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  • Inorganic Chemistry  (773)
  • Chemical Engineering  (643)
  • 2015-2019
  • 1990-1994  (1,416)
  • 1991  (1,416)
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  • 2015-2019
  • 1990-1994  (1,416)
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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 111-122 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The time-averaged void fraction, pressure drop and flow regime transition behavior of horizontal air-water two-phase flows is studied experimentally and numerically for 2-cm-inner-diameter tubes with various flow dividing junctions at its end. The time-average void and pressure drop behavior along the channel is simulated using a two fluid separated flow model. The results show that two-phase behavior (flow regime, void fraction, and pressure drop) is affected strongly by the presence of a flow division in the system. These effects extend far upstream of the junction for low-momentum flows and far downstream for high-momentum flows. Both numerical and experimental results show that there occurs a large increase in void just downstream of the junction owing to the halving of the fluid volume flow rates and the liquid deceleration.
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  • 2
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 147-149 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 3
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 169-181 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Nonequilibrium diffusion behavior in nonionic and ionic surfactant microemulsion systems has been studied experimentally using the open-ended capillary method. Experimental results for these systems have been compared with a drop theory of diffusion for microemulsions under conditions where large concentration and electrostatic gradients exist. The results show good agreement in concentration profiles between theory and experiment for the microemulsion components - water, benzene, and phenol. Furthermore, under certain conditions the theory predicts that over a limited time interval phenol will diffuse from low-concentration regions to regions of higher concentration. This phenomenon has been observed.
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  • 4
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 285-289 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 5
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 307-309 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 6
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 7
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 39-47 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Selective oxidation kinetics of n-butane to maleic anhydride in air were studied over a commercial, fixed-bed vanadium-phosphor oxide catalyst. The temperature range was 573-653 K with butane concentrations up to 3 mol % in the feed, which is within flammability limits but below ignition temperatures.The rate data were modeled using power law kinetics with product inhibition and included total oxidation and decomposition reactions. Kinetic parameters were estimated using a multiresponse, nonlinear regression algorithm showing intercorrelation effects. The kinetics were combined with independent measurements of catalyst diffusivity and reactor heat transfer using a one-dimensional heterogeneous reactor model. Model predictions and observed temperatures and concentrations from non-isothermal pilot plants were compared up to 115 days on stream. Agreement was acceptable with inlet butane concentrations up to 2.7 mol %. For example, runaway was predicted at a salt temperature 3 K higher than observed. Effectiveness factors around the hot spot were estimated at 0.6 with the catalyst surface temperature 2-3 K higher than the average gas temperature.
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  • 8
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 448-460 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Efforts to model the turbulent flow in stirred tanks require accurate boundary conditions at the tip of the impeller, not just of velocities, but of the turbulence quantities k and ε. Kolar's (1982) phenomenological, swirling radial jet model of the impeller region is extended by using a two-equation k - ε turbulence model to obtain direct estimates of k and ε on the impeller periphery. The model is extended and clarified, so that the number of parameters required for its application is reduced to two: the rotational speed and the diameter of the impeller. Three-dimensional simulations allow a realistic treatment of the baffles. Agreement of the modeling results with recently published experimental data is excellent. This is particularly true in the important impeller discharge zone, where details of the predicted behavior of the turbulence kinetic energy and dissipation rate are in quantitative agreement with the available data. Based on these results, average values of ε are calculated, along with the zones over which the apply. For the impeller discharge zone, the dimensionless, volume-averaged ε is 0.19.
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  • 9
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 470-474 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 10
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 347-359 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Rate process concerning the formation of TiO2 fine crystalline particles by the gas-phase reaction of TiCl4 and O2 are studied using aerosol reactors. Chemical reaction of TiCl4, sintering of particles, mixing of reactants, and transformation from anatase to rutile are evaluated as the system parameters of the simulation model proposed. The crystallite size in the range of 55-65 nm at 1,273 K is predicted well by a model that assumes the maximum fusible particle size, 15 nm in this case.The defect concentration in the TiO2 crystallites strongly affects the transformation rate, and anatase particles produced at 1,173 K are transformed to rutile more rapidly than those produced at 1,373 K. The transformation is simulated quantitatively by the model with the coordinates for elapsed time, particle size and rutile fraction. The model can be applied to such particle production processes as collision, sintering and crystal transformation occurring simultaneously.
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  • 11
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    AIChE Journal 37 (1991), S. 383-393 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Citric acid was successfully separated from an aqueous solution using the hollow fiber contained liquid membrane (HFCLM) technique. In this technique, the organic liquid membrane is contained in the shell side between two sets of hollow fibers; feed solution flows through one set of fibers and the strip solution flows through the other set. Tri-n-octylamine diluted in various organic solvents was used as a complexing agent for facilitated transport of citric acid from an aqueous solution. Pure water and aqueous sodium hydroxide were used as stripping agents. Membrane life and stability problems encountered in supported liquid membranes are eliminated. A mathematical model of facilitated solute transport through HFCLM that accounts for the interfacial reversible reaction kinetics and diffusion process inherent in carrier-facilitated transport is presented. Experimental data agreed well with the theoretical predictions for permeators achieving almost complete solute recovery.
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  • 12
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 429-436 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The sensitivity of the calculated micropore size of zeolite Y in a fluidized cracking catalyst based on empirical models for argon adsorption has been tested by examining the effect of curvature and by systematically verifying the magnitude of physical constants in the model equations. With a consistent set of physical parameters the slit model provided a pore size value of 0.45 nm, while the new cylindrical models provided values of 0.69 and 0.74 nm. The latter values are found to correspond well with the known aperture size of zeolite Y, 0.74 nm. By separately varying the magnitudes of five of the physical constants in the model over a range of ±30%, it was concluded that the diameter of the oxide ion at the surface had a large effect on the calculated pore size, while the other parameters had only moderate to small effects. Preliminary application of the cylindrical pore model to isotherms of argon on other zeolites and molecular sieves leads to promising results, especially for medium to large pore zeolites. These results suggest that the cylindrical pore model is a useful means for the transformation of argon adsorption data on a zeolite into a micropore size distribution.
