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The microcapillary was combined with the liquid-liquid slug flow to build the separation field. The partition behavior of seventeen kinds of substrates was investigated by using six kinds of water/organic biphasic systems under hy...
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The microcapillary was combined with the liquid-liquid slug flow to build the separation field. The partition behavior of seventeen kinds of substrates was investigated by using six kinds of water/organic biphasic systems under hydrothermal conditions (25 – 190~(o)C at 10 MPa). The scale of hydrophobicity (HF ) of water/organic biphasic system was estimated. The HF value for the biphasic system used here was comparable to the conventional aqueous two-phase systems and depended on the (de)solvation of substrates by water and organic solvent. Besides, the vortex field in the slug contributed to the enhanced mass transfer of substrates. Those results are available for the selection of water/organic biphasic system as the reactive separation of target materials.
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Submicron-sized bubbles are now officially called ultrafine bubbles (UFBs) by the international standard. The concentration of UFBs is generally low (<109 particles/mL; <0.001 vol%) compared to other colloidal dispersions. To over...
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Submicron-sized bubbles are now officially called ultrafine bubbles (UFBs) by the international standard. The concentration of UFBs is generally low (<109 particles/mL; <0.001 vol%) compared to other colloidal dispersions. To overcome this practical problem, we concentrated UFBs in ultrapure water prepared by a commercial UFB generator and quantified the effect of rotary evaporation of the dispersion media on the stability of UFBs. The UFB dispersions were characterized by a particle tracking analysis (PTA) instrument. The experimental results showed that the UFBs can be diluted and concentrated without changing the size distribution and there was little or no loss of UFBs. By using a rotary evaporator, UFB dispersions were about 30-fold concentrated and the resultant number concentration reached over 3 × 1010 particles/mL. Increasing the concentration of UFBs allowed for satisfactory dynamic light scattering (DLS) measurements. The differences among the three algorithms for analyzing the raw data, i.e., autocorrelation function, obtained by DLS are discussed, along with the characteristics of the particle size distribution derived from each algorithm.
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Ultrafine bubble (UFB) is a bubble with a diameter of less than 1 μm. Little attention has been paid to the defoaming and removal of UFBs. This study proposes a method to destabilize UFBs by using indirect ultrasonic irradiation....
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Ultrafine bubble (UFB) is a bubble with a diameter of less than 1 μm. Little attention has been paid to the defoaming and removal of UFBs. This study proposes a method to destabilize UFBs by using indirect ultrasonic irradiation. Besides, the destabilization mechanism of UFB was investigated. The ultrasonic frequency was 1.6 MHz and the dissipated power was 30 W. UFB dispersions were prepared using two different types of bubble generators: pressurized dissolution method and swirling liquid flow method. The effects of ultrasonic irradiation on the stability of UFBs were evaluated by particle tracking analysis (PTA) and electrophoretic zeta potential measurement. Results showed that the indirect ultrasonic irradiation for 30 min reduced the number concentration of UFBs by 90% regardless of the generation method. This destabilization was attributed to a decrease in the magnitude of zeta potential of UFBs due to the changes in pH and electrical conductivity. These changes in the electrochemical properties were caused by the formation of nitric acid. To study the destabilization mechanism, the pH of the UFB dispersions were modified by titration;the chemical and mechanical effects of ul trasound were separately examined. It was found that not only the chemical effect caused by the formation of nitric acid but also the mechanical effect contributed to the destabilization of UFB. Feasibility studies were also performed for UFBs in an aqueous surfactant solution and UFBs in a solid particle dispersion. The proposed method selectively destabilized UFBs in the solutions.
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The present study focuses on the aeration of aqueous triethanolamine acting as reaction medium for biocatalytic carboxylations. For enhancing mass transfer in a bubble column reactor, microbubble aeration is applied and compared t...
