We are now in an era when we need to look downstream as well as upstream regarding chemical production processes. It is necessary that a chemical production process be carefully investigated and various forms of wastes generated by the process be targeted so as to reduce environmental risk to any media. We must understand the potential problems that can occur due to the release of various chemicals into the environment. In this paper, a concept of enclosing a chemical process to minimize wastes, along with waste minimization assessment, and multimedia environmental transport, exposure, and health risk assessment due to chemicals are briefly reviewed.
This paper presents a new mathematical model for the dynamics of a liquid-liquid phase-transfer catalyzed batch reaction system. The model is formulated as a system of coupled nonlinear differential and algebraic equations in which the differential equations describe the slow reactions in the organic phase, whereas the algebraic ones describe the rapidly established dissociation equilibria in the aqueous phase and the mass balances of the species. A two-stage optimal parameter estimation method is used to estimate the values of the model parameters, such as the reaction rate constants, the overall mass transfer coefficients, the distribution coefficients, and the dissociation constants, from the experimental data. The reversible reaction between organic-phase benzyl chloride and aqueous-phase sodium bromide, with tetrabutylammonium bromide as a catalyst, was carried out to verify the mathematical model. Simulation results reveal that by the proposed model one can successfully make a correct judgement as to whether the quaternary onium salts in the two phases are in extractive equilibrium. Also, one can explicitly determine the respective contributions of the reaction and the mass transfer to the overall rate. Moreover, the fact that a high-concentration inorganic salt in the aqueous phase salts out the quaternary onium salts into the organic phase and thereby alters the distribution coefficients of the phase-transfer catalysts can be explained by our model.
Enhanced cell density culture of Thiobacillus ferrooxidans was achieved by using a membrane-type bioreactor with cell filtration and iron recycling units. Using an electrolytic bath with an anion exchange membrane, microbially produced Fe3+ could be reduced to Fe2+ without loss of main nutrients in the medium. It was confirmed that T. ferrooxidans exhibited active growth in the electrochemically regenerated medium. In the repeated-batch culture with cell filtration and feeding of the regenerated medium, the cell concentration obtained was at least 4–11 times higher than that in a conventional batch culture. In this culture system, the measurement of medium redox potential made it possible to estimate the concentrations of cells and iron, and to determine the time for culture filtration and medium-feeding operations.
The dynamic phenomena of skin diffusion/bioconversion of a provitamin have been described by assuming a bilayer skin consisting of the stratum corneum as a main diffusion barrier and the viable skin as a major site of bioconversion. The mathematical model adequately describes the time courses of the in vitro appearance profiles of the provitamin and its metabolites, vitamins C and E, in the hairless mouse skin. The present model can be used not only to investigate transdermal delivery of prodrugs but also to elucidate mechanisms of skin detoxification of xenobiotics entering the skin.
The extraction of vanadium(V) from hydrochloric acid solution by tri-n-octylmethylammonium chloride (TOMAC) was studied, employing benzene and chloroform as diluents with differing solvating characteristics to the extractant. The reduction of vanadium(V) to vanadium(IV) in the acid solution and the association of the extractant in the organic phase are taken into consideration. The vanadium extraction is assumed to occur via monomeric species of TOMAC in competition with the formation of acid complex in both diluent systems. Extraction equilibrium formulations that can express the vanadium(V) extraction over a wide range of metal loading of the extractant in both diluent systems are presented.
The synergistic extraction of rare-earth nitrates was studied, using tri-n-octylmethylammonium nitrate (TOMAN) and β-diketone(α-acetyl-m-dodecylacetophenone: LIX54 and α-perfluoro-alkanoyl-m-dodecylacetophenone: LIX51) in xylene as extractants and ammonium nitrate as salting-out agent. The capability of this mixed extractant is essentially identical to that of TOMAN alone in the range of pH = 2–3. with increasing pH a strong synergism appeared, and the degree of adduct complex formation became greater with position in the atomic number series. The extraction of heavier element is, thus, most favored at pH = 6 and least favored at pH = 2. The mixed adducts involved in the extraction were identified as Ln(NO3)2R·5S, Ln(NO3)R2·4S and their aggregates as Ln(NO3)3Ln(NO3)2R·5S and Ln(NO3)3Ln(NO3)R2·4S, where R: anion of β-diketone and S: monomer of TOMAN. The fraction of adducts containing two molecules of β-diketone increases with increasing atomic number of the element.
A practical isotherm equation based on the scaled-particle theory and a patchwise model has been developed for single- and multi-component adsorption on a heterogeneous surface. The surface energy distribution function used in the model is the asymmetric Gaussian function; however, the continuous distribution is formally changed to four discrete patches, called the four-point approximation model, by means of the Hermite-Gauss quadrature formula in the numerical integration. The model is applied to single-gas adsorption on an activated carbon fiber, KF-1500, at elevated pressures and three temperatures with satisfactory agreement. Four binary gas adsorption data on KF-1500 at 298.15 K and 500 kPa have been obtained and analyzed by the model. The geometric mean assumption for the binary interaction parameters between adsorbed molecules is adequate for binary mixtures of methane + ethane and methane + ethylene, while an adjustable parameter for the binary interactions, kij, is required for binary mixtures of carbon dioxide + ethane and carbon dioxide + ethylene.
