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  • 1985-1989  (41,782)
  • Chemistry  (41,782)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Aquatic sciences 51 (1989), S. 108-128 
    ISSN: 1420-9055
    Keywords: Chemistry ; mountain lakes ; silica ; acidity ; sediment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Alpine lakes in siliceous catchments of Tyrol and Carinthia (Austria) show signs of acidification. About 9% of the studied lakes have no alkalinity, more than 20% are below pH 6. About two thirds of all lakes have acid neutralizing capacities below 100 μeq 1−1. In spite of moderate precipitation acidity, some lakes show considerable concentrations of dissolved reactive aluminum during or shortly after snowmelt. High altitude lakes of the Alps are definitely more acidic than high mountain lakes in remote areas. Large differences in water and soil chemistry of nearby situated lakes were attributed to heterogeneities of bedrock geology. Paleolimnological investigations on former pH values of five lakes, based on diatom assemblages in the sediment, showed different developments: recent and past acidification, stable conditions, and alkalinization.
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 279-286 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In order to describe the translational diffusion of polymers in dilute solution, an elastic dumbbell model is used for which the effects of both hydrodynamic interaction and a nonlinear connector force are treated in a self-consistently averaged form. For this model, the diffusion tensor in the presence of a homogeneous flow field is obtained from (i) the mass flux caused by concentration gradients, (ii) the average polymer velocity caused by external forces, and (iii) the mean-square displacement of a polymer caused by the Brownian forces. From the second and third approaches the same expression for the diffusion tensor is found, whereas a different expression is obtained from the first approach. This means that the Nernst-Einstein equation cannot be generalized to the case of flowing solutions. The model predictions for the diffusion tensors in steady shear flow are discussed in detail.
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  • 4
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    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 311-313 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 373-384 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Steady states with different flow rates and temperature profiles may exist in different tubes of a multitube packed-bed reactor due to the coupling among the species, energy and momentum balances, and the change of physical properties with temperature and pressure. Under typical operating conditions if no axial conduction of heat occurs thermoflow multiplicity can be found only for unrealistically high heats of reaction and/or over a very narrow range of exit pressures. However, accounting for the finite but small heat conduction in the reactor tubes leads to multiplicity for typical parameters and a reasonable range of exit pressures. Cooling tends to decrease the region of parameters for which the multiplicity occurs.
    Additional Material: 16 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 385-392 
    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 model is developed for fluid-solid reaction kinetics in a porous solid. The model is based on a convergent-divergent pore structure and accounts for pore blockage and inside cavities. A numerical study applied the model to the process of coke removal for catalyst regeneration. The calculated results show that in the presence of pore occlusion, the reaction rates are significantly reduced at the beginning of reaction. At higher levels of coke loading the reaction behavior can be especially affected by the volume fraction of the divergent pores. This behavior can be used to select catalysts with pore structures that improve control of the regeneration process.
    Additional Material: 11 Ill.
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  • 8
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 365-372 
    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 approximate equations of Hassler and Brunner and of van Domselaar are often used to deduce the capillary pressure curve of a porous medium from centrifuge data. The use of these equations restricts the centrifuge method to short samples. Also, these equations require differentiation of data. We report here methods to determine the capillary pressure curve by the midpoint and least-squares solution of the fundamental equation, relating the average saturation S1 of liquid in the porous medium to the capillary pressure Pc1 at the end of the sample nearest the axis of rotation. The methods do not require differentiation of data and are not restricted to short samples. We introduce and evaluate an approximation based on an exact result derived by Rajan. This new approximation requires the same inputs as do the Hassler-Brunner and the van Domselaar approximations, but it is accurate over a wider range of sample sizes. In addition, an approximate solution which can be used to estimate capillary pressure curves for long cores is developed.
