Hideaki Tokuyama

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.

Preparation of poly(N-isopropylacrylamide) emulsion gels and their drug release behaviors

Stimuli-sensitive drug delivery systems (DDSs) have attracted considerable attention in medical and pharmaceutical fields; thermosensitive DDS dealing with poly(N-isopropylacrylamide) (poly(NIPA)) have been widely studied. Novel NIPA emulsion gels, i.e., NIPA hydrogels containing distributed oil (oleyl alcohol) microdroplets, were synthesized by means of an emulsion-gelation method in which the polymerization of hydrogels in an aqueous phase in an oil-in-water (O/W) emulsion and the loading of a lipophilic drug (indomethacin) dissolved in an oil phase were accomplished simultaneously. The pulsatile (on-off) drug release from the NIPA emulsion gel loading indomethacin to a phosphate buffered saline (PBS) solution was successfully controlled by a temperature swing between 25 degrees C (release off) and 40 degrees C (release on). The mechanism of the pulsatile drug release was discussed in relation to the diffusion rate, distribution ratio, solvent exchange of NIPA hydrogels, and drug release from an NIPA organogel. The mechanism was as follows: the solvent exchange occurred within the NIPA emulsion gel (the NIPA gel-network absorbed oleyl alcohol with indomethacin) at temperatures above the LCST, and the diffusion rate of indomethacin through the solvent-exchanged gel was higher at 40 degrees C than at 25 degrees C.

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.

Propagation Properties of the Precipitation Band in an AlCl3/NaOH System

When inherently immobile solid particles collectively form precipitates in a reaction-diffusion system involving a redissolution reaction, a propagation phenomenon may occur in which a dynamic pattern of precipitation bands forms. This propagating precipitation phenomenon has been studied by many researchers. However, two completely different processes-i.e., the reaction-diffusion of reactants and the crystal growth of products-progress simultaneously in the system, thereby rendering the phenomenon complex. There are no well-established experimental laws for this propagating precipitation phenomenon, such as the spacing, time, and width laws associated with the well-known Liesegang phenomenon, which is static in the sense that precipitation bands form and remain at the same position. In fact, it has not been clarified which of the processes controls the propagation phenomenon. Accordingly, we have investigated the apparent diffusion coefficient associated with the dynamics of propagating precipitation band in an AlCl3/NaOH system for the case in which a large excess of outer electrolytes (i.e., OH(-)) diffuses into gel in which inner electrolytes (i.e.,Al(3+)) are homogeneously distributed. An isolated precipitation band of Al(OH)3 was formed horizontally in a test tube and propagated vertically in proportion to the square root of time. In our experimental results, we found that the apparent diffusion coefficient, D(p), possesses an exponential dependence on the initial concentrations of the outer electrolyte, and the inner electrolyte; the measured relation was D(p) = D[Al(3+)](-0.6)[OH(-)](0.6), where D = (0.63 ± 0.04) × 10(5) cm(2)/s. From our model equations based on the prenucleation theory, which take into account a redissolution reaction, we found that the dynamics of the reaction front of the outer and the inner electrolytes was an important factor in controlling the propagation of the precipitation band. In our simulation results, we obtained a similar dependence of the apparent diffusion coefficient on the electrolyte concentrations.

Detection of AU(III) ions using a poly(N,N-dimethylacrylamide)-coated QCM sensor

A polymer-coated quartz crystal microbalance (QCM) sensor has been developed for the detection of Au(III) ions in a HCl aqueous solution. Poly(N,N-dimethylacrylamide) (poly(DMAA)) gel was used as a sensing material. The poly(DMAA) gel adsorbs Au(III) ions in the HCl aqueous solution, whereas it is inactive toward most other metal ions. The equilibrium adsorption of Au(III) ions onto the poly(DMAA) gel can be expressed by the Henry-type isotherm. The oscillation behavior of the poly(DMAA)-coated QCM sensor was investigated, and linear relationships between the resonance frequency shift and the concentration of Au(III) ions were obtained for concentrations of less than 0.032 mol/m(3) (6.3 mg/m(3)) in the single and multicomponent metal systems. The poly(DMAA)-coated QCM sensor detects Au(III) ions successfully with high selectivity and sensitivity even in the presence of other metal ions and organic compounds.

