bluuebunny/crossref_metadata_2025 huggingface dataset:
NMR Measurements of chemical theory equilibrium constants for hydrogen‐bonded solutions
Authors: Eckert C. A. , McNiel M. M. , Scott B. A. , Halas L. A.
Published: June 2004

Although various chemical theories have often been used to characterize hydrogen‐bonded systems with some success, they have been limited by the fact that the equilibrium constants were adjustable parameters. This paper reports a method to measure directly these constants by proton nuclear magnetic resonance spectroscopy. Results are reported for several systems and are used with a chemical‐physical theory to predict vapor‐liquid equilibria.
Exploiting the Gibbs‐Duhem equation in separation calculations
Authors: Venkataraman S. , Lucia Angelo
Published: June 2004

Various ways of building quasi‐Newton matrix approximations that satisfy the special form of the Gibbs‐Duhem equation are studied. Partition symmetry, the separability of the functions in γ and in ϕ, and the method of iterated projections are used in order to develop thermodynamically consistent matrix approximations with good secant information. Many examples are presented which show that exploiting the special form of the Gibbs‐Duhem equation results in improved numerical performance. Ways of exploiting the Gibbs‐Helmholtz equation in addition to the special form of Gibbs‐Duhem equation, and thus the isobaric form of the Gibbs‐Duhem equation, are also discussed.
Particle size improvement by a countercurrent tower crystallizer
Authors: Farmer R. W. , Beckman J. R.
Published: June 2004

A continuous, staged‐feed column crystallizer was investigated to obtain enlarged product size distribution in precipitation from solution. Stage population balances, in moment form, were solved analytically for several single‐feed configurations. It was found that internal staging permits control of the solids concentration profile, and if collision nucleation is unimportant then countercurrent operation yields the greatest product size enlargement. Nucleation kinetic parameters for a given salt indicate the potential product size improvement, compared to product from an MSMPR crystallizer of equal volume.
Infinite dilution fugacity coefficients and the general behavior of dilute binary systems
Authors: Debenedetti P. G. , Kumar S. K.
Published: June 2004

A universally valid formal expression for the composition dependence of solute and solvent fugacity coefficients in any dilute binary system far from criticality is derived in this paper. In the present context, dilution denotes the y1 → O limit, regardless of the mixture's molar density. The results are independent of the system under study and of the choice of equation of state. The solute fugacity coefficient is simply the product of a composition‐independent term (the infinite dilution fugacity coefficient) and an exponential decay composition correction. These two parameters have important thermodynamic implications: their temperature and pressure derivatives are related to the solute's partial molar enthalpy and volume, respectively. When applied to activity coefficients, the same theoretical analysis yields universal relationships for the composition dependence of activity coefficients which can be used as consistency checks for empirical correlations. The relationship between infinite dilution activity and fugacity coefficients can be used to estimate relative solubilities of a given solute in different solvents. Excellent agreement is found when the theoretical expressions are tested with three different binary systems involving a nonvolatile solid solute and a supercritical fluid.
Modeling of coal liquefaction kinetics based on reactions in continuous mixtures. Part I: Theory
Authors: Prasad G. N. , Wittmann C. V. , Agnew J. B. , Sridhar T.
Published: June 2004

Based on the concept of reactions in a continuum, a mathematical model has been developed to simulate coal liquefaction kinetics. In an excess hydrogen donor environment, the rate‐limiting reactions are considered to be irreversible cracking reactions involving cleavage of carbon and oxygen linkages. Concurrent evolution of a wide spectrum of products, with an initial rapid formation of species of high carbon and oxygen contents, followed by progressively slower reactions leading to lower carbon and oxygen content species is predicted. Simple lumping functions are employed to obtain conventional lumped pseudocomponents (preasphaltenes, asphaltenes, and oils). Parameter analysis has been carried out.
Turbulent reactive mixing with a series‐parallel reaction: Effect of mixing on yield
Authors: Li K. T. , Toor H. L.
Published: June 2004

The yield of a nonpremixed series‐parallel reaction at complete conversion was measured in a turbulent, tubular‐flow reactor with single and multijet feeds. The yield of the intermediate decreased as mixing was slowed relative to the chemical kinetics, either by decreasing the Reynolds number, or by using a less efficient mixing device, or by increasing the feed concentration.

Four models, a modified slab model, a modified stretch model, the Harada mass transfer model, and a new closure model, adequately predict the yield when chemical and mixing kinetics are known from independent measurements of the conversion of acid‐base reactions. Without modification, the original slab and stretch models are unable to account for the earlier observed invariance of conversion to Schmidt number of very rapid, single‐step reactions or to satisfactorily predict the yield of the series‐parallel reaction.
Inhibition of gas hydrates by methanol
Authors: Anderson F. E. , Prausnitz J. M.
Published: June 2004

A molecular‐thermodynamic correlation has been developed for calculating the inhibition effect of methanol on the formation of hydrates in moist gas mixtures. Six phases are potentially present in these mixtures: gas, aqueous liquid, hydrocarbon liquid, ice, and hydrate structures I and II. For a given temperature and system composition, the molecular‐thermodynamic method described here allows computation of the hydrate‐point pressure as well as relative amounts and compositions of all coexisting phases. Good agreement is obtained when calculated results are compared with diverse experimental data reported in the literature. The correlation given here may be useful for computeraided design for gas processing and transportation.
Identifiability and distinguishability of fundamental parameters in catalytic methanation
Authors: Walter Eric , Lecourtier Yves , Happel John , Kao Juo‐Yu
Published: June 2004

