MIL-100(Fe) is a metal-organic framework (MOF) with high water adsorption capacity but poor stability under continuous adsorption–desorption cycling. This paper reports on a novel method for improving the cyclic adsorption stability of MIL-100(Fe) by coating it with ZIF-7 or ZIF-8 to form MOF–MOF composites. This process is meant to prevent the direct exposure of MIL-100(Fe) to moisture, and thereby extend its lifespan. The structure of resulting MIL-100(Fe)@ZIF-7 and MIL-100(Fe)@ZIF-8 was characterized using a number of solid-state techniques, including scanning electron microscopy, energy dispersive spectroscopy, FT-IR spectroscopy, and powder X-ray diffraction with synchrotron source. Pure MIL-100(Fe) and the two composites were subjected to cyclic water adsorption–desorption tests at 25°C under 80% relative humidity. After 25 cycles, the water adsorption capacity of pure MIL-100(Fe) dropped by approximately 30%. The adsorption uptake of the MOFs remained almost unchanged; however, their overall adsorption capacity is slightly lower than that of pure MIL-100(Fe).
This paper reports on monometallic Pt nanoparticle (Pt-NP) and bimetallic SnPt nanoparticle (SnPt-NP) catalysts with different SnxPty alloy structures. The catalysts were fabricated using a polyalcohol reduction process, and the catalytic activity of each alloy phase for the hydrogenation of acetic acid to ethanol was investigated. High-resolution transmission electron microscopy (HR-TEM) results confirmed that SnPt-NP catalysts with different Sn/Pt atomic ratios can be successfully synthesized by controlling the Sn/Pt atomic ratios of each metal precursor (platinum(II) acetylacetonate and tin(II) acetate) in the starting mixture during a polyalcohol reduction process. Analyses by inductively coupled plasma spectroscopy and X-ray diffraction (XRD) indicated the formation of uniform Sn1Pt3 and Sn1Pt1 alloy structures in the SnPt at Sn/Pt atomic ratios of 0.32 and 1.09, respectively. Compared with the monometallic Pt metal phase in the Pt-NP catalysts, the Sn1Pt3 alloy phase markedly accelerated the hydrogenation of acetic acid. However, hydrogenation of acetic acid was not observed over the SnPt-NP catalysts at Sn/Pt=1.09, suggesting that the Sn1Pt1 alloy phase is inactive for the hydrogenation of carboxylic acids to corresponding alcohols. Therefore, we conclude that the Sn1Pt3 alloy phase is the most effective bimetallic SnPt alloy phase for catalyzing the hydrogenation of carboxylic acids.
Micro-partition (MP; supplied by Nano Cube Japan Co., Ltd.) which is commercially available as a heat sink for precision electronic parts (and generally not as a catalyst support), was adopted as a structured catalyst support. The MP was made from aluminum; it was converted into an alumite catalyst as structured catalyst and applied for a gas–solid catalytic reaction. The MP has micro fins and holes; therefore, the reactivity was expected to improve because the reactant fluid would be disarranged. In this research, we linked the disarrangement of the fluid with the reactivity, analyzed the flow state of the reactants in detail, and evaluated its effect on the reactivity. Experiments and a three-dimensional simulation were carried out to investigate the relationship between the structure and reactivity. Steam reforming of methanol was adopted as the model reaction. When the structured catalyst was used, the conversion increased by 80% at 553 K compared with that of a non-characteristic structured catalyst plate, and it was implied that the improvement in reactivity was better at lower temperature. The characteristic structure of the MP, not only the fins but also the holes significantly improved the reactivity. An analysis of the reaction rate showed that the contact frequency between the reactants and the catalyst increased. Furthermore, an index to evaluate the promotion of mass transfer was introduced when analyzing the mass transfer around the catalyst using dynamics simulation. The simulation showed that the structure promoted the mass transfer by convection, and a similar trend as the experiments was observed; the effect of the structured catalyst was larger at lower temperature condition. The factor of the reactivity improvement by the structured catalyst became clear from the results of the experiments and simulation.
To promote nucleation in nanoparticle synthesis, high-power operation is desirable. However, at high power, heat generation due to the rapid microwave absorbance of particles often results in rapid bubble growth, unstable nucleation, and superheating. Therefore, a trade-off between suppressing superheating and producing stable and finer nanoparticles is necessary. This study aims to investigate and confirm the synergistic effect between the high power of microwaves and addition of different types of antisolvents. Results show that the addition of an antisolvent prevents superheating and produces fine-sized particles at high-power operation. In addition, it was observed that glycerin is a better antisolvent than ethylene glycol.
This study experimentally investigates a comprehensive mass transfer model for a packed column distillation process. The experimental data for the local analysis of distillation mass transfer were obtained by observing the vertical distribution of the temperature of the liquid using thermocouples embedded in the packing sections. To analyze the vapor- and liquid-phase film coefficients and/or the height of the transfer unit, a simultaneous equation method for calculating film coefficients was primarily considered by applying the film resistance equation based on the two-film theory at two vertically adjacent positions. The results showed that although this method can provide an appropriate solution in the middle-bed region of the column, the simultaneous equations in the near-top and near-bottom regions become inconsistent, owing to the almost constant slope of the equilibrium curve. Therefore, to overcome this difficulty as well as to simplify model construction, another countermeasure was considered based on the assumption that a set of the tangential vector of the equilibrium curve and the tie-line vector defined at the crossing point is pairwise orthogonal at the “vapor–liquid” interface at each theoretical stage. As a result, the local analysis of the film resistances and/or volumetric mass transfer coefficients was sufficiently improved in these regions. The experimental mass transfer knowledge acquired using the proposed model could contribute to the construction of an engineering database, which would not only be useful for the development of novel or highly efficient packings, but also for improving the design of the practical columns, resulting in process intensification.
