bluuebunny/crossref_metadata_2025 huggingface dataset:
2‐D Solution for drying with internal vaporization of anisotropic media
Authors: Perré Patrick , Turner Ian W. , Passard Joë
Published: April 2004

A set of physical assumptions for a straighfforward and eficient simulation of the dying of a porous medium submitted to a conuective and/or radiative heating is proposed. All of the parameters used are physical (liquid migration coefficient, peimeability values along the thickness and the length, thermal conductive, and external exchanges), but the relevant geometrical properties (length and thickness of the slab) were also included in the analysis. The 2‐D pressure field generated within the medium during the dying process is obtained by using an analytical expression. The treatment of the pressure field, especially for a strongly anisotropic medium, is an important feature of the model, which allows an analytical model for such a complicated porous medium as wood to be used across a wide range of dying conditions. The computer code developed from the proposed formulation permits a complete simulation of the drying process within a few seconds on a personal computer. Different configurations have been tested for both anisotropic (wood) and isotropic (light concrete) porous media. Agreement with the experimental results is reasonable in terms of the obserued physical phenomena. For instance, the model highlights dependence of the duration of the first diying rate on both material properties and drying conditions. This new model can be used for a global physical characterization of products by curve fitting and the collated information for the design of dryers.
Modeling shock layers in ion‐exchange displacement chromatography
Authors: Natarajan Venkatesh , Cramer Steven M.
Published: April 2004

In ideal displacement chromatography (systems with infinite mass‐transfer kinetics), various solutes are separated by sharp discontinuities. In real systems, however, the shocks are eroded into shock layers because of the finite rates of mass transfer. The thickness of these shock layers, which can reduce the yields achievable in these systems, depend on the flow rate, particle diameter and the “difficulty” of these separations. The steric mass action formalism of ion‐exchange chromatography was used in concert with a solid film linear driving force model to describe the effects of flow rate, particle diameter, and the degree of difficulty of the separation on ion‐exchange displacement systems. Simple pulse techniques are employed to estimate the thermodynamic and mass‐transfer parameters. The simulations are then compared to experimental results over a range of conditions. The results demonstrate that this relatively simple modeling approach can be employed to describe the behavior of these nonideal displacement systems.
Absorption of NOx gases in aqueous NaOH solutions: Selectivity and optimization
Authors: Pradhan M. P. , Joshi J. B.
Published: April 2004

A mathematical model is presented for multicomponent gas absorption with multiple reactions by considering the case of NOx absorption in aqueous solution of NaOH. Procedures are developed for estimating the overall reaction rates and selectivity. The effects of temperature, pressure, and NOx composition are examined. Optimum design strategy is suggested by proper configuration of the oxidation and absorption stages and by appropriate selection of levels of oxidation and absorption. A comparison between the model predictions and the performance of two operating plants is presented.
Modeling, analysis and control of ethylene glycol reactive distillation column
Authors: Kumar Aditya , Daoutidis Prodromos
Published: April 2004

The dynamic behavior and control of an ethylene glycol reactive distillation column were studied. A detailed tray‐by‐tray model that explicitly includes the vapor‐phase balances is derived and compared with a conventional model that ignores the vapor holdup. The steady‐state variation of the product purity (the key output to be controlled) with respect to reboiler heat duty was studied, identifying a region of output multiplicity with three branches corresponding to different conversion and product selectivity. Further analysis of the process on the steady‐state branch with high conversion and selectivity reveals a transition from minimum phase behavior at moderate purity to nonminimum phase behavior at high purity. The nonminimum phase behavior was analyzed and addressed in the design of a nonlinear inversion‐based controller that performs well with stability in the high purity region.
Design of reactive crystallization systems incorporating kinetics and mass‐transfer effects
Authors: Kelkar Vaibhav V. , Ng Ka M.
Published: April 2004

A coherent approach for the design of reactive crystallization systems is presented by incorporating reaction and crystallization kinetics, and mass transfer, into an existing equilibrium‐based conceptual design method. A generic model for a well‐mixed crystallizer is developed; it is applicable to reacting systems with any number of components. The reaction, mass‐transfer and dissolution Damköhler numbers, and the nucleation and growth numbers which result from the generic model, represent the relative rates of the individual steps, and their effect on the resulting crystal‐size distribution and the crystallizer productivity is discussed. Estimates are provided for the typical values of the dimensionless numbers. To describe the solubility behavior of solid‐liquid systems, a generalized equation for the isothermal solubility of a solute in the presence of an arbitrary number of other components is presented. The effects of the dimensionless numbers on the process paths are shown on the phase diagrams for systems involving up to four components. The utility of this integrated approach in the design of reactive crystallization systems is discussed using examples involving single and coprecipitation systems, and a salting out crystallization system.
State observation of a nonlinear system: Application to (bio)chemical processes
Authors: Farza M. , Hammouri H. , Jallut C. , Lieto J.
Published: April 2004