Methods are presented to determine structural identifiability and distinguishability of parametric models. Results are applied to transient isotope tracing of methanation over a nickel catalyst. More meaningful information is obtained in this way about fundamental parameters than is possible by empirical curve‐fitting.
Liquid extraction during drop formation: Effect of formation time
Authors: Heideger W. J. , Wright M. W.
Published: June 2004

This study was designed to evaluate the effects of internal droplet convection on the extraction that occurs during generation of a dispersed phase. A photographic determination of dispersed‐phase controlled mass transfer from liquid droplets in the formation stage demonstrates a strong dependence on formation time. Convection appears to control mass transfer during rapid drop formation, but an abrupt transition in transfer coefficient occurs as time of formation increases. Diffusion calculations overestimate total extraction for long formation times.
Electrooxidation of urea at the ruthenium titanium oxide electrode
Authors: Wright J. C. , Michaels A. S. , Appleby A. J.
Published: June 2004

Urea adsorbs on the ruthenium titanium oxide electrode, depressing the observed current. For artificial kidney dialysate concentrations of urea and NaCl (0.50 kg/m3 and 100 mol/m3, respectively), the major electrolysis products are N2, CO2, O2, and H2, and the reaction mechanism is solution oxidation of urea by anodically generated active chlorine. A nitrogen‐yielding direct electrode reaction is observed at high urea concentration (30 kg/m3) and low NaCl concentration (10–100 mol/m3).
Conversion of propylene and butylene over ZSM‐5 catalyst
Authors: Tabak S. A. , Krambeck F. J. , Garwood W. E.
Published: June 2004

Using the zeolite ZSM‐5, new technology has been developed for catalytically oligomerizing light olefins (C3 to C4) to gasoline (C5 to C10) and diesel (C10 to C20) range product. This reaction produces product constrained by both the shape selectivity of the zeolite catalyst and the thermodynamics governing the oligomerization reaction.
Transient behavior of heterogeneous catalytic reactions with educt inhibition
Authors: Truffer M. A. , Renken A.
Published: June 2004

Under periodic operating conditions, the instantaneous rate of the heterogeneous catalytic addition of acetic acid to ethylene can be an order of magnitude higher than at steady state. A real surface, multistep control model takes into account the strong inhibition of the acid to ethylene sorption and describes the steady state and transient behavior quantitatively.
Simplified vent sizing equations for emergency relief requirements in reactors and storage vessels
Authors: Leung J. C.
Published: June 2004

Simplified vent sizing equations for emergency relief requirements in reaction kettles and storage vessels are obtained from analytical consideration. Venting modes include homogeneous‐vessel venting, all‐vacor venting, and all‐liquid venting; energy sources due to runaway chemical reactions and external heating are treated separately. The resulting equations have been shown via numerical examples to yield good agreement with detailed computer simulations, both in terms of temperature and pressure histories during venting and in vent size predictions. These equations are generally applicable over a wide range of overpressure situations and reduce to the correct limit at no overpressure. The relative merit of allowing for overpressure in various venting modes can be demonstrated using these equations. Because of their simple forms, requiring only pertinent physical property and thermal data, these equations readily lend themselves to quick but accurate vent sizing predictions.
Local composition model for chainlike molecules: A new simplified version of the perturbed hard chain theory
Authors: Kim Choon‐Ho , Vimalchand P. , Donohue M. D. , Sandler S. I.
Published: June 2004

A simple analytical equation for chainlike molecules interacting with square‐well potential is derived by replacing the complicated attractive term in the perturbed hard chain theory (PHCT) of Beret, Donohue, and Prausnitz with a theoretical but simple expression derived by Lee, Lombardo, and Sandler. The resulting simplified perturbed hard chain theory (SPHCT) reproduces both experimental vapor pressure and liquid density data for a number of fluids over a wide temperature and pressure range with good accuracy.

The three pure‐component parameters in the SPHCT have been obtained for several n‐alkanes and multipolar fluids. Average errors in predicted vapor pressures and liquid densities, over a wide temperature and pressure range, are about 3 and 4%, respectively. Preliminary mixture calculations indicate that the SPHCT predicts K factors and Henry's constants with reasonable accuracy without the use of any binary parameters.
Uniqueness of solutions to single‐stage isobaric flash processes involving homogeneous mixtures
Authors: Lucia Angelo
Published: June 2004