    Additional Material: 6 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 423-428 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A technique based upon transmission FTIR to obtain rate constants for adsorption and desorption over supported metal catalysts has been developed and tested. The technique requires the use of a sinusoidal perturbation function imposed on steady state linearized adsorption-desorption kinetics. The measurement of a phase lag between the sinusoidal inlet gas phase forcing concentration and the response of surface coverage, together with a measurement of the maximum amplitudes of the forcing function and surface response enable the calculation of the relevant adsorption and desorption rate constants.The technique has been successfully applied to the measurement of both adsorption and desorption rate constants for CO adsorbed on a 1% Pt/SiO2 catalyst. The values obtained for these rate constants at 343 K were: Ka = 0.147 s-1 and Kd = 7.28 × 10-3 s-1. A sticking coefficient corresponding to the adsorption of weakly bonded CO on Pt under conditions of high CO surface coverage was obtained.
    Additional Material: 5 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 490-499 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Orthogonal collocation is used to analyze the dispersion and chemical conversion of a multicomponent fluid pulse in a laminar isothermal flow in a catalytic tube. Homogeneous and heterogeneous first-order chemical reactions are included, and a full matrix diffusion law is used. The collocation method represents the dynamics well over wide ranges of system parameters and reaction time. Radial averaging approaches prove less convenient, since the dispersion coefficients thus introduced are complicated functions of time, transport properties and chemical kinetics.
    Additional Material: 4 Ill.
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  • 11
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    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 514-518 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 30-36 
    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 simple one-dimensional mathematical model validated with high-temperature entrained-flow reactor data successfully explained dispersed calcium hydroxide particle surface area evolution resulting from concomitant calcination and sintering. An integrated first-order calcination rate expression and a second-order sintering rate form accurately predicted time-resolved surface area generation and degradation. The effects of water vapor and gaseous carbon dioxide concentration on asymptotic specific surface areas and sintering rates were noted. This methodology for predicting sorbent surface area evolution will enable more accurate sulfation modeling efforts in furnace sorbent injection (FSI) applications, where calcination, sintering, and sulfation can all occur on the same time scale.
    Additional Material: 7 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 69-74 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Certain nonfunctional macroreticular polymeric adsorbents are nonwet by suffciently dilute aqueous solutions and enable separations not achievable with adsorbents in the prewet state. Fixed-bed adsorption data were obtained for a multisolute aqueous solution containing acetic acid, 1,3-butanediol, and succinic acid, with Porapak Q and Amberlite XAD-4 as adsorbents in both the prewet and nonwet states. The prewet breakthrough data agree with a model allowing for axial dispersion and a linear rate law, using independently estimated parameters. Break-through curves for the nonwet case depend strongly upon solute volatility since mass transport within the particles appears to occur by Knudsen diffusion, and is rate limiting. Data for Porapak Q reflect an effective particle diffusivity about ten times lower than for Amberlite XAD-4.
    Additional Material: 5 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 97-103 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Given the intrinsic kinetics, the tortuosity factor of a Ni/MgAl2O4 catalyst was determined under reaction conditions by minimizing the sum of squares of residuals of the experimental and the simulated conversions. The parallel cross-linked pore model with uncorrelated pore size distribution and orientation was used in the calculation of the effective diffusivities. A modified collocation method was used to obtain the partial pressure profiles of the reacting components in the catalyst pellet. The simulation of the experimental reactor during the optimization of the tortuosity factor also yielded the effectiveness factors of the reactions. The results of the simulation of an industrial steam reformer are also discussed.
    Additional Material: 7 Ill.
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  • 15
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 104-108 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Particle to gas heat transfer studies were carried out for the exothermic benzene hydrogenation and endothermic cyclohexane dehydrogenation reactions on the same catalyst bed. A recirculation type reactor and eggshell type commercial platinum on alumina catalyst were used. When the thermodynamic value for the heat of reaction is used for both reactions in the steady-state energy balance, local JH factors for the exothermic reaction were found to be, in general, higher than those for the endothermic reaction. This was attributed to product molecules leaving the catalyst surface with excess vibrational energy, which implies that the actual heat of reaction would be different than the thermodynamic value used in the JHfactor calculations. The study also indicated significant variations in the local JH factors; these were attributed to variations in the linear velocity in the radial direction.
    Additional Material: 7 Ill.
