bluuebunny/crossref_metadata_2025 huggingface dataset:
Inverse problems in population balances: Growth and nucleation from dynamic data
Authors: Mahoney Alan W. , Doyle Francis J. , Ramkrishna Doraiswami
Published: April 2004

Particulate process modeling is critical for system design and control used widely in the chemical industly. Previous methods have focused on the assumption of appropriate models that can capture system behavior. A new technique presented is based on viewing the population balance from an inverse problem perspective that allows to determine appropriate models directly from experimental data. Under suitable assumptions (deterministic growth rate, no aggregation), the population balance equation may be solved by the method of characteristics, which associates the number density for any size at any time with a single point from the initial or boundary condition. The key to using this is the recognition that these characteristics correspond to the size history of individual particles and can be associated with constant cumulative number densities (quantiles) of the population. These quantiles are easily identifiable from experimental data. The variation of size and number density along these characteristics provides decoupled equations used to determine the growth rate. Validity of the determined growth law is checked by the collapse of the experimental data onto initial and boundary conditions.
Visualization of high‐dimensional phase diagrams of molecular and ionic mixtures
Authors: Wibowo Christianto , Ng Ka M.
Published: April 2004

A general method for visualizing high‐dimensional phase diagrams of systems containing a mixture of molecular and ionic species is presented. Based on geometric modeling with homogeneous coordinates, canonical coordinates are developed to represent cuts and projections, which, being reaction‐invariant, do not depend on the degree of ionization. Examples are provided to illustrate the application of this method for identifying useful transforms with potential applications in separation system synthesis.
On the theory of optimal sensor placement
Authors: Chmielewski Donald J. , Palmer Tasha , Manousiouthakis Vasilios
Published: April 2004

On the Theory of Optimal Sensor Placement

An optimal sensor placement is defined as a sensor configuration that achieves the minimum capital cost while observing prespecified performance criteria. Previous formulations of this problem have resulted in the definition of a mixed‐integer nonlinear program (MINLP) with dimensions dependent on the value of the integer decision variables. The main contribution of this work is an equivalent reformulation of the design problem such that the dimension of the NLP is independent of all decision variables. Additionally, the traditional sensor‐placement problem, based on static process conditions, is extended to linear dynamic processes. The final contribution is the exact conversion of the general NLP into a convex program through the use of linear matrix inequalities. The aggregation of these results show that the sensor‐placement problem can be solved globally and eficiently using standard interior‐point and branch‐and‐bound search algorithms.
Online estimation and control of polymer quality in a copolymerization reactor
Authors: Park Myung‐June , Hur Su‐Mi , Rhee Hyun‐Ku
Published: April 2004

The validity of an online state estimator for a semi‐batch MMA/MA solution copolymerization reactor was established using online densitometer and viscometer. Using the conventional extended Kalman filter (EKF) as the state estimator, the experiment was conducted under both isothermal and nonisothermal conditions for application to the control of copolymer properties. Further analysis was made by using ofline measurement data for the mol fraction of MMA in the remaining monomers and the solid content. The EKF was found to provide a good estimate for the state of the copolymerization system. A model predictive controller was designed and implemented to obtain copolymers with uniform copolymer composition and the desired weight average molecular weight by adopting the feed flow rate of MMA and the reaction temperature as control inputs. The controller was proven effective with a satisfactory performance for the control of polymer properties in the semi‐batch copolymerization reactor.
Analyzing enhancement of CO2, reforming of CH4, in Pd membrane reactors
Authors: Raybold Troy M. , Huff Marylin C.
Published: April 2004

It is demonstrated that H2, removal through Pd foil membranes can enhance the CO2, reforming of CH4. At 550°C and low flows over Pt/γ ‐Al2O3, pellets, conversions were twice that of a conventional reactor, while H2O formation was suppressed, resulting in H2/CO effluent ratios of 1.0. Larger sweep flows enhanced the reaction somewhat, and the replacement of Pt/γ ‐Al2O3, with Pt/ZrO2 mitigated catalyst deactivation in H2‐poor operating environments. A quantitative correlation was established between reaction enhancement and the overall H2 removal to production ratio. Based on this correlation, a simple membrane reactor equilibrium model was developed for comparison against experimental data. Subsequently, a unique and useful “on‐the‐fly” method of gauging membrane limitations, catalyst limitations, and modes of deactivation within a membrane reactor was demonstrated.
Modeling monomer transport by convection during olefin polymerization
Authors: Parasu Veera U. , Weickert G. , Agarwal U. S.
Published: April 2004

During olefin polymerization on heterogeneous catalyst, a catalyst particle undergoes fragmentation, and the formed polymer gets deposited on the fragments. These polymer‐coated fragments (microparticles) together form a porous polymer particle (macroparticle). The multigrain model (MGM) gives a detailed description by accounting for the monomer diffusion phenomena at both levels. The original approach to solution involved a sequential shell‐by‐shell determination of monomer concentration profiles, with both radial boundaries of the shells moving with the particle growth. A fixed boundaly system of simultaneous differential equations enables easier computer implementation of the MGM model. Further, in a new development presented here, the interstitial spaces between the microparticles make up the pores through which monomer transport occurs not only by diffusion, but also by convection. The convection is driven by the pressure gradient created by the monomer consumption within the particle. Consistent with recent experimental observations, significantly higher monomer transport rates are thus predicted.
Miniature fuel cells fabricated on silicon substrates
Authors: Kelley S. C. , Deluga G. A. , Smyrl W. H.
Published: April 2004