All single‐stage isobaric flash processes involving multicomponent homogeneous mixtures are shown to have unique two‐phase solutions. No simplifications with regard to nonideal phase behavior are made. The main result for the isothermal, isobaric (TP) case is established with the aid of a different characterization of material stability, the Gibbs‐Duhem equation, and the Cauchy interlace theorem. Results for the other traditional specifications of heat duty and pressure (QP), and total vapor flow rate and pressure (VP) are proved by establishing a one‐to‐one correspondence between the solution sets for TP and QP and the solution sets for TP and VP flash problems, respectively. Construction of these one‐to‐one mappings results in some interesting analysis associated with the appropriate plane curves in the TQ and TV planes. Some new properties of the underlying matrices involved in the phase equilibrium of homogeneous mixtures are presented.
Analysis of gas chromatography pulse dispersion data for the system n‐butane/zeolite nay
Authors: Fu Chen‐Chen , Ramesh M. S. P. , Haynes H. W.
Published: June 2004

An analysis of gas chromatography pulse dispersion data for the system n‐butane/zeolite NaY is presented. The data were analyzed in terms of two models, an intracrystalline diffusion limiting model and a surface barrier model. Both models provided acceptable fits to the pulse dispersion data; however, the temperature dependence of the apparent mass transport parameters strongly suggests that a surface barrier is responsible for the observed transport resistance. The Henry's law constants were independent of choice of model and the isosteric heat of sorption was consistent with literature values.
Optimization of catalytic activity distributions in series and parallel reaction schemes
Authors: Dougherty R. C. , Verykios X. E.
Published: June 2004

Optimal activity distributions within nonisothermal porous hetergeneous catalysts for series and parallel reaction networks are determined employing a numerical search procedure based on orthogonal collocation techniques. At high values of the Thiele modulus, a shell profile is found to be optimal at moderate heat of reaction parameters. In certain cases a pendulum effect, in which activity shifts from shell to core and back to shell profiles, is observed with increasing value of the heat of reaction parameters.
A population balance approach to direct‐contact secondary refrigerant freezing
Authors: Byrd L. W. , Mulligan J. C.
Published: June 2004

A population balance approach is used in developing an analysis of homogeneous freezing in a brine‐ice slurry by direct‐contact heat transfer to a dispersed secondary refrigerant. Exponential and beta distributions are assumed for the ice crystals and refrigerant droplets, respectively. The effects of freezer pressure (refrigerant temperature), inlet refrigerant drop size, and refrigerant and brine flow rates on well‐mixed freezer characteristics are presented.
Light intensity models for annular UV disinfection reactors
Authors: Suidan M. T. , Severin B. F.
Published: June 2004

The finite‐length lamp model was compared to the infinite‐length lamp model (or parallel radiation model) for annular reactors, specifically for the purpose of calculating average light intensities. Based upon the specified conditions that both models must apply equal energy to a reactor, such as is expected when the average surface flux of energy is measured by a chemical actinometric method, the results for the average intensity were very similar for the two models. Long lamp length and short reactor radius favored conditions where the finite‐length model predicted a slightly higher average intensity than that calculated using the infinite‐length model.

The inactivation of f2 virus was predicted in a completely mixed flow‐through reactor using kinetic data obtained from batch reactions. For the particular flow‐through reactor used, very little difference for the average intensity was calculated using the two intensity models. Indeed, predictions of reaction results using both models yielded results well within the range of experimental error.
Vapor‐liquid equilibria from perturbation gas chromatography. Part I: Multicomponent parameter estimation
Authors: Ruff W. A. , Glover C. J. , Watson A. T.
Published: June 2004

Elution times determined from perturbation chromatography experiments are functions of all sorbing species isotherms through the concentration partial derivatives. Measurements at a sufficient number of appropriate compositions along with isotherm models and adjustable parameters allow reduction of the retention time data to VLE by a nonlinear parameter estimation procedure described in this paper. The method can be implemented for both empirical isotherm models, which can be used to minimize model deficiencies, and for theoretical thermodynamic models, which have extrapolation potential and may require fewer parameters.
Prediction of rate constants for combustion and pyrolysis reactions by bimolecular QRRK
Authors: Westmoreland P. R. , Howard J. B. , Longwell J. P. , Dean A. M.
Published: June 2004

Bimolecular QRRK (Quantum Rice‐Ramsperger‐Kassel) analysis is a simple method for calculating rate constants of addition and recombination reactions, based on unimolecular quantum‐RRK theory. Input parameters are readily derived, and rate constants and reaction branching can be predicted with remarkable accuracy. Such predictive power makes the method especially useful in developing mechanisms of elementary reactions. Furthermore, from the bimolecular QRRK equations, limiting forms of the rate constants in the limits of low and high pressure are developed. Addition/stabilization is pressure‐dependent at low pressure but pressure‐independent at high pressure, as is conventionally understood for simple decomposition, its reverse. In distinct contrast, addition with chemically activated decomposition has the opposite behavior: pressure independence at low pressure and pressure dependence [as (pressure)−1] at high pressure. The method is tested against data and illustrated by calculations for O + CO → CO2; for H + O2 → HO2 or O + OH; for H + C2H4 → C2H5 or C2H3 + H2; and for H + C2H3 → C2H4 or H2 + C2H2.
Diffusion and catalytic activity studies on resid‐deactivated HDS catalysts
Authors: Johnson B. G. , Massoth F. E. , Bartholdy J.
Published: June 2004