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  • 16
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 592-602 
    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 model is introduced for analyzing diameter variations occurring in glass fibers drawn from preforms. The heat transfer is shown to be radiation-dominated, and approximate expressions for radiative exchange are developed. The expressions are used in the one-dimensional governing equations for extensional flows to derive a set of linearized disturbance equation as an eigenvalue problem. The sensitivity to an oscillatory take-up rate is also studied as a boundary-value problem. Calculated amplitudes of final diameter perturbations are found to agree well with experimental values.
    Additional Material: 7 Ill.
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  • 17
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    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 614-624 
    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 Galerkin finite-element method is used to study the rotating, thermocapillary fluid flow in the cylindrical float zone configuration for crystal growth. Results are presented for a fluid of Prandtl number 1.0 in a zone of unit aspect ratio under microgravity conditions. In the absence of rotation, the thermocapillary flow is responsible for large radial non-uniformities in the heat transfer, especially at the cold boundary. A sufficiently strong uniform corotation of the end rods leads to a rigid rotation of the fluid in the interior of the zone; in this case, the thermocapillary flows are considerably attenuated and confined to a region near the free surface of the zone. This provides a more uniform thermal environment over the bulk of the crystal-melt boundary, which is a very desirable processing condition. When the end rods are counterrotated, inertially driven meridional flow cells appear in the zone. The interaction of the rotational forced convection with the thermocapillary flow causes the region of the local heat transfer minimum at the cold boundary to gradually shift away from the axis of the zone toward the meniscus.
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  • 18
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 875-875 
    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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  • 19
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 666-669 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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  • 20
    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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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 876-876 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 22
    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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  • 23
    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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  • 24
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 923-930 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper presents an efficient method for the design of controllers for integrating and runaway processes. The method is based on model matching in the frequency domain. The presence of open-loop instability as well as pure time delay in the process models make the design task challenging for these classes of processes.The goal is to achieve low-order, easily implementable cascade controllers in a unity-output-feedback configuration. It is shown that the central problem is in the selection of appropriate reference models. Several key constraints are developed which relate a given process model to a class of reference models for achieving total stability. Typical design examples are presented to clearly illustrate the various mathematical techniques.
    Additional Material: 6 Ill.
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  • 25
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 415-422 
    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 non-Newtonian viscosities of polymerically stabilized colloidal suspensions are usually predicted and correlated on the basis of data and scaling principles for Brownian hard spheres. Here, the specific effect of the stabilizer layer is investigated using suspensions of monodisperse PMMA particles with a chemically attached stabilizer layer. The ratio between particle radius and stabilizer layer thickness is changed between 5 and 61. At high values of this ratio the data show Brownian hard sphere behavior. At lower values deviations appear. As a first approximation, the “softness” of the particles can be characterized through the concentration at maximum packing. A more detailed comparison with hard sphere data provides a measure for softness that changes with concentration and shear rate. A theoretical estimate of the concentration effect is in line with the experiments. The critical shear stress (or Peclet number) is not a constant but goes through a maximum when the concentration is increased.
    Additional Material: 7 Ill.
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  • 26
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 908-922 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Erosion in bubbling fluidized-bed combustors is a serious issue that may affect their reliability and economics. Available evidence suggests that the key to understanding this erosion is detailed knowledge of the coupled and complex phenomena of solids circulation and bubble motion. A thin transparent “two-dimensional” rectangular fluidized bed with an obstacle served as a rough model for a fluidized-bed combustor. This model was studied experimentally and computationally using two hydrodynamic equation sets. The computed hydrodynamic results agree reasonably well with experimental data. Bubble frequencies and sizes compare well with those obtained from analyzing a high-speed motion picture frame-by-frame. Time-averaged porosities computed from both models agree with time-averaged porosity distributions measured with a gamma-ray densitometer. The principal diferences between the data and the computations in this paper are due to asymmetries present in the experiment and to the simplified solids rheology used in the hydrodynamic models.
    Additional Material: 13 Ill.
