bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relative gain array analysis for uncertain process models
Authors: Chen Dan , Seborg Dale E. 
Published: April 2004

AbstractRelative gain array (RGA) analysis has been widely used in process control to identify promising control structures and to characterize the degree of process interactions between controlled and manipulated variables. However, the influence of process model uncertainty on RGA analysis has received little attention. Analytical expressions for RGA uncertainty bounds are derived for 2 × 2 control problems and for general, n × n control problems. Both worst‐case bounds and statistical uncertainty bounds are derived. Several simulation examples illustrate the new results. The RGA uncertainty bounds provide useful information concerning model accuracy requirements and the robustness of decentralized control systems.
Stress development in drying coatings after solidification
Authors: Lei H. , Francis L. F. , Gerberich W. W. , Scriven L. E. 
Published: April 2004

AbstractAs a coating solidifies by drying, it tends to shrink. It is liquid enough in early stages that any shrinkage stress is rapidly relieved by viscous flow. It becomes solid enough in later stages to support elastic stress, which results from shrinkage inhibited by adherence to the substrate. Stress can relax by viscous creep in the coating. Thus, the stress level is an outcome of competing shrinkage and relaxation. A theoretical model of diffusion and mass transfer, large shrinkage‐induced deformation and stress, together with yielding and post‐yielding viscous deformation, was developed to predict stress evolution in drying of polymer coatings after solidification. The coupled equations of diffusion and stress development are solved by the Galerkin/finite‐element method. This model is used in polymer coatings to study the effect of a grooved substrate and embedded particles to the stress and drying, and to simulate cantilever deflection method used to measure stress experimentally.
Bivariate moment simulation of coagulating and sintering nanoparticles in flames
Authors: Rosner Daniel E. , Pyykönen Jouni J. 
Published: April 2004

AbstractThe design/control of particle synthesis reactors is hampered by the cumbersome nature of simulation methods (such as “sectional” representations of the particle population balance equation) to track the evolution of coagulating, restructuring populations in complex flow environments. Bivariate PBE‐methods were investigated using generalizations of a recent Gaussian quadrature‐based “moment” approach (McGraw, 1997; Wright et al., 2001). A 9‐moment method was applied to an extensive data set recently obtained using a “seeded” laminar flame reactor with laser‐based, as well as TEM‐grid thermophoretic sampling. Alumina nano‐aggregate population evolution is predicted using available rate/transport laws (for coagulation, thermophoresis and sintering) and the efficacy is predicted, and, together with the efficacy of such simulation methods for parameter estimation, is also illustrated inferring a “best fit” activation energy for nanoparticle sintering. Variants/extensions of these techniques should enable their incorporation into, say, full PDF‐methods for turbulent synthesis reactors, using improved rate laws.
Consolidation during drying of aggregated suspensions
Authors: Brown L. A. , Zukoski C. F. , White L. R. 
Published: April 2004

AbstractDrying of aqueous suspensions containing aggregated particle networks is important in a wide variety of solid/liquid unit operations where, in addition to optimizing the drying rate, there is a need for dimensional control of the dried product. During drying, the bed consolidates and then dehydrates. The degree of consolidation is sensitive to the strength of particle attractions altered by solution conditions such as pH, ionic strength, and particle size. These interaction forces are characterized in terms of an independently measurable quantity, the compressive yield stress Py, and link Py to the compressive capillary forces to which the suspension is subjected during drying. Using Py and a two‐phase fluid model for drying, a dimensionless parameter Q is identified to provide a guide for conditions where interparticle forces and mass‐transfer limitations will dominate drying behavior. This model yields a quantitative measure of the shape changes that can be expected upon drying. Model predictions are tested using drying experiments on 0.65 μm alumina particles in aqueous suspensions at different pH and salt concentrations.
Design of reactive extraction systems for bioproduct recovery
Authors: Pai Rajaram A. , Doherty Michael F. , Malone Michael F. 
Published: April 2004