The design of simple nonlinear observer‐based estimators for the on‐line estimation of the reaction rates in chemical and biochemical processes is presented. The proposed estimators do not assume or require any model for the reaction kinetics and are very successful for accurately estimating these variables. They are first presented in a continuous‐time version. Then, the stability and convergence of a discrete‐time version, obtained by a direct forward Euler discretization of these estimators, are established. A main characteristic of these estimators lies in the easiness of their implementation and in particular their calibration. Indeed, their gain does not necessitate the resolution of any dynamical system and is explicitly given. Moreover, its tuning is reduced to the calibration of a single parameter, and this is true regardless of the number of reaction rates to be estimated. The performances of the proposed estimators are highlighted through experimental results dealing with biological and chemical reactions performed in stirred‐tank reactors.
Robust dynamic state estimation of nonlinear plants
Authors: Alvarez Jesús , López Teresa
Published: April 2004

An on‐line state‐estimation design for multiinput multioutput nonlinear plants, either observable or detectable, is presented. The design considers a stage of analysis, in which the solvability of the estimation problem with robust convergence is assessed a priori, and a stage of synthesis, in which the estimator is constructed and its gains are tuned with a systematized procedure. The approach, which stems from a suitable definition of robust nonlinear observability or detectability, provides a methodological framework that identifies the compromise between the performance and the robustness of the estimator and interprets the functioning of the estimator with notions and vocabulary from conventional‐type linear filtering and control techniques. The problem for a class of free‐radical homopolymerization reactors is studied as an application example showing how the proposed design, together with available nonlinear dynamics modeling and characterization methods, can be applied to polymer reactor engineering in particular and to chemical‐process engineering in general.
Lumped kinetic model for catalytic wet oxidation of organic compounds in industrial wastewater
Authors: Zhang Qinglin , Chuang Karl T.
Published: April 2004

A simplified reaction pathway was proposed to describe the kinetic behavior of catalytic wet oxidation of organic mixture. The oxidation reactions were divided and lumped into two groups: (1) the deep or complete oxidation reactions with formation of CO2 and H2O; (2) the partial oxidation reactions with formation of all intermediates in aqueous solution of the industrial wastewater. The concentrations of all reactants in wastewater and those of the intermediates formed during the reaction are also represented by a lumped concentration of total organic carbon (TOC). To test the model, catalytic oxidation of organic pollutants in an effluent from a softwood Kraft pulp mill was investigated in a slurry reactor using a Pd‐Pt/Al2O3 catalyst. Sodium hydroxide was used to adjust the initial pH of wastewater to 7.3 to avoid the problem of metal leaching and excessive corrosion. The lumped kinetic model developed in this study describes well both our experimental data and those reported in literature. The lumped kinetic model proposed in this study can be used for both catalytic and noncatalytic wet oxidation processes.
3‐D nonisothermal flow simulation model for injected pultrusion processes
Authors: Mustafa I. , Khomami B. , Kardos J. L.
Published: April 2004

Injected pultrusion (IP) is an efficient process for high‐quality, low‐cost, high‐volume manufacturing of polymeric composites with relatively simple cross sections. This process was developed recently, and efforts to develop tools for model‐based design and optimization of this process have only just begun. This work focuses on developing a 3‐D nonisothermal computer simulation model for the IP process. First, the governing equations for transport of mass, momentum, and energy are formulated by using a local volume‐averaging approach. In turn, a computer simulation model of the IP process is developed using the finite‐element/control‐volume (FE/CV) approach. Specifically, the continuity equation and the conservation of momentum equation are solved using a Galerkin FE/CV technique. The chemical species balance equation is solved in the Lagrangian frame of reference, whereas the energy equation is solved using the streamline upwind Petrov‐Galerkin approach. Using the simulation model, the effect of fiber pull speed, reinforcement anisotropy, and taper of the die on the product quality was demonstrated. In addition a simple pulling‐force model was developed and integrated with the simulation model. Overall, the simulation model can be effectively used to design the die geometry and to optimize the operating conditions for a given product.
Growth processes in a cascade of bioreactors: Mathematical models
Authors: Mantzaris Nikolaos V. , Daoutidis Prodromos , Srienc Friedrich , Fredrickson Arnold G.
Published: April 2004

Mathematical modeling of continuous multiple bioreactors is complicated by two factors. First, the chemical environments differ in different reactors, so biomass receives an environmental shock when it is transferred between reactors. Second, biomass occurs as discrete cells, which of course are and remain segregated from one another, so an element of biomass that enters a reactor does not mix with the biomass already present. This differs from the behavior of an element of liquid which enters a reactor in that such an element quickly mixes with the liquid already present. The biomass in a bioreactor receiving biomass from an external source is therefore heterogeneous with respect to the history of environmental conditions and composition. This article shows how to construct a mathematical model of multiple bioreactor apparatus that accounts for these complications. It also describes simpler models that do not account for both of them.
Growth processes in a cascade of bioreactors: Comparison of modeling approaches
Authors: Mantzaris Nikolaos V. , Daoutidis Prodromos , Srienc Friedrich , Fredrickson Arnold G.
Published: April 2004

The theory of a two‐tank cascade of bioreactors developed by Mantzaris et al. (1998) was used to calculate the performance of such a cascade predicted by two chemically structured models: one for gene expression of Bentley and Kompala (1989) and Bentley et al. (1991) and the other a cybernetic model of Kompala et al. (1986) for multiple substitutable substrates. Two modeling approaches developed previously—one that accounts for biomass segregation and one that does not—were used with the model of Bentley and Kompala (1989) and Bentley et al. (1991). These modeling approaches showed that, in general, biomass segregation is an important feature of what happens in the second tank of the cascade and cannot be neglected. The same two approaches as well as a third approach based on the use of a chemically unstructured model were applied to the model of Kompala et al. (1986). It was found that biomass segregation in the second tank was important under some circumstances but not all and that the unstructured model failed to describe accurately what happens in the second tank under all circumstances.
Letter to the Editor
Authors: Zhang Weidong , Xu Xiaoming , Tan K. K.
Published: April 2004

No Abstrast.
Concentration profile for linear driving force model for diffusion in a particle
Authors: Li Zhong , Yang Ralph T.
Published: April 2004

No Abstrast.
Methane formation on H2 purification using a commercial Pd‐Ag membrane
Authors: Hsiung T. H. , Christman D. D. , Hunter E. J. , Homyak A. R.
Published: April 2004

No Abstrast.
Simulation of hydrodynamic performance of stirred extraction column
Authors: Steiner Ladislav , Balmelli Marco , Hartland Stanley
Published: April 2004

The hydrodynamic behavior of countercurrent extractors is described by balancing numbers of incoming and outcoming drops against those formed and destroyed by breakage and coalescence. The laws for these processes are still poorly understood, and no reliable experimental data exist. Special empirical equations were, therefore, derived from measurements in a stirred cell. Using a simplified model, a computer program for simulating the variation of the drop‐size distribution along the height of a pilot‐plant sized stirred column solved the equations for all column stages and preselected characteristic drop volumes. A comprehensive set of holdup and drop‐size distribution profiles measured earlier with the same column and o‐xylene dispersed in water has been simulated, with the average mean deviation of local drop‐size distributions not exceeding 20%. Transitional phenomena such as the startup time necessary for obtaining a new steady state after changing the operating parameters and the flooding were successfully predicted.
Capillary transport in adsorption from liquid phase on activated carbon
Authors: Aarden Frans B. , Kerkhof Piet J. A. M. , van der Zanden Antonius J. J.
Published: April 2004

Two models presented here predict the kinetics of adsorption from solution. The adsorbate is considered to form a capillary separated phase inside the micropores. The transport in the adsorbed phase is modeled as capillary transport under the influences of gradients in capillary pressure. In model I the capillary separated phase is assumed to be continuous, while in model II it is assumed to be discontinuous. The effective adsorbed phase diffusion coefficient for this transport is directly related to the pore‐size distribution, which can be found from the sorption isotherm. In both models the overall apparent diffusion coefficients are compared with experimental data. Both models satisfactorily predict the dependency of the diffusion coefficient on carbon loading. Model I slightly underestimates the temperature dependency of the effective diffusion coefficient, while model II gives a good prediction of the influence of temperature on the rate of adsorption.
Model for the interparticle surface separation in concentrated mono‐ and polydisperse suspensions
Authors: Hoffmann A. C. , Kevelam J.
Published: April 2004

The interparticle surface separation in mono‐ and polydisperse concentrated suspensions of spherical particles is discussed. For monosized particles, it is shown that the “expansion” argument of Frankel and Acrivos (1967) can be extended from cubic to arbitrary packing geometries. This argument is then further extended to polydisperse suspensions, resulting in an equation of the same form, but incorporating the surface mean particle diameter for the interparticle surface separation in terms of the packing fraction of the equivalent packed bed (a packed bed with the same packing geometry as the suspension) and that of the suspension. Another approach to interparticle surface separation in suspensions (the “volume of free liquid” argument) confirms the usefulness of the surface mean particle diameter for polydisperse suspensions. A relation potentially useful for suspensions of nonspherical particles is also given.
Dependence of cooled reverse‐flow reactor dynamics on reactor model
Authors: Khinast J. , Jeong Y. O. , Luss D.
Published: April 2004

Extensive simulations indicate that in most but not all cases the single‐ and two‐phase models predict similar dynamic behavior of a reverse‐flow reactor, when catalyst pellet multiplicity does not occur at any point in the reactor. Differences in the predictions are found in some cases close to the dynamic bifurcation loci of a cooled RFR, or in others when the qualitative dynamic behavior is very sensitive to the value of the parameters, such as close to a transition to chaotic behavior. The two models can lead to rather different predictions of the dynamic features when there are large differences between the feed and coolant temperatures.
Locating sensors in complex chemical plants based on fault diagnostic observability criteria
Authors: Raghuraj Rao , Bhushan Mani , Rengaswamy Raghunathan
Published: April 2004

