Showing papers in "Journal of Chemical Engineering of Japan in 1991"

Calculation of ion rejection by extended nernst-planck equation with charged reverse osmosis membranes for single and mixed electrolyte solutions

Abstract: The extended Nernst–Planck equation, which takes account of the effective charge densities, was used to calculate rejection of single- and mixed-electrolyte solutions. Ion rejections with negatively charged membranes were calculated for single electrolytes of various valences (sodium chloride, hydrochloric acid, magnesium chloride, sodium hydroxide, magnesium chloride, sodium sulfate), mixed electrolytes having common cations (sodium chloride/sodium sulfate, sodium hydroxide/sodium sulfate) and mixed electrolytes having common anions (sodium chloride/magnesium chloride, hydrochloric acid/magnesium chloride). Mono- and divalent coions in mixtures were found to be separated effectively, and monovalent ions in particular showed negative rejections in a certain condition. Mono- and divalent counter ions in mixtures were not separated as efficiently as coions in mixtures. Rejections were found to be strongly dependent upon volume flux, mole fraction of the mixture and ratio of fixed charge density to feed concentration. For the single solution of mono-monovalent electrolyte, rejection obtained from the extended Nernst–Planck equation was compared with that from the previous model based on the irreversible thermodynamics.

Reverse Osmosis of Single and Mixed Electrolytes with Charged Membranes: Experiment and Analysis

Abstract: Reverse osmosis experiments using single electrolytes, mixed electrolytes having common cations (sodium chloride/sodium sulfate and sodium hydroxide/sodium sulfate) and mixed electrolytes having common anions (sodium chloride/magnesium chloride and hydrochloric acid/magnesium chloride) were carried out with negatively charged membranes. Rejection occurred only due to the charge effect and was dependent upon volume flux, the ratio of the membrane charge density to feed concentration and the mole fraction in mixtures. Mono- and divalent anions in mixed electrolytes having common cations were found to be separated effectively. In particular, monovalent anion showed negative rejection. Mono- and divalent cations could not be separated as efficiently as mono- and divalent anions.Experimental results for single electrolyte solutions were well explained by applying the extended Nernst–Planck equation, and two transport parameters (effective charge density and structural parameters) were obtained. Rejection of ions in mixtures was well predicted by the extended Nernst–Planck equation with the transport parameters obtained from the single-electrolyte experiments.

Marangoni convection during steam absorption into aqueous LiBr solution with surfactant.

Abstract: The Marangoni convection during steam absorption into aqueous LiBr solution with a small amount of surfactant was observed by Schlieren photography, and the surface tension of the absorbing solution was measured to investigate the mechanism of the convection. Also, a numerical simulation of the Marangoni convection was carried out.It is found experimentally that the surface tension of LiBr solution with surfactant decreases with increasing LiBr concentration and that the Marangoni convection in this system is not essentially induced by the presence of surfactant islands on the surface of the solution as proposed by the previous workers, but is in accordance with the general criterion of Marangoni instability. The calculated results could simulate qualitatively the initiation and growth of convection in this system.

Phase Equilibrium Study of Extraction and Concentration of Furfural Produced in Reactor Using Supercritical Carbon Dioxide

Abstract: To obtain fundamental data for the extraction and concentration of furfural produced in a reactor by using supercritical CO2, the isothermal high pressure vapor–liquid equilibria for two binary systems (CO2–water and CO2–furfural) and a ternary system (CO2–water–furfural) were measured in the temperature range from 343 to 421 K. Additionally, the experimental data were compared with results calculated by various equations of state. As a result, it was found that (1) the Peng–Robinson and Soave–Redlich–Kwong equations of state combined with the mixing rules proposed by Panagiotopoulos correlated the two binary systems satisfactorily and predicted the ternary system well, and (2) the furfural produced could be selectively extracted from the reactor and concentrated to 95 wt% by a new process proposed on the basis of a knowledge of the vapor–liquid equilibria.

Prediction of Intrinsic Pore Properties of Ultrafiltration Membrane by Solute Rejection Curves: Effects of Operating Conditions on Pore Properties

Abstract: An improved method is presented for describing the apparent intrinsic pore properties (mean pore size and pore size distribution) of ultrafiltration membrane from solute rejection curves To obtain the apparent intrinsic pore properties, firstly the mean pore diameter is determined from the solute rejection curve by correcting the steric and hydrodynamic hindrance effect of pores on molecules, and secondly the effects of operating conditions (pressure, feed concentration and recirculation velocity) on the pore properties are examined by ultrafiltration of seven solutes using SEPA-PS-0 membrane and are eliminated by extrapolating to “zero” operating conditionsThe pore property parameters (μ, Dp and θ) obtained from the solute rejection curve are affected by two factors: 1) the plugging of membrane pores by the solute and 2) the deformation of solute due to the variation of pressure and feed concentration But the recirculation velocity does not affect the pore property parameters the mean pore diameter is about 60 A and the pore diameter distribution range is from 30 A to 103 A for SEPA-PS-0 membrane at the “zero” operating condition state

Frequency analysis of pressure fluctuation in fluidized bed plenum.

