Showing papers in "Journal of Chemical Engineering of Japan in 1993"

Extraction of Peppermint Oil by Supercritical Carbon Dioxide

Abstract: The extraction of essential oil from peppermint leaves with supercritical carbon dioxide was studied in a semibatch-flow extraction apparatus. The extraction rates of the major components, l-menthol and menthone, were measured at various conditions: 313–353 K, 8.83–19.6 MPa. The exit concentration of l-menthol extracted from peppermint leaves was much smaller than the solubility of l-menthol. The extraction curves at various flow rates coincide in the plot of yield versus quantity of CO2 consumed. A mathematical model based on the local adsorption equilibrium of essential oil on lipid in leaves and mass transfer well described the extraction results. The adsorption equilibrium constant determined by filling the theoretical extraction curve to the experimental data increased with temperature and decreased with pressure.

Noncatalytic Conversion of Cellulose in Supercritical and Subcritical Water

Abstract: This paper describes the noncatalytic conversion of cellulose in supercritical and subcritical water. First, it was demonstrated that even without any acid catalyst, cellulose was rapidly converted to water soluble species with a relatively high glucose yield in near critical water and glucose yield increased with elevating temperature. Then the rate constants for cellulose decomposition and glucose decomposition were evaluated at a pressure of 25 MPa over a temperature ranging from 473 K to 673 K by using semi-batch reactor and a flow reactor, respectively. From the reported cellulose pyrolysis rate constant and the evaluated cellulose decomposition rate constant, cellulose hydrolysis rate constant was evaluated. By using the cellulose hydrolysis rate, cellulose pyrolysis rate and the glucose decomposition rate, glucose yield obtained in the semi-batch experiment was reasonably explained.

Formation of CO2 Hydrate in Pure and Sea Waters

Abstract: The formation of CO2 hydrates in both pure and sea waters along the three-phase coexistence of CO2, H2O, and hydrate is measured by use of a convenient temperature-cycle method proposed in the present study. Four kinds of three-phase coexisting curves are investigated in the temperature range from 270 to 283 K and pressures up to 9 MPa. By applying the Langmuir adsorption model based on statistical thermodynamics, the three-phase coexisting pressures obtained are correlated satisfactorily. The enthalpy changes of hydration in both systems are calculated from the Clapeyron equation of the three-phase coexisting curve. The apparent rate constant of hydration is estimated under the assumption of pseudo-first order reaction with respect to CO2 concentration.

Experimental Study of Optimal Operation for a Honeycomb Adsorber Operated with Thermal Swing

Abstract: A new example of thermal swing adsorption using a honeycomb rotor with a thin sheet of silica gel as adsorbent has been developed for dehumidification of air. Owing to improvement in the dynamic adsorption capacity and rapid thermal response of the rotor, the product humidity was reduced to 10-20% of the feed at an air velocity of 1-2 m/s through a 0.2 m-long honeycomb. The existence of an optimal rotation speed of rotor has been observed. It increased in proportion to a single term of velocity of regeneration air, divided by width of the rotor and bulk density of the rotor; the effects of temperature and humidity of the feed and regeneration air were small. A dimensionless formula for the optimal rotation speed was derived on an empirical basis

Pervaporation-aided esterification of oleic acid

Abstract: Esterification of oleic acid with ethanol in the presence of p-toluenesulfonic acid was carried out at temperatures up to 383 K and initial molar ratios of ethanol to oleic acid, m0, up to 6. A kinetic equation having both a term of rate reduction due to water and a m0-dependent rate constant are presented. The esterification, aided with pervaporation through asymmetric polyimide membranes, was carried out at 348 K and 371 K under atmospheric and elevated pressures respectively. Almost complete conversion was attained for m0 of 2 in a short time with a low concentration of the catalyst at 371 K. Only water and ethanol permeated through the membranes. The permeation flux was expressed by the product of the permeability constant, P, and the permeant concentration of the liquid. P depended on the concentration of oleic acid and ethyl oleate at 371 K, but not at 348 K. A model in which the kinetic equation is combined with the permeation flux equation taking both volume change and sampling loss of the reaction mixture into consideration represented the experimental time course of the reaction sufficiently well. The influence of operating parameters on the reaction time required for a conversion of 98% and on the productivity was investigated by simulation from the model.