AbstractLiquid‐liquid extraction, combined with chemical reaction, can improve overall yields of product. Reactive extraction is an alternative for separations in bioprocessing, for example, for the production of carboxylic acids such as lactic or citric acid, alcohols such as ethanol, or antibiotics such as penicillin, cephalosporin or streptomycin. A method for the design of reactive extraction cascades was used for the recovery of Penicillin G and for lactic acid from aqueous mixtures using mixtures of organic solvents with reactive amines as extractants. Effects of such variables as residence time, flow rates, pH, number of stages and amine concentration are quantified. Designs capable of essentially complete recovery are reported.
New synthesis framework for the optimization of complex distillation systems
Authors: Shah Piyush B. , Kokossis Antonis C. 
Published: April 2004

AbstractA new synthesis framework screens and examines complex distillation sequences. Conventional superstructure developments are replaced in favor of a novel representation that assumes the form of a supertask model. The supertask is based on simple tasks that accommodate for basic sequences. Hybrid tasks account for complex columns and sloppy splits. Discrete instances of simple tasks are combined with hybrid transformations to optimize operating conditions. The optimization problem is formulated as a simple MILP problem that is possible to solve to global optimality. The proposed representation can develop different nonconventional and novel designs featuring fully integrated columns, parallel sequences, and multiple‐effect columns. The approach is illustrated with several literature and industrial problems. In all cases solutions are reported in the form of nonconventional designs that perform as optimal or near‐optimal schemes.
General local‐equilibrium chromatographic theory for eluents containing adsorbing buffers
Authors: Frey Douglas D. , Narahari Chittoor R. , Butler Christy D. 
Published: April 2004

AbstractAn efficient, general strategy was developed for numerically solving the system of equations that describe a pH gradient under local‐equilibrium conditions when the elution buffer contains arbitrary numbers of both adsorbed and unadsorbed buffering species (weak electrolytes) and for a weak‐ or strong‐base ion‐exchange column packing. Since the method involves the solution of algebraic equations, instead of partial differential equations, it can be used to rapidly determine the effluent pH profile given the adsorption equilibrium constants for the buffering species. It can also be used iteratively to determine the adsorption equilibrium constants for the buffering species from an experimentally determined effluent pH profile as well as to determine the composition of the elution buffer required to achieve a desired shape for the pH gradient given the adsorption equilibrium constants for the buffering species. The calculation method is verified experimentally and used to illustrate the behavior of chromatographic methods which employ retained pH and ionic strength gradients.
Dynamics of a fixed‐bed adsorptive reactor for synthesis of diethylacetal
Authors: Silva Viviana M. T. M. , Rodrigues Alírio E. 
Published: April 2004

AbstractDiethylacetal from ethanol and acetaldehyde catalyzed by the acid resin Amberlyst 18 was synthesized. Adsorption and reaction experiments were performed in a laboratory‐scale fixed‐bed adsorptive reactor, operating isothermally at 15°C and at atmospheric pressure. Experimental results of dynamic adsorption of binary nonreactive mixtures were used to obtain multicomponent adsorption equilibrium isotherms of the Langmuir type. The reaction kinetics reported earlier were used in the model of the adsorptive reactor, which also included axial dispersion, external and internal mass‐transfer resistances, and multicomponent Langmuir isotherms. Model equations were solved by orthogonal collocation on finite elements (OCFE), implemented by the PDECOL package, using the measured model parameters, and were validated by experimental data for reaction and regeneration steps, with good accuracy.
Gas permeance measurement of hollow fiber membranes in gas‐liquid environment
Authors: Lund Laura W. , Hattler Brack G. , Federspiel William J. 
Published: April 2004

AbstractAn apparatus and methodology were developed to measure the oxygen and carbon dioxide permeance of hollow fiber membranes (HFMs) in a gas‐liquid environment. The gas‐liquid permeance measurements were compared with measurements made in a gas‐gas environment to validate the methodology and to determine whether the permeance of an HFM in a gas‐liquid environment differs inherently than in a gas‐gas environment. The methodology is based on measuring the overall system permeance for a range of liquid velocities and isolating the membrane resistance to gas flux from the liquid boundary layer resistance by regression of a nonlinear system model to the data. The success of the methodology in accurately estimating membrane permeance depended on the maximum liquid velocity which the system could consistently generate past the fibers.
Mechanisms of photoresist dissolution
Authors: Hunek Balazs , Cussler E. L. 
Published: April 2004