Novel miniature fuel cells were fabricated from micromachined silicon wafers. The cells used methanol and air as reactants, and a thin polymer electrolyte as separator. The assembled cells had a working volume of 12 mm3 and could be scaled down in size by three orders of magnitude by simple adjustments of the masking and etching procedures. Electrodeposition of Pt‐Ru as the anode catalyst (oxidation of methanol) was successful in lowering the loading to 0.25 mg/cm2 without loss of performance. Cell performance approached that of the best, state‐of‐the‐art, large fuel cells, when scaled for size. In particular, single miniature cells yielded 822 Wh/kg and 924 Wh/L when operated at 70°C. The same chip design was also used for the hydrogen/air system, and the cell current, power, and specific energy density were higher than those of methanol/air, Further tailoring of the chips for spefici fuels could lead to further improvements.
Thermodynamics of gas‐solid flow
Authors: Collado Francisco J. , Sevilla Eduardo , Valcárcel Carlos
Published: April 2004

New thermodynamic fundamentals for vertical pneumatic conueying are proposed with derivation based strictly on mass conservation and continuum concept. For a 1‐D, vertical, steady gas‐solid flow, these new mass and energy balances allowed the derivation of a new nondimensional energy factor containing the pressure drop. This energy factor correlated quite well with the difference between the inlet gas velocity and solids terminal velocity, when tested against high‐pressure, 15‐m‐high, vertical pneumatic transport data from Institute of Gas Technology. The energy factor was also checked against atmospheric‐pressure data of the 5‐m lift line of the Pennsylvania State Uniuersity. The new energy factor covers quite well both the atmospheric‐ and high‐pressure sets of data (923 tests) including two heights, lean‐ and dense‐phase transports, several pipe diameters, broad and narrow particle‐size distributions, and different materials. The dissipation terms in gas‐solid flow were also clearly identified.
Redistribution of adsorbed VOCs in activated carbon under electrothermal desorption
Authors: Cheng Z.‐M. , Yu F. D. , Grevillot G. , Luo L. , Tondeur D. , Yuan W. K.
Published: April 2004

Electrothermal desolption is an electricity‐promoted desolption technology developed only in the last decade. It is extremely eficient and straightforward when the adsorbent is electrically conductive, since heating can be achieved by the Joule effect. The volatile organic compound (VOC) vapors desorbing from micropores might redistribute and condense in mesopores with high concentration, which is possible since no dilution occurs. To study this problem, benzene and activated carbon were used as the working system, and a theoretical analysis was developed. In a wide temperature range up to 400°C, no VOC vapor could be condensed in mesopores with the strong micropore adsorption effect. With the weak micropore adsorption effect, however, mesopore condensation will occur, but it only takes place in mesopores smaller than 3 nm in diameter, and the amount is generally negligible. To prevent any possible condensation, the desorption temperature should at least equal the liquid boiling point calculated in a 2‐nm capillary tube.
Transient measurements of adsorption and diffusion in H‐ZSM‐5 membranes
Authors: Gardner Tracy Q. , Flores Ana I. , Noble Richard D. , Falconer John L.
Published: April 2004

A transient permeation method presented here not only determines the adsorption and diffusion properties of the pores that are the transport pathways through zeolite membranes, but nondestructively estimates the effective thickness of the membrane. Transient responses of the permeate concentration to step changes in the feed were measured on two H‐ZSM‐5 tubular membranes and modeled assuming Maxwell‐Stefan diffusion and Langmuir adsorption. The adsorption isotherms determined from these transient measurements at 298 K of N2 and CO2 were nearly identical to those measured by calorimetry on H‐ZSM‐5 powders. The CH4 isotherm at 298 K was similar to isotherms measured by calorimetry and gravimetric techniques on Na‐ZSM‐5 and silicalite powders. The similarity of the isotherms indicates that transport of these light gases occurs mainly through zeolite pores. The Maxwell‐Stefan diffusion coefficients DMS depended on concentration and were higher for higher feed partial pressures. Average DMS values for the two membranes were 7.5, 5 and 1.5×10−10 m2/s for N2, CH4, and CO2, respectively; these are in the same range and order as diffusion coefficients measured in zeolite crystals.
Product‐centered processing: Manufacture of chemical‐based consumer products
Authors: Wibowo Christianto , Ng Ka M.
Published: April 2004

