Masaki Kubo

Kinetics of ultrasonic disinfection of Escherichia coli in the presence of titanium dioxide particles.

The ultrasonic disinfection of Escherichia coli was carried out in the presence of anatase‐type TiO2 particles, and the effectiveness of the combination of ultrasonic irradiation with TiO2 addition was verified. The rate constant was determined from the plot of the common logarithm of the survival cell ratio versus the ultrasonic irradiation time using first‐order kinetics. In the absence of particles, the rate constant was proportional to the ultrasonic power. When ultrasonic disinfection was carried out in the presence of TiO2 particles, which have a radical generation ability, the rate of disinfection was remarkably faster than that in the absence of TiO2. In the presence of silica particles, which have no radical generation ability, the rate of disinfection was the same as that in the absence of TiO2. These results suggest that the radical generation ability of TiO2 appeared as a result of the ultrasonic irradiation. The effect of the amount of TiO2 on the rate of disinfection was also examined. The rate constant for disinfection in the presence of TiO2 was saturated to a certain value and was represented using the Langmuir‐type equation. The proposed model well describes the effects of the ultrasonic power and the amount of TiO2 on the rate constant for disinfection.

Pretreatment combining ultrasound and sodium percarbonate under mild conditions for efficient degradation of corn stover.

Ultrasound (US) can be used to disrupt microcrystalline cellulose to give nanofibers via ultrasonic cavitation. Sodium percarbonate (SP), consisting of sodium carbonate and hydrogen peroxide, generates highly reactive radicals, which cause oxidative delignification. Here, we describe a novel pretreatment technique using a combination of US and SP (US-SP) for the efficient saccharification of cellulose and hemicellulose in lignocellulosic corn stover. Although US-SP pretreatment was conducted under mild condition (i.e., at room temperature and atmospheric pressure), the pretreatment greatly increased lignin removal and cellulose digestibility. We also determined the optimum US-SP treatment conditions, such as ultrasonic power output, pretreatment time, pretreatment temperature, and SP concentration for an efficient cellulose saccharification. Moreover, xylose could be effectively recovered from US-SP pretreated biomass without the formation of microbial inhibitor furfural.

Biodiesel Production from Waste Cooking Oil Using Anion-Exchange Resin as Both Catalyst and Adsorbent

A novel production process of biodiesel fuel was developed using an expanded-bed reactor packed with an anion-exchange resin having catalytic and adsorption abilities. Waste cooking oil was used as a cheaper feedstock, and methanol was added at the stoichiometric molar ratio of 3:1. The main constituent of the feedstock, triglyceride was completely converted to the biodiesel by the resin’s catalytic ability. The impurities of the feedstock, free fatty acid, water, and dark brown pigment were removed from the product by the adsorption on the resin. In addition, the by-product glycerin was also removed from the product by the adsorption on the resin. The product eluted from the reactor was directly used for the standard tests of the biodiesel properties. The eluted product almost met the biodiesel quality standards (EN14214 in Europe and ASTM D6751 in North America). Thus, the proposed system permitted the simple production of biodiesel from the waste cooking oil without the upstream processing to remove the impurities (free fatty acid and water) and the downstream processing to remove the catalyst and by-products (glycerin and soap).

Continuous Synthesis of Titanium Dioxide Fine Particles Using a Slug Flow Ageing Tube Reactor

A continuous reactor system for titanium dioxide fine particle synthesis has been proposed, in which a packed bed for the nucleation of fine particles was connected in series with a slug flow ageing tube for growth of the particles. By injection of nitrogen gas into the inlet of the ageing tube, the continuous liquid feed was separated into small portions so that slug flow was formed. Spherical unagglomerated fine particles of titanium dioxide were obtained using this reactor system, and the effectiveness of using slug flow was elucidated. The effects of some operation variables such as liquid flow rate in the ageing tube and tube diameter were also examined. The particles obtained under the slug flow condition had narrower particle size distribution than those under a laminar flow condition at any flow rate. Particle geometric standard derivation (GSD) was found to be as small as that obtained in a batch process. No quality difference in particle GSD exists between ageing tubes of 2 mm i.d. and 3 mm i.d. for the slug flow. Chronomal analysis assuming diffusion-controlled growth was applied and was found to be effective for simulating a continuous particle synthesis process of titanium dioxide.

Continuous synthesis of TiO2 fine particles and increase of particle size using a two-stage slug flow tubular reactor

A novel continuous process has been developed, which consists of a two-stage slug flow tubular reactor (SFTR) to increase the size of titanium dioxide fine particles. In a single-stage process, particle growth stops at a certain conversion level with unreacted titanium ethoxide remaining. In this process, however, water is added to the particle suspension containing unreacted titanium ethoxide to allow the particle growth to proceed again. The particles prepared using the two-stage SFTR process have a larger mean particle size and smaller geometric standard deviation (GSD) than those from the single-stage process. The two-stage process also provides a higher conversion to particles than the single-stage process does. A smaller amount of water fed into the first stage and a larger amount of water fed into the second stage results in a larger mean particle size, higher conversion to particles, and smaller GSD. The width of the particle size distribution of the two-stage process is almost the same as that of the single-stage process. The calculated results using a mathematical model are in agreement with the experimental data.