AbstractThe comprehensive physical picture developed describes the dissolution of a broad range of materials, including novolak‐based photoresists and can be applied to the dissolution in aqueous base of both small molecules and polymers that can ionize. The model was verified by measuring the dissolution of solute‐coated spinning discs. Key experimental variables included the flow (as a Reynolds number) and the base concentration, which was in this case of sodium hydroxide. The physical and chemical characteristics of the dissolving species determine the rate‐limiting steps, which cause different dissolution behavior. The dissolution of low molecular weight phenolic resin is controlled by a combination of solute release and solute mass transfer, without the formation of any significant intermediate gel phase. Several other dissolution mechanisms are rationalized based on a simple “strings of buoys” analogy, which can be extended to other cases as well.
Hydrodynamics of trickling flow in packed beds: Relative permeability concept
Authors: Lakota Ana , Levec Janez , Carbonell Ruben G. 
Published: April 2004

AbstractLiquid holdups and pressure drops for gas and liquid concurrent flow in packed beds were measured experimentally. To calculate the Ergun type constants, pressure drops were also measured for single‐ (gas)‐phase flow through the same packings. These measurements reveal that the Ergun type inertial constant depends on the particle shape. The beds were packed with porous and nonporous spheres, cylinders, extrudates, and Raschig rings. The experimental data were analyzed using the concept of relative permeabilities. The liquid‐phase relative permeability correlated well with the reduced liquid saturation in a unique power‐law form for all particles independent of their shape. The gas‐phase relative permeability as a function of the gas‐phase saturation followed the same law, but the exponent depends on the particle shape and gas‐phase Reynolds number. Predicted and experimental values for liquid holdups for all particle shapes agreed well with mean relative deviations less than 10%. Predictions of pressure drops for spherical particles, cylinders, and extrudates are at least as accurate as other less rigorous correlations (mean relative errors between 25 and 40%). Pressure drop predictions for Raschig rings are poorer (mean relative deviations of 90%), reflecting in part the variations in pressure drops from experiment to experiment with these particles.
Elastohydrodynamics of a moving substrate over a curved plate
Authors: Carvalho M. S. , Huelsman G. L. , Kolb W. B. 
Published: April 2004

AbstractConventional drying of coated substrates usually uses air impingement to support and heat the coated web. Because of the high‐velocity air flow, most of the heat is transferred by convection and the heat transfer coefficient is not uniform, leading to drying defects. To overcome this and obtain a high uniform heat transfer coefficient, the energy is supplied to the backside of the substrate by conduction through a thin air‐layer between a heated plate and the moving substrate. To obtain heat transfer coefficients comparable to those from air impingement, the distance between the web and plate has to be very small, yet not touch the plate. It is essential to form and control a thin, uniform and stable air layer between the substrate and heating plate by wrapping the moving web over a plate with a large radius of curvature. Air‐layer thickness entrained between the web and plate is related to the air flow rate between the two surfaces. The flow between a moving flexible substrate and curved solid surface was analyzed by theory and experiments to examine this elastohydrodynamic action and changes in air‐layer thickness with the plate geometry, substrate material, and operating conditions. The theoretical model consisted of the Navier–Stokes equation to describe the air motion and cylindrical shell approximation to model the web deformation. Differential equations describing the problem were solved by the Galerkin's/finite‐element method. The nonlinear algebraic system was solved by Newton's method with initialization by pseudo‐arc‐length continuation. In experiments, the distance between the moving web and curved plate was measured at different operating conditions. The predicted air‐layer thicknesses agreed well with experimental measurements. The air‐layer thickness is controlled by the flow in the plate entrance.
Linearized transport model for nanofiltration: Development and assessment
Authors: Bowen W. Richard , Welfoot Julian S. , Williams Paul M. 
Published: April 2004