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  • 13
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 59-64 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An analytical solution is found for flow in a converging channel for Reynolds numbers in the range of 102 to 103. The solution applies to an axisymmetric channel, for which the shape is given by R2z=constant, where R is the channel radius at the axial distance z. This shape produces a center-line or core velocity that increases linearly with z, thus making the extensional rate constant. The analytical solution is a pseudosimilarity solution of the axial momentum equation, and its accuracy was gauged by comparison to other results. Comparisons of velocity and pressure distributions to experimental data and to finite-element results indicate that the analytical solution is accurate to about 5%.
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  • 14
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Microkinetic simulations have been carried out to describe the partial oxidation of methane over silica-supported molybdena and vanadia. The objective of this study was to formulate a physically reasonable reaction network to capture the basic aspects of the surface catalytic chemistry and to use this network to link methane oxidation kinetics with the kinetics observed for the oxidation of subsequent gaseous products, i.e., methanol, formaldehyde, and carbon monoxide. The most abundant reactive intermediates on the catalyst surface are suggested to be oxygen and hydroxyl groups. This reaction network successfully predicts the catalytic activities, selectivities, activation energies, and reaction orders observed over silica-supported molybdena and vanadia; and the microkinetic model also semiquantitatively explains the kinetic trends for related catalyst systems and is consistent with surface bonding energetics reported in the literature over various oxide catalysts. The microkinetic reaction network properly reduces to the more simple macrokinetic model reported previously for methane partial oxidation.
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  • 15
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 142-146 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 16
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 161-168 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: There exists a narrow operating window in bubble columns where the motion is so gentle that the normally dominating forces of coalescence and breakup no longer define the bubble size, hence formation dynamics must control. Elementary force balances are presented to predict bubble size, which compares favorably with experimental data and is shown to be applicable to both rigid and flexible spargers. The main focus is on the prediction and performance of a small-holed flexisparger, for which it is proved that the gas momentum term is highly significant. Also, it is shown that the intermediate drag law is more appropriate than Stokes for forming bubbles.
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  • 17
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    AIChE Journal 37 (1991), S. 202-214 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A single-pellet reactor has been used to investigate the impact of partial external wetting on catalyst performance in a multiphase reaction system. The novel design simulates the local environment within a trickle-bed reactor, and permits the direct measurement of the degree of wetting under reaction conditions. Experimental data of the hydrogenation of α-methylstyrene (AMS) over a Pd/Al2O3 pellet provide unequivocal evidence of effectiveness enhancement by partial wetting, a predicted single-pellet phenomenon (e.g., Harold and Ng, 1987; Funk et al., 1988, 1989). The overall reaction rate is an increasing (decreasing) function of the degree of wetting if the overall limiting reactant is more effectively supplied through the wetted (nonwetted) part of the surface. A maximum in the reaction rate can occur at an intermediate degree of wetting, signaling a transition from an overall AMS-limited to hydrogen-limited reaction. The dependence of the degree of wetting on the liquid flow rate for low reaction rates is consistent with a simple rivulet flow model. At higher reaction rates the degree of wetting decreases, with all other conditions fixed. Possible mechanisms for this interesting link between the degree of wetting and reaction are discussed.
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  • 18
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 244-254 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new computational procedure based on the finite difference methods is developed to solve the coupled partial differential equations describing nonisothermal and nonequilibrium sorption of multiple adsorbate systems on a fixed bed that contains bidispersed pellets. In this numerical method, a solution-adaptive gridding technique (SAG) is applied in combination with a four-point quadratic upstream differencing scheme to satisfactorily resolve very sharp concentration and temperature variations occurring in the case of small dispersing effects. Furthermore, the method resorts to a noniterative implicit procedure for solving the coupling between the column transport equations and the adsorption kinetics inside the pellets, which may be particularly efficient when the particle kinetics equations are highly stiff.The numerical model will be tested for one-, two- and three-transition systems. The results are compared to available analytical and equilibrium theory solutions.
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  • 19
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    AIChE Journal 37 (1991), S. 277-280 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 20
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    AIChE Journal 37 (1991), S. 281-284 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 21
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    AIChE Journal 37 (1991), S. 290-298 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 22
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 23
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    AIChE Journal 37 (1991), S. 377-382 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A steady-state, two-dimensional model for cocurrent gas and liquid flow in a trickle-bed reactor is described. The model includes gas-liquid interaction and isothermal, incompressible flow without phase change or chemical reaction. The momentum equation proposed by Saez and Carbonell is used, along with their expressions for relative permeabilities of gas and liquid phases. Capillary pressure equations determine the difference in the pressures of flowing phases. The results of the model simulation agree with experimental data on flow distribution, liquid spreading, and phase segregation in a two-dimensional trickle bed with air-water flow in both low- and high-interaction flow regimes.
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  • 24
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    AIChE Journal 37 (1991), S. 403-428 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Local two-phase flow measurements were obtained in a pilot-scale, external-loop airlift bioreactor using hot-film anemometry and resistivity probe techniques. The radial dependence of both gas and liquid velocities and of the void fraction was substantial. Developing flow effects were pronounced, as evidenced by distinct changes in the radial profiles of fluid flow properties with axial position. For high gas flow rates, liquid acceleration effects near the sparger resulted in greatly reduced slip velocities in a substantial portion of the riser. A significant reduction in mass transfer may occur under such conditions.The point equations of continuity and motion were used to develop a differential, two-fluid model for two-phase flow in airlift risers. The only empirical parameters in the model represent frictional effects. The developing two-phase flow characteristic of airlift risers was observed to create significantly higher frictional effects at the wall than is routinely observed for fully-developed flow. Model predictions were compared to our own experimental results as well as those of Merchuk and Stein (1981). Agreement between the predicted and measured values was typically within 10% for both cases.
