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  • Chemical Engineering  (3,294)
  • Animals
  • 1990-1994  (5,563)
  • 101
    Electronic Resource
    Electronic Resource
    Multicomponent separation using a column-switching chromatographic method (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1843-1849 
    Details
    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 cyclic chromatographic process based on the method of column switching was used to separate a three-component carbohydrate mixture. It permits continuous introduction of the feed and is designed to produce higher product concentration compared to a normal elution cyclic process. A fixed-bed model incorporating axial dispersion and a linear driving force for mass transfer was successfully used to estimate optimum operating conditions (switch times and fluid-flow rates). Its experimental setup can be easily constructed by modifying the apparatus of a simulated countercurrent process since both systems comprise segmented columns equipped with on-off valves for fluid-flow control. This allows one to conduct either multicomponent separation based on elution operation or binary separation based on countercurrent operation using essentially the same set of experimental apparatus with minor modification.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401108
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  • 102
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    Correction (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1900-1900 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690401113
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  • 103
    Electronic Resource
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    Colloidal gel filtration: Experiment and theory (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1876-1891 
    Details
    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 filtration of colloidal gels, consisting of octadecyl-coated silica spheres in hexadecane, is examined experimentally using CAT scanning. A number of interparticle strengths are explored, with significant differences in qualitative behavior relative to the filtration of stable dispersions. For stiff gels, the transmission of stresses from the cell wall to the dispersion results in a fracturing phenomenon during consolidation on a length scale substantially larger than the particle size. For more pliant gels, the radial propagation of stress is more local to the wall region and gravitational effects play a prominent role. The existing theory of network consolidation is compared against our experimental results for pliant gels, independent of the form of the constitutive functions for the sedimentation velocity and yield stress. Though our measurements seem consistent with the theory at early times, deviations at later moments question whether a compressive yield stress is actually present.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401111
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  • 104
    Electronic Resource
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    Electrostatic spraying of nonconductive fluids into conductive fluids (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1920-1923 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401116
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  • 105
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    Chaotic and fractal dynamics - an introduction for applied scientists and engineers. By Francis C. Moon, John Wiley & Sons, New York, 508 pp., $59.95 (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1924-1925 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690401118
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  • 106
    Electronic Resource
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    Displacement chromatography of amino acids: Effects of selectivity reversal (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1618-1628 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Separating mixtures of α-amino butyric acid (ABA) and isoleucine (Ile) by displacement chromatography with a cation exchange resin and an alkaline displacer leads to the formation of a displacement train, in which only ABA is recovered as a pure component, while Ile is recovered in a mixed band with ABA. The purity of the Ile band depends on the concentration of the displacer, and essentially pure Ile is obtained when the displacer concentration is reduced to a low value. The observed behavior is explained by considering the nonideality of the equilibrium uptake of these amino acids by the resin. An equilibrium model, representing the pure component isotherms, predicts variable selectivity and the occurrence of selectivity reversal in the two-component system. Analyses using this model based on the theory of coherent waves and a numerical solution of the conservation equations for the displacement chromatography process agree with the observed behavior, predicting the formation of “azeotropic” bands during the development of the displacement train. Such analyses are used to determine under what conditions a complete separation may be obtained for a given experimental system.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401004
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  • 107
    Electronic Resource
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    Automatic synthesis of batch plant procedures: Process-oriented approach (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1650-1664 
    Details
    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 strategy for the automatic synthesis of plant operating procedures, through the integration of artificial intelligence and mathematical modeling tools is discussed. This “predicative/numerical” modeling paradigm integrates qualitative and quantitative aspects of the problem in a same framework. It uses a “process-centered” qualitative modeling approach together with MILP optimization techniques to automatically generate operating strategies. The operation procedures network (OP-Net), formulated in terms of processes from a generic library, describes abstract (hardware-independent) processing paths leading to the desired operational goals. In this approach, the model assumptions, conservation expressions and data are described at the same level of abstraction, using the same formal representation. This permits the direct, automatic generation and modification of operation procedures in situations involving changes in basic assumptions and initial scenarios. Thus, flexibility, an essential feature of batch processing, is safeguarded.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401007
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  • 108
    Electronic Resource
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    Solubilization of trichloroethylene by polyelectrolyte/surfactant complexes (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1969-1975 
    Details
    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 automated vapor pressure method is used to obtain solubilization isotherms for trichloroethylene (TCE) in polyelectrolyte/surfactant complexes throughout a wide range of solute activities at 20 and 25°C. The polyelectrolyte chosen is sodium poly (styrenesulfonate), PSS, and the surfactant is cetylpyridinium chloride or N-hexadecylpyridinium chloride, CPC. Data are fitted to the quadratic equation K = K0 (1 - αX + βX2), which correlates the solubilization equilibrium constant (K) with the mole fraction of TCE (X) in the micelles or complexes at each temperature. Activity coefficients are also obtained for TCE in the PSS/CPC complexes as a function of X. The general solubilization behavior of TCE in PSS/CPC complexes resembles that of TCE in CPC micelles, as well as that of benzene or toluene in CPC micelles, suggesting that TCE solubilizes in ionic micelles both within the hydrocarbon micellar interior and near the micellar surface. The presence of the polyelectrolyte causes a small decrease in the ability of the cationic surfactant to solubilize TCE, while greatly reducing the concentration of the surfactant present in monomeric form. PSS/CPC complexes may be useful in colloid-enhanced ultrafiltration processes to purify organic-contaminated water.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401206
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  • 109
    Electronic Resource
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    Chaotic mixing of shear-thinning fluids (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1782-1793 
    Details
    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 article investigates the effect of shear-thinning viscosity on chaotic mixing when the kinematics first begin to deviate from Newtonian flow. Computations are done for a 2-D, time-periodic flow between eccentric cylinders. The effectiveness of mixing is analyzed by examining the asymptotic coverage of a passive tracer, character and location of periodic points, and the rate of stretching of fluid elements. Small variations in the velocity field associated with non-Newtonian kinematics produce large effects in the chaotic advection of a passive tracer. The stretching rate remains exponential, but with a long time constant as the shear-thinning effect increases, often resulting in the birth of new periodic islands and a decrease in the asymptotic coverage of the tracer. Exceptions to these observations are possible: both the stretching rate and the asymptotic coverage might increase as shear thinning increases. Results also indicate that suitable manipulation of operating conditions can produce shear-thinning flows which mix as well as Newtonian flows. Since significant effects are observed with less than a 4% difference in the velocity fields, the assumption of Newtonian kinematics can lead to large errors in the design and operation of process mixing equipment for non-Newtonian fluids.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401103
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  • 110
    Electronic Resource
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    Effect of kinetics on residue curve maps for reactive distillation (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1814-1824 
    Details
    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 class of models is derived for studying the effects of chemical kinetics on residue curve maps for reactive distillation. Activity-based rate and phase equilibrium expressions provide an accurate and thermodynamically consistent description of composition changes in nonideal, reacting vapor-liquid mixtures. For certain strategies of operation, which dictate the rate of product removal, the model equations are nonautonomous, leading to unusual dynamic behavior. However, for a certain special product removal policy, the effects of kinetics can be described by a single parameter, the Damköhler number, which measures the rate of reaction relative to product removal. For small values of the Damköhler number, the nonreactive simple distillation residue curve map is recovered and the singular points are the pure components and azeotropes in the nonreactive mixture. A bifurcation analysis shows the deformation and, in some cases, the disappearance of these singular points as the Damköhler number is increased until the equilibrium reactive residue curve map is recovered at large values. This bifurcation analysis reveals the limitations of the equilibrium analysis. A model problem for the reactive distillation of methyl tertbutyl ether from isobutene and methanol is solved.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401106
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  • 111
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    Mass-transfer mechanisms for zeolite ion exchange in wastewater treatment (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 2045-2054 
    Details
    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 spite of the increasing commercial use of zeolites for binary and multicomponent ion exchange, understanding of the basic mass-transfer processes associated with multicomponent zeolite systems is quite limited. This study evaluates Na-Ca-Mg-Cs-Sr ion exchange from an aqueous solution using a chabazite zeolite. Mass-transfer coefficients are determined from experimental batch-reactor data for binary and multicomponent systems. The experimental data indicate that diffusion through the microporous zeolite crystals is the primary diffusional resistance. Macropore diffusion also significantly contributes to the mass-transfer resistance. Various mass-transfer models are compared with the experimental data to determine values for intraparticle diffusivities. Effective diffusivities obtained accurately predict experimental data using a variety of models. Only the model accounting for micropore and macropore diffusion occurring in series accurately predict multicomponent data using diffusivities from the binary system. Liquid and surface diffusion both contribute to macropore diffusion. Surface and micropore diffusivities are concentration-dependent for the system of interest.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401214
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  • 112
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    Mixing in polymer processing edited by Chris Rauwendaal, Marcel Dekker, new york, 1991, 496pp., $160.00 (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 383-383 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690400224
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  • 113
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    Thermodynamics of phase equilibria in aqueous-organic systems with salt (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 676-691 
    Details
    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 semiempirical thermodynamic method is developed to establish a framework for calculating vapor-liquid and liquid-liquid equilibria in ternary systems containing water, an organic solvent, and a salt. Careful attention is given to precise definition of standard states. Short-range ion-solvent forces are taken into account primarily by a chemical-equilibrium method based on stepwise ion solvation; however, physical contributions also contribute. Water-cosolvent nonideality is described by an extended equation of the van Laar form. Long-range electrostatic forces between ions are taken into account by an extended Debye-Hückel equation with corrections for transferring from a McMillan-Mayer to a Lewis-Randall framework.The new method is illustrated with results for several systems including saturated aqueous mixtures of LiBr or LiCl with methanol where the salt concentration exceeds 20 molal. The method developed here is of particular interest for process calculations in extractive crystallization, a low-energy operation for producing salt from aqueous solution.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400411
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  • 114
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    Modeling of supercritical extraction of organics from solid matrices (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 777-785 
    Details
    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 desorption profiles of various organics from soil and activated carbon using dense liquid and supercritical carbon dioxide were modeled. The model accounts for effective diffusion of the organics in the solid pores, axial dispersion in the fluid phase, and external mass transfer to the fluid phase from the particle surface. This model, involving partial differential equations, is solved using the orthogonal collocation on finite elements. The model is able to predict the experimental data quite well without any adjustable parameters. The importance of each parameter depended on the system, although adsorption equilibrium and the effective pore diffusion of the organic were the most significant parameters in all the systems investigated.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400505
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  • 115
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    Factors affecting coalescence frequency of droplets in a stirred liquid-liquid dispersion (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 767-776 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Liquid-liquid dispersions are commonly used for separations and reaction systems, because the added interfacial area due to dispersion aids in mass transfer and chemical reaction rates. Transient coalescence experiments have been performed for a wide range of dispersed-phase fractions and impeller speeds. A similarity transformation of the experimental drop-size distribution is possible for most of the experiments. The drop-size-dependent coalescence frequency is obtained from an inverse problem procedure previously developed. Over the range of drop sizes encountered in our experiments, the coalescence frequency increases with increases in the size of the coalescing drops, the dispersed-phase fraction, and the impeller speed. For a dispersephase system of neutrally buoyant droplets of benzene/carbon tetrachloride in water, the coalescence frequency is K(v, v′)= 3.72 (10-3)φ1.42N20.52(v1/2+v′1/2) as a function of dispersed-phase fraction, φ, impeller speed, N2, and volumes of the coalescing droplets, v and v′. The results are compared with previous models for the coalescence frequency. Models predicting an eventual decrease in coalescence rates with drop size are disqualified unless this decrease occurs beyond the sizes observed in our experiments.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400504
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  • 116
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    Process monitoring and diagnosis by multiblock PLS methods (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 826-838 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Schemes for monitoring the operating performance of large continuous processes using multivariate statistical projection methods such as principal component analysis (PCA) and projection to latent structures (PLS) are extended to situations where the processes can be naturally blocked into subsections. The multiblock projection methods allow one to establish monitoring charts for the individual process subsections as well as for the entire process. When a special event or fault occurs in a subsection of the process, these multiblock methods can generally detect the event earlier and reveal the subsection within which the event has occurred. More detailed diagnostic methods based on interrogating the underlying PCA/PLS models are also developed. These methods show those process variables which are the main contributors to any deviations that have occurred, thereby allowing one to diagnose the cause of the event more easily. These ideas are demonstrated using detailed simulation studies on a multisection tubular reactor for the production of low-density polyethylene.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400509
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  • 117
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    Oxide ion transport for selective oxidative coupling of methane with new membrane reactor (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 870-877 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Oxidative coupling of methane was conducted by using membrane reactors. The nonporous membrane film that consisted of PbO modified by alkaline or alkaline earth compound was supported on porous SiO2-Al2O3 tube. Higher hydrocarbons were successfully synthesized with high selectivity (about 90%). A kinetic analysis was conducted to clarify whether oxide ion transportation through PbO film participated in the oxidative coupling of methane. The evaluated value of the diffusion coefficient of oxide ion transport based on the methane oxidation agreed well with that of published data. The simulated gradient of the oxide ion concentration through the PbO membrane agreed well with that measured by electron probe X-ray microanalyzer. A transient response simulated by using kinetic parameters evaluated from steady-state analysis also agreed well with the experiment. These results prove the validity of the reaction model that consists of surface reactions of methane with oxide ion which is transferred from inside to outside of the membrane reactor. Alkali modifiers on the PbO membrane surface exhibited a promotional effect on the surface reaction of methane coupling. Another membrane reactor containing Bi2O3 showed higher activity than the PbO membrane.
    Additional Material: 17 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400513
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  • 118
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    Masthead (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994) 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690400101
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  • 119
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    Gravity-Driven reactive coating flow down an inclined plane (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 2-10 
    Details
    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 coating flow of a reactive fluid on an inclined plane is studied. The fluid viscosity steadily increases due to a sustained cross-linking reaction. Using well-known long wave approximations and a simple kinetic relation, we find that the linear stability of a uniform coating is affected not only by the inclination angle but also by the reaction order. In the weakly nonlinear limit, a generalized Kuramoto-Sivashinsky (K-S) equation is derived. Two interesting cases are identified in the limit of creeping flow. One is when surface tension is moderate and a generalized Burger's equation results, and the other is when the surface tension is large and the traditional K-S equation is recovered when the inclination angle is greater than 90°. The solution in this case represents a shock-like traveling wave down the incline and it appears to be unique for reacting coating flows.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400103
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  • 120
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    u′v′ Reynolds stress in the viscous sublayer over a wide range of Re numbers (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 29-39 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: To test the ability of different turbulence models to predict the turbulent momentum transport in the viscous sublayer, measurements are performed with a laser Doppler velocimeter (LDV). The main objective of the experiments is to measure the u′v′ correlation in the near wall region. The results support the correlation: -u′v′+ = Aky+3. The results of 2-D computer simulations using four different low Reynolds number k-∊ turbulence models are compared with the experimental LDV data. The models tested are the original low Reynolds number k-∊ model of Jones and Launder (1972, 1973) and three later modifications by Chien (1980), Lam and Bremhorst (1981), and Nagano and Hishida (1987). The u′v′ correlation was found to be underestimated with all four models, but the Chien model was superior, with only a 40% underestimation in the viscous sublayer.
    Additional Material: 15 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400106
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  • 121
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    Rate enhancement and multiplicity in a partially wetted and filled pellet: Experimental study (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 97-111 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Phase transition during an exothermic multiphase reaction was studied experimentally using a single catalytic pellet reactor. Cyclohexene hydrogenation (to cyclohexane) and disproportionation (to benzene and cyclohexane) on Pd/Al2O3 comprised the test reaction system. The steady-state behavior of the pellet exposed on part of its surface by a flowing liquid rivulet containing the liquid reactant (cyclohexene) and the other part by a flowing gas containing the gaseous reactant (hydrogen) was examined. Measurements included the pellet weight (liquid holdup), degree of external wetting, center and surf ace temperature and overall reaction rates. Two regimes observed are: a low-rate regime for all hydrogen gas-phase concentrations in which the partially wetted pellet is filled mostly with liquid and nearly isothermal; a high-rate regime for hydrogen concentrations exceeding a critical value in which the pellet is filled only partially with liquid and the pellet temperature rise is considerable. Benzene formation was observed in this state. The difference in overall cyclohexane formation rates between the two states was as high as a factor of 20 for the same bulk conditions. Over the range where multiple states were observed, the steady state of the pellet depended on whether the pellet was pref tiled with the reactive gas mixture or with liquid cyclohexene. The range over which the high-rate state was sustained was the largest for the most active catalyst and declined as the catalyst slowly deactivated. Data features are interpreted using the theoretical foundations of the half-wetted catalytic slab model (Harold and Watson, 1993).
    Additional Material: 13 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400112
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  • 122
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    Turbulent gas-particle flow in vertical risers (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 215-228 
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    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 experimental studies on the cross-sectional distribution of particles in vertical risers have revealed marked segregation of particles. These flows are inherently unsteady with large fluctuations in suspension density. In this article, we have analyzed the time-smoothed equations for the motion of dense suspensions to demonstrate the role of these fluctuations on the occurrence of segregation. It is shown that the particles will congregate in regions where the kinetic energy of fluctuations associated with the particles is small. In the context of transport of small particles such as FCC, a simplified model based on the mixture velocity can be constructed. A speculative K-∊ model based on this velocity is analyzed to illustrate the extent of segregation of particles afforded by unsteady fluctuations.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400204
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  • 123
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    Minimum entrainer flows for extractive distillation: A bifurcation theoretic approach (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 243-268 
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    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 addition to a minimum reflux, every extractive distillation exhibits a maximum reflux, above which the desired separation is impossible, and a minimum entrainer flow rate, below which the separation is also impossible. Both of these quantities correspond to bifurcations of the finite difference equations describing the middle section of the column and, given a VLE model, can be easily calculated knowing only information about the column feed and the desired product compositions, that is, prior to any column design calculations.Both maximum reflux and minimum entrainer flows have important implications for the design and operation of extractive distillations. By limiting the range of feasible operating reflux ratios, the maximum reflux affects the flexibility, operability and controllability of the column. Ranking a set of feasible extractive entrainers according to their minimum entrainer flows provides a simple effective method for identifying the most promising candidates. Near optimal design values of the entrainer flow can then be estimated using the heuristic presented.
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    Brownian dynamics of sterically-stabilized colloidal suspensions (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 283-293 
    Details
    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 Brownian dynamics, equilibrium and dynamic properties are calculated for colloidal suspensions that are stabilized throug the Milner, Witten and Cates (1988) steric potential. Results are reported for osmotic pressure, radial distribution functions, static structure factors, and self-diffusion coefficients. The sterically-stabilized systems are also approximated by equivalent hard spheres, with good agreement for osmotic pressure and long-range structure. The suitability of the potential to model the behavior of a real system is explored by comparing static structure factors calculated from Brownian dynamics simulations to those measured using SANS (Markovic et al., 1986). Finally, the effects of Hamaker and hydrodynamic forces on calculated properties are investigated.
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    URL: http://dx.doi.org/10.1002/aic.690400208
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    Random motility of swimming bacteria: Single cells compared to cell populations (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 334-348 
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    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 motility of a population of swimming bacteria can be characterized by a random motility coefficient, μ, the operational equivalent of a diffusion coefficient at the macroscopic level and in the absence of interacting chemical gradients. At the microscopic level, random motility is related to the single-cell parameters: speed, tumbling probability, and index of directional persistence (related to the angle a cell's path assumes following a change in direction). Various mathematical models have been proposed for relating the macroscopic random motility coefficient to these microscopic single-cell parameters. In separate experiments, we have measured motility at both the cell-population and single-cell levels for Escherichia coli. The agreement of these results shows that the macroscopic transport behavior of a population of motile bacteria can be predicted from straightforward microscopic observations on single cells.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400212
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    Influence of increased gas density on hydrodynamics of bubble-column reactors (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 112-119 
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    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 mechanistic background to the understanding of the hydrodynamics of high-pressure bubble column reactors in both the homogeneous and heterogeneous flow regimes is discussed. An important parameter determining the stability of homogeneous bubbly flow in a bubble column is shown to be the Richardson-Zaki exponent in the bubble swarm velocity relationship Vswarm = v∞(1-∊)n-1. Experimental data for the bubble swarm velocity were obtained in 0.05- and 0.1-m-dia. bubble columns with various gases (helium, air, argon, sulfur hexafluoride) using water as the liquid phase. Bubble swarm velocity data show that with increasing gas density the Richardson-Zaki exponent value decreases; physically this means that increasing gas density reduces interaction between neighboring bubbles and, consequently, reduces chance of propagation of instabilities. This rationalizes the experimental observation that the influence of increased gas density ρG is to delay the transition from homogeneous bubbly flow to churn-turbulent flow: increasing ρG increases the regime transition velocity. A stability analysis rationalizes the observations. The hydrodynamics of bubble columns in the churn-turbulent regime is considered to be analogous to that of a bubbling gas-solid fluidized bed, and the two-phase theory of gas-solid fluid beds is extended to describing bubble columns by identifying the “dilute” phase as the fast-rising large bubbles and the “dense” phase as the liquid phase with entrained small bubbles. A simple coalescence rationalizes experimental large-bubble holdup data.
    Additional Material: 11 Ill.
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    Stokes flow through a thin screen with patterned holes (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 419-423 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Three-dimensional Stokes flow through a thin screen which has a regular array of holes with two orthogonal axes of symmetry has been studied. The governing equation is simplified by the Roscoe potential and solved by an efficient eigenfunction expansion and collocation method. The resistance is found for circular and square holes in square arrays, and circular and hexagonal holes in triangular arrays.
    Additional Material: 7 Ill.
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    Family plots for evaluating physical properties of organosilicon compounds (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 373-377 
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    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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    URL: http://dx.doi.org/10.1002/aic.690400217
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    Protein precipitation: Effects of mixing on protein solubility (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 349-360 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mixing effects in protein precipitation processes are very poorly understood. They impact apparent protein solubility, protein structure in precipitates, particle size, morphology and recoverable activity. In this work, a model is proposed to describe the impact of mixing on protein solubility in precipitation processes. A series of semibatch-mode precipitation experiments were performed using bovine liver catalase and ammonium sulfate to test model predictions. The process variables studied include initial protein supersaturation, agitation rate, and rate of addition of salt solution to the initial protein solution. The mixing model parameters were estimated independently with the aid of a series-parallel dye reaction. The results showed good agreement between model and experiment. The initial protein supersaturation was the most important variable at the 1-L scale. The influence of mixing on recoverable activity was also examined. Scale-up guidelines are suggested based on model simulations and experimental results.
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    Continuous cocurrent processes in the nonsteady state (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 369-372 
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    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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    URL: http://dx.doi.org/10.1002/aic.690400216
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    Heat-transfer characteristics in viscous gas-liquid and gas-liquid-solid systems (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 745-755 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Local heat-transfer measurements are performed using a special heat-transfer probe in gas-liquid and gas-liquid-solid systems with viscous Newtonian liquids as the continuous phase. Effects of viscosity on bubble-liquid and bubble-liquid-solid interactions affecting local heat transfer are studied through heat-transfer experiments with simultaneous flow visualization in a simplified system involving single bubbles or a chain of gas bubbles moving in viscous liquids and liquid-solid systems. Effects of viscosity on bubble wake and local heat transfer are examined with reference to heat transfer in freely-bubbling beds (bubble columns and three-phase fluidized beds). The kinematic viscosity of the fluid greatly influences the nature of flow in the wake which affects local heat transfer in the bed. The local heat transfer decreases with the viscosity due to the rapid decay in the circulation strength of the bubble wake caused by increased viscous dissipation of vorticity. Local heat transfer due to cyclic/periodic injection of bubbles is significantly enhanced due to increased bubble-wake interactions which rapidly accelerate bubbles and increase average bubble rise velocity. Heat transfer in simplified liquid and liquid-solid systems with single- and chain-bubble injections characterizes the local heat-transfer performance of freely-bubbling beds (bubble columns and three-phase fluidized beds). A mechanistic model developed accounts for the heat-transfer behavior in bubble columns and three-phase fluidized beds with viscous liquids.
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    Oxygen permeation through thin mixed-conducting solid oxide membranes (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 786-798 
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    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 approach for developing fundamental equations of oxygen permeation through thin mixed-conducting oxide ceramic is presented considering both surface reactions on membrane-gas interfaces and the diffusion of charged species in the bulk oxide. The essence of this work is the coupling of surface reactions with the bulk diffusion using a novel approach which differs from the conventional Wagner. Theory applicable only to limited cases. With this approach, fundamental equations based on various permeation mechanisms can be derived for oxygen permeation through thin mixed-conducting oxide membranes, which is impossible using conventional approach. In general, the final results are a complex implicit equation correlating the oxygen permeation flux to the driving force, membrane thickness, and rate constants with physical significance in each step. Somewhat simpler theoretical oxygen permeation equations are obtained for some special cases (mixed-conducting membranes with a rate-limiting step, ionic-conducting membranes, ionic-conducting membranes with a reducing agent in permeate side). Theoretical results derived using this new approach agree excellently with the experimental oxygen permeation data. It is theoretically and experimentally shown that for ionic conductors, the surface permeation parameter measured by the dynamic permeation method is directly related to the oxygen isotope exchange rate constant measured under equilibrium conditions.
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    Optimization of distillation units using collocation models (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 813-825 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Reduced-order models are developed based on orthogonal collocation on finite elements for the steady-state optimization of multicomponent distillation units. The formulation divides the column sections into subdomains (finite elements) to track irregularities in the column profiles accurately and requies that plates with discontinuities in the flows introduced by feedstreams or sidestreams should be treated as discrete equilibrium stages. Application of the model formulation to a number of examples show that reduced-order models converge to the same optimal solution as the full-order, tray-by-tray model. Optimization results show that computational time can be reduced significantly using the more compact model formulation, and it is possible to converge to the optimal solution from a larger region for the initial set of variable values.
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    A novel reactor for determination of kinetics for solid catalyzed gas reactions (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 862-869 
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    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 novel perfectly mixed laboratory reactor for determining kinetics of heterogeneously catalyzed gas-phase reactions has been developed. Perfect mixing is achieved by circulating the gas in the reactor using an axial flow impeller in a well streamlined enclosure. Pellets are fixed in a rectangular opening in the blades of the impeller. They rotate with the impeller, thus realizing high particle velocities in the reactor. Interparticle mass transfer was studied experimentally by vaporization of naphthalene pellets. The mass-transfer coefficient in the novel reactor was found to depend on the velocity of a particle in the reactor. Mass-transfer coefficients in an internal recycle reactor at equal impeller tip speeds are 4-6 times lower than those in the novel reactor, and conditions can be chosen easily where at higher rotational speeds the mass- and heat-transfer rates are 8-10 times higher than in classical recycle reactors. The recycle flow rate in a recycle reactor was found to depend strongly on the resistance to flow caused by the catalyst bed itself. The novel reactor was tested under reacting conditions using the hydrogenation of ethene.
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    Simple approximate rate law for both short- and long-chain rice Herzfeld kinetics (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 908-910 
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    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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    URL: http://dx.doi.org/10.1002/aic.690400517
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    Hysteresis-dependent adsorption-desorption cycles: Generalization for isothermal conditions (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 913-924 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Hysteresis-dependent adsorption-desorption equilibrium cycles are measured for the systems water vapor-silica gel at 25°C. Various and distinct types of equilibrium cycles are observed, depending on the relative positions of the limiting partial pressures with respect to the closure points of the main hysteresis loop as well as the history of the cycle. Hysteresis-dependent cycles are classified accordingly. The simple theoretical model based on the network pore blocking theory for predicting primary and secondary adsorption and desorption isotherms (Rajniak and Yang, 1993) is extended for predicting isotherms of higher orders and equilibrium cycles of all types. Only primary adsorption and desorption isotherms are needed for the predictions. Furthermore, there exists an infinite number of equilibrium cycles between any two partial pressures within the main hysteresis loop; the exact path of the cycle depends on the history before the cycle is initiated - it is memory-dependent.
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    Errata (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 956-956 
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    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
    URL: http://dx.doi.org/10.1002/aic.690400606
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    Foam-enhanced devolatilization of polystyrene melt in a vented extruder (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 670-675 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Vented extruder devolatilization (DV) of PS melt containing 6,000 ppm styrene was studied by scanning electron microscopy (SEM) and video photography. Vacuum DV of a polymer is accompanied by foaming, which starts instantaneously upon supersaturation of the stretched melt and is enhanced at higher speeds of the vented extruder screw. As the volatiles are removed from the melt, foaming gradually ceases, starting with the pushing flight of the screw. The experimental installation design allowed us to quench the polymer melt in the DV zone at various stages of the process. Samples taken from four areas of the channel width were investigated by SEM. Bubble nucleation in the melt appears to take place mainly in the border area adjoining the gas phase. In the shear field caused by screw rotation, large bubbles become noticeably elongated. Their surface, as well as the free surface of the melt, is covered with blisters, 1-100 μm in size. Microblisters are often concentrated in areas subjected to stretching. Calculations of cooling due to volatile evaporation and of heating due to viscous dissipation near a growing bubble shows that the process of foam-enhanced DV of a PS/styrene system can be regarded isothermal if the initial volatile concentration does not exceed approximately 1%.
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    Solubility of HFC-134a refrigerant in glycol-type compounds: Effects of glycol structure (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 726-737 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Environmental concerns have dictated the replacement of CFC-12 refrigerant with HFC-134a in automotive air-conditioning (A/C) systems. Since polyglycols are synthetic compounds compatible with HFC-134a and considered as lubricants for the A/C compressor, interations of HFC-134a with glycol-type compounds and thermodynamic properties of the solutions are important in designing an A/C system. In this work, the solubility of HFC-134a in four glycol-type compounds was measured at -5 to 80°C and 90 to 960 kPa. HFC-134a had the greatest solubility in tetraethylene glycol dimethyl ether. HFC-134a was less soluble in hexylene glycol and tetraethylene glycol and least soluble in triethylene glycol. Mixtures of HFC-134a with TRIG or TGDE showed phase separation. Solubility data were used to calculate the activity coefficient of HFC-134a in glycol solutions. An equation of the form, lnγr = (1 - xr)[A + Bxr], was found to correlate γr to the mole fraction of HFC-134a in the solution where A and B are constants which may depend on the temperature. Based on a model assuming a specific interaction between molecules and using the activity of HFC-134a, a higher degree of interaction is expected between HFC-134a and tetraethylene glycol dimethyl ether molecules than between the molecules of HFC-134a and other glycols. In general, glycols with free -OH groups may have less affinity for HFC-134a. Solubility is discussed in terms of its parameters and chemical structure of the glycols, as well as the effect of temperature on the solubility, the activity coefficient, and the thermodynamic properties of the HFC-134a/glycol solutions.
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    Estimation of crystallization kinetics from batch cooling experiments (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 799-812 
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    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 direct optimization method to estimate nucleation and crystal growth rate parameters from seeded batch cooling crystallization experiments is evaluated. The experimental information applied comprises the concentration of the solution and the temperature as functions of time and the final product size distribution. Parameters in kinetic equations are determined by nonlinear optimization of a dynamic model of the experiment, by which intermediate approximations of experimental data are avoided. The optimization objective function includes both solution concentration data and product size distribution data. Kinetics are estimated for succinic acid crystallizing in aqueous solutions. Results from several different cooling crystallizations are simultaneously supplied into one single optimization to determine seven parameters.
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    Stability in optimal design: Synthesis of complex reactor networks (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 849-861 
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    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 methodology applicable to the optimal design of stable process systems is presented. It is based on the formulation of a parametric problem that provides bounds on the optimal stable solution and an iterative algorithmic approach that attains convergence of the bounds in a finite number of iterations. The bounds on the optimal stable solution are based on analytical expressions of bounds on the eigenvalues of the Jacobian matrix using the concept of the measure of the matrix. When extended to the synthesis problem of reactor networks, the approach is able to couple the optimization problem with stability issues even in cases where the number of reactors is large and the reaction mechanism is described by a general complex reaction scheme. Furthermore, since at the synthesis level the reactor network represents an exhaustive superposition of the existing structural and operational alternatives, the approach fully exploits these alternatives and coordinates a weighted optimal search that improves the objective and accommodates a stable reactor network. This approach is not restricted to the synthesis of reactor networks and can be applied to the design of total process flowsheets.
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    Prediction of the properties of model polymer solutions and blends (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 878-887 
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    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 this work we present an extension of the statistical associating fluid theory (SAFT) developed for associating fluids by applying this extension to polymer solutions and blends. The polymer molecule is modeled as a flexible chain made of bonded spherical segments. These segments interact with the Lennard-Jones potential. The extension of SAFT is compared with molecular simulation results for polymer solutions and blends. Since the same force model is used in the simulation and theory, this comparison is a strong test of the assumptions made in deriving the theory. Results are presented for pure polymers of up to 50 segments long, polymer solutions of a polymer 20 segments long dissolved in its own monomer, and blends of polymers of 25 segments each. The theory produces results that are in better agreement with simulation results than the Flory-Huggins theory for the systems studied.
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    Prediction and correlation of accessible area of large multiparticle aggregates (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1167-1182 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Aggregates (composed of large numbers of primary particles) are produced in many engineering environments. One convenient characterization is the fractal dimension, the exponent describing how the number of primary particles in each aggregate scales with radial distance from its center of mass. We describe a finite-analytic pseudo-continuum prediction of the normalized accessible surface area of an isothermal quasi-spherical fractal aggregate containing N (≫ 1) primary particles, on the surfaces of which a first-order chemical process occurs. Results are displayed for specific fractal dimensions (2.5, 2.18, and 1.8) frequently observed in aggregating systems. An effective Thiele modulus is used to develop an efficient and accurate scheme for predicting/correlating the effectiveness factor for an aggregate containing N primary particles in terms of aggregate fractal dimension, reaction probability, and Knudsen number. Our methods now allow calculations of the accessible surface area of populations of aggregates, provided pdf \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} \rlap{--} ($\end{document}N, Df, …\documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--})$\end{document} is known for the populations of interest.
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    Self-diffusion coefficients of sol-gel intermediates (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1193-1202 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Sol-gel techniques have shown great potential for producing ceramic materials of designed composition and properties. A typical sol-gel process involves the hydrolysis and polymerization of one or more metal alkoxides in an alcohol solution in a batch reactor to form a homogeneous gel, which is then further treated to provide the type of ceramic desired (such as aerogel, glass, crystal, and coating). Several authors have suggested that diffusion effects may influence the development of the gel microstructure. We investigate what governs the diffusivity of the precursors using the pulsed-gradient-spin-echo NMR technique. This initial report focuses on the early stages of the batch reaction.The system chosen is the acid catalyzed hydrolysis and condensation of tetraethyl orthosilicated in ethanol. 1H PGSE NMR and 29Si NMR show that the diffusivities of the silicate precursors are strong functions both of the molecular weight and of hydrogen bonding between the polar functional groups and the solvent. Moreover, since hydrolysis increases and polymerization reduces the concentration of these polar groups, the mobility of the reactive oligomers changes in a complex manner. Combining our results from PGSE NMR and gas chromatography, we estimate the extent of hydrogen bonding effect on the mobility of various oligomers, providing a model to predict diffusivity trends throughout the batch reaction.
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    Kinetics of p-xylene liquid-phase catalytic oxidation (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1156-1166 
    Details
    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 Semibatch gas-liquid reactor model based on a lumped kinetic schem for the liquid-phase oxidation of p-xylene to p-toluic acid catalyzed by cobalt naphtenate is developed. The model accounts for the complex nature of the involved reaction network, as well as for the interphase and intraphase mass transport processes of both reactants and products. The model reliability is tested by comparison with suitable experimental data obtained in a semibatch oxidation reactor, where the role of the composition of both the gaseous and the liquid feed has been investigated. It is shown that the model describes the reactor behavior in any of the regimes which may prevail depending upon the operating conditions and the depletion of liquid reactants in time.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400707
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    Competition between TiCl4 hydrolysis and oxidation and its effect on product TiO2 powder (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1183-1192 
    Details
    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 competition between hydrolysis and oxidation of TiCl4 during vapor-phase synthesis of titania powders was experimentally investigated. The effects of reactor temperature, reactant mixing and H2O/TiCl4 ratio were studied in a hot wall aerosol flow reactor. The presence of water vapor resulted in rounded particles instead of the faceted ones observed in the absence of water; this effect was most pronounced at lower reactor temperatures. Mixing the water and TiCl4 vapor streams at low temperature resulted in anatase titania. Larger aggregates with smaller primary particles were observed for powders synthesized in the presence of water vapor. The mixing temperature of the water and TiCl4 vapors, as well as the H2O/TiCl4 ratios, did not affect the aggregate size or specific surface area. Analysis of micrographs of titania aggregates made in the presence of water revealed that the fractal dimension increased with process temperature.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400709
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    Physics of polymer surfaces and interfaces. Edited by Isaac C. Sanchez, Butterworth-Heinemann, 1992, 336 pp. (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1088-1089 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690400623
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    Flow structure in a three-dimensional bubble column and three-phase fluidized bed (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1093-1104 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Macroscopic flow structures of 3-D bubble columns and gas-liquid-solid fluidization systems under various operating conditions are studied using particle image velocimetry. Flow visualization is also conducted with the aid of a laser sheeting technique. The refractive index matching technique is used to eliminate the opaqueness of solid particles occurred in the visualization study of gas-liquid-solid fluidization. Three flow regimes (dispersed bubble, vortical-spiral flow, and turbulent flow) are identified. The flow structure is investigated for various operating variables including liquid velocity, gas velocity, and particle holdups. Four flow regions (descending flow, vortical-spiral flow, fast bubble flow, and central plume) can generally be characterized in the vortical-spiral flow regime where the gross circulation pattern occurs. A conceptual model for the flow structure in the vortical-spiral flow regime is discussed. The transition of the flow regimes and structure in the vortical-spiral flow regime is postulated to be related to the Taylor instability for flow between two concentric rotating cylinders. Similarities between the flow structures of 2- and 3-D beds are also discussed.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400702
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    Pressure swing adsorption reactors: Simulation of three-step one-bed process (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1118-1137 
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    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 three-step (feed, delay, and purge), one-column pressure swing adsorption reactor has been analyzed. An equilibrium model taking into account species mass balances, overall mass balance, momentum balance, reaction rate, and nonlinear multicomponent adsorption equilibrium isotherms was derived to describe the PSA reactor process. Numerical solution of model equations was obtained by using the method of orthogonal collocation on finite elements, and simulation results showed that 10-20% higher conversion than reaction equilibrium conversion in a fixed-bed reactor could be obtained from the PSA reactor for a reversible reaction A ⇄ B + C, such as dehydrogenation of ethane to ethylene and hydrogen on cadmium-exchanged zeolites, where only product B was assumed to be adsorbed. When both reactant A and product B are adsorbed, 10% higher conversion over the reaction equilibrium limit was observed for pure reactant feed. The effects of system and operating parameters on the process performance of the PSA reactor have been studies, as well as the bed dynamics of the PSA reactor at the cyclic steady state.
    Additional Material: 20 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400705
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    Constraint handing and stability properties of model-predictive control (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1138-1155 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Effects of hard constraints in the stability of model-perdictive control (MPC) are reviewed. Assuming a fixed active set, the optimal solution can be expressed in a general state-feedback closed form, which corresponds to a piecewise linear controller for the linear model case. Changes in the original unconstrained solution by the active constraints and other effects related to the loss of degrees of freedom are depicted in this analysis. In addition to modifications in the unconstrained feedback gain, we show that the presence of active output constraints can introduce extra feedback terms in the predictive controller. This can lead to instability of the constrained closed-loop system with certain active sets, independent of the choice of tuning parameters. To cope with these problems and extend the constraint handling capabilities of MPC, we introduce the consideration of soft constraints. We compare the use of the l2-(quadratic), l1-(exact), and l∞-norm penalty formulations. The analysis reveals a strong similarity between the control laws, which allows a direct extrapolation of the unconstrained tuning guidelines to the constrained case. In particular, the exact penalty treatment has identical stability characteristics to the correspondent unconstrained case and therefore seems well suited for general soft constraint handling, even with nonlinear models. These extensions are included in the previously developed Newton control framework, allowing the use of the approach within a consistent framework for both linear and nonlinear process models, increasing the scope of applications of the method. Process examples illustrate the capabilities of the proposed approaches.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400706
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    Chaotic mixing of viscous fluids by periodic changes in geometry: Baffled cavity flow (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1769-1781 
    Details
    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 baffled cavity flow - the first representative of a class of chaotic flows produced by time-dependent changes of geometries - is introduced and extensions to spatially-periodic systems proposed. Both experimental and computational results are reported. The goal of the study is to put into evidence some of the steps and considerations when designing a new mixing flow; a related objective is to demonstrate the use of an efficient and accurate numerical technique (BIEM) suitable for mixing studies in time-dependent geometries. Several parameters that affect the degree of mixing are studied: the mixing protocol - how the baffles are alternated and how many baffles are used in the flow during each piecewise motion; baffle sizes and shapes; geometrical and flow parameters, such as the wall displacement per period; and details of the baffle's motions.
    Additional Material: 17 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690401102
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    Fouling of tube surfaces: Modeling of removal kinetics (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1804-1813 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fouling of tube surfaces from flowing solutions or suspensions is examined. A new approach to the removal aspects of this process is presented linking removal to the morphological and mechanical characteristics of deposit microstructure. A simplified description of deposit microstructure is employed, involving a collection of geometrically similar roughness elements. A dynamic situation is envisioned whereby these elements grow due to deposition and suffer breakage under the action of hydrodynamic forces. A mathematical model for the macroscopic fouling behavior based on the techniques of population balances is obtained and numerically analyzed. The behavior found is in agreement with experimental evidence.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690401105
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    On-line terpolymer composition control in semicontinuous emulsion polymerization (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1850-1864 
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    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 closed-loop strategy for terpolymer composition control in semicontinuous emulsion polymerization of high solids content systems is presented. This strategy is based on a nonlinear adaptive controller that calculates the flow rate of the more reactive monomers to be added into the reactor to produce a terpolymer of a given composition. The nonlinear adaptive controller is based on a simplified mathematical model of the process that includes the on-line estimation of an adjustable parameter. The addition of a conventional feedback proportional-integral (PI) controller to the prediction of the nonlinear controller was studied by simulation. It is shown that the contribution of the PI controller is negligible. The controller was checked by computer simulation and also experimentally verified during the semicontinuous emulsion terpolymerization of high solids content (55 wt. %) of vinyl acetate, methyl methacrylate and butyl acrylate.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690401109
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    Dynamic data rectification by recurrent neural networks vs. Traditional methods (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1865-1875 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recurrent neural networks are used to demonstrate the dynamic data rectification of process measurements containing Gaussin noise. The performance of these networks is compared to the traditional extended Kalman filtering approach and to published results for model-based nonlinear programming techniques for data reconciliation. The recurrent network architecture is shown to provide comparable, if not superior, results when compared to traditional methods. The networks used were trained using conventional nonlinear programming techniques in a batch fashion.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690401110
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    Retention of proteins in cross-flow UF through asymmetric inorganic membranes (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1901-1910 
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    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 flow and retention of 0.1% w/w aqueous solutions of pepsin, bovine serum albumin (BSA), lipase, γ-globulin, and invertase with molecular weights of 36,000, 67,000, 80,000, 150,000, and 270,000 dalton (g/mol) are studied when they are tangentially filtered through an inorganic microporous membrane with a nominal pore size of 0.02 × 10-6 m made by Anopore, with transmembrane pressure differences up to 100 kPa. The data were analyzed within the frame of the film layer theory for the concentration polarization phenomenon. This allows the mass-transfer coefficient to be obtained for the cell used as a function of the feed circulation speed and the molecular weight of the solute. Apparent and true retention curves obtained lead to a size exclusion radius smaller than the nominal one but very similar to that obtained from scanning electronic photographs.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690401114
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    Analysis of steric hindrance effects on adsorption kinetics and equilibria (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1685-1696 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most existing adsorption models do not properly consider steric hindrance effects of preadsorbed solutes. As a consequence, the models often fail to represent the adsorption kinetics and equilibria accurately. In this work, we extend the random sequential adsorption concept for irreversible adsorption to analyze reversible adsorption on a continuous surface and a random site surface. Based on simulation results of these processes, general kinetic equations for one-component adsorption are developed. The equations are used to correlate chromatography frontal curves of lysozyme and isotherm data of ethane adsorption on activated carbon and ethylene adsorption on a molecular sieve. The significance of the equations, as compared with the Langmuir equation, lies not only in their ability to correlate the experimental data more accurately, but in the physical significance of the adsorption parameters such as the maximum adsorption capacity obtained from the correlation. Our study shows that steric hindrance effects alone result in nonlinear Scatchard and Hill plots with negative cooperativity.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690401010
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    Characterizing patterns in plant somatic embryo cultures: Its morphology and development (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1728-1740 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: While being developed, plant somatic embryos change shape and increase size. An effective kinetic description of growth and development of somatic embryos is important for process scale-up and optimization. An essential component of such a kinetic description is the developmental characterization of the individual embryos present in culture. Embryo morphological data obtained by image processing techniques were transformed into sizeand size-independent morphological descriptors. Qualitative relations between the descriptors and geometric properties of the embryos were established to interpret the results. For training, a branch-and-bound search technique was used to search for optimal subsets of descriptors, as determined by member clustering and class separability properties evaluated from within-class and between-class scatter matrices. In the classification mode, individuals were identified using a voting nearest neighbor classifier. This nonparametric nearest-neighbor classifier was trained on optimal projections of the feature space established from developmental stage discrimination (branch-and-bound algorithm). Using a test population, normal and abnormal embryos and callus were assigned to six morphological classes. The image-analysis-based classification was in 80-90% agreement compared to the results obtained through visual classification by an experienced operator.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690401013
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    Experimental study on a four-bed PSA air separation process (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1976-1982 
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    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 200-s PSA cycle involving both pressure equalization and product backfill steps has been experimentally studied on a four-bed system, where LINDE 5 A zeolites were used as the adsorbent to separate oxygen from air. This cycle is operated under a pressure ratio of 4.3. During the experiment, the pressure history and flow rates, as well as the concentration of the product stream have been continuously monitored. This is the first time detailed experimental data on a four-bed system are presented. Under favorable conditions, this system produces better than 90% oxygen at a recovery of 17%. For the low-pressure ratio, such a recovery could not have been achieved without the pressure equalization step and the reduced purge operation. Recovery and throughput, however, are not as high as one would expect from a linear local equilibrium model. The self-broadening effect of the purge wave has been identified as the major cause of underperformance.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690401207
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    Control of emulsion polymerization reactors (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1993-2021 
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    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 interest in emulsion polymerization is strong because it offers the possibility of producing products with special properties not easily produced by other types of polymerization processes. Because the main reaction medium is water, not an organic solvent, its importance is steadily increasing with efforts to design environmentally benign processes. The control of emulsion polymerization is a challenging problem due to major limitations encountered in its modeling and on-line monitoring. Although emulsion polymerization has been studied and used for several decades, progress has been slow. Industrial practice relies heavily on experience while several controversial issues are still being studied. The literature related to this issue is vast and sometimes contradictory, and most deals with experimental investigation of specific emulsion polymerization systems to improve the process understanding and develop a process model. However, universally accepted conclusions are scarce. This article reviews the major issues related to control of emulsion polymerization. The latest contributions in process understanding, mathematical modeling, sensor technology, and process control techniques for emulsion polymerization are discussed. Emphasis is on contributions, which are important in resolving the control of emulsion polymerization processes.
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    Granular matter: An interdisciplinary approach. Edited By A. Mehta, Springer-Verlag, New York, 306 pp., 1994 (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1925-1925 
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    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
    URL: http://dx.doi.org/10.1002/aic.690401119
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    Fluctuational effects in the dynamics of liquid crystals. By E. I. Kats and V. V. Lebedev, Springer-Verlag, New York, 1994, 170 pp. (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1926-1926 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690401121
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    Experimental study and parameterization of gas absorption by water drops (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1950-1960 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Liquid-phase mass-transfer coefficients are determined for the absorption of sulfur dioxide by water drops larger than 1.1 mm in dia. A local model based on the large eddy interfacial model proposed by Fortescue and Pearson (1967) is obtained by the characteristic interfacial scaling. In particular, the agitation process of the liquid phase in the interfacial region is characterized by the interfacial liquid friction velocity. Experiments of sulfur dioxide absorption and desorption from large individually free-falling water drops are also carried out in a 5-m rain shaft under various environmental conditions. These experimental results agree well with those from the local model characterizing the interfacial process in water drops greater than 1.1 mm in dia.
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    Erratum (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1982-1982 
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    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
    URL: http://dx.doi.org/10.1002/aic.690401208
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    Diffusion of oxygen, nitrogen and their mixtures in carbon molecular sieve (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 577-585 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Diffusivities of oxygen, nitrogen and their mixtures in carbon molecular sieve are measured under conditions used for kinetic separation of air by adsorption (elevated pressures). In binary diffusion, codiffusion enhances fluxes for both components, whereas counterdiffusion has the opposite effects; for both cases, the effects are significantly more pronounced for the fast diffusing component. The multicomponent diffusion theory developed earlier in this laboratory for surface diffusion is reformulated for diffusion in molecular sieves. Multicomponent diffusivities can be predicted from the following pure-component information: concentration-dependent diffusivities and diffusional activation energies. Predicted binary diffusion results agree fairly with the experimental data for oxygen and nitrogen in carbon molecular sieve.
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    Continuous-Mixture kinetics of thermolytic extraction of coal in supercritical fluid (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 131-142 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Thermolysis of coal yields a complex mixture of many extract products whose molecular-weight distribution (MWD) varies with time for continuous-flow, semi-batch experiments. A laboratory flow reactor with a differential fixed bed of coal particles contacted by supercritical tert-butanol was used to provide dynamic MWD data by means of HPLC gel permeation chromatography of the extract. The experimental results, multipeaked, time-dependent MWDs of extract molecules, are interpreted by a novel mathematical model based on continuous-mixture kinetics for thermal cleavage of chemical bonds in the coal network. The parameters for the MWDs of extractable groups in the coal and the rate constants are determined from the experimental data. The effect of temperature on the kinetics of the extraction is explained in terms of one- and two-fragment reactions of the extractable groups in the coal. At lower temperatures (613 and 633 K) single-fragment reactions dominate, but at higher temperatures (653 and 673 K) more bonds in the coal are broken and the two-fragment reactions become significant. Also, the detailed MWDs are related to conventional lumped data for the thermolytic extraction process. The results yield information about the structure of coal, as well as the kinetics and mechanism of supercritical thermolytic reactions.
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    URL: http://dx.doi.org/10.1002/aic.690400115
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    Determination of vapor pressure in vapor-induced puffing (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 160-165 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Water vapor pressure for cornstarch and popcorn grits at a temperature of between 100 and 180° C was determined by measuring vapor pressures generated at various moisture contents in a heated, closed system. At a higher temperature, fugacity of water increased with increasing temperature probably because of melting or partial melting of starch. The apparent heat of sorption for cornstarch changed significantly with moisture content and temperature. Noncondensible gases were produced by heating popcorn grits to temperatures above 150°C. It is not accurate to estimate vapor pressure based on the heat of sorption or extrapolation of currently used empirical isotherm equations to a temperature above 100°C. Vapor pressure inside popcorn at the instant of popping are. roughly 758 to 827 kPa (110 to 120psia).
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    Explicit calculation of multicomponent equilibria for ideal adsorbed solutions (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 182-186 
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    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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    URL: http://dx.doi.org/10.1002/aic.690400121
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    Fluidization: Idealized and bubbleless, with applications by M. Kwauk, ellis horwood, new york, 1992, 277 pp., $85.50. (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 380-380 
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    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
    URL: http://dx.doi.org/10.1002/aic.690400219
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    Masthead (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994) 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690400301
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    Electrochemical membrane process for flue gas desulfurization (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 143-151 
    Details
    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 flue gas desulfurization process being developed for coal-fired power plants removes and concentrates sulfur oxides (SOx). The key element is an electrochemical cell using a sulfur oxide selective membrane. It achieves 90% sulfur oxide removal with near 100% electric current efficiency.Recent research has focused on improving the structure of the electrochemical membrane and its interface with the electrodes. The capillary forces of the membrane and porous electrodes establish an equilibrium. To maintain electrode surface area enhancement, it is necessary to retain the electrolyte in the membrane and allow only wetting of the electrode pores. Chemically-stable matrix materials for the membrane have been identified; several fabrication techniques were used to prepare the actual membrane structure. A new electrode material, (LiO)xNiO, possesses the proper chemical stability and electrical properties in the corrosive environment. These modifications have led to an order of magnitude increase in flux and operating lifetime.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400116
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    Hydrodynamic behavior of circulating fluidized bed with polymeric particles (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 193-206 
    Details
    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 study conducted explores the hydrodynamics of a circulating fluidized bed with polymeric particles employing polyethylene resins with a particle density of 660 kg/m3 and size ranging from 90 to 500 μm. The study indicates that polyethylene resins can be fluidized smoothly in the fast fluidization regime. However, the operating range of the fast fluidization regime for these particles is smaller than that for FCC particles. The deviation of the fluidization behavior of polyethylene particles from that of common Group-A particles is explained considering the interparticle forces. Experiments with fine polyethylene particles are also conducted with coarse particles added in a circulating fluidized bed. Axial profiles of solid holdups in a bed with and without coarse particles, as well as overall fine particle holdup, are studied. The results show a significantly wider operating range of the fast fluidization regime and enhancement of fine particle holdups in a bed with the presence of coarse particles. For comparison, fluidization with FCC particles is also conducted. A mechanistic model considering particle-particle collision is proposed. The model accounts for the momentum exchange rate between a coarse particle and a cloud of fine particles, which explains the enhancement of fine particle holdups observed experimentally.
    Additional Material: 18 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400202
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    Hydrodynamic assist of dynamic wetting (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 229-242 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dynamic wetting speeds are limited by the gross entrainment of air between the liquid and the moving substrate. We present experimental data for the curtaincoating method, in which liquid impinges at high speed on the substrate. We also show that air entrainment is strongly affected by macroscopic hydrodynamics and is subject to hysteresis. Using boundary-layer theory, a simple hydrodynamic model is developed for the flow field in the impingement zone away from the dynamic wetting line. The model approximately accounts for the shear thinning of polymer solutions and for the influence of surface tension. We apply the molecular kinetic theory of dynamic wetting, modified to account for hydrodynamic stress, to the immediate vicinity of the wetting line. The main result is a correlation for airentrainment data.The experimentally calibrated model predicts that the hydrodynamic assist of wetting is greatest when the dynamic wetting line is located beneath the impinging curtain. Flow visualization supports this physical picture.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400205
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    Kinetic modeling of free-radical graft polymerization (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 294-311 
    Details
    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 kinetic model of free-radical surface graft polymerization developed is based on a conservational polymerization and molecular-weight distribution (CPMWD) numerical algorithm. The CPMWD model uses an implicit numerical technique to solve for the coupled monomer, surface site, and total growing polymer differential rate equations, which ensure that conservation of mass is maintained. The model formulation allows for the incorporation of kinetic rate coefficients, which are a function of the chain length of the reacting species, the solution viscosity, and the concentration of surface grafted polymer. The model also makes it possible to evaluate the monomer conversion, the graft yield and the molecular weight distributions of the homopolymer and surface-grafted polymer for the complete duration of the graft polymerization reaction. Its application was demonstrated for a model system of vinylpyrrolidone graft polymerization onto the surface of a silica substrate.
    Additional Material: 18 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400209
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    Model-predictive pH control using real-time NARX approach (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 269-282 
    Details
    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 comprehensive real-time identification/control methodology based on the concept of nonlinear autoregressive exogenous input (NARX) models and adaptive, nonlinear, model-predictive control (ANMPC) is applied to a pH neutralization process. The existing NARX model theory has been extended by incorporating measured disturbances. NARX models have shown superior predictive characteristics in comparison to linear models. The proposed real-time methodology uses a pointer vector being created during an initial identification and model structure selection procedure. Using this pointer vector, which allocates the chosen elements from the pool of all possible linear and nonlinear combinations, one needs no explicit information about the model structure for the closed-loop control. The nonlinear programming problem encountered in ANMPC is solved by a gradient-based modified Marquardt and finite difference methods. The design procedure and explicit algorithms are discussed for the multiinput/multioutput case. A pH wastewater neutralization process used illustrates and verifies the procedure by computer simulations and a real-time laboratory-scale experiments.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400207
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    Measurement of diffusion coefficient using a closed capillary technique (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 365-368 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400215
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    Drop size distribution and holdup profiles in a multistage extraction column (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 407-418 
    Details
    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 population-balance-equation model is employed for the analysis of liquid-liquid extraction columns. This model considers drop breakage, coalescence, and exit phenomena for the drop phase caused by drop-drop and drop-continuous phase interactions. Drop breakage and coalescence rates are employed from a previous study on liquid dispersions in stirred-tank contactors. A drop exit frequency is developed based on a stochastic modeling approach. The model is tested by drop size distribution and dispersed-phase volume fraction (holdup) data obtained for a multistage column contactor of pilot-plant scale. Steady-state drop size distribution and transient holdup measurements are obtained by a photomicrographic technique and an ultrasonic technique, respectively. The model can predict flooding of the column. The effect of mass transfer on the hydrodynamic parameters of the contactor is also examined. The population-balance-equation model can be used for the control of extraction columns and can be extended to include mass-transfer calculations for the prediction of extraction efficiency.
    Additional Material: 13 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400304
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    On-line molecular weight distribution estimation and control in batch polymerization (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 445-462 
    Details
    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 molecular weight distribution (MWD) estimator for batch methyl methacrylate solution polymerization is implemented experimentally for on-line control and estimation of the MWD. The estimator is based on an extended Kalman filter and provides current estimates of the entire MWD, reaction temperature, monomer conversion, and initiator conversion. It uses a detailed polymerization model, on-line monomer conversion measurements, temperature measurements, and periodic, time-delayed measurements of the MWD from an on-line size-exclusion chromatograph. The estimator is shown to perform well with several on-line MWD estimation experiments. Real-time feedback control of the molecular weight is presented by utilizing the on-line MWD information. Temperature, monomer-addition, and simultaneous temperature and monomer-addition control are investigated experimentally to achieve a specific constant weight-average molecular weight. The on-line feedback control is effective in rejecting realistic disturbances which deteriorate molecular weight control.
    Additional Material: 34 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400308
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    Dynamic modeling of product grade transitions for olefin polymerization processes (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 506-520 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most olefin polymerization processes produce a wide range of resin grades to suit market demand. Determining the transition policy between these grades is an important consideration that can affect process economics and safety. In this article, we compare several grade transition strategies and the relative performance of solution, slurry, bulk and gas-phase processes for the production of polypropylene, linear low-density polyethylene, high-density polyethylene and ethylene-propylene rubber. It is shown that the most important parameters that determine the grade transition performance of a process are reactor design, residence time, runtime per grade and residence time distribution of the polymer, gas and/or solution phases. Slow hydrogen dynamics severely retard grade changes involving increases in product molecular weight. The simulation results are obtained by using the dynamic simulation package “POLYRED” developed at the University of Wisconsin-Madison.
    Additional Material: 29 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400312
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    Modeling, simulation and kinetic parameter estimation in batch crystallization processes (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 586-593 
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    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 dynamic model of a seeded batch crystallizer is used to investigate the process-dependent aspects of nucleation and growth kinetic parameter estimation by computer simulation. The satisfactory identification of all parameters in power-law-type kinetics with respect to supersaturation requires the use of nonlinear parameter transformations. The proper choice for transformation is problem-dependent, becoming more sensitive as nucleation rates increase, and the percentage of crystals below the measurable range increases.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400403
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    Structural analysis and output feedback control of nonlinear multivariable processes (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 647-669 
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    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 article concerns general multivariable nonlinear processes, particularly those with singular characteristic matrix. A precise characterization of the structural process properties that give rise to generic singularity of the characteristic matrix is initially developed within a graph-theoretic analysis framework. An output feedback controller synthesis problem is then formulated for multivariable processes with singular characteristic matrix. A comprehensive solution to this problem is obtained through a combination of dynamic state feedback controllers and state observers. The performance and robustness characteristics of the proposed control methodology are illustrated through simulations in a double-effect evaporator.
    Additional Material: 19 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400409
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    Modeling the spontaneous ignition of coal stockpiles (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 991-1004 
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    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 spontaneous ignition of coal stockpiles is a serious economic and safety problem. This phenomenon is analyzed using the approach of modern reaction engineering, which is made challenging by the nonlinear interactions of chemical reaction, heat transfer, and buoyancy-driven flows within and around the stockpile. A model developed represents reaction and transport within a realistically-shaped stockpile and transport and flow in the surrounding air. A new methodology based on the Galerkin finite-element method (Salinger, 1993b) allows for efficient solution of flows in both porous and open domains. Bifurcation analysis is used to track steady-state model solutions of relevant parameters, such as the Damköhler number (dimensionless reaction rate), Rayleigh number (dimensionless driving force for buoyant flow), and dimensionless permeability of the stockpile. The solutions provide an understanding of the roles of various transport mechanisms on the ignition behavior and nonlinear coupling between these mechanisms. Results clearly demonstrate the need for incorporating realistic descriptions of flow and transport in the surrounding air into the model.
    Additional Material: 9 Ill.
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    Physical forces and the mammalian cell. Edited by J. A. Frangos, Academic Press, 1993, 400 pp. (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 738-739 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690400417
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    Structure of falling film heat and mass transfer on a fluted tube (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 756-766 
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    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 falling liquid film has become a popular means of transferring heat and mass from a vapor to a binary liquid, especially in gas-fired heat pump systems. Ideally, the required amount of heat and mass transfer can be accomplished by using a simple cylindrical tube; however, increasingly stringent size and weight requirements for the machine prohibit use of the simple cylindrical surface, and other more complex surfaces with higher absorption capacities have been sought. In this article, absorption of a single component and condensation of a binary mixture on an axially fluted tube is considered. The solution to the problem hinges on the energy equation, although the entire energy transfer process is mass-transfer-limited. Significant mass transfer is limited to a thin layer near the liquid-vapor interface. Solutions to the energy equation are obtained for both the conduction- and convection-dominated regimes. In the latter, significant heat transfer occurs within a thin layer near the liquid-vapor interface which contains the mass transfer layer; this “boundary layer” structure does not appear to have been recognized in previous work in this area. Using the present results, the capacity of a given tube may be predicted as a function of governing geometrical and physical parameters. The principal objective of this work is to develop the theoretical tools from which computations may be carried out during a design process. The theoretical results may be applied to mixtures typical of application in the absorption heat pump industry.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400503
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    Masthead (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994) 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690400501
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    Microhydrodynamics: Principles and selected applications. By Sangtae Kim and Seppo J. Karrila, Butterworth-Heinemann, Boston, 1991, 507 +xxiii pp., $69.95 (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 739-743 
    Details
    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
    URL: http://dx.doi.org/10.1002/aic.690400418
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    Diagnosis of multiple simultaneous fault via hierarchical artificial neural networks (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 839-848 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We discuss a new type of macroarchitecture of neural networks called a HANN and how to train it for fault diagnosis given appropriate data patterns. The HANN divides a large number of patterns into many smaller subsets so the classification can be carried out more efficiently via an artificial neural network. One of its advantages is that multiple faults can be detected in new data even if the network is trained with data representing single faults. The use of a HANN is illustrated in fault diagnosis of a chemical reactor.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400510
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    Optimal fed-batch control of induced foreign protein production by recombinant bacteria (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 899-907 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Optimal control strategies for maximizing the production of induced foreign protein by recombinant bacteria were sought by the optimal control theory. Nutrient and inducer feeding rates were selected as key control variables. Since the problem is linear in the control variables, the optimal control is bang-bang or singular. Singular solutions are shown to exist. The optimal control theory showed that the specific growth rate with respect to nutrient concentration must be kept in its maximum phase and that there exist both a cell growth period and a protein production periods. The optimal control theory calculates exactly the growth and production periods. The glucose concentration is controlled along a singular are to give a maximum specific growth rate. The inducer level is controlled along a separate singular arc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400516
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    Simulation and optimization of NOx absorption system in nitric acid manufacture (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 944-956 
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    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 mathematical model has been developed for the prediction of the optimum design of packed and plate columns for the manufacture of nitric acid. The effects of inlet NOx composition, extent of oxidation and extent of absorption in each stage, temperature, and pressure have been included in the model. The optimization of the preoxidizer and the condenser has also been discussed.
    Additional Material: 17 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400605
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    Products in methane combustion near surfaces (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1018-1025 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Emission of carbon monoxide (CO), formaldehyde (CH2O), and unburned methane (CH4) are calculated for premixed methane/air mixtures impinging on a flat surface as functions of surface temperature, equivalence ratio, and strain rate with detailed chemistry involving 46 reversible reactions and 16 species using numerical bifurcation theory. Multiple solutions with different selectivities to stable products are found. On the extinguished branch unburned CH4, molecular hydrogen (H2), CO, and CH2O dominate, whereas on the ignited branch carbon dioxide (CO2) predominates near the surface. Cold walls can promote the selectivity to CO and CH2O near extinction, and high flow rates can increase considerably the formation of CO, CH2O, and unburned CH4. For example, an ignited stoichiometric methane/air mixture (9.5% CH4 in air) impinging on a surface of 1,000 K is calculated to produce 2% CO, 150 ppm CH2O, and 3% unburned CH4 for a strain rate of 500 s-1. Maximum efficiency of CH4 and minimum selectivity to CH2O occur near the stoichiometric ratio, whereas minimum selectivity to CO occurs for fuel lean mixtures. Comparison of combustion near surfaces with freely propagating flames is also shown.
    Additional Material: 10 Ill.
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    Ion adsorption and ion exchange in ultrathin films of fatty acids (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1046-1054 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ion exchange equilibria of ultrathin Langmuir and Langmuir-Blodgett films of stearic and arachidic acids in contact with aqueous electrolyte solutions were studied experimentally and theoretically. A model considering electrochemical and thermodynamic aspects of the adsoption of protons, calcium, and cadmium ions from solution to the film has been developed. Key parameters are the binding constants (K's) of ions and the mixing characteristics (or Flory-Huggins interaction parameters x's) of ions in the two-dimensional film lattice plane. The ternary system can be described by the parameter values determined with binary proton-calcium ion, proton-cadmium ion, and calcium-cadmium ion systems: KCa = 2.9 × 102, KCd = 8.6 × 103, KH = 3.6 × 106, χH - Ca = -0.76, χH-Cd = 0.13, and χCa-Cd = 1.0. Competitive ion adsorption was measured by FTIR ATR spectroscopy of either collapsed or ordered LB films. Data for the proton-calcium-cadmium ion system agreed well with the model predictions. The results show possible future applications of such thin films as ion sensors or ion exchange materials.
    Additional Material: 9 Ill.
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    Vapor-liquid equilibrium of polymer solutions using a cubic equation of state (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1203-1209 
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    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 recently proposed mixing rule has been combined with a cubic equation of state to correlate the vapor-liquid equilibria of various polymer + solvent and solvent + long chain hydrocarbon mixtures. We find that the two-parameter version of this model can correlate the solvent partial pressure in concentrated polymer solutions with high accuracy over a range of temperatures and pressures with temperature-independent parameters. For the solvent + long chain hydrocarbon systems, for which accurate vapor-phase concentrations are also important, the model is best used as a three-parameter correlation. Advantages of this approach are that it extends the application of cubic equations of state to polymer + solvent systems in a simple fashion and that generally only temperature-independent parameters are required which allow for accurate interpolation and extrapolation of available data.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400711
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    Determining fluid saturations during multiphase flow experiments by NMR imaging techniques (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1238-1245 
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    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 quantitative determination of porosity and saturation distributions in porous media using unclear magnetic resonance imaging techniques is addresed. A method based on multiple image acquisitions with extrapolation within a model of transverse relaxation was investigated for new experimental situations. The determination of saturation was validated with limestone and sandstone samples. Experimental evidence for dependencies of transverse relaxation and linewidth on saturation is discussed, as well as their impact on image resolution and quantitation. An automatic production measurement device for independent verification of average saturations during dynamic experiments is investigated.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690400714
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  • 193
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    Computation of holdups in fluidized and trickle beds by computer-assisted tomography (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1254-1261 
    Details
    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 fourth-generation X-ray computer-assisted tomography (CAT) scanner was used for the study of fluidized and trickle beds. A variety of exploratory experiments were performed, and images of density and holdup were obtained in three dimensions as a function of time. The gas/solid fluidized beds were glass bead/nitrogen and polyethylene/nitrogen systems. The trickle bed was a glass bead/nitrogen/water system. The algorithms presented can be used to determine holdup from X-ray absorption data. These algorithms - extensions of similar algorithms used for the calculation of fluid saturations in porous media - are applied on data of CAT scanner images as they are generated by the scanner and after they are transferred to a workstation. The results of the presented tests demonstrate how detailed holdup calculations can be performed in a chemical reactor. Radial and longitudinal variances of the holdup can be easily defined. The proposed algorithms can assist in the design of chemical reactor prototypes.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400716
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  • 194
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    Structure of the stretching field in chaotic cavity flows (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1273-1286 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Stretching of material elements in time-periodic cavity flows is investigated numerically. The spatial structure of the stretching field is determined not only by nonchaotic islands and by unstable manifolds of hyperbolic periodic points, but also by singularities of the flow field at the cavity corners. For the short time scales interesting to most mixing applications, regions of very high stretching (good local mixing) are determined by unstable manifolds that pass close to the corners of the cavity. Low stretching (poor local mixing) regions are usually found both inside and near islands. In some cases, however, the unstable manifolds wrap themselves around the islands, preventing the formation of segregated low stretching subregions within the chaotic region.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400802
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  • 195
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    Monitoring batch processes using multiway principal component analysis (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1361-1375 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Multivariate statistical procedures for monitoring the progress of batch processes are developed. The only information needed to exploit the procedures is a historical database of past successful batches. Multiway principal component analysis is used to extract the information in the multivariate trajectory data by projecting them onto low-dimensional spaces defined by the latent variables or principal components. This leads to simple monitoring charts, consistent with the philosophy of statistical process control, which are capable of tracking the progress of new batch runs and detecting the occurrence of observable upsets. The approach is contrasted with other approaches which use theoretical or knowledge-based models, and its potential is illustrated using a detailed simulation study of a semibatch reactor for the production of styrene-butadiene latex.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400809
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  • 196
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    Calculating critical transitions of fluid mixtures: Theory vs. experiment (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1376-1403 
    Details
    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 progress in predicting critical transitions in fluid mixtures is reviewed. The critical state provides a valuable insight into the general phase behavior of a fluid and is closely linked with the nature and strength of intermolecular interaction. Calculations of critical equilibria have been confined mainly to binary mixtures. The prediction of binary gas-liquid critical properties was initially limited to empirical correlations. These techniques have been superseded by rigorous calculations of the critical conditions using realistic models of the fluid or equations of state. All of the known types of critical phenomena exhibited by binary mixtures can be, at least, qualitatively calculated. If an optimal combining rule parameter is allowed, continuous gas-liquid properties can be calculated accurately for a wide variety of mixtures. Similarly, the pressure and composition dependence of upper critical solution phenomena can be accurately predicted. Progress has been achieved in predicting discontinuous critical transitions in polar and nonpolar binary mixtures. There is increasing interest in calculating the critical properties of ternary and multicomponent mixtures. Although the techniques applied to binary mixtures often can be directly extended to ternary mixture calculations, calculated critical properties of ternary mixtures indicate that their behavior cannot be considered as a simple extension of binary mixture phenomena. Consequently, ternary critical calculations are likely to provide a superior insight into the phase behavior of multicomponent fluids.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400810
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  • 197
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    Rise of gas bubbles in quiescent liquids (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1418-1421 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400814
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  • 198
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    Automated synthesis of distillation sequences using fuzzy logic and simulation (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1341-1348 
    Details
    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 automated distillation sequencing system (DSEQSYS) is presented, which consists of three components: a control program, a fuzzy heuristic synthesis program, and a process simulator. DSEQSYS, when applied to problems previously reported in the literature, overcomes some of the disadvantages of using heuristics or mathematical programming alone. DSEQSYS can address problems involving nonsharp separations, nonideal chemical behavior, and conflicting heuristics. A simple approach for converting the traditional separation heuristics into corresponding fuzzy heuristics is also demonstrated.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400807
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  • 199
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    Rapid three-dimensional velocimetry by nuclear magnetic resonance imaging (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1404-1407 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400811
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  • 200
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    Synthesis of nonequilibrium reactive distillation processes by MINLP optimization (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1479-1487 
    Details
    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 mixed integer nonlinear programming (MINLP) model is presented for synthesizing reactive distillation columns when chemical reaction equilibrium cannot be assured. The MINLP minimizes the total annual cost subject to a rigorous tray-by-tray model. The solution of this MINLP yields the optimal number of trays, the optimal feed rates, and the optimal feed tray locations. The liquid holdup per tray, the reflux ratio, and the temperature and composition profiles within the column are optimized as well. The MINLP is solved using generalized Benders decomposition, and the technique is illustrated with ethylene glycol synthesis.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400907
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