bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design and operation of convective industrial dryers
Authors: Kiranoudis C. T. , Maroulis Z. B. , Marinos‐Kouris D. 
Published: June 2004

AbstractDesign and operational performance of convective industrial dryers are an important field of chemical engineering, which is still governed by empiricism. This article addresses the design vs. operation problem for three basic types of continuous convective industrial dryers: conveyor‐belt, fluidized bed, and rotary. Design procedures determined the optimal construction and operational characteristics in terms of total annual cost for each type involved and for a given production capacity through appropriate mathematical modeling. All dryer were compared by evaluating optimum configurations for a wide range of product characteristics and production capacity values. Once the dryer configuration was specified, its operational performance was evaluated by comparing the optimum operational cost vs. production capacity for predefined optimum designed structures. Rotary dryers were more expensive to design than fluidized bed dryers. Operationally, however, it is the other way around due to the favored heat transfer achieved in rotary dryers. Conveyor‐belt dryers lie somewhere between producing satisfactory results in terms of both design and operation. Case studies on foods and inorganics are included to demonstrate the performance of each process as well as the effectiveness of the proposed approach.
Model discrimination and criticism with single‐response data
Authors: Stewart Warren E. , Henson Thomas L. , Box George E. P. 
Published: June 2004

AbstractThe inverse probability theorem of Bayes is used, along with sampling theory, to obtain objective criteria for choosing among rival models. Formulas are given for the relative posterior probabilities of candidate models and for their goodness of fit, when the models are fitted to a common data set with Normally distributed errors. Cases of full, partial and minimal variance information are treated. The formulas are demonstrated with three examples, including a kinetic study of a catalytic reaction.
Wave model for longitudinal dispersion: Application to the laminar‐flow tubular reactor
Authors: Kronberg A. E. , Benneker A. H. , Westerterp K. R. 
Published: June 2004

AbstractThe wave model for longitudinal dispersion, published elsewhere as an alternative to the commonly used dispersed plug‐flow model, is applied to the classic case of the laminar‐flow tubular reactor. The results are compared in a wide range of situations to predictions by the dispersed plug‐flow model as well as to exact numerical calculations with the 2‐D model of the reactor and to other available methods. In many practical cases, the solutions of the wave model agree closely with the exact data. The wave model has a much wider region of validity than the dispersed plug‐flow model, has a distinct physical background, and is easier to use for reactor calculations. This provides additional support to the theory developed elsewhere. The properties and the applicability of the wave model to situations with rapidly changing concentration fields are discussed. Constraints to be satisfied are established to use the new theory with confidence for arbitrary initial and boundary conditions.
Kinetics of silica particle formation in nonionic W/O microemulsions from TEOS
Authors: Chang Chia‐Lu , Fogler H. Scott 
Published: June 2004

AbstractThe kinetics of silica particle formation by the ammonia‐catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) in water‐in‐oil (W/O) microemulsions containing a nonionic surfactant was investigated using Fourier‐transform infrared spectroscopy, transmission electron microscopy, and light‐scattering techniques. The results show that TEOS hydrolysis and silica‐particle growth occur at the same rate, indicating the growth of silica particles is rate‐controlled by the hydrolysis of TEOS. The rate of TEOS hydrolysis in microemulsions is first order with respect to the concentration of aqueous ammonia (29 wt. % NH3), but depends weakly on the concentration of water. Based on the fact that TEOS hydrolysis follows a nucleophilic (SN2) substitution of the TEOS's ethoxy group with hydroxyl ion, the kinetic data suggest that both water and ammonia remain predominately in W/O microemulsion droplets. The rate of TEOS hydrolysis also depends on the surfactant concentration that controls the molecular contact between hydroxyl ions and TEOS in the solution. Due to the reaction‐controlled growth mechanism, the silica‐particle size distribution retains virtually the same shape over the growth period. The final average size of silica particles can be varied from 26 to 43 nm by adjusting concentrations of water and surfactant. Increasing the water concentration decreases the average size and uniformity of silica particles. For a given water concentration, the smallest and most uniform silica particles are produced at intermediate water‐to‐surfactant molar ratios (about 1.9). The results are discussed in terms of the effect of water concentration on the stability of the hydrolyzed silica reacting species during the nucleation of particles and of the water‐to‐surfactant molar ratio on the compartmentalization of silica species in microemulsions.
Miscibility of polymer blends with engineering models
Authors: Harismiadis Vassilis I. , van Bergen A. R. D. , Saraiva Ana , Kontogeorgis Georgios M. , Fredenslund Aage , Tassios Dimitrios P. 
Published: June 2004

AbstractThe miscibility behavior of polymer blends that do not exhibit strong specific interactions is examined. Phase equilibrium calculations are presented with the van der Waals equation of state and three group‐contribution models (UNIFAC, Entropic‐FV, and GC‐Flory). Performance of these models is also compared. The van der Waals equation of state was recently shown to accurately correlate and predict vapor–liquid and liquid–liquid equilibria for binary polymer/solven solutions. In this work, it is demonstrated that it correlates the upper critical solution behavior of polymer blends with excellent accuracy using the usual mixing and combining rules and a single temperature‐ and composition‐independent binary interaction parameter. This interaction parameter can be predicted via a generalized expression that uses only the pure component equation‐of‐state parameters. Using this generalized expression, the upper critical solution temperature can be predicted with an average error of less than 45°C. The van der Waals equation of state can correlate the lower critical solution behavior of polymer blends, using an interaction parameter that is a linear function of temperature. The UNIFAC and Entropic‐FV models, in general, are able to predict qualitatively the phase behavior of polymer blends, but quantitative predictions of the critical solution temperatures are not achieved. The GC‐Flory equation of state fails to predict the upper critical solution behavior in polymer blends.
Molecular thermodynamic model for gibbs energy of mixing of nonionic surfactant solutions
Authors: Chen Chau‐Chyun 
Published: June 2004

AbstractA segment‐based molecular thermodynamic model for the Gibbs energy of polymer solutions or oligomer solutions is used to represent the Gibbs energy of mixing for aqueous nonionic surfactant solutions. In contrast to the mass‐action models and pseudophase models, which are often discussed in the literature, the Gibbs‐energy model provides an explicit account of the solution nonideality, including activity coefficients of monomeric amphiphiles in the aqueous phase. The equilibrium between monomeric amphiphiles and micellar amphiphiles is described by the equal‐activity relationship. The Gibbs‐energy model makes it possible to use a well‐accepted molecular thermodynamic framework to correlate and represent phase behaviors of aqueous nonionic surfactant solutions.
Chaotic mixing of two similar fluids in the presence of a third dissimilar fluid
Authors: Zhang D. F. , Zumbrunnen D. A. 
Published: June 2004

AbstractTwo‐dimensional chaotic mixing of similar Newtonian fluids in the presence of an advected dissimilar minor phase fluid body with specified size, interfacial tension, and viscosity ratio was numerically investigated. Interfacial tension was sufficiently high to allow only small deformations in the dissimilar minor phase body. Mixing was confined to a rectangular cavity with periodically driven upper and lower surfaces. Regions of regular motion (i.e., islands) of comparable size to the minor phase body were eventually destroyed or replaced by the minor phase body. Islands persisted for longer times when the initial separation distance between the minor phase body and island was large or when the viscosity ratio was small. When interfacial tension was small enough to deform the minor phase body more readily, islands showed little indication of instability. Results suggest opportunities for improving mixing uniformity in practical processes and disclose how interactions between dissimilar fluids affect mixing.
Decomposition techniques for the solution of large‐scale scheduling problems
Authors: Bassett Matthew H. , Pekny Joseph F. , Reklaitis Gintaras V. 
Published: June 2004

AbstractWith increased product specialization within the chemical‐processing industries, the ability to obtain production schedules for complex facilities is at a premium. This article discusses ways of quickly obtaining solutions for industrially relevant, large‐scale scheduling problems. A number of time‐based decomposition approaches are presented along with their associated strengths and weaknesses. It is shown that the most promising of the approaches utilizes a reverse rolling window in conjunction with a disaggregation heuristic. In this method, only a small subsection of the horizon is dealt with at a time, thus reducing the combinatorial complexity of the problem. Resource‐ and task‐unit‐based decompositions are also discussed as possible approaches to reduce the problem to manageable proportions. A number of examples are presented throughout to clarify the discussion.
Quartz dissolution kinetics from 100–200°C as a function of pH and ionic strength
Authors: Worley W. G. , Tester J. W. , Grigsby C. O. 
Published: June 2004

AbstractOf importance to geothermal energy development, oil, gas and mineral recovery, and waste storage is the characterization of the dissolution rate of host reservoir rock as a function of temperature, pressure and liquid‐phase composition. As a major constitutive mineral in natural geologic systems, quartz was selected for study. Dissolution experiments were carried out in a continuous‐flow, titanium autoclave reactor system at 100–200°C in various chemical environments. Acidification to pH 1.1 using nitric acid showed very little effect on the quartz dissolution rate. The effect of hydroxide ion concentration and ionic strength were evaluated in NaOH, NaOH/NaCl and NaOH/Na2SO4 solutions. The fractional‐order dependency of the quartz dissolution rate on hydroxide ion and sodium ion (or ionic strength) concentration was determined in NaOH/NaCl solutions. The results that extend the available range of kinetic data for quartz generally agree with previous work. The observed fractional‐order kinetics were qualitatively described using classical adsorption isotherms. No significant variation in the apparent reaction order of the hydroxide ion with increasing temperature could be determined due to the scatter in the data. Quartz dissolution rates were slower by about 40% in NaOH/Na2SO4 solutions than in NaOH/NaCl solutions at sodium concentrations higher than 0.01 molal. The apparent activation energy from 100 to 200°C in NaOH/NaCl solutions up to 0.01 molal hydroxide ion and 0.1 molal sodium ion was estimated to be 72 (±6) kJ/mol.
Intrinsic nitridation kinetics of high‐purity silicon powder
Authors: Maalmi Mostafa , Varma Arvind 
Published: June 2004

AbstractThe intrinsic nitridation kinetics of high‐purity silicon solid to form silicon nitride were determined by thermogravimetric analysis technique. The initial rate method was used to avoid kinetics falsification due to intraparticle diffusion limitation caused by the formation of silicon nitride layer around the silicon particles. Relatively small sample sizes were used to eliminate the interparticle diffusion limitation (compact effect) that becomes important as the reaction proceeds, owing to the expansion of the individual particles and filling of the initial pores within the compact. The effect of hydrogen addition to the nitriding gas, as well as the influence of the flow rate, on the reaction progress was also investigated.
Miniaturization of hydroprocessing catalyst testing systems: Theory and practice
Authors: Sie S. T. 
Published: June 2004

AbstractMain factors limiting downscaling of fixed‐bed integral reactors are discussed, which operate with a gas stream or with gas and liquid in trickle flow, as used in hydroprocessing of oil. Criteria developed for a sufficiently close approach to plug flow and for good contacting of the catalyst show that they can be met in very small reactors, both for processes with reactants in the gas phase and for trickle‐flow processes, provided that the catalyst bed is diluted with fine inert material in the latter case. Experimental tests show that microreactors with typical catalyst volumes of 5–10 mL can be used to obtain representative results that can very well match data from industrial reactors. It appears to be feasible to miniaturize catalytic test reactors further to “nanoscale” reactors with as little as 0.2–0.4 mL of catalyst while maintaining the results to be meaningful. Even though there are advantages as well as limitations, miniaturization can enhance safety and reduce manpower.
Diffusion of proteins and nonionic micelles in agarose gels by holographic interferometry
Authors: Kong Donna D. , Kosar T. Fettah , Dungan Stephanie R. , Phillips Ronald J. 
Published: June 2004

AbstractDiffusion coefficients measured by holographic interferometry are presented for two globular proteins and three nonionic surfactant species in agarose gels. The cloud points for the surfactants in agarose solutions are also given. In all cases, rates of diffusion in the gel are smaller than those in bulk solution, with the hindering effect of the gel increasing both with increasing gel concentration and with increasing solute size. It is shown that the diffusion rate of the surfactant micelles is very similar to that of proteins having similar hydrodynamic radii; it would therefore appear that the size and shape of the micelles in the solution and gel phases are similar. In addition, the measured rates of hindered diffusion agree very well with rates predicted by a rigorous hydrodynamic theory in which the solutes are modeled as hard spheres and the gel fibers are modeled as straight, cylindrical fibers. Hence, for the range of conditions considered, rates of hindered diffusion for both the globular proteins and the micellar species are determined primarily by hard‐sphere hydrodynamic and steric interactions between the solute and the gel matrix.
Analysis of cake growth in cake filtration: Effect of fine particle retention
Authors: Tien Chi , Bai Renbi , Ramarao B. V. 
Published: June 2004

AbstractEquations were derived that describe the dynamics of cake growth in cake filtration, and methods for their solutions were developed. In deriving the equations, the moving boundary nature of the cake formation process and the effect of fine particle retention were considered. It was shown that fine particle retention may contribute significantly to the decrease of cake permeability and thus alters the performance of cake filtration even if the amount of fine particles involved is small. Through numerical examples, it was also demonstrated that fine particle retention in filter cakes may cause serious errors in determining the constitutive relationships from filter test data.
Synthesis of drowning‐out crystallization‐based separations
Authors: Berry David A. , Dye Susan R. , Ng Ka M. 
Published: June 2004

AbstractA method is presented to synthesize drowning‐out crystallization‐based separation schemes for binary mixtures. The method tracks how the composition of each process stream changes from unit to unit on a phase diagram by assuming that the system is at equilibrium. Features of phase behavior favorable to drowning‐out processes are identified. Two types of systems are highlighted. In the first, the drowning‐out agent causes the solute to become sparingly soluble. Several process alternatives to separate the feed into pure components are proposed. Dominant costs of each configuration are identified. In the second, the solute is extracted into a phase rich with respect to the drowning‐out agent. The extraction can be performed in a decanter, countercurrent extractor, or fractional countercurrent extractor. Guidelines are given to select an extractor type and to choose between crystallizer‐extractor and extractor‐crystallizer equipment trains.
Analysis of rate enhancement in a periodically operated trickle‐bed reactor
Authors: Gabarain L. , Castellari A. T. , Cechini J. , Tobolski A. , Haure P. 
Published: June 2004

AbstractWhen a trickle‐bed reactor (TBR) is operated periodically, the bed is fed with liquid on and off, while the gas phase passes continuously. Rates and conversions could be higher than those corresponding to the steady‐state operation. In the “dry cycles” the heat generated by the reaction can drive the vaporization of the liquid phase, and a much more rapid “gas phase” reaction may occur. There is a trade‐off between the potential for hot‐spot formation and the fact that overall rates are higher during cycling. A qualitative understanding of the phase transition in TBRs is obtained by a simple phenomenological model that takes into account different transport and reaction mechanisms occurring in a catalytic particle under different cycling conditions. A mathematical model is used to predict results.
Vapor–liquid equilibria of the ternary mixture CH4 + C2H6 + CO2 from molecular simulation
Authors: Vrabec Jadran , Fischer Johann 
Published: June 2004

AbstractThe NpT + test‐particle method for the calculation of vapor–liquid equilibria by molecular simulations is extended to ternary mixtures. It is applied to the system methane + ethane + carbon dioxide, for which all binary molecular interaction models are available from previous work. Methane is described as one‐center Lennard‐Jones fluid, ethane as two‐center Lennard‐Jones fluid, and carbon dioxide as two‐center Lennard‐Jones plus point quadrupole fluid. The unlike interactions are treated in the same way as the binary mixtures, using two parameters for each binary interaction. No ternary parameters are introduced. Vapor–liquid phase equilibria are calculated for the ternary mixture at the following temperature–pressure pairs: 233.15 K ‐ 2 MPa; 250.5 K ‐ 2 MPa; and 250.5 K ‐ 3.04 MPa. Comparison of the simulation data with experimental and equation‐of‐state results shows excellent agreement. Bubble and dew densities are also reported.
Pressure‐fluctuation analysis of a Gas–Solid fluidized bed using the wigner distribution
Authors: He Zhen , Zhang Dongming , Cheng Bochuan , Zhang Weidong 
Published: June 2004

AbstractPressure fluctuations in gas–solid fluidized beds have long been recognized as an important index for the quality of fluidization. Due to their highly random nature, many researchers have resorted to stochastic signal‐processing methods to extract useful information. However, methods such as power‐spectral density are based on a priori hypothesis of the stationarity of the signals, whose validity has not been investigated. In this article, using the Wigner distribution (WD), the signal's strong nonstationary feature is demonstrated and signal properties are addressed. Local frequency information is extracted from the defined parameter—the local peak weighted average (LPWA), which can be regarded as a generalized concept of the major frequency of power‐spectral density in the nonstationary case. Experimental results indicate that LPWA is stochastically much more reproducible than the major frequency of power‐spectral density. The change in LPWA under different operating conditions may reflect the corresponding change in the bubble phase. This information is useful in characterizing the quality of fluidization.
Comminution of limestone during batch fluidized‐bed calcination and sulfation
Authors: Scala Fabrizio , Cammarota Antonio , Chirone Riccardo , Salatino Piero 
Published: June 2004

AbstractBatchwise fluidized‐bed calcination and sulfation of a limestone were done to investigate particle comminution phenomena and their relation with parallel occurrence of reactions. Operating conditions of the bed were those typical of atmospheric bubbling fluidized‐bed combustors. A general framework of comminution phenomena is outlined, which includes different types of fragmentations as well as attrition by abrasion. Comminution processes were characterized by following the modifications of bed sorbent particle‐size distribution and the elutriation rates of fines throughout conversion. Mutual interactions between comminution processes and the progress of chemical reactions are assessed.
Attainable regions for reaction with separation
Authors: Nisoli Alberto , Malone Michael F. , Doherty Michael F. 
Published: June 2004

AbstractThe attainable region approach for reaction – mixing systems is combined with geometric methods for the feasibility of separations. The result is a systematic approach to identify the feasible compositions that can be achieved in processes combining simultaneous reaction, mixing, and separation. An activity‐based formulation for both nonideal VLE and reaction‐rate expressions is applied to develop hybrid reactor–separator models for the multiphase CSTR and PFR with simultaneous vapor removal. A reaction–separation vector is defined that satisfies the same geometric properties as the reaction vector. Therefore, the attainable region can be constructed following the existing procedure for reaction–mixing systems. This approach provides a method to generate feasible process alternatives. The technique is demonstrated on two nonideal ternary mixtures: the production of dimethyl ether by dehydration of methanol, and the production of methyl tert‐butyl ether from isobutene and methanol. It is shown that for hybrid reaction–separation devices the entire composition space is not always attainable. In such cases, combining a hybrid device with traditional nonreactive separation is required to attain certain products.
Chemical imaging of multicomponent viscous fingering in chromatography
Authors: Dickson Matthew L. , Norton T. Tucker , Fernandez Erik J. 
Published: June 2004

AbstractResolution in chromatographic separations can be compromised by nonuniform flow distribution, heterogeneous packing, or flow instabilities such as viscous fingering. In this work, the displacement of solutes within a chromatographic column was monitored with an advanced magnetic‐resonance technique, echo‐planar spectroscopic imaging (EPSI). Unlike conventional magnetic‐resonance imaging, this approach allows multiple solutes to be observed simultaneously, providing separate “chemical images” for each component. Qualitative chemical images were obtained in approximately 1 min with approximately 1 mm3spatial resolution. EPSI allowed us to examine the multi‐component viscous fingering problem for the first time. While many features of the instability are preserved, solute retention appears to slow the growth of solvent fingers.