Fault diagnosis is an important task for the safe and optimal operation of chemical processes. Hence, this area has attracted considerable attention from researchers in the past few years. A variety of approaches have been proposed for solving this problem. All approaches for fault detection and diagnosis in some sense involve the comparison of the observed behavior of the process to a reference model. The process behavior is inferred using sensors measuring the important variables in the process. Hence, the efficiency of the diagnostic approach depends critically on the location of sensors monitoring the process variables. The emphasis of most of the work on fault diagnosis has been more on procedures to perform diagnosis given a set of sensors and less on the actual location of sensors for efficient identification of faults. A digraph‐based approach is proposed for the problem of sensor location for identification of faults. Various graph algorithms that use the developed digraph in deciding the location of sensors based on the concepts of observability and resolution are discussed. Simple examples are provided to explain the algorithms, and a complex FCCU case study is also discussed to underscore the utility of the algorithm for large flow sheets. The significance and scope of the proposed algorithms are highlighted.
Solvent recovery targeting
Authors: Ahmad Berit S. , Barton Paul I.
Published: April 2004

One of the environmental challenges faced by the pharmaceutical and specialty chemical industries is the widespread use of organic solvents. With a solvent‐based chemistry, the solvent necessarily has to be separated from the product. Chemical species in waste‐solvent streams typically form multicomponent azeotropic mixtures, and this often complicates separation and, hence, recovery of solvents. A design approach is presented whereby process modifications proposed by the engineer to reduce the formation of waste‐solvent streams can be evaluated systematically. This approach, called solvent recovery targeting, exploits a recently developed algorithm for elucidating the separation alternatives achievable when applying batch distillation to homogeneous multicomponent mixtures. The approach places the composition of the waste‐solvent mixture correctly in the relevant residue curve map and computes the maximum amount of pure material that can be recovered via batch distillation. Solvent recovery targeting is applied to two case studies derived from real industrial processes.
Thermocapillary pumping of discrete drops in microfabricated analysis devices
Authors: Sammarco Timothy S. , Burns Mark A.
Published: April 2004

A nonmechanical pumping mechanism, thermocapillary pumping (TCP), is described for moving nanoliter‐ and picoliter‐sized drops of liquid within microfabricated flow channels. In TCP, one end of a single drop is heated to create a surface tension difference between the ends of the drop. The induced surface tension difference causes a capillary pressure difference between the two drop ends and results in drop motion. TCP velocities of up to 20 mm/min were measured for several liquids at temperature differences between 10 and 70°C. An expression developed for TCP velocity yields predictions that agree with experimental velocities within corresponding uncertainty limits. Several techniques for assisting TCP are also suggested when contact angle hysteresis, the major factor limiting TCP velocities, is too large. These techniques include using surface treatments to reduce the contact angle hysteresis, converging channels to offset hysteresis, or an applied pressure to assist in movement.
Combined calcination, sintering and sulfation model for CaCo3‐SO2 reaction
Authors: Mahuli Suhas K. , Agnihotr Rajeev , Jadhav Raja , Chauk Shriniwas , Fan L.‐S.
Published: April 2004

A mathematical model developed accounts for the multiple rate processes involved in the reaction of solid CaCO3 or Ca(OH)2 with SO2 at high temperatures in the combustion environment. The model, based on the grain‐subgrain concept, considers the concomitantly occurring calcination, sintering and sulfation reactions and their interactive effects on pore structure and reaction kinetics. It incorporates internal diffusion, reaction, and product layer diffusion in simulating the calcination of the CaCO3 grain and subsequent sintering and sulfation occurring on the CaO subgrains. It is the first sulfation model to incorporate the true mechanism of diffusion through the solid product phase: the solid‐state ionic diffusion of Ca2+ and O2− ions in a coupled manner through the nonporous CaSO4 (Hsia et al., 1993, 1995). Its predictions are compared with the random pore model (Bhatia and Perlmutter, 1981a) and the grain model (Szekely and Evans, 1971) using experimental CaO sulfation data from the literature as well as short‐contact‐time CaCO3 and Ca(OH)2 sulfation data reported previously. Mahuli et al. (1997) discussed a high reactivity modified calcium carbonate synthesized by optimizing the pore structural properties. This modified CaCO3 can convert 70–75% of sulfation within 0.5 s, which is substantially higher than any other sorbents reported for similar particle size and reaction conditions. The model is used to predict the calcination and sulfation kinetics, as well as to simulate the surface area evolution of the modified CaCO3, which provides further insights into its exceptional reactivity.
Theoretical analysis on extrusion die flow of electronic packaging materials
Authors: Pan Jing‐Pin , Liu Ta‐Jo , Wu Ping‐Yao
Published: April 2004

A mathematical model has been developed to describe the extrusion die flow of reactive electronic packaging materials. This model assumes that the flow is 1‐D in the manifold of the die, but the flow obeys the 2‐D Hele–Shaw model in the slot section. A realistic viscosity expression that includes the effects of chemical reaction and heat transfer has been adopted. A linearly tapered coat‐hanger die was selected for illustration and the packaging material was chosen to be the epoxy system. Some example calculations are presented to illustrate the effects of several parameters on the flow distribution. Two optimization approaches were adopted to improve the uniformity of the flow; both the Taguchi method and the method of inserting a specially designed choker bar are applicable. However, using a choker bar appears to be more effective and flexible.
NMR imaging of flow velocity in porous media
Authors: Chang C. T. Philip , Watson A. Ted
Published: April 2004

Two NMR velocity imaging methods based on the pulsed field gradient stimulated‐echo technique are evaluated for the measurement of fluid flow in porous media. The spatial resolution and dynamic scale of velocity imaging experiments are chosen to represent the macroscopic behavior of the complex motion of fluid molecules. A theoretical formulation for data interpretation is presented and demonstrated with experimental data for water flow in a glass‐bead pack and sandstone samples. Velocity imaging methods investigated include the use of flow‐induced phase shifts and the measurement of spatially resolved velocity distributions. The results show that the phase‐shift method is not suitable for some porous media. By contrast, the measurement of spatially resolved velocity distributions not only allows a map of mean velocity to be determined, but also provides information about the velocity field within each elemental volume of the image.
Prediction of flow fields in a dual‐impeller stirred vessel
Authors: Micale Giorgio , Brucato Alberto , Grisafi Franco , Ciofalo Michele
Published: April 2004

Numerical simulations were conducted for the flow field in a baffled tank stirred by a dual Rushton impeller. For this geometry, LDV measurements show a characteristic dependence of the flow patterns upon the position of the impellers. Two advanced modeling approaches were tested. In the first, the vessel was divided into two concentric blocks, coupled by a sliding grid technique, and simulations were conducted in time‐dependent mode. In the second approach, the vessel was modeled as two partially overlapping regions, the inner one rotating with the impeller and the outer one stationary; simulations were run in steady‐state mode for each of the two regions, while information was iteratively exchanged between them after azimuthally averaging and transforming for the relative motion. A third set of simulations was conducted for comparison purposes by using a more conventional method, in which the impellers were not explicitly simulated, while their effects were modeled by imposing suitable values of velocities and turbulence quantities (derived from single‐impeller experiments) at the blade periphery. The first two techniques gave similar predictions and successfully reproduced the dependence of the flow patterns on the position of the impellers. The latter method required far less computational effort. On the other hand, the impeller boundary conditions technique failed to reproduce the experimental flow patterns, because of the inadequacy of single‐impeller boundary conditions for the present geometry.
New thermally coupled schemes for ternary distillation
Authors: Agrawal Rakesh , Fidkowski Zbigniew T.
Published: April 2004

The fully thermally coupled system of distillation columns for ternary separation has two, two‐way connections between the columns. New, simplified (and easier to control) systems of columns for ternary separations, with a reduced number of connecting streams, are proposed. The new systems contain one one‐way and one two‐way connection between the columns. Depending on which connection is located on top and which phase stream (liquid or vapor) is used in the one‐way connection, there are four possible configurations for these new systems. For certain feed compositions and relative volatilities of components, these new systems can replace the fully thermally coupled system of columns without any increase in energy demand. The optimum system selected from the four proposed configurations consumes no more, and frequently much less, energy than the side stripper or side rectifier configurations or than a system with a prefractionator.
Modeling permeation of binary mixtures through zeolite membranes
Authors: van de Graaf Jolinde M. , Kapteijn Freek , Moulijn Jacob A.
Published: April 2004

The separation of ethane/methane and propane/methane mixtures with a silicalite‐1 membrane was investigated as a function of composition, total hydrocarbon pressure (up to 425 kPa), and temperature (273–373 K). The selectivity of the membrane is highly dependent on these operating conditions. The generalized Maxwell–Stefan equations were used to predict the fluxes and the associated selectivities. These model predictions, based on separately determined single‐component adsorption and diffusion parameters, were in excellent agreement with the experimental data. Using the empirical Vignes relation for the prediction of the binary Maxwell–Stefan surface diffusivity, there were no fitting parameters involved in the model prediction. The importance of incorporation of adsorbate–adsorbate interactions in the model is clearly shown, both for transient and steady‐state mixture permeation. Theoretical analysis showed that for mixtures of a fast, weakly adsorbing component and a slow, strongly adsorbing component the maximum selectivity obtained with microporous membrane separation is always a factor of 2 lower than the one obtained under equilibrium adsorption conditions.
Pervaporation for the mixture of benzene and cyclohexane through ppop membranes
Authors: Sun Yi‐Ming , Chen Yuan‐Kai , Wu Chi‐Huang , Lin Albert
Published: April 2004

Pervaporation and sorption for the liquid mixture of benzene and cyclohexane by using poly[bis(phenoxy)phosphazene] (PPOP) membranes were characterized. Diffusivities, solubilities, interaction parameters, plasticization coefficients, and heats of sorption for benzene and cyclohexane in the membrane were determined from the vapor sorption kinetics and isotherms, which were measured gravimetrically by a continuous microbalance. Pervaporation operations offered a maximum selectivity of 3 at 35°C and the 35–50% feed concentration level of benzene. Normalized fluxes increased but the pervaporation selectivity decreased slightly with temperature. The binary transport in the membrane was modeled by the solution–diffusion model with an exponential form diffusivity to the concentration of each permeant. Coupling coefficients imbedded in the model were numerically determined by a proposed computation method. The model can illustrate not only concentration and diffusivity profiles for the permeants within the membrane, but their transport mechanism, which is consistent with the hypothesis of “two layers” in the membrane. The analysis of activation energy for transport indicates that the permeation barrier for pervaporation is reduced much more than that of the single‐vapor permeation through an unswollen membrane.
Effects of carbon‐to‐zeolite ratio on layered bed H2 PSA for coke oven gas
Authors: Lee Chang‐Ha , Yang Jaeyoung , Ahn Hyungwoong
Published: April 2004

Effects of carbon‐to‐zeolite ratio on a layered bed H2 PSA using activated carbon and zeolite 5A were studied experimentally and theoretically. Coke oven gas (56.4 vol. % H2, 26.6 vol. % CH4, 8.4 vol. % CO, 5.5 vol. % N2, and 3.1 vol. % CO2) was used as a feed gas for the seven‐step two‐bed PSA process incorporating a backfill step. In these experiments, the effects of three operating variables such as adsorption pressure, feed rate and purge rate on the performance of a layered bed PSA were investigated. The layered bed gave better purity than the single‐adsorbent bed at the same operating condition, except at low purge rate. Since every component had its own front velocity at each layer, a carbon‐to‐zeolite ratio affected product purity at a given recovery or throughput. Moreover, for a high‐purity H2 product from coke oven gas, an optimum carbon‐to‐zeolite ratio had to be determined to control a leading wavefront of N2. In layered bed PSA processes, the temperature variations inside the bed reflected a kind of inflection or plateau at which a roll‐up phenomenon occurred and showed the dynamics of adsorption well at each step during a cycle. Simulated results of the dynamic model incorporating mass, energy and momentum balances agreed well with the PSA experimental results.
Hybrid first‐principles/neural networks model for column flotation
Authors: Gupta Sanjay , Liu Pi‐Hsin , Svoronos Spyros A. , Sharma Rajesh , Abdel‐Khalek N. A. , Cheng Yahui , El‐Shall Hassan
Published: April 2004

A new model for phosphate column flotation is presented which for the first time relates the effects of operating variables such as frother concentration on column performance. This is a hybrid model that combines a first‐principles model with artificial neural networks. The first‐principles model is obtained from material balances on both phosphate particles and gangue (undesired material containing mostly silica). First‐order rates of net attachment are assumed for both. Artificial neural networks relate the attachment rate constants to the operating variables. Experiments were conducted in a 6‐in.‐dia. (152‐mm‐dia.) laboratory column to provide data for neural network training and model validation. The model successfully predicts the effects of frother concentration, particle size, air flow rate and bubble diameter on grade and recovery.
Dynamic behavior of iron forms in rapid reduction of carbon‐coated iron ore
Authors: Sugawara Katsuyasu , Morimoto Koji , Sugawara Takuo , Dranoff Joshua S.
Published: April 2004

As a part of a fundamental study of the kinetics of rapid smelting reduction of iron oxide with solid carbon, particles of carbon‐coated iron ore were prepared by heating a mixture of iron ore and phenolphthalein (a model compound of coal tar) at 773 K in a nitrogen stream. The reduction behavior of the carbon‐coated iron ore particles during rapid heating was studied using a drop‐tube reactor at temperatures from 1,073 to 1,773 K. The reduction extent increased rapidly with the beginning of melting at temperatures over 1,650 K, reaching 60% at 1,773 within 0.7 s. The observed changes in the distribution of iron states in the particles were successfully simulated.
Carbochlorination of tantalum and niobium oxides: Thermodynamic simulation and kinetic modeling
Authors: Yang Fenglin , Hlavacek Vladimir
Published: April 2004

Carbochlorination reactions of tantalum and niobium pentoxides represent an interesting route of extraction of tantalum and niobium from ores or minerals. Both reactions have not been systematically studied in the literature. The kinetic study reported here was carried out in a fixed‐bed reactor in a temperature domain T = 800–1,000°C. The products of the reaction under the conditions studied are in the gaseous phase. With CO as a reducing agent, the reactions in question are of the noncatalytic gas–solid type, and the experimental data fit the shrinking core model. When using carbon as a reducing agent, the reactions are of the gas–solid–solid type, and the reactivity is much higher than that using CO alone. A reaction model based on phase boundary control was used to process the experimental data. Thermodynamic calculations revealed that at temperatures below 1,000°C the carbochlorination reactions result in the corresponding pentachlorides.
Methane hydrate crystallization mechanism from in‐situ particle sizing
Authors: Herri J. M. , Pic J. S. , Gruy F. , Cournil M.
Published: April 2004

A new experimental setup that makes possible in‐situ determinations of the population density function of the methane hydrate particles during its crystallization in a pressurized reactor is used. Thanks to this equipment, new results can be obtained, in particular concerning the granular aspects of the crystallization processes and the influence of the stirring rate. These results are discussed in the framework of a model including gas absorption, primary and secondary nucleation, crystal growth, agglomeration, and breakage. From this discussion, the relevant processes and parameters of methane hydrate crystallization can be determined and quantified.
Dynamic behavior issues in three‐way catalyst modeling
Authors: Koltsakis Grigorios C. , Stamatelos Anastasios M.
Published: April 2004

Mathematical modeling of three‐way catalytic converter (3WCC) operation is used increasingly in automotive catalyst and converter systems optimization. The majority of these models employ a “quasi‐steady” approach in the reaction kinetics computations, which is useful in predicting real‐world performance of the catalyst. However, certain improvements produced by the application of specially tuned redox oscillations cannot be predicted. The approach presented embodies certain types of dynamic phenomena in an existing 3‐WCC quasi‐steady model. The dynamic model based on this approach is validated against data in the literature and experimental results. It is confirmed that the catalyst behavior under dynamic exhaust composition conditions significantly differs from predictions under the quasi‐steady‐state assumption. Oxygen storage and the transient character of water gas shift reaction affect dynamic behavior. The results of this investigation encourage further application of mathematical modeling in such areas as lambda control strategy optimization that lie beyond the scope of traditional 3WCC models.
Estimation of pure compound properties using group‐interaction contributions
Authors: Marrero‐Morejón Jorge , Pardillo‐Fontdevila Eladio
Published: April 2004

A family of models proposed here estimate the critical constants and normal boiling points of pure organic compounds from chemical structure by using a new structural approach called group‐interaction contributions, which considers the contributions of interactions between bonding groups in the molecule instead of the contributions of simple groups. Compared to the conventional group‐contribution techniques, the proposed models demonstrate significant improvements in accuracy, as well as the ability to distinguish among isomers.
RTD analysis of a novel Taylor‐Couette flow device for blood detoxification
Authors: Ameer G. A. , Grovender E. A. , Obradovic B. , Cooney C. L. , Langer R.
Published: April 2004

Heparin is an anticoagulant used in extracorporeal procedures such as hemodialysis and open heart surgery. Unfortunately, heparin may induce potentially fatal complications in patients at high risk of bleeding. The use of an immobilized heparinase I reactor makes heparin therapy safer, but the design of a safe and efficient reactor for medical use had been a significant problem. A novel reactor, based on simultaneous separation‐ reaction and Taylor‐Couette flow, was designed and successfully tested in vitro with human blood and ex vivo in sheep. The objective of this study was to understand the flow dynamics in the reactor in order to predict and optimize heparin neutralization. Residence‐time distribution studies were performed and a mathematical model was developed. The model was able to predict experimental conversions within a mean relative error of 5.5%. Bypass flow through the reactive section was also predicted.
Maximum stable bubble size and gas holdup in high‐pressure slurry bubble columns
Authors: Luo Xukun , Lee D. J. , Lau Raymond , Yang Guoqiang , Fan Liang‐Shih
Published: April 2004

Experiments of pressure effects on gas holdup and bubble size in slurry bubble columns at 5.6 MPa and at gas velocities up to 45 cm/s indicate that the gas holdup increases with an increase in pressure, especially at high slurry concentration. At ambient pressure, a higher solids concentration significantly lowers gas holdup over the entire gas‐velocity range, while at 5.6 MPa, the effect of solids concentration on gas holdup is relatively small at gas velocities above 25 cm/s. An empirical correlation was developed based on these data and those in the literature to predict gas holdup in bubble and slurry bubble columns over a wide range of operating conditions. An analysis of bubble flow characteristics during dynamic gas disengagement indicates that large bubbles play a key role in determining gas holdup due to the large bubble and wake volumes that induce the acceleration of small bubbles. Direct measurement of bubble size shows that elevated pressures lead to smaller bubble size and narrower bubble‐size distributions. Bubble size increases significantly with increasing solids concentration at ambient pressure, while at high pressures this effect is less pronounced. A theoretical analysis of circulation of gas inside the bubble yields an analytical expression for maximum stable bubble size in high‐pressure slurry bubble columns. Based on this internal circulation model, the maximum stable bubble size at high pressures is significantly smaller due to the high gas inertia and low gas–liquid surface tension. The smaller bubble size and its reduced bubble rise velocity account for the observed pressure effect on gas holdup.
Bubble growth in a viscous liquid in a simple shear flow
Authors: Favelukis Moshe , Tadmor Zehev , Semiat Raphael
Published: April 2004