Modelling of Continuous Synthesis Process of TiO2 Particles Using Slug Flow Tubular Reactor

Acontinuous synthesis process for TiO 2 particles using a slug flow tubular reactor is modelled using population balance equations. In this reactor, continuous liquid feed is separated into small portions by injecting nitrogen gas, so that each liquid portion can be treated as a batch reactor. It is assumed that each particle consists of nuclei, and the particles grow by aggregation of particles. A fixed number of nuclei, N agg , is regarded as a constituent unit of particle growth to reduce the number of governing equations. By using a reduced number of equations, mean particle size, conversion to particles, geometric standard deviation, and particle number density are fitted to the experimental data. The fitted results explain well the fact that a higher initial H 2 O concentration gives a higher conversion, larger particle number density and smaller mean particle size. Simulated results of particle size distribution using estimated constants of reaction rate and particle interaction energies are also in agreement with the experimental data. Aggregation between small particles and large particles is found to be dominant after large particles are formed.

Normal spectral emissivity measurement of molten copper using an electromagnetic levitator superimposed with a static magnetic field

The normal spectral emissivity of molten copper was determined in the wavelength range of 780?920?nm and in the temperature range of 1288?1678?K, by directly measuring the radiance emitted by an electromagnetically levitated molten copper droplet under a static magnetic field of 1.5 T. The spectrometer for radiance measurement was calibrated using the relation between the theoretical blackbody radiance from Plancks law and the light intensity of a quasi-blackbody radiation source measured using a spectrometer at a given temperature. As a result, the normal spectral emissivity of molten copper was determined as 0.075 ? 0.011 at a wavelength of 807?nm, and it was found that its temperature dependence is negligible in the entire measurement temperature range tested. In addition, the results of the normal spectral emissivity and its wavelength dependence were discussed, in comparison with those obtained using the Drude free-electron model.

Thermal conductivity measurement of molten copper using an electromagnetic levitator superimposed with a static magnetic field

The thermal conductivity of molten copper was measured by the periodic laser-heating method, in which a static magnetic field was superimposed to suppress convection in an electromagnetically levitated droplet, to extend the measurement range of the method up to a relatively high thermal conductivity. Before measuring the thermal conductivity, the optimum conditions for static magnetic field, the laser frequency of periodic heating and sample diameter were investigated by numerical simulation both for the flow and thermal fields in an electromagnetically levitated droplet and for the periodic laser heating of the droplet in the presence of melt convection. As a result, the temperature dependence of the thermal conductivity of molten copper was proposed in the temperature range between 1383 and 1665 K. In addition, by comparing our results with those of previous studies, it was demonstrated that the present method of measuring thermal conductivity is also available for molten materials with a relatively high thermal conductivity, such as molten copper.

Kinetic model for formation of DMPO-OH in water under ultrasonic irradiation using EPR spin trapping method

The rate of the formation of the 2-hydroxy-5,5-dimethyl-1-pyrrolidinyloxy (DMPO-OH) radical in water during ultrasonic irradiation was evaluated both experimentally and theoretically. The hydroxyl radical (OH radical) was indirectly detected using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as the spin trapping compound, and the generated DMPO-OH by the reaction between the OH radical and DMPO was measured by an electron paramagnetic resonance. The rate of change in the concentration of the DMPO-OH decreased with time, suggesting that not only the formation reaction of DMPO-OH but also the degradation reaction would take place by ultrasonic irradiation. The formation rate of the DMPO-OH was higher with ultrasonic power intensity and lower with reaction temperature. Based on the experimental results, a kinetic model for the formation of the DMPO-OH was proposed by considering the formation reaction, the ultrasonic degradation, and spontaneous degradation of DMPO-OH. The model well described the effect of the ultrasonic power intensity and the reaction temperature on the formation rate of DMPO-OH. The rate of the formation of the DMPO-OH was evaluated with the aid of the kinetic model.

Rigorous kinetic model considering positional specificity of lipase for enzymatic stepwise hydrolysis of triolein in biphasic oil-water system

A rigorous kinetic model describing the stepwise triglyceride hydrolysis at the oil–water interface, based on the Ping Pong Bi Bi mechanism using suspended lipase having positional specificity, was constructed. The preference of the enzyme to cleave to the ester bonds at the edge and the center of the glycerol backbone of the substrates (tri-, di- or monoglyceride) was incorporated in the model. This model was applied to the experimental results for triolein hydrolysis using suspended Porcine pancreatic lipase (an sn-1,3 specific lipase) and Candida rugosa lipase (a non-specific lipase) in a biphasic oil–water system under various operating conditions. In order to discuss the model’s advantages, other models that do not consider the positional specificity of the lipase were also applied to our experimental results. The model considering the positional specificity of the lipase gave results which fit better with the experimental data and described the effect of the initial enzyme concentration, the interfacial area, and the initial concentrations of triolein on the entire process of the stepwise triolein hydrolysis. This model also gives a good representation of the rate for cleaving the respective ester bonds of each substrate by each type of lipase.