A systematic framework for product‐centered processing is useful particularly in developing chemical‐based consumer product manufacturing processes. The objective is to provide directions and guidelines toward the development of a process for manufacturing a product with the desired performance in reduced time and effort. The product performance, represented by several quality factors, is related to product ingredients and structural attributes, as well as the process flowsheet and operating conditions. The procedure consists of five steps. First, the product functionality, form, and packaging are defined. Second, relevant quality factors are identified. Third, necessary ingredients are selected and product microstructure is determined. Fourth, the manufacturing process is designed in light of the desired product properties. Limitations on achievable product quality are also identified. Finally, the product and process are evaluated with the help of experimental data. The framework is illustrated using industrial examples, including the production of dry toner, laundry detergent, shampoo, and cosmetic lotion.
Solubilities of nonvolatile solutes in polymers from molecular thermodynamics
Authors: Fornasiero F. , Olaya M. M. , Wagner I. , Brüderle F. , Prausnitz J. M.
Published: April 2004

Because there is no simple, general method for measuring solubilities of nonvolatile solutes in a polymer, this work presents a thermodynamic framework for estimating such solubilities from infinite‐dilution distribution‐coefficient data for aqueous solutions of the solute in equilibrium with the polymer. The experimental infinite‐dilution distribution coefficient is related to that calculated from a molecular‐thermodynamic model (Flory–Huggins). The three binary Flory parameters are obtained from water–solute and water–polymer data, and from the solute's distribution coefficient. Solubilities of 19 nonvolatile aromatic solutes were estimated in three polymers: ethyl‐vinyl acetate copolymer (EVAc) with 33 (EVAc33), 45 (EVAc45) wt. % vinyl acetate content, and poly(vinyl acetate) (PVAc) at 25°C, where most of the solutes are solids. For some of these systems, predicted solubilities are compared with new experimental results. The calculations reported here may be useful for various applications, including the design of membrane processes or drug‐delivery systems, and for packaging technology for foods, chemicals, and pharmaceuticals.
Generalized model for predicting phase behavior of clathrate hydrate
Authors: Yoon Ji‐Ho , Chun Moon‐Kyun , Lee Huen
Published: April 2004

An improved and generalized model was developed to predict the dissociation pressures of hydrate‐forming gases and the complicated phase behavior of multicomponent hydrate systems. Based on the van der Waals‐Platteeuw theory with the Kihara spherical‐core potential function, a new equation for the water fugacity in the filled hydrate phase is provided. Instead of vapor pressures of ice for conventional approaches, it adopts the molar enthalpy difference between ice and liquid water. Since it always maintains its unique form whether the hydrates coexist with ice or water, it can be successfully applied to predict the multiphase equilibria of simple and mixed hydrate systems. The fugacities of all components in vapor and liquid phases coexisting with hydrates were calculated by the Soave‐Redlich‐Kwong (SRK) equation of state incorporated with the modified Huron‐Vidal second‐order mixing rule. Lower and upper quadruple points and neighboring four three‐phase curves around these quadruple points were described correctly by this model calculation. The Kihara potential parameters for the interaction between water and gas molecules are presented by fitting experimental dissociation pressures. Various types of systems involving hydrate mixtures containing either two guest components or inhibitors were extensively tested to examine the model's potential applicability to predicting the complicated phase equilibria.
Pore‐scale modeling of fluid transport in disordered fibrous materials
Authors: Thompson Karsten E.
Published: April 2004

The modeling of fluid transport in fibrous materials is important for many applications. Most models operate at the continuum level, which requires an a priori knowledge of spatially averaged transport parameters. Alternatively, highly detailed models, in which the momentum equations are solved directly, require major simplifying assumptions. Thus, it is desirable to use intermediate‐level techniques that model transport using first principles, but that are appropriate for real engineering processes. In this work, pore‐scale network modeling is adapted for fibrous materials and tested for a large range of fibrous structures and solid volume fractions. A novel technique is used to generate prototype network structures from Voronoi diagrams. The Voronoi networks are coupled with two different multiphase flow algorithms, enabling the modeling of various displacement processes relevant to engineering. Permeability predictions agree well with known values. Effects of dynamics, wettability, and material structure on displacement were studied. This modeling technique not only allows for better quantification of how microscale properties affect macroscopic transport, but helps reduce the number of experiments required to predict continuum transport parameters for various materials and processes.
Antierosion in a 90° bend by particle impaction
Authors: Fan J. R. , Yao J. , Cen K. F.
Published: April 2004

Ribbed bend protection, a new method to protect duct bends against erosion in gas–solid flows, was studied theoretically. In this method, ribs are evenly welded on the outer wall of the inside bend at 20°–80°, and the material of the bend is medium carbon steel. An experimental system is set up to perform 3‐D numerical work simultaneously. Experimental and numerical results agree well and confirm that the method is simple and efficient for erosion protection. Numerical simulation is used to study the axial gas‐flow characteristics along the bend and the secondary flow at the cross section. Detailed analyses involving the impact of velocity and the incidence angle of particle–metal (particle‐rib or particle‐duct) impact show the mechanism of the antierosion effect. As a result, both experimental and theoretical predications demonstrate that the average erosion rate of ribbed bends is only one‐third of the bare bend under test conditions, and that rectangular ribs possess greater antierosion ability than square ribs do. Besides, the predictions suggest that the erosion of the wall is more serious than that of the ribs on a ribbed bend, while the wear distribution pattern remains unchanged after adding ribs at the bend.
CFD simulation of flow and turbulence in a slurry bubble column
Authors: Matonis Diana , Gidaspow Dimitri , Bahary Mitra
Published: April 2004