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  • 25
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    AIChE Journal 37 (1991) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 26
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    AIChE Journal 37 (1991), S. 512-526 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The enhanced dispersion resulting from solute exchange between phases was investigated experimentally for the case of a long, cylindrical capillary tube, in which a stationary absorbing phase formed a thin annular film around a flowing fluid. Solute diffusion into the stationary phase was analyzed in detail to accurately determine the coupling of film diffusion and hydrodynamic effects. The experimental results and analyses showed an increase in dispersion relative to the usual Taylor effect. The increased dispersion was a function of the relative partitioning of solute between phases and was in quantitative agreement with predictions from previously published theoretical studies.
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  • 27
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    AIChE Journal 37 (1991), S. 547-554 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The interstitial pressure buildup and the internal stresses on the skeleton of a cylindrical green body during burnout are analyzed numerically. The intrinsic kinetics of pyrolysis is coupled with the Carman-Kozeny equation or the slip-flow model of Wakao and Smith to evaluate the pressure distribution. The stress distributions before failure are estimated from elasticity theory. The stresses are tensile, and their maxima are located at the center of the cylinder. The tangential stress is larger than the radial stress. The effects of green body size, specific surface area, and pressurized atmosphere are discussed. The approximate solution is accurate for small green bodies. The pressurized atmosphere reduces the interstitial pressure and the internal stresses effectively.
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    AIChE Journal 37 (1991), S. 555-568 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A versatile reaction-separation (VERSE) model was developed to quantitatively simulate the behavior of chromatographic separations coupled with reactions. Detailed mass transfer and reaction mechanisms are considered. Aggregation data of myoglobin and β-lactoglobulin A verified the model. The effects of concentration, equilibrium distribution, reaction rate, convection rate, particle radius, and relative affinity are shown for a dimerizing system. When the aggregation rate is relatively slow compared with convection and mass transfer rates, the individual forms behave as separate species in frontal, elution, and displacement chromatography. For rapid aggregation rates, the individual forms behave as a single component with an average affinity. The wave asymmetry and increased spreading due to aggregation depend on relative affinity differences. Serious error may result if aggregation is overlooked in parameter estimation using frontal or pulse analysis. The dimensionless group principles developed here are useful in scaling and predicting when peak or wave splitting or merging will occur in reaction chromatography systems.
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    AIChE Journal 37 (1991), S. 581-588 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We have shown that ionomeric membranes of perfluorosulfonic acid (PFSA) polymer allow selective pervaporation of polar organic compounds from their azeotropic mixtures with less polar compounds. A composite membrane of a thin PFSA polymer film, cast on a porous Teflon support, provided desirable permeant fluxes with good selectivity. Model binary azeotropes, composed of alcohols and hydrocarbons, were separated with total pervaporation fluxes of up to 9.5 kg/h·m2 using a stirred membrane permeation cell, the product side of which was exposed to vacuum. Fluxes increased with increasing alcohol content of the feed and with temperature. But the selectivity of the more permeating component remained reasonably constant around the azeotropic point and also over the range of temperature used in the study (25-55°C). Total pervaporation fluxes depended little on downstream pressure up to 6.66 kPa (50 torr). These separation data were explained by a mathematical model based on a solution-diffusion mechanism.
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    AIChE Journal 37 (1991), S. 569-580 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Deep knowledge about process behaviors plays an important role in the diagnosis of chemical processes. Cause-and-effect reasoning using deep knowledge is useful especially for interacting malfunctions. This work explores the integration of deep knowledge into task-specific, knowledge-based architectures for resolving interacting multiple malfunctions and presents a novel methodology called diagnostically focused simulation (DFS). Invoked in an auxiliary manner, DFS uses deep knowledge and performs qualitative simulation in a highly constrained manner. The close integration with other problem solvers is an evolutionary approach to using qualitative simulation in diagnosis and manages a normally computationally-explosive procedure. Diagnostic results from the compiled problem solver provide a situation-specific assessment of the chemical process, identify possible malfunction scenarios, and focus on appropriate levels of process detail. DFS effectively demonstrates a balance between run-time simulation and compiled problem solving in diagnosis.
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    AIChE Journal 37 (1991), S. 589-596 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An understanding of the eddy diffusivity on a distillation tray is important to accurately predict the distillation tray efficiency from the point efficiency. This article presents a new correlation to predict liquid-phase eddy diffusivity (De) on sieve trays. This correlation has been developed by modeling backmixing as the trajectory motion of liquid droplet elements through the two-phase layer height on the tray. The trajectory model indicates that De is a strong function of the two-phase layer height. An expression for froth height is derived.The new De correlation offers two main improvements over existing literature correlations. First, this model is phenomenologically-based and, therefore, not limited to air/water. Second, the new De correlation gives significantly lower average actual and relative errors and a lower standard deviation of the actual error than do other available correlations.
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    AIChE Journal 37 (1991), S. 629-632 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 37 (1991), S. 617-628 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recent advances in knowledge engineering have led to develop the qualitative (deep) model based diagnostic systems. As process knowledge accumulated, however, the diagnostic system remains strictly qualitative. This limits the usefulness of such systems. In this work, a framework is developed for integrating quantitative process knowledge into the qualitative model. Once quantitative process information, e.g., steady-state gains, is available, it can be incorporated into the simplest qualitative process model called the signed directed graph. The quantitative process knowledge is described in terms of membership functions of fuzzy set theory. According to the measurement pattern, the truth values of a hypothesis (e.g., a fault origin) can be calculated based on the fuzzy logic. Consequently, the diagnostic resolution can be improved significantly. Furthermore, the proposed method becomes a strictly qualitative diagnostic system, if no quantitative information is available. A chemical reactor example illustrates the design and performance of the qualitative/quantitative model-based diagnostic system. The proposed approach can also be extended to the multiple-fault situations in a straightforward manner.
