bluuebunny/crossref_metadata_2025 huggingface dataset:
Size‐Dependent growth and contact nucleation of calcite crystals
Authors: Tai Clifford Y. , Chen Pao‐Chi , Shih Shin‐Min
Published: June 2004

The growth kinetics and contact nucleation of calcite crystals were studied in a pH‐stat crystallizer. Large seed crystals up to 230 μm were successfully prepared by the gel growth technique. The crystal growth data over a wide range of crystal sizes were evaluated from titration curves by an initial slope method and then analyzed by the two‐step model. The mass‐transfer and surface integration rates were found to be functions of crystal size with the exception of mass‐transfer rates of small crystals less than 10 μm. The controlling step of crystal growth process was tested using the effectiveness factor concept. Large seed crystals of calcite induced contact nucleation when a stainless‐steel impeller was used for agitation. The important features of contact nucleation for calcite crystals were explored and compared with those of soluble substances.
Application of integral‐equation theory to aqueous two‐phase partitioning systems
Authors: Haynes C. A. , Benitez F. J. , Blanch H. W. , Prausnitz J. M.
Published: June 2004

A molecular‐thermodynamic model is developed for representing thermodynamic properties of aqueous two‐phase systems containing polymers, electrolytes, and proteins. The model is based on McMillan‐Mayer solution theory and the generalized mean‐spherical approximation to account for electrostatic forces between unlike ions. The Boublik‐Mansoori equation of state for hard‐sphere mixtures is coupled with the osmotic virial expansion truncated after the second‐virial terms to account for short‐range forces between molecules.

Osmotic second virial coefficients are reported from low‐angle laser‐light scattering (LALLS) data for binary and ternary aqueous solutions containing polymers and proteins. Ion‐polymer specific‐interaction coefficients are determined from osmoticpressure data for aqueous solutions containing a water‐soluble polymer and an alkali chloride, phosphate or sulfate salt.

When coupled with LALLS and osmotic‐pressure data reported here, the model is used to predict liquid‐liquid equilibria, protein partition coefficients, and electrostatic potentials between phases for both polymer‐polymer and polymer‐salt aqueous two‐phase systems. For bovine serum albumin, lysozyme, and α‐chymotrypsin, predicted partition coefficients are in excellent agreement with experiment.
Dean vortices in curved tube flow: 5. 3‐D MRI and numerical analysis of the velocity field
Authors: Chung Kun Yong , Belfort Georges , Edelstein William A. , Li Xianming
Published: June 2004

The velocity contour profiles within Dean vortices produced by flowing water in a solid‐walled curved tube are quantitatively measured. Magnetic resonance flow imaging using flow encoding with spin warp imaging is used in two and three dimensions to obtain these velocities. These experimental measurements are then compared with simulations obtained from solutions of the Navier‐Stokes and continuity equations for three axial flow rates. Numerical solutions were obtained with a finite volume method for curved tube Poiseuille flow.
Optimization of the countercurrent moving‐bed chromatographic separator
Authors: Fish Barry B. , Carr Robert W. , Aris Rutherford
Published: June 2004

A dispersionless, adsorption equilibrium, plug‐flow model of a countercurrent moving‐bed chromatographic separator operating at steady state is investigated. The flux of the constituents of a binary mixture is examined via concentration‐phase plane plots, which reveal a complex behavior depending on a parameter ó, the ratio of solid‐ and fluid‐phase flow of the mobile phase. When the model is modified by incorporating finite mass‐transfer rates, axial concentration profiles exhibit behavior that is characteristic of experimental observations, rather than the predictions of the ideal model. Numerical simulations with the finite mass‐transfer model reveal an optimum operating condition.
Role of energy distribution in multicomponent sorption kinetics in bidispersed solids
Authors: Hu Xijun , Do Duong D.
Published: June 2004

The heterogeneous macropore, surface and micropore diffusion model recently proposed by Hu et al. (1993) for single‐component systems is exiended to multicomponent systems in the description of sorption kinetics of gaseous adsorbates in bidispersed (macropore and micropore diffusions), heterogeneous microporous particles. This model describes sorption of gaseous adsorbates with allowance for the energy distribution of adsorption site for both equilibrium and diffusion of the adsorbed species. A uniform distribution is used to describe this energy distribution, and the cumulative energy distribution function is assumed the same for all species in the analysis of multicomponent mixtures. Extensive experimental data of ethane and propane in Ajax activated carbon are collected to study the effects of energy distribution on the binary adsorption, desorption, and displacement dynamics.
Output estimation using multiple secondary measurements: High‐purity distillation
Authors: Mejdell Thor , Skogestad Sigurd
Published: June 2004