Three different pore size CoMo/Al2O3 catalysts, which had been deactivated to the same extent during bench‐scale tests with an atmospheric resid, were examined for coke and metal deposits, diffusivity, and intrinsic activity for hydrodesulfurization, hydrogenation, and hydrodenitrogenation using model compounds. The aged catalysts had very low effective diffusivities and lower intrinsic activities than the fresh catalysts. Both metals and coke deposits were responsible for lowering diffusivity, but activity reduction appears to be predominantly due to metal deposits.
Solids circulation pattern and particles mixing in a large jetting fluidized bed
Authors: Yang Wen‐Ching , Ettehadieh B. , Haldipur G. B.
Published: June 2004

Macroscopic behavior of solids circulation in a large jetting fluidized bed was surveyed with a force probe. Particles mixing was studied by pulse injection of tracer particles, and a simple mechanistic model was developed on the basis of the solids circulation pattern observed. The model compares favorably with experimental tracer concentration profiles.
Production of ultrafine metal oxide aerosol particles by thermal decomposition of metal alkoxide vapors
Authors: Okuyama Kikuo , Kousaka Yasuo , Tohge Noboru , Yamamoto Satoru , Wu Jin Jwang , Flagan R. C. , Seinfeld J. H.
Published: June 2004

Ultrafine spherical titanium, silicon, and aluminium oxide particles were prepared by the thermal decomposition of their alkoxide vapors, produced by evaporation and subsequent heating. High‐concentration ultrafine particles having geometric mean diameters ranging between 0.01 and 0.06 μm and a geometric standard deviation of about 1.4 were obtained by varying the temperatures of the evaporator containing the liquid alkoxides and the reactor furnace, and the flow rate of carrier gas. For furnace temperatures lower than 400°C for TiO2 and 1000°C for SiO2 and Al2O3, the particles obtained were found to be amorphous. The observed changes in the particle size distributions due to changes in operating conditions were compared with those predicted theoretically by solving the discrete‐continuous aerosol general dynamic equation accounting for coagulation and generation of monomer by thermal decomposition. The effect of monomer number concentration on the size distribution of generated particles was found to be qualitatively explained.
Two‐phase flow behavior in the freeboard of a gas‐fluidized bed
Authors: Hamdullahpur F. , MacKay G. D. M.
Published: June 2004

An experimental and theoretical study was conducted to identify the flow behavior of gas and particulates in the freeboard of a gas‐fluidized bed. The axial velocity and turbulence intensity distributions were measured along the centerline and across the freeboard. A laser Doppler velocimeter (LDV) was used for the experiments. A technique based on fluorescence emission was developed to discriminate between gas‐phase and particle‐phase velocity information. The gas phase measurements revealed a strong influence of bubble induced turbulence on gas velocity distribution. The axial particle velocity indicated a two‐stage decay with height. Models were developed to predict centerline gas velocity and transport disengagement height.
Population balance modeling of the dissolution of polydisperse solids: Rate limiting regimes
Authors: Leblanc S. E. , Fogler H. S.
Published: June 2004

Significant errors can result in modeling dissolution processes if the polydispersity of the solid particles is ignored and the sample is treated as a collection of monodisperse spheres having the average size of the mixture. Population balance modeling provides an effective analytical means of predicting the effect of polydispersity on a wide variety of heterogeneous reaction systems including dissolution processes.
Low‐stress hemolysis in laminar blood flow: Bulk and surface effects in capillaries
Authors: Beissinger R. L. , Laugel Jean‐Francois
Published: June 2004

Human blood (blood bank, expired) sheared through stainless steel capillary tubing (508 μm ID) is analyzed for plasma hemoglobin to study the effect of shear‐induced blood damage within the low‐stress regime (stress ≤ 20 Pa). Blood damage results are described in terms of capillary length (related to blood residence time) and wall shear rate for assessing bulk and surface effects. A phenomenological model is proposed to explain these experimental results, obtained over a shear rate range to 7,000 s−1.
Equilibria of nitrogen, oxygen, argon, and air in molecular sieve 5A
Authors: Miller G. W. , Knaebel K. S. , Ikels K. G.
Published: June 2004

Pure‐component equilibrium data for nitrogen, oxygen, and argon, and multicomponent equilibrium data for air in 20 × 40 mesh 5A molecular sieve were measured at 297.15, 233.15, and 203.15 K and up to pressures of 4 bar. The multicomponent data were analyzed by a statistical thermodynamic model, ideal adsorbed solution theory, an extended Langmuir‐Sips equation, and an extended Langmuir equation. The multicomponent system exhibited nonideal behavior at 233.15 and 203.15 K. Isotherm parameters determined in this work may be useful in the design and evaluation of molecular sieve air separation systems.
Alternating flow model for mass and heat dispersion in packed beds
Authors: Klingman K. J. , Lee H. H.
Published: June 2004