Preparation of poly(N-isopropylacrylamide) hydrogel beads by sedimentation polymerization combined with electrostatic atomization

The preparation of monodisperse, millimeter- or submillimeter-sized polymeric hydrogel beads by a novel production method combining sedimentation polymerization and electrostatic atomization is presented herein. The beads were prepared by drop-wise addition or spray of a pre-gel aqueous solution into silicone oil through a nozzle with application of high voltage, and subsequent free-radical polymerization of the pre-gel droplets during their descent. The thermosensitive poly(N-isopropylacrylamide) hydrogel that was used as the model hydrogel has attracted much attention for application in reaction and separation processes. The size of the pre-gel droplets dispensed from the tip of the nozzle corresponded to the size of the resultant hydrogel beads and was controlled by adjusting the applied voltage. The diameter of the pre-gel droplet was estimated from the equilibrium of forces caused by gravity, the electrostatic force, and the liquid–gas surface tension.

Motion-Based Detection of Lanthanides (III) Using Self-Propelled Droplets

The directional and controllable transportation of self-propelled chemical objects in response to chemical signals in environmental media holds considerable promise for diverse applications. We investigated the chemotaxis of oil droplets loaded with surfactants to detect spatial gradients of lanthanide(III) ions, among which Dy3+ and Tm3+ were the most effective chemoattractants for steering droplets toward the targets. Patterns within a chemotactic index of the lanthanide series exhibited a convex tetrad effect and a breakpoint at Gd3+. The Jørgensen-Kawabe equation, which is based on the refined spin-pairing energy theory, quantitatively demonstrated the tetrad effect. The self-propelled droplets served as a motion-based detection mechanism for lanthanides(III).

Rheological flow models of banana peel pectin jellies as affected by sugar concentration

ABSTRACT In the present study, peel pectin jellies (PPJ) were isolated from banana peel Musa acuminata Colla (AAA, cv ‘Berangan’) varieties using water bath extraction; five jellies were produced, namely, PPJ_68%, PPJ_70%, PPJ_71%, PPJ_72%, and PPJ_76%. The effect of sugar content on the rheology of the PPJ and commercial fruit jelly was conducted at 25°C within 0.05–100 s−1 shear rate. Flow behaviour was evaluated on the test dispersions while frequency sweeps (Ea) to obtain the viscoelastic (G’ and G”) were performed on the jellies. PPJ dispersion showed shear thinning flow behaviour, a good fit to the Casson model. Sugar concentration does not affect Casson parameters (Kc, Koc, ɳca, and σoc). Frequency sweep decreased as viscosity increased which revealed high dependence for both G’ and G”. Tan δ for PPJ was more than unity which showed that jelly has less elastic properties. PPJ with the lowest sugar concentration, PPJ_68%, conducted at a high shear rate showed it was compatible with validation of the Cox–Merz rule.

Pd(II) ion adsorption onto emulsion gel beads in a fixed bed

ABSTRACT We developed previously an emulsion gel adsorbent for improved metal adsorption. This study focuses on a continuous adsorption–desorption process of metal ions from a solution onto emulsion gel beads using the fixed-bed method. The monodisperse millimeter-sized emulsion gel beads, a polymeric hydrogel containing randomly distributed oil microdroplets of di-n-hexylsulfide as an extractant, were prepared using an automatic production method combining sedimentation polymerization and two-fluid atomization. The isotherms and the kinetics for Pd(II) adsorption were investigated. A continuous adsorption–desorption process was successfully demonstrated, and the breakthrough curve was successfully predicted by a mathematical analysis.

Propagating Precipitation Waves in Disordered Media

The study presented in this paper investigates form changes of propagating waves generated through precipitation reactions in a gel matrix that possesses an inhomogeneous microstructure. The waves demonstrate form changes from a single ring-like pattern to multiple target-like waves. Subsequently, the waves take up a spiral form and ultimately manifest themselves in the form of a turbulence pattern that intensifies with increasing fluctuations within the gel structure. An investigation into the dynamics of the precipitation waves reveals the existence of an anomalous diffusion. The effective diffusion coefficients are found to increase linearly with the quenching temperature. Further, it is revealed through the analysis of the anomalous diffusion dynamics that precipitation patterns could be adequately controlled by adjusting the permeability fluctuations within the gel structure. The findings of this study lead to a greater understanding of the spontaneous creation of precipitation patterns by a system driven by disorder.