Susumu Nii

Separation of Co(II)/Ni(II) via micellar-enhanced ultrafiltration using organophosphorus acid extractant solubilized by nonionic surfactant

Ultrafiltration (UF) of cobalt(II) and nickel(II) in the presence of a micelle-solubilized hydrophobic ligand has been investigated, using polyoxyethylene nonyl phenyl ether with 10 ethylene oxide units (PONPE10) and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (EHPNA) as a nonionic surfactant and an extractant, respectively. In aqueous media, the metals are entrapped within the surfactant micelles containing the extractant, and are effectively rejected by UF membranes with their consequent concentration in the retentate solution. The selective rejection of Co(II) over Ni(II) can be attained; the separation is enhanced with increasing solution pH and the extractant concentration. On the other hand, it was found that sodium dodecyl sulfate (SDS) as a surfactant and di-2-ethylhexyl phosphoric acid (D2EHPA) as an extractant give no selectivity between these heavy metals in the same operation. The effects of the surfactant concentration, applied pressure, salt addition and the membrane geometry on the rejection were also examined in the EHPNA/PONPE10 system.

Quantitative approach to ultrasonic emulsion separation

Ultrasound of 2 MHz was irradiated to the emulsion prepared from canola oil and water and flocculation of the oil droplets occurred immediately. By putting the emulsion sample in a thin glass cell and setting it in bath type irradiation equipment, the progress of the separation was quantitatively monitored with the optical absorbance. The use of the cell enables visual observation of the behavior of oil droplets. Pictures show the formation of flocks of the dispersed phase and the appearance of checkered pattern consisting of flocks at a regular interval. The observation indicates that the action of radiation forces on oil droplets, which causes the flocculation. The flocks started to rise after stopping irradiation with holding their shape. The rising rate of the flocks was significantly greater than that of oil droplets in the original emulsion. Ultrasonic irradiation caused a rapid decrease in the absorbance, which expresses a progress of the separation. Effects of two major operation parameters, power and time on the separation degree were examined. The degree improved with increasing power input and irradiation time. The dataset was arranged in a plot of normalized separation degree against the input energy. The plot suggests that effective separation was attained with a lower power input and a longer irradiation time. The plot provides a guide for setting condition for the separation.

Separation of La and Ce with PC-88A by counter-current mixer-settler extraction column

Abstract The separation of La and Ce with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (commercially known as PC-88A) from nitrate media was studied with a multistage counter-current mixer-settler extraction column of seven stages developed by the authors. The effect of flow rate ratio of the aqueous phase ( Q w ) to the organic phase ( Q o ) on the separation was studied. The maximum separation was obtained at Q w / Q o =3.2 and the separation degree was 63. Scrubbing of the organic phase was also studied in order to enhance the separation. La was scrubbed from the organic phase with nitric acid at pH 2.7 and the separation degree during scrubbing was 45. Simulations of the extraction and scrubbing processes were carried out and compared with the obtained experimental results. Stripping of Ce was achieved by using 100 mol/m 3 nitric acid. The organic phase was successfully recycled during the experiments without any effect on the extraction efficiency.

Removal of CO2 and/or SO2 from gas streams by a membrane absorption method

Abstract Studies were made on the membrane absorption of CO2 and/or SO2 using hydrophobic microporous hollow-fibre (HF) membrane modules. The absorbent liquids used were aqueous solutions of NaOH, K2CO3, alkanolamines and Na2SO3, flowing on the lumen side of the HF in laminar flow. A semi-empirical correlation was derived for the gas-phase mass-transfer coefficient on the shell side, by including geometrical factors of the HFs and the shell tube in the general correlation for mass transfer. It was found that the CO2 absorption rate in various aqueous solutions of alkalis and alkanolamines is successfully described by a model based on gas diffusion through the membrane pores subsequent to gas absorption accompanied by chemical reaction. The simultaneous membrane absorption of SO2 and CO2 was also studied using aqueous Na2SO3 solution, the selective removal of SO2 to CO2 being successfully achieved when both the liquid flow rate and solute concentration are low. This suggests that this membrane absorption method provides an energy saving process for SO2 removal from flue gases.

Study of drop coalescence behavior for liquid-liquid extraction operation

Abstract Using a video camera, a time course of coalescence was observed for toluene droplets formed at the top of adjacent nozzles in water. Several parameters which may control the coalescence have been investigated, such as concentration of acetone added to toluene, direction of mass transfer, time for attaining contact of the droplets, and flow rate of the continuous phase. The average coalescence times decrease with acetone concentration when acetone is transferred from the dispersed phase towards the continuous phase, and they increase with the time required for attaining contact. At high acetone concentration, oscillation of droplets appears, which restrains the coalescence. The average coalescence time increases when the acetone is transferred from the continuous phase towards the dispersed phase. An attempt has been made to predict coalescence times at low solute concentration (no oscillation) by assuming that the difference of interfacial tension causes the film drainage and leads to the drop coalescence. The agreement between the calculated and experimental values is not sufficiently quantitative but reasonable. For lower solute concentration, calculated coalescence times depend strongly on the time for attaining contact, which is in agreement with our experimental observation.