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  • 27
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 951-958 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Models are developed for isothermal desorption in a fixed bed of adsorbent particles. While more general models require numerical solution of the governing equations, two practically important cases have analytical solutions: (1) an equilibrium desorption model where the rate of desorption is controlled by external and intraparticle mass transfer; and (2) a kinetic model where external and intraparticle mass transfer and a first-order irreversible desorption step control the overall process.Recent experimental data (Tan and Liou, 1988) for the desorption of ethyl acetate from activated carbon with supercritical carbon dioxide are found to fit the local-equilibrium model. Data for the effect of temperature on fractions desorbed indicate a reversal of the temperature dependence of the adsorption isotherm as the supercritical pressure is increased. This phenomenon is analogous to the observed cross-over region for the effect of temperature on the solubility of a solid at supercritical conditions.
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  • 28
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 988-994 
    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 extent of high temperature (900-1,300°C), short time (〈1 s) SO2 capture was found to be limited by temperature-dependent losses in the porosity of calcium based sorbents. At 970°C these porosity losses were caused by CO2-activated sintering. Sulfation of the sorbents either prevented or reduced the extent of porosity losses. Differences in SO2 capture between hydroxides from different commercial sources, and significantly lower levels of capture by calcium carbonates compared to hydroxides were attributed to differences in particle size and the degree of porosity loss.
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  • 29
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 1017-1028 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Systems having transfer functions of the form \documentclass{article}\pagestyle{empty}\begin{document}$$ G_P (s) = \frac{{P_1 (s) - P_2 (s)e^{ - t_d s} }}{{Q(s)}}, $$\end{document} where P1(s), P2(s) and Q(s) are polynomials, are called quasirational distributed systems (QRDS). They are encountered in processes modeled by hyperbolic partial differential equations. QRDS can have an infinity of right half-plane zeros which causes large phase lags and can result in poor performance of the closed-loop system with PID controllers. Theory on the asymptotic location of zeros of quasipolynomials is used to predict the nonminimum phase characteristics of QRDS and formulas are presented for factoring QRDS models into minimum and non-minimum phase elements.A generalized Smith predictor controller design procedure for QRDS, based on this factorization, is derived. It uses pole placement to obtain a controller parameterization that introduces free poles which are selected to satisfy robustness specifications. The use of pole placement allows for the design of robust control systems in a transparent manner. Controller selection is generally better, simpler and more direct with this procedure than searching for optimal PID controller settings.
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  • 30
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 523-526 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 7 Ill.
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  • 31
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 549-558 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Configuration of feedback loops between input and output variables of a given plant constitutes a subtask of control system synthesis. In the past, this subtask has been tackled through direct decomposition of either the process or the set of input-output variables. Linear interaction analysis has been used in both approaches to assess and minimize sub-system interactions. Since most chemical processes exhibit nonlinear behavior, it is evident that a measure is needed for assessment of interactions in the presence of system nonlinearities. In this paper we focus on input-output variable set decomposition and introduce the notion of nonlinear block relative gain (NBRG) as a nonlinear interaction measure. Both the statistic and dynamic versions of NBRG are discussed, and a computational procedure is presented for their evaluation. Direct simulations on a CSTR verify the interactions predicted by NBRG for different feedback configurations. Moreover, nonsymmetry of the effect of one loop on another, a fact not captured by the linear BRG, is accurately predicted by NBRG.
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  • 32
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 579-591 
    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 infinite-horizon, discrete-time optimal averaging level control problem for surge tanks, with minimization of the rate of change of outlet flow as its objective, is formulated and a solution is presented. A finite moving-horizon approximation is introduced and analytical solutions are obtained for two important special cases. These results provide a quantitative measure of the impact of a secondary objective, integral action, on flow filtering. The problem is then generalized to include nonconstant level and outlet flow constraints. A model predictive control formulation is presented which addresses the objectives of the generalized problem. The resulting controller minimizes the maximum rate of change of outlet flow, provides integral action, and handles constraints on the tank level and outlet flow rate. The proposed controller includes a single adjustable parameter that directly effects the trade-off between the incompatible objectives of good flow filtering and rapid settling time. Examples are presented to demonstrate the properties of the model predictive controller. An implementation, involving imbedded feedback, is developed which guarantees internal stability of the model predictive scheme for open-loop unstable processes (such as integrators).