Abstract: Pressure fluctuations in the plenum chamber of a solid-gas fluidized bed were measured and analyzed in order to develop a method for the diagnosis of fluidization conditions.Power spectral density functions obtained by FFT analysis of the pressure fluctuation data had three principal frequencies. These frequencies were compared with the bubble eruption frequency observed at the bed surface and the bubble generation frequency, which was obtained by an optic fiber probe installed above the distributor opening, and two of the three frequencies were found to agree well respectively with the obtained frequencies of bubble generation and of eruption. The third principal frequency was judged to be a natural frequency of the fluidized bed, since the frequency depended on the particle content in the fluidized bed and on the plenum volume. The frequency corresponding to bubble generation was observed to be influenced significantly by the natural frequency of the fluidized bed when the natural frequency had a low value.

Permeation equations developed for prediction of membrane performance in pervaporation, vapor permeation and reverse osmosis based on the solution-diffusion model

Abstract: General permeation equations based on the solution-diffusion model were proposed for pervaporation (PV), vapor permeation (VP) and reverse osmosis (RO) on two different assumptions about the pressure gradient inside a membrane: a flat gradient (case 1) and a linear gradient (case 2). With these equations the permeation properties in PV, RO and VP can be estimated once the transport parameter of a membrane is known.The effect of upstream pressure on selectivity and flux in RO and PV was estimated by sample calculations for water- and ethanol-selective membranes in ethanol–water system. Flux and selectivity in RO is smaller and, reaching that in PV at infinite pressure. This ultimate value is different in cases 1 and 2, and in the latter the molar volume ratio of the permeants becomes important. The effect of downstream pressure in PV was also estimated and compared with the case of vacuum-enhanced membrane distillation (MD) with a porous membrane. With increasing pressure the separation factor approaches that of vapor–liquid equilibrium in both PV and MD. With decreasing pressure that in MD is governed by the ratio of diffusion coefficients inside the membrane. Since the Knudsen diffusion coefficient of water is larger than that of ethanol, the separation factor decreases in ethanol–water separation with decreasing downstream pressure. This was verified by experiment, using PTFE membranes.

Effect of solution environment on unstirred dead-end ultrafiltration characteristics of proteinaceous solutions

Abstract: The effects of pH and the addition of such salts as NaCl on the structure of the gel-cake in dead-end ultrafiltration of BSA solutions are examined by using a batchwise filter which has an abrupt reduction in its filtration area. Both the average porosity eav and the average specific filtration resistance αav of the gel-cake may be determined accurately on the basis of measurements of the variation of filtrate volume with time. The most compact gel-cake, which provides a large flow resistance, forms on the membrane around the isoelectric pH. By the addition of NaCl at pH extremes the gel-cake structure becomes compact, thereby decreasing the filtration rate. Such internal structures as the solute concentration and the compressive pressure acting on the solutes within the gel-cake, which may serve as a basis for evaluating the sweeping performance of the gel-cake in crossflow ultrafiltration, are evaluated on the basis of the overall filtration characteristics obtained under various filtration pressure conditions.

A method for estimating flash points of organic compounds from molecular structures.

Abstract: In a previous report, the principal-component analysis (PCA) of a set of data including flash points and ten other flammability-related physicochemical properties of 50 organic compounds was performed to explore the number of significant structural factors affecting the flash point. Just two structural factors were found to be sufficient to reproduce the flash-point data. This study is designed to extend the above analysis to a broader data set for 100 compounds. The object is to interpret the second factor more clearly and to develop a practically applicable method for estimating the flash point

Extraction Equilibria of Amino Acids with Quaternary Ammonium Salt

Abstract: The extraction equilibria of various amino acids with tri-n-octylmethylammonium chloride (TOMAC) were studied in the high pH range. TOMAC reacted with the anion of amino acid and OH– according to the stoichiometric ratio determined by ionic valency. The extraction equilibrium constants KA of various amino acids differed considerably and could be correlated well with each hydrophobicity scale. The highest KA value obtained for tryptophan was larger than the lowest value for glycine by a factor of about 260. These findings suggested that separation of amino acids is possible by utilizing the differences in KA values. The extraction equilibrium constants of inorganic anions which were present in the fermented broth was comparable to those of amino acids exhibiting a low degree of extraction.

Membrane Transport Properties of Pervaporation and Vapor Permeation in Ethanol–Water System Using Polyacrylonitrile and Cellulose Acetate Membranes

Abstract: Although permeation flux in PV and that in VP at saturated vapor pressure in feed should theoretically be equal, results obtained so far are contradictory. In the present work, theoretically predicted behavior of transport properties in PV and VP were first examined, based on the permeation equations developed in the previous paper, in particular for ethanol–water system.Next, experiments in PV and VP were performed in this system to check the conclusions obtained above using PAN and CA membranes. Results with PAN membranes showed good agreement between PV and VP, but the results with CA membranes showed larger permeation flux and a lower separation factor for water in PV than in VP. From observation from outside the cell, wrinkles on membrane surfaces were seen in PV experiments, but were not observed in VP experiments. Since the amount of sorption of solution in CA membranes is large, small difference in swelling conditions during experiments between PV and VP can have a large effect on the permeation fluxes.

Analysis of Electroosmotic Dewatering

Abstract: The electroosmotic dewatering of a homogeneous semisolid material is investigated. The basic differential equation for electroosmosis through compressible materials is derived by use of Kobayashi’s equation, which considers the tortuosity of a flow path and the effect of the hydraulic pressure profile in the materials. It is recognized from Kobayashi’s equation that at the impermeable upper wall the electroosmotic flow and the pressure flow compensate each other. The relation among local hydraulic pressure, solid compressive pressure and external pressure is also derived, and is the same as those in mechanical filtration and expression. It is assumed in the analysis that no electroosmotic flow occurs in the layer where the local void ratio is smaller than a certain critical value. Based on numerical calculation, the pressure flow opposed to the net flow propagates from the upper electrode to the lower electrode. The electroosmotic dewatering rates of a homogeneous bentonite clay material calculated by the present method compare favorably with experimental observations.

Size Classification of Submicron Powder by Air Cyclone and Three-Dimensional Analysis

Abstract: Experimental and theoretical studies were made of the separation efficiency of an air cyclone separator. The results of numerical calculations of three-dimensional Navier–Stokes equations indicate that the flow field changes with circumferential angle. The upward and downward velocity components merge strongly near the entrance of the dust box. Large particles are collected on the upper wall, small particles on the conical wall.It is also confirmed that particles with small inertia enter the dust box first, but finally exit from the cyclone because of the upward velocity component. The experimental partial separation efficiencies obtained agree well with the numerical calculations when the data are rearranged according to the particle inertia parameter.

Recovery of Gallium and Vanadium from Coal Fly Ash

Abstract: A process has been developed to recover gallium and vanadium from coal fly ash in which they exist at very low concentration in a mixture of high concentration of less desirable species. Aqueous solution containing 2.8 mg/l gallium and 35 mg/l vanadium was obtained by leaching with 1.5 mol/l sulfuric acid. These metals were then concentrated by use of a chelating resin column with a functional group of iminodiacetic type after reduction of ferric ion to ferrous ion and pH adjustment. the eluate was conditioned and passed again through the column. Gallium was concentrated to 4.0 g/l and vanadium to 26.0 g/l in the resulting eluate. This liquor was further treated to remove impurities by a solvent extraction technique, employing TOMAC and D2EHPA as extractants. Stripping solutions of 96.6% gallium purity and 94.8% vanadium purity were finally obtained.

An evolutionary method of arranging the plot plan for process plant layout.

Abstract: The equipment layout of a process plant is a multi-objective problem in which not only various costs (piping, site and so on) but also preferences about the equipment arrangement influencing its operability, maintenance and the like. It is difficult to obtain the best solution of this problem analytically. In this study, preferences are weighted as penalities so that they can be evaluated in an objective function with costs. To reduce the calculation load, equipment having spatial relations in a local area is put together into “modules” as units in layout work, and these modules are grouped into “sections” as functional groups of equipment. Furthermore, the module arrangement in each section is considered to be two variables (permutation and partition), and an algorithm based on an evolutionary method is developed to search a good plot plan efficiently. The effectiveness of this proposed method is demonstrated by an example problem.