To develop a predictive, experimentally verified computational fluid dynamic model for gas–liquid–solid flow, a 3‐D transient computer code for the coupled Navier–Stokes equations for each phase was developed. The principal input into the model is the viscosity of the particulate phase, which was determined from a measurement of the random kinetic energy of the 800‐micron glass beads and a Brookfield viscometer. The computed time‐averaged particle velocities and concentrations agree with PIV measurements of velocities and concentrations, obtained using a combination of gamma‐ray and X‐ray densitometry, in a slurry bubble column, operated in the bubbly‐coalesced fluidization regime with a continuous flow of water. Both the experiment and simulation show a downflow of particles in the center of the column, and an upflow near the walls, and a nearly uniform particle concentration. Normal and shear Reynolds stresses were constructed from the computed instantaneous particle velocities. The PIV measurement and the simulation produced similar nearly flat horizontal profiles of turbulent kinetic energy of particles.
Convection cells and segregation in a vibrated granular bed
Authors: Hsiau Shu‐San , Wang Pai‐Chei , Tai Chi‐Hwang
Published: April 2004

Granular materials may be circulated in a container with two symmetric convection cells under external vertical vibration conditions. Effects of the container geometry on the convection strength and segregation process are studied experimentally. First, the wall tilted outward angles are changed to observe the direction of the convection roll and convection strength. The strength of the normal convection rolls decreases by increasing the wall angles of the container from 0° (vertical walls). The convection rolls become reversed when the wall tilted outward angles are greater than a transition angle. The wall roughness and vibration velocity amplitude are also changed to investigate their influences on the convection cell strength. The segregation of a larger disk induced by the convection cells of smaller disks shows that the normal convection rolls induce the upward motion of the larger disk, and the reverse convection rolls result in the downward motion of the larger disk. The separation velocity increases linearly with the convection flow rate.
Using discrete distributions to analyze CSD data from MSMPR crystallizers
Authors: Jones Christopher M.
Published: April 2004

A novel technique for treating continuous mixed‐suspension, mixed‐product removal (MSMPR) crystal‐size distribution (CSD) data uses a discrete probability distribution to represent the growth rate distribution of crystals in a crystallizer. It is based on the premise that individual crystals in a population each have their own intrinsic growth rate, but the growth rates of crystals in the population may vary. Treatment of CSD data using this discrete distribution technique enables the calculation of crystallizer kinetics data, including the nucleation rate and characterization of the nuclei growth rate distribution and using both graphical representation and descriptive statistics. Previously published data for a system exhibiting growth rate dispersion is used to demonstrate the efficacy of the technique. Furthermore, the results of the data analysis using the discrete distribution technique are compared to the results of data analysis using the continuous distribution technique.
New adsorbents for purification: Selective removal of aromatics
Authors: Takahashi Akira , Yang Ralph T.
Published: April 2004

Adsorption of benzene and cyclohexane on various Y‐zeolites was investigated to develop sorbents for the purification of aliphatics by removal of aromatics. Ag‐Y showed superior benzene/cyclohexane selectivities to Na‐Y, Pd‐Y, and H‐USY. Separation factors greater than 105 were obtained with Ag‐Y at low concentrations of benzene. High selectivities were achieved by the strong interaction between benzene and Ag‐Y, while the interaction with cyclohexane was not influenced by the cations. Molecular orbital calculation revealed that benzene formed a classic π‐complexation bond with Ag‐Y: donation of electron charges from the p‐orbitals of benzene to the vacant s‐orbital of the silver (σ donation) and, simultaneously, back donation of electron charges from d‐orbitals of silver to π*‐orbital of benzene (d–π* back donation). Grand canonical Monte Carlo simulations were also performed for adsorption isotherms. Potential parameters of benzene on Ag‐Y, including π‐complexation, were developed first. Simulation and experiments of GCMC agreed excellently for adsorption of benzene on Y‐zeolites.
Modeling of air separation in a LSCF hollow‐fiber membrane module
Authors: Tan Xiaoyao , Li K.
Published: April 2004

Mixed ion‐conducting ceramic membranes are promising in oxygen separation from air due to their infinite permselectivity. Hollow‐fiber‐shaped membranes can provide a high surface area for such an application. A mathematical model for a hollow‐fiber La0.6Sr0.4Co0.2F0.8O3−δ(LSCF) membrane module for air separation was developed and a performance of the module at various operating conditions was studied theoretically. The simulation results reveal that the cocurrent is a better operating flow pattern than the countercurrent flow pattern. The vacuum operation on the lumen side of the membrane module is preferable to the elevated pressure operation on the shell side for achieving high oxygen productivity. A high vacuum level and a desired membrane area are essential to produce the pure oxygen and nitrogen simultaneously. Experimental results and kinetic parameters in the literature obtained from the LSCF membrane for air separation agreed satisfactorily with the theoretical solutions.
Development of fluidized catalytic reactors: Screening and scale‐up
Authors: Kelkar Vaibhav V. , Ng Ka M.
Published: April 2004