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  • 33
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 645-648 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 34
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 1245-1252 
    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 rates of reduction of hematite to magnetite and of magnetite to iron in hydrogen / nitrogen / water vapor atmospheres were each studied with respect to variation in temperature, gas composition, and solid pore structure. It is shown that at temperatures below 350°C, the reactions are under chemical kinetic control, and diffusional limitations are negligible. The activation energies for the reduction of hematite to magnetite and of magnetite to iron were found to be 185 kJ / mol and 76.6 k J / mol, respectively. Both reactions exhibit first-order behavior for hydrogen partial pressures less than 76 kPa. The conversion and rate data for each reaction were interpreted in terms of the random pore model of Bhatia and Perlmutter (1980), which takes into account the detailed pore structure of the starting material as well as the changes that occur as the reaction proceeds. The model predictions of conversion with time agree with the measured data to within 2%, and the rate vs. conversion predictions agree to within 5%.
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  • 35
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    AIChE Journal 35 (1989), S. 1282-1292 
    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 macroscopic model based on the volume-averaged equations of motion is presented for countercurrent gas-liquid flow in a packed bed. The model yields a column-limited flooding point as the loss of existence of uniform states. It correctly predicts the existence of two uniform states below the flooding point. The lower branch corresponds to the trends commonly observed experimentally. It is shown that the upper branch is made unattainable by the gas distributor/support plate at the bottom of the column. The occurrence of premature flooding induced by the support plate is also explained. It is suggested that the occurrence of spontaneous liquid segregation, necessitating frequent liquid redistribution in columns with large dumped packings and porosities, is a consequence of the loss of stability of the uniform state in the lower branch.
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  • 36
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989) 
    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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  • 37
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    AIChE Journal 35 (1989), S. 1227-1228 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 38
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    AIChE Journal 35 (1989), S. 1263-1270 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When the ratio of the drop radius to the distance separating any two drops and the relative importance of gravitational to surface forces are both small, the small amplitude oscillations of a drop of one viscous fluid immersed in another fluid are governed by the nonlinear dispersion relation derived by Miller and Scriven (1968). The dispersion relation has been solved numerically to determine the character of oscillations for arbitrary values of drop size, physical properties of the two fluids, and interfacial tension. The new theoretical results determine the range of validity of the low-viscosity approximation of Miller and Scriven, and are also shown to be essential for proper interpretation of many previously reported experimental results. New experimental measurements of natural frequencies of oscillation of water drops falling in 2-ethyl-1-hexanol, a system having properties characteristic of many others in solvent extraction, agree well with the theoretical predictions when drop radius is smaller than a critical size. The frequencies of oscillations of larger drops are better described by the dispersion relation due to Subramanyam (1969), which accounts for the relative motion of the two phases.
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  • 39
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    AIChE Journal 35 (1989), S. 1304-1314 
    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 laser-Doppler velocimeter (LDV) was used in a cold-flow study of a simulated entrained-flow coal gasifier. The study was designed to provide fundamental information about the flows in such a gasifier and to provide data for the validation of a turbulence submodel used in modeling combustion processes. Measurements in 20 swirling and nonswirling flow cases were made with several levels of replication. This study emphasized the effects of inlet conditions on flow properties within the simulated reactor.Unsteady flow phenomena with time scales on the order of seconds to minutes were sometimes observed. The unsteadiness was apparently associated with relaminarization-type flow transitions.Comparisons were made with model predictions from PCGC-2, a model for combustion processes based on the k,  -  ∊ turbulence model. Several areas of weakness in the model results were observed, but the unusual flow regimes measured in this study may be beyond the abilities of practical computer models.
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  • 40
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    AIChE Journal 35 (1989), S. 1409-1427 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Supercritical fluids (SCF's) are powerful solvents with many unique properties. They have great potential for many extraction processes, but reliable and versatile mathematical models of the phase equilibrium thermodynamics are needed for their use in process design and economic feasibility studies. This paper reviews existing experimental data and analytical methods and attempts to delineate their strengths and limitations. Also discussed are new data needs and possible new directions for a better fundamental understanding of the molecular processes in SCF solutions.
