bluuebunny/crossref_metadata_2025 huggingface dataset:
More fundamentals of dilute suspension collapse and choking for vertical conveying systems
Authors: Xu Guangwen , Nomura Kousuke , Gao Shiqiu , Kato Kunio
Published: April 2004

Using gas‐solid flows in circulating fluidized‐bed risers to analogize vertical pneumatic conveying systems, the collapse of dilute suspension, that is, the choking of accumulative type, was studied in three different risers with respect to different particles. The collapse of dilute suspension was dominated by an identical differential pressure drop over the measuring section. This differential pressure drop was independent of gas velocity and riser diameter, but varied with particle properties. The saturation carrying capacity, the solid flow rate at the dilute suspension collapse, was closely related to particle characteristics and riser diameter. With an increase in the riser diameter, it increased for lighter and smaller particles, but decreased for heavier and larger particles. Based on these experimental measurements, as well as the related literature reports, a correlation was developed for the saturation carrying capacity by analyzing its dependencies on gas velocity and riser diameter. More than 150 experimental data of the saturation carrying capacity available in the literature were compiled to evaluate the accuracy of the proposed correlation by comparing with 13 other literature correlations, demonstrating that this new method has the highest accuracy.
Disjunctive optimization design models for complex liquid–liquid multistage extractors
Authors: Reyes‐Labarta Juan A. , Grossmann Ignacio E.
Published: April 2004

A new method for the optimal design of multicomponent liquid–liquid extraction processes using multistage countercurrent extractor systems is proposed. The method determines the optimum number of equilibrium stages and flow rates needed to obtain a specified product separation and recovery, and accounts for the possibility of side feed streams and product extractions. A superstructure is proposed that has embedded all potential configurations and interconnections. Based on this superstructure representation, the problem is formulated as an optimization problem using generalized disjunctive programming (GDP) to minimize the total cost of the process, subject to design specifications. The robustness and computational efficiency of the model is illustrated with different cases involving single and complex countercurrent cascades in a quaternary liquid–liquid system.
A new approach in the modeling of the critical heat flux and enhancement techniques
Authors: Sefiane Khellil
Published: April 2004

Understanding of the boiling crisis mechanism is still incomplete; starting from experimental observations of the dry spots during boiling crisis, a new approach to bridge this gap is proposed. The thermal instabilities occurring at the triple contact lines where evaporation is intense are focused on. The “dry‐out” phenomenon is local; it depends on the local conditions at a very tiny evaporating meniscus adjacent to the heating surface. The enhancing role of EHD for CHF is studied through a stability analysis of the meniscus subjected to an electrical‐field. The equations describing the evaporating system are modified to account for the effect of electrical forces. We have found that the electrical‐field delays thermocapillary instability. Our analysis revealed that the onset of instability is very sensitive to the interface deformation.
Crystallization of para‐xylene in scraped‐surface crystallizers
Authors: Patience Daniel B. , Rawlings James B. , Mohameed Hazim A.
Published: April 2004

Crystallization kinetics of para‐xylene in batch pilot‐scale scraped‐surface crystallizers were determined for commercial crystallization of a xylene mixture currently produced in Amoco plants. Dynamic mass and energy balances, coupled with the dynamic population balance, were used to model the scraped‐surface crystallizer. The model assumes that crystal nucleation occurs at the walls of the crystallizer and crystal growth occurs in the bulk. The parameters in the kinetic models were estimated from online measurements of bulk temperature and slurry transmittance. Concentration measurements show that the xylene mixture is always saturated (supersaturation is essentially zero) during all crystallization runs. Therefore, a reduced, two‐parameter, high growth rate model was developed to describe these crystallizers. The kinetic parameters were correlated highly for the reduced model. A new batch experiment with an alternative temperature profile was determined that removes the correlation and allows both parameters to be determined uniquely.
Design of integrated crystallization systems
Authors: Wibowo Christianto , Chang Wen‐Chi , Ng Ka M.
Published: April 2004

A systematic procedure is developed for designing an integrated crystallization system by considering the interaction between crystallization and downstream processing. Potential problems related to unit operations such as filtration, washing, dewatering, recrystallization, and drying are anticipated and resolved by determining an operating policy and configuration for the crystallizer as well as the downstream units. The approach can be applied to both batch and continuous crystallizers. First, the possible impacts of particle‐size distribution (PSD) on the downstream processing units are identified. This forms the basis for determining a target PSD in the second step. Third, possible means by which the desired PSD can be achieved are selected. Fourth, the alternatives thus generated are evaluated and compared to identify the best design. Heuristics are provided along the way to guide the decision making. Shortcut equipment models are used to compare the performance of the alternatives. The procedure is illustrated with two industrial examples, including the production of adipic acid.
Model‐based control of batch chromatography
Authors: Dünnebier Guido , Engell Sebastian , Epping Achim , Hanisch Felix , Jupke Andreas , Klatt Karsten‐Ulrich , Schmidt‐Traub Henner
Published: April 2004

