Power consumption was measured for rectangular eccentric mixing vessels with several kinds of impellers. The power number of rectangular eccentric mixing vessels corresponded to that of a cylindrical vessel with a diameter of 2 times the short side of the horizontal cross section of the rectangular vessel and with one baffle with a width of 1/10 of the rectangular vessel diagonal.
The validity of a hybrid of Brownian dynamics and lattice Boltzmann methods for simulating the activation of Brownian motion of magnetic particles in suspension was examined. In this method, random forces were added to the equations of motion of magnetic particles in the usual Brownian dynamics. In order to activate the Brownian motion at a physically reasonable level, a viscosity–modifying method was introduced in adjusting the random displacements of the particles. The main results obtained are summarized as follows. The aggregate structures of magnetic particles were in good agreement with the results of the Monte Carlo method, and the pair correlation functions agreed well with the Monte Carlo results both qualitatively and quantitatively: the Monte Carlo method is a well-established method and is regarded as yielding theoretical solutions. The magnetization curves were also in good agreement with Monte Carlo results, and this verifies that the rotational Brownian motion is activated at a physically reasonable level. The viscosity–modifying coefficients were almost independent of the strengths of the magnetic particle-particle and the particle-field interactions, and also of the volumetric fraction. From these results, we conclude that the present hybrid simulation method has potential for investigating the behavior of magnetic particles in a non-uniform applied magnetic field and in a general flow field.
In the Heat Integrated Distillation Column (HIDiC), the driving force of mass transfer and heat transfer is different at each stage due to the difference in irreversibility at each stage. Accordingly, a higher energy saving should be possible by optimal allocation of heat duties to appropriately selected and discrete internal heat exchangers rather than having internal exchanges at all stages. We have previously developed a design methodology for HIDiC that incorporates the reversible distillation curve and the operating locus on H-xy diagram, which is further integrated with the T-xy diagram, but have yet to establish criteria for the applicability of HIDiC. Here, by utilizing the H-xy and T-xy diagrams, we investigated characteristics of systems in which use of HIDiC is advantageous and showed that the feed composition and the product purity are determinative parameters under the identical target of energy saving based on reboiler duty. HIDiC was found to be advantageous in all applications other than where a light key component is rich in the feed and the product specification in both distillate and bottoms is for high purity.
Removal of CO2 from a simulated biogas consisting of CO2, CH4 and water vapor by pressure swing adsorption (PSA) was experimentally tested for the enrichment of CH4. SAPO-34 and 13X zeolites were employed as adsorbents, of which the former was originally developed for adsorptive desiccant dehumidification. Under the experimental conditions, SAPO-34 adsorbed a smaller amount of CO2 than zeolite 13X, but desorption of adsorbed water vapor from zeolite 13X could not be achieved by vacuum regeneration at room temperature, and thus CO2 separation by PSA zeolite 13X became impossible. In contrast, PSA with SAPO-34 kept its separation performance for the feed gas containing a small amount of water vapor. This allows simplification or omission of pre-drying of the feed gas.
Adsorption of heavy metal ions onto activated carbon is explained as a consequence of ion exchange with acidic functional groups such as the carboxyl group. In this study, bead-shaped activated carbon (BAC) was oxidized with nitric acid or ammonium persulfate to introduce surface acidic functional groups. Cadmium ions (Cd(II)) were employed to evaluate the heavy metal adsorption capacity of the oxidized BAC. The amount of surface functional groups was determined by Boehm titration. Surface area and pore volume were measured from N2 adsorption/desorption isotherms. The results showed that, although similar amounts of surface carboxyl groups were introduced by nitric acid and ammonium persulfate oxidation, BAC oxidized by ammonium persulfate adsorbed a larger amount of Cd(II) (0.76 mmol/g) than that oxidized by nitric acid (0.61 mmol/g) at an initial pH of around 5.0. The amount of Cd(II) adsorbed increased with increasing equilibrium solution pH, and the maximum Cd(II) adsorption for BAC oxidized by ammonium persulfate reached as much as 1.8 mmol/g in the solution equilibrium pH range of 7.1–7.6. The surface area and pore volume were decreased in each oxidized BAC. Since N2 is not adsorbed onto macropores, this implies that the oxidation process increases pore radius, causing the expansion of micro and mesopores into macropores.
Boehmite and boehmite-GPTMS hybrid membranes were fabricated on porous α-alumina support tubes using boehmite nanofibers for selective water separation from a liquid H2O/IPA mixture. The average sizes of the boehmite nanofibers were ca. 4 nm in width and ca. 1,200 nm, 1,400 nm and 2,000 nm in length. The influence of preparation conditions on the dehydration performance of the composite membranes was examined. As a result, the nanofiber membranes showed the higher separation performance when the withdrawal velocity of the alumina support tube was below 100 cm/min. The separation performance also increased with the number of coatings. Boehmite nanofibers of 1,200 nm and 1,400 nm in length were oriented in the lengthwise direction on the porous alumina support tube and formed slit-shaped micropores in the coated layer. Moreover, the separation factor was increased significantly to 1,628 by the hybridization with GPTMS, and the permeation flux was 0.88 kg·m-2·h-1.
The separation of calli and recovery of extracellular polysaccharides (TPS) by filtration from culture broth of Polianthes tuberosa were studied. The solids (calli or cell debris) to be separated included particles smaller than TPS molecules. Dead-end filtration of calli alone at a constant flow rate produced a compressible cake layer, but the use of filter aids such as diatomite, silica or cellulose powder resulted in an incompressible cake layer under the operational conditions, and the separation of calli and recovery of TPS were achieved. This result is attributable to electrical repulsion among calli, filter aids and TPS molecules. Addition of 3% NaCl and small filter aids (average particle size 27.9 µm) allowed stable calli separation, giving a filtrate of 95% optical transmittance and TPS recovery of almost 100%.
The biodegradation reaction of volatile organic compounds (VOCs) in a sealed reactor was studied using toluene and octane as model VOCs. Pseudomonas putida mt-2 and Pseudomonas oleovorans, which are known to degrade toluene and octane, respectively, were selected as model strains for the biodegradation. In addition, benzyl alcohol and octanol, which are the first degradation products of toluene by P. putida mt-2 and of octane by P. oleovorans were selected as target substrates. The octane-degrading strain, P. oleovorans, could not degrade toluene, and in the presence of toluene its ability to degrade octane was reduced due to the toxicity of toluene. The toluene-degrading strain, P. putida mt-2, could also degrade octanol, but in a mixture of toluene and octanol, it died due to the toxicity of the mixture. Except when analyzing the degradation mechanism of a single substrate, it is found to be important to take into account the effect of multiple substrates on the microorganisms concerned.
In contrast with the Generalized Fick (GF) equation and estimated Fick diffusion coefficient hitherto employed in mathematical modeling of coating drying, in this study a set of basic equations was derived based on the Generalized Maxwell–Stefan (GMS) equation and use of measured mutual diffusion coefficient, and the drying processes of binary and ternary components system were considered. Restrictions of wet coating on base film without penetration were considered through the derivation as follows: volumetric flux of mass transfer is always zero on the bottom of the coating, and the coating shrinks during drying.
A series of computer simulations was performed for a binary Fick type coating on different base films for drying with low-temperature hot air, high-temperature hot air, and constant heat generation in the coating with low-temperature hot air, which is assumed for infrared drying. Differences in drying rate curves of the same coating on different base films were investigated under practical drying conditions of coatings from the results of the computer simulation. In a period of decreasing drying, it was found that the decrease in the drying rate due to increased heat capacity of base film increased with the increase in thermal energy required to raise the temperature of the coating relative to the total amount of thermal energy supplied to the coating. Next, a method was proposed to estimate the drying rate of the same coating on different base films. The drying rate curve of the coating without base film was estimated by the proposed method with the simulated curve for the coating with a base film. The estimated curve showed good agreement with the simulated one, suggesting the validity of the proposed method.
Chemical interface controlled dispersion and high-speed shearing (CDS) washing was conducted for highly radioactive (over 570,000 Bq/kg) contaminated soils from school grounds, moorland and roadsides in Fukushima and the following results were obtained. (1) Washing rate of the three kinds of contaminated soils reached 60–98% after 30 min of CDS water washing. (2) Amounts of reclaimed soil (<8,000 Bq/kg) recovered were 60–82 wt%. In the case of moorland soil, 506 Bq/kg×33 wt% was achieved. (3) Volume reductions of 60–85 wt% were achieved for all contaminated soils. (4) Recoverable quantities of total radioactive sources contained in soils were over 90%. (5) The main FP-trapping mineral contained in the contaminated soil of school grounds was lamellar silicate, and that of moorland and roadside soils was mordenite.