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  • 41
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    AIChE Journal 35 (1989), S. 1457-1464 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Parameterization with respect to the aqueous reflux ratio has been carried out for the steady-state analysis of a tower to dehydrate secbutanol using disecondary butyl ether as the entrainer. With an equilibrium-stage model, singularities are observed as the second liquid phase is introduced on the trays and regions of steady-state multiplicity are demonstrated. Furthermore, a critical aqueous reflux ratio, in the vicinity of which two liquid phases are introduced on most of the trays, varies only slightly with the number of trays in the tower. The model predicts that the product purities and recoveries remain high using one-third of the trays in the industrial SBA-II tower. Bifurcation analysis for a single stage does not explain these observations, and the effect of recycle is suspected.
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  • 42
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    AIChE Journal 35 (1989), S. 1403-1404 
    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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  • 43
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    AIChE Journal 35 (1989), S. 1445-1456 
    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 kinetics of a semibatch melt transesterification of dimethyl terephthalate (DMT) with ethylene glycol (EG) is studied with zinc acetate as a catalyst. This paper quantifies the effect of various reactor operating conditions on the transesterification rate and the product composition distribution. Our experiments support the assumption that the methylesters in DMT and growing oligomer chains have the same reactivities for transesterification with EG and that the reactivity of hydroxyl groups in pure EG for esterification with DMT is twice that of the hydroxyl group in oligomers. With a molecular species model in which various oligomers are identified by the type of functional end groups, the progress of the transesterification and the oligomer concentration distribution were estimated and the agreement between the model predictions and the experimental data were excellent. It has also been shown that 30 wt. % of oligomers are produced for [EG]/[DMT] molar ratio of three, and up to 70 wt. % oligomers are produced at the [EG]/[DMT] molar ratio of one.
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  • 44
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    AIChE Journal 35 (1989), S. 1487-1496 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This work presents a phenomenological correction to improve a classical equation of state for representing phase equilibria and densities in the vapor-liquid critical region. This correction consists of two steps. The first step is a volume translation which locates the correct critical point; this volume translation also improves density predictions for pure fluids and mixtures. The second step provides a near-critical contribution to the residual Helmholtz energy which accounts for aomalous behavior near the critical point. For pure fluids, the near-critical contribution flattens the coexistence curve and pressure-density isotherms near the critical point. For mixtures, the near-critical contribution has only a small effect on the calculated coexistence curve; this effect is often masked by the choice of binary parameters in the classical equation which have a more profound effect on the calculated results.
    Additional Material: 11 Ill.
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  • 45
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    AIChE Journal 35 (1989), S. 1585-1591 
    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 simple design technique for heterogeneous distillation columns has been developed. The underlying geometric conditions which govern minimum reflux are shown to share certain common features with homogeneous distillations, but differ in some important respects. It is shown that heterogeneous columns display some unusual sensitivities to the design parameters. The most notable being the drastic swings in the composition and temperature profiles with very small changes in the level of trace impurities in the product stream.
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  • 46
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    AIChE Journal 35 (1989), S. 1631-1638 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Calculations of the ionization constant of H2O are presented for densities ranging from those of subcritical water to those of supercritical steam. A recently-proposed semicontinuum model is used to calculate the standard-state hydration properties for the ions, H3O+, and OH- (Tanger and Pitzer, 1989). Calculated ionization constants are in good agreement with reported measurements at pressures from vapor-liquid saturation to 500 MPa and temperatures from 273 to 1,073 K. These measurements cover H2O densities ranging from ∼ 1,000 to 450 kg · m-3. At H2O densities less than 400 kg · m-3, our calculated ionization constants should be more reliable than those obtained from the commonly-used equation of Marshall and Franck (1981).