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    AIChE Journal 37 (1991), S. 597-606 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The tray hydrodynamics were determined for a system containing water and kerosene as immiscible liquids. Plates with hole diameters ranging from 3.18 to 12.70 mm were used in a 44.5-cm2 perspex air-water-kerosene simulator. Experiments were also carried out in a 50-mm-ID column using different depths of oil and water mixtures to study the drop and bubble mechanisms. A spray-to-bubble transition occurred for the two liquid-phase system experiments. The liquid holdup at the transition increased directly with gas velocity and hole diameter, and decreased with increasing free area. At the same hole velocity, the presence of two liquid phases caused the transition to occur at different liquid holdups than for the single pure liquid. Two different modes of coalescence were observed in the small column work. New correlations have been proposed for the liquid holdup at the transition which allow for the presence of two liquid phases.
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    AIChE Journal 37 (1991), S. 607-616 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The distribution coefficients of the solutes (toluene, naphthalene, and phenanthrene) are reported at infinite dilution between silicone rubber and supercriticalfluid carbon dioxide. A new technique is described in which a thin film of polymer is coated and cross-linked onto silica, and the distribution coefficient is measured rapidly by elution supercritical-fluid chromatography. Because CO2 significantly enhances the solute's volatility and its diffusion coefficient in the polymer, it is possible to study solute-polymer interactions at room temperature for nonvolatile compounds which would be difficult to study by conventional techniques such as gas chromatography. These infinite dilution data are used to determine solutepolymer interaction parameters to calculate phase diagrams over a wide concentration range. The residual, combinatorial, and cross-link contributions to the solute activity coefficient in the polymer are discussed as a function of concentration. In addition, pronounced pressure and temperature effects are described in terms of experimentally measured solute partial molar volumes (to - 14 L/mol) and partial molar enthalpies (to - 850 kJ/mol) in the fluid phase.
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    AIChE Journal 37 (1991), S. 633-635 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    AIChE Journal 37 (1991), S. 636-640 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991) 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 641-649 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ignition, extinction and autothermal behavior of surface and homogeneous oxidation reactions of CH4, NH3, and mixed NH3/CH4 fuel systems in air over resistively heated Pt foils was studied in an atmospheric pressure flow reactor. Also examined were the effects of varying fuel concentration on the ignition, extinction, and autothermal surface temperatures. Heterogeneous ignition occurred at ∼200°C for NH3 and at ∼600°C for CH4. The mixed fuel systems exhibited two surface ignitions (∼200°C and ∼600°C), implying a sequential ignition of the two fuels. The effects of removing one of the fuels during autothermal operation gave results consistent with this hypothesis.In homogeneous ignition, two types of flames were observed: a boundary layer flame associated with NH3 systems and an independent flame observed in all systems. Homogeneous ignition of the two fuels and the mixtures occurred at surface temperatures ranging from 1,100°C to 1,600°C and appeared to be dominated by CH4 in the mixed systems. A generic behavior is proposed for homogenous-heterogeneous combustion of single and mixed fuels.
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    AIChE Journal 37 (1991), S. 650-660 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Condensation-evaporation hysteresis associated with the internal wetting of catalyst particles is examined here by the Kelvin and Cohan equations. It is shown that in the absence of information on the thermal history, it is difficult to predict the extent of internal wetting and the associated reaction rate, for states with partial internal wetting, with the actual rate lying anywhere between the limits specified by the Kelvin and Cohan equations. Hysteresis effects arising from thermal cycling are discussed, and the predictions are shown to agree with the experimental data of Kim and Kim (1981a). Experimentally observed transitions between states with markedly different extents of internal wetting and with associated sudden evaporation or condensation are also rationalized by the theory.
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    AIChE Journal 37 (1991), S. 661-670 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Notes: Gorring (1973) reported a phenomenon, the “window effect,” whereby the diffusivities of normal paraffins within zeolite T do not decrease monotonically with increasing carbon number N, as would be expected intuitively. Rather, following an initial decrease with N, the diffusivities exhibit a local minimum at C8 followed by a pronounced local maximum at C12. This article presents a theoretical analysis of the window effect and related phenomena, based on an analogy of the configurational diffusion process with an “equivalent” one-dimensional Brownian motion of a rod through a periodic sequence of potential barriers. Numerical calculations are found to be in reasonable agreement with Gorring's experimental data and quantify his qualitatively-stated mechanism, namely that n-alkanes longer than C8 are too large to fit entirely within the potential wells formed by erionite cages and therefore experience smaller energetic barriers to diffusion.
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    AIChE Journal 37 (1991), S. 671-678 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Adsorption of a strongly bound absorbate in a bidisperse-pore system is modeled using a Turner pore structure. This idealized system leads to an analytical solution for the micropore uptake of adsorption that is valid for a part of the adsorption-time profile. The analytical solution yields a well-defined criterion that establishes the boundary between an adsorption process dominated by macropore resistance and one dominated by micropore resistance. The range of the analytical solution is extended to include the entire adsorption-time profile using an approximate analytical solution and two asymptotic solutions.
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    AIChE Journal 37 (1991), S. 679-686 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: High-surface-area, Zr-pillared, layered clays are synthesized and characterized for their adsorption properties. Although large free interlayer spacings are claimed in the literature (as also found in this work, 14.3 Å), the limiting pore size is the narrow interpillar spacing. The distribution of interpillar spacing is determined by molecular probing and adsorption data along with a theoretical framework available from the literature. Interpillar spacing can be tailored by controlling the number density of pillars inserted during the ion exchange (oligomer inserting) step. The following variables in the ion exchange solution result in lowering the pillar density: higher pH, lower oligomer concentration, and introduction of competitive cations. By changing these variables, peak interpillar spacing is shifted by nearly 2 Å (from 5 to 7 Å). The versatility of pillared clays as sorbents for kinetic separation (i.e., separation based on diffusivity differences) has been demonstrated by the separations of air and xylene isomers.
