摘要:

AbstractExtensive studies on dispersion‐free solvent extraction have been carried out using modules made with either hydrophobic or hydrophilic microporous hollow‐fiber membranes. Membrane and boundary layer resistances have been characterized for both kinds of hollow fiber using solvent extraction systems with a wide variation of distribution coefficients and interfacial tensions. It has been found that the Graetz solution for a constant wall concentration describes satisfactorily mass transfer on the lumen side of a hollow‐fiber device. A correlation of the formNSh= [Dh(1 − ϕ)/L]N Re0.6N Sc0.33appears to provide a close fit to the shell‐side mass transfer coefficient data. The perforamnce characteristics of dispersion‐free extraction in hollow‐fiber modules have been considered against those of commercial packed‐bed extractors. A perspective has been provided on comparative utilities of hydrophobic or hydrophilic hollow fibers for a given solven

ISSN:0001-1541    

DOI:10.1002/aic.690340202

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractMicellar‐enhanced ultrafiltration can be used to remove multivalent anions or cations from aqueous streams. In the removal of chromate ions (CrO 42−), the cationic surfactant hexadecylpyridinium chloride is added to the solution, and the chromate ions preferentially adsorb at the surface of the highly charged surfactant micelles. The solution is processed by ultrafiltration, using a membrane with pore sizes small enough to block the passage of the micelles and adsorbed ions. The permeate solution has a chromate concentration less than 0.1% that in the original stream. A new equilibrium model, combining the simple two‐phase polyelectrolyte theory of Oosawa with thermodynamic activity, material‐balance, and charge‐balance equations, successfully correlates ultrafiltration and equilibrium dialysis results for chromat

ISSN:0001-1541    

DOI:10.1002/aic.690340203

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe charge‐transfer reactions in the three‐phase interfacial region, between a platinum catalyst, an yttria‐stabilized zirconia (YSZ) support, and the gas phase, were studied electrochemically during carbon monoxide oxidation. From electrochemical and reaction‐rate measurements, it appeared that oxygen was being removed from the support by carbon monoxide adsorbed on the platinum, while being supplied to the support by atomic oxygen adsorbed on either the platinum or the YSZ.Highly disperse Pt/YSZ catalyst outperformed a Pt/Al2O3catalyst, the rate difference being explained in terms of interfacial reactions. Even in the presence of species such as water and sulfur dioxide, catalysts with YSZ supports outperformed those with alumina s

ISSN:0001-1541    

DOI:10.1002/aic.690340204

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA model is presented for convection and chemical reacton in porous media. An irreversible chemical reaction of arbitrary order is considered. Reactant depletion allows for basic solutions in either the kinetic or the diffusion regime. The cases of forced flow parallel to the lateral walls of the cavity and a closed system are addressed. A linear stability analysis of the basic states is performed and critical values of the thermal Rayleigh number for the onset of natural convection are determined. A dispersion relation is derived and a graphical representation of the linear stability analysis results is provided for typical values of the system parameters. Analytical predictions are verified by results obtained by numerical integration of the complete set of nonlinear partial differential equations. The effect of natural convection is discussed when the basic state is either in the kinetic or in the diffusion regime. For large gradients, associated with the diffusion regime, chemical reaction can drive free convection even for low values of the Rayleigh number. In forced flow systems, natural convection can change substantially the flow pattern of the system.

ISSN:0001-1541    

DOI:10.1002/aic.690340205

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe dispersion of emissions from a plume in a cross stream was studied using both experimental and theoretical techniques. Wind tunnel experiments were done for three jet to cross stream velocity ratios:R= 0.5, 1, and 2. The concentration in the plane perpendicular to the cross stream was measured using light scattering and photographic image analysis. The analysis of the negatives revealed the presence of two counterrotating vortices that greatly affected dispersion of smoke in the plume.Convection and random turbulent dispersion were modeled with a statistical convection simulator on a CYBER 205 computer. The input velocities to the convection model were obtained using experimental measurements. The model revealed the effects of the vortices on dispersion, and the concentration distributions across the plume were determined once the vortices had dissipated. The existence of the counterrotating vortices and their effects upon plume dispersion showed that the Gaussian plume model, which is widely used for modeling pollutant dispersion, is inapplicable in the near range of the model stack.