A systematic procedure that helps develop gas‐solid and gas‐liquid‐solid catalytic fluidized‐bed reactors has two components—screening and scale‐up. In screening, a reactor type is selected first from the variety of multiphase reactors. If fluidized‐bed reactors are chosen, further screening is carried out using experimentally verified models to account for the detailed hydrodynamic features of the reactor. Decisions are made on the fluidization regime, heat management scheme, solid recirculation, use of reactor internals, and so on. In addition, heuristics are presented to anticipate and address issues such as catalyst agglomeration, breakage and deactivation, and changes in the nature of fluidization over the long term. The second component provides criteria to directly scale up the bench reactor to the production reactor, while maintaining a selected reactor performance index such as conversion, product yield, and selectivity.
Reaction and transport kinetics for depolymerization within a porous body
Authors: Krug Steffen , Evans Julian R. G. , ter Maat Johan H. H.
Published: April 2004

Polyoxymethylene is used as the organic vehicle for ceramic and metal powder injection moulding. It is ideal for studies of shrinking‐core reaction kinetics in porous systems because it decomposes exclusively to monomer in the solid state in the presence of nitric acid vapor. The solid–gas reaction interface can be defined to within 3 μm by electron microscopy and about 50 μm optically. Reaction rates were measured in crowded powder assemblies containing 56 vol % alumina powder by observation of the boundary; a method that avoids the ambiguities of gravimetry. The reaction‐rate constant and the effective diffusion coefficient of gas in the porous reacted layer were calculated from the shrinking core kinetics. The diffusion coefficient was in good agreement with theoretical estimates involving counterdiffusion. The time for complete depolymerization of a moulding was estimated for different powder characteristics, geometries, and volume fractions.
Experiments on chaotic mixing in a screw channel flow
Authors: Hwang W. R. , Jun H. S. , Kwon T. H.
Published: April 2004

Mixing patterns of a passive dye were investigated experimentally in an unwound screw channel flow with periodic barriers that serve to induce a chaotic flow. Continuous cross‐sectional and longitudinal mixing patterns were observed as a function of the barrier fraction and were interpreted in terms of dynamical systems theory, along with 3‐D numerical simulations. Observations include: periodically invariant cross‐sectional mixing patterns due to the resonance bands; pile‐up of dye streaks caused by stretching and folding of manifolds near hyperbolic points; unmixed zones due to KAM tori; longitudinal deformation patterns with exit time distributions; and effects of the barrier fraction on the size of unmixed islands, the thickness of the band of dye streaks, and the distribution of exit times.
Silicon array of elongated through‐holes for monodisperse emulsion droplets
Authors: Kobayashi Isao , Nakajima Mitsutoshi , Chun Kyoseok , Kikuchi Yuji , Fujita Hiroyuki
Published: April 2004

Monodisperse emulsions are of great significance in both scientific and industrial fields, since they have advantages such as their better stability and simplified physical properties. A novel micromachined emulsification device has been developed for monodisperse emulsion droplets. It has uniformly sized through‐holes, called straightthrough microchannel (MC), on a silicon microchip. An oblong straightthrough MC successfully yielded monodisperse oil‐in‐water (O/W) emulsion droplets with an average droplet diameter of 32.5 μm and a coefficient of variation below 2% by forcing the dispersed phase into the continuous phase through the straightthrough MC. On the other hand, a circular straightthrough MC yielded polydisperse emulsion droplets. Straightthrough MC emulsification revealed that an elongated cross‐sectional shape in the oblong straightthrough MC contributes significantly to the spontaneous formation of monodisperse emulsion droplets without any turbulent mixing.
Connections between density waves in fluidized beds and compressible flows
Authors: Johri Jayati , Glasser Benjamin J.
Published: April 2004

Under certain simplifying assumptions, model equations of motion and continuity for the particles in a fluidized bed can be related to those of a compressible fluid acted on by a density dependent force. A linear stability analysis shows that the base state of the compressible flow equations can lose stability in the form of plane density waves. The plane waves emerge through a Hopf bifurcation and propagate through the bed as traveling waves. Through a bifurcation analysis coupled with parameter continuation, the solution structure of the fully‐developed plane waves was computed. As the amplitudes of the plane waves increase, they lose stability in the lateral direction. A comparison of these results with previous work on gas‐fluidized beds shows that salient features of the instability of a gas‐fluidized bed are captured by the basic physics of compressible flows.
Mass transport and flow regimes in centrifugal partition chromatography
Authors: Marchal L. , Legrand J. , Foucault A.
Published: April 2004