Theoretical and Experimental Studies of Circulations Inside and Outside a Deformed Drop under a Uniform Electric Field

Abstract: A finite element computational technique has been developed for exactly calculating circulations inside and outside a dielectric drop suspended in another dielectric fluid under a uniform electric fifeld. This technique allows the prediction of not only the circulations but also drop deformation caused by electric and dynamic forces acting over the drop surface. Computed results show that the direction of the circulations and the drop deformation depend on physical properties of the fluids, especially the drop-to-medium ratios of electric conductivity and dielectric constant. These results are in good agreement with Taylor’s analytical solutions and authors’ experimental observations.

Recent Advances in Separation of Metals by Liquid Surfactant Membranes

Abstract: Recent advances in the separation of metals by liquid surfactant membranes are reviewed, with emphasis placed on development of a suitable surfactant. In establishing a metal recovery process using liquid surfactant membranes, the choice of a suitable surfactant is a key factor. It is important to elucidate the role of the surfactant on the behavior of liquid surfactant membranes, e.g., the break-up rate and the swelling rate of W/O emulsion globules in a mixer, the demulsification rate of the emulsions in an electrical coalescer and the extraction rate of metal by liquid surfactant membranes. These problems are discussed. The application of liquid surfactant membranes to the metal separation processes is also described

Crystallization behavior and transformation kinetics of L-histidine polymorphs

Abstract: The crystallization and transformation behavior of the polymorphs of L-histidine (A, B) and the transformation kinetics were investigated in aqueous solutions. Both polymorphs precipitate in almost the same ratio from solutions in a wide concentration range. The ratio of the polymorphs. in the precipitate was scarcely influenced by temperature, unlike the behavior of L-glutamic acid. Transformation from B to A with a solution-mediated transformation mechanism occurred. The activation energy for the overall transformation was estimated as about 38 kJ/mol. From measurements of the solubilities at temperatures between 283 and 333 K, it was confirmed that A is a stable and B a metastable form. From a van’t Hoff plot the heat of fusion of L-histidine polymorphs was obtained as 15 kJ/mol, which is about half that of L-glutamic acid. No seed effect of either A or B crystals on the precipitation behavior was observed. A kinetic study of the transformation process was carried out and both the rate constants of growth of A(kG) and dissolution of B crystals(kD) were estimated simultaneously. At 313 K kD was nearly six times larger than kG, indicating that the transformation process is growth-controlled.

Bubble sizes and coalescence rates in an aerated vessel agitated by a rushton turbine

Abstract: For an improved understanding of gas-liquid mass transfer in a stirred-tank reactor and its spatial variation, knowledge of local bubble sizes (mean and distribution), gas holdups and coalescence rate is very important.In this work, bubble sizes at eight positions in an aerated vessel agitated by a 6-blade Rushton turbine were measured for an air-deionized water system by using flash photography. Bubble sizes near the vessel wall (and especially near the baffles) or in the upper levels of the vessel were more than four times those in the impeller region, The number of bubbles was also counted in a given area, and the population density was determined knowing the depth of focus.The coalescence rate during passage of the bubbles from the impeller to the vessel wall was calculated for different gases and liquids by measuring bubble sizes on photographs taken across the annular plane. It was found that coalescence occurs very near the impeller. The calculated values of coalescence rate were almost the same as those reported earlier by other investigators.

Neural model predictive control for nonlinear chemical processes

Abstract: A neural model predictive control strategy combining a neural network for plant identification and a nonlinear programming algorithm for solving nonlinear control problems is proposed. A constrained nonlinear optimization approach using successive quadratic programming combined with a neural identification network is used to generate the optimum control law for complex continuous chemical reactor systems that have inherent nonlinear dynamics. The neural model predictive controller (NMPC) shows good performance and robustness.