Measurements of temperatures (secondary outputs) and flows (inputs) are used to estimate product compositions (outputs) in a distillation column. The problem is characterized by strong collinearity (correlation) between temperature measurements and an ill‐conditioned model from inputs to outputs. In a linear study, three estimator methods, the Kalman‐Bucy filter, Brosilow's inferential estimator, and principal component regression (PCR), are tested for performance with μ‐analysis. One can achieve remarkably good control performance with the static PCR estimator, which is almost as good as the dynamic Kalman filter. The quality of the estimate for these two estimators is improved by additional temperature measurements, although the improvement is only minor for more than about five measurements. On the other hand, the performance of the Brosilow inferential estimator may not improve by adding measurements due to sensitivity to modeling errors. For all estimators, the use of flow (input) measurements does not improve the estimator performance and does in fact damage the performance if a static estimator is used.
Analysis of steady‐state reaction fronts in a porous medium
Authors: Escobedo F. , Viljoen H. J.
Published: June 2004

A pseudohomogeneous model is used to analyze the steady state of a sharp reaction front in a porous medium. The reaction rate is described by the flame sheet approximation, and an asymptotic matching analysis is used to determine the temperature, conversion and position of the reaction front. Both adiabatic and nonadiabatic operations are considered, and the effect of radiation is included in the adiabatic case. The results show that there exists a maximum molar flux before blowout occurs. The critical molar flux is decreased by higher activation energies, but it is increased by higher rate constants and flame temperatures. Radiation further stabilizes the flame against blowout. Expressions are provided for the flame temperature, reactant conversion and the conditions when blowout occur. It is also shown that under certain conditions the front has two steady‐state positions.
Flow along porous media by partical image velocimetry
Authors: Saleh S. , Thovert J. F. , Adler P. M.
Published: June 2004

Velocity measurements near porous media are performed by particle image velocimetry. Fully established laminar flows along flat media are studied and compared with the predictions of classical models. Five types of porous media are investigated. Two‐dimensional pictures of the flow, average velocities, and local fluctuations are discussed.
Mathematical modeling of heat and mass transfer in packed‐bed adsorbers/regenerators
Authors: Gouvalias G. S. , Markatos N. C.
Published: June 2004

Nonisothermal adsorption is studied by incorporating its mathematical description into a model consisting of the full two‐dimensional Navier‐Stokes equations and energy and species concentration equations to simulate the processes in fixed‐bed industrial adsorbers/regenerators. The model partial‐differential equations are solved numerically by using well‐established computational fluid dynamics techniques. The equilibrium between gas and solid is considered nonlinear, which is described by Freundlich‐type equations. The transport and adsorption of a compound from a solvent to and into an adsorbent are described by a two‐step process: transport through the “film” to the outer surface of the particle and diffusion into the porous particle. The effect of fill resistance is discussed, as well as a two‐equation turbulence model. Solutions obtained for a typical industrial adsorber/regenerator demonstrate the potential of this method. The computed results for various flow ratios and parameters in the Freundlich equations are shown to be physically plausible.
Chemical vapor infiltration: Dispersed and graded depositions for ceramic composites
Authors: Chung G. Y. , McCoy B. J. , Smith J. M. , Cagliostro Domenick E.
Published: June 2004

A structured‐geometry model for dispersed and graded deposits was developed for chemical vapor infiltration of multiply‐woven substrates of carbon filters. An earlier model was modified to allow for two reactants in the feed. The model predicts gas‐phase concentration profiles in the voids of substrates and deposition amounts of two reactants as a function of time and location. Results are shown for feeding reactant gases simultaneously for dispersed deposition and periodically for the study of the graded deposition for a typical substrate. The variation in relative contents of reactants in the feed with time shows how the composition of the deposit varies. Porosities and changes of dimensions with time everywhere in the substrate are also predicted. This is an advantage of the structured‐geometry model vs. a simplified homogeneous geometry for the substrate. Such a simplification may preclude predicting failure, such as delamination, which would require a local description of the composite structure.

Sensitivity to input parameters such as temperature, pressure, and reactant feed concentration is discussed, and two substrate geometries are compared.

The behavior of the system is predicted to be dominated by the times to fill gaps between filaments at the ply surfaces and the outermost space between plies. Furthermore, faster kinetics and slower reactant diffusion favor deposition of one material near the surface of a ply or the matrix and the other near the center of the ply or matrix. By manipulating feed rates of reactants, uniformity of material and overall porosity of the composites are predicted to be enhanced.
Robust stability analysis of constrained l1‐norm model predictive control
Authors: Genceli Hasmet , Nikolaou Michael
Published: June 2004

Sufficient conditions for robust closed‐loop stability of a class of dynamic matrix control (DMC) systems are presented. The l1‐norm is used in the objective function of the on‐line optimization, thus resulting in a linear programming problem. The ideas of this work, however, are expandable to other DMC‐type controllers. The keys to the stability conditions are: to use an end‐condition in the moving horizon on‐line optimization; to have coefficients of the move suppression term in the objective function of the on‐line optimization satisfy certain inequalities; and to express the uncertainty as deviations in the unit pulse response coefficients of the nominal plant. These deviations and disturbances must also satisfy certain inequalities.

An off‐line tuning procedure for robust stability and performance of a class of DMC controllers is also included, which determines an optimal moving horizon length and optimal values for coefficients of the move suppression term. The applicability of our approach is elucidated through numerical simulations.
Effects of molecular structure upon complex‐support interactions
Authors: Bruce David , Bertrand J. Aaron , White Mark G.
Published: June 2004

Two cationic, copper metal complexes with different ligands were synthesized: ethylenediamine (en) [Cu(C2N8N2) (ClO4)2] and diethanolamine (Deta) {[Cu‐C8H21N2O4]ClO4}. These complexes were mounted on Cab‐O‐Sil using nonaqueous impregnation techniques, and the loadings were determined at which multilayers formed. These samples were analyzed for copper, carbon, nitrogen and hydrogen content to determine if ligand dissociation occurred during the impregnation. Samples were decomposed in a thermal gravimetric apparatus to determine the kinetics of the thermolysis reaction in air, and the evolved gases were analyzed by gas chromatograph‐mass spectrometry to determine the products of the thermolysis reaction. The results of these and earlier studies are summarized in a model that describes the effects of molecular structure upon complex‐support interactions. Complexes with the ability to form hydrogen bond interactions between the ligand and the support form strong interactions with the surface of silica, whereas complexes without such hydrogen bond interactions are only weakly attracted to the silica surface. Strong interactions with the surface may also arise as a result of ligand dissociation and direct interaction of the metal ion with the surface oxygens. The charge on the complex and its shape play less important roles in determining the affinity of the metal complex with the silica.
Electrochemical membrane process for flue gas desulfurization
Authors: McHenry Dennis J. , Winnick Jack
Published: June 2004

A flue gas desulfurization process being developed for coal‐fired power plants removes and concentrates sulfur oxides (SOx). The key element is an electrochemical cell using a sulfur oxide selective membrane. It achieves 90% sulfur oxide removal with near 100% electric current efficiency.

Recent research has focused on improving the structure of the electrochemical membrane and its interface with the electrodes. The capillary forces of the membrane and porous electrodes establish an equilibrium. To maintain electrode surface area enhancement, it is necessary to retain the electrolyte in the membrane and allow only wetting of the electrode pores. Chemically‐stable matrix materials for the membrane have been identified; several fabrication techniques were used to prepare the actual membrane structure. A new electrode material, (LiO)xNiO, possesses the proper chemical stability and electrical properties in the corrosive environment. These modifications have led to an order of magnitude increase in flux and operating lifetime.
Generalized quartic equation of state for pure nonpolar fluids
Authors: Shah Vinod M. , Bienkowski Paul R. , Cochran Hank D.
Published: June 2004

A generalized quartic equation of state has been developed for pure nonpolar fluids. The equation of state contains four parameters which depend on three properties of the fluid—critical temperature, critical volume, and acentric factor. A mathematical approximation based on previously reported hard‐sphere molecular dynamics simulations has been used to model repulsive contributions to the pressure. Attractive forces were modeled using an empirical term. While the quartic equation yields four roots, one root is always negative and hence physically meaningless, and three roots behave like three roots of a cubic equation. Thus, the new equation of state has the advantages of a cubic, simplicity and unequivocal identification of the roots, while correctly modeling the attractive and repulsive contributions to the pressure. The new equation of state is more accurate than either the Peng‐Robinson or a previously proposed quartic equation of state. Accuracy in the supercritical and compressed liquid regions is improved substantially.
Minimum entrainer flows for extractive distillation: A bifurcation theoretic approach
Authors: Knapp Jeffrey P. , Doherty Michael F.
Published: June 2004

In addition to a minimum reflux, every extractive distillation exhibits a maximum reflux, above which the desired separation is impossible, and a minimum entrainer flow rate, below which the separation is also impossible. Both of these quantities correspond to bifurcations of the finite difference equations describing the middle section of the column and, given a VLE model, can be easily calculated knowing only information about the column feed and the desired product compositions, that is, prior to any column design calculations.

Both maximum reflux and minimum entrainer flows have important implications for the design and operation of extractive distillations. By limiting the range of feasible operating reflux ratios, the maximum reflux affects the flexibility, operability and controllability of the column. Ranking a set of feasible extractive entrainers according to their minimum entrainer flows provides a simple effective method for identifying the most promising candidates. Near optimal design values of the entrainer flow can then be estimated using the heuristic presented.
Kinetic modeling of free‐radical graft polymerization
Authors: Chaimberg Mark , Cohen Yoram
Published: June 2004

The kinetic model of free‐radical surface graft polymerization developed is based on a conservational polymerization and molecular‐weight distribution (CPMWD) numerical algorithm. The CPMWD model uses an implicit numerical technique to solve for the coupled monomer, surface site, and total growing polymer differential rate equations, which ensure that conservation of mass is maintained. The model formulation allows for the incorporation of kinetic rate coefficients, which are a function of the chain length of the reacting species, the solution viscosity, and the concentration of surface grafted polymer. The model also makes it possible to evaluate the monomer conversion, the graft yield and the molecular weight distributions of the homopolymer and surface‐grafted polymer for the complete duration of the graft polymerization reaction. Its application was demonstrated for a model system of vinylpyrrolidone graft polymerization onto the surface of a silica substrate.
A thermodynamic model for structure‐H hydrates
Authors: Mehta Ajay P. , Dendy Sloan E.
Published: June 2004

A statistical thermodynamics model based on the original work of van der Waals and Platteeuw is presented for structure‐H hydrates. The model is an extension of the hydrate prediction method generalized by Parrish and Prausnitz for structure‐I and‐II hydrates. Four structure‐H‐forming systems, methane+ adamantane, methane+ neohexane, methane+isopentane, and methane+methylcyclohexane, were considered. Optimized Kihara core parameters are presented for each of the large hydrocarbon guest molecules. The optimized reference chemical potential difference and reference enthalpy difference for structure‐H hydrates are also presented. The results show good agreement with the experimentally determined phase‐equilibria conditions. A sensitivity analysis is presented for the parameters in the model, and their relative order of influence on the accurate evaluation of the quilibrium pressure is determined.
Activated carbon catalyzes reactions of phenolics during liquid‐phase adsorption
Authors: Cooney David O. , Xi Zhenpeng
Published: June 2004

Various phenolic compounds in aqueous buffer solutions were contacted batchwise with powdered activated carbon. Relatively slow, but continual, decreases in the solution phenolic concentrations were measured over a period of several weeks. The decreases were due to oxidative coupling reactions of the phenolics which occurred on the carbon surface subsequent to adsorption. The effects of time, pH, dissolved oxygen, and the molecular nature of the phenolic were determined.
Prediction of micromixing effects in precipitation: Case of double‐jet precipitators
Authors: David René , Marcant Bruno
Published: June 2004