Centrifugal partition chromatography (CPC) is a support‐free liquid–liquid separation process that depends for efficiency on the behavior of the two liquid phases. Hydrodynamics of phases was studied according to flow rate and centrifugal acceleration, using a transparent column and a stroboscopic video system. For the heptane‐methanol two‐phase system, three main flow regimes—stuck film, oscillating sheet, and atomization—are observed, highlighting the coriolis acceleration effect as well as the influence of the column shape. Mass transport in the CPC column is modeled by a plug flow with axial dispersion and mass transfer with a stagnant volume. Model parameters (residence time, Péclet number, partition ratio, and mass‐transfer coefficient) are fitted on solute residence‐time distribution. Off‐column dispersion is an important source of peak broadening in CPC, whereas its irregular geometry provides a plug flow for mobile phase. Importance of flow pattern on mass transfer is demonstrated. CPC interest for preparative applications is confirmed.
Modeling ultrafiltration of complex biological solutions
Authors: Darnon E. , Belleville M. P. , Rios G. M.
Published: April 2004

The ultrafiltration of a single protein (β‐lactoglobulin) solution was compared with a mixture of yeast extract and β‐lactoglobulin to show that, even when all the compounds of a complex biological solution interfere with the results of filtration, it can estimate its performance just using some major assumptions connected to a mass‐transfer model. Preliminary experiments based on these assumptions showed that the filtration of a single rejected protein like β‐lactoglobulin builds a dynamic layer at the wall, the selectivity and resistance of control by the protein concentration and formation of this dynamic membrane. Adding yeast extract, a complex biological medium, can alter this layer. But at neutral pH, away from the protein isoelectric point, these modifications are weak and their effects more negligible than those arising from a modified concentration. Using these assumptions, a model based on the theory of thermodynamics of irreversible processes is proposed that provides the correct description of selectivity and flux during the filtration of such complex and badly known mixtures.
Optimal design of batch‐storage network using periodic square wave model
Authors: Yi Gyeongbeom , Reklaitis Gintaras V.
Published: April 2004

This study is to find the analytic solution for determining the optimal capacity (lot size) of a multiproduct, sequential, multistage production and inventory system to meet the finished product demand. It overcame the limitation of the classical lot sizing method developed based on the single product and single‐stage assumption. The superstructure of the plant consisted of a network of serially and/or parallel interlinked batch processes and storage units. The processes involve chemical reactions with multiple feedstock materials and multiple products, as well as mixing, splitting, or transportation of materials. The objective function for optimization is minimizing the total cost composed of setup and inventory holding costs, as well as the capital costs of constructing processes and storage units. The resulting simple analytic solution can greatly enhance the proper and quick investment decision for the preliminary plant design problem confronted with diverse economic situations.
Control‐relevant scheduling of polymer grade transitions
Authors: Mahadevan Radhakrishnan , Doyle Francis J. , Allcock Andrew C.
Published: April 2004

Grade transition is a critical step in the operation of a polymerization reactor. The nonlinear input‐output behavior of the reactor can lead to severe differences in the dynamic response of different grade transitions. These differences are analyzed under the assumption that the polymerization reactor is regulated by a linear controller. The cost of each transition is calculated based on a linear first‐order model of the transition. Robust control theory is employed to propose screening tools and heuristics for the identification of the transitions that are “difficult” from an operational perspective in the presence of uncertainty. The dependence of the transition cost on the gain and the time constant of various transitions is analyzed to determine the effect of process nonlinearities on the scheduling problem. This approach is demonstrated on the problem of scheduling grade transitions in an isothermal methyl methacrylate polymerization reactor.
Process modeling by Bayesian latent variable regression
Authors: Nounou Mohamed N. , Bakshi Bhavik R. , Goel Prem K. , Shen Xiaotong
Published: April 2004

Large quantities of measured data are being routinely collected in various industries and used for extracting linear models for tasks such as process control, fault diagnosis, and process monitoring. Existing linear modeling methods, however, do not fully utilize all the information contained in the measurements. A new approach for linear process modeling makes maximum use of available process data and process knowledge. Bayesian latent‐variable regression (BLVR) permits extraction and incorporation of knowledge about the statistical behavior of measurements in developing linear process models. Furthermore, BLVR can handle noise in inputs and outputs, collinear variables, and incorporate prior knowledge about regression parameters and measured variables. The model is usually more accurate than those of existing methods, including OLS, PCR, and PLS. BLVR considers a univariate output and assumes the underlying variables and noise to be Gaussian, but it can be used for multivariate outputs and other distributions. An empirical Bayes approach is developed to extract the prior information from historical data or maximum‐likelihood solution of available data. Examples of steady‐state, dynamic and inferential modeling demonstrate the superior accuracy of BLVR over existing methods even when the assumptions of Gaussian distributions are violated. The relationship between BLVR and existing methods and opportunities for future work based on this framework are also discussed.
Large‐scale oscillations of a feedstream inside a stirred tank reactor
Authors: Verschuren Iris L. M. , Wijers Johan G. , Keurentjes Jos T. F.
Published: April 2004