The nucleation and growth of a bubble in a Newtonian liquid in simple shear and creeping flow were studied experimentally in a Couette apparatus operating under vacuum. A low molecular weight polyisobutylene was chosen as a typical high‐viscosity Newtonian liquid. The volatile solvent in our experiments was simulated by air, and the formed or growing bubbles were photographed under shear. The experimental foaming results indicate that vacuum (at a level of supersaturation conditions) is not sufficient to boil a viscous solution, even in the presence of bubbles (nucleation sites), as shear also has to be applied. Furthermore, there is probably a critical shear rate (or stress) at which boiling appears. Bubble growth experimental results indicate that the growth rate of a slender bubble increases as the shear rate increases and as the pressure decreases. The experimental results agree well with theoretical models developed by Lee and Biesenberger (for bubble nucleation) and by the authors (for bubble growth).
Equilibria and dynamics for mixed vapors of BTX in an activated carbon bed
Authors: Yun Jeong‐Ho , Choi Dae‐Ki , Kim Sung‐Hyun
Published: April 2004

Experimental and theoretical studies were made on the adsorption of benzene, toluene, p‐xylene, and their binary and ternary mixtures by activated carbon in an isothermal condition of 303 K. Experimental isotherms for pure components were measured by two kinds of experimental techniques: the static volumetric method and breakthrough data analysis. Breakthrough data analysis shows that both the extended Langmuir equation and the ideal adsorbed solution theory could explain mixture isotherm data with good accuracy. In addition, a mathematical model was developed to simulate the column dynamics of pure and mixed‐vapor adsorption systems. To represent the mass‐transfer rate inside the adsorbent particle, the linear driving‐force approximation model was applied. By optimizing the pure‐ and the binary‐component breakthrough curve data with a dynamic model, an empirical correlation was proposed to represent the overall mass‐transfer rates for the BTX vapor‐activated carbon system. Results with this correlation, which is a function of the partial pressures for each adsorbate and interstitial bulk fluid velocities, showed that the prediction agrees well with the experimental data of ternary breakthrough curves.
Adsorption equilibrium of α‐amylase in aqueous solutions
Authors: Bautista L. Fernando , Martínez Mercedes , Aracil José
Published: April 2004

The influence of pH, ionic strength and temperature on the equilibrium of adsorption of α‐amylase from Aspergillus oryzae on a hydrophobic (Duolite XAD‐761) and an anion‐exchange (Duolite A‐568) polymer‐based adsorbent was studied by moment analysis of the chromatographic peak responses in HPLC. The adsorption isotherms were also measured in batch experiments at different temperatures. Both systems show a nonlinear equilibrium within the concentration range studied, and the results were fitted to both the Langmuir and Freundlich equations. Enthalpies and entropies of adsorption were estimated from the equilibrium adsorption constant obtained both by moment analysis and by the limit region of the Langmuir isotherm corresponding to Henry´s law. The results show that the process of adsorption of α‐amylase on the hydrophobic resin was exothermic, while the anion exchange process is endothermic.
Thermodynamic approach to the structural stability of process plants
Authors: Hangos Katalin M. , Alonso Antonio A. , Perkins John D. , Ydstie B. Erik
Published: April 2004

A thermodynamic approach for analyzing the structural stability of process plants is presented. The results are connected with a theory of systems described by dynamic conservation balances using a potential for stability analysis that generalizes the availability/exergy. This theory is used to show that interconnected systems with no source terms and Kirchhoff convection are structurally asymptotically stable. The approach is applicable for systems where only Kirchhoff convective transport and transfer processes with equilibrium take place. Systems with constant mass holdup in every balancing volume satisfy the condition of Kirchhoff convection. The general results are illustrated in examples of practical importance including heat exchanger networks, multicomponent flash, and multicomponent distillation with constant molar flows.
Optimal location of vertical wells: Decomposition approach
Authors: Ierapetritou M. G. , Floudas C. A. , Vasantharajan S. , Cullick A. S.
Published: April 2004

The generation of a reservoir development plan with well locations, given a reservoir property map and a set of infrastructure constraints, represents a very challenging problem. The problem of selecting the optimal vertical well locations was formulated with 3‐D information as a MILP problem where the binary variables correspond to the decisions of well locations and vertical well completions. A novel decomposition‐based solution procedure is proposed to address real fields characterized by 60,000 grid points. The approach is based on the ideas of refining the feasible set of candidate well locations by applying quality cut constraints. For the solution of the subproblems required at each iteration, a model reformulation was then suggested that enables the efficient determination of the optimal well locations. Two industrial case studies are considered to illustrate the applicability of the proposed procedure to realistic large‐scale problems.
Model reduction for chemical kinetics: An optimization approach
Authors: Petzold Linda , Zhu Wenjie
Published: April 2004

The kinetics of a detailed chemically reacting system can potentially be very complex. Although the chemist may be interested in only a few species, the reaction model almost always involves a much larger number of species. Some of those species are radicals, which are very reactive species and can be important intermediaries in the reaction scheme. A large number of elementary reactions can occur among the species; some of these reactions are fast and some are slow. The aim of simplified kinetics modeling is to derive the simplest reaction system which retains the essential features of the full system. An optimization‐based method for reduction of the number of species and reactions in chemical kinetics models is described. Numerical results for several reaction mechanisms illustrate the potential of this approach.