Mixing effects are evaluated for double jet semibatch and continuous stirred precipitators by a model which gives the variation of the primary nucleation flux from the mixing conditions. The predicted trends are compared with results of various authors, including those from a new study of calcium oxalate semibatch double‐jet precipitation. Satisfactory qualitative agreement is found for the different chemical systems as a function of feed rate, stirring speed and feed locations for calcium oxalate precipitation. Two types of precipitation systems are demonstrated, depending on the ratio added/tank volume, the initial supersaturations and the intrinsic stiffness factor of a given precipitation. The difference between the two types depends on the increase or reduction of the primary nucleation flux by imperfect mixing with respect to the reference primary nucleation flux obtained with perfect mixing.
Modeling, simulation and kinetic parameter estimation in batch crystallization processes
Authors: Farrell Robert J. , Tsai Yen‐Cheng
Published: June 2004

A dynamic model of a seeded batch crystallizer is used to investigate the process‐dependent aspects of nucleation and growth kinetic parameter estimation by computer simulation. The satisfactory identification of all parameters in power‐law‐type kinetics with respect to supersaturation requires the use of nonlinear parameter transformations. The proper choice for transformation is problem‐dependent, becoming more sensitive as nucleation rates increase, and the percentage of crystals below the measurable range increases.
Application of Voronoi tessellation for modeling randomly packed hollow‐fiber bundles
Authors: Chen Vicki , Hlavacek Marc
Published: June 2004

Influence of local voids on flow maldistribution in randomly packed fiber bundles is examined by Voronoi tessellation. A theoretical expression for the local void distribution caused by random placement of fibers is developed by using a randomcell model. Simulations and packing experiments have been conducted to assess the accuracy of the theoretical distribution of cell sizes. In the case of shell side, laminar flow parallel to the fibers, the theoretical distribution is used to estimate fRe (friction factor times Reynolds number) and volumetric flows, and to compare results with ordered arrays and experimental data from literature. The results are used to assess the contributions of local voidage variation to flow bypass. This has implications for the prediction of pressure drop and heat and mass transfer in hollow‐fiber module applications where transport is dominated by flow on the shell side.
Removal of hydrogen sulfide from natural gas through an electrochemical membrane separator
Authors: Alexander Steven Ray , Winnick Jack
Published: June 2004

An advanced process is developed for the separation of H2S from natural gas through an electrochemical membrane. H2S is removed from natural gas by reduction to the sulfide ion and H2 at the cathode. The sulfide ion migrates to the anode through a molten salt electrolyte suspended in an inert ceramic matrix. Once at the anode it is oxidized to elemental sulfur and swept away for condensation in an inert gas stream. The natural gas is enriched with H2. Order‐of‐magnitude reductions in H2S concentration have been repeatedly recorded on a single pass through the cell. This process allows removal of H2S, while producing H2 and elemental sulfur directly. No absorbents are used, and there is no need for subsequent treatment of a concetrated H2S stream as with conventional gas sweetening technology. This makes the process economically attractive, since it is much less equipment‐intensive than conventional technology.
Application of electrolyte theory to extractive separations using hydrotropes
Authors: Narayanan K. V. , Ananth M. S.
Published: June 2004

The use of polar hydrotropes in extractive and in liquid‐liquid extraction has been extensively reported in the literature. In this article, the effect of hydrotropes on increasing the effectiveness of separation is explained in terms of the effect of the dipole‐induced dipole and the ion‐induced dipole interactions on the activity coefficients of the neutral solutes in the aqueous phase. The self‐consistent local composition theory is used to correlate quantitatively the observed behavior in systems involving liquid‐liquid equilibria. The theory yields composition‐dependent expressions for the effect of each independent pair interaction on the activity coefficient of a neutral solute in the aqueous phase. The ratio of the activity coefficients of the two solutes is of interest in this context. The resulting expression for the separation factor is elegant and admits simple physical interpretation. The essential features of hydrotrope‐assisted extraction are correctly described by the theory. The ability of the theory to correlate data is demonstrated for two systems.
Thermodynamics of phase equilibria in aqueous‐organic systems with salt
Authors: Zerres H. , Prausnitz J. M.
Published: June 2004

A semiempirical thermodynamic method is developed to establish a framework for calculating vapor‐liquid and liquid‐liquid equilibria in ternary systems containing water, an organic solvent, and a salt. Careful attention is given to precise definition of standard states. Short‐range ion‐solvent forces are taken into account primarily by a chemical‐equilibrium method based on stepwise ion solvation; however, physical contributions also contribute. Water‐cosolvent nonideality is described by an extended equation of the van Laar form. Long‐range electrostatic forces between ions are taken into account by an extended Debye‐Hückel equation with corrections for transferring from a McMillan‐Mayer to a Lewis‐Randall framework.