Mechanics of motion and deformation of a single bubble rising through quiescent highly viscous newtonian and non-newtonian media

Abstract: The present paper, which is predominantly experimental, provides information on bubble shape, drag coefficient and bubble rocking in highly viscous Newtonian and non-Newtonian media, which was hitherto lacking. Results covering a wide range of bubble size (about 0.2–3 cm equivalent spherical diameter) are reported. The observed changes in bubble shape as the ratio of the major axis of the bubble to equivalent spherical diameter and the aspect ratio are shown, and empirical correlations are obtained. The drag coefficient calculated from the terminal velocity data for gas bubbles provides reasonable agreement with the Hadamard-Rybczynski equation in both highly viscous Newtonian and non-Newtonian media in the low Reynolds number region. Furthermore, bubble rocking caused by wake shedding was observed in the higher Reynolds number region in non-Newtonian media. The Strouhal number including bubble rocking frequency is correlated with the Reynolds number and the Morton number.

Mutual Diffusion Coefficient of Aqueous Sugar Solutions

Abstract: The mutual diffusion coefficient of aqueous solutions with sugars of various molecular weight, obtained by drying experiment of the solution, was investigated for the effects of concentration, temperature and molecular weight of sugar.The mutual diffusion coefficient of dilute solution was correlated using Wilke’s diffusion factor. The concentration dependence was presented by linear relation of the logarithm of the diffusion coefficient vs. the sugar mole fraction regardless of temperature. The slopes of the linear relations were expressed by a power function of the molecular weight. From the linear relation, the activation energy was expressed also by linear relation of the sugar mole fraction, in which the slopes were expressed by the other power function of the molecular weight. The resultant estimation equation covers well for the temperature range 298–323 K and for the molecular weight range of sugars, from 180 for glucose to 6100 for maltodextrin.

Enzyme release kinetics in a cell disruption chamber of a bead mill

Abstract: The kinetics of enzyme release from yeast using a bead mill was investigated. The enzymes investigated were invertase, acid phosphatase, alcohol dehydrogenase and alkaline phosphatase. A two-step consecutive process model was proposed to describe the behavior of enzyme release. The model described well the release of both membrane-bound and non membrane-bound enzymes, such as alkaline phosphatase and other enzymes, respectively.

Two-Component Heat Pipes Utilizing the Marangoni Effect

Abstract: This paper describes the resultsof microgravity experiments involving water-ethanol two-component heat pipes, using a large-scale dropping tower in Kamisunagawa

Drop Breakup and Intermittent Turbulence

Abstract: Recent studies on the fine structure of turbulent flow are applied to drop breakup in the inertial sub-range. A multifractal method describes intermittency and the distribution of velocity fluctuations etc. For a given drop size and a given time-averaged energy dissipation rate, a wide range of stresses acts to cause breakup. These stresses and their relative frequencies are calculated. The most likely exponent on the Weber Number is close to –0.6. Smaller values (possibly as low as –0.93) arise from rare, but violent intermittent turbulence. Such low exponents are likely after long agitation times and for small tanks.

Measurement and Correlation of Phase Equilibria for the Carbon Dioxide-Ethanol-Water System

Abstract: Phase equilibria for the carbon dioxide-ethanol system and the carbon dioxide-ethanol-water system were measured to provide the thermodynamic base for the extraction of ethanol from its aqueous solutions using near-critical carbon dioxide as solvent. The experiments were carried out at 283 K–298 K and 5–7 MPa, including extraction conditions and solvent-recovery conditions in a wide range of ethanol concentration.An empirical mixing rule for the Helmholtz function with ternary as well as binary non-randomness parameters was proposed based on the density-dependent local composition concept. A correlation model was derived by a combination of the mixing rule with the Helmholtz function obtained from the Patel-Teja equation of state. The model successfully correlated the phase equilibria of the carbon dioxide-ethanol-water system.

