Experimental results for the thermal conductivities of liquid CO₂ are reported. The thermal conductivities were measured by a transient short-hot-wire method. Experimental temperatures ranged from 273.8 to 294.5 K, and pressures from 4.0 to 15.0 MPa. The uncertainty of the reported thermal conductivity data was estimated to be within ±3.0%. The experimental data were compared with calculated values from the REFPROP 8.0.

View full abstract

To promote the biodiesel production, low-quality fats in addition to waste vegetable oils are still required. Low-quality waste vegetable oils and low-quality fats as feed mixtures contain free saturated fatty acids and/or commercial solidifiers in addition to triolein as a main component, and they are solid at room temperature. However, liquid feed is desired for biodiesel production processes. In this study, solidification properties of a system of commercial solidifier and commercial vegetable oil as low-quality fats and a binary system of palmitic acid and triolein as low-quality vegetable oils were investigated, and the melting temperature was calculated by a simple thermodynamics function of composition. The binary mixture of palmitic acid and triolein could be liquefied at above 65°C regardless of the composition, and the melting temperature of the mixture could be represented by the simple thermodynamic function. On the other hand, the melting temperature of the mixture of the commercial solidifier and commercial vegetable oil increased sharply to 80°C even at low solidifier concentration, and the melting temperature of waste fats could not be represented by the simple thermodynamic function.

View full abstract

We have developed pressure-oscillating defoaming for shear-thinning fluids. A bubble undergoes alternating expansion and contraction in a pressure-oscillating field, where the oscillating flow damps quadratically with the distance from the surface, giving biaxial elongational flow and shear flow in the vicinity of the bubble surface. In this study, a rheo-optic technique was applied to measure the stress arising from such local flow around the bubble. By using CTAB/NaSal solution with a good photoelastic correlation and rheological property similar to the UCM model, the profile of the maximum retardations was measured experimentally with respect to the distance from the bubble surface. The profile was very similar to shear stress profile around an alternately expanding and contracting bubble calculated by the unsteady state finite element analysis. Based on the stress-optic law, the thickness of stressed fluid around the bubble was estimated by comparison of the two profiles.

View full abstract

A method is presented to predict the surface tension and contact angle for Newtonian fluids by measuring either the shape of a small droplet on a solid surface or the shape of a small bubble attached to a solid surface in the fluid. Bubble shape can be calculated theoretically under stable condition from the point of view of the momentum balance and force balance along the interface for given physical properties and conditions such as surface tension, density and gravity. Optimizing of three non-dimensional parameters (the Bond number, the ratio of height to contact radius, b/a, and a shift factor to adjust the origin point) for the numerical analysis is carried out until the experimental interface shape coincides well with the numerical results within a given tolerance. It was found that obtained the surface tension and contact angles obtained agreed well with values reported in the literature.

View full abstract

A mathematical model was proposed that gave the binder saturation profile in a convectively dried porous sphere, cylinder or slab wetted with the binder solution. The model was obtained from an expansion of the authors' previous model. The expanded model was applicable to a dried porous sphere, cylinder or slab wetted with binder solution of various initial water concentrations, while the previous model was applicable only to a dried porous slab wetted with binder solution of a fixed initial water concentration.
Convective drying experiments were performed by using a porous sphere of glass particles wetted with styrene-butadiene rubber latex. The binder saturation profile in the dried porous sphere was successfully measured, while the profile was measured only for dried porous slabs in the previous studies. Agreement between the calculated and the measured results was satisfactory for the sphere case or for the slab case in a previous study by calculation with the same parameter as in the sphere case.

View full abstract

The adsorption of cobalt, nickel, copper and zinc into microcapsules containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester was investigated. First, the particle size distributions, surface features as photographed by scanning electron microscopy and the amount of extractant contained were measured in order to evaluate the characteristics of the microcapsules. Next, the adsorption equilibrium and the adsorption rate were measured to estimate the adsorption mechanism of the metals. Finally, the separation of nickel and cobalt from a multi-component system using the microcapsules packed in a column was examined. The microcapsules prepared were found to be white and spherical. The adsorption equilibrium of each metal was found to follow the Langmuir adsorption isotherm. Both the complex formation reaction and the diffusion of the complex through the pores in the microcapsules were found to contribute to the overall adsorption rate of the metals. The separation of the metals by the microcapsule-packed column could be increased by decreasing the flow rate and increasing the height of the packed column. Separation of individual metals in an adsorption step was difficult, but in a desorption step the separation was possible by choosing a suitable solution for desorption.

View full abstract

Solubilities of flavone and 6-methoxyflavone in supercritical carbon dioxide (SC–CO₂) were measured at temperatures ranging from 313 to 333 K and pressures ranging from 10 to 22 MPa by a flow type apparatus. The solubilities were determined from ultraviolet-visible spectroscopic analysis of solute concentration of ethanol solution in the trap and the corresponding CO₂ amount. Solubility parameters (SP) of solutes were also estimated from correlation with a regular solution model, and these were comparable to the values obtained by solubility measurement using organic solvents under ambient conditions. The method for determining SP of solutes from solubilities in supercritical conditions is expected to be useful for SC–CO₂ extraction processing.

View full abstract

A sol–gel method was applied for the preparation of palladium-doped silica membranes for hydrogen separation. Hydrogen permeation performance and stability (thermal, hydrothermal) were evaluated by measuring the time and temperature dependence of gas permeances (N₂, H₂, He) in N₂ and steam atmospheres (steam: 70 kPa) at 500°C, respectively. It was found that the Pd-doped silica layer has a thickness of approximately 80 nm, and Pd particles of several nanometers were well dispersed in an amorphous silica matrix. Pd-doped silica membranes (Si/Pd=3/1) fired at 550°C in air were quite stable in N₂ atmosphere at 500°C, but a drastic decrease of gas permeances (He, H₂, N₂) and an increase of activation energy of gas permeation (He, H₂) were observed under H₂ atmosphere at 500°C due to aggregation of Pd particles. Pd-doped silica membranes (Si/Pd=3/1) fired at 550°C in H₂ showed high stability in hydrogen and steam atmospheres (steam: 70 kPa) at 500°C. This is because well-dispersed Pd particles in amorphous silica networks could not move in hydrogen and steam atmospheres.

View full abstract

Wakkanai siliceous shale, a natural mesoporous material, is impregnated with lithium chloride, calcium chloride and sodium chloride solutions to improve its moisture adsorption capacity. However, excess impregnation leads to elution of sorbed moisture from pores to the surface under humid conditions, and the surface of the sample becomes wet. To determine appropriate concentrations of impregnating chlorides, the surface wettedness of the chloride-impregnated shale was estimated from the surface color changes of samples exposed to 75%RH air by using a digital scanner. The appropriate concentrations of lithium chloride and calcium chloride for the shale were 4 and 5 wt%, respectively. Moreover, the maximum moisture sorption of the shale impregnated with the appropriate chloride concentration agreed with the moisture retention predicted from the mesopore volume. This indicates that, in order to avoid elution of the chloride solution to the surface, the maximum moisture sorption of the chloride-impregnated shale should be smaller than the mesopore volume.

View full abstract

The pressure swing adsorption method (PSA) is one of the energy-saving technologies and adopted for dehydration of bioethanol, however further progress in cost-saving is unlikely because the PSA method has some restrictions in its process. On the other hand, the zeolite membranes have the potentiality to improve energy consumption and the acid-resistant zeolite has been developing to overcome the weak property of materials.
In the present study, the required membrane performances and process applications were studied through the process simulations for the distillation and dehydration of bioethanol to achieve the economical advantages over the conventional processes.
Increase of the water flux is effective in reducing energy because it enables to operate in the low-energy mode without a vacuum pump. However, the reduction ratio is relatively a little because the distillation energy is majority in total energy. The equipment cost can be reduced due to the decrease of membrane modules. Fluctuations of separation factor have little effect on the energy consumption and cost, but the separation factor of about 10,000 is thought to be necessary for controlling ethanol leakage through the membrane. Reducing the ethanol concentration at the outlet of the distillation tower in order to lower the load of distillation can decrease the energy consumption significantly and also decrease the cost. Additionally, the cost reduction of 6 JPY kg-EtOH⁻¹ can be achieved if the membrane which has flux of 36 kg·m⁻²·h⁻¹ and separation factor of 10,000 is applied for the concentrating process substituted for distillation. The comparable cost reduction of 6 JPY kg-EtOH⁻¹ is realized for the hydrous ethanol production in the similar process of replacing distillation to membrane separation. These calculated cost reductions are enough for stimulating the progress of membrane separation for bioethanol enrichment.

View full abstract

Filtration characteristics of an asymmetric depth filter (nominal pore size: 0.2 μm) were investigated by using suspensions of two bacteria, Lactobacillus plantarum and Bacillus amyloliquefaciens. In the filtration of L. plantarum suspensions, the permeation flux was 3–8 times higher with the depth filter than with a screen filter at 10–150 kPa. Apparent specific resistance of the cell layer in the depth filter reduced to about 1/10–1/100 of that of the filter cake formed on the screen filter. Scanning electron microscopy revealed that the trapped microbial cells were dispersed to a depth of 2/3 from the inlet side of the depth filter. In the filtration of B. amyloliquefaciens suspensions, the permeation flux of depth and screen filters was comparable at 10–50 kPa, and filter cakes formed on both filters. However, the permeation flux increased remarkably at 100–150 kPa with the depth filter but scarcely increased with the screen filter. The smallness of increase with the screen filter was due to the high compressibility of the microbial filter cake, while the remarkable increase with the depth filter was due to the penetration of the chain bacterium into the filter. The increase in transmembrane pressure was highly effective in the filtration of agglomerated chain bacteria such as B. amyloliquefaciens in trapping cells in the asymmetric depth filter.

View full abstract

The effect of ascorbic acid concentration on the absorption of NO₂ into an aqueous ascorbic acid solution was investigated experimentally. A gas mixture that includes nitrogen dioxide was passed through a bubble column type batch absorption apparatus, and concentrations of nitrite and nitrate in the liquid absorbent were measured. With an aqueous ascorbic acid solution, nitrite can be selectively produced and production of nitrate can be inhibited. When ascorbic acid was used as reductant, an active oxygen removal capacity comparable to that of the sulfite absorbent was observed at about 1/10 of the sulfite concentration.

View full abstract

Application of slurry of finely powdered adsorbent in LiBr solution was proposed as a means to enhance the performance of lithium bromide/water absorption heat pump. The effect of the slurry on the performance was analyzed by the heat and mass transfer model in the case where a film of the slurry or the solution flows down the surface of the heat transfer plate in the absorber and the generator of the heat pump system. In the open system analysis for the absorber and the generator, temperatures of the slurry and the solution rose remarkably in the inlet zone of the absorber due to the large heat transfer resistance between cooling water and the slurry or solution compared with the water vapor absorption rate. The LiBr concentration in the slurry was higher in the absorber and lower in the generator than that in the solution without adsorbent. In the closed loop system analysis where the slurry or the solution circulates between the absorber and the generator, the refrigeration energy output of 280 K was enhanced over 10% by employing the slurry when the waste heat source of 360 K and cooling water of 290 K were used. These analyses revealed that LiBr adsorbed on the adsorbent is desorbed when the solution absorbs water vapor in the absorber, thus acting as a buffer against dilution of the solution and thereby raising performance of the heat pump. If a fine powder of activated carbon of under 100 μm was suspended as adsorbent in the solution, the equilibrium adsorption amount of LiBr was proportional to the concentration in the solution, and the equilibrium adsorption parameter was 1.5 equivalent to that used in the analysis.

View full abstract

Optimization problems of chemical process can generally be formulated as nonlinear programming problems, but the objective functions and the constraints of problems are often linear for most variables. In this paper, we propose a new decomposition method for nonlinear programming problems with two types of variables; linear and nonlinear variables. The proposed method is more effective than a nonlinear optimization method without decomposition to solve problems containing a relatively small number of nonlinear variables, because the dimension of the decomposed problem is much smaller than that of the original problem. Some computational results for the Rosen-Suzuki test problem indicate that the proposed method is useful for reducing the computational time.

View full abstract

Efflorescence occurred on the surface of mortar blocks in which sand produced in Sanuki City, Kagawa was employed. To investigate the efflorescence behavior caused by aggregates, bulk and surface compositions were analyzed for the effloresced sand and non-effloresced sand as a reference. Leaching behavior of relevant components related to the efflorescence was observed after immersing the sands in water, in Ca(OH)₂ slurry, which simulates the conditions in mortar, and in alkaline KOH solution. Soluble Na₂SO₄ was leached from the effloresced sand in water; and in addition to Na₂SO₄, Na salts originating from sodium silicate in silica were released in Ca(OH)₂ slurry and KOH solution. It seems likely that these Na salts react with Ca(OH)₂ in mortar to produce strongly alkaline NaOH, which facilitates absorption of CO₂ in the atmosphere to yield carbonates such as Na₂CO₃, NaHCO₃, and CaCO₃, promoting the efflorescence on the mortar blocks. Gypsum (CaSO₄), which was not detected in the efflorescence material on the mortar blocks, was leached from the non-effloresced sand immersed in water and the alkaline solutions.

View full abstract

A new oil absorbent composed of polymer material, which could absorb various kinds of organic solvents and oil and whose absorbed amount of organic solvents and oil was high, was developed. For this purpose, 282 μm of polymer particles synthesized by suspension copolymerization of 2-hydroxyethyl acrylate and various cross linkers was reacted with hydrophobic fatty acid chloride. Produced particles could absorb various kinds of organic solvents and oils. Monodisperse polymer particles synthesized by seed copolymerization using 2,2′-azobis[N-(2-propenyl)-2-methylpropionamide] had azo group incorporated polymer network. Using this azo group as an initiator, graft chain composed of 2-hydroxyethyl acrylate and hydrophobic fatty acid chloride was introduced in the particles. The amount of organic solvent or oil of produced particles was 1.2–3.7 times of that of particle synthesized from suspension polymerization.

View full abstract

As a countermeasure against global warming, large scale afforestation of arid land has been performed as a means to fix atmospheric CO₂ into plants. Arid land and semi-arid land account for about one third of all land area and are characterized by extremely low productivity, which is mainly caused by low precipitation. In these areas, a considerable amount of rainwater is lost due to runoff and evaporation, but runoff water is available for tree growth when it is collected and allowed to penetrate into the deep root zone. Therefore, the selection of afforestation area suitable for effective use of rainfall/runoff water for tree growth is required for arid land afforestation.
In this study, we constructed an original runoff model to represent water movement in a watershed area of several km by several km in an arid area of Western Australia. For numerical calculation with ten meter grids, the maximum required time difference value was determined to give negligibly small calculation errors. Suitable fitting parameters in our model were determined by comparing the numerical results with actual data of runoff behavior after rainfall. As a result, the water movement in the flow area could be expressed by our model calculation.

View full abstract

Sludge HAP was prepared from concrete sludge and ortho-phosphorus ions. The sludge HAP is composed of small crystals of hydroxyapatite (HAP) formed on the surface of cement powder of the concrete sludge. The sludge HAP showed the capacity to remove cadmium, copper and fluoride ions from aqueous solutions. The ions captured by the sludge HAP were stable under acid conditions with nitric acid (pH=4). The ion removal capacities of the sludge HAP were comparable to those of HAP prepared from other wastes. The sludge HAP can be applied to heavy metal ions or fluorine ions in water.

View full abstract