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    AIChE Journal 37 (1991), S. 687-693 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The familiar batch concept of extent of reaction is reexamined for systems of reactions occurring in open systems. Because species concentrations change as a result of transport processes as well as reactions in open systems, the extent of reaction has been less useful in practice in these applications. It is shown that by defining the extent of the equivalent batch reaction and a second contribution to the extent of reaction due to the transport processes, it is possible to treat the description of the dynamics of flow through porous media accompanied by many chemical reactions in a uniform, concise manner. This approach tends to isolate the reaction terms among themselves and away from the model partial differential equations, thereby enabling treatment of large problems involving both equilibrium and kinetically controlled reactions. Implications on the number of coupled partial differential equations necessary to be solved and on numerical algorithms for solving such problems are discussed. Examples provided illustrate the theory applied to solute transport in groundwater flow.
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    AIChE Journal 37 (1991), S. 694-704 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Concentration profiles were determined in both phases for the system methyl isobutyl ketone (MIBK) - water-acetic acid in a Kühni 72.45-mm-dia. Extraction column of 25 stages. Mass transfer and backmixing parameters were estimated numerically from the profiles in terms of the backflow model. The results indicated that backmixing of the continuous phase was appreciable, while that of the dispersed phase was negligible. Independent values of the continuous-phase backmixing coefficient, αc, were also determined by both unsteady-state and continuous tracer injection, in the former case both with and without mass transfer. The results indicated that αc is increased by mass transfer, and that the tracer values, both with and without mass transfer, are greater than those obtained from the profile data.
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    AIChE Journal 37 (1991), S. 705-723 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Notes: A major difficulty in control of distillation columns stems from their nonlinear behavior, especially of columns producing high-purity products. Based on a previous development that adapted fixed-bed theories to simple countercurrent processes, this study has established a nonlinear wave theory for the nonlinear and distributed dynamics of binary distillation columns by including the effects of reflux, reboil, and combination of sections. This theory clearly elucidates the intriguing dynamic behavior of distillation columns such as high steady-state gains, large response lags, strong dependence of dynamics on the magnitudes and directions of disturbances, and asymmetric dynamics of the transitions between two steady states. It also underlines the inadequacy of conventional linearized models for high-purity columns. With fairly simple mathematics, this nonlinear wave approach may be useful for model development, control system design, dual-composition control, and feedforward control.
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    AIChE Journal 37 (1991), S. 724-734 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model of the process of polymer devolatilization in a heated slit is presented. Momentum, heat, and mass transfer in the slit are taken into consideration, and only one adjustable parameter is used. The model predicts pressure and temperature profiles, and residual volatile contents at the exit which are in good agreement with those measured in a single instrumented slit.
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    AIChE Journal 37 (1991), S. 735-746 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model of the hydrocyclone, based on the physics of fluid flow, has been developed. The model equations are solved in a computer code that takes as input the hydrocyclone dimensions and feed slurry characteristics. The output of the computer code is the velocity profiles of the fluid and the separation efficiency curve. To validate the model, an LDV was used to measure the velocity profiles inside a 75-mm hydrocyclone. Pure water and glycerol-water mixture were used as the working media to simulate the increase of slurry viscosity in the presence of solid particles. The predicted velocity profiles agree well with the experimental measurements. Dilute limestone slurry was also classified with the same hydrocyclone, and predicted the separation efficiency curve shows good agreement with experimental observation.
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    AIChE Journal 37 (1991), S. 747-758 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Slow rotation of a cylindrical kiln, partially filled with powder or granular solid, produces a planar interface between the bulk of the solid and the gas phase, tilted at the angle of repose. Particles cascade downward on this plane, moving relatively freely and randomly, providing the principal mechanism for particulate diffusion and mixing in the kiln. The plane is also the most favorable location for chemical reactions that require efficient gas-solid heat and mass transfer. Conservation equations are constructed for planar and bulk regions, coupled by the particulate exchange produced by rotation. Sample problems of mixing and heat exchange illustrate problem formulation and useful simplifications. A penetration model predicts wall-to-bed heat transfer coefficients, leading to better agreement with experiment than is obtained when planar processes are omitted.
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    Notes: Uniform submicron crystals of B4C, boron-enriched boron carbide, and B4C/TiB2 composite powders have been synthesized continuously by rapid carbothermal reduction at approximately 2,200 K in a 0.14 m ID × 1.68 m long pilot-scale graphite transport reactor. A unique reactor design allowed for continuous feeding of a meltable boron oxide containing precursor, rapid heating rates that completed the carbothermal reduction reaction in seconds, and an expanded cooling that allowed for the precipitation in space of volatile excess boron oxides. Powder morphology resembled that of powder synthesized by laser pyrolysis of gaseous reactants. Rapid heating rates and minimized reaction times at high temperatures promoted nucleation with limited crystal growth. Dense parts fabricated from these powders had fine grains and extreme hardness.
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    AIChE Journal 37 (1991), S. 781-784 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 769-779 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Notes: Adsorption of air in 5A zeolites was studied using Monte Carlo simulations in the grand canonical ensemble (μ, V, T constant). Site-site potentials were used to model the adsorbate-zeolite and adsorbate-adsorbate interactions. The potential model contains one adjustable parameter that was fit to a single experimental isotherm data point. Adsorption isotherms and heats of adsorption were determined for pure argon, oxygen, and nitrogen at 203.15 K, 233.15 K, and 297.15 K from 0.1 bar to 4.0 bar. Multicomponent adsorption isotherms were determined for binary mixtures of oxygen and nitrogen at 203.15 K. The results for the pure-component isotherms are in excellent agreement with experimental data. The results for the heat of adsorption are in good agreement with experimental data for argon and oxygen, but not for nitrogen. The results for multicomponent adsorption isotherms are qualitatively correct; however, the simulation was not able to quantitatively predict mixture data.
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    AIChE Journal 37 (1991), S. 785-789 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 800-800 
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    AIChE Journal 37 (1991), S. 803-803 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 802-802 
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    AIChE Journal 37 (1991), S. 805-824 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The electrical double-layer free energy is computed numerically for a model colloidal suspension of charged, hexagonally-packed monodisperse cylinders in a symmetric electrolyte solution using the Poisson-Boltzmann equations. Comparison is made to the energies estimated from sums of pair interactions and from two versions of a radially-symmetric cell model: one in which the outer boundary of the cylindrical cell is chosen to make the particle volume fraction Φ in the approximate model agree with that of the full lattice and the other in which the position of the outer boundary is chosen as half the nearest neighbor separation in the lattice. Calculations are performed for ranges of particle volume fractions from infinite dilution to 98% of closest packing, ionic strengths (in terms of the ratio of Debye length to particle radius λ/a) from 0.1 to 10.0, and dimensionless surface potentials and charge densities from 0.1 to 10.0.The pair approximation is valid only when typical interparticle spacings are greater than the Debye length. The first implementation of the cell model proves quite accurate, while the second is only qualitatively correct. The magnitude of particle surface charge density or potential has little effect on these conclusions.
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    AIChE Journal 37 (1991), S. 836-844 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Notes: Equilibrium adsorption data for the N-benzoyl derivatives of D- and L-phenyl alanine in water/propanol solutions have been determined on a chiral-selective stationary phase, bovine serum albumin immobilized on silica. These data are well accounted for by an isotherm equation resulting from the sum of two Langmuir terms. The first term corresponds to the chiral-selective interactions, and the second to the nonselective molecular interactions between the enantiomers and the stationary phase. The individual band profiles of the two enantiomeric amino acids, either pure or in binary mixtures of various compositions, are predicted exactly by an equilibrium dispersive model using this bi-Langmuir isotherm. A classical Langmuir isotherm fails to predict these band profiles, illustrating the importance to collect accurate adsorption data and to use a correct isotherm model when calculating chromatographic band profiles.
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    AIChE Journal 37 (1991), S. 855-862 
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    Keywords: Chemistry ; Chemical Engineering
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    Notes: Extractions using hollow fibers can be faster and more efficient than those in conventional equipment. These advantages, due to the large area per volume possible with fibers, can be compromised by accidental convection through the fibers' pores. When these pores are filled with gels of crosslinked polyvinyl alcohol, convection through the pores is stopped but the overall mass transfer is unaltered. The separations across these gel-filled fiber walls provide excellent yield and purity, especially in the case of fractional extraction.
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    AIChE Journal 37 (1991), S. 931-943 
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    Notes: An important application of the recently developed techniques in qualitative mathematical modeling is to qualitatively predict how changes in the operation of chemical units affect their behavior. Weld (1987, 1988a,b) has developed a series of comparative techniques that analyze the effect of perturbations to the parameters of a given qualitative unit model. In this article we demonstrate a system, based on the qualitative process theory of Forbus (1984), which extends comparative analysis in two ways. First, it predicts the effects of changes in the qualitative equations and in parameter values. Secondly, it compares physical descriptions, rather than comparing models directly, and builds and compares the associated models automatically.
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    AIChE Journal 37 (1991), S. 953-954 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 944-950 
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    Keywords: Chemistry ; Chemical Engineering
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    Notes: Supercritical fluid extraction (SCFE) for the removal of organic toxins from water has been studied using a continuous-flow view cell system. Distribution coefficients (ratio of mole fraction of contaminant in supercritical CO2 to mole fraction in the aqueous phase at equilibrium) have been determined for a homologous series of contaminants as individual components in pure water: benzene, phenol, p-chlorophenol, and m-cresol. Data were obtained at two temperatures (313 and 323 K) and over a pressure range of 9.65 to 17.23 MPa for each contaminant. The distribution coefficients of the contaminants follow a pattern that can be explained in terms of molecular interactions both with water in the aqueous phase (as quantified by the pure contaminant solubility in water) and with CO2 in the SCF phase (as quantified by the pure contaminant solubility in near-critical CO2 and crossover phenomena in SCF CO2). These results have been accurately modeled using a hardsphere, perturbation-theory-based Carnahan-Starling-DeSantis-Redlich-Kwong equation of state and simple van der Waals mixing rules.
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    AIChE Journal 37 (1991), S. 1096-1100 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 1101-1106 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 1109-1112 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 1113-1116 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 1107-1108 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 37 (1991) 
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    AIChE Journal 37 (1991), S. 1121-1128 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The solubility of L-serine in water was measured as a function of temperature, and the solubility in methanol-water solutions was determined as a function of temperature and methanol concentration. Solubility in aqueous solutions was found to be a linear function of temperature. Additionally, a statistical design of experiments was used to identify the kinetic variables that influence the purity of L-serine crystals recovered by batch crystallization. Agitation and the rate at which super-saturation was generated through cooling and methanol addition were found to influence the methanol content of the recovered crystals. The size of the recovered crystals also was found to depend on agitation and the rate at which methanol was added to the L-serine mother liquor.
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    AIChE Journal 37 (1991), S. 1117-1119 
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    AIChE Journal 37 (1991), S. 1139-1150 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An emulsion layer model is presented which predicts the thickness of a downward-moving emulsion layer along the wall of a circulating fluidized bed, the mean solids velocity, and the solids flux in the layer. Also presented is a heat transfer model which, in combination with the emulsion layer model, predicts the low-temperature data very well. An alternate slab model proposed for the radiative component in a high-temperature circulating fluidized bed agrees well with experimental data. The heat transfer predictions of the overall model for such operating parameters as solid circulation flux, suspension temperature, length of the heat transfer surface, superficial gas velocity, and mean particle size are in good agreement with the published data for long surfaces.