During the transport of coarse particles through a pipeline, if unexpected accidents such as sudden pump stoppage due to failure of the power supply occurs, particles in the pipeline settle and form a deposit bed in the pipe bottom. In such cases, the settled particles must be removed prior to resuming operation. There are several ways of removing particles deposited in pipelines. One of them uses fluid drag force. in this paper we propose a new criterion: the fluid velocity at which dunes are formed on the surface of the deposit bed, taking into account both the shortening of removal time and the avoidance of pipe blockage. The stability criterion for the surface of the deposit bed in pipelines was theoretically and experimentally studied by using the linear stability theory.
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.
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.
It is usually difficult to estimate process parameters used in digital simulation because online data from chemical plants include errors. To improve the reliability of data, this paper proposes a data reconciliation method based on direct use of the measured variables, called SEBDARM, instead of the conventional method with balanced variables. The new method is applied to a pilot plant and its validity is discussed by use of experimental data and simulation. As a result, the following conclusions were obtained. 1) On-line data can be adjusted satisfactorily by SEBDARM. 2) It is easy to investigate the necessity of calibration of each sensor because there is one-to-one correspondence between measured variables and reconciled variables. 3) The reconciled data are not influenced by the numbers of reduced balance equations, so we can attempt to observe variables corresponding to some purpose by using the minimum number of balanced equations. This method can be utilized to observe the change of parameters and the state of the operation.
Monodispersed latex particles in aqueous solutions were deposited on a semipermeable membrane through which electrolytes permeated, and it was found that a two-dimensional ordered structure of these particles was formed under a certain condition. The mechanism of ordering was studied qualitatively using the DLVO theory, and the formation of an ordered structure was found to be closely related to the existence of the secondary minimum of the potential between the substrate surface and the particles.
Two-dimensional ordering of uniform spherical particles on a surface caused by Brownian motion is simulated by use of the Monte Carlo method, where the hydrodynamic interaction and potential between particles are taken into account. It is predicted that particles coagulated in the secondary minimum of the interparticle potential form either an ordered, a disordered or a dispersed structure, and that the ordering is obtained in the region of the electrolyte concentration where the interparticle potential has a relatively shallow secondary minimum. This dependence of ordering on the electrolyte concentration is compared with experimental results reported elsewhere.6) The reason why particles in the secondary minimum do not necessarily form and ordered structure is also discussed.
A simplified model for sulphur absorption in circulating fluidized beds has been proposed. It could provide a preliminary assessment of the effect of design, operating and feedstock parameters on sulphur capture performance. The model prediction was compared to sulphur capture data from a 0.3 MWt pilot-scale CFB combustor and a 22 MWe commercial-scale CFB boiler and good agreement was observed. The effects of Ca/S ratio, solid circulation rate, bed suspension density and superficial gas velocity on sulphur capture were shown both analytically and experimentally.
Reverse osmosis separations of alcohol aqueous solutions were performed over a wide range of feed concentrations up to 60 wt% using water-selective membranes. The validity of the nonequilibrium thermodynamics model by Spiegler and Kedem was confirmed theoretically and experimentally under the conditions of this study. The parameters of this model were found to have a large dependency on the feed alcohol concentration.
A suspension of yeast, which is one of the most common microorganisms, was microfiltered in an unstirred batch cell. It was found that the properties of cake are constant in spite of the differences in experimental conditions covered in this work. On the other hand, partitioning at the pore entrance by yeast was observed more frequently at higher applied pressure and for small-pore size membrane in scanning electron microscope investigations. The conventional constant-pressure filtration theory could not represent these experimental results. To describe the data consistently, a new model taking into account the partitioning in terms of effective membrane area was developed.
The behavior of encapsulated LaNi5, a typical hydrogen storage alloy, was investigated with the aim of improving unfavorable behavior such as disintegration. A sieved fraction (250/400 mesh) of LaNi5 particles was encapsulated with polystyrene (polymerization degree 1000–1400). The effect of polystyrene/LaNi5 weight ratio (0.015, 0.075, 0.15 and 0.30) on the material characteristics was investigated by using an absorption-desorption apparatus. The number of activation pretreatment increased with increasing of the polystyrene/LaNi5 ratio. The absorption capacity was not influenced by the encapsulating treatment. The initial absorption rate decreased with increasing polystyrene/LaNi5 ratio. Disintegration did not occur in the range of polystyrene/LaNi5 ratio larger than 0.15. From these results, the optimum ratio was found to be 0.15.