The alternating flow model (AFM) views dispersion in packed beds as a sequence of streamline plugs that must repeatedly split and merge as the bulk fluid traverses the vessel. Thus, the flow in the AFM is ordered, as opposed to the random flow implied by the Fickian analogy. For mass dispersion only, model parameters arise from a priori considerations of packing geometry. Steady state and transient data (5.6 < Dt/dp < 54.4, 100 < Rep < 1,000, gases and liquids) show the AFM to surpass the Fickian analogy (based on correlations for dispersion coefficients) in most cases. Further, it can describe well the radial velocity profile trends in packed beds. For heat dispersion, two additional parameters (heat transfer coefficients) arise that are not functions of packing geometry. Simple correlations for these parameters and the justifications are given. Most of the comparisons made with the literature experimental results show the AFM to be at least as good as the back‐fit Fickian analogy. The AFM should be most useful for packed beds with a relatively small Dt/dp.
A generalized pore model for gas‐solid reactions exhibiting pore closure
Authors: Yu Huei‐Chung , Sotirchos S. V.
Published: June 2004

A model of pore structure evolution has been developed for gas‐solid reactions exhibiting pore closure behavior. A cylindrical pore network of constant coordination number is used to represent the porous medium, and both discrete and continuous distributions of pore size are considered. The mathematical model takes into consideration the effects of pore overlapping and nonuniform pore growth, and follows the formation of inaccessible volume in the interior of the reacting particles by use of percolation theory concepts. The model is applied, along with an appropriate diffusion and reaction model, to the investigation of the transient behavior of calcined limestone particles in an environment of sulfur dioxide.
Continuous and discontinuous models for transport phenomena in polymers
Authors: Ocone Raffaella , Astarita Gianni
Published: June 2004

A model for transport phenomena in polymers accompanied by morphological changes is presented that includes the essential features of a variety of seemingly disparate models available in the literature. The latter are classified as special cases of the model considered, and according to whether discontinuities of the morphology are or are not explicitly described. An ordering analysis is presented that indicates under which conditions one or more of the terms appearing in the differential equations can be neglected. A special subcase, termed surface crystallization, is shown to emerge in a well‐defined asymptotic sense from the general model, and is also shown to yield predictions which are closely analogous to those of a model of Astarita and Sarti that has been very successful in correlating experimental data of the type called case II transport. The advantage of the surface crystallization model is that it is not an ad hoc model. The models considered result in hyperbolic differential equations, as is often the case when relaxation phenomena are taken into account. A procedure for numerically solving hyperbolic equations with great ease is presented.
Equilibrium theory for complete adiabatic adsorption cycles
Authors: Davis M. M. , Levan M. D.
Published: June 2004

Complete adiabatic fixed‐bed adsorption cycles with adsorption, heating, and cooling steps are analyzed using simple wave theory. Solutions consist of simple waves, shocks, combined waves, and wave interactions with patterns established by a mapping between hodograph and physical planes. The system considered is benzene adsorbed on activated carbon with nitrogen as the carrier gas.
Prediction of multicomponent liquid adsorption equilibria
Authors: Price P. E. , Danner R. P.
Published: June 2004

A new method of predicting adsorption equilibria for multicomponent liquid solutions on solids has been developed which combines the thermodynamic and kinetic treatments of liquid adsorption. Multicomponent equilibria can be predicted using parameters obtained from binary adsorption data. The method requires the adsorbent capacities, the bulk and surface phase activity coefficients, and the binary adsorption equilibrium constants. The calculation procedure is simpler than other available methods. Predictions are made for the mixture of benzene, ethyl acetate, and cyclohexane on activated carbon at 303 K. The predictions are in quantitative agreement with published experimental data for this system.
Tracer diffusion measurement in polymer solutions near the glass transition by forced rayleigh scattering
Authors: Huang W. J. , Frick T. S. , Landry M. R. , Lee J. A. , Lodge T. P. , Tirrell Matthew
Published: June 2004

Forced Rayleigh scattering, a relatively recently developed optical technique, is used to measure tracer diffusion coefficients in polymer‐solvent mixtures near the system glass transition temperature, Tg. The technique has a wider range of potential application than has yet been realized, and so is presented in some detail. The objectives were to obtain data necessary to scrutinize free volume theory, and to understand so‐called anomalous, non‐Fickian diffusion effects observed by others in polymer‐solvent mixtures near Tg. Data on dye tracer diffusion coefficients in the systems polyvinyl acetate‐toluene, polystyrene‐toluene, and polystyrene‐tri‐m‐tolyl phosphate were obtained over a polymer concentration range from infinite dilution to 96 wt. %. Small molecule diffusion coefficients are seen to vary by as much as nine orders of magnitude (10−14 to 10−5 cm2/s) over this concentration range. The data are in reasonable accord with expectations based on the Duda‐Vrentas version of free‐volume theory.
Microflow calorimeter design for heats of mixing
Authors: Raal J. D. , Webley P. A.
Published: June 2004

Microflow calorimeter design for heats of mixing is surveyed. Precise temperature equilibration of the fluids before mixing, the elimination of frictional energy effects from the instrument response, and the absence of flow‐rate and physical‐property‐dependent heat leaks are particularly important. A design using a differential mode of operation is based on a careful analysis of entropy generation in flows with mixing and friction. The compensation for frictional heating and the lack of dependence of measurements on flow rate and mixture physical properties other than hE represents a major advance. Measured data for the welltested cyclohexane‐hexane system had an average deviation of only 0.41%. For the more viscous cyclohexane‐1‐hexanol system, measured data of similar precision are considered the best available.
The periodic, electrochemical codeposition of cadmium and tellurium
Authors: Verbrugge M. W. , Tobias C. W.
Published: June 2004

