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  • 101
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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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  • 102
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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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  • 103
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    AIChE Journal 37 (1991), S. 268-268 
    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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  • 104
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    AIChE Journal 37 (1991), S. 274-276 
    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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  • 105
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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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  • 106
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    AIChE Journal 37 (1991), S. 310-310 
    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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  • 107
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    AIChE Journal 37 (1991), S. 323-339 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Absorption of nitrogen oxides was studied in three packed columns in series. Two were 254 mm ID and 6 m tall, the third was 800 mm ID and 3 m tall. Absorption was also studied in two packed columns of 800 mm ID, 7 and 10 m tall, operated in series. Solutions of mixed nitric and sulfuric acids were used as absorbents. Specific rates of absorption were measured using a stirred cell with a flat interface.A mathematical model is developed for an adiabatic operation. The gas phase reactions and equilibria, gas phase mass transfer, interface equilibria, and liquid phase reactions are included in the model. Heterogeneous gas-liquid equilibria are included in the model for the first time. The variation in the rates of absorption with chemical reaction (of NO2, N2O3, and N2O4) with respect to acid concentration is considered. The formation of nitric acid in the gas phase is also considered in the model. Favorable agreement is shown between the model predictions and the experimental observations.
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  • 108
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    AIChE Journal 37 (1991), S. 1281-1292 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Induction phenomena are explained that exist in the only two reproducible sets of kinetic data in the literature for gas hydrate formation from an agitated ice surface. The previously unexplained data are interpreted using recent crystal diffraction results. The induction explanation is validated through cyclopropane hydrate kinetic experiments. The induction reasoning forms the basis of an hypothesis for a molecular mechanism of hydrate formation from ice. The hypothesized mechanism is quantified and given physical interpretation. The hypothesis may have significant implications for inhibiting hydrate formation.
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  • 109
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    AIChE Journal 37 (1991), S. 1354-1364 
    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 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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  • 110
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    AIChE Journal 37 (1991), S. 1529-1536 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Studies of the motion of a dilute suspension of 100-micron glass and stainless steel spheres in water flowing turbulently down a pipe revealed that they could be trapped in necklace formations that move slowly at a distance of less than one particle diameter from the wall. The tendency toward trapping increases with particle density and decreases with flow rate. The phenomenon is interpreted as occurring when the Saffman lift force toward the wall overcomes the ability of fluid turbulence to mix the particles. The location of the particles is dictated by a balance between the Saffman lift force and a wall-induced force associated with the displacement of fluid as a particle moves parallel to the wall.
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  • 111
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    Biotechnology and Bioengineering 38 (1991), S. 1020-1028 
    ISSN: 0006-3592
    Keywords: hybridoma ; cell culture ; continuous culture ; kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A hybridoma cell line, AFP-27-P, was cultivated in continuous culture under glucose-limited conditions. The viable cell concentration, dead-cell concentration, and cell volume all varied with the dilution rate. A model previously developed for a nonproducing clone of the same cell line, AFP-27-NP, was extended to describe the behavior of the cells. The relationship between the specific growth rate and glucose concentration is described by a function similar to the Monod model. A threshold glucose concentration and a minimum specific growth rate are incorporated; the model is meaningful only at glucose concentration and a minimum specific growth rate are incorporated; the model is meaningful only at glucose concentrations and specific growth rates above these levels. The relationship between the death rate and the glucose concentration is described by an inverted Monod-type function. Furthermore, the yield coefficient based on glucose is constant in the lower range of specific growth rates and changes to a new constant value in the upper range of specific growth rates. No maintenance term for glucose consumption is used; in the plot of specific glucose consumption rate vs. specific growth rate, the line intercepts the specific growth rate at a value close to the minimum growth rate. The productivity of antibody as a function of the specific growth rate is described by a mixed type model with a noon-growth-associated term and a negative-growth-associated term. The values for the model parameters were determined from regression analysis of the steady state data.
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  • 112
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    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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  • 113
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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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  • 114
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    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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  • 115
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    AIChE Journal 37 (1991), S. 302-306 
    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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  • 116
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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  • 117
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    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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  • 118
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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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  • 119
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    AIChE Journal 37 (1991), S. 437-447 
    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 procedure is formulated for the separation of a binary mixture by means of extractive crystallization. It shous that two flowsheet structures can handle systems with a wide variety of solid-liquid phase behaviors, including components with simple eutectics, multiple eutectics, and compound formation. Design equations are presented for both flowsheet structures. In addition, design variables and constraints are identified. The economic trade-offs in extractive crystallization processes are examined through the analysis of an example: the complete separation of paraxylene from meta-xylene using n-pentane as the extractive solvent. Comparison of our general methodology with the system-specific designs reported in the literature shows that the latter are process alternatives of the former.
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  • 120
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    AIChE Journal 37 (1991), S. 466-469 
    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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  • 121
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    AIChE Journal 37 (1991), S. 481-489 
    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 structure of thin, wavy falling films was studied to evaluate whether the random-appearing wave structure is a result of deterministic chaos or a purely stochastic process. The time-varying film thickness was obtained at different spatial locations near the point of wave inception for flow rates in the range of Re=3-10. Under all conditions the wave structure was aperiodic in nature and displayed none of the known transitions to chaos. However, the power spectra followed an exponential decay law at high frequencies that is characteristic of chaotic systems. The estimated attractor dimension, used to characterize the complexity of a chaotic system, was much higher than those of known model chaotic systems. It is demonstrated that these high values could be explained due to small levels of noise present in experimental situations. Since experimental data are seldom noise free, a basic limitation in applying these methods to experimental measurements is demonstrated.
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  • 122
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    AIChE Journal 37 (1991), S. 527-538 
    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 concerns general multiple-input/multiple-output (MIMO) nonlinear systems with nonsingular characteristic matrix. For these systems, the problem of inversion is revisited and explicit formulas are derived for the full-order and the reduced inverse system. The reduced inverse naturally leads to an explicit calculation of the unforced zero dynamics of the system and the definition of a concept of forced zero dynamics. These concepts generalize the notion of transmission zeros for MIMO linear systems in a nonlinear setting. Chemical engineering examples are given to illustrate the calculation of zero dynamics. Input/output linearization is then interpreted as canceling the forced zero dynamics of the system, and precise internal stability conditions are derived for the closed-loop system.
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    AIChE Journal 37 (1991), S. 905-914 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Kinetic experiments for the hydrolytic depolymerization of cellobiose and amylose were performed in acidic medium. In the case of amylose, only the production rate of glucose was monitored. Then, a Monte Carlo procedure was developed to simulate long-chain saccharide acid hydrolysis using the kinetic information obtained from the model compound, cellobiose. This stochastic procedure, which is applicable to the homogeneous acid hydrolysis of highly amorphous polysaccharides of sufficient degree of polymerization, provides estimated curves for the time evolution of all intermediate products. Literature data on the hydrolysis of oligoxylans were also compared to the results obtained from the Monte Carlo procedure. The depolymerization of linear polysaccharides, which should normally be viewed as a nonhomogeneous Markov chain, could be considered as a homogeneous Markov chain, provided that the chain is visited at specifically determined time intervals.
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  • 124
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    AIChE Journal 37 (1991), S. 951-952 
    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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  • 125
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    AIChE Journal 37 (1991), S. 1035-1052 
    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 examines reaction-induced flow maldistributions in adiabatic, downflow packed beds. Using linear stability analysis it is shown that for the case of a constant heat source, the uniform flow loses stability when a certain dimensionless group, the Darcy buoyancy number, exceeds a critical value. Center manifold theory is used to analyze the local bifurcation picture for the case of a simple and double zero eigenvalue. It is found that for large Peclet numbers, all the bifurcations from the uniform solution are subcritical in nature and are unstable locally. Orthogonal collocation and continuation techniques are combined with the local theory to determine the various branches of bifurcating solutions. The temperature and flow distributions of stable and unstable solution branches are presented for several aspect ratios and Peclet numbers. Numerical simulations predict direct transitions from uniform flow to periodic or chaotic flows. It is also found that there is a wide range of the Darcy buoyancy number in which the uniform and maldistributed flows are stable and coexist.
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  • 126
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    AIChE Journal 37 (1991), S. 1093-1095 
    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. 1511-1516 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Computer simulations have been used to examine the approximations upon which the van der Waals-Platteeuw theory of hydrate stability is based, and in particular, the extent to which the water lattice relaxes about the guest molecules. It is found that the behavior of the water lattice depends significantly on both the nature and number of guest molecules present - an effect that is neglected in the van der Waals-Platteeuw theory. The simulations also indicate an important role for the repulsive guest-host interactions in generating the mechanical stability of gas hydrates in the bulk. On the basis of these simulations, it is conjectured that surface interactions (particularly at a water/guest interface) are fundamental to the phase behavior of gas hydrates.
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  • 128
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    AIChE Journal 37 (1991), S. 1550-1560 
    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 inclusion of output constraints in the on-line optimization problem solved by quadratic dynamic matrix control (QDMC) can result in a unstable, closed-loop system, even when the corresponding unconstrained algorithm is stable. The presence of constraints in the optimization problem produces a nonlinear, closed-loop system, although the plant and model dynamics are assumed linear. This article quantifies the effect of output constraints on both nominal and robust stability for single-input/single-output processes. Stability conditions provided can be used to select the QDMC parameters and constraint window. Examples demonstrate that these conditions can capture the nonlinear effect of the constraints and that tuning rules developed for the unconstrained case should not be used with output constraints. An example with dead time error illustrates the use of this framework to guarantee the robustness of constrained QDMC with respect to modeling error.
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    AIChE Journal 37 (1991), S. 1571-1578 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Using rigorous models to simulate batch distillation involves the solution of many stiff differential equations. The dimensionality of the problem also increases with an increase in the number of plates and components, which imposes limitations on the use of rigorous models. Furthermore, problems in design, optimization, synthesis, and control involve iterative procedures, and considerable computational efforts would be required to solve them rigorously. As an alternative, the short-cut method (Diwekar and Madhavan, 1991a) provided reasonably accurate solutions without much computational effort. This method in the present form, however, cannot be applied to azeotropic systems because of the impassable barrier of the azeotropic point and needs to be modified. The azeotropic approximation proposed by Anderson and Doherty (1984) was used to modify the short-cut method for binary azeotropic systems. The modified algorithm presented here was tested extensively with a number of binary azeotropic systems for both constant reflux and variable reflux modes of operation, and the results were shown to compare well with the rigorous models. The method requires significantly less computational efforts and is very useful in analyzing feasible region of operation.
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    AIChE Journal 37 (1991), S. 1593-1594 
    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. 1613-1624 
    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 family of alkyl-substituted polycyclic aromatic hydrocarbons was pyrolyzed in microbatch reactors at temperatures between 350°C and 425°C. A general pyrolysis network was deduced for these compounds, and it comprised two major and one minor parallel pathways. The first major pathway resulted in products analogous to the major products observed from alkylbenzene pyrolysis. The second major pathway led to products via the cleavage of the strong aryl-alkyl C—C bond. The third pathway led to small amounts of products, presumably through cyclization and condensation reactions. The relative importance of the two major pathways varied for the different compounds. The rates of aryl-alkyl bond cleavage differed for the different compounds, and these rates were quantitatively related to the compounds' localization energies through Dewar reactivity numbers.
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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 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    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. 123-135 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A detailed linear and nonlinear analysis of void wave phenomena in two-phase flow is presented. A state-of-the-art, one-dimensional two-fluid model was used as the basis for this analysis. It is shown that void wave dispersion is strongly influenced by phasic slip. In particular, the smaller the slip the more dispersion occurs. It has also been found that nonlinear wave forms, such as shocks and solitons, may occur. Moreover, the virtual mass force was found to be an important parameter in the modeling of void waves. It is shown that void wave analysis is an excellent means of assessing the closure assumptions used in two-fluid models. It is also implied that carefully taken void wave data are needed for this purpose.
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    AIChE Journal 37 (1991), S. 147-149 
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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), S. 193-201 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A generalized linear dynamic model or singular model, for which the standard state space representation and the Kalman filtering cannot be applied, is used to develop a new algorithm to solve the linear dynamic material balance problem. This algorithm is based on the method developed in the steady-state case and leads to a recursive scheme, which is very useful in real-time processing. It reduces the computational problem such as singularities and round-off errors that may occur in complex systems. Convergence conditions are given and verified for the dynamic material balance case.
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    AIChE Journal 37 (1991), S. 215-224 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An equation-of-state-based sorption isotherm is developed and used in modeling isothermal supercritical fluid desorption in fixed beds. The conventional fixed-bed desorber model when coupled with density-dependent sorption isotherm predicts the temperature, pressure, and density effects on desorber dynamics and regeneration efficiencies that are experimentally observed in supercritical fluid regeneration of fixed beds.Experimentally observed phenomena such as the presence of pressure-dependent optimal regeneration temperature, high-pressure-favored regeneration, and the reversal of temperature dependence of sorption isotherm - which formerly were attributed to supercritical fluid density and viscosity, and to the endothermicity of sorption isotherm - were fully predicted and explained in terms of a density-dependent sorption isotherm.The proposed method also promises prediction of regeneration efficiencies in cosolvent-aided supercritical fluid desorption.
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    AIChE Journal 37 (1991), S. 255-268 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The utility of the Hammerstein model, which is composed of a static nonlinear element in series with a linear dynamic part, was investigated to represent the dynamics of nonlinear chemical processes. Different methods to identify the parameters of Hammerstein models were tested. The methods were applied to the identification of simulated distillation columns and to an experimental heat exchanger process. The results show that the dynamics of such processes can be better represented by Hammerstein-type models than by linear models.
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    AIChE Journal 37 (1991), S. 269-273 
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    AIChE Journal 37 (1991), S. 394-402 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The production of particulate magnetic disks or tapes requires consistent and uniform magnetic characteristics over the entire disk or tape to have as few defects as possible. To achieve this goal, the magnetic particle suspension used to coat the disk must be well dispersed. This article describes the use of a rheomagnetic instrument that provides an indirect measurement of the dispersion quality prior to coating application. The instrument was designed, tested, and put on a manufacturing scale line to characterize the relationships between the measured dispersion quality and functional characteristics of the magnetic coating. The results of tests done during scaleup for production yielded a qualitative correlation between the in-situ measurements made on the magnetic particle suspension at the coater with the surface roughness due to flocs, the on-disk orientation ratio, and the signal to noise ratio. The current results are the first demonstration of the dispersion quality measurement in a practical manufacturing environment.
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    AIChE Journal 37 (1991), S. 470-474 
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    AIChE Journal 37 (1991), S. 512-526 
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    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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    AIChE Journal 37 (1991), S. 1096-1100 
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    AIChE Journal 37 (1991) 
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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. 1129-1138 
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    Keywords: Chemistry ; Chemical Engineering
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    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. 1107-1108 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 1151-1163 
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    Keywords: Chemistry ; Chemical Engineering
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    Notes: A mathematical model for an ion-exchange membrane attached to a gas-fed porous electrode is derived and discussed. The model is applied to simulate the oxygen electrode of a polymer-electrolyte fuel cell. Our discussion focuses on cell polarization characteristics, water transport, and catalyst utilization - all of which must be considered for fuel-cell design. Calculated polarization behavior is shown to compare favorably with published experimental data. Our results indicate that if the membrane maintains full saturation, its contribution to the total cell resistance is most significant at higher operating current densities (greater than 200 mA/cm2). Polarization resistance due to the oxygen reduction reaction appears to be important for all practical current densities. Water transport, driven by pressure and electric-potential forces, is shown to be a complicated function of the cell operating conditions. The utilization and distribution of noble-metal catalyst is discussed.
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    AIChE Journal 37 (1991), S. 1175-1186 
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    Keywords: Chemistry ; Chemical Engineering
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    Notes: Effective Knudsen diffusion coefficients are presented for fibrous structures consisting of parallel, nonoverlapping or partially overlapping fibers. They are computed by means of a Monte Carlo simulation scheme which is employed to determine the mean square displacement of molecules travelling in the interior of the porous medium for large travel times. The results show that structures of paralle, non-overlapping fibers have smaller effective diffusion coefficients parallel to the fibers than structures of parallel, randomly overlapping fibers of the same porosity and fiber radius, but larger in directions perpendicular to the fibers. Partially overlapping fiber structures are found to exhibit behavior intermediate to those of the two extreme cases. Molecular trajectory computations are also used to obtain results for the structural properties of partially overlapping fiber structures (e.g., porosity and internal surface area, accessible porosity and internal surface area, and percolation threshold), which are compared with some results of the literature for the equivalent problem of partially overlapping disks on a plane.
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    AIChE Journal 37 (1991), S. 1205-1218 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Melt crystallization manufacturing systems are characterized mathematically and optimized. Directional solidification and sweating are modeled, and the results are correlated to plant data. A nonlinear programming algorithm is constructed to determine the optimal design and operation of a production plant. Process constraints include product purity, process yield, capital cost, phase equilibria, kinetic, and operational factors. An objective function is constructed from scaled yield and capital outlay formulae, and is optimized over a variably constrained feasible space. The dependence of the optima on the separation distribution coefficients and on the constraints is given for specific one-stage examples for three operational regimes. The one-stage analyses are applied for the solution of the n-stage problem.
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    AIChE Journal 37 (1991), S. 1245-1248 
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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), S. 1265-1269 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 1293-1304 
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    Notes: A method to evaluate nucleation and crystal growth rates from batch cooling crystallization experiments is presented. Solute concentration and suspension temperature are recorded during the experiment and the product crystal size distribution is analyzed. The crystal growth and nucleation rates at any instant are calculated by solving the population balance equation using the method of characteristics, together with the mass balance equation. Based on a set of different cooling crystallization experiments, kinetics for succinic acid are determined. Applying these kinetics in process simulation allows for a reasonably accurate prediction of the product weight mean size.
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    AIChE Journal 37 (1991), S. 1379-1391 
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    Keywords: Chemistry ; Chemical Engineering
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    Notes: An accurate, yet simple, equation of state was developed for pure fluids ranging from nonpolar to H2O and their mixtures. The equation consists of a virial expansion truncated after the fourth virial coefficient and a closed-form term approximating higher coefficients. For nonpolar or weakly polar compounds, the equation is generalized using critical temperature, critical pressure, and acentric factor. Despite its simplicity, the equation represents the P-V-T and saturation properties of pure fluids with a very good accuracy, which is comparable to that of multiparameter, generalized BWR-type equations. For mixture calculations, mixing rules were formulated based on the rigorously known composition dependence of virial coefficients. The equation represents vapor-liquid, gas-gas and liquid-liquid equilibria, as well as volumetric properties of mixtures containing nonpolar components and/or water. Binary parameters can be generalized for series of mixtures containing a common component.
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    AIChE Journal 37 (1991), S. 1634-1644 
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Generic model control (GMC) takes care of parametric mismatch for underdamped, closed-loop specification, whereas robust generic model control (RGMC) can handle parametric mismatch for any closed-loop specification. But, neither GMC nor RGMC is capable of compensating for structural mismatch. In this study, adaptive GMC(AGMC) and adaptive RGMC (ARGMC) structures are proposed, and their effectiveness over GMC and RGMC is demonstrated with several examples. AGMC exhibits better performance over ARGMC, GMC, and RGMC in all the cases of no process/model mismatch, parametric mismatch as well as structural mismatch.Distillation adaptive generic model control (DAGMC) structure is also proposed for dual composition control of distillation. Since embedding of distillation state-space model in the basic GMC law is practically impossible, linear and nonlinear models are proposed with adaptation using distillation process data, and DAGMC is applied to two typical nontrivial distillation units. Nonlinear DAGMC exhibited better performance over linear DAGMC.
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    AIChE Journal 37 (1991), S. 1673-1679 
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    Notes: A numerical model describing performance of a liquid-liquid spray column heat exchanger is developed. The model is for a disperse packed column operating in steady state. The fundamental equations for the continuous and distributed phases are developed in Eulerian and Lagrangian forms, respectively. The model predicts simultaneously the volume fraction, velocity, and temperature for each phase. Energy and momentum are exchanged between phases through source variables. Empiricism in the model is limited to the specification of droplet drag coefficient and Nusselt number correlations which are utilized to calculate momentum and energy source terms. Application of the computer model to column operation yields predictions that compare closely with experimental results.
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    AIChE Journal 37 (1991), S. 1725-1729 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 1497-1510 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental data are obtained for bovine serum albumin transport through asymmetric polyethersulfone ultrafiltration membranes of differing molecular weight cutoff in a stirred ultrafiltration device. The actual membrane sieving coefficient is determined from filtrate concentration measurements using a stagnant film model to account for bulk mass transport effects. These sieving coefficients are then used to evaluate the relative contributions of diffusive and convective transport to the overall protein flux. The results are in good agreement with available hydrodynamic models for the hindrance factors for convective and diffusive transport of spherical solutes through well-defined pores, with the effective solute to pore size ratio evaluated from a partitioning model that explicitly accounts for the ellipsoidal shape of the protein and the membrane pore size distribution. The implications of these results to the analysis of experimental data for membrane sieving and to the design of effective protein fractionation devices are also discussed.
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    AIChE Journal 37 (1991), S. 1537-1549 
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    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. 1583-1588 
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    AIChE Journal 37 (1991), S. 1625-1633 
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    Notes: Injecting an acidic aqueous solution into a carbonate-rich permeable medium can cause the formation of a mobile gas phase through mineral dissolution. The flowing gas can cause significant changes in mineral identities through interaction with the initially present mineral and aqueous species. We have developed a solution to such transport problems based on a finite difference implicit-pressure/explicit-saturation formulation for two-phase flow, using the local equilibrium assumption as calculated with the Villars-Cruise-Smith stoichiometric chemical equilibrium algorithm.We illustrate the changes that occur to a calcite/iron (II) hydroxide medium upon injection of hydrochloric acid and the stripping of hydrogen sulfide gas from carbon dioxide gas injected into a siderite-rich medium. The examples demonstrate that the formation and/or presence of a gas phase can alter resident minerals and that minerals can remove impurities from a gas phase.
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    AIChE Journal 37 (1991), S. 1657-1667 
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new configuration of a membrane reactor-separator for homogeneous catalysis is described that is designed not only to encapsulate the catalyst solution, but to simultaneously separate the product from reactant. It is composed of a porous support layer that is impregnated partially or completely with the liquid-phase catalyst and is sandwiched between two different membranes. Membrane 1 is readily permeable to the reactant but not to the product, whereas membrane 2 allows free permeation of both the reactant and the product while encapsulating the catalyst solution. The performance of a differential stirred-cell membrane reactor-separator was theoretically investigated for the case of a first-order irreversible reaction. The extent of product separation was studied as a function of membrane permselectivity for reactant and product, the difference in resistance of membrane and catalyst layer, liquid loading of the catalyst layer, and the sweep fluid flow rate. The efficacy of the device was experimentally demonstrated using ethylene hydroformylation with hydridocarbonyltris (triphenyl phosphine) Rh(I) catalyst dissolved in dioctyl phthalate solvent.
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    AIChE Journal 37 (1991), S. 1411-1414 
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    AIChE Journal 37 (1991), S. 1420-1424 
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    AIChE Journal 37 (1991), S. 1485-1496 
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The simultaneous deposition of particles and material from the vapor phase gives rise to surface deposits having characteristic structure. A mathematical model of the particle-vapor codeposition process is developed that predicts the structure and properties of these deposits as well as their growth rate over a wide range of conditions. A random sphere formulation is developed that provides the framework for a unified treatment of both subprocesses: ballistic particle deposition and porous media densification through vapor deposition. The model is applied to particleenhanced chemical vapor deposition (PECVD) processes for the production of ceramic materials. In PECVD, particles are introduced into a CVD process, either in the form of an aerosol created in situ by a controlled amount of gas-to-particle conversion or in the form of independently charged powder. The model identifies PECVD conditions that produce deposition rates substantially higher than those achievable by conventional CVD.
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    AIChE Journal 37 (1991), S. 1668-1672 
    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 effects of taper on the steady-state expansion characteristics of a homogeneous fluidized bed are examined theoretically and experimentally. It is shown that secondary factors that might be thought to influence the expansion (fluid accelerational effects including added mass and particle phase elasticity) are unlikely to be of significance in practical situations.
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    AIChE Journal 37 (1991), S. 1687-1697 
    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 generalized kinetic model for wet oxidation (WO) of organic compounds was developed based on a simplified reaction scheme considering acetic acid as the rate-limiting intermediate. The selectivity of product vs. intermediate formations was quantified by the ratio of the two reaction rate constants. This point selectivity α may be used to characterize the “strength” of the feed stream to be treated. This global model was validated using WO kinetic data reported for temperatures ranging from 150°C to 550°C and pressures varying from 20 bar to 440 bar. Organic conversions predicted by this model, as compared to other models, more accurately reflect the actual performance of WO processes. The model has practical validity for a variety of organic compounds, wastewaters and sludges in both subcritical and supercritical water oxidation processes.
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    AIChE Journal 37 (1991), S. 1711-1723 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Nonlinear predictive control (NLPC) is an effective strategy for controlling nonlinear chemical processes with constraints and time delays. In this article, a number of important issues in NLPC are addressed, emphasizing continuous stirred tank reactors (CSTR's) with parametric and model structure uncertainty. In particular, the effects of various choices for the initial conditions are discussed. The selection of initial conditions is particularly important in the presence of plant/model mismatch. A nonlinear programming-based approach is used for process identification. The effect of model structure uncertainty is included in our analysis by using a cascade control structure on the coolant temperature. Our CSTR results indicate that a simple PI (with anti-reset windup) cascade loop on coolant temperature is adequate for operation over a wide range of operating conditions. A particularly interesting result of this work is that a predictive controller based on an open-loop observer can be used to stabilize an open-loop unstable process, although this is not recommended in practice.
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    AIChE Journal 37 (1991), S. 1744-1748 
    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. 1900-1903 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    Biotechnology and Bioengineering 37 (1991), S. 575-579 
    ISSN: 0006-3592
    Keywords: inulin ; inulinase ; fructose ; enzymic hydrolysis ; kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A kinetic study of the hydrolysis of inulin was performed by using as catalyst a commercial inulinase from Aspergillus ficuum. The reaction was studied carrying out initial rate as well as time course measurements. Both inulinase and invertase activities of the enzyme were taken into account, and the corresponding kinetic parameters were determined in the temperature range 30-50°C. The activation energies of the turnover constant for inulinase and invertase activities were found to be similar (56-57 kJ · mol-1). The ratio S/I of invertase to inulinase activity was 1.6 regardless of temperature. The thermal degradation of the enzyme was also investigated up to 70°C, and an activation energy of 350-370 kJ · mol-1 was evaluated.
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    Biotechnology and Bioengineering 38 (1991), S. 116-126 
    ISSN: 0006-3592
    Keywords: Bombyx mori ; repeated-batch ; kinetics ; suspension cultures ; nutritional requirements ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetics and growth characteristics of the BM-5 insect cell line of Bombyx mori (silkworm) have been experimentally investigated in order to develop optimal growth protocols when these cells are used to produce large quantities of human proteins by recombinant baculoviruses. Experiments were performed in 200-mL spinner flasks, which were operated at 80 rpm with 0.3% methyl cellulose (MCL) added to the medium to protect the cells from shear stress. Exposure of the cells to varying nutrient and metabolite concentrations was accomplished through a repeated-batch mode of feeding. The results indicate that glutamine is a limiting nutrient and that lactate has an inhibitory effect on cell growth. Ammonia depletion from the medium was accompanied by uric acid accumulation suggesting that ammonia is converted to this metabolic product by the “uricotelic” and “nucleicolytic” metabolic pathways. With the examined medium formulation, glucose, fructose, and sucrose remained at high concentrations throughout the cultivation period.
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    Biotechnology and Bioengineering 37 (1991), S. 567-574 
    ISSN: 0006-3592
    Keywords: xanthan fermentation ; temperature ; kinetics ; model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Batch fermentation kinetics of xanthan gum production from glucose by Xanthomonas campestris at temperatures between 22°C and 35°C were studied to evaluate temperature effects on cell growth and xanthan formation. These batch xanthan fermentations were modeled by the logistic equation for cell growth, the Luedeking-Piret equation for xanthan production, and a modified Luedeking-Piret equation for glucose consumption. Temperature dependence of the parameters in this model was evaluated. Growth-associated rate constants increased to a maximum at ∼30°C and then decreased to zero at ∼35°C. This temperature effect can be modeled using a square-root model. On the contrary, non-growth-associated rate constants increased with increasing temperature, following the Arrhenius relationship, in the entire temperature range studied. The model developed in this work fits the experimental data very well and can be used in a simulation study. However, due to the empirical nature of the model, the parameter values need to be reevaluated if the model is to be applied to different growth conditions.
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    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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    AIChE Journal 37 (1991), S. 98-110 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fluid-mediated interaction between catalyst particles alone is shown to yield several interesting and significant phenomena in a catalytic reactor that have been generally attributed in the past to direct interaction between particles. Thus, collaborative interaction between particles and the fluid may enhance or abate steady-state multiplicity, and reverse stability behavior. From the simple setting of a population of particles in a well-mixed CSTR, it is shown that the catalyst phase in a catalytic reactor is susceptible to very fine pattern formation in the face of steady-state multiplicity in single particles, which negates the usual assumption that particles exposed to a given fluid have identical states. In a reactor such variability in behavior must be accompanied by a corresponding variability in conversion and selectivity (in multireaction systems) and may have strong implications for reactor control strategies.
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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. 636-640 
    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. 650-660 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    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. 800-800 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 825-835 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A major difficulty affecting the control of product quality in industrial polymerization reactors is the lack of suitable on-line polymer property measurements. In this article a scheme is developed to predict melt index and density in a fluidized-bed ethylene copolymerization reactor. Theoretically-based models are derived to predict quality variables from the available on-line temperature and gas composition measurements. Adjustable parameters in these models are updated on-line using infrequent laboratory measurements and a recursive parameter estimation technique. The application of this methodology is illustrated using operating data from an industrial reactor. It is shown that both melt index and density can be successfully predicted. Knowledge of product property deviations from desired targets is required so that manufacturers can take corrective actions to reduce the quantity of off-grade material made and produce a consistent product.
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    AIChE Journal 37 (1991), S. 863-870 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Transport properties of various uncross-linked and cross-linked non-Newtonian slurries in horizontal pipes are studied. Flow data are gathered in three long, different diameter, transparent horizontal pipes. Investigated are the effects of the pipe size, polymer concentration, fluid rheological properties, cross-linking effects, particle size and density, solids concentration, fluid density, and slurry rate on the critical deposition velocities and particle resuspension velocities. It is found that critical deposition and resuspension velocities for the non-Newtonian carrier fluids tested are significantly lower than those for water. Both velocities depend greatly on pipe size and particle density. Higher critical velocities are required to minimize settling (1) in larger pipe sizes and (2) for pumping solids denser than sand. For less viscous fluids, critical deposition and resuspension velocities increase slightly with increasing solids concentration. They are, however, independent of solids concentration for more viscous fluids.
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    AIChE Journal 37 (1991), S. 1392-1400 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Baffle effects on the performance of a catalytic circulating fluidized bed reactor were examined experimentally. The circulating fluidized bed reactor or riser was 102 mm in diameter and 6.32 m in height. Reaction was the catalytic decomposition of ozone using FCC particles with a mean diameter of 89 μm, impregnated with ferric oxide as catalysts. Four ring-type baffles, mounted horizontally around the riser wall, were used in this study. Ozone concentrations were measured in both axial and radial directions under various operating conditions in a riser with and without baffles. Experimental results showed that in a riser with baffles, the ozone concentration in the radial direction was more uniform and the ozone conversion was higher than that in a riser without baffles except at the lowest gas velocity used. A mathematical model developed accounted for the gas-phase ozone conversion under various operating conditions. The gas-solid contact efficiency in the riser was discussed in light of the model.
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    AIChE Journal 37 (1991), S. 1425-1436 
    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. 1645-1656 
    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 two-dimensional channel structure of clinoptilolite has been altered systematically by ion exchange to study the effects of cation type, size, location, and distribution on the diffusion of N2 and CH4 probe molecules. Concentration-dependent diffusion time constants (D/L2) were determined from gravimetric uptake measurements for fully-exchanged K+, Na+, and H+ clinoptilolites, and highly-exchanged Ca2+ (89%) and Mg2+ (72%) clinoptilolites. Both plane sheet and parallel channel diffusion models were developed from the one-dimensional plane sheet diffusion equation and fit to the uptake data. Resulting values of D/L2 varied by a factor of more than 1,000 for both N2 and CH4, while kinetic selectivity spanned nearly two orders of magnitude for this group of modified clinoptilolites. Achieving this range in performance for the difficult N2/CH4 separation demonstrates the excellent potential for tailoring clinoptilolite by cation manipulation for the kinetic separation of other gas mixtures.
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    AIChE Journal 37 (1991), S. 1680-1686 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dissolved carbon dioxide and bicarbonate ions in fermentation broths can (independently) inhibit or promote microbial growth and productivity. In research facilities with a large number of fermenters, dissolved carbon dioxide sensors tend not to be used, and as a result this variable will generally go unmonitored, making the meaningful analysis of data more difficult. For aerobic fermentations, mass transfer of carbon dioxide can be described in an analogous way to oxygen transfer. The mass transfer coefficient for carbon dioxide is 0.89 times that for oxygen. The maximum dissolved carbon dioxide concentration as a function of exit gas composition is compared with the concentration obtained by assuming equilibrium between the broth and exit gas. The difference between these two concentrations is typically 20-40% of the equilibrium concentration. In large fermenters, a degree of plug flow behavior in the gas and the generally lower specific aeration rates will serve to produce a better approach to equilibrium than for research fermenters.
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    AIChE Journal 37 (1991), S. 1730-1732 
    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. 1738-1738 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 37 (1991), S. 182-192 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental measurements of the crystal-size distribution (CSD) clearly indicate a pronounced difference in the dynamic behavior of a 20- and 970-L continuous crystallizer that produces ammonium sulfate. The difference in their circulation time offers a probable explanation for this phenomenon. It causes different supersaturation profiles in the two crystallizers, which leads to internal fines dissolution in the large crystallizer. This contributes to the observed oscillations in the 970-L crystallizer as opposed to the first-order responses in the 20-L crystallizer. To numerically study the effect of the supersaturation profile a dynamic model, from which the MSMPR (mixed suspension mixed product removal) assumption is omitted, is developed. Calculated supersaturation profiles differ considerably for the 20-L, the 970-L and an imaginary 50,000-L continuous evaporative crystallizer. Coincident with changes in the supersaturation profiles, the numerical solution of the model indicates the tendency of large crystallizers to oscillate and supports this suggested explanation.
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    AIChE Journal 37 (1991), S. 233-243 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Nonlinear principal component analysis is a novel technique for multivariate data analysis, similar to the well-known method of principal component analysis. NLPCA, like PCA, is used to identify and remove correlations among problem variables as an aid to dimensionality reduction, visualization, and exploratory data analysis. While PCA identifies only linear correlations between variables, NLPCA uncovers both linear and nonlinear correlations, without restriction on the character of the nonlinearities present in the data. NLPCA operates by training a feedforward neural network to perform the identity mapping, where the network inputs are reproduced at the output layer. The network contains an internal “bottleneck” layer (containing fewer nodes than input or output layers), which forces the network to develop a compact representation of the input data, and two additional hidden layers. The NLPCA method is demonstrated using time-dependent, simulated batch reaction data. Results show that NLPCA successfully reduces dimensionality and produces a feature space map resembling the actual distribution of the underlying system parameters.
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    AIChE Journal 37 (1991), S. 281-284 
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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), S. 340-346 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetic invariant model has been reformulated and an approximate analytical form of a kinetic function is obtained for the dissolution accompanied by a chemical reaction of large solid particles. A restriction on the analytical solution is provided in the form of a sufficient condition for the convergence of the series involved. Expressions for the concentration of unreacted, dissolved solid reactant, the time of complete conversion, and the ratio of driving forces available for the reaction and mass transfer steps are presented. Solutions for the rate-limiting regimes are deduced as special cases of the general solution. The small-particle solution is recovered as a special case in the limit of a vanishingly small Reynolds number. Rigorous numerical solution has been obtained to assess the accuracy of the pseudostationary-state solution and to discern the validity of the approximations.
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    AIChE Journal 37 (1991), S. 377-382 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    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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    AIChE Journal 37 (1991), S. 465-465 
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    AIChE Journal 37 (1991), S. 569-580 
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    Keywords: Chemistry ; Chemical Engineering
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    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. 629-632 
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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), S. 633-635 
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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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    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 671-678 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 200
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 661-670 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    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.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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