameter in cubic equations of state has been developed. The composition dependence of the mixture volume u = v/b at zero pressure is approximated by a two-parameter Redlich-Kister expansion (RKU2). The RKU2 coefficients are determined from pure component parameters of a cubic equation of state and activity coefficients at infinite dilutions. The RKU2 mixing rule combined with the SRK equation of state has been tested for seven isothermal and nine isobaric binary systems. At moderate temperatures the model performs comparably to the treatment requiring an additional iterative procedure (Heidemann and Kokal, 1990). Extensions to ternary systems and the importance of correct temperature dependence of the activity coefficient models used in the mixing rules are discussed.
The heterogeneous phase transition of mixed benzene and cydohexane vapors on a cold copper substrate was observed by slowly cooling the substrate under reduced pressure conditions. In the conversion of the vapor to the condensed phase, vapor-to-liquid or vapor-to-solid phase transitions occurred depending on the mixing ratio of both vapors. By measuring the critical vapor pressure and temperature, corresponding critical supersaturation ratios were determined for various mixing ratios of both vapors. The critical pressure for the formation of solid benzene from mixed vapor agreed closely with that of pure vapor having higher composition. The critical pressure for the formation of solid cyclohexane from mixed vapor decreased from 6 to 9% compared with that from pure vapor. Liquid condensate was formed at critical supersaturation ratios of almost unity. A phase diagram was constructed by solving a non-linear simultaneous equation derived from vapor-liquid equilibrium and critical pressure-temperature relationships. It agreed in a practical sense with the observed results.
The behavior of selected heavy metals in sewage sludge during incineration was investigated in a two-stage swirl-flow fluidized-bed incinerator. Leaching tests were also carried out to evaluate the leachability of the metals in the ash discharged from the incinerator. Selected heavy metals were quantitatively retained in the output stream ash due to both the effects of a low incineration temperature and a uniform temperature distribution in the incinerator. Further, it can be found that the metals contained in the ash were highly stable.
Studies were made of the application of a block copolymer of polyethylene oxide and polypropylene oxide, Pluronic F68, to aqueous two-phase extraction of proteins. For Pluronic F68/salt systems, the effects of temperature, salt concentration and pH on the binodials and protein partitioning were studied. Pluronic F68/salt system had a region in which Pluronic F68 becomes solid in phase diagram at 25°C. Partitioning of the proteins between the two phases could be controlled by varying salt composition. Further applicability of the Pluronic F68/ammonium sulfate system was examined for the purification of monoclonal antibodies from various hybridoma culture broths. Aqueous two-phase extraction provided a simple and rapid separation and concentration method with high recovery.
The extraction of yttrium(III) from thiocyanate solutions by alkyl and aryl sulphoxides and tri-n-octyl phosphine oxide and their mixtures in benzene has been studied. Synergistic effects have been observed with a mixture of extractants which are ascribed to the formation of mixed ligand complexes. These extraction data have been analysed theoretically by taking into account aqueous-phase speciation and all plausible complexes extracted into the organic phase. The extraction behaviour of yttrium(III) has also been compared with that of some lanthanides. It was observed that yttrium(III) behaves like a lighter rare earth in thiocyanate solutions during extraction with dialkyl sulphoxides. Separation factors have also been evaluated. The influence of metal ion concentration and of the diluent on the extraction of yttrium(III) has also been investigated.
The extraction of Ce(III) from thiocyanate solutions with mixtures of 2-ethylbexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) and di(2-ethylhexyl)-phosphoric acid (DEHPA) or tri-n-butyl phosphate (TBP) in benzene has been studied systematically over a wide range of conditions. A relatively small synergistic enhancement has been observed with mixtures of acidic organophosphorus extractants (EHPNA + DEHPA) and also with mixtures of acidic and neutral organophosphorus extractants (EHPNA + TBP). These extraction data have been analysed theoretically, taking into account complexation of the metal in the aqueous phase by inorganic ligands and plausible complexation in the organic phase.
Microcapsules containing tri-n-octyl amine as core material were prepared by in situ polymerization of styrene and divinylbenzene over a wide range of relevant preparation conditions. The extraction equilibrium and extraction rate of propionic acid in aqueous phase were investigated by using the microcapsules. The extraction equilibrium of propionic acid/tri-n-octyl amine in a suspended microcapsules system was well consistent with that in a liquid-liquid system. From the experimental results, the rate-determining step was concluded to be the pore diffusion of propionic acid through the porous film of microcapsules. The activation energy was found to be 34.6 kJ/mol. The extraction rate decreased with increase in monomer concentration, divinylbenzene/styrene weight ratio and average diameter of microcapsules.
The mechanism of mathane-air combustion on the surface of a porous ceramic plate was studied by experimental testing and analysis of a simplified theoretical model based on one-dimensional flow of methane-air mixture and the overall chemical reaction rate. The effects of such parameters as thickness of porous ceramic plates, equivalence ratio of mixed-gas and heat load on the combustion characteristics were examined. A thicker plate achieves higher surface temperature as premixed gas is preheated on the porous ceramic plate. The combustion zone is closest to the porous ceramic plate with equivalence ratio Φ = 1.2. The surface temperature has peak value at a certain heat load. It is observed that combustion begins just off the porous ceramic plate, and the flame is kept less than 1 mm from the surface. The position is influenced by the combustion conditions. These phenomena can be explained by a theoretical model and such aspects of the combustion mechanism as temperature profile of premixed gas and porous plate and chemical reaction on the plate are made clear.
Large lipid-vesicles having a diameter of about 5–50 μm, consisting of Span8O (sorbitan monooleate), Tween80 (polyoxyethylene (20) sorbitan monooleate) and lecithin, were successfully prepared, with Span80 as the main constituent of the vesicle. The preparation was performed by applying the procedure of two-step emulsification for providing a W/O/W emulsion. The characteristics of the lipid membrane of the vesicle were experimentally examined and the main results can be described as follows.1) The vesicle could be observed with a phase-contrast microscope but not with an optical microscope. 2) With increase in the amount of an additive, soybean-lecithin, to Span80, the yield of the vesicle increased and the vesicle started to coagulate. 3) The vesicle yield increased with increase in weight ratio of water in water-lipid mixture, which was prepared by removing organic solvent from W/O emulsion. 4) The rupture percentage of the vesicle prepared with distilled water as the aqueous-phase solution was below 5% even after twenty days under an incubation temperature of 4°C. The applicability of the vesicle for encapsulation of enzyme was also examined. The model reaction in the vesicle was the enzymatic conversion of ethanol to acetaidehyde with NAD+-recycling catalyzed by malate dehydrogenase (MDH) and yeast alcohol dehydrogenase (ADH). It was found that enzymatic NAD+-recycling in the vesicle could occur successfully.