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Showing papers in "Aiche Journal in 1987"


Journal ArticleDOI
TL;DR: In this article, the authors present a review of the state-of-the-art work on hindered transport in liquid-filled pores of molecular dimensions, and the present status of this research is reviewed.
Abstract: Transport in liquid-filled pores of molecular dimensions plays an important role in membrane separations, in various forms of chromatography, and in catalysis, to name a few examples. A frequent observation is that if the pore dimensions are of the same order as those of a solute molecule, the apparent diffusion coefficient of that solute is much lower than in bulk solution. Likewise, rates of convective transport of such solutes are generally lower than the product of bulk concentration and volume flow rate. Thus, solute transport is typically “hindered” or restricted. A key objective of research on hindered transport is to be able to predict the applicable transport coefficients from such fundamental information as the size, shape, and electrical charge of the solutes and pores. The present status of this research is reviewed.

1,111 citations


Journal ArticleDOI
TL;DR: In this article, a method based on finite-element collocation is presented, which converts differential equations to algebraic residual equations with unknown coefficients, and then a nonlinear program is formulated, with residuals incorporated as equality constraints and coefficients as decision variables.
Abstract: Many chemical engineering problems require the optimization of systems of differential and algebraic equations. Here a method is presented based on finite-element collocation, which converts differential equations to algebraic residual equations with unknown coefficients. A nonlinear program is then formulated, with residuals incorporated as equality constraints and coefficients as decision variables. Also, adaptive knot placement is used to minimize the approximation error, with necessary and sufficient conditions for optimal knot placement incorporated as additional equality constraints in the nonlinear program. All equality constraints are then solved simultaneously with the optimization problem, thus requiring only a single solution of the approximated model. Finally, problems with discontinuous control profiles can be treated by introducing an extra level of elements (superelements) as decisions in the optimization problem. This approach is demonstrated on a simple optimal control problem as well as a reactor optimization problem with steep temperature profiles and state variable constraints.

430 citations


Journal ArticleDOI
TL;DR: In this article, the design of feedback controllers for trajectory tracking in single-input/single-output nonlinear systems is studied, and a nonlinear transformation of the form v = k (x) + λ(x) u that transforms this nonlinear input/output system into a linear system is first constructed.
Abstract: This paper studies the design of feedback controllers for trajectory tracking in single-input/ single-output nonlinear systems x = f(x) + g(x) u, y = h(x). A nonlinear transformation of the form v = k(x) + λ(x) u that transforms this nonlinear input/output system into a linear system is first constructed. On the basis of this transformation, an approach for designing control laws for trajectory tracking is presented. The control law is robust in the sense that small changes in it do not produce large steady state errors or loss of stability. The theory provides a unified framework for treating control problems arising in nonlinear chemical processes; this is illustrated by a batch reactor control example.

344 citations


Journal ArticleDOI
TL;DR: In this paper, the cyclohexane deshydrogenation in benzene and hydrogene is reversible, and a membrane de palladium is used to separer l'hydrogene au fur and a mesure de sa formation.
Abstract: La deshydrogenation du cyclohexane en benzene et hydrogene est une reaction reversible; pour obtenir une reaction complete, on utilise une membrane de palladium pour separer l'hydrogene au fur et a mesure de sa formation

290 citations


Journal ArticleDOI
TL;DR: A very efficient method of identifying the possible causes of process disturbances using the signed directed graph (digraph) representation of process interactions and can be integrated with other rules on plant operations using an expert systems framework.
Abstract: Fault diagnosis is the problem of determining the root causes of process upsets. This paper presents a very efficient method of identifying the possible causes of process disturbances using the signed directed graph (digraph) representation of process interactions. The analysis is based on forming logical statements (rules) derived from the process digraph; these are evaluated using on-line data to yield the diagnosis. Evaluation of rule antecedents is more efficient than the previous algorithmic approach of Shiozaki et al. In the rule-based approach, the diagnostic criteria are represented explicitly, not hidden by a complex algorithmic procedure. This allows the diagnostic rules to be tailored to reflect the best available knowledge of plant behavior. The rules generated by this technique can be integrated with other rules on plant operations using an expert systems framework.

254 citations


Journal ArticleDOI
TL;DR: In this article, the authors calculated the interfacial stresses from new measurements of liquid height and pressure drop for fully developed horizontal stratified flow, which are related to wave properties.
Abstract: Interfacial stresses are calculated from new measurements of liquid height and pressure drop for fully developed horizontal stratified flow. These are related to wave properties. An improved design method is suggested.

231 citations


Journal ArticleDOI
TL;DR: In this article, the local compositions of supercritical fluid carbon dioxide and a cosolvent about a solute at infinite dilution have been estimated for the first time using spectroscopic measurements.
Abstract: The local compositions of supercritical fluid carbon dioxide and a cosolvent about a solute at infinite dilution have been estimated for the first time using spectroscopic measurements. The solute was phenol blue, the bulk concentrations of the cosolvents n-octane, acetone, ethanol, and methanol ranged from 0 to 100 mol%, and the pressure ranged from 80 to 300 bar. In each case, the clusters of solvent about the solute are enriched in cosolvent. Solubility data have been measured for phenol blue in CO2 with and without the cosolvent acetone, and regressed using an augmented van der Waals-density-dependent local composition model to determine the relevant binary interaction energies. The local compositions calculated from the model agree with those that were esimated spectroscopically. The model was used to predict solubilities of solids in supercritical fluid CO2 with various cosolvents.

202 citations


Journal ArticleDOI
TL;DR: The network representation of the porous medium together with the population balances and the rates of deposition and release provide a consistent model that finds application in filtration and fines migration processes.
Abstract: A mathematical model is formulated for the general class of problems that involve the transport of stable particulate suspensions in porous media. The porous medium is represented by a network of pore bodies (sites) and pore throats (bonds). Population balances for the species responsible for particle retention and permeability reduction are written in terms of the various mechanisms of particle capture and reentrainment. Rates of capture and release are evaluated using appropriate physical models. The authors specifically concentrate on mass transfer limited processes. The effective medium theory is suitably formulated to determine the fluid flow distribution in the network and to calculate the permeability. The network representation of the porous medium together with the population balances and the rates of deposition and release provide a consistent model that finds application in filtration and fines migration processes.

186 citations


Journal ArticleDOI
TL;DR: In this paper, a steady state biofilm model was proposed that considers the simultaneous diffusion and reaction of oxygen and phenol within the biofilm and the external mass transfer resistance between the biofilms and the completely mixed bulk liquid phase.
Abstract: Experiments on phenol biodegradation by a mixed culture in a draft-tube, three-phase fluidized-bed biofilm reactor (DTFBR) at the steady state were performed. The characteristics of biofilms developed in the DTFBR were identified. A steady state biofilm model was proposed that considers the simultaneous diffusion and reaction of oxygen and phenol within the biofilm and the external mass transfer resistance between the biofilm and the completely mixed bulk liquid phase. The proposed model assumes a double-substrate limiting mechanism for microbial growth kinetics, and Haldane and Monod type expressions were used to characterize the dependence of microbial specific growth rate on phenol and oxygen, respectively. The experimental results were used to test the validity of the proposed model.

182 citations


Journal ArticleDOI
TL;DR: In this paper, a new bubble diameter correlation is derived to predict bubbling characteristics of fluidized beds of varieties of powders, based on the postulate that the steady bubble size observed in a bed of Geldart group A powder is formed as a result of an equilibrium of successive coalescence and splitting.
Abstract: A new bubble diameter correlation is derived to predict bubbling characteristics of fluidized beds of varieties of powders. The present model is founded on the postulate that the steady bubble size, which is often called the maximum stable diameter, observed in a bed of Geldart group A powder is formed as a result of an equilibrium of successive coalescence and splitting. For the cases of group B powders the present correlation automatically converges to the conventional correlation. For group A powders the present correlation is validated by comparison with experimental data in the literature. Based on this correlation a theoretical explanation is presented for the fact that the maximum bubble diameters observed were up to 50 to 100 times as large as those from the stable bubble theory.

173 citations


Journal ArticleDOI
TL;DR: In this paper, a nouvelle methode statistique is utilisee for detecter, identifier and estimer les grosses erreurs (erreurs systematiques and fuites) which peuvent se presenter dans les procedes chimiques en regime permanent.
Abstract: Une nouvelle methode statistique est utilisee pour detecter, identifier et estimer les grosses erreurs (erreurs systematiques et fuites) qui peuvent se presenter dans les procedes chimiques en regime permanent. Developpement d'un modele mathematique pour decrire les fuites et les erreurs systematiques. Une nouvelle strategie de detection de grosses erreurs multiples basee sur la compensation serielle des grosses erreurs est aussi proposee