Gas absorption enhancement of gas–liquid slug flow by adding non-porous fine particles into the liquid phase was investigated. A glass tube with a millimeter-size diameter was used as the flow channel, and the gas and liquid slugs were air and distilled water, respectively. When the absorption rates of oxygen with and without the addition of non-porous silica fine particles in water were compared by the liquid-side mass-transfer coefficient, kL, the rate with particles was enhanced and increased as the concentration and diameter of the particles increased. This is because the frequency of particle circulation in the liquid slug increased at higher concentration, and the larger particles caused stronger disturbances at the boundary layer at the interface on the liquid-phase side.
We present size-based separation of nanoparticles using deterministic lateral displacement (DLD) arrays in poly(dimethylsiloxane) (PDMS). Unlike conventional dry-etched silicon DLD devices for nanoparticle separation, our proposed devices are fabricated from PDMS by standard soft lithography. Using a DLD device having a critical diameter Dc of 0.7 µm, we could separate fluorescent polystyrene particles of diameters 1 and 0.5 µm. In addition, we could demonstrate solution exchange for 0.5-µm beads by using a DLD device having a smaller Dc of 0.3 µm.
Aqueous dispersions of polystyrene particles were prepared containing sodium carboxymethylcellulose (CMC) and sodium chloride (NaCl). The destruction process of the aggregates at a time scale less than one second was observed directly using a parallel disk geometry with startup rotation. The shear history differs with vertical positions under this unsteady shear flow and affects the time variation of aggregate size. It is found that the destruction process of aggregates at any position was correlated well by the introduction of cumulative shear strain. The effects of the additives on the fragility and stable size of aggregates under the unsteady shear flows have been investigated. It was revealed that the dominant factor of the fragility was changed from electrostatic repulsion to steric repulsion as increasing polymer concentration. In the electrostatic dominant regime, aggregates were easily destroyed at lower ionic strength. In contrast, stable aggregate size was decreased monotonically by increasing CMC concentration even in the electrostatic dominant regime.
The effects of surfactant concentration on the sedimentation characteristics of silica hard-shell microcapsules containing trimethylolethane clathrate hydrates as phase change materials have been investigated. A combination additive of a cationic surfactant system and poly vinyl alcohol (PVA) was used to inhibit sedimentation. The concentration of surfactants was varied between 0 and 6,000 ppm, while that of PVA was maintained at 2,000 ppm. The apparent shear viscosities and the apparent volume fractions of the sedimentation were measured. In each solution, the hydraulic diameter of the molecular structure in each solution was also determined. From the results of sedimentation experiments, it was found that the sedimentation was effectively reduced when the surfactant concentration was greater than 4,000 ppm. The extensional viscosity of the fluid was found to dominate the sedimentation characteristics of the systems with high concentrations. In contrast, the sedimentation velocity was observed to be comparatively high for a surfactant concentration of 2,000 ppm. In the present study, surfactant molecules were found to adsorb on the surface of the microcapsules. This leads to the disappearance of high-order structure of the combination additives, increasing counter-ion molar ratio, while the extensional viscosity decreases. Considering that the viscosity affects the flow characteristics, a surfactant concentration of 4,000 ppm was found to be optimal among the present conditions.
In this study, we evaluated three types of stabilizers for preventing oil layer formation and particle sedimentation in magnetorheological fluids (MRFs). Stabilizer dispersion and dissolutions were characterized by rheological measurements of mineral oil and MRF. Centrifugal stability tests were also conducted for MRFs containing the stabilizers. We found that the relationship between the non-Newtonian flow index and the concentration of stabilizers in the oil was similar to that in the MRFs. In addition, we found that a suitable degree of internal structure created a sufficiently stable MRF that also exhibited sufficient fluidity.
The rheological behavior of viscoelastic fluids in the vicinity of singular points, where stress and pressure tend to infinity due to the abrupt change in boundary conditions, such as die lips or sharp edge corners of re-entrant flow, is not yet fully understood. We have developed sector singular elements, that are placed in a small core around the singularity, and are suitable for finite element analysis of viscoelastic fluids; such finite elements have been previously reported for Newtonian flow problems. Each element has special interpolation functions along its radial direction which take into account the nature of the singularity, and conventional elements are used in the rest of the domain. The problem was solved by a 'decoupled method', which alternatively solves the velocity-pressure fields and the stress field, in combination with several numerical techniques to enhance the upper limits of the Weissenberg number. Compared to the conventional FEM, the sector singular finite element method is better at yielding smoother results even near the singularity, but poorer at convergency, and requires a larger amount of system core memory due to its more complicated topology. These disadvantages represent serious problems for multi-mode and/or 3D flow simulation of viscoelastic fluids. Therefore, we developed a modified version of the sector singular finite element method for the purpose of improving the simulation performance.
Hydration reaction characteristics of a composite of calcium chloride and silica microcapsules with nano-holes were investigated. Silica hollow microcapsules with holes were fabricated via a double emulsion method, and calcium chloride was inserted in the capsules. The properties of the cell were compared with those of calcium chloride/expanded graphite treated in a previous study. The hydration reaction experiments show that the reaction rate was considerably higher than that of the composite of calcium chloride/expanded graphite at the initial stage. This was because of the high thermal conductivity and the low contact thermal resistance between the composites and the heat transfer plates of the present cell. Further the power of the present composite cell was 9.78 times greater than that of the expanded graphite because the proposed capsules contains a larger amount of calcium chloride. Thus, the present composite is a promising item not only for realizing the chemical heat pumps but also for the machine start-up heating.