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    AIChE Journal 37 (1991), S. 1129-1138 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: For a multitube catalytic reactor in which catalyst occupies the shell side of the cooling tubes, a two-dimensional model is developed to determine the nonuniform radial distribution of the temperature and concentration. The cross-section of the fixed bed is divided into a number of equivalent portions proportional to the number of cooling tubes. Each portion is approximated by either an equivalent annular fixed bed or a transformed circular fixed bed in the complex plane. Enthalpy and mass balances are performed on the equivalent annular fixed bed while the radially varying flow distribution and the transport properties are considered in a transformed circular fixed bed. A correlation is developed for the equivalent annular model based on the relationship of the two different approximations. The model can also account for variations in radial porosity, radial velocity, and transport properties.
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    AIChE Journal 37 (1991), S. 1219-1226 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A correlation was developed to quantitatively describe the flux in a high-speed rotating filtration device using a minimum set of parameters. The experimental results were found to be consistent with the concentration polarization (CP) model. Beyond a threshold pressure flux ceases to depend on membrane permeability. The CP model was modified to include the concentration dependence of the diffusivity. This approach was found to be consistent with the strong dependence of flux on pH. Protein concentration in the polarized layer adjacent to the membrane surface was estimated using a procedure that corrects for some of the inconsistencies in the methods usually applied. Four dimensionless numbers were necessary to correlate the experiments with good accuracy. Previously-reported correlations used only three dimensionless numbers. Usage of four numbers could be justified by dimensional analysis. Finally, the performance of rotary or vortex filtration was compared to that of other configurations.
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    AIChE Journal 37 (1991), S. 1237-1241 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 1318-1332 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A flexible and structured methodology for the computer-aided molecular design (CAMD) by the group contribution approach is presented. The proposed CAMD algorithm takes the following four steps: 1. preselect groups and target properties; 2. generate only a feasible set of compound structures in an optimal fashion; 3. predict properties for the screening of the set of feasible compound structures; and finally 4. select/design the compound. Since the success of any CAMD algorithm depends to a large extent on its ability to predict/compute the needed properties, the importance of the choice and applicability of these methods is considered along with the computational aspects related to the development of a computer program based on the proposed methodology. Finally, the scope of CAMD technology is highlighted using several practical examples.
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    AIChE Journal 37 (1991), S. 1354-1364 
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    Notes: A new steam cracking technology has been developed that uses honeycomb-type ceramic reactors with high surface to volume ratios and is heated by flue gas. “Rectangular” process gas temperature profiles are possible with such a reactor. An optimal combination of temperature profile and residence time leads to a very significant increase in olefins yield with respect to conventional cracking units. Benchscale results are compared with predictions based on a reactor model, which accounts in great detail for the geometry of the structure and the associated heat transfer, combined with a rigorous kinetic model based on radical reaction mechanisms.
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    AIChE Journal 37 (1991), S. 1420-1424 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991) 
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    AIChE Journal 37 (1991), S. 1441-1449 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An expanded liquid molecular thermodynamic model is developed to predict the solubilities of pure solids in a liquid expanded with a gaseous antisolvent. Experimental data are presented for systems containing naphthalene, phenanthrene, and a mixture of both in toluene expanded with a gas antisolvent, CO2. The pressure range is 1 to 64 bar and the temperature is 25°C. The data are predicted accurately with regular solution theory up to moderate pressures, but not at the higher pressures where the liquid phase is nearly pure CO2. In contrast, the new expanded liquid equation of state model describes the wide range of behavior from the nearly ideal liquid solution at ambient pressure to the highly nonideal compressible fluid at elevated pressures. As a result, it predicts solubilities accurately over three orders of magnitude by using only binary interaction parameters. The implications of the phase behavior on fractional crystallization with a gas antisolvent are discussed.
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    AIChE Journal 37 (1991), S. 1425-1436 
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    AIChE Journal 37 (1991), S. 1450-1458 
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    Keywords: Chemistry ; Chemical Engineering
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    Notes: Longitudinal solids mixing was studied experimentally in circulating fluidized bed risers of internal diameter 0.152 m and 0.305 m. Superficial gas velocity and mean solids flux used were 2.8-5.0 m/s and 5.0-80 kg/m2·s, respectively, and the bed solids had a surface volume mean diameter of 71 μm and a particle density of 2,456 kg/m3. A sodium chloride tracer was used in impulse injection experiments. A simple, one-dimensional dispersion model describes measured solids mixing satisfactorily. Peclet numbers (UoL/Dz) found, in the range 1.0-9.0, were correlated with the riser diameter and mean solids flux. The modeling approach described here permits residence time distribution curves to be calculated directly from the knowledge of superficial gas velocity, mean solids flux, and riser diameter. Longitudinal solids mixing in the riser decreased with increasing riser diameter. The results are consistent with recent hydrodynamic studies.
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    AIChE Journal 37 (1991), S. 1471-1484 
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    Keywords: Chemistry ; Chemical Engineering
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    Notes: A model for the photochlorination of methyl chloride in the liquid phase was developed, with numerical solution and experimental verification. The reaction was carried out under pressure, using carbon tetrachloride as a solvent with polychromatic radiation in a nonisothermal tubular reactor. Momentum, thermal energy, mass and photon balances were established rigorously and solved numerically. Reaction constants were taken from the known reaction mechanistic kinetics in the gas phase. Theoretical results agreed well with bench-scale experiments performed inside an elliptical reflector in the prediction of both reactant conversion and product selectivities. The validated model was used to show the existence of significant temperature and concentration gradients inside the reactor, both in the radial and in the axial directions.
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    AIChE Journal 37 (1991), S. 1517-1528 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: It is well known that separation efficiency and solute rejection change when two or more proteins are ultrafiltered. This phenomenon is primarily due to membrane fouling and is not significantly influenced by concentration polarization. If membrane fouling is the dominant resistance, then negative transmembrane pressure pulsing might significantly reduce this barrier.A study was performed to determine the effect of negative transmembrane pressure pulsing on solute rejection for an albumin and gamma-globulin mixture in ultrafiltration. Pulsing improved solute flux for all cross-flow rates investigated including turbulent conditions by as much as two orders of magnitude. Under certain pulsing conditions, substantially higher solute flux was obtained for operations involving increased concentration polarization. This study reveals that negative transmembrane pressure pulsing can be effective in lowering the solute flux resistance that is observed in binary protein mixture ultrafiltration.