Journal ArticleDOI
TL;DR: In this article, a model developed by Sharma and Yortsos (1987a) is applied to the processes of fines migration and fines injection in a porous medium, and simple solutions are provided for both processes by considering size exclusion as the dominant particle retention mechanism.
Abstract: A model developed by Sharma and Yortsos (1987a) is applied to the processes of fines migration and fines injection in a porous medium. The first is a problem frequently encountered in oil reservoirs when release of fines is triggered by physicochemical interactions of the porous formation with the injected fluids. The second may be a problem in the filtration of relatively large particulates. Simple solutions are provided for both processes by considering size exclusion as the dominant particle retention mechanism. The solutions developed provide expressions for the particle concentration profiles, the open pore density and pore size distribution profiles, as well as the permeability reduction. These expressions are of importance in the evaluation of the extent and depth of formation damage and can be used as designing tools for remedial treatment, such as acidizing or fracturing.

Journal ArticleDOI
TL;DR: In this paper, the energy requirements of four different thermally coupled distillation systems were minimized for an assumed ideal ternary solution being separated, and the minimum vapor flows and values of decision variables were found in the form of analytical expressions.
Abstract: Energy requirements of four different thermally coupled distillation systems were minimized for an assumed ideal ternary solution being separated. Minimum vapor flows and values of decision variables have been found in the form of analytical expressions. This enables making a quick and simple comparison of these systems. The solution method can be used for synthesis of separation systems or for screening calculations.

Journal ArticleDOI
TL;DR: In this article, a corner flow hydrodynamic theory is outlined for the time to snap-off of a gas bubble moving through a smoothly constricted noncircular capillary as a function of the pore geometry and the capillary number, Ca.
Abstract: A corner flow hydrodynamic theory is outlined for the time to snap-off of a gas bubble moving through a smoothly constricted noncircular capillary as a function of the pore geometry and the capillary number, Ca. Above a transition capillary number the time to snap-off is independent of Ca, while below it the time to snap-off is inversely proportional to the capillary number. Thin films of liquid deposited along the capillary walls are shown to play a minor role; they are accordingly neglected in the analysis. The proposed theory is compared to new experimental results for snap-off in two constricted square capillaries (dimensionless constriction radii of 0.3 and 0.5) over a range of capillary numbers (10/sup -5/ to 10/sup -3/), wetting-liquid viscosities (1.0 to 8.5 mPa . s), and surfactant types. Good agreement is found between theory and experiment.

Journal ArticleDOI
TL;DR: In this paper, the authors compared experimental data from both gas-liquid and liquid-liquid dispersions to show that only one theory can predict both gas bubble and liquid drop sizes with a single constant.
Abstract: Bubble sizes for dilute dispersion in horizontal pipelines under turbulent liquid flow conditions are shown to be predicted by a theory. This theory contains the dependence of dispersed-phase density on the bubble size, which is not included in theories presented by others. Theories are compared using experimental data from both gas-liquid and liquid-liquid dispersions to show that only one theory can predict both gas bubble and liquid drop sizes with a single constant. Additionally, a generalized equation is proposed that includes the effect of the dispersed-phase viscosity.

Journal ArticleDOI
TL;DR: In this article, gas holdups and volumetric mass transfer coefficients kLa are studied in a bubble column of 0.095 m dia with 50 different gas-liquid systems comprising pure and mixed organic liquids and various gases.
Abstract: Gas holdups and volumetric mass transfer coefficients kLa are studied in a bubble column of 0.095 m dia. with 50 different gas-liquid systems comprising pure and mixed organic liquids and various gases. The gas holdups measured in pure organic liquids can be represented by existing correlations but the values in liquid mixtures are high. On the other hand, all mass transfer coefficients can be correlated uniformly by a new dimensionless equation, with 13.3% mean error.

Journal ArticleDOI
TL;DR: In this paper, the rate constant of α-chlorobenzyl methyl ether was adjusted continuously over two orders of magnitude for the unimolecular decomposition using the supercritical fluid solvent 1, 1 diffluoroethane.
Abstract: The reaction rate constant was adjusted continuously over two orders of magnitude for the unimolecular decomposition of α-chlorobenzyl methyl ether using the supercritical fluid solvent 1, 1 diffluoroethane. Activation volumes were observed as low as −6,000 cm3/mol, which is about an order of magnitude more negative than those reported previously in the literature for a homogeneous reaction. Spectral shift (solvatochromic) data were measured for phenol blue in the same fluid in order to interpret the rate data. A method is presented to predict solvent effects on rate constants at supercritical fluid conditions.

Journal ArticleDOI
TL;DR: In this article, Galerkin finite-element analysis is used to predict the isothermal free-surface flow of a Newtonian liquid near the advancing front between parallel plates, and the most interesting visualization of the calculated flow is obtained by tracking lines of material, thus producing numerical tracer experiments.
Abstract: Moldability criteria and process optimization for both reactive and thermoplastic injection molding hinge on the mold-filling step. The fluid mechanics of the filling step is typically described in terms of a one-dimensional main flow and a complex two-dimensional flow near the advancing front, often termed the “fountain flow.” A unique apparatus which permits direct observation of the fountain flow in a rectangular cavity is described. The motion of tracer lines as well as the pathlines have been photographed for both Newtonian and shear-thinning liquids. The data show clearly the main flow, the transition to the front flow, and the deceleration and acceleration zones in the fountain flow, which lead to a “mushrooming” of the tracer line. In addition, Galerkin finite-element analysis is used to predict the isothermal free-surface flow of a Newtonian liquid near the advancing front between parallel plates. The most interesting visualization of the calculated flow is obtained by tracking lines of material, thus producing numerical tracer experiments. The calculations show the widely varying residence times and the complex shear and extensional deformation histories of fluid elements as they move through the fountain flow region. The calculations are in agreement with the experiments and clarify previous results, both theoretical and experimental, that did not capture the details of the entire flow field.

Journal ArticleDOI
TL;DR: An approach to chemical plant fault diagnosis is presented that utilizes patterns of violation and satisfaction of the quantitative constraints governing the process to improve the stability and sensitivity of the diagnosis in the presence of noise.
Abstract: An approach to chemical plant fault diagnosis is presented that utilizes patterns of violation and satisfaction of the quantitative constraints governing the process. Process knowledge consists of a list of the operational constraints on the plant together with sufficient conditions for violation of each constraint. Interpretation of the pattern of constraint violations is treated by Boolean and non-Boolean techniques. It is shown that non-Boolean reasoning techniques increase the stability and sensitivity of the diagnosis in the presence of noise. The techniques introduced in this paper are easily implemented in rule-based expert systems using certainty factors.

Journal ArticleDOI
TL;DR: In this article, the problem of diffusion in pore networks of a certain class is considered, and a procedure for estimating diffusivities is formulated, where the effective medium theory is used to obtain an effective conductance for the network, which is then used to determine the effective diffusivity starting from first physical principles and utilizing the observation that a network of uniform conductance satisfies the smooth field approximation.
Abstract: The problem of diffusion in pore networks of a certain class is considered, and a procedure for estimating diffusivities is formulated. The effective-medium theory is used to obtain an effective conductance for the network, which is then used to determine the effective diffusivity starting from first physical principles and utilizing the observation that a network of pores of uniform conductance satisfies the smooth field approximation. Comparison of the estimated intraparticle diffusivities with those obtained from the exact solution of the transport equation for large networks reveals high accuracy and reliability of the method. Results for a number of pore networks show that the smooth field assumption should not be employed arbitrarily since it always predicts higher effective diffusion coefficients than the exact ones, by more than one order of magnitude in some cases.


Journal ArticleDOI
TL;DR: In this paper, the facilitated transport of CO2 through ion exchange membranes containing organic amine counterions was studied, and the transport data support a mobile, reactive-carrier facilitated transport mechanism with a carbamate zwitterion complex.
Abstract: The facilitated transport of CO2 through ion exchange membranes containing organic amine counterions was studied. Steady state CO2 fluxes were measured from pure gas streams and mixtures with CH4. Facilitation factors for CO2 up to 26.7 were calculated from transport data. Transport measurements were binary mixtures of CO2 and CH4 yielded ratios of CO2 flux to CH4 flux ranging from 29.0 to 264. Conversion of flux ratios to permeabilities yielded separation factors up to 551 for CO2 over CH4, which are compared to literature data for polymeric membranes. The transport data support a mobile, reactive-carrier facilitated transport mechanism with a carbamate zwitterion complex. Effective diffusivities for CO2 and the carrier-gas complex were determined from transport data. A reaction equilibrium model predicted facilitation factors that were in very good agreement with experimental values. Potential applications are also discussed.

Journal ArticleDOI
TL;DR: In this article, a two-phase approach to control and operation of complex chemical processes at their optimum operating conditions is presented, which is particularly suited to those processes that exhibit slow dynamic responses and are subject to disturbances that have a significant economic impact.
Abstract: A two-phase approach to the control and operation of complex chemical processes at their optimum operating conditions is presented. The first phase consists of on-line parameter identification and state estimation of approximate nonlinear dynamic process models using on-line and off-line measurements. In the second phase, the optimum operating strategy is determined by integrating and optimizing this identified process model over a selected time horizon into the future. The method is particularly suited to those processes that exhibit slow dynamic responses and are subject to disturbances that have a significant economic impact. Examples include batch chemical reactors, large distillation towers, and processes with significant holdup times such as large fluidized-bed reactors.

Journal ArticleDOI
TL;DR: In this article, auteurs montrent comment une cinetique d'ordre deux, caracterisant une reaction ou une partie des composes chimiques est inactive.
Abstract: Les auteurs montrent comment une cinetique d'ordre deux, caracterisant une reaction ou une partie des composes chimiques est inactive, peut devenir une cinetique d'ordre inferieur a deux lorsque ces composes chimiques deviennent actifs. Ils etudient le cas d'une reaction de craquage catalytique

Journal ArticleDOI
TL;DR: In this paper, a special case of the deep bed filtration problem is studied, where the pore density and pore size distributions are modeled as functions of the system parameters, such as fluid flow rate, pore densities, and size distribution.
Abstract: Equations for the deep bed filtration problem are obtained as a special case of a general model formulated earlier. The filtration coefficient λ is expressed as an explicit function of system parameters such as fluid flow rate, pore density, and pore size distribution. For a unimodal pore size distribution it is found that λ remains constant both in space and time. In general, however, λ is shown to decrease. Explicit solutions to the problem, including particle density profiles and permeability, are obtained for the two cases of large values of the coordination number Z (capillary tube model), and for a bimodal pore size distribution with a finite coordination number.

Journal ArticleDOI
TL;DR: Etude des limitations du transfert de chaleur lors de la dissociation d'hydrates de methane as discussed by the authors, lors of the dissociation of methane.
Abstract: Etude des limitations du transfert de chaleur lors de la dissociation d'hydrates de methane

Journal ArticleDOI
TL;DR: In this article, the authors provide guidelines for step 1, which is considered to be the most important step in a 2 × 2 controller for composition control, and show that ratio configurations are effectively complex multivariable controllers that provide, among other features, improved flow disturbance rejection.
Abstract: Most two-product distillation columns can be described as 5 × 5 plants, but the control system design is usually simplified by means of the following procedure: 1Choose two manipulated inputs for composition control (corresponding to a specific control configuration). 2Design the level and pressure control system (usually three SISO controllers). 3Design a 2 × 2 controller for composition control. This paper provides guidelines for step 1, which is considered the most important. Ratios (e.g., L/D or V/B) are frequently chosen as manipulated inputs in step 1. It is shown that the ratio configurations are effectively complex multivariable controllers that provide, among other features, improved flow disturbance rejection.


Journal ArticleDOI
TL;DR: In this paper, the wall and Reynolds shear stresses were measured using a hot-film anemometry technique, and the predicted interfacial shear stress data were approximated by the formula relating the interfacial friction factor with the void fraction and gas and liquid Reynolds numbers, and were compared with other reported data.
Abstract: Experimental values are presented for the wall and interfacial shear stresses in stratified gas-liquid flow in a pipe. The wall and Reynolds shear stresses were measured using a hot-film anemometry technique. The interfacial shear stress was determined using two methods: from a momentum balance, using the wall shear stresses and void fraction measurements, and from an extrapolation of the Reynolds shear profile at the gas-liquid interface. The predicted interfacial shear stress data were approximated by the formula relating the interfacial friction factor with the void fraction and gas and liquid Reynolds numbers, and were compared with other reported data.

Journal ArticleDOI
TL;DR: In this article, experimental data on the rate of dissociation of methane hydrates were obtained from hydrate mass loss measurements using an electrobalance, and a mathematical model describing the dissociation process was also presented.
Abstract: Experimental data on the rate of dissociation of methane hydrates are presented. The data were obtained from hydrate mass loss measurements using an electrobalance. A resistance heater with a known heat flux was used in the dissociation experiments. A mathematical model describing the dissociation process is also presented. The model, based upon first principles, assumes that the water formed during dissociation is blown away by the methane gas produced so that the dissociation process may be regarded as a moving-boundary ablation problem. Agreement between the model and the data is within 10%.