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  • 47
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    AIChE Journal 35 (1989), S. 1659-1666 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental results are reported for equilibrium adsorption and diffusivities of CH4, C2H6 and CO2 in type A zeolite containing mixed Na and K cations ranging from 0 to 100% in composition, at two temperatures and 1 atm. Two simple theoretical solutions are given for the diffusivity. One is for diffusion with pore (aperture) blocking using the effective medium approximation, which is readily available from the literature on percolation theory. The other is a kinetic solution derived in this work for cavities containing heterogeneous sites, which is a case where the percolation theory is not applicable. The equilibrium adsorption results show that K+ has a preference for the aperture (or pore-blocking) sites (site type II), and these results are interpreted by the bond percolation theory. The diffusivity results are successfully interpreted by the poreblocking theory in zeolites containing less than 25% K+ and by the kinetic theory for zeolites with higher K+ contents.
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  • 48
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    AIChE Journal 35 (1989), S. 1044-1048 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 9 Ill.
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  • 49
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    AIChE Journal 35 (1989), S. 1049-1052 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 50
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    AIChE Journal 35 (1989), S. 1509-1520 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Differences in the dispersion and/or catalytic pellet size between laboratory and commercial reactors, operating at the same average residence time, may lead to differences in the yield of a desired product. Bounds are developed for predicting the maximal design uncertainty introduced by these phenomena for a network consisting of an arbitrary number of irreversible first-order reactions. A major advantage of these bounds is that they do not require any knowledge of the rate constants. It is shown that in a packed-bed reactor, the fractional yield loss is smaller than: \documentclass{article}\pagestyle{empty}\begin{document}$$ 0.5{\rm }(m - 1){\rm }\left[{\sigma _\theta ^{\rm 2} + \left({1.2 + \frac{2}{{Bi_m }}} \right)p^2 } \right] $$\end{document} where m - 1 is the number of reaction steps involved in converting a reactant to the desired product, σθ2 is the dimensionless variance of the residence time density function, Bim is the Biot number, p2 = [(Vp/Sx)2(1/Deτ)], and τ is the average residence time.
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  • 51
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    AIChE Journal 35 (1989), S. 1791-1802 
    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 kinetics of the char-steam gasification reaction and the accompanying pore structure changes have been investigated experimentally and interpreted through the use of the random pore model of Bhatia and Perlmutter (1980) and its extensions developed in this study. To allow model evaluations, surface areas and pore-size distributions were obtained for various partially-reacted char samples. Surface areas follow the reaction rates as a function of conversion, supporting the interpretation that the reaction of porous char with steam is governed by the structural changes that occur as conversion proceeds. Reaction rate constants were obtained from the kinetic data.A pyrolytic change of char mass was observed during the heatup period from room temperature to reaction temperature for each of the two char samples tested. This results in a significant increase in surface area and a decrease in pore structure parameter. It is shown that this pore structure parameter is very sensitive to changes in conversion when the initial parameter is large and the conversion is small.
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  • 52
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    AIChE Journal 35 (1989), S. 1602-1616 
    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 systematic method for synthesizing feedforward/state feedback controllers for a broad class of SISO nonlinear systems with measurable disturbances is presented. Depending on the structural characteristics of the system, the control law can be static or dynamic. The closed-loop system is independent of the measurable disturbances and linear with respect to set point changes. The performance of the proposed control scheme is illustrated through an example of composition control in a system of three CSTR's in series.
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  • 53
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    AIChE Journal 35 (1989), S. 1625-1630 
    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 final properties and end use of many organic solids often depends on their crystal-size distribution (CSD), e.g., bioavailability for pharmaceutical solids. The objective of this study was to develop an alternate technology for crystallizing and manipulating size distribution of organic solids by crystallization from supercritical fluids. Such a technology might be superior to conventional-size manipulation techniques, such as milling and recrystallization from organic solvents, which might contaminate the products and affect their physical-chemical stability. Supercritical carbon dioxide was used as solvent to dissolve and then crystallize benzoic acid. A batch crystallizer was constructed and operated in the supercritical region. Seeded and unseeded crystallization experiments were performed. Different depressurization vs. time profiles for the supercritical fluid were used to produce crystals of various sizes.