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    AIChE Journal 37 (1991), S. 1537-1549 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Electrophoresis is a useful analytic technique for the separation of proteins and other large molecules, but has proven resistant to scale-up to production levels. In this article we describe a new technique that permits the use of much greater feed rates than possible in a conventional electrophoresis unit. The technique, in its simplest form similar to the cyclical field-flow fractionation technique developed by Giddings (1986) and extended by Shmidt and Cheh (1990), relies on the application of an oscillatory electric field across the narrow gap of the electrophoretic cell. The motion of the solute species induced by this field interacts with an oscillatory cross-flow to cause a separation based on the electrophoretic mobility of the species. This horizontal separation is combined further with a gradient in the strength of the oscillating electric field and oscillations in the vertical downflow to lead to different steady streamlines for species with different mobilities.
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    AIChE Journal 37 (1991), S. 1733-1736 
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    AIChE Journal 37 (1991), S. 1737-1738 
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    AIChE Journal 37 (1991), S. 1738-1738 
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    AIChE Journal 37 (1991), S. 1739-1743 
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    AIChE Journal 37 (1991), S. 1744-1748 
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    AIChE Journal 37 (1991), S. 1749-1752 
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    AIChE Journal 37 (1991), S. 1753-1757 
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    AIChE Journal 37 (1991), S. 1780-1788 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most existing criteria for predicting parametric sensitivity or runaway in a catalytic reactor are based on a single-phase model that does not account for interparticle heat and mass transfer resistances and intraparticle diffusion. Accounting for these effects, the simple criterion \documentclass{article}\pagestyle{empty}\begin{document}$$\frac{E}{{RT_f }}\frac{{(- \Delta H)r(T_f,C_f)}}{{T_f }}\left[{\frac{{d_t }}{{4U}} + \frac{{d_p }}{{6h}}} \right] 〈 0.368f(\phi _0)$$\end{document} defines the boundary of operating conditions, in which a catalytic reactor is insensitive to small perturbations. Here, r(Tf,Cf) is the intrinsic reaction rate at inlet conditions, dt(dp) and U(h) are the diameter of reactor tube (catalyst particle) and heat transfer coefficient between the fluid and tube wall (catalyst particle), respectively. The function f(φ0), where φ0 is the normalized Thiele modulus at inlet conditions, accounts for the effects of intraparticle diffusion. For the common case of equal coolant and feed temperatures, f(φ0) = 1 for φ0 〈 0.5 and f(φ0) = 2 φ0 for φ0〉0.5. The conservatism associated with the above criterion is comparable to the uncertainty involved in determining the parameters of the packed bed.
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    AIChE Journal 37 (1991), S. 1825-1832 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of flow nonuniformities existing near the distributor of a liquid fluidized bed containing very low-density particles (ρs = 1.05 g/mL) has been investigated experimentally. Immobilized enzyme or cell bioreactors operated as liquid fluidized beds often employ low-density particles as the support matrix containing the immobilized biocatalyst. With poorly designed multihole distributors, dead zones can be created which seriously undermine the performance of the bioreactor due to the lack of nutrients. Design guidelines are provided for distributors to minimize the inlet flow disturbances, and hence eliminate potential distributor region problems. As a result, the dispersion model, which is normally used for design purposes, can then be applied.
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    AIChE Journal 37 (1991), S. 1833-1843 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An experimental study of the dynamics of electrodissolution of iron in sulfuric acid is reported. The experiments were done under potentiostatic conditions with a rotating disk electrode as a function of two parameters, potential and electrode diameter. The dynamic behavior depends strongly on the latter parameter; with increasing electrode size we observe transitions from periodic oscillations to low-order chaos to higher-order chaos. The attractor dimension increases with increasing electrode size. In addition, for the large electrodes at more positive potentials, a secondary higher frequency oscillation also arises.
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    AIChE Journal 37 (1991), S. 1-38 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: As steady-state and dynamic simulators with optimal controllers have evolved, tools for nonlinear analysis have been developed by reactor and thermophysical property specialists. Designers lag behind in developing and utilizing these tools, as many design strategies assume idealized behavior even though processes contain an increasing number of nonlinear elements. This article examines the sources of the nonlinear elements, often associated with physical and chemical interactions, in designs and their control systems. Promising methods for nonlinear analysis are reviewed.In each design activity, involving simulation, economic optimization, projections of controllability and operability, emphasis is on the sources of nonlinearities and solution methods. These are examined for the equality constraints and nonlinear programs in phase and chemical equilibria, in reactors and separators, and in the simulation and optimization of flowsheets. Also examined are the impact of non-linear predictive control in screening designs and methods to insure operability, in the face of uncertainties.
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    AIChE Journal 37 (1991), S. 65-73 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Common models for excess Gibbs energy account primarily for physical forces and do not represent strong specific interactions. However, purely chemical models neglect strong nonspecific forces and combined chemical-physical treatments involve an unreasonable number of adjustable parameters. One way to ameliorate this limitation is to make independent measurements of the parameters by a nonther-modynamic technique. We report an investigation of hydrogen bonding, a localized and very directional specific interaction, conducted in various alcohol mixtures using Fourier transform nuclear magnetic resonance to measure the number of complexed species in solution. A chemical-physical association model with variable equilibrium constants has been developed. The distinguishing feature of this model is that the species in solution do not have equal probability of forming yet require only a single chemical interaction parameter determined from fitting NMR data and a physical interaction parameter determined from infinite dilution activity coefficients. The AVEC model successfully predicts vapor-liquid equilibrium and excess enthalphy as well as liquid-liquid equilibrium, an especially stringent test.
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    AIChE Journal 37 (1991), S. 310-310 
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    Keywords: Chemistry ; Chemical Engineering
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