Unstable phenomenon of flow in a mixing vessel with a marine propeller

Abstract: Unstable flow phenomena in a mixing vessel with a marine propeller were investigated experimentally using flow visualization and LDV techniques. It was found that the instantaneous bulk flow profiles were usually asymmetric with respect to the impeller shaft and they fluctuated in the large time scale. The circulation flow patterns in the space between two adjacent baffles were classified into quick-return flow (QR), full-circulation flow (FC) and intermediate-circulation flow (IC), which were replaced randomly one after another with time. Their lifetimes were widely distributed from about half a second to several minutes. Connected with the circulation flow patterns, the impeller stream was directed vertically downward or obliquely outward to the vessel wall and held a high level of angular momentum when pattern FC took place, while the impeller stream was directed obliquely inward to the impeller shaft with a low level of angular momentum when pattern QR took pace.

Application of Fuzzy Control System to Coenzyme Q10 Fermentation

Abstract: A fuzzy control system for a fed-batch culture was constructed and applied to coenzyme Q10 fermentation. For inputs, cell concentration ([OD] and [OD2]), specific growth rate ([SGR]) and fermentation time ([BTIM]) were selected. A base value of aeration rate ([AIRB]) and an adjustment term for [AIRB] ([DAIR]) were defined as outputs. In this system, cell concentration was measured on-line by a turbidimeter and specific growth rate was then calculated. After cell concentration, specific growth rate and fermentation time were transferred into four inputs using membership functions, and these were further transferred into two outputs by 70 fuzzy rules. After defuzzification of [AIRB] and [DAIR], a set value of the aeration rate was determined as the sum of defuzzied [AIRB] and [DAIR]. In this fuzzy control system, the aeration rate was set at two-hour intervals according to its state and the productivity was higher and had less deviation than model fermentation (predetermined stepwise shift up each 20 hours in the aeration condition). Such result was also obtained even in the case of low initial cell concentration. These data indicated the usability and stability of this fuzzy control system.

Extraction and Separation of Rare-Earth Elements by Tri-n-Octylmethylammonium Nitrate and β-Diketone Using Water-Soluble Complexing Agent

Abstract: Extraction and separation of rare-earth elements by tri-n-octylmethylammonium nitrate (TOMAN) and β-diketone (α-acetyl-m-dodecylacetophenone: LIX54) in the presence of water-soluble complexing agent (ethylenediaminetetraacetic acid: EDTA) was investigated. All EDTA make 1:1 complex with rare earth, and only free (not complexed) rare-earth ions can take part in the extraction. Although the distribution ratio of the metals decreases by addition of EDTA, the separation factor increases since extractability of the heavier rare earth is further reduced by formation of inactive EDTA complex. The effect of EDTA on the separation factor can be predicted using the distribution ratio of each element in the absence of EDTA, the ratio of stability constants of the complexes and the feed concentration of the species. Separation and recovery of rare-earth elements from the aqueous raffinate solution was feasible by extraction of metals using tri-n-butylphosphate (TBP) in acidic conditions. Simulation of Nd/Pr separation by continuous counter-current batteries showed that Pr was highly purified by addition of EDTA in aqueous phase.

A New Experimental Method of Vapor–Liquid Equilibria at High Pressures

Abstract: A new experimental method of vapor–liquid equilibria at high pressures for binary systems which requires no analysis of phase compositions is proposed in the present study. The equilibrium vapor and liquid compositions can be evaluated by combining a couple of data at the same temperature and pressure, based on mass balance and the phase rule. A new apparatus for vapor–liquid equilibria at high pressures was constructed for use with the present experimental method. Vapor–liquid equilibria and saturated densities at high pressures were measured for the carbon dioxide–acetone system at 298.15 K. The experimental data obtained were correlated with the pseudocubic perturbed hard-sphere equation of state proposed previously.

Soot oxidation in a silent discharge

Abstract: A study of soot oxidation in silent discharge aiming for the development of an efficient soot removal technique, is presented. The soot collected on the filter decreased in silent discharge by the addition of H2O and/or O2 to Ar carrier gas. In the case of a flow system also, the soot concentration was reduced with an increase of residence time in the discharge reactor. These facts support the conclusion that the soot particles were oxidized by OH radicals generated by the destruction of water vapor in the exhaust gas. To explain the soot reduction by OH radicals quantitatively, simple kinetic simulations were carried out. In this model, the electron energy in the discharge was adjusted to obtain agreement with experimental measurements of OH radical concentration as measured by resonance absorption spectroscopy. The calculated results well explained the observed trends of soot reduction when the collision efficiency of OH radicals with the soot surface was assumed to be 0.1.

Relationship between Apparent Bed Viscosity and Fluidization Quality in a Fluidized Bed with Fine Particles

Abstract: The apparent viscosity was measured in a fluidized bed with fine particles. The measurement was performed in the bed expanded uniformly at gas velocities between minimum fluidizing velocity and minimum bubbling velocity by means of the falling-sphere method. As the apparent viscosity obtained decreased with the diameter of the falling spheres, the viscosity value was determined by extrapolation. The apparent viscosity obtained was correlated with particle diameter, density and bed voidage. An equation for predicting the apparent viscosity in the emulsion phase in a bubbling fluidized bed was introduced by combination with the correlation of the voidage of the emulsion phase. Comparison of the values predicted from this equation with the data in the literature shows good agreement. To investigate the influence of the apparent viscosity on the fluidization quality, deviations of pressure fluctuations and bubble diameter were correlated with the apparent viscosity. It was shown that the proposed correlation for the apparent viscosity was useful for predicting the fluidization quality.

Compression characteristics of excess activated sludges treated by freezing-and-thawing process

Abstract: Excess activated sludge is very difficult to be filtered, but its solid–liquid separation characteristics can be improved by a freezing-and-thawing process. In this study, centrifugal and the gravitational settling experiments were done by using unfrozen and frozen activated sludges.An equation for the average solid compressive pressure ((ps)av) in the sediment zone was derived, based on the general equation for the local compression characteristics of a solid–liquid mixture. Also, the relationship between (ps)av and the average porosity ((es)av) in the sediment zone (1 – (es)av) = E(ps)avβ; E and β = constants) was confirmed by centrifugal and the gravitational settling experiments.The order of magnitude of (e)av was unfrozen sample

Analysis of filtration mechanism of crossflow upward and downward ultrafiltration.

Abstract: The filtration characteristics of crossflow ultrafiltration are studied for two types of solutes, a protein (BSA) and a colloid (silica sol), under constant-pressure conditions. It is shown that the time variation of the filtration rate coincides with that of dead-end ultrafiltration until the filtration rate drops to a certain value, and that the gel-cake is easily swept away at a relatively small crossfiow velocity. Effects of the crossflow velocity, the filtration pressure and the solute concentration on the dynamically balanced filtration rate are explained by considering the balance between the “particulate” solutes accumulating on the gel-cake surface and those to be swept away by the shear force due to crossflow at steady state. It was also found that the dynamically balanced filtration rate in crossfiow upward ultrafiltration coincides with that in dead-end upward ultrafiltration under conditions below the critical shear stress τw·c, whereas it is in accord with that in crossflow downward ultrafiltration above τw·c.

Factors Influencing Constant Drying Rate of Wet Granular Bed Irradiated by Infrared Radiation

Abstract: The present study aims at gaining a good understanding of the mechanism of infrared radiation drying of a wet granular bed in the constant-rate period. Our attention was focussed on the factors influencing the constant drying rate of a granular bed irradiated by infrared radiation. As the variables, the conditions of the granular bed (emissivity of the powder materials and the particle size of the powders) and the radiative heat source (the spectral distribution of irradiation power) were examined. Infrared radiation drying of the granular bed was performed and the heat transfer model in the constant-rate period was studied. The constant drying rate was calculated by using the model. The calculated results were quantitatively compared with the experimental results, and agreed consistently with the latter by taking account of the spectral distribution of absorption of irradiation power by the granular bed.

Polymer particle formation in styrene polymerization in aqueous media at low surfactant concentrations

Abstract: Emulsion polymerizations of styrene were carried out in the absence and presence of a surfactant and the number of polymer particles was measured mainly in a range of surfactant concentrations up to the critical micelle concentration with a change in initiator concentration. Experimental results for the number of polymer particles in the absence of the surfactant were compared with predictions from a homogeneous nucleation model which includes the assumption that the rate of radical entrance into the polymer particles is proportional to particle surface area uncovered by ionic end-groups of polymers contained in the polymer particles. The model also takes into account electrostatic effects on radical entrance into the polymer particles and coagulation between polymer particles. The experimental results in the absence of the surfactant compared well with the predictions. The model was extended to the reaction system in the presence of the surfactant, taking into consideration surfactant adsorption to the polymer particles and the adhesion of surfactant molecules to growing radicals. The model predicted well the tendency of the experimental results of the number of particles.

Maximum conversion of dehydrogenation in palladium membrane reactors.

Abstract: The objective of the study is to compare the maximum conversions in two flow models, cocurrent and countercurrent, for the palladium-membrane reactor with that in a conventional catalytic reactor, whose maximum conversion is determined thermodynamically