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  • 54
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    AIChE Journal 35 (1989), S. 1210-1210 
    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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  • 55
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    AIChE Journal 35 (1989), S. 1912-1914 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
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  • 56
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    AIChE Journal 35 (1989), S. 1921-1926 
    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 assumption commonly, but by no means universally, made in the stability analysis of the homogeneously fluidized state is that the pressure field may be well approximated by its gravitational component alone. This assumption is critically examined: the results indicate that it is valid for most cases of practical interest but can lead to significant discrepancies for liquid fluidization of low-density particles.
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  • 57
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    AIChE Journal 35 (1989), S. 2029-2032 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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    AIChE Journal 35 (1989), S. 1749-1752 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 6 Ill.
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  • 59
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    AIChE Journal 35 (1989), S. 2058-2060 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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  • 60
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    AIChE Journal 35 (1989), S. 1975-1979 
    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 model is developed describing consecutive gas-solid reactions occurring in porous media. The model calls for independently measurable parameters and predicts two maxima in the reaction rate at intermediate conversions. The low temperature (350°C) reduction of hematite to iron in a hydrogen-nitrogen atmosphere was used to test the model. The experimental data confirmed the expected rate maxima. The conversion predictions are very close to the data for conversions below 30%, but are systematically somewhat lower than the experimental values for higher levels of conversion. An explanation for the discrepancy is offered in terms of the description of the pore structure.
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  • 61
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    AIChE Journal 35 (1989), S. 1980-1992 
    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 study was made of phenol degradation by bacteria immobilized onto particles of calcined diatomaceous earth in a draft-tube, three-phase fluidized-bed reactor.A mathematical model is used to describe simultaneous diffusion and reaction of oxygen and phenol in the reactor. Kinetic parameters for the growth of nonsupported cells were obtained in batch and chemostat experiments. Liquid-solid mass transfer coefficients were determined experimentally and showed good agreement with literature values for conventional three-phase fluidized beds. Experimental steady-state degradation data were used to calculate biofilm substrate diffusivities. These were found to decrease as the biofilm density increased.The transition from phenol to oxygen-limiting biofilm kinetics predicted by the model was shown to exist experimentally. A critical ratio of phenol/dissolved oxygen concentration was found at which this transition occurred. This provides a criterion for establishing whether increased aeration will increase the volumetric degradation rate.
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    AIChE Journal 35 (1989), S. 1876-1882 
    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 precipitation of organic particles from supercritical fluids (SF) by expansion (SFX) has become an interesting alternative to milling without thermal decomposition. Through the rapid expansion process, a dramatic change of the solute supersaturation ratio is created causing subsequent precipitation with a narrow particle-size distribution. It was found that β-carotene precipitates from SF ethylene and ethane have the feed material crystallinity. However, SF CO2 reacted with β-carotene and did not give characteristic β-carotene X-ray spectra. The mean particle sizes of these precipitates were in the submicron range (ca 0.3 μm). Increased solubility was obtained by addition of toluene as cosolvent in SF ethylene. It was found that the mean size of β-carotene particles, generally remained unchanged if the toluene concentration was less than 11/2 mol %. The SFX process appears to be in a single fluid phase when up to 11/2 mol % toluene cosolvent is used.
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    AIChE Journal 35 (1989), S. 2037-2039 
    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 35 (1989), S. 2053-2057 
    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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  • 65
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    AIChE Journal 35 (1989), S. 1907-1911 
    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 35 (1989), S. 1933-1941 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Many industrial proceses require the circulation of particles between reacting fluidized compartments at a stable, but flexible rate, so that the processes can be operated at different solids rates. In order to understand the phenomena involved in the circulation and its control, circulation of sand particles has been studied through a new experimental approach, using an open-loop two compartment circulating system.Experimental results show that the control of the circulation rate depends on three phenomena: the vertical resisting force in the fluidized compartments, the contraction of flow in the communication zone, and the bypass of gas between the compartments. For industrial purposes, the first appears to be predominant in the control of the solids rate. The second ensures neither the strict control of this rate nor the required flexibility. The link between the gas bypass and the circulation phenomena is explained and recommendations for the design and operation of circulating systems are given.
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    AIChE Journal 35 (1989), S. 2033-2036 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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