Drag Reduction and Heat Transfer Reduction by Cationic Surfactants

Abstract: The study is aimed at giving a clear prospect of surfactant additives as drag-reducing agents, and to provide the basic design data for district heating and cooling systems

Sorption equilibria of pyridine derivatives in aqueous solution on porous resins and ion exchange resins

Abstract: Studies have been made of the sorption equilibria of pyridine, picoline and lutidine in aqueous solution on ion-exchange and porous resins. The sorption behaviors of these pyridines on strong acid ion-exchange resin can be expressed by the Langmuir isotherms, and those on both weak acid ion-exchange and porous resins by the Freundlich isotherms. The sorption mechanisms followed either a neutralization reaction with the H-form ion-exchange resins, or a hydrophobic interaction with the porous resins. Methanol content of the aqueous solution as well as solution pH was found to have a significant effect on the sorption of pyridines.Furthermore, the separations of these pyridines from each other were examined for three binary solute solutions in a batch mode. The pyridines were sorbed preferentially on the resins in the following sequence:pyridine where the selectivity increased as follows:strong acid ion-exchange resin

Corresponding-States Model for Viscosity of Liquids and Liquid Mixtures

Abstract: A corresponding-states viscosity model using oxygen, octane and water as the reference fluids was developed for a variety of liquids and liquid mixtures. The present model is generally accurate for most pure liquids being tested. A set of quadratic mixing rules is adequate to correlate the viscosity of non-aqueous solutions. Using an augmented asymmetric mixing rule to calculate the pseudo-critical temperature yields a good representation for the binary and ternary aqueous solutions

Preparation and Extraction Properties of Microcapsules Containing Tri-n-Octyl Amine as Core Material

Abstract: Microcapsules containing tri-n-octyl amine as core material were prepared by in situ polymerization of styrene and divinylbenzene over a wide range of relevant preparation conditions. The extraction equilibrium and extraction rate of propionic acid in aqueous phase were investigated by using the microcapsules. The extraction equilibrium of propionic acid/tri-n-octyl amine in a suspended microcapsules system was well consistent with that in a liquid-liquid system. From the experimental results, the rate-determining step was concluded to be the pore diffusion of propionic acid through the porous film of microcapsules. The activation energy was found to be 34.6 kJ/mol. The extraction rate decreased with increase in monomer concentration, divinylbenzene/styrene weight ratio and average diameter of microcapsules.

A study of the electrophoretic mobility of a very small inert gas bubble suspended in aqueous inorganic electrolyte and cationic surfactant solutions

Abstract: On the basis of the experimental technique proposed by one of present authors, this work is devoted to the measurement of the electromobility of a very small nitrogen bubble suspended in a few aqueous electrolyte solutions. It was confirmed that the isoelectric point (i.e.p.) of a bubble in water exists in a pH range between 2 and 3 irrespective of bubble size in light of the experimental results previously reported.When the mono- and divalent inorganic salts NaCl and MgSO4 were added to water, the negative mobility at a pH of 5.6 was monotonically depressed with increasing concentration of each salt.As for the trivalent salts AlCl3 and Al2(SO4)3, a charge reversal was observed at a certain concentration of each salt which agreed with previous data reported by other workers.Four n-alkyltrimethylammonium bromides of different n-alkyl chain length were also examined and it was observed that the i.e.p. of a surfactant with a smaller total number of carbon atoms in the n-alkyl chain of a n-alkyltrimethylammonium bromide tends to shift to a higher concentration. When the concentration giving the i.e.p. is plotted against the number of carbon atoms, a good linear correlation on a semilogarithmic scale was obtained. Incorporating the Stern-Graham double-layer model and the above linear correlation, the transfer energy required by the n-alkyltrimethylammonium ion when it is brought from the water phase to the nitrogen-water interface was estimated and the result was found to be reasonable.

Column Sorption and Separation of Divalent Metals by a Macromolecular Resin Containing Organophosphorus Acids

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Evaluation of Surface Hydrophobicities during Refolding Process of Carbonic Anhydrase Using Aqueous Two-Phase Partitioning Systems

Abstract: Changes in conformational and surface properties in refolding processes were quantitatively investigated in aqueous two-phase systems, using bovine carbonic anhydrase (CAB) as a model protein. Surface net hydrophobicity (PS) of a native CAB was determined as -84kJ.mol -1 , showing a moderately hydrophilic surface. By addition of 1.5-2M guanidine hydrochloride (GuHCl), CAB was denatured and HFS increased drastically up to about 300kJ.mol -1 , accompanied by some increment of local hydrophobicity. The fully unfolded state was achieved in 5M GuHCl. The unsteady change of local hydrophobicity during CAB refolding was also quantified using phase separation of Triton solution