A mathematical model is presented for the codeposition of cadmium and tellurium onto a rotating‐disk electrode. The treatment incorporates the equation of convective diffusion for liquid phase mass transport, Butler‐Volmer expressions for charge‐transfer reactions, and a thermodynamic model for individual component activities in the solid state. Because of the formation of CdTe, a compound that has a large negative free energy of formation, the cadmium deposition reaction occurs at potentials substantially positive to its standard electrode potential (Uθ = −0.40 V). This reaction, along with the deposition of tellurium (Uθ = + 0.55 V), produces an electrodeposit that contains cadmium, tellurium, and cadmium telluride. The model can be used to calculate transient current‐potential relationships, ionic concentration profiles, and deposit compositions. Transport and kinetic parameters for cadmium and tellurium deposition are reported; a multidimensional optimization routine is used to evaluate physiochemical parameters from experimental data for the codeposition process.
Snap‐off of gas bubbles in smoothly constricted noncircular capillaries
Authors: Ransohoff T. C. , Gauglitz P. A. , Radke C. J.
Published: June 2004

A corner flow hydrodynamic theory is outlined for the time to snap‐off of a gas bubble moving through a smoothly constricted noncircular capillary as a function of the pore geometry and the capillary number, Ca. Above a transition capillary number the time to snap‐off is independent of Ca, while below it the time to snap‐off is inversely proportional to the capillary number. Thin films of liquid deposited along the capillary walls are shown to play a minor role; they are accordingly neglected in the analysis. The proposed theory is compared to new experimental results for snap‐off in two constricted square capillaries (dimensionless constriction radii of 0.3 and 0.5) over a range of capillary numbers (10−5 to 10−3), wetting‐liquid viscosities (1.0 to 8.5 mPa · s), and surfactant types. Good agreement is found between theory and experiment.
Flow and diffusion of gases through porous substrates
Authors: Allawi Z. M. , Gunn D. J.
Published: June 2004

An experimental study of simultaneous flow and binary diffusion through four porous catalyst substrates was conducted in the range of pressure from 1 to 3 bar absolute. Experiments on the flow of pure gases and isobaric binary diffusion were carried out on the same catalyst substrates. The differential equations describing simultaneous flow and diffusion in the form of the Chapman‐Enskog first‐order approximations were solved analytically, taking into account the variation of viscosity with composition. The parameters for the diffusion and flow processes were found from separate experiments on flow and diffusion, from experiments on nonisobaric flow and diffusion, and from composition transients in fixed beds. There was good agreement between theory and experiment except for permeability experiments at low pressures, where significant differences were found.
Silicon particle growth in a fluidized‐bed reactor
Authors: Hsu George , Rohatgi Naresh , Houseman John
Published: June 2004

This paper describes the overall operation of a 15 cm dia. fluidized‐bed reactor for silicon production via silane pyrolysis. The fluidized‐bed reactor has been characterized by its performance data and parametric effects. A withdrawal system is used to selectively remove big particles. Seed generation is provided by a fluid jet milling device, which avoids metallic grinding contamination. The silicon particle size growth calculated from a scavenging/deposition model agrees with actual size measurements.
Reaction front propagation in nonadiabatic exothermic reaction flow systems
Authors: Gatica J. E. , Puszynski Jan , Hlavacek Vladimir
Published: June 2004

A general analysis of the reaction wave propagation in nonlinear exothermic nonadiabatic diffusion‐convection‐reaction systems is presented. The following topics are considered: approximation of temperature profiles based on the idea of infinitesimaly thin reaction front, estimation of maximum temperature, estimation of the conversion at the hot spot, a priori calculation of the front velocity, analysis of the self‐ignition phenomena and their relation to wave propagation, and discussion of the effect of the heat loss parameter on the direction of propagation and shape of traveling waves. A comparison of the analytical work with exact numerical results reveals excellent agreement. The main objective of this paper is to provide a definite analysis of reaction wave propagation in reacting flow systems.
Effect of pore‐distributed coke on catalyst regeneration kinetics
Authors: Chang Yuli , Perlmutter D. D.
Published: June 2004

Prior experimental study by Haldeman and Botty has demonstrated that catalyst regeneration rates vary with conversion, showing a nearly constant rate of reaction in the early stages of regeneration and falling off rapidly at higher conversion levels. This peculiar reaction behavior calls for explanation in terms of pore structural changes. In this work a mathematical model is developed based on the interaction between catalyst pore structure and coke distribution in the pores. The model is able to associate overall regeneration kinetics with alternative pore‐distributed coke deposition patterns. Results exhibit a slight shallow rate maximum at an intermediate conversion level, in agreement with the prior experimental report. The model makes coke distribution in the pores accessible to experimental determination. The numerical results indicate that among pore structures with the same mean and overall pore volume, a larger variance offers a higher threshold for coke loading; for a given degree of dispersion, a smaller mean allows a higher coke loading.
Hydration of isobutene in a trickle‐bed reactor: Wetting efficiency and mass transfer
Authors: Leung P. C. , Recasens F. , Smith J. M.
Published: June 2004