The new method is illustrated with results for several systems including saturated aqueous mixtures of LiBr or LiCl with methanol where the salt concentration exceeds 20 molal. The method developed here is of particular interest for process calculations in extractive crystallization, a low‐energy operation for producing salt from aqueous solution.
Simulation and optimization of NOx absorption system in nitric acid manufacture
Authors: Suchak N. J. , Joshi J. B.
Published: June 2004

A mathematical model has been developed for the prediction of the optimum design of packed and plate columns for the manufacture of nitric acid. The effects of inlet NOx composition, extent of oxidation and extent of absorption in each stage, temperature, and pressure have been included in the model. The optimization of the preoxidizer and the condenser has also been discussed.
Concentric‐tube airlift reactors: Effects of geometrical design on performance
Authors: Merchuk J. C. , Ladwa N. , Cameron A. , Bulmer M. , Pickett A.
Published: June 2004

Pressure drops, gas holdup, and mass‐transfer coefficients were measured in two concentric‐tube airlift reactors of 30 and 300 L (nominal volume). The aspect ratio and the ratio of riser to downcomer cross section were the same for both reactors, but the geometry of the gas separation section was different. The influence of the bottom and top clearances was studied using water and carboxymethyl cellulose solutions and covering a range of effective viscosity from 10−3 to 25 × 10−3 Pa·s. The pressure drop results expressed as a Euler number were satisfactorily correlated with Fr, Ga, and a bubble disengagement group M. Correlations are presented also for the gas holdup in the riser, downcomer, and gas separator. The last‐mentioned coincides with the correlation for the total holdup in the reactor. The gas‐liquid mass‐transfer coefficients for all the liquids and geometric variables in both reactors were successfully correlated as Sherwood numbers.
Prediction of pH in complex aqueous mixtures using a group‐contribution method
Authors: Achard Christian , Dussap Claude‐Gilles , Gros Jean‐Bernard
Published: June 2004

Expressions that suitably describe the behavior of weak electrolytes in aqueous systems are developed. A new numerical procedure is presented to allow for partial dissociation phenomena and so consider the whole species in solution. It is based on mass balances, the electroneutrality assumption, and dissociation constants of electrolytes. Combining it with a modified UNIFAC electrolyte group‐contribution model based on the solvation concept directly allows calculation of pH, activities, and concentrations of species. The validity and usefulness of the expressions are tested using data for the pH of buffer solutions and complex aqueous mixtures such as fermentation media and liquid foods: pH values accurate to within ±0.05 pH units were obtained.
Heavy metal removal and recovery by contained liquid membrane permeator
Authors: Guha Asim K. , Yun Chang H. , Basu Rahul , Sirkar Kamalesh K.
Published: June 2004

Heavy metals like Cu2+, Cr6+, and Hg2+ were removed successfully from wastewater and concentrated in a strip aqueous solution for recycle using the hollowfiber‐contained liquid membrane (HFCLM) technique. Using cotransport, Cr6+ and Hg2+ present as anions in the feed solution were transferred individually through a liquid membrane containing tri‐n‐octylamine in xylene and concentrated in an alkaline solution on the strip side. The removal efficiency of each heavy metal was studied as a function of the aqueous feed flow rate in an HFCLM permeator. Copper present as cation Cu2+ was removed and concentrated by countertransport using LIX84 in n‐heptane as the liquid membrane. The efficiency of copper removal was studied as a function of feed copper concentration, feed flow rate, strip flow rate, and area ratio between the feed fiber set and strip fiber set. The strip side flow rate did not affect the Cu2+ transfer rate. A theoretical model presented predicts the copper transport rate from the feed solution to the strip solution in an HFCLM permeator with a variable feed to strip‐side membrane area. Both feed aqueous boundary layer and interfacial complexation reaction on the feed side dominate the observed Cu2+ removal process through LIX 84 in n‐heptane for feed concentration levels used 90–500 mg/L. It was verified by providing two times larger liquid‐liquid interfacial area in the feed aqueous side or in the strip aqueous side. The model can be used to design the membrane area required on the feed and strip fiber sides to remove essentially all of the copper from a given wastewater stream.
X‐ray computed tomography studies of gas storage and transport in Devonian shales
Authors: Lu X. , