Ken-Ichiro Sotowa

Intermittent partition walls promote solvent extraction of metal ions in a microfluidic device

Liquid–liquid extraction of metal ions was carried out in a microfluidic device which had intermittent partition walls in the center of the confluent microchannel 100 µm wide, 20 µm deep and 3 cm long. The intermittent partition walls (50 µm long) stabilized a two-phase (n-heptane–water) flow and allowed clear phase separation at the end-junction of the microchannel. Using this two-phase flow in the microchannel, yttrium ions were successfully extracted in a complex form with an extractant PC-88A (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) from a feed aqueous phase to a n-heptane phase within a contact time of 1.5 s. Although the apparent interfacial area in the microchannel was reduced by introducing the partition walls, the presence of the partition walls improved the extraction efficiency 2–3 fold at a contact time of 0.12–0.24 s. Flow analyses using fluorescent beads and a computational fluidic dynamics simulation revealed that the partition walls induced a slight turbulence in the two-phase flow in the microchannel. This slight turbulence would result in the mixing of the aqueous phase and promote the transport of yttrium ions from the aqueous feed phase to the organic extractant phase.

On the isosteric heat of adsorption of non-polar and polar fluids on highly graphitized carbon black

Isosteric heat of adsorption is indispensable in probing the energetic behavior of interaction between adsorbate and solid, and it can shed insight into how molecules interact with a solid by studying the dependence of isosteric heat on loading. In this study, we illustrated how this can be used to explain the difference between adsorption of non-polar (and weakly polar) fluids and strong polar fluids on a highly graphitized carbon black, Carbopack F. This carbon black has a very small quantity of functional group, and interestingly we showed that no matter how small it is the analysis of the isosteric heat versus loading can identify its presence and how it affects the way polar molecules adsorb. We used argon and nitrogen as representatives of non-polar fluid and weakly polar fluid, and methanol and water for strong polar fluid. The pattern of the isosteric heat versus loading can be regarded as a fingerprint to determine the mechanism of adsorption for strong polar fluids, which is very distinct from that for non-polar fluids. This also allows us to estimate the interplay between the various interactions: fluid-fluid, fluid-basal plane and fluid-functional group.

Application of the method of characteristics to crystallizer simulation and comparison with finite difference for controller performance evaluation

Abstract Finite difference methods are widely used to simulate crystallization processes, although they suffer from numerical dispersion. The method of characteristics can tackle this problem, but the traditional algorithm cannot simulate crystallization processes, if the growth rate depends on crystal size, or if discrete control actions are taken. This paper shows how the method of characteristics can be applied to simulate such processes. Furthermore, the impact of numerical dispersion is discussed by comparing simulation results obtained from these two algorithms. It is revealed that the optimal gains and the responses obtained with a finite difference method are clearly different from those with the method of characteristics.

Enhancement of CO oxidation by use of H2-selective membranes impregnated with noble-metal catalysts

Abstract In order to oxidize CO, which is diluted in H2, two types of catalytic membranes have been developed. In this study, the characteristics of the membranes are briefly summarized for a typical reaction temperature of 523 K , and the permeation and oxidation mechanism of those membrane reactors are analyzed. (i) A defect-free Y-type zeolite membrane was synthesized on the inner surface of a porous α-alumina support tube by a hydrothermal process. The membrane was ion-exchanged and calcined in air and, finally, reduced in a flow of H2, to give a Pt-loaded Y-type zeolite membrane (PtY membrane). A mixture of H2, CO (10 000 ppm ) and O2 (0– 12 000 ppm ) was permeated through the PtY membrane at 523 K . The total pressure on the feed and permeate sides was maintained at atmospheric pressure, and the permeate side was swept with an inert gas. The PtY membrane rejected CO at a H2/CO separation factor of approximately 10. When the O2 feed rate exceeded the CO feed rate of the stoichiometry, the CO concentration on the permeate side, 1000 ppm , was decreased to less than 8 ppm . Since H2 and CO are able to enter the Y-type zeolitic pores without size discrimination, the H2/CO separation factor can be attributed to the slow diffusivity of CO in the membrane. Thus, CO has a longer residence time in the pores, and the oxidation proceeds effectively. (ii) A γ-Al2O3 layer was formed on the outer surface of a porous α-Al2O3 support tube using a boehmite sol. The layer was then impregnated with Rh using an aqueous solution of RhCl3, and calcined in air at 573 K . A microporous silica layer was then formed on the surface of the Rh-impregnated γ-Al2O3 layer using a silica sol. The SiO2 membrane showed a H2/CO separation factor of 100. Thus, the CO concentration of 50 000 ppm on the feed side was decreased, with no feed of O2, to 500 ppm at 523 K on the surface of the Rh/γ-Al2O3 layer. When O2 was added to the feed, CO was oxidized in the Rh/γ-Al2O3 layer, and a corresponding decrease in CO concentration on the permeate side was observed.

Mixing and enzyme reactions in a microchannel packed with glass beads

Mixing behavior in a microchannel was investigated by means of a spectrophotometer equipped with optical fiber probes. Microreactors with a Y-shaped channel were fabricated on poly(methyl methacrylate) substrates. Glass beads were packed in the intersection and the downstream regions to improve mixing performance. An NaOH solution and a BTB solution as a pH indicator were fed to the microchannel with a syringe pump. As the mixing progressed, the color of the mixed solution changed to blue. The degree of mixing was evaluated by the change in absorbance at 623 nm of the mixing solution. The packed glass beads strongly enhanced the mixing performance in the microchannels, especially in the case of packing in the intersection. The effect of mixing in the microchannel on an enzyme reaction was also investigated. The hydrolysis of o-nitrophenyl-\-D-galactopyranoside by \-galactosidase was used as a model reaction. The results showed that the enzyme reaction was enhanced in the microreactor with glass beads compared with a batch reactor. The microreactor packed with glass beads gave the highest reaction rate.

Preparation of a hydroxyapatite film and its application in the removal and regeneration of aqueous cations.

Aqueous Pb(2+), Cd(2+), Co(2+), and Cu(2+) were continuously removed and regenerated using a bulk powder of calcium hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2), CaHAp) and a glass plate coated with a thin film of CaHAp. Although use of CaHAp effectively removed aqueous Pb(2+) from the wastewater, lead cations immobilized on CaHAp could not be regenerated in an aqueous solution due to the formation of lead hydroxyapatite (Pb(10)(PO(4))(6)(OH)(2)), which is insoluble in water at acidic and neutral pH. In contrast, Co(2+) and Cu(2+) immobilized on CaHAp were easily regenerated in an aqueous solution by treatment with an acidic aqueous solution containing Ca(NO(3))(2), as previously reported for the CaHAp-Cd(2+) system. We found that the combination of the removal of the aqueous divalent cations by the CaHAp film and subsequent regeneration of the immobilized divalent cations from the film allowed for recycling of the film and for removal and regeneration of aqueous Cd(2+), Co(2+), and Cu(2+).

Dehydrogenation of cycloalkanes over noble metal catalysts supported on active carbon

Dehydrogenation of decalin to naphthalene through tetralin and that of dicyclohexyl to biphenyl through phenylcyclohexane with Pt/C and Pd/C was investigated mainly under the liquid film state, in which the catalyst was just wet but not suspended and covered with a thin film of liquid substrate. To improve the catalytic activities, the effects of the addition of tellurium into Pd/C were investigated to reveal that the combination of tellurium, palladium and conjugated systems produced during the dehydrogenation of cycloalkames was important to the improvement of the activities.

Permeation behavior during the catalytic oxidation of CO in a Pt-loaded Y-type zeolite membrane

A Pt-loaded Y-type zeolite (Pt/NaY) membrane was prepared on the surface of a porous α-Al2O3 support tube by hydrothermal synthesis and then ion-exchanged with platinum. The thickness of the zeolite layer and the amount of Pt loaded were ca. 12μm and 1wt%, respectively. The membrane was employed in the form of a cylindrical thin catalyst for the selective oxidation of CO in an H2-rich mixture. A mixture of CO, O2 and H2 was fed to the outer surface of the membrane, and CO was selectively oxidized during its permeation through the thin layer. The permeation fluxes for H2 and CO were determined at 423–523K. Permeation fluxes also calculated by means of a mathematical model using effective diffusion coefficients and reaction kinetics. The effective diffusion coefficients through the zeolite membrane were estimated from gas permeation test data, obtained at 423–523K, and the oxidation rates of CO were determined over a particulate catalyst that had the same composition as the Pt/NaY membrane. As a result, the diffusion coefficients of O2, N2 and CO were determined to be (0.7–1.0) ×10−7m2s−1 at 423–523K, and the activation energies for the rate constants for CO oxidation were 61–77kJmol−1. The predicted permeation fluxes of H2 and CO using the mathematical model were in good agreement with the experimental data, when the oxidation selectivity of CO to H2 was assumed to be 80% in the model calculation.

Adsorption of Water and Methanol on Highly Graphitized Thermal Carbon Black and Activated Carbon Fibre

Adsorption of water and methanol on different carbonaceous solids was carried out to investigate the roles of porous structure and functional groups on the adsorption of associating fluids. A highly graphitized thermal carbon black, non-porous Carbopack F, was chosen to study the effects of functional groups and their concentration, and two samples of porous activated carbon fibre (ACF), microporous A-5 and micro-mesoporous A-15, were used to investigate the interplay between the functional groups and confinement. On Carbopack F, adsorption of water at 298 K is not experimentally detectable until the relative pressure reaches about 0.9, and the adsorption isotherm exhibits a large hysteresis loop spanning a very wide range of pressure; by contrast methanol adsorption at the same temperature shows an onset of adsorption at a lower relative pressure of 0.2 and the isotherm has a very small hysteresis loop. This early onset, compared with water, is due to the dispersion interaction between the methyl group and the graphene surface; an interaction which is absent in water. For the porous ACF samples, the onset of water uptake shifts from a relative pressure of 0.9; as observed for Carbopack F, to the much lower values, depending on pore size, of 0.3 for microporous A-5 and 0.5 for micro-mesoporous A-15.

Optimal operation of a continuous DTB crystallizer

Abstract The optimal operation of a continuous crystallizer is studied by taking a real industrial scale crystallizer as an example. The objective function to be maximized is the production rate of the crystals which are larger than a certain size. Since continuous crystallizers exhibit sustained oscillation, it is important to find the optimal operation under oscillatory condition. In this study, the optimal operating condition is derived for two types of operation: one is the case where the manipulated variables are kept constant (constant input operation), and the other is the case where the values of manipulated variables are changed periodically (time varying input operation). The optimization result of time varying input operation indicates that the production rate of large crystals can be increased if the number of fine crystals in the vessel is reduced by withdrawing along with the product. Furthermore, this study examines the optimal operation of the crystallizer in the case where the sustained oscillation is eliminated by a stabilizing controller. The optimization result clearly indicates that the production rate of large crystals can be significantly increased if the operation is optimized under the condition where crystal size distribution (CSD) is stabilized.