Recent studies have shown feedstreams inside stirred tank reactors to oscillate. When multiple feed points are used, these oscillations can cause feedstreams to overlap. The objective of this study is to determine a description of the oscillations that can be used to prevent the feedstreams to overlap. The oscillations are analyzed by determining the displacements of the centers of the mass of a feedstream in radial cross sections. The growth of the root‐mean‐square radius of these displacements with time is linear, corresponding to the “initial growth stage.” The growth rate of the root‐mean‐square radius with time proved to equal the velocity fluctuations related to turbulent motions with a size larger than the diameter of the feedstream, indicating that these large‐scale turbulent motions are responsible for large‐scale oscillations. With the description obtained for the root‐mean‐square radius, the minimal distance between two feed pipes necessary to prevent the overlap of the feedstreams can be calculated.
Experimental measurement of radiative heat transfer in gas‐solid suspension flow system
Authors: Han Guiyoung , Tuzla Kemal , Chen John C.
Published: April 2004

An experimental measurement of the radiative heat flux from a gas‐solid suspension to wall was made in a water cooled heat exchanger. The heat‐transfer test section was 5 cm ID and 90 cm long. Operating temperature ranged from 200 to 600°C and the gas velocity at the inlet of the test section varied from 6 to 11 m/s. The suspension densities covered a range from 3 to 35 kg/m3. Time‐averaged radiative heat flux was directly measured using a radiometer, which allowed to determine suspension emissivity using a measured suspension temperature. Radiative heat flux and suspension emissivity showed strong dependence on the suspension density. The effect of particle size on suspension emissivity was also studied by using two different sizes of particles. Experimentally determined suspension emissivities, which ranged from 0.3 to 0.85, agreed well with the predictable suspension emissivities based on an independent scattering theory. The contribution of radiation to total heat transfer was about 40–50% for the operating condition used in this study.
Separation of mono‐ and dibranched hydrocarbons on silicalite
Authors: Jolimaitre E. , Ragil K. , Tayakout‐Fayolle M. , Jallut C.
Published: April 2004

Breakthrough curves for mixtures of C5 and C6 hydrocarbons with different degrees of branching were obtained experimentally on a silicalite molecular sieve by fixed‐bed experiments. The kinetic separation of di‐ from monobranched hydrocarbons was feasible on this type of zeolite: dimethyl molecules enter silicalite crystals very slowly, whereas monomethyl molecules are quickly adsorbed. Experimental results were compared to a theoretical isothermal model, considering the variation of diffusivity with concentration according to the Maxwell–Stefan theory. The parameters of the model (adsorption equilibria and diffusivities) were determined from single‐component breakthrough curves. Experimental curves were generally well represented by the model, but the variation of diffusivity with concentration, as predicted by the Maxwell–Stefan theory, did not significantly improve the model prediction of experimental breakthrough curves by using a mean value of diffusivity.
Vacancy solution theory for binary adsorption equilibria in heterogeneous carbon
Authors: Ding L. P. , Bhatia S. K.
Published: April 2004

A heterogeneous modified vacancy solution model of adsorption developed is evaluated. The new model considers the adsorption process through a mass‐action law and is thermodynamically consistent, while maintaining the simplicity in calculation of multicomponent adsorption equilibria, as in the original vacancy solution theory. It incorporates the adsorbent heterogeneity through a pore‐width‐related potential energy, represented by Steele's 10–4–3 potential expression. The experimental data of various hydrocarbons, CO2 and SO2 on four different activated carbons—Ajax, Norit, Nuxit, and BPL—at multiple temperatures over a wide range of pressures were studied by the heterogeneous modified VST model to obtain the isotherm parameters and micropore‐size distribution of carbons. The model successfully correlates the single‐component adsorption equilibrium data for all compounds studied on various carbons. The fitting results for the vacancy occupancy parameter are consistent with the pressure change on different carbons, and the effect of pore heterogeneity is important in adsorption at elevated pressure. It predicts binary adsorption equilibria better than the IAST scheme, reflecting the significance of molecular size nonideality.
Nonlinear model predictive control of end‐use properties in batch reactors
Authors: Valappil Jaleel , Georgakis Christos
Published: April 2004

Significant economic benefits can be derived from reducing the variability of product properties around their specification targets in batch reactors. End‐use properties in batch reactors using dynamic models that relate the operating conditions to the end‐use properties are related through a static nonlinear model to the molecular properties of the product and are controlled directly. Their values are required to lie in a desired target region in the property space. The control of end‐use product properties is formulated as a nonlinear model predictive control problem, and an efficient numerical technique using successive linearizations is utilized for the solution. A parameter adaptive extended Kalman filter is used for state estimation of the molecular properties that are not measured directly. The emulsion polymerization of styrene is chosen as a case study, and an approximate mathematical model is developed. The model is detailed enough to predict the end‐use properties, which depend on both the molecular weight and particle‐size distributions of the product. The end‐use product properties, such as tensile strength and melt index, are controlled in desired target regions by adding a monomer and a chain transfer agent, as well as the flow rate of the coolant, as the manipulated variables.
YSZ‐SrCo0.4Fe0.6O3‐δ membranes for the partial oxidation of methane to syngas
Authors: Gu Xuehong , Jin Wanqin , Chen Changlin , Xu Nanping , Shi Jun , Ma Y. H.
Published: April 2004