In the chemical industry, life science products are considered the most promising markets for the near future. Since pharmaceutical products, food, and fine chemicals are subject to increasingly more complex standards and stricter legal restrictions, efficient methods for the separation of thermally unstable products are needed. Chromatographic separations, for example, usually create the main costs of the overall production process. To realize the full potential of the chromatographic separation, the desired product quality has to be maintained, while operating the process at the economic optimum by reliable and efficient process monitoring and control. For control of batch chromatography, model parameters were estimated and operating parameters were optimized online. The concept has been tested on a laboratory‐scale column with an industrial process control system. Experimental results for a sugar separation are given.
Theoretical account of a dry sorption injection experiment
Authors: Allen R. W. K. , Archer E. D. , MacInnes J. M.
Published: April 2004

A theoretical representation of adsorption by particles injected into a gas stream that was developed previously is used to assess results from a dry sorption injection experiment. The particle‐size distribution is required in the theoretical model, and this distribution is measured for the experimental particles. The pore‐size distribution is also measured and used to determine particle properties, including the effective diffusivity in the pore passages within the particles, which is required by the model. Comparison of the model and experiment establishes the crucial importance of accurate knowledge of the equilibrium relation for the actual adsorbate–adsorbent system considered and of a reliable representation of particle size and shape.
Coupled model of concentration polarization and pore transport in crossflow nanofiltration
Authors: Bhattacharjee Subir , Chen Jim C. , Elimelech Menachem
Published: April 2004

A coupled model of concentration polarization and pore transport of multicomponent salt mixtures in crossflow nanofiltration rigorously predicts local variations of ionic concentrations, flux and individual ion rejections along a rectangular crossflow filtration channel by a coupled solution of the convective‐diffusion and extended Nernst‐Planck equations. Coupling the pore transport model with the multicomponent convective‐diffusion equation in the concentration polarization layer provides a comprehensive understanding of the interplay between concentration polarization and salt rejection. The coupled model is used to predict the local variations of ion rejection, permeate flux and mixture composition in a rectangular crossflow filtration channel for three‐component salt mixtures. The total membrane surface concentration of the ions and the ratio of different ions in the mixture (salt ratio) can change considerably along a crossflow filtration channel, and, consequently, cause remarkable variations in intrinsic ion rejections with axial position in the channel.
Effect of pore structure, randomness and size on effective mass diffusivity
Authors: Mezedur Minas M. , Kaviany Massoud , Moore Wayne
Published: April 2004

The effective mass diffusivity 〈 Dm 〉 of large specific surface area catalytic porous coatings is analyzed using 2‐D network models of connecting arms and verified experimentally for a multiple pore length scale coating layer. The network model includes effects of variation in the lattice randomness (Voronoi tessellation in the form of Delaunay lattice triangulation), pore coordination number, pore size (Knudsen effect), and pore‐size distribution on the predicted 〈 Dm 〉. The effect of pore poisoning, resulting in a pore blockage, is analyzed. Correlations for the porosity and pore‐blockage dependency of 〈 Dm 〉, as well as relationships for the pore size (low‐dimensionality) and multiple pore length scale effects, are also discussed. An experiment performed on a catalytic converter washcoat segment (represented by three pore length scales) placed on an otherwise impermeable wall of an electrochemical sensor shows a good agreement with the predicted 〈 Dm 〉 based on a multiple pore length scale medium with parallel diffusion paths.
Steady‐state and decay dynamics for impellers of varying aspect ratio in unbaffled tanks
Authors: Maynes D. , Butcher M.
Published: April 2004

Hydrodynamic torque measurements on impellers of square cross section were conducted for 33 different impellers in 3 different cylindrical unbaffled tanks. The tanks differed in volume by two orders of magnitude, and the Reynolds number range of the data was 104–105. A wide range of impeller sizes and aspect ratios was investigated, focusing on the decay regime where the tank walls impacted the torque measurement, and the steady state where the torque is constant on average. The number of revolutions required for spin‐up to steady state is a function of the tank radius and height and the impeller radius and height, and an expression is presented that describes the spin‐up time in terms of these variables and is valid for all of the data. At steady state and for a Reynolds number of 105, the torque coefficient or power number depended primarily on the height of the impeller and tank, but not on the impeller radius. During the decay regime, the measured torque coefficient decreases with a power‐law relation and is proportional to the number of revolutions raised to the k power. The k value did not depend on the height of the tank, but only on the impeller radius, impeller height, and tank radius. Expressions relating the steady‐state torque coefficient and the decay exponent, k, to the geometric variables model all of the data quite well. With these relations, the effects of the varying impeller aspect ratios on the energy required for mixing of momentum, and on the time required for mixing to occur, can be quantified.
Dispersive granular flow in a horizontal drum stirred by a single blade
Authors: Laurent B. F. C. , Bridgwater J.
Published: April 2004

To understand the detailed processes occurring in stirred systems for particulate materials, experiments were conducted in a horizontal cylindrical mixer, 270 mm dia. and 650 mm long. It was stirred by a single long flat blade, varying the level of fill between 20 and 70% and the agitator speed between 20 and 45 rpm. The dispersion of blobs in three regions—in the transaxial plane near the wall, in the path of the blade, and in the bulk—suggested two classes of behavior. The dispersive behavior of particles was characterized by axial dispersion coefficients and root mean‐square radial displacements, parameters commonly useful for process design. Both parameters showed that powder flow was independent of blade speed and controlled by the number of blade passes. Agitation was nonuniform in the transaxial plane with two regions of enhanced axial and radial displacement. These occurred near the free surface and immediately beneath the region where the blade arm was horizontal so that material readily slides off the blade. The axial dispersion coefficient was a maximum at a fill level of 40%, contributing effects arising from the free surface area of the bed and the conveying capacity of the blade.
Constrained process monitoring: Moving‐horizon approach
Authors: Rao Christopher V. , Rawlings James B.
Published: April 2004

Moving‐horizon estimation (MHE) is an optimization‐based strategy for process monitoring and state estimation. One may view MHE as an extension for Kalman filtering for constrained and nonlinear processes. MHE, therefore, subsumes both Kalman and extended Kalman filtering. In addition, MHE allows one to include constraints in the estimation problem. One can significantly improve the quality of state estimates for certain problems by incorporating prior knowledge in the form of inequality constraints. Inequality constraints provide a flexible tool for complementing process knowledge. One also may use inequality constraints as a strategy for model simplification. The ability to include constraints and nonlinear dynamics is what distinguishes MHE from other estimation strategies. Both the practical and theoretical issues related to MHE are discussed. Using a series of example monitoring problems, the practical advantages of MHE are illustrated by demonstrating how the addition of constraints can improve and simplify the process monitoring problem.
Thermodynamics of adsorption in porous materials
Authors: Myers A. L.
Published: April 2004

Thermodynamic equations are developed for adsorption of multicomponent gas mixtures in microporous adsorbents based on the principles of solution thermodynamics. The conventional spreading pressure and surface area variables, which describe 2‐D films, must be abandoned for adsorption in micropores, in which spreading pressure cannot be measured experimentally or calculated from intermolecular forces. Adsorption is divided into two steps: (1) isothermal compression of the gas, (2) isothermal immersion of clean adsorbent in the compressed gas. Thermodynamic functions (Gibbs free energy, enthalpy, and entropy) from solution thermodynamics provide a complete thermodynamic description of the system. Applications are described for characterization of adsorbents, gas storage at high pressure, mixture adsorption, enthalpy balances, molecular simulation, adsorption calorimetry, and shape selectivity in catalysis.
Ionic strength dependence of protein adsorption to dye‐ligand adsorbents
Authors: Zhang Songping , Sun Yan
Published: April 2004

The adsorption equilibria and kinetics of bovine serum albumin (BSA) and lysozyme to two Cibacron Blue 3GA (CB) modified agarose gels, that is, 6% agarose‐coated steel (6AS) and Sepharose CL‐6B, in 0.01 kmol·m−3 tris‐HCl buffer (pH 7.5) were studied. Effects of aqueous‐phase ionic strength on both the adsorption equilibrium and uptake rate of the proteins were significant and distinctly different between BSA and lysozyme. The adsorption of lysozyme decreased monotonically with increasing ionic strength. Ionic strengths, however, maximized BSA adsorption capacities of the two CB‐modified agarose gels in the tris‐HCl buffer (about 0.2 kmol·m−3 for CB‐6AS and 0.05 kmol·m−3 for CB‐Sepharose), when the pore‐size difference of the two matrixes and electrostatic interactions between the BSA and CB molecules of like charge were considered. The effective diffusivity of BSA, derived from a pore‐diffusion model, to both the CB‐modified agarose gels increased significantly with the increasing ionic strength at the ionic strength range of 0.01 to 0.3 kmol·m−3, due to the electrostatic interactions between the BSA and CB molecules of like charge. In contrast, the effective diffusivities of lysozyme to CB‐Sepharose in the buffer containing 0.1 and 0.3 kmol·m−3 NaCl were nearly the same.
Maximum order tree algorithm for optimal scheduling of product distribution lines
Authors: Mokashi S. D. , Kokossis A. C.
Published: April 2004

Research on scheduling and planning in the chemical engineering community subscribes to one of two schools of thought. A general‐purpose optimization approach resorts to using conventional mathematical programming techniques on generic models of a scheduling problem, which has a limitation in its application to large‐scale industrial problems in terms of the computational time involved. The other extreme of heuristic methods lacks guarantees on the quality of the solution. A philosophy is proposed of contextual optimization that exploits problem‐specific knowledge to develop efficient algorithms. This concept is applied to a delivery scheduling problem to generate a tailored graph‐based method called the maximum order tree algorithm, which reduces the CPU time dramatically compared to conventional methods without compromising on the quality of the solution. When applied to a single‐site distribution case study, it resulted in savings of over a quarter of a million dollars per year over the existing heuristic‐rule‐based system.
Enhancing model predictive control using dynamic data reconciliation
Authors: Abu‐el‐zeet Z. H. , Roberts P. D. , Becerra V. M.
Published: April 2004

The use of data reconciliation techniques can considerably reduce the inaccuracy of process data due to measurement errors. This in turn results in improved control system performance and process knowledge. Dynamic data reconciliation techniques are applied to a model‐based predictive control scheme. It is shown through simulations on a chemical reactor system that the overall performance of the model‐based predictive controller is enhanced considerably when data reconciliation is applied. The dynamic data reconciliation techniques used include a combined strategy for the simultaneous identification of outliers and systematic bias.
Influence of product adsorption on the operation of a reverse‐flow reactor
Authors: Garg Rohit , Garayhi Abdul , Luss Dan
Published: April 2004

The adsorption on the catalyst surface of the product of an exothermic reaction in a reverse‐flow reactor (RFR) may lead to large variations in the temporal effluent product concentration. Using a dilute reactant feed, the adsorbed product effluent concentration is low following each flow reversal, but it eventually exceeds the feed reactant concentration. The product adsorption may decrease the range of operating conditions (parameter values) for which the RFR can attain an ignited state. A cooled RFR may attain, for certain parameter values, complex dynamic states such as quasi‐periodic and chaotic states. An increase in the adsorption capacity of the catalyst decreases the range of parameter values for which complex dynamic states exist. The desired period‐1 operation of the RFR is more robust in the presence of product adsorption. Product adsorption may lead to surprising dynamic features, such as the coexistence of up to three stable quasi‐periodic states for the same operating conditions.
Optimal design for flow uniformity in microchannel reactors
Authors: Commenge J. M. , Falk L. , Corriou J. P. , Matlosz M.
Published: April 2004

Velocity and residence time distributions play a crucial role in the performance of microreactors for chemical synthesis. The specific features of fluid flow through multiplate microchannel reactors are examined by an approximate pressure drop model whose validity is confirmed through comparison with more detailed finite‐volume calculations. The model results allow for determination of the influence of the geometrical characteristics of the microchannel structures on the flow distributions and are used to optimize the reactor design for maximum flow uniformity.
Fast solvent screening via quantum chemistry: COSMO‐RS approach
Authors: Eckert Frank , Klamt Andreas
Published: April 2004

COSMO‐RS, a general and fast methodology for the a priori prediction of thermophysical data of liquids is presented. It is based on cheap unimolecular quantum chemical calculations, which, combined with exact statistical thermodynamics, provide the information necessary for the evaluation of molecular interactions in liquids. COSMO‐RS is an alternative to structure interpolating group contribution methods. The method is independent of experimental data and generally applicable. A methodological comparison with group contribution methods is given. The applicability of the COSMO‐RS method to the goal of solvent screening is demonstrated at various examples of vapor–liquid‐, liquid–liquid‐, solid–liquid‐equilibria and vapor‐pressure predictions.
Lattice‐fluid equation of state with hydrogen‐bond cooperativity
Authors: Muthukumaran Poongunran , Brinkley Ray L. , Gupta Ram B.
Published: April 2004

Hydrogen bonding plays an important role in thermodynamic properties of polar fluids. Existing equations of state that include h‐bonding cannot accurately predict the phase behavior for polar fluids. In the theories for h‐bond‐chain forming molecules, h‐bonding strength is considered a constant at a given temperature and pressure. Infrared spectroscopy and ab initio calculations show that the h‐bonding strength depends on whether or not the molecule was previously h‐bonded at other sites. When an h‐bond is formed between an already hydrogen‐bonded species and a free species, the second h‐bond has different energetic characteristics from the primary h‐bond. In the case of l‐alkanol self‐h‐bonding, the equilibrium constant for the second h‐bond is ten times that for the primary h‐bond. This phenomenon called h‐bond cooperativity was incorporated in a lattice‐fluid‐hydrogen‐bonding equation of state. Calculations for pure l‐alkanols, show that the theory can be improved significantly by the incorporation of h‐bond cooperativity. Agreement with the phase behavior and spectroscopic h‐bonding data improves using cooperativity, without any additional adjustable parameters. Heat of mixing calculations agree well with the experimental data.
Characterization of flow and mixing in an SMX static mixer
Authors: Zalc J. M. , Szalai E. S. , Muzzio F. J. , Jaffer S.
Published: April 2004

Laminar flow and mixing of a Newtonian fluid are characterized in a four‐element Koch‐Glitsch SMX static mixer. The computational analysis on a fine, unstructured mesh containing more than 3.5 million tetrahedral elements led to high‐resolution numerical data for velocity and pressure. Computed pressure drops agreed excellently with those in the literature. The flow in this static mixer is essentially independent of the flow rate up to Re = 1, thereby causing the flow characteristics to deviate substantially from those observed when Re < 1. Furthermore, mixing behavior is examined using Lagrangian particle tracking simulations, as well as statistical methods to facilitate comparisons with experimental data. The mixing rate calculated from the simulations agreed closely with experimentally measured values. Both exponential decrease in the variation coefficient as a function of downstream length and the evolution of a self‐similar mixing structure are both evidence of chaotic mixing in the SMX mixer.
Characteristics of acoustic standing waves in fluidized beds
Authors: Herrera C. A. , Levy E. K. , Ochs J.
Published: April 2004