AbstractFinite difference linearization of pore concentration gradient in nanofiltration membranes greatly simplifies the solution of a three‐parameter model (pore radius, membrane charge, and pore dielectric constant) for electrolyte rejection by removing the requirement for numerical integration of the extended Nernst–Planck equation. The validity of the linearized model is first experimentally tested by comparing with a rigorous characterization of the Desal‐DK nanofiltration membrane, the linearized model closely agreeing with the numerical solution of the full model. Investigation of pore concentration profiles showed the assumption of linearity to be valid over a wide range of nanofiltration conditions. The linearized model was also successfully extended to ternary electrolyte mixtures, highlighting its main advantage over analytic solutions. Overall, the model is a powerful tool for characterization of nanofiltration membranes and subsequent prediction of separation performance. Computational demands are modest in terms of time and complexity.
Feasible region for a countercurrent cascade of vapor‐liquid CSTRS
Authors: Gadewar Sagar B. , Malone Michael F. , Doherty Michael F. 
Published: April 2004

AbstractThe attainable region approach for reaction‐mixing systems was applied to systems with simultaneous reaction and separation. A model developed for a countercurrent cascade of two‐phase CSTRs can be considered as a surrogate for the stripping or rectifying sections of a reactive distillation column. An overall composition vector defined satisfies the same geometric properties as the reaction vector. The necessary conditions for the reaction‐mixing attainable region were applied to the cascade of two‐phase CSTRs. This article focuses only on the countercurrent cascade of two‐phase CSTRs; therefore, the region identified is a feasible region, which is a subset of the attainable region for reaction‐separation systems. For consecutive reactions, the boundary of the feasible region is given by the trajectory for a cocurrent cascade of two‐phase CSTRs. The overall composition vector for the cocurrent cascade of two‐phase CSTRs is tangent to the trajectory. For single reversible reactions, the attainable region for single‐phase reactors is significantly expanded by using a countercurrent cascade of vapor‐liquid CSTRs. Two examples used are transalkylation of toluene and the synthesis of isopropyl acetate.
A multiple microreactor system for parallel catalyst preparation and testing
Authors: Pantu Piboon , Gavalas George R. 
Published: April 2004

AbstractA system containing nine catalytic microreactors for parallel preparation and testing of heterogeneous catalysts is described. The catalyst samples are prepared in the form of thin films coated on thin quartz rods by dip‐coating in solutions of different composition. Catalyst‐coated rods are placed within thin tubes housed inside a wider tube heated in an electrical furnace. A multiport valve serves to sequentially conduct the reaction products from each microreactor to a mass spectrometer for analysis. The system was tested with the reaction of methane reforming with carbon dioxide over Pt/Ce1−xGdxO2−0.5x and Pt/Ce1−xSmxO2−0.5x at 650 and 700°C. Individual catalysts were characterized by X‐ray analysis, and induction‐coupled plasma mass spectrometry for catalyst mass and elemental composition. The measurements showed that Pt/CeO2 had the highest activity among the series of catalysts tested and generally the activity increased with the cerium oxide content. After exposure to the feedstream for 2–3 h at 700°C, most catalysts suffered significant deactivation except the mixed oxides with 25–85% samarium oxide that maintained relatively stable activity.
Radiation field inside a reactor of glass‐fiber meshes coated with TiO2
Authors: Esterkin Carlos R. , Negro Antonio C. , Alfano Orlando M. , Cassano Alberto E. 
Published: April 2004

