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Showing papers in "Aiche Journal in 1992"


Journal ArticleDOI
TL;DR: In this article, a mixing rule for cubic equations of state is proposed, which equates the excess Helmholtz free energy at infinite pressure from an equation of state to that from an activity coefficient model.
Abstract: A new mixing rule developed for cubic equations of state equates the excess Helmholtz free energy at infinite pressure from an equation of state to that from an activity coefficient model. Use of the Helmholtz free energy insures that the second virial coefficient calculated from the equation of state has a quadratic composition dependence, as required by statistical mechanics. Consequently, this mixing rule produces the correct low- and high-density limits without being density-dependent. As a test, the mixing rule is used for ternary mixtures of cyclohexane + benzene + water, ethanol + benzene + water and carbon dioxide + n-propane + water, and all the constituent binaries. The new mixing rule and a simple cubic equation of state can be used for the accurate correlation of vapor-liquid and liquid-liquid equilibria for binary mixtures. Using the parameters obtained from binary systems, the phase behavior of ternary mixtures can be predicted. Also, unlike previous empirical mixing rules, this theoretically based mixing rule is equally applicable and accurate for simple mixtures containing hydrocarbons and inorganic gases and mixtures containing polar, aromatic and associating species over a wide range of pressures. This mixing rule makes it possible to use a single equation of state model with equal accuracy for mixtures usually described by equations of state and for those traditionally described by activity coefficient models. It is the correct bridge between these two classes of models.

942 citations


Journal ArticleDOI
TL;DR: In this article, a hybrid neural network-first principles modeling scheme is developed and used to model a fedbatch bioreactor, which combines a partial first principles model, which incorporates the available prior knowledge about the process being modeled, with a neural network which serves as an estimator of unmeasuredprocess parameters that are difficult to model from first principles.
Abstract: A hybrid neural network-first principles modeling scheme is developed and used to model a fedbatch bioreactor. The hybrid model combines a partial first principles model, which incorporates the available prior knowledge about the process being modeled, with a neural network which serves as an estimator of unmeasuredprocess parameters that are difficult to model from first principles. This hybrid model has better properties than standard “black-box” neural network models in that it is able to interpolate and extrapolate much more accurately, is easier to analyze and interpret, and requires significantly fewer training examples. Two alternative state and parameter estimation strategies, extended Kalman filtering and NLP optimization, are also considered. When no a priori known model of the unobserved process parameters is available, the hybrid network model gives better estimates of the parameters, when compared to these methods. By providing a model of these unmeasured parameters, the hybrid network can also make predictions and hence can be used for process optimization. These results apply both when full and partial state measurements are available, but in the latter case a state reconstruction method must be used for the first principles component of the hybrid model.

753 citations


Journal ArticleDOI
TL;DR: A steric mass-action (SMA) ion-exchange equilibrium formalism is presented, which explicitly accounts for the steric hindrance of salt counterions upon protein binding in multicomponent equilibria, and the analytical solution of ideal isotachic displacement profiles with the SMA formalism enables rapid methods development and optimization of ion-Exchange displacement separations.
Abstract: The study of nonlinear competitive equilibrium is of fundamental importance in understanding the behavior of proteins in preparative ion-exchange chromatographic separations. In this work we present a steric mass-action (SMA) ion-exchange equilibrium formalism, which explicitly accounts for the steric hindrance of salt counterions upon protein binding in multicomponent equilibria. An analytical solution has been derived for the calculation of isotachic effluent profiles of displaced proteins and induced salt gradients under ideal chromatographic conditions. A stability analysis has been employed to establish the order of the feed components in the displacement train. Theoretical predictions are compared to experimental results for the separation of proteins by cation-exchange displacement chromatography. These results demonstrate the efficacy of the SMA formalism in predicting complex behavior present in ion-exchange displacement systems. Furthermore, the analytical solution of ideal isotachic displacement profiles with the SMA formalism enables rapid methods development and optimization of ion-exchange displacement separations.

490 citations


Journal ArticleDOI
TL;DR: The Vrentas/Duda free-volume diffusion model accurately correlates polymer/solvent diffusion coefficients over wide ranges of concentration and temperature as mentioned in this paper, but the model is semipredictive: limited diffusion data are required to estimate model parameters that can then be used to predict diffusion coefficient behavior over different conditions.
Abstract: The Vrentas/Duda free-volume diffusion model accurately correlates polymer/solvent diffusion coefficients over wide ranges of concentration and temperature. Currently the model is semipredictive: limited diffusion data are required to estimate model parameters that can then be used to predict diffusion coefficient behavior over sundry conditions. In this work, we present methods for estimating all of the model parameters without any diffusion data and examine the accuracy of the resulting diffusion coefficient predictions. This is the only technique known that predicts polymer/solvent diffusion behavior without any use of any diffusion data.

384 citations


Journal ArticleDOI
TL;DR: In this paper, a new improved gas hold-up equation is developed that incorporates the influence of gas and liquid properties with an average error of approximately 10% for two column sizes.
Abstract: Experiments were carried out in bubble columns for a number of liquids at pressures between 0.1 and 2.0 MPa for two column sizes. Based on the experimental results as well as extensive literature data, the extent of the effect column dimensions have on gas holdup were determined, both at low and high pressures (which is of importance to scale-up). It was also demonstrated that none of the published empirical gas holdup equations incorporate the influence of gas density accurately. Therefore, a new improved gas hold-up equation is developed that incorporates the influence of gas and liquid properties with an average error of approximately 10%. Finally, it is also discussed to what extent the influence of pressure on other important design parameters such as the interfacial area, the liquid volumetric mass transfer coefficient, and gas and liquid mixing, can be estimated on the basis of empirical equations.

354 citations


Journal ArticleDOI
TL;DR: In this paper, the hydrodynamics of gas-solid flow, usually referred to as circulating fluidizedbed flow, was studied in a 7.5 cm clear acrylic riser with 75-μm FCC catalyst particles.
Abstract: The hydrodynamics of gas-solid flow, usually referred to as circulating fluidizedbed flow, was studied in a 7.5-cm clear acrylic riser with 75-μm FCC catalyst particles. Data were obtained for three central sections as a function of gas and solids flow rates. Fluxes were measured by means of an extraction probe. Particle concentrations were measured with an X-ray densitometer. In agreement with previous investigators, these data showed the flow to be in the core-annular regime, with a dilute rising core and a dense descending annular region. However, unlike the previous studies conducted worldwide, the data obtained in this investigation allowed us to determine the viscosity of the suspension. The viscosity was a linear function of the volume fraction of solids. It extrapolates to the high bubbling-bed viscosities.

253 citations


Journal ArticleDOI
TL;DR: In this paper, a computational procedure for the prediction of dispersed two-phase, solid-liquid and gas-liquid, turbulent flows in baffled, impeller-stirred vessles common in the chemical industry is presented.
Abstract: This article outlines a computational procedure for the prediction of dispersed two-phase, solid-liquid and gas-liquid, turbulent flows in baffled, impeller-stirred vessles common in the chemical industries. A two-flow Eulerian model is employed, based on the main assumption of interpenetrating coexisting continua. Mean momentum and mass conservation equations are solved for each phase and turbulent closure is effected by extending the single phase k- epsilon turbulence model to two-phase flows. The resulting set of highly coupled equations is solved by a two-phase implicit algorithm, PISO-2P, which allows calculation for a wide range of phase fraction, particle size and phase density ratios. Predictions are presented for solid-liquid and gas-liquid (bubbly) flows. Comparisons are made with experimental data for the mean phase velocities and volume fraction, mean slip velocity and turbulence quantities. (from Authors)

244 citations


Journal ArticleDOI
TL;DR: Two-and one-dimensional steady-state isothermal mathematical models of monolith reactors for selective catalytic reduction (SCR) of NOx by NH3 are compared for circular, square and triangular geometry, as well as for linear and Rideal kinetics as discussed by the authors.
Abstract: Two-and one-dimensional steady-state isothermal mathematical models of monolith reactors for selective catalytic reduction (SCR) of NOx by NH3 are compared for circular, square and triangular geometry, as well as for linear and Rideal kinetics. Solutions for the two-dimensional model demonstrate that, as the reaction rate decreases from infinity to zero, the Sherwood number varies from the values of the Nusselt number characteristic of the Graetz-Nusselt problem with constant wall temperature to those with constant wall heat flux but with peripherally varying temperature. A lumped-parameter treatment, based on similarity with the constant wall temperature heat transfer problem, agrees satisfactorily with the solutions for a far more expensive two-dimensional model. The agreement is excellent for square channels, but the NH3 slip tends to be underestimated in the triangular geometry. The one-dimensional model reproduces successfully experimental effects of the NH3/NO feed ratio, and of the area velocity and the size of monolith channels.

207 citations


Journal ArticleDOI
TL;DR: Methods for modeling such data are described, emphasizing parameter estimation strategy and available software, and experiences in multiresponse modeling are reviewed for several chemical engineering problems.
Abstract: Multiresponse data are familiar outputs of experiments and processes involving multicomponent mixtures, multiple streams or multiple methods of observation. The resulting arrays of data exhibit various structures, including rectangular (no missing values), block-rectangular, and irregular (missing values with no simple pattern). Methods for modeling such data are described, emphasizing parameter estimation strategy and available software. Experiences in multiresponse modeling are then reviewed for several chemical engineering problems.

206 citations


Journal ArticleDOI
TL;DR: In this article, a computer model for a hot gas-fluidized bed has been developed based on a TFM approach in which both phases are considered to be continuous and fully interpenetrating, and local wall-to-bed heat-transfer coefficients have been calculated by the simultaneous solution of the TFM conservation of mass, momentum and thermal energy equations.
Abstract: A computer model for a hot gas-fluidized bed has been developed. The theoretical description is based on a two-fluid model (TFM) approach in which both phases are considered to be continuous and fully interpenetrating. Local wall-to-bed heat-transfer coefficients have been calculated by the simultaneous solution of the TFM conservation of mass, momentum and thermal energy equations. Preliminary calculations suggest that the experimentally observed large wall-to-bed heat-transfer coefficients, frequently reported in literature, can be computed from the present hydrodynamic model with no turbulence. This implies that there is no need to explain these high transfer rates by additional heat transport mechanisms (by turbulence). The calculations clearly show the enhancement of the wall-to-bed heat-transfer process due to the bubble-induced bed-material refreshment along the heated wall. By providing detailed information on the local behavior of the wall-to-bed heat-transfer coefficients, the model distinguishes itself advantageously from previous theoretical models. Due to the vigorous solids circulation in the bubble wake, the local wall-to-bed heat-transfer coefficient is relatively large in the wake of the bubbles rising along a heated wall.

204 citations


Journal ArticleDOI
TL;DR: In this article, a one-dimensional model of countercurrent fixed-bed coal gasification is developed, and results are compared to experimental data from commercial-scale gasifiers, and the steady-state model considers separate gas and solid temperatures, axially variable solid and gas flow rates, variable bed void fraction, coal drying, devolatilization based on chemical functional group composition, oxidation and gasification of char, and partial equilibrium in the gas phase.
Abstract: In this paper, a one-dimensional model of countercurrent fixed-bed coal gasification is developed, and results are compared to experimental data from commercial-scale gasifiers. The steady-state model considers separate gas and solid temperatures, axially variable solid and gas flow rates, variable bed void fraction, coal drying, devolatilization based on chemical functional group composition, oxidation and gasification of char, and partial equilibrium in the gas phase. Generalized treatment of gas-phase chemistry and accounting for variable bed void fraction were necessary to predict realistic axial temperature and pressure profiles in an atmospheric fixed-bed gasifier. Model evaluation includes sensitivity of axial temperature profiles to model options, model parameters and operational parameters. Model predictions agree reasonably well with experimental temperature and pressure profile data for gasification of eight coal types ranging from lignite to bituminous. The relative importance of char oxidation resistances to bulk film diffusion, ash diffusion, and chemical reaction is identified.

Journal ArticleDOI
TL;DR: In this paper, the extraction of caffeine from whole coffee beans with supercritical carbon dioxide was studied in a continuous-flow extraction apparatus and the decaffeination rates were determined as a function of CO2 flow rate, temperature and pressure by continuously monitoring the caffeine in the effluent with a flame ionization detector.
Abstract: The extraction of caffeine from whole coffee beans with supercritical carbon dioxide was studied in a continuous-flow extraction apparatus. Decaffeination rates were determined as a function of CO2 flow rate, temperature and pressure by continuously monitoring the caffeine in the effluent with a flame ionization detector. Soaking the raw beans in water prior to decaffeination enhanced the rate of extraction, which increased markedly with water content. Using CO2 saturated with water also increased the rate of extraction. The rate of decaffeination increased with pressure and temperature and was influenced by both intraparticle diffusion in the water-soaked beans and external mass transfer. A mathematical model based on a linear-driving-force approximation of mass transfer and partitioning of caffeine between the water and the supercritical CO2 describes the time-dependent process. The partition coefficient for caffeine distributed between water and supercritical CO2, the only parameter determined from the dynamic extraction rate data, increases with temperature and pressure.

Journal ArticleDOI
TL;DR: In this article, the authors introduce the concept of synthesizing reverseosmosis networks (RONs) for waste-reduction applications, which can separate a set of waste streams into lean and rich streams at minimum total annualized cost.
Abstract: The purpose of this work is to introduce the novel notion of synthesizing reverseosmosis networks (RONs) for waste-reduction applications. The RON design task aims at synthesizing a network of reverse-osmosis units, booster pumps and energy-recovery devices that can separate a set of waste streams into lean (product) streams and rich (retenate) streams at minimum total annualized cost. A systematic and generally applicable procedure for tackling RON synthesis problems is developed. First, a structural representation is devised to embed all potential network configurations

Journal ArticleDOI
TL;DR: The experimental results show the excellent servo and regulatory performance of the nonlinear controller in the presence of modeling and observer initialization errors and active manipulated input constraints and its tuning is much easier.
Abstract: This work studies the experimental application of the globally linearizing control (GLC) method to a batch polymerization reactor. The nonlinear controller is implemented on a microcomputer to start up the reactor and then track a precalculated optimal temperature profile. The reactor temperature is controlled by manipulating two coordinated inputs: power to an electrical heat and cooling water flow rate. A reduced-order observer is used to estimate the concentration of initiator and monomer. Systematic tuning guidelines are proposed for the nonlinear control method. The experimental results show the excellent servo and regulatory performance of the nonlinear controller in the presence of modeling and observer initialization errors and active manipulated input constraints. Furthermore, in comparison to a conventional PID controller, the performance of the nonlinear controller is significantly superior, and its tuning is much easier.

Journal ArticleDOI
TL;DR: In this article, a series of three polyethylene products, model-based dynamic optimization is used to determine optimal grade changeover policies, and it is shown that large transitions in melt index are hampered by slow hydrogen dynamics, and that the time required for such a transition can be reduced by manipulating the temperature setpoint and the bleed stream flow.
Abstract: Using gas-phase technology many grades of polyethylene can be produced in a single reactor. For a series of three polyethylene products, model-based dynamic optimization is used to determine optimal grade changeover policies. Optimal manipulated variable profiles are determined for hydrogen and butene feed rates, reactor temperature setpoint, gas bleed flow, catalyst feed rate, and bed level setpoint. It is shown that large transitions in melt index are hampered by slow hydrogen dynamics, and that the time required for such a transition can be reduced by manipulating the temperature setpoint and the bleed stream flow. Reduction of the bed level and catalyst feed rates during changeovers can significantly reduce the quantity of off-specification polymer produced. It is demonstrated that melt index and density are not sufficient to characterize the properties of polymer produced during grade transitions, and that the shape of the cumulative copolymer composition distribution is very sensitive to the grade changeover policy used. Optimal transition policies should not be implemented without feedback control. Disturbances and model mismatch can result in product property trajectories which deviate significantly from the nominal optimal trajectory.

Journal ArticleDOI
TL;DR: In this article, the finite element method was used to predict the power absorbed and the resulting temperalure rise in samples of square and circular cross-section of long rods of lossy dielectric materials.
Abstract: Transient temperature profiles for long rods of lossy dielectric materials with thermally-dependent dielectric properties exposed to uniform plane waves are obtained. Maxwell's equations and the heal equation are simultaneously solved using the finite element method to predict the power absorbed and the resulting temperalure rise in samples of square and circular cross-section. Following the method introduced recently, we derive an exact radiation boundary condition which is independent of the rod cross-section

Journal ArticleDOI
TL;DR: In this paper, a virial equation of state for pure solvent is used to predict fiber formation in a supercritical chlorodifluoromethane solution in a fine diameter capillary.
Abstract: The precipitation of polymers via the rapid expansion of a supercritical chlorodifluoromethane solution to ambient conditions across a fine diameter capillary has been studied experimentally. The morphology of the polymers precipitated—polycaprolactone, poly(methyl methacrylate) and a styrene/methyl methacrylate block copolymer—is influenced strongly by conditions of the expansion process. Conditions of high temperature, high polymer concentration, low pressure or low capillary L/D ratio enhance the formation of high aspect ratio fibers, while opposite conditions favor the formation of spherical particles of micron size. Each of the conditions favoring fiber formation favors precipitation farther upstream in the expansion process. Based on one-dimensional compressible flow calculations using a virial equation of state for pure solvent, it is proposed that fiber formation occurs when a polymer-rich phase is rejected from solution in the entry region to the capillary. The location of precipitation is shown to be crucial in determining the characteristic time scale for the density reduction process, which may be as small as 10−7 s.

Journal ArticleDOI
TL;DR: In this paper, the Fischer-Tropsch synthesis reaction was conducted in a supercritical fluid medium using a fixed-bed reactor and the influence of the catalyst pore size on the mass transfer of reactants and products was also characterized.
Abstract: The Fischer-Tropsch synthesis reaction was conducted in a supercritical fluid medium using a fixed-bed reactor. Tailor-made catalyst supports which had sharp pore diameter distributions were prepared by the pH swing method. The relationships between the catalyst pore structure and the catalytic activity or the product distribution were studied. The influence of the catalyst pore size on the mass transfer of reactants and products was also characterized. The catalyst pore size affected not only catalytic activity but also product selectivity. The diffusion of reactants inside the catalyst pellets in the supercritical fluid media was simulated and the effects of catalyst pore size and catalyst particle size on catalytic performances were consistent with simulation results.

Journal ArticleDOI
TL;DR: A huge amount of data is collected by computer monitoring systems in the chemical process industry, and such tools as principal component analysis and partial least squares have been shown to be very effective in compressing this large volume of noisy correlated data into a subspace of much lower dimension than the original data set.
Abstract: A huge amount of data is collected by computer monitoring systems in the chemical process industry. Such tools as principal component analysis and partial least squares have been shown to be very effective in compressing this large volume of noisy correlated data into a subspace of much lower dimension than the original data set. Because most of what is eliminated is the collinearity of the original variables and the noise, the bulk of the information contained in the original data set is retained. The resulting low dimensional representation of the data set has been shown to be of great utility for process analysis and monitoring, as well as in selecting variables for control. These types of models can also be used directly in control system design. One way of approaching this is to use the loading matrices as compensators on the plant. Some advantages of using this approach as part of the overall control system design include automatic decoupling and efficient loop pairing, as well as natural handling of nonsquare systems and poorly conditioned systems.

Journal ArticleDOI
TL;DR: In this paper, aqueous solutions of phenol were oxidized in a flow reactor at temperatures between 300 and 420{degrees}C and pressures from 188 to 278 atm (0.86,le} P, {le} 1.27).
Abstract: This paper reports tht aqueous solutions of phenol were oxidized in a flow reactor at temperatures between 300 and 420{degrees}C (0.89 {le} T{sub r} {le} 1.07) and pressures from 188 to 278 atm (0.86 {le} P, {le} 1.27). These conditions included oxidations in both near-critical and supercritical water. Reactor residence times ranged from 1.2 to 111 s. The initial phenol concentrations were between 50 and 330 ppm by mass, and the initial oxygen concentrations ranged from 0 to 1,100% excess. The oxidation experiments covered essentially the entire range of phenol conversions. Analysis of the kinetics data for phenol disappearance using a combination of the integral method and the method of excess revealed that the reaction was first order in phenol and 1/2 order in oxygen, and influenced by pressure. The global reaction order for water was taken to be nonzero, and the global rate constant was assumed to be independent of pressure so that the only effect of pressure was to alter the water concentration and hence the reaction rate.

Journal ArticleDOI
TL;DR: In this article, a new method for optimizing measurement design is proposed based on multiple Gauss-Jordan elimination of the system of linear mathematical model equations and solves the problem of instrumentation design in new plants as well as solving existing measuring systems.
Abstract: For reliable information on operating plants it is essential to design measuring points well by selecting directly measured quantities from the set of all measurable quantities. This article deals with a new method for optimizing measurement design. It is based on multiple Gauss-Jordan elimination of the system of linear mathematical model equations and solves the problem of instrumentation design in new plants as well as the problem of optimizing existing measuring systems. Optimization methods for linear objective functions and for objective functions of general type are proposed. The method also offers a complex classification of quantities (observability and redundancy). After the optimization, the problem is presolved and is ready for an optimal processing of measured data. The mathematical model is reduced to the minimum set of equations and quantities relevant to the solution of a given problem. From a numerical standpoint, the solution is efficient.

Journal ArticleDOI
TL;DR: In this article, the in-situ catalytic hydrodechlorination of chlorinated hydrocarbons in waste-water-generating HCl and a hydrocarbon-free chlorine is demonstrated as a viable wastewater remediation technique.
Abstract: The in-situ catalytic hydrodechlorination of chlorinated hydrocarbons in waste-water-generating HCl and a hydrocarbon-free chlorine is demonstrated as a viable wastewater remediation technique. Catalyst screening studies with a shaker-type hydrogenation reactor have shown that the commercial Pd/C catalyst is highly effective in hydrochlorinating various chlorinated hydrocarbons in synthetic wastewater at room temperature and near atmospheric pressure. 1, 1, 2-trichloroethane hydrodechlorination experiments in an autoclave reactor shows that initial rates are well correlated with first-order dependence of the reactant hydrocarbon adsorbed on carbon. Initial rates are also independent of hydrogen pressure, and adsorption on the carbon support is Langmuir type. Activation energies calculated at different catalyst loadings varied from 29 to 38 MJ/mol. 1,1,2-trichloroethane hydrodechlorination activity is much lower for Pd/Al2O3 than Pd/C because the reactant hydrocarbon does not adsorb on alumina. When the carbon support does not readily adsorb the reactant hydrocarbon, the hydrodechlorination rates dropped significantly. These results confirm the role of the carbon support in providing the major path to reaction and thereby significantly increasing reaction rates compared to direct adsorption from solution onto the palladium.

Journal ArticleDOI
TL;DR: In this article, a distillation network synthesis is viewed as an interacting heat-and mass-exchange network synthesis problem, where familiar tools from both heat exchange network and mass exchange network synthesis are used to arrive at energy-efficient distillation networks.
Abstract: This article introduces the “state space” conceptual framework to process synthesis, which is used to provide a novel representation of a distillation network as a composite heat- and mass-exchange network. This representation suggests that distillation network synthesis may best be viewed as an interacting heat- and mass-exchange network synthesis problem. In that regard, familiar tools (such as pinch diagrams) from both heat-exchange network (HEN) and mass-exchange network (MEN) synthesis are shown to be of use in arriving at energy-efficient distillation network designs. Examples of propylene-propane and solvent-water separations are used to illustrate the proposed conceptual framework.

Journal ArticleDOI
TL;DR: Methods for the estimation of the intraparticle diffusivity in polymer gels have been developed and were applied to the diffusion of seven model proteins in agarose particles, resulting in a correlation based on the restricted diffusion model of Ogston et al. (1973) and Cukier (1984).
Abstract: The diffusion of proteins in polymer matrices is an important step in the adsorptive and chromatographic processes used for protein purification, as it is often rate-limiting. Methods for the estimation of the intraparticle diffusivity in polymer gels have been developed and were applied to the diffusion of seven model proteins in agarose particles. The intraparticle diffusivity was not affected by particle diameter. A correlation based on the restricted diffusion model of Ogston et al. (1973) and Cukier (1984) has been proposed. This correlation allows the estimation of protein diffusivity in these matrices based on the molecular weight of the protein and the polymer concentration.

Journal ArticleDOI
TL;DR: In this article, the authors examine the simplest homogeneous azeotropic distillation sequence of industrial relevance, where an entrainer is added to a binary azeotrope to recover both the light and heavy components as pure products.
Abstract: We examine the simplest homogeneous azeotropic distillation sequence of industrial relevance, where an entrainer is added to a binary azeotrope to recover both azeotropic constituents as pure products. Despite its apparent simplicity, such distillation columns can exhibit an unusual behavior not observed in zeotropic distillation: For some mixtures, separation as a function of reflux goes through a maximum. At infinite reflux, no separation is achieved. In some cases, achieving the same specifications with a larger number of trays requires a larger reflux. Sometimes the only feasible separation yields the intermediate component as a pure distillate, while the bottom product contains the light and heavy components. Sometimes the only feasible separation yields the intermediate component as a pure bottom product while the distillate contains the light and heavy components. While these unusual features can be regarded as curiosities, they are essential for proper entrainer selection and design. For a minimum boiling azeotrope, the existing and conflicting entrainer selection rules state that one should use a component that introduces no distillation boundary between the azeotropic constituents (Doherty and Caldarola, 1985), and either a low or high boiling component that introduces no additional azeotrope or a component which introduces new minimum boiling azeotropes (Stichlmair et al., 1989). By taking advantage of the curious aforementioned features, as well as our experience involving more than 400 mixtures, we have been able to analyze the assumptions behind these criteria, show when those assumptions break down, and therefore understand the limitations of the criteria.

Journal ArticleDOI
TL;DR: This work proposes a generic methodology for qualitative analysis of the temporal shapes of continuous process variables designed to be embedded into a real-time KB environment and is applicable to bioprocesses, as well as to other complex dynamic systems.
Abstract: One of the limitations of today's knowledge-based (KB) systems for diagnostics and supervision is a lack of adequate temporal reasoning mechanisms. Most of these systems are designed primarily to operate with the current values of the process variables and, sometimes, with their derivatives. Such simple capabilities, however, are not always sufficient to identify some complex dynamic phenomena, which in many cases leave their own unique “stamp” on the process behavior, expressed in the form of characteristic temporal shapes of the related variables. To detect and diagnose adequately the events of interest, the KB system should be able to reason about the temporal shapes of the process variables. Although during manual supervision process operators rely heavily on such characteristic shapes as reliable symptoms of underlying phenomena, their exploitation has not been considered seriously by the designers of KB control systems. We propose a generic methodology for qualitative analysis of the temporal shapes of continuous process variables designed to be embedded into a real-time KB environment. It is applicable to bioprocesses, as well as to other complex dynamic systems.

Journal ArticleDOI
TL;DR: In this paper, the velocity and the drag coefficient of freely-rising light spheres were determined and compared with that predicted for the case of free settling, and the results showed that free settling is more stable than free settling.
Abstract: The aim of the note is to determine the velocity and the drag coefficient of freely-rising light spheres, and to compare these data with that predicted for the case of free settling

Journal ArticleDOI
TL;DR: In this article, an octanol solution of dodecyl-l-hydroxyproline flows countercurrently outside of the fibers and the interface between feed and extractant is stabilized by filling the pores in the hollow-fiber walls with a cross-linked polyvinylalcohol gel which offers negligible resistance to mass transfer.
Abstract: Racemic leucine can be separated into d- and l-isomers by fractional extraction across microporous hollow fibers In this extraction, an aqueous solution of the racemate is fed to the lumen of the fibers, and an octanol solution of dodecyl-l-hydroxyproline flows countercurrently outside of the fibers The interface between feed and extractant is stabilized by filling the pores in the hollow-fiber walls with a cross-linked polyvinylalcohol gel which offers negligible resistance to mass transfer The extraction with dodecyl-l-hydroxyproline deliberately imitates earlier studies, facilitating comparisons of hollow-fiber extraction with other techniques The results show that the isomer yield per equipment volume of racemic separation is 100 times greater than that in a continuously rotating extractor, and 1,000 times greater than that in a conventional packed tower

Journal ArticleDOI
TL;DR: In this article, a method for the easy determination of possible top and bottom fractions of a ternary distillation is presented, which is especially useful in the first steps of process synthesis and design since impossible separations can be determined and thus excluded from further analysis so that work can be concentrated on feasible processes.
Abstract: The rigorous calculation of top and bottom fractions of a multicomponent distillation is very time consuming and involved as it can only be done iteratively, and convergence problems are often encountered, especially in azeotropic systems. This article presents a method for the easy determination of possible top and bottom fractions of a ternary distillation. This method, which works for zeotropic as well as for azeotropic mixtures, is especially useful in the first steps of process synthesis and design since impossible separations can be determined and thus excluded from further analysis so that work can be concentrated on feasible processes. A very important application of the method developed in this article is to the design and analysis of processes for complete separation of binary azeotropic mixtures by use of an entrainer (for example, Azeotropic Distillation and Extractive Distillation). Knowledge of the separation regions in the distillation diagram allows for the development of a generalized process and the formulation of criteria for entrainer selection. The effectiveness of the method is demonstrated on a number of industrial important processes.

Journal ArticleDOI
TL;DR: A model-based verification method is developed and applied to validation of VLSI circuits and to reveal discrete event errors, the method is applied to a simple combustion system and an alarm acknowledge system.
Abstract: Clarke et al. (1986) have developed a model-based verification method and have applied it to validation of VLSI circuits. We have used the method to test automatically the safety and operability of discrete chemical process control systems. The technique involves: (1) a “system model” describing the process and its software; (2) “assertions” in temporal logic expressing user-supplied questions about the system behavior with respect to safety and operability; and (3) a “model checker” that determines if the system model satisfies each of the assertions and provides a counterexample to locate the error if one exists. Temporal logic is used for reasoning about occurrence of events over time. To reveal discrete event errors, we have applied the verification method to a simple combustion system and an alarm acknowledge system.