Reaction rates for the hydration of isobutene were measured at 323 K and atmospheric pressure in a trickle‐bed reactor over a sixfold range of liquid rates. Three widely different feed conditions were used to vary the effect of mass transfer and wetting efficiency. The effect of wetting efficiency on the rate was analyzed using the additive procedure of Tan and Smith. The results showed that mass transfer from liquid to particle, wetting efficiency, and intraparticle kinetics all influenced the total rate, but that the gas‐to‐liquid mass transfer resistance was unimportant. Most of the resultant values of wetting efficiency and liquid‐to‐mass transfer coefficients were a little lower than literature values. This may be due to the high surface tension of our aqueous system. The derived total rate equations agreed well with the experimental rates, suggesting that the additive procedure is a satisfactory method of accounting for wetting efficiency.
Thermoflow multiplicity in a packed‐bed reactor Part I: Adiabatic case
Authors: Lee J. P. , Balakotaiah V. , Luss Dan
Published: June 2004

Steady states with different flow rates and temperature profiles may exist in a packed‐bed reactor operating under a prescribed pressure drop, due to the coupling among the species, energy, and momentum balances and the change of the physical properties with temperature and pressure. This thermoflow multiplicity may be found even for reactions whose rate is rather insensitive to temperature changes (low activation energy) and may lead to highly undesirable operation of multitube packed‐bed reactors. A hierarchy of models based on different assumptions is used to derive criteria for predicting the conditions under which this thermoflow multiplicity may occur.
Transient free‐surface flows: Motion of a fluid advancing in a tube
Authors: Behrens R. A. , Crochet M. J. , Denson C. D. , Metzner A. B.
Published: June 2004

The fluid motion at a free surface advancing into a mold or duct is appreciably different from its steady state behavior in well‐developed flow; this affects the residence time distribution and structure of macromolecular fluids as they are frozen in injection molding processes. In this work such motion is treated numerically and measured precisely for Newtonian fluids. While the three‐phase contact line represents a special problem conceptually and analytically, a very simple algorithm is seen to represent the fluid motion in this region accurately.

Good agreement is found over wide ranges of the governing dimensionless groups (the Reynolds, Jeffrey, and capillary numbers). Since viscous forces are dominant under the circumstances studied, this finding is not surprising but it confirms the applicability of the numerical methods developed herein to the modeling of these flows under conditions of actual interest. As a result, simulations may be made with confidence to predict flow patterns encountered in practice but difficult to reproduce in laboratory experiments.
Chemically driven convection in a porous medium
Authors: Viljoen H. , Hlavacek V.
Published: June 2004

This paper is focused on the analysis of interaction of free convection and exothermic chemical reaction. As a consequence of the chemical reaction, free convection effects can result. It is difficult to perform an analytical bifurcation analysis of the full nonlinear governing equations; however, Fourier expansion combined with a Galerkin approximation results in a small set of ordinary nonlinear differential equations (initial‐value problem) that are amenable to analysis. Conditions for branching of the solution can be determined in an analytical way. A continuation algorithm makes it possible to calculate the branches of stability. The results of the approximative analysis are supported by the numerical integration of the full governing nonlinear equations.
Limitations of the equilibrium theory of countercurrent devices
Authors: Sundaresan S. , Wong J. K. , Jackson R.
Published: June 2004

In the analysis of countercurrent adsorption processes, an equilibrium theory in which local equilibrium between the fluid and the adsorbent phases is assumed has been used in the past to determine the composition of the pinch state that would be obtained for long columns. It is shown that this equilibrium theory is deficient and that certain mass transfer parameters, which are lost in the procedure by which the model equations for the equilibrium theory are formulated, can have a profound effect on the composition of the pinch.
Design of multivariable linear‐quadratic controllers using transfer functions
Authors: Harris T. J. , Macgregor J. F.
Published: June 2004

Optimal linear‐quadratic (LQ) controller design is usually associated with state space techniques. However, when one has measurements of the outputs to be controlled, there are many advantages to designing these LQ controllers using input‐output transfer function models. The design procedure leads to a discrete equivalent of the Wiener‐Hopf equation, which can be solved using a spectral factorization approach.

In this paper the design procedure is presented and various interpretations of the resulting controllers are discussed. In particular, the controllers are shown to be of the internal model controller (IMC) form, and the Wiener‐Hopf procedure is shown to be a powerful way of selecting approximate model inverses and filters that yield good performance and robustness characteristics. The approach treats the problem of simultaneous disturbance rejection and set‐point tracking, and it easily handles nonsquare systems.

The design approach, its performance/robustness trade‐offs, and the structure of the resulting controllers are demonstrated using models for several processes, including a two‐input/one‐output sheet forming process, a (3 × 3) multivariable level control problem, and a (2 × 2) multivariable catalytic reactor.
Application of LQ and IMC controllers to a packed‐bed reactor
Authors: Kozub D. J. , Macgregor J. F. , Wright J. D.
Published: June 2004

A practical application of advanced, model‐based, multivariable control to a pilot plant packed‐bed reactor carrying out highly exothermic butane hydrogenolysis reactions is presented. The system is first stabilized by using butane flow rate to control the reactor hot‐spot temperature. Propane production and butane conversion are then controlled using multivariable controllers that manipulate the hot‐spot temperature set point and hydrogen flow rate. The controller designs are based on multivariable transfer function models developed using multivariable time series and process identification methods.