AbstractA photocatalytic reactor for treating polluted gaseous streams was developed with a flat‐plate configuration and parallel, glass‐fiber meshes coated with TiO2. It was irradiated from both sides with UV light provided by tubular lamps placed at both sides of the reactor. The first step in the description of the reactor performance is the knowledge of the local values of radiation intensities. The radiation field was modeled by special adaptation of the ray‐tracing technique. The model uses two optical properties of the glass‐fiber meshes: transmittance and reflectance. To validate the mathematical description of the reactor with experiments, the exiting radiative flux from one side was measured using a precise UV detector. Predictions show a maximun error of 8.3% with respect to experimental values measured at the center of the apparatus. This description of the radiation distribution is indispensable to model the photooxidation reaction.
Transient kinetics of n‐Butane oxidation to maleic anhydride over a VPO catalyst
Authors: Huang Xiao‐Feng , Li Cheng‐Yue , Chen Biao‐Hua , Silveston P. L. 
Published: April 2004

AbstractTransient reaction kinetics is usually needed to model the reactor system operated under unsteady‐state mode to improve the performance of the catalyst packed in such a reactor system and to match operating conditions of different reaction steps in this system. The transient reaction kinetics of n‐butane oxidation to maleic anhydride over a commercial VPO catalyst was systematically studied, using online MS/GC measurements, transient response, and forced periodic operation methods. A simplified scheme with respect to the reaction network is proposed based on the previous studies and the observations in this work. Combining the results on the roles of lattice and adsorbed oxygen in the reaction process with the data obtained in transient response experiments, a transient kinetic model taking account of the oxygen storage and diffusion in the bulk‐phase of the catalyst was introduced and its parameters were estimated. The model was examined by the transient response experimental data and time‐average concentrations of butane and maleic anhydride under forced unsteady‐state operation.
Optimal operation of extractive distillation in different batch configurations
Authors: Low K. H. , Sørensen E. 
Published: April 2004

AbstractOptimal operations of extractive distillation for regular and middle‐vase1 batch columns are presented based on a profit function. Detailed models are used for the rigorous dynamic optimization considering all operational decision variables, including reflux ratio, solvent feed rate, heat duties, and possible product withdrawals during the process. Optimal feed distribution and stream configuration at the middle section of the middle‐vessel column are investigated. Separation of a minimum boiling azeotropic binary mixture (acetone and methanol using water as solvent) involving different separation duties and feed compositions is presented as a case study. The pereformanance of the middle‐vessel column is signicantly influenced by the middle‐section stream configuration, with the best profit when the stream configuration is allowed to vary during the operation. The optimal operating policy for the middle‐vessel column involved the feed being charged mainly to the reboiler still with low holdup in the middle vessel during the operation.
Homogenization of mesoscopic theories: Effective properties of model membranes
Authors: Lam R. , Vlachos D. G. , Katsoulakis M. A. 
Published: April 2004

AbstractA new mathematical framework for modeling diffusion in nanoporous materials or on surfaces exhibits heterogeneity in properties over large length scales and retains molecular scale information, typically captured only by molecular simulations (kinetic Monte Carlo). It first uses newly developed mesoscopic equations derived rigorously from underlying master equations by coarse‐graining statistical mechanics techniques. Homogenization techniques are then used to derive the leading‐order effective mesoscopic models that are subsequently solved by spectral methods. These solutions are also compared to direct numerical simulations for selected 2‐D model membranes with defects, when attractive adsorbate‐adsorbate interactions affect particle difSsion. Both the density and dispersion of defects significantly alter the macroscopic behavior in terms of fluxes and concentration patterns, especially when phase transitions can occur. In the presence of adsorbate‐adsorbate interactions, permeation through a nanoporous film can depend on the face of a membrane exposed to the high‐pressure side. Homogenization techniques also could offer a promising alternative to direct numerical simulations, when complex, large‐scale heterogeneities are present.
Use of COSMO‐RS for the prediction of adsorption equilibria
Authors: Mehler C. , Klamt A. , Peukert W. 
Published: April 2004

AbstractThe novel method COSMO‐RS for the calculation of thermodynamic partition equilibria based on quantum chemical calculations is applied for the first time to the correlation and prediction of adsorption equilibria. In the limit of small adsorbate concentrations, very good predictions have been achieved for adsorption equilibria of activated carbon for both the phase and the aqueous phase.