Assuming a simple mixing section built into a small-scale flow reactor operated mainly under laminar flow conditions, we investigated the mixing characteristics in a co-current double-tube mixing section with an orifice plate. The mixing characteristics of two liquids in the mixing part were evaluated by the segregation factor in the Villermaux–Dushman reaction for flows in the region where Reynolds number was 4000 or less and the flow ratio of the annular region to the inner pipe was 100 : 1. The parameters examined were the orifice diameter and the total flow rate of the fluid (sum of the flow rate from the annular part and the inner pipe). It was found that by installing an orifice plate just downstream of the inner pipe outlet, extremely good two-liquid mixing characteristics were exhibited even under laminar flow conditions. The smaller the orifice diameter was, the better were the mixing characteristics. In addition, the mixing characteristics improved with increasing total flow rate. In order to investigate the reason for the improvement of mixing characteristics by installing an orifice plate, water colored with pigment was supplied from the inner pipe under the same conditions as in the mixing characteristics evaluation experiment, and the flow state in the pipe was visualized. It was found that the vortex from the shear layer formed at the boundary between the jet from the orifice and the surrounding fluid and the turbulence of the jet itself contributed greatly to the mixing characteristics. It was clarified that mixing performance comparable to existing micromixers could be obtained depending on the conditions.

In a bead mill, shear force becomes dominant for disintegrating aggregated particles in particle processing. For nanoparticle processing, fine beads are required, because nanoparticles are broken if especially high contact energies are applied. Since bead motion cannot be observed experimentally, simulation is a promising approach to predicting bead behavior. In simulation studies in the literature, the coefficient of friction was optimized to reproduce bead behavior. However, optimization of the friction parameters is not sufficient for precisely reproducing bead behavior, because the spatial distribution of beads might influence solid-fluid interaction forces. In this study, an annular-type bead mill was simulated by our Advanced DEM (discrete element method)-CFD (computational fluid dynamics) method. The simulation method was validated by comparing the simulated and experimentally observed bead behavior. In particular, the influence of bead-wall friction parameters on solid-fluid interaction forces as well as macroscopic bead behavior was examined. The simulation results suggest that bead-wall friction influences not only the tangential component but also the normal component of bead-bead contact energies.

Adsorption experiments for a mixed acid (phosphoric acid+acetic acid) with a silica gel adsorbent and the adsorption-assisted batch crystallization of phosphoric acid were performed. In the adsorption experiments, the impurity concentration of acetic acid in the solution was efficiently reduced by the selective adsorption of acetic acid from the mixed acid by silica gel. The crystallization temperature and the weight fraction of silica gel adsorbent were varied as the operative variable for the adsorption-assisted crystallization. It was found that crystals of phosphoric acid having the purity more than 99% were obtained. As the weight fraction of adsorbent increased, the purity of phosphoric acid’s crystals also was slightly increased. When the crystallization temperature was lowered, the yield of phosphoric acid’s crystals was also increased, but the purity of phosphoric acid’s crystals did not change much. As for the adsorption-assisted crystallization using silica gel adsorbent, the crystals of phosphoric acid changed from needle-like crystals to plate-like crystals as the weight fraction of the adsorbent increased. It was consequently suggested that the smaller crystals of phosphoric were generated in the solution, the higher purity of phosphoric acid’s crystals were formed.

Solid–liquid two-phase flow was studied on inclined and bent settling plates. A 40% glycerol solution was used for the continuous phase, and 400 µm glass beads were used as the settling substance. In the visualization experiment, the fluid velocity vector of the continuous phase was obtained by the PIV method. In numerical analysis, the flow behavior was considered using the DEM method and CFD. Good agreement was found between the results of the visualization experiment and the numerical analysis. Furthermore, characteristic flow was observed around the bent section: the flow rate of the continuous phase was almost equal in the upper and lower layers in the initial state.

Interfacial modification caused by fluctuation or desorption of surfactant during microwave irradiation has been proposed by utilizing the characteristic of microwaves to pass through the oil phase and be absorbed at the liquid–liquid interface. Because of the variety of surfactants, aqueous solutions and oils, the systematization of heat transfer related to irradiation method is required for optimization of interfacial modification. In this study, interfacial tension was measured during pulsed microwave irradiation when a surfactant with a long hydrophilic group was stably adsorbed at the liquid–liquid interface. First, the interfacial modification related to the rapid increase in interfacial tension observed as non-thermal effect of microwaves was discussed in terms of the dimensionless number that our group recently proposed as an indicator of microwave energy concentration at the interface, and the validity of the approach was confirmed. Finally, effective conditions for pulsed irradiation were predicted by use of the dimensionless number.

To construct a recycling process for spent lithium-ion batteries, the hydrothermal leaching by organic acid of lithium-ion battery positive electrode materials and spent lithium-ion batteries was examined by treatment with citric acid (0.4–2.0 mol/dm³) at 80–200°C for 5–60 min. Leaching efficiencies of Li, Co and Ni were found to increase with increasing reaction temperature and time. The leaching efficiency of Mn was more than 90% under mild conditions of 110°C for 5 min, but it decreased as the reaction temperature increased, and a white solid precipitated. However, when the temperature was further increased, the leaching efficiency increased again. When the effect of reaction temperature on leaching efficiency was investigated with spent lithium-ion batteries, the positive electrode elements Li, Co, Ni and Mn were all leached. Furthermore, it was suggested that in the leaching of spent lithium-ion batteries, the crystal structure of the positive electrode elements was changed by the pretreatment, which affected the leaching mechanism.

A novel rotating coil-shaped spiral gas–solid contacting device was proposed. JIS 20^A size 180° long elbows made of stainless steel were connected to form a five-cycle spiral. This metal model spiral was continuously driven by a motor to transport particles. The external surface of the spiral was heated by use of flexible heaters and the temperature was maintained constant. From the difference in temperature of particles between the inlet and the outlet of the spiral, heat transfer rate was determined. The heat transfer coefficient increased with increasing rotation rate. An empirical equation to estimate the heat transfer coefficent using thermal properties of solids and rotaton rate was obtained. From the results of visual observation of a transparent cold model of the spiral, a packet renewal model of heat transfer was proposed. The model assumed periodical exchange of solids attached to the reactor wall. The heat transfer rate was estimated with this model using the thermal properties of the solid samples. The experimental results of heat transfer coefficent were 0.38–0.50 times the predicted value.