Two types of multivariable controllers are applied. The first is an internal model controller (IMC) utilizing a stabilized approximation of the model inverse and a tunable exponential filter. The second is a linear‐quadratic (LQ) controller design using pulse transfer function models to characterize the process dynamics and autoregressive‐moving average models to characterize the disturbances. The optimal control solution was arrived at via a spectral factorization solution to the Wiener‐Hopf equations. The results indicate that both designs, if well tuned, provide good performance and robustness over a wide range of operation.
Clustering in supercritical fluid mixtures
Authors: Kim Sunwook , Johnston K. P.
Published: June 2004

The local compositions of supercritical fluid carbon dioxide and a cosolvent about a solute at infinite dilution have been estimated for the first time using spectroscopic measurements. The solute was phenol blue, the bulk concentrations of the cosolvents n‐octane, acetone, ethanol, and methanol ranged from 0 to 100 mol%, and the pressure ranged from 80 to 300 bar. In each case, the clusters of solvent about the solute are enriched in cosolvent. Solubility data have been measured for phenol blue in CO2 with and without the cosolvent acetone, and regressed using an augmented van der Waals‐density‐dependent local composition model to determine the relevant binary interaction energies. The local compositions calculated from the model agree with those that were esimated spectroscopically. The model was used to predict solubilities of solids in supercritical fluid CO2 with various cosolvents.
A network model for deep bed filtration processes
Authors: Sharma M. M. , Yortsos Y. C.
Published: June 2004

Equations for the deep bed filtration problem are obtained as a special case of a general model formulated earlier. The filtration coefficient λ is expressed as an explicit function of system parameters such as fluid flow rate, pore density, and pore size distribution. For a unimodal pore size distribution it is found that λ remains constant both in space and time. In general, however, λ is shown to decrease. Explicit solutions to the problem, including particle density profiles and permeability, are obtained for the two cases of large values of the coordination number Z (capillary tube model), and for a bimodal pore size distribution with a finite coordination number.
High‐pressure particulate expansion and minimum bubbling of fine carbon powders
Authors: Jacob K. V. , Weimer A. W.
Published: June 2004

Particulate expansion and minimum bubbling parameters (n, u′t, umB, εmB) are measured for fine carbon powders (dp = 44 and 112 μm) fluidized with synthesis gas (H2/CO = 0.8) at pressures within the range 2,070 < P < 12,420 kPa in an industrial, pilot‐scale fluidized bed. Deviations between minimum bubbling (umB and εmB) and minimum fluidization (umf and εmf) conditions increase with increasing pressure, P. The expansion index, n, decreases with increasing P and always exceeds values recommended by Richardson and Zaki for solid/liquid systems. Particulate bed expansion for the fine powders is well characterized by the equations of Foscolo et al. and Abrahamsen and Geldart. The theory of Foscolo and Gibilaro adequately estimates the onset of bubbling for both powders at all P, provided that experimentally determined values of n and u′t, are applied. For the dp = 112 μm powder, the theory of Foscolo and Gibilaro is applicable with calculated values of ut and experimental values of n.
Modeling the pore structure of coal
Authors: Bhatia S. K.
Published: June 2004

The predictions of the random‐pore model, and various other models formulated here, are compared with experimental data for the uptake of methane by coal. It is found that the most appropriate is a modified model considering coal to be comprised of microporous grains, with the random‐pore model holding for the micropores in the grains. The new model still predicts the same reaction behavior as the random‐pore model.
Studies in the heat integration of chemical process plants
Authors: Viswanathan Murali , Evans L. B.
Published: June 2004

A method for solving the problem of heat exchanger network synthesis in chemical process plants is presented based on the use of the out‐of‐kilter algorithm. The method represents an extension of previous approaches based on network flow problem formulations. A new approach to overcome the constraints in forbidden‐match problems, termed the dual stream approach, has been developed based on the use of a stream as both a hot and a cold stream. This approach results in considerable savings in utility costs in certain forbidden‐match problems. An algorithm to deal with heating or cooling utilities that undergo temperature changes, termed non‐point‐temperature utilities, is presented using the transshipment model. The new algorithm determines the utility mass flow rates and pinch points accurately.
Diffusion path analysis of dynamic behavior of oil‐water‐surfactant systems
Authors: Raney K. H. , Miller C. A.
Published: June 2004

The diffusional processes that occur when oil contacts an aqueous surfactant solution have been investigated. These are pertinent to enhanced oil recovery by surfactant flooding and to detergency in certain systems. The theory of diffusion paths was used to solve the diffusion equations for a model pseudoternary system. Although detailed comparison with experimental results was not possible due to a lack of necessary data, calculated diffusion paths and interface velocities were found to be useful for explaining various phenomena observed experimentally in an oil recovery system.

Because the surfactant “solutions” studied commonly exist as dispersions of liquid crystal, extension of the theory to allow for initial compositions in two‐phase regions was carried out. Also novel was investigation of the effect of the three‐phase regions that occur in these systems on the position and shape of calculated diffusion paths.