Fine particles are typically difficult to fluidize with gas, due to interparticle forces that cause the bed material to be cohesive. The use of acoustic waves, generated by a loudspeaker positioned above the bed, to agitate the bed material and enhance fluidization, has been investigated. The bed was fluidized with air at conditions near minimum bubbling. Sound‐pressure measurements within the bed showed the presence of acoustic standing waves throughout the bed. Acoustic standing‐wave theory, which assumes that the bed behaves as a 1‐D, quasi fluid with constant speed of sound, was used to model the sound‐pressure‐level data. It was found that the parameter kh, where k is the wave number and h is the bed depth, determines the sound‐pressure amplitude throughout the bed. The system reaches its highest sound pressure at resonance conditions for kh = (2n − 1)π/2. A comparison indicates good agreement between the theory and the experimental data.
Mass‐Transfer modeling in the pervaporation of VOCs from diluted solutions
Authors: Urtiaga Ane , Gorri Daniel , Ortiz Inmaculada
Published: April 2004

A generic model is derived for studying the mass‐transfer kinetics of the pervaporation of multicomponent mixtures of volatile organochloride compounds. Applying it to the pervaporation of dilute mixtures of trichloromethane, dichloromethane and trichloroethylene using tubular polydimethylsiloxane (PDMS) membranes permits: (1) estimation of the representative mass‐transfer parameters, that is, solute diffusivity in the aqueous phase and membrane permeability of the individual components; (2) discrimination of the relative importance of the mass‐transport resistances to the pervaporation flux as a function of operation variables; and (3) determination of the selectivity in multicomponent pervaporation. Diffusivity values calculated with the model agree well with predictions by the Wilke–Chang correlation for nonelectrolyte solutes. Permeability values of PDMS membranes change in the trichloroethylene > trichloromethane > dichloromethane direction. The relative importance of mass‐transfer resistances for the considered volatile organic compounds depends on the operation variables, that is, flow rate of the feed solution and membrane thickness. Furthermore, for trichloroethylene the main resistance is located in the feed solution, whereas for dichloromethane for high values of feed flow rate the resistance in the membrane could exert a major influence on kinetic control, and the behavior of trichloromethane is intermediate between both compounds.
Formation and dynamics of a hot zone in radial flow reactor
Authors: Marwaha B. , Luss D.
Published: April 2004

An infrared camera was used to study the formation and dynamics of hot zones normal to the flow direction on the surface of a radial‐flow reactor, placed horizontally, inside a vessel. The test reaction—the atmospheric oxidation of carbon monoxide—exhibited steady‐state multiplicity. Slow cooling of the vessel caused a shift from a fully‐ignited state to one with a hot zone in the center of the reactor bounded by cold zones at both reactor ends. The hot zone was separated by sharp temperature fronts from the adjacent cold zones. It shrank upon further cooling of the vessel and eventually extinguished. In certain cases, two stable states existed for the same operating conditions with qualitatively different hot zones and reaction rates. A slow back‐and‐forth motion of the temperature fronts (breathing) caused complex oscillations in the overall reaction rate. The dynamic features of the two fronts were different in some cases due to nonuniform catalytic activity and inefficient thermal dispersion. The amplitude and frequency of the temperature breathing motion increased upon cooling of the vessel containing the reactor. Experiments suggest that transversal hot zones are likely to form in packed‐bed reactors close to the extinction temperature.
Population balance modeling of aerated stirred vessels based on CFD
Authors: Venneker Bart C. H. , Derksen Jos J. , Van den Akker Harrie E. A.
Published: April 2004

A developed model predicts local gas fraction and bubble‐size distributions for turbulent gas dispersion in a stirred vessel, based on the population balance equations (PBE), with relations taken from literature for bubble coalescence and breakup derived from isotropic turbulence theory. The transport of bubbles throughout the vessel is simulated by a scaled single‐phase flow field obtained by CFD simulations. Model predictions for the gas fractions in pseudoplastic Xanthan solutions are compared with local measurements and agree well qualitatively. This formulation overcomes the necessity of choosing a constant bubble size throughout the domain, as is done in two‐fluid models and is, therefore, more reliable in mass‐transfer calculations.
Adaptive process monitoring via multichannel EIV lattice filters
Authors: Li Weihua , Bhargava Abhishek , Shah Sirish L.
Published: April 2004