The perovskite‐related yttria‐stabilized zirconia promoted SrCo0.4Fe0.6O3‐δ (SCFZ) oxides were used to construct membrane reactors for the partial oxidation of methane to syngas (POM). The oxygen permeability study of the SCFZ membrane in the air/helium gradient showed that the apparent activation energy was about 69±5 kJ/mol at 1,023∼1,223 K, and the oxygen flux was controlled by the bulk diffusion and surface exchange rate. In a cofeed reactor packed with SCFZ pellets and a blank SCFZ membrane reactor without any catalyst packing, the SCFZ oxides showed low catalytic activity for POM in the fixed‐bed reactor and no POM catalytic activity in the membrane reactor. An SCFZ membrane reactor with NiO/Al2O3 catalyst was continuously running for over 220 h under constant operational conditions. While about 64% of methane was converted with 100% CO selectivity after reaching the steady state, the oxygen flux was about 10 times the value of the air/helium gradient, in the reactor packed with the catalyst. The oxygen flux of SCFZ membranes in the reducing atmosphere could be limited by the surface reaction rate at the reaction side.
Using CFD to understand chaotic mixing in laminar stirred tanks
Authors: Zalc J. M. , Szalai E. S. , Alvarez M. M. , Muzzio F. J.
Published: April 2004

High‐accuracy CFD results for laminar flow in a stirred tank agitated by three Rushton turbines are used as a starting point for an in‐depth analysis of mixing. Asymptotic mixing performance is investigated as a function of the Reynolds number by means of Poincaré sections, which reveal large segregated regions with sizes and shapes that vary greatly over a relatively small range of Reynolds numbers. The spatial distribution of mixing intensities is also examined by computing the stretching field, which can be used to optimally choose injection locations for dispersing additives in the tank. When mixing dynamics is examined by particle tracking, the structures observed at short times expose the mechanism of laminar mixing by Rushton turbines. The computed mixing structures are compared with experimental images of dye concentration using planar laser‐induced fluorescence. A remarkable agreement is observed for the short‐term, as well as the asymptotic evolution, of mixing patterns. Simulations of dye concentration fields as a function of Re confirm large differences in mixing behavior for the four different flow conditions. Strong axial segregation revealed by the stretching field, as well as the location of poorly mixing regions, are accurately predicted.
Scaling of granular flow processes: From surface flows to design rules
Authors: Ottino J. M. , Khakhar D. V.
Published: April 2004

Scale‐up of granular processes is notoriously difficult and there is little guidance at the present time. This is true even in the simplest case of noncohesive powders consisting of spherical grains, the scenario considered here. However, flows in granular materials are often restricted to thin regions of rapid surface flow with the rest of the material suffering only slow plastic rearrangements. This seemingly trivial observation leads to understanding of the entire system and to the concept that an understanding of surface flows constitutes the key element for scale‐up of granular flow processes. A surface flow is characterized primarily by its thickness and the shear rate. For large particles, both are controlled primarily by the Froude number and the particle‐size ratio (particle diameter to cylinder radius), whereas material properties have a secondary effect. Modern experimental techniques are yielding further insight into the physics of shear flows and theoretical analysis is providing guidance and scaling insights. The assembly of experimental and theoretical components opens the class of problems dominated by surface flows to serious engineering analysis and predictability. Current understanding is extended and integrated, the governing scaling laws are made explicit, and the results obtained in terms of rules are summarized. The use of the integrated knowledge by means of an example is exemplified.
High‐dimensional solid‐liquid phase diagrams involving compounds and polymorphs
Authors: Wibowo Christianto , Samant Ketan D. , Ng Ka M.
Published: April 2004

A systematic procedure for the generation and visualization of high‐dimensional isobaric phase diagrams for systems exhibiting compound formation and/or polymorphism is presented. Such phase diagrams are useful in synthesizing crystallization‐based separation processes for systems involving compounds and polymorphs, which are common in the production of pharmaceuticals. Polythermal as well as isothermal phase diagrams of multicomponent systems can be generated. Examples are provided to illustrate the procedure.
Equilibria for adsorption of phosphates on OH‐type strongly basic ion exchanger
Authors: Yoshida Hiroyuki , Galinada Wilmer A.
Published: April 2004

The equilibrium isotherms for adsorption of phosphate ions using an OH‐type, strongly basic ion exchanger, DIAION SA10A, were studied experimentally and the results appeared technically feasible. Four different types of phosphate ions, H3PO4, H2PO, HPO, and PO, were used. In all the systems considered, the experimental adsorption isotherms showed a high amount of phosphate adsorption. Moreover, differences in the adsorption behaviors were observed. These differences were highly influenced by the pH of the equilibrated solutions. The ion‐exchange reaction models were then proposed. By the mass action law, the theoretical equations for the adsorption isotherms were derived and the unknown experimental equilibrium constants were determined. These equilibrium models were able to correlate the experimental data well and explained the peculiarities in the obtained experimental adsorption isotherms.