ISSN:0001-1541    

DOI:10.1002/aic.690340206

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractTheories of batch sedimentation, taking into account the compression zone effect, are reinterpreted and modified. According to the discussion presented and the experimental results shown, characteristics—which are the loci of points representative of layers with the same settling rate and the same solids concentration in the settling zone—rise tangentially to the sediment curve on a height vs. time plot. Mathematical expressions that relate the solids concentration to the variations of the pulp‐supernatant interface height and of the sediment height are presented. In addition, the model presented is proposed for use when it is not possible to measure the sediment height. A procedure for calculating the concentration at the top of the sediment is also indicated.Calcium carbonate suspensions in water were selected for testing the equations deduced. The relation between the continuous thickener unit area and the underflow solids concentration was obtained from the batch tests, and is compared with that calculated by the graphic methods of Talmadge and Fitch, and

ISSN:0001-1541    

DOI:10.1002/aic.690340207

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe equations governing consolidation in a continuous‐flow gravity thickener are developed based on the assumption that a flocculated suspension possesses a compressive yield stressPy(ϕ) that is a function of local volume fraction only. These equations are used to model the steady state operation of a thickener. The bed height required to achieve a given underflow concentration is found to be a relatively sensitive function of the details of thePy(ϕ) function, particle flux through the thickener, and variations in the cross‐sectional area of the thickener. The limiting values of the underflow concentration ϕufor a given flux or the limiting values of flux for a desired ϕuare studied and shown to exist only for cylindrical and converging thi

ISSN:0001-1541    

DOI:10.1002/aic.690340208

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractAerosol deposition in model filters composed of layers of parallel fibers with the orientation of the fiber of each layer kept arbitrary was simulated stochastically. Particle positions at the inlet of the filter were assumed to be randomly distributed over the inlet plane with the trajectory assumed to be rectilinear because of the particles' high inertia. In the simulation, the track of each particle through the filter was monitored and the possible bounce‐off from collision surfaces was allowed for. Deposition behavior and the structure of deposits were studied with various aerosol flow conditions and filter characteristic

ISSN:0001-1541    

DOI:10.1002/aic.690340209

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractTwo models are presented that can simulate two peaks in a temperature‐programmed desorption (TPD) spectrum from a high surface area catalyst at atmospheric pressure: a multisite model and a subsurface diffusion model. The multisite model assumes that the two peaks arise from two distinct adsorption sites on the catalyst surface with different activation energies for desorption. The subsurface diffusion model assumes that the high‐temperature peak is produced by adsorbate that diffuses into the subsurface region of the catalyst during heating, and then back to the surface when it becomes depleted by the desorption process. It is shown that one can distinguish between the two models experimentally by measuring the effect of carrier gas flow rate and heating rate on the TPD spect

ISSN:0001-1541    

DOI:10.1002/aic.690340210

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe transient behavior of polymer properties following a step change in feed conditions during copolymerization in a continuous‐flow stirred‐tank reactor has been investigated by both modeling and experiment. For kinetics appropriate to Ziegler catalyzed olefin polymerization, the dynamic response of polymer molecular weight and composition is predicted to be relatively slow; four to six reactor turnovers could be required to reach steady state. In addition, response time depends on the direction and magnitude of change and is generally shorter when a property value is decreased. These model predictions were confirmed by measurement of the transient response of copolymer composition and molecular weight for ethylene‐propylene‐ethylidene norbornene terpolymerization.The model equations also were used to simulate reactor startups, and it was found that steady state following a startup can be reached in about three reactor turnovers. The initial absence of polymer in the reactor causes the dynamic response to be faster for a startup than for reactor

ISSN:0001-1541    

DOI:10.1002/aic.690340211

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY