Even though purely steric partitioning within well-defined pores was treated, analytical approximations based on perturbed approach have been proved to be unreliable predictions of concentrated colloids for the whole range of relative pore size from wide to narrow. In this study, simulation results from Gibbs ensemble Monte Carlo method on electrostatic partitioning of concentrated colloids have been addressed for a cylindrical pore. The concentration profiles representing the effects of solute concentration as well as solution ionic strength are obtained via a stochastic process, and compared with the results of virial expansion. In order to determine the respective electrostatic energies between the solute and the pore wall, and between pairs of solutes, we employ previous analyses such as a solution with series representation and a singularity method. Electrostatic partitioning shows a clear dependence on solute concentration as well as ionic strength. Consistent effects of solute concentration including ionic strength are explicitly estimated by comparing the configurational order of restriction. Remarkably, our simulations reveal a possible occurrence of physical adsorption inside narrow pores, of which the partition coefficient exceeds one in the system of charged solutes and uncharged pore wall with higher solute concentration. The hindered diffusion coefficient for the dilute limit of charged system is predicted to decrease with decreasing solution ionic strength for a given pore size.
We propose a simple method for identifying interaction strength between an adsorbate molecule and a solid surface. The interaction strength is necessary for precise evaluation of pore sizes of the nanometer order, in which the conventional Kelvin model fails to describe the condensation phenomena, and for which we proposed an alternative model taking account of the effect of attractive potential from pore walls on the condensation: The model contains a constant to express the interaction strength between an adsorbate and a solid surface, and it should be determined from a standard isotherm. For investigation and verification of the method, standard adsorption isotherms were prepared by the grand canonical Monte Carlo simulations for the system of a Lennard-Jones particle on a homogeneous solid surface. The Frenkel theory was basically applied for this purpose because of its explicit inclusion of the interaction parameter within the equation. The theory shows good agreement with simulation results in a limited range of relative pressures from 0.005 to 0.25, while certain deviations exist in other portions of the isotherm. The result is that only the portion of the standard isotherm with good agreement should be used to evaluate the interaction strength employing the Frenkel theory. Through examinations in systems with various interaction strengths, it is found that the interaction strength is able to be evaluated correctly if the equation is applied to the range of surface coverage from 0.8 to 1.8 in all cases. The interaction constant calculated by this method is proved to have sufficient accuracy for use in characterization of nano-scale pores.
Four three-phase coexisting curves for the trifluoromethane hydrate system were obtained over a pressure range up to 72 MPa and temperature range from 283 to 302 K. Two invariant points determined in the present study are the critical end point of 299.44 K and 4.85 MPa, and the quadruple point of 292.25 K and 4.07 MPa. The former, where the gas and liquid are critically identical in the presence of water phase, is located very close to the critical point of the trifluoromethane fluid. The latter is the terminal point of four three-phase coexisting curves. The overall enthalpy change of hydration is estimated over the whole temperature region. The important finding is that trifluoromethane hydrate is the border system having a quadruple point (hydrate + two liquids + gas) in a series of critical temperatures of known guest species. It is also identified that xenon hydrate is the opposite border system having no quadruple point.
A new method is proposed to disclose the role of each component in a chemical process system. There are many methods for analyzing a process system from energy viewpoints. But these viewpoints cannot be applied to the behavior of each chemical component especially related to environmental problems, because the energy of such a dilute component is negligibly small as compared with that of the main component. Hence, a new diagram with ordinate of ln pj and abscissa of njRT0 for component j is proposed and it is called a material-utilization diagram. The relationship between this diagram and the energy-utilization diagram is demonstrated from the entropy production.
In order to investigate the effect of interaction between diffusion fluxes on mass transfer from a binary solution drop, numerical analyses of mass transfer around a binary solution drop under forced convection are made by using a finite difference method for driving force ratios ΔωB/ΔωA = –10 – 10, diagonal Schmidt number ScAA = 1–3, ScBB = 0.5–3, nondiagonal Schmidt number ScAB = 1–10, ScBA = 1–10 and Reynolds number ReP =1–200. The effect of driving force ratios, Reynolds numbers, and multicomponent Schmidt numbers on the concentration profiles and the diffusion fluxes of a binary solution drop are discussed. A new correlation is proposed for the effect of interaction between diffusion fluxes on mass transfer around a binary solution drop under forced convection.
To make uniformly sized liquid droplets in immiscible liquid, the condensable vapor bubbles uniformly generated from a nozzle were fed into cold continuous liquid phase. To estimate the size of the condensed dispersed droplets, a non-spherical bubble formation model with phase change is proposed. By using the present model, the two-phase bubble growth curves, the bubble shape change, and the molar number of uniformly dispersed droplets were simulated. The simulations correspond relatively well with experimental results.
An aluminum anodic oxide (AlAO) membrane consisting of highly regulated cylindrical pores of 20–30 nm pore radius was prepared to clarify the applicability of two transport models, the original pore (OP) model and the steric-hindrance pore (SHP) model, to the structural characterization of ultrafiltration (UF) membranes. Filtration and diffusion experiments were performed with the linear macromolecules dextran and polyethyleneglycol. The reflection coefficient (σ) and solute permeability (P) were determined by analyzing rejection properties with the Spiegler-Kedem equation. In addition, the value of P was measured by diffusion experiments. Comparing the observed values with the theoretical predictions makes it clear that membrane structure can be quantitatively evaluated with the OP model by characterizing the size of the macromolecular solute by its radius of gyration (rg), but not by the Stokes-Einstein radius (rs).
We present a numerical procedure based on the finite element method in combination with the Lagrangian technique to predict the time-dependent deformation of a dielectric drop which is suspended stationarily in another dielectric liquid under the influence of a uniform DC electric field. The effects of the electric field strength and the physical properties on the drop deformation are then shown. The computed results reveal that Taylor’s circulation appears in the drop in addition to the hyperbolic flow pattern due to the deformation, depending on the physical properties of the drop and continuous phases, and affects the drop deformation.
A water droplet was slid on an inclined plate whose lower surface was kept at a temperature between room temperature and 510 K. The dependence of the dynamic advancing and receding contact angles on the wall temperature and the contact line velocity was measured from the shape of the droplet sliding on the high temperature surface. The experimental results demonstrate that a rise in the wall temperature increases the dynamic contact angles due to evaporation from the meniscus. The dynamic receding contact angles at high temperatures increase with increasing the receding velocity of the contact line. This result is contrary to the well-known fact at room temperature. The velocity dependence of the dynamic advancing contact angle is similar to the well-known dependence at room temperature.
To analyze the performance of a vertical tube reactor involving a gas-slurry reacting system in dispersed bubble flow and upflow, downflow, and upflow-downflow (alternating) configurations, several performance indicators are defined and expressed in terms of integral equations. A local effectiveness factor associated with the efficiency for gas-slurry mass transfer, conversion of the liquid reactant, the local unconverted mass fraction of the gas phase, and the pressure drop are taken as performance indicators. Bounding criteria for diffusion-controlled and chemical reaction-controlled regimes are established, and their transitions along the reactor are also discussed. A generic heterogeneous catalytic hydrogenation, exemplified by the single reaction A(l) + H2(g) → B(l), is taken as a suitable reference system.
The behavior of an isothermal, vertical tube reactor in a dispersed bubble flow environment in either upflow, downflow or upflow-downflow configurations is examined, using the performance indicators defined in Part I. The hydrogenation of a coalescent organic system, like the one found in the mild hydrogenation process of soybean oil, is taken as a reference system. The likelihood of the axial changes of the local gas-slurry mass transfer efficiency and, then, of the controlling regimes of the process rate is discussed. Further effects of the configuration on the conversion of the liquid reactant, the unconverted mass of the gas phase, and the pressure drop are also analyzed.
A new method for analyzing the kinetics of CVD reactions is proposed using area-controlled CVD. Catalyst particles were set at the dead end of a narrow straight tube. Water vapor generated at the catalyst from H2 and CO2 was fed into the reaction zone to react with TiCl4, which diffused from the opposite side. Then, TiO2 was formed and deposited on the tube surface. The rate-controlling step in the CVD process was clarified by investigating the dependence of deposition width on the inner diameter of the reaction tube. From the experimental results, it is found that diffusion and surface reaction-step were the rate-controlling step at 373–393 K and 413–513 K, respectively. It is elucidated that the value of rate constant of surface reaction can be evaluated as 1.5 × 10−3 m s−1, which is almost constant in the temperature range, 413–513 K. The value is so small that estimation by using the step coverage method can not give a reliable value.
We simulated the performance degradation in a reformer for phosphoric-acid-fuel-cell (PAFC) power plants caused by deterioration of the catalyst loaded in the reformer. We found that the temperatures of the catalyst bed, steam-reformed gas, reformer-tube outer-wall, and burner-exhaust gas rise as the catalyst deteriorates. Increases in the steam-reformed and burner-exhaust gas temperatures at the reformer outlet proved to be the most useful parameters for estimating the drop in reformer performance caused by catalyst deterioration because they could be easily measured during power generation. These temperatures rise and the methane-conversion rate decreases as the catalyst deteriorates. By comparing the simulation results with measurements taken for a 200 kW PAFC power plant, we found that increases in the steam-reformed and burner-exhaust gas temperatures at the reformer outlet, instead of the methane-conversion rate, can be used as parameters for estimating the reformer-performance degradation, and that the steam-reformed-gas temperature is the better parameter of the two.
The kinetics of esterification of lactic acid with methanol in the liquid phase are studied by using a cation exchange resin in the H+ form (DOWEX-50W) as an acid catalyst. Experiments were carried out in a stirred batch reactor at different temperatures (323, 333, 343, 353 K) under atmospheric pressure. The effects of reaction temperature and catalyst loading on the reaction rate are investigated. It is found that catalyst size and stirring speed have no significant effects on reaction rate. The reaction rate data are correlated with a kinetic model based on pseudo-homogeneous catalysis. The activity of resin is compared with that of sulfuric acid as a catalyst. A kinetic equation for describing the reaction catalyzed by cation exchange resin is developed.
In order to commercialize a photochemical reactor for treatment of biohazard organic compounds in aqueous solution, a film-shaped photocatalyst composed of platinum-loaded TiO2/water glass/substrate was fabricated, immobilizing pretreated TiO2 powders on a substrate plate by a double spread method. A new type of photocatalytic reactor, called a TiO2 photocatalyst coated rotating-drum reactor, was proposed, in which the surface of the drum is the reaction site so that the photocatalyst can effectively contact aqueous solution and receive light. A experiment in decomposing phenol in an aqueous solution using this reactor was carried out. In consequence, it is shown that phenol can be decomposed in a relatively short time, not only under artificial ultraviolet light, but also under solar light.
The effect of Ni3Al on nickel grain growth inhibition is investigated during the sintering process of a Ni-based porous molten carbonate fuel cell (MCFC) anode including 4 to 10 wt% fine Ni3Al intermetallic particles. Nickel grain growth is retarded and the grains are kept the proper size due to the pinning effect of Ni3Al intermetallics that control nickel grain boundary movement, and due to the dominant surface diffusion in the vicinity of necks formed between nickel powders. It is found that the nickel grain growth rate of the anode including Ni3Al intermetallics follows the kinetics law; Gm – Gom = Kt with m = 4.5, in which the grain size exponent is higher than that of porous pure nickel anode. A pore size distribution in the anode ranges from 3 to 6 μm, which is compatible with the electrochemical reaction of the MCFC.
A continuous DC electric field has been generally used for fundamental study and practical application of electro-osmotic dewatering. Under DC conditions, however, the electrical contact resistance between the electrode and the dewatered material is excessively increased in the dewatering process, resulting in interruption of the dewatering process. For efficient performance of electroosmotic dewatering, intermittent power application was used to reduce such excessive increase of the electrical contact resistance with the lapse of time. An intermittent electric field was made by rectifying an AC electric field, and it was constituted of half waves. Both rectangular and sine waves were used as the wave form of an AC electric field. Electro-osmotic dewatering under the rectified half-wave intermittent electric field was investigated experimentally, under both conditions of the same peak-value voltage and the same effective-value (r.m.s.-value) voltage as the voltage applied under DC and AC electric fields. Intermittent power application is suggested to reduce the increase of the electrical contact resistance with time caused by the DC process. In the case of intermittent power application having the same effective voltage as DC and AC, the rate and the amount of removed water were increased compared with DC and AC fields, and the efficiency of electric power consumption for the amount of removed water was much higher than them.
Polymeric membranes were prepared from homogeneous solutions of two different mixtures: polysulfone (PSF)/dimethylformamide (DMF) and PSF/polyvinylpyrrolidone (PVP)/DMF. PSF solutions of 15 wt%, after cast on glass plates, were solidified either by direct immersion into distilled water or by 5-hr exposure under an environment of 72.5% relative humidity followed by immersion in a water bath. The prepared membranes are compared to each other on morphological and functional characteristics. In the vapor exposure process, the demixing rate of a cast solution film is enhanced with the addition of a polymer additive, PVP, in a casting solution. However, the enhancement of demixing rate did not result in an increase in water permeability or a significant morphology variation of the prepared membranes. On the contrary, when a cast film is coagulated by direct immersion into a water bath, the PVP in a solution film worked as a significant flux enhancer. It is concluded that at the specific concentration of 15 wt% polymer, PVP addition induces an increase in demixing rate of a casting solution, which results in an increase in permeability of the prepared membranes, only if the coagulation of a cast film is carried out in a nonequilibrium state.
This investigation is undertaken to obtain information on the effect of vortex orifice air distributors on the granule growth in conical fluidized bed granulation with a bottom entry spray. The five types of vortex orifice distributors suitable for a strong swirling air supply at the base of the conical bed were prepared. Although all these orifices consisted of four tangential injection nozzles with the same opening, the opening size of the air injection nozzle in each of the orifices was different. Intensity of the air injection nozzle torque within the vortex orifice was measured by a torque balance method. The granule formation of fluidizing lactose particles in the process of size-enlargement was carried out by spraying an aqueous HPC solution into the bed where the moisture content of granules was maintained at or below 0.30 wt%. As a result, granule growth in the bed could be precisely controlled by changes in the air injection nozzle torques arising from the vortex orifice distributor. The extent of granule growth, namely the granule growth conversion increasing with accumulated content of HPC in the bed particles during the operating time decreased according to the air injection nozzle torque within the vortex orifice. Using these process variables, granule growth conversion could be arranged experimentally. It is finally found that one of the features of the proposed air distributor is useful for size-control of granule products in the conical fluidized bed granulation with a bottom entry spray.
The effect of gas velocity (0.56–1.15 m/s) on radial voidage distribution and cluster properties is determined by using an optical fiber probe in the freeboard of a FCC regenerator (0.48 m-I.D. × 3.4 m-high). The normalized standard deviation of pressure fluctuation in the freeboard region decreases with increasing gas velocity. Local voidage distribution in the radial direction is relatively flat in the bubbling flow regime. However, in the turbulent flow regime, voidage in the core region is higher than that in the wall region. Clusters move up and down simultaneously, and cluster velocity in the core region is higher than that in the wall region. Cluster length decreases with increasing gas velocity. As the gas velocity is increased, cluster frequency, fraction and voidage decrease in the transition from bubbling to turbulent fluidization regime, but increase in the turbulent flow regime. Variation of the normalized standard deviation of pressure fluctuation in the freeboard can be related with the cluster properties. Cluster length decreases with increasing the suspension density. The cross-sectional mean cluster length in the freeboard zone is correlated with the suspension density as well as the experimental variables.
Vertical columns 1- and 2-m in height were packed with coarse coke particles, and were used as the cold model for a blast furnace. In order to estimate the transient accumulation behavior of fines from the gas phase to the surfaces of the packings, a mixture of gas and fines was injected into the bottom of each packed bed, and the transient discharge rate of fines at the outlet of the column was determined. Fines used in the present experiment were sieved coke particles 75-, 125-, 210- and 375-μm in diameter. The time required to attain a constant discharge rate decreases with increasing feed rate of fines and gas velocity, but is not greatly affected by the diameter of fines. A mathematical model for the transient discharge rate of fines was proposed assuming a transportation rate of fines to the packing surfaces from the upward stream, and that to the upward stream from the packing surfaces. Values of these parameters are correlated with experimental variables.
The objectives of this study are two-fold; to apply robust control tools hitherto used mostly for lumped parameter systems (LPS) to distributed parameter systems (DPS); and to investigate robustness of decentralized distributed controllers when operated under a full MIMO plant in the presence of unmeasured disturbance. The energy balance model of the packed-bed reactor is discretized using orthogonal collocation with the heat of reaction regarded as unmeasured disturbance. The resulting MIMO state space model is used for designing a decentralized temperature controller. Employing the IMC tuning rules as baseline, a decentralized PI controller is designed using only the diagonal elements of MIMO model treating off-diagonal terms as uncertainty. The off-diagonal interactions are used to design bounds called “μ-interaction measures” which are imposed on nominal closed-loop transfer functions. Satisfaction of these bounds guarantees that the designed decentralized controller will yield robustness over the full MIMO plant.
19% of the sewage sludge produced in Germany is presently incinerated. The emissions from sludge combustion in Germany are regulated by the 17th Regulation of the Federal Immission Protection Law. These emission limits can only be met, however, with a large technical effort. To fulfill the mercury emission limit of 0.05 mg/m3 (dry, standard conditions) in particular, special measures are necessary. This paper presents an overview on the various measures for emission control which are used at German sludge incineration plants. Furthermore, future trends of thermochemical sludge treatment in Germany, including co-combustion in power stations and gasification processes, are discussed.
Detailed study of heat and mass transfer inside a silica-gel packed bed, especially extraparticle diffusion for adsorption of water vapor, was carried out in a densely packed adsorbent bed, which normally prevails for realizing AHP technology. Experimental data for temperature and pressure distributions in the packed bed of adsorbent for adsorption of water vapor on silica gel is evaluated in terms of heat and mass transfer numerical calculation based on the model of water vapor transport which accounts for both heat and mass transfer of the interparticle void and the adsorbent particle. Subsequently, the effect of particle size and the rate of adsorption are discussed from the viewpoint of adsorption mechanism. It is found that the model calculation was appropriate since the results were found to agree with the experimental values. For the experimental conditions, mean adsorption rate is found to increase with particle size under dp ≤ 500 μm, above which the adsorption drastically decreases with an increase in particle size. From this result, it is concluded that there is an optimum value of particle size relative to the bed height for attaining a maximum adsorptivity.
A simple model has been developed to predict the heterogeneous ignition temperature for single coal particles under conditions of negligible, natural and forced convections. These conditions cause different sizes of the volatile matter cloud surrounding the coal particle. The model is based on the ignition of a single coal particle heated by irradiation from spot heaters in cold (ambient) surroundings. Energy from the particle surface oxidation, volatile matter combustion and physical heating from the spot heaters are all included in the particle energy balance. General ignition criterion is used to determine the ignition point. The model results agree quite well with experimental findings obtained earlier as far as the effects of particle size and volatile matter are concerned. Gas temperature emerged as the most effective model parameter influencing the ignition temperature. In the absence of volatiles in the particle vicinity, as for the forced convection case, the gas temperature remains almost constant and so does the ignition temperature. For cases where volatiles surround the particle, high gas temperatures as well as ignition temperatures are obtained. This is mainly attributed to the combustion of the volatiles contributing to the gas temperature rise, and possibly raising the particle temperature.
Particle dispersion in ceramic injection molding mixtures is investigated from the shear viscosity data of the mixtures. The degree of agglomeration of the mixture is examined using the Krieger and Dougherty equation on the viscosity for a concentrated suspension. The number of particles in a single agglomerate is evaluated by the shape factor parameter of suspended particles in the Krieger and Dougherty model with the scaling law of fractal analysis on particle agglomerates. The number of particles per agglomerate predicted are four particles for a zirconia sample, and for a alumina sample the particles are in a well dispersed state. These values of agglomeration in the molding mixtures predicted by the viscometric method are almost consistent with those predicted by the visualized technique.