Online monitoring of multivariable processes is crucial to operational safety and product quality. For this, multivariable statistical analysis methods, such as principal‐component analysis (PCA), partial least squares, and canonical variate analysis have been widely applied. However, few recursive monitoring techniques have been developed for fully dynamic and time‐varying processes. Recursive PCA has been successfully applied to monitor static time‐varying processes, but does not work for fully dynamic processes. Dynamic PCA has been developed, but its recursive variant is not available. Many processes operate in dynamic states and are often time‐varying, and the time‐varying property includes the variation of parameters and of process structure, e.g., the change of model order. A novel approach to the adaptive monitoring of multivariate dynamic and time‐varying processes by the recursive multichannel instrumental variable (IV) lattice filters was developed using the errors‐in‐variables (EIV) state space model to represent a dynamic process. To show the relationship between EIV state‐space representation of the process and a multichannel IV lattice filter, the lattice filter was used to generate a residual vector for process monitoring. By using lattice filter's ability of recursively updating the process model both in time and order, a real time, on‐line algorithm was used to update the residual vector with newly sampled process data, including a practical approach to recursive determination of the process model order. Based on the residual vector, the Hotelling T2 statistic and the associated confidence limits are used as the monitoring index. The proposed scheme was evaluated on a simulation example and a pilot plant to support the theoretical results.
Solubility of H2S and CO2 in N‐octyl‐2‐pyrrolidone and of H2S in methanol and benzene
Authors: Fischer Kai , Chen Jian , Petri Martin , Gmehling Jürgen
Published: April 2004

The solubility of hydrogen sulfide and carbon dioxide in N‐octyl‐2‐pyrrolidone (NOP) was measured up to 1.4 MPa at 303 and 324 K using the static synthetic method. Experimental results were compared to those of the predictive Soave–Redlich–Kwong (PSRK) model, wherein the group interaction parameters for the NMP‐group (N‐methyl‐2‐pyrrolidone) were applied to the NOP systems. The reliability of the apparatus used and the applied data treatment were checked by comparing new experimental data for the system hydrogen sulfide+benzene at 304 and 324 K and pressures up to 1.2 MPa, and for the system hydrogen sulfide+methanol at 298 K and up to 0.4 MPa, with published data measured with the analytical method.
Prediction of fully developed turbulent convection with minimal explicit empiricism
Authors: Churchill Stuart W. , Zajic Stefan C.
Published: April 2004

From a purely theoretical analogy between energy and momentum transfer in fully developed turbulent Convection, an expression without explicit empiricism, and which appears to be applicable for all channels, all modes of heating on the surface(s), all values of Re in the turbulent regime, and all moderate and large values of Pr, was deduced for Nu. An analogous complementaly expression for small values of Pr has the same generality, but incorporates one explicit empirical exponent. The numerical implementation of these two expressions for Nu for specific values of Re and Pr introduces some empiricism, but the resulting uncertainty in Nu, including that associated with the aforementioned exponent, is truly negligible. Because of their accuracy and generality, these two expressions, together with several supplementaly relationships, appear to be superior to all existing ones for design calculations. Because of their simple and fundamental structure, they appear to be equally superior for educational purposes.
Velocity of isolated particles along a pipe in stratified gas–liquid flow
Authors: Stevenson P. , Thorpe R. B.
Published: April 2004

The average velocity of isolated grains of sand was experimentally measured in smooth stratified flow in slightly declined pipes. Isolated particles in smooth stratified flow behave similarly to isolated particles propelled by both hydraulic conveying and intermittent gas/liquid flow. In all three cases, particle velocity is linear with respect to the average liquid velocity of the flow (or the average fluid velocity in the slug body for intermittent flow) and has a gradient of approximately one. The data in stratified flow are successfully correlated dimensionlessly (Eq. 7). The correlation is extrapolated to zero particle velocity to estimate the conditions required to ensure sand transport in a flowline in smooth stratified flow. The experimental results suggest that particle velocity is strongly governed by the size of a particle relative to the depth of the viscous sublayer at the pipe wall. If a particle is larger than the viscous sublayer, it is exposed to more coherent turbulent structures and therefore experiences a greater drag.
Cycle detection and characterization in chemical engineering
Authors: Briens L. A. , Briens C. L.
Published: April 2004

Nonperiodic cycles occur in times series obtained in many chemical engineering applications. Variations in the cycle characteristics provide valuable information about the system in which the time series was measured. New methods are developed to detect cycles and determine their characteristics such as the cycle time, its regularity, the cycle strength, and the regularity of the cycle amplitude. These methods are thoroughly validated with both mathematically generated and experimental time series. The best detection method for nonperiodic cycles uses either the V statistic or, if it fails, the new, more sensitive, but more complex, P statistic. Cycle characteristics can be used to detect flow regime transitions in multiphase systems such as risers, gas‐solid, and gas‐liquid‐solid fluidized beds using signals from a variety of simple probes.
Real‐time multirate state estimation in a pilot‐scale polymerization reactor
Authors: Zambare Neeraj , Soroush Masoud , Grady Michael C.
Published: April 2004

Real‐time implementation of a robust multirate state estimator on a continuous stirred‐tank, free‐radical, styrene polymerization reactor is presented. The estimator is designed based on a first‐principles model of the process. It has integral action that allows for robust estimation of the process states. The estimator calculates frequent robust estimates of polymer weight‐average and number‐average molecular weights and monomer concentration. These are estimated from frequent online measurements of the reactor temperature, and infrequent offline and delayed measurements of polymer weight‐average and number‐average molecular weights and monomer concentration. In‐frequent measurements of monomer concentration are obtained by gas chromatography and gravimetry, and those of weight‐average and number‐average molecular weights by gel permeation chromatography.
Simulation of microalgae growth in limiting light conditions: Flow effect
Authors: Pruvost J. , Legrand J. , Legentilhomme P. , Muller‐Feuga A.
Published: April 2004

Effect of hydrodynamical conditions on a microalgae culture growth was investigated in a photobioreactor with annular light chambers, with the focus on the relation between the cell displacement and the amount of light received by microorganisms, by comparing two different flow conditions in light chambers: an axial flow generating a poor radial mixing and a 3‐D swirling motion. To determine microorganism trajectories, a Lagrangian approach was retained, allowing light received to be considered from a single microalga point of view. The light distribution was calculated using Beer–Lambert law, and a biological modeling of the culture growth was proposed, with consideration of light/dark cycle effects induced by cell displacement in the depth of the culture. Finally, batch cultures of Porphyridium purpureum were simulated for both hydrodynamical conditions in light chambers. The advantage of applying a three‐dimensional motion to generate cell renewal in front of the light source, allowing microorganisms to use light more efficiently, is clearly shown.
Feasibility of heterogeneous batch distillation processes
Authors: Rodríguez Donis Ivonne , Gerbaud Vincent , Joulia Xavier
Published: April 2004

Synthesis of heterogeneous batch distillation is discussed, which aims at splitting azeotropic mixtures by adding an entrainer partially miscible with one of the initial binary mixture components. Key operational parameters are identified such as the amount of entrainer added in the ternary feed, the reflux policy, and the vapor line position by examples. Synthesis and operation are less straightforward for heterogeneous batch distillation than those for the homogeneous case, but offer many advantages: more design alternatives, simplified distillation sequences, a lower consumption of entrainer, and a crossing of distillation boundaries by the still path. Feasibility is assessed using simplified modeling and confirmed using a commercial batch process simulator package. Synthesis expectations and simulated results are verified throughout bench‐plant experiments for the separation of the acetonitrile—water mixture using acrylonitrile as a light heterogeneous entrainer.
Deterministic global optimization for error‐in‐variables parameter estimation
Authors: Gau Chao‐Yang , Stadtherr Mark A.
Published: April 2004

Standard techniques for solving the optimization problem arising in parameter estimation by the error‐in‐variables (EIV) approach offer no guarantee that the global optimum has been found. It is demonstrated here that the interval‐Newton approach can provide a powerful, deterministic global optimization methodology for the reliable solution of EIV parameter estimation problems in chemical process modeling, offering mathematical and computational guarantees that the global optimum has been found. Although this methodology is typically regarded as being applicable only to very small problems, it is successfully applied here to problems with over 200 variables. It is a general‐purpose technique and is applied here to a diverse group of problems, including examples in reactor modeling, in modeling vapor‐liquid equilibrium, and in modeling a heat exchanger network.
Optimal operation of distillation processes under uncertain inflows accumulated in a feed tank
Authors: Li Pu , Wendt Moritz , Arellano‐Garcia H. , Wozny Günter
Published: April 2004

A new method of optimizing the operation of distillation processes with uncertain inflow streams from upstream plants is discussed. The case considered is the streams that will be first accumulated in a tank before feeding to the column. To minimize the total amount of operating energy while keeping a stable column operation under these inflows, a novel decomposed optimization strategy consisting of two steps was used. For an optimal planning of the dynamic operation, a smooth feed flow policy to the column is developed in the first step by stochastic optimization under chance constraints by ensuring a predefined probability of holding the tank level inside the desired range. An easy‐to‐use method developed computes the maximum reachable probability of holding the constraints so that a feasible solution of the chance constrained problem can be guaranteed. Since the uncertainty in the inflow stream variability is absorbed in the stochastic optimization over the tank, the operation of the dowstream distillation column is deterministic. Therefore, in the second step, the reflux and reboiler duty policies of the column are developed by deterministic dynamic optimization. The optimal overall strategy is obtained by the maximized smoothness of the feed flow to the distillation column. The approach is applied to a pilot column, and the developed operating policies are implemented on the real plant by experiment.
Selective hydrogenation of acetylene through a short contact time reactor
Authors: Vincent Matthew J. , Gonzalez Richard D.
Published: April 2004

A novel approach to the selective hydrogenation of acetylene involves a short contact time reactor. A thin Pd/γ‐Al2O3 catalytic membrane (about 5 μm thick) was observed to be void of minor defects. Forcing a dilute C2H2/H2/Ar mixture through the layer produced high conversions coupled with high selectivity at high temperatures. The selectivity was observed to increase with temperature. A gas‐dispersion model with derived kinetics was employed to explain the results. A solution to the corresponding coupled nonlinear differential equations resulted in a Peclet number of 64.5 and a contact time of 9.5 × 10−3 s through the reactor at 100°C. A critical thickness is predicted to exist for a maximum in ethylene concentration. A value of 2.5 μm at 200°C is representative. Lastly, permeability experiments agree with modeling results to show that Knudsen diffusion is absent despite a narrow pore‐size distribution.
FBR for catalytic propylene polymerization: Controlled mixing and reactor modeling
Authors: Meier G. B. , Weickert G. , van Swaaij W. P. M.
Published: April 2004