Growth and size control in anti-solvent crystallization of glycine with high frequency ultrasound

Antisolvent crystallization of glycine was performed under ultrasonic irradiation of 1.6 MHz. The irradiation enhanced both the growth of α-glycine crystal and the uniformity in the crystal size. The degree of both enhancement effects increased with increasing ultrasonic power. While under the irradiation of 20 kHz ultrasound, no growth enhancement was observed, but the crystal size reduced as was reported in the literature. To elucidate the mechanism of growth enhancement, another experiment was designed and conducted to avoid the effect of nucleation from the sonocrystallization. The result suggests that the ultrasound enhances the incorporation of microcrystals to larger crystals. Probably, the collision between solid particles is intensified by the disturbance characterized by the high frequency ultrasound. The crystal growth was modeled with an apparent reaction of microcrystal and larger crystal. The result of the growth experiment was successfully predicted with a rate equation for pseudo first order reaction with a single parameter of rate constant. The rate constant linearly increased with the ultrasonic power. The analysis enables quantitative evaluation of the ultrasonic effect on the crystal growth.

Extraction of rare earth metals with a multistage mixer-settler extraction column

Abstract Extraction behavior of rare earth metals within a mixer–settler extraction column has been analyzed with the stage efficiency calculated from mass transfer coefficients and interfacial area. The mass transfer coefficient within the dispersed drops is determined from a rigid sphere model by taking into account the residence time distribution of drops, and the coefficient around the drops is calculated by Ranz–Marshalls correlation with the terminal settling velocity of a rigid sphere. The interfacial area of dispersed drops is calculated by the use of correlations for the drop diameter and the holdup of dispersed phase in the mixer–settler extraction column. The calculated results for the separation of samarium and gadolinium with a five-stage mixer–settler extraction column are compared with the experimental results at various agitation speeds and flow ratios between two phases. The extraction behavior in the multistage column is explained by a model based on the hydrodynamics and the mass transfer within the mixer. Effects of the pH value in aqueous phase, the extractant concentration in organic phase and the number of stages on the extraction behavior in the mixer–settler column are also shown.

Transport behavior of protein in bulk liquid membrane using reversed micelles

Abstract Transport of lysozyme through a liquid membrane of reversed micelles of aerosol-OT (AOT) was studied. The feed phase was aqueous KCl or NaCl solution of lysozyme, and the recovery phase was aqueous KCl or BaCl 2 solution, while the membrane is the solutions of AOT with or without contacting the feed solution. The cations in feed phase are transferred through the liquid membrane and this cation transfer affects that of lysozyme and the size of reversed micelles of the membrane phase. Following transfer mechanisms have been proposed for the three systems investigated: the system NaCl–KCl, for which formation of large aggregates in the membrane phase was observed, has a so flexible interface that the micelles could become unstabilized in the membrane phase. For KCl–BaCl 2 system, the divalent ion Ba 2+ is selectively and excessively adsorbed on the interface and the negatively charged lysozyme molecules may be re-extracted at the interface of the recovery side by the electrostatic interaction with the adsorbed Ba 2+ ions. Both sides of the interfaces of the system KCl–KCl have an adequate flexibility that extraction and back-extraction of lysozyme through the membrane are attainable, although the transfer rate is rather low.

Pervaporation with sweeping gas in polymeric hollow fiber membrane module Separation of alcohols from aqueous solution

Abstract Gas sweeping pervaporation has the advantages of no limitation of membrane configuration and its mechanical strength in operation. A permeation model of pervaporation processes is presented, which incorporates a hypothetical liquid concentration in equilibrium with a permeant concentration in the membrane phase as well as in the gas phase. On the basis of the simple model, an overall mass-transfer coefficient for the transmembrane process can be obtained from the individual transfer coefficient, which facilitates the designing of the pervaporator. The application this method was examined on the pervaporation of ethanol and isopropanol from the respective aqueous solutions across a poly(dimethylsiloxane) hollow fiber membrane using nitrogen as the sweeping carrier gas. The solubility and diffusion coefficients of the two alcohols in the membrane were also measured. The permeation data are in agreement with the model predictions.

Process Development for Recovery of Vanadium and Nickel from Heavy Oil Fly Ash by Leaching and Ion Exchange

A process for recovering V and Ni from oil fly ash and for making the ash harmless has been developed. More than 80% of V and Ni are recovered. This process involves two-step leaching and ion exchange. The first step is leaching with water to dissolve Ni, Mg, Al, and Zn, and acid solution is used in the second step to recover V. The metals Ni and V are separated from other metals in each leached liquor. After neutralization and oxidation of the first liquor, Fe and Al are precipitated and removed from solution. Both Ni and Zn are then loaded on CR20 resin. Nickel can be selectively desorbed from the resin due to a remarkable difference in ion exchange isotherm between Ni and Zn. By using the resin C467, V is selectively separated from the second leached liquor containing V and Fe. The advantage of this separation process is that acidic leachant can be reused, saving separation energy.