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The present study focuses on the aeration of aqueous triethanolamine acting as reaction medium for biocatalytic carboxylations. For enhancing mass transfer in a bubble column reactor, microbubble aeration is applied and compared to conventional macrobubble aeration. Application of a 0.5 μm porous sparger enables microbubble CO _(2) aeration with bubble size distributions below 150 μm in Sauter mean diameter, correlating with the highest measured mass transfer rates. During CO _(2) saturation of the aqueous triethanolamine, bubble size distributions changed according to the level of CO _(2) saturation. For microbubbles, less foaming was observed compared to macrobubble aeration by a 10 μm porous sparger. This microbubble effect is attributed to their accelerated dissolution assisted by the Laplace pressure lowering the amount of bubbles reaching the surface of the liquid. The experiments reveal that the rate of interfacial area generation, which is calculated based on measured bubble size distributions, influences the biocatalyst activity.
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The purpose of this study is to examine the possibility of establishing a novel CO_(2) absorption process with molten alkali carbonate using a bubble column reactor. In our previous study, a hot CO_(2) recovery process using Li_(4...
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The purpose of this study is to examine the possibility of establishing a novel CO_(2) absorption process with molten alkali carbonate using a bubble column reactor. In our previous study, a hot CO_(2) recovery process using Li_(4)SiO_(4) suspended in molten Li_(2)CO_(3)–K_(2)CO_(3) was developed. In the process, molten alkali carbonate itself showed great potential for CO_(2) absorption at high temperature. If a hot CO_(2) absorption process were established using only molten alkali carbonate, it could make the system simpler and the operating temperature range could be extended without the limitation of reaction temperature of solid absorbent. In the study, molten Li_(2)CO_(3), Na_(2)CO_(3), K_(2)CO_(3) and its eutectic mixture were selected as CO_(2) absorbent. A bubble column was chosen as the device for gas absorption at high temperature. First, the CO_(2) absorption performance of each single molten alkali carbonate was investigated. The result showed that the molten Li_(2)CO_(3) had a great ability to absorb CO_(2) at high temperature. Li_(2)O was thought to be produced by decomposition of Li_(2)CO_(3) during the melting and purging process and a reaction of CO_(2) with Li_(2)O occurred during the absorption process. Further, the CO_(2) absorption performance of eutectic mixture increased exponentially with increasing the ratio of Li_(2)CO_(3) in composition. Second, the possibility of establishing a CO_(2) absorption process using molten Li_(2)CO_(3) was examined. The overall CO_(2) absorption process in the bubble column was investigated and the experimental results showed that the mass transfer of CO_(2) into molten Li_(2)CO_(3) was the rate-controlling step. The operational conditions of the bubble column were optimized. The superficial gas velocity was an important operational parameter that affected both the CO_(2) absorption rate and total amount of CO_(2) finally absorbed in the bubble column. The operating temperature also greatly affected the amount of absorbed CO_(2).
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The clarification of the partition property of substrates in a water / organic biphasic system is useful in the development of a reaction / separation process for value-added materials, especially under high temperature and pressu...
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The clarification of the partition property of substrates in a water / organic biphasic system is useful in the development of a reaction / separation process for value-added materials, especially under high temperature and pressure conditions. In this study, the water / methyl isobuthyl ketone (MIBK) biphasic system was investigated under various temperatures (25 – 190 ~(o)C) at 10 MPa. The partitioning behavior of substrates such as furfural derivatives, amino acids, and saccharides, depended on the temperature and the flow rate ratio of MIBK to the water phase. The scale of hydrophobicity (HF ) of the water / MIBK biphasic system to determine the partitioning behavior of substrates was estimated based on the partitioning behavior of amino acids. The HF value for the water / MIBK phase flow system of was greater than that for the batch system and comparable to that for conventional aqueous two-phase systems such as polyethylene glycol / dextran and liposome membrane systems. It was probably because an increase of the surface-to-volume ratio and the vortex field in the slug flow contributed to the mass transfer of substrates and their distribution.
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The effects of operating conditions on bubble volume formed from a nozzle submerged in some viscous media with yield stress were experimentally investigated. Pressure fluctuations in the gas chamber accompanied by bubble formation...
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The effects of operating conditions on bubble volume formed from a nozzle submerged in some viscous media with yield stress were experimentally investigated. Pressure fluctuations in the gas chamber accompanied by bubble formation as well as bubble growth curves were measured. By analysis of the time course of pressure change in the gas chamber, the dependency of the gas flow rate into the gas chamber and the chamber volume on the polytropic coefficient of gas in the gas chamber was discussed. To simulate the bubble formation at a single nozzle in a viscous medium having yields stress, the non-spherial bubble formation model was proposed. The calculated bubble volumes agreed relatively well with the experimental ones.
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Many chemical and biocatalytic reactions are consuming gaseous species like oxygen, provided by the mass transfer across interfaces of multiphase contact apparatuses. For biocatalytic reactions a macroscopic aeration can lead to r...
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Many chemical and biocatalytic reactions are consuming gaseous species like oxygen, provided by the mass transfer across interfaces of multiphase contact apparatuses. For biocatalytic reactions a macroscopic aeration can lead to reduced enzyme activity by foaming and shear forces and for fast chemical reactions in multiphase flows, the mass transfer limitation is often the bottleneck for a process optimization. The present study investigates the use of bubbles with diameters less than 100?μm for aeration of a 3?L lab scale stirred tank reactor. For demineralized water and a solution of glucose and bovine serum albumin (BSA) as biocatalytic model protein solution, two different membrane spargers with a mean pore size of 1?μm and 2?μm are investigated. Determining the influence of the energy input on the hydrodynamics of the system, endoscopic measurements of bubble size distributions are carried out. The mass transfer performance of the two spargers is analyzed by measurements of the oxygen k _(l)a value for varying gas flow rates. As a result microbubble aeration shows a significant higher mass transfer performance compared to an open tube aeration saving 60% of the gaseous phase by reaching the same k _(l)a values. Besides high specific interfacial areas and long residance times, the Laplace pressure inside the bubble is identified as an enhancing force for mass transfer at microscale.
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To estimate mass transfer rate during bubble formation at an orifice, a theoretical model is proposed for soluble gas bubble formation in liquid by modifying the non-spherical bubble formation model. The absorption rate from pure ...
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To estimate mass transfer rate during bubble formation at an orifice, a theoretical model is proposed for soluble gas bubble formation in liquid by modifying the non-spherical bubble formation model. The absorption rate from pure SO_2 gas bubble to water is experimentally measured as well as bubble shape and growth rate. Mass transfer from the gas-liquid interface during bubble growth is described well by the penetration theory. Experimental bubble shape, bubble volume at its detachment from an orifice. growth rate and mass transfer rate are estimated well by the present model.
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Escapable gas holdups and volumetric oxygen transfer coefficients were measured at several concentrations of xanthan aqueous solutions in four standard bubble columns in which a slug bubble flow was observed. The experimental esca...
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Escapable gas holdups and volumetric oxygen transfer coefficients were measured at several concentrations of xanthan aqueous solutions in four standard bubble columns in which a slug bubble flow was observed. The experimental escapable gas holdups were well estimated by the semi-theoretical Nicklin's equation modified for non-Newtonian xanthan aqueous solutions having yield stress. Although the escapable gas holdups increased with decreasing column diameter and increasing superficial gas velocity, it was hardly influenced by the concentration or apparent viscosity of the xanthan aqueous solutions. The volumetric oxygen transfer coefficient increased with decreasing yield stress of the liquid, increasing diffusion coefficient, decreasing column diameter, and increasing gas holdup. By correlating all experimental results, an empirical equation was proposed. To design a more efficient bioreactor, the partitioning perforated plate which is used in columns larger than those used by Terasaka and Shibata, was inserted in the standard bubble columns. The gas holdup and volumetric oxygen transfer coefficient in the partitioned bubble columns were measured and were compared with those in the standard bubble columns. The volumetric oxygen transfer coefficients in the partitioned bubble columns became larger than those in the standard bubble columns at a fixed superficial gas velocity, even for large column diameters. Therefore, in this study, partitioned-bubble column-bioreactors were developed for more suitable production of xanthan gum.
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