Particle mixing and segregation have been studied in a small‐scale fluidized‐bed reactor (FBR) under pressure. The solids mixing is relatively faster than the residence time of catalyst particles in the case of a polymerization process, but smaller particles accumulate in the upper zone. Semibatch propylene polymerization experiments showed that the vertical temperature gradients are caused mainly by catalyst segregation. At low gas velocities, segregation and mixing can differ under reacting conditions compared to nonreacting conditions due to particle–particle interactions. Catalyst concentration gradients caused by incomplete mixing are strengthened remarkably by the exothermic reaction even at low polymerization rates. These observations do not represent an industrial situation. The FBR has therefore been equipped with a draft tube and cone to control vertical solids mixing. The internal solids circulation rate is a nonlinear function of the gas velocity. Strongly reduced segregation, elutriation, and entrainment observed were compared to experiments without a draft tube. Temperature profiles observed during polymerization can be controlled by the solids circulation rate. Hydrogen injections led to an instantaneously increased polymerization rate, probably due to the reactivation of dormant sites. Irreversible deactivation rates of dormant and active sites seem to be the same. Moreover, hydrogen appeared to be very effective for widening the molecular‐weight distribution. A compartment model developed describes the temperature profile in the reactor and related molecular‐weight distribution of the polymer.
Monolayer hydration governs nonideality in osmotic pressure of protein solutions
Authors: Yousef M. A. , Datta R. , Rodgers V. G. J.
Published: April 2004

Strong nonideality observed in the osmotic pressure of concentrated globular proteins in aqueous media of moderate salt concentrations has long been associated with protein–protein interaction. As a consequence, virial expansions, based on the McMillan–Mayer theory, have been used to extract the physical phenomena observed. Our recent articles showed that a free‐solvent model assuming hydration and salt binding are dominate factors for nonlinearity, successfully modeled BSA (67 kDa) and IgG (155 kDa) protein aqueous solutions at moderate salt concentrations. Similar findings for lysozyme (HEL, 14 kDa) and ovalbumin (45 kDa) are reported here. More significantly, the independently calculated hydration values regressed from the osmotic pressure data were compared with the solvent accessible surface areas of each protein investigated. The results showed that the hydration values determined from the free‐solvent model are remarkably a monolayer equivalent of water.
Hygroscopic properties of mixed ammonium sulfate and carboxylic acids particles
Authors: Hämeri Kaarle , Charlson Robert , Hansson Hans‐Christen
Published: April 2004

The hygroscopic growth of internally mixed ammonium sulfate and carboxylic acid particles was measured as a function of relative humidity by using a tandem differential mobility analyzer (TDMA). In TDMA experiments the organic compounds with different solubilities act in several ways, ranging from the behavior of totally insoluble substance to that of soluble compounds. The hygroscopic properties for mixtures containing either adipic acid or phthalic acid together with ammonium sulfate indicate that the organic fraction of the particles behaves as an inert mass and does not contribute to water uptake. The mixtures involving malonic acid or succinic acid increased the water uptake of the ammonium sulfate part only. The results indicate that the solubility of the organic fraction in individual aerosol particles clearly influences the aerosol–water interaction.
Thermodynamic equilibrium of organic‐electrolyte mixtures in aerosol particles
Authors: Ming Yi , Russell Lynn M.
Published: April 2004

This thermodynamic model describes the phase equilibria of mixtures of electrolytes and organic species in aqueous solutions existing as aerosol particles. The activity coefficient of each species in solution is explicitly related to the chemical composition by treating the (inorganic) ion–water, organic–water and ion‐organic interactions with a combined Pitzer–UNIFAC thermodynamic approach. It was parameterized with a new type of multifunctional “meta‐group” to better represent measured properties of long‐chain monofunctional compounds and short‐chain multifunctional compounds. Interactions between dissolved electrolytes and organic species are modeled using the “salting‐out” effect of NaCl with organic compounds to predict the hygroscopic growth of particles composed of a salt and diacid. The predicted growth agrees well with laboratory measurements. The presence of 50% malonic acid decreases the growth of pure (NH4)2SO4 by 20% at high relative humidities, while mixtures with 50% succinic acid and 50% glutaric acid cause decreases of 35% and 38%, respectively. The mixing of organic compounds with solubility higher than 4 mol·L−1 with salt can decrease the observed DRH. The mixture of malonic acid and (NH4)2SO4 is predicted to start taking up water at 58%, much lower than the DRH of pure (NH4)2SO4 (80%). Insoluble compounds do not change the observed DRH, while reducing the amount of water taken up. The predicted water contents for internal and external mixtures are largely similar, with small differences predicted for mixtures of soluble organic species. The largest deviation of 10% between the water contents of internal and external mixtures occurs for 50% malonic acid with 50% (NH4)2SO4. For less soluble compounds such as succinic acid and glutaric acid, the two types of growth generally agree within 3%.