Monte Carlo Simulation of Adsorption of Gases in Carbonaceous Slitlike Pores

Abstract: To obtain the theoretical maximum adsorption isotherms of methane in a slitlike pore of graphite carbon, the single-plane wall model, which allows molecules to be adsorbed on both sides of the graphite basal plane, is considered. The LJ potential function is used for describing interactions between both molecule-molecule and molecule-surface carbon. The equilibrium densities in a pore and in a gas phase are calculated by using the Gibbs ensemble Monte Carlo simulation technique. When the slitwidth is designed such that methane molecules are accommodated in two layers, the theoretical adsorptions in the single-plane wall pore almost quantitatively coincide with the experimental isotherms of methane and ethane on high-surface area carbon M-30 at 298 K, which suggests that carbon M-30 adsorbs methane to almost the theoretical maximum quantity. Comparisons are made with a different slitwidth pore and the double-plane wall model which assumes that only one side of the graphite plane is effective for adsorption.

A simulated moving-bed adsorber for the separation of tricomponents

Abstract: A mixture of three components was separated into its components by using a simulated moving-bed adsorber in which columns packed with one kind of resin was arranged so as to alternate with columns packed with another kind of resin. One component adsorbs weakly on both the resins, whereas each of the other two components adsorbs strongly on one (but not both) of the two resins. The first component moves with the flow of the desorbent solution, whereas the others move with the resins in the opposite direction to the liquid flow. The first component, therefore, is obtained continuously in the raffinate stream, while the other two are recovered alternately in the extract stream. The validity of this type of adsorber was examined of a computer simulation and was confirmed by the experimental separation of a starch-glucose-NaCl mixture.

Correlation of concentration-dependent surface diffusivity in liquid phase adsorption

Abstract: Concentration dependency of surface diffusivity of nitrobenzene and benzonitrile was measured at different temperatures for adsorption from aqueous solution onto an activated carbon, by batch kinetic experiments within limited ranges of amount adsorbed. The isotherms obeyed the potential theory of adsorption, and were only partially expressed by Freundlich equations. Eyring’s rate theory was applied to the elemental steps of surface diffusion with the assumption that the rate-controlling step was the hole-making step for the systems under the potential theory. The activation energy was found to be a certain fraction of the sum of the evaporative energy of adsorbate and the adsorption potential. Thus the derived correlation equation had two parameters, and was tested with the measured concentration/temperature dependence of surface diffusivity. Good correlation was obtained, with reasonable values of the parameters from the viewpoint of their definition and/or accord with other research results. The success in the correlation manifested the importance of the hole-making step in surface diffusion.

A multilayer model for adsorption of water on activated alumina in relation to adsorption potential

Abstract: Adsorption of water vapor on activated alumina was examined by a gravimetric method. The experimental results are described by a Freundlich-type polynomial with respect to the adsorption potential. In order to characterize the adsorption, a multilayer of water is assumed here on the alumina surface. Considering the hydrogen-bonding, several types of formation are modeled on structural hydroxyl groups supposed as the surface sites. In the modeling, two kinds of rules are observed in the relationship between the accumulating layers; structural ratios of molecules and allotment ratios of the potentials. In accordance with these rules, an attempt is made to derive an expression for the multilayer adsorption in a model by applying a Freundlich-type equation to the surface monolayer adsorption. The derivation gives a polynomial similar to the empirical expression. It is found from comparison of the parameters of both equations that the model multilayer is consistent in the examined adsorption system.

Correlation of transient drop sizes in breakup process in liquid-liquid agitation

Abstract: In a liquid-liquid agitation system containing a surface-active agent, transient size distributions of emulsion drops were measured at various impeller speeds after the initiation of agitation. The absence of drop coalescence in the system was confirmed experimentally. In breakup processes at each impeller speed, drop size distributions revealed a similar distribution form. The evolutions of Sauter mean drop sizes in the present work were compared with previous ones that were obtained in breakup processes in a range of relatively large drop sizes. It was found that the present data showed time-variation similar to that of the previous data. A new correlation equation, which expresses the evolution of Sauter mean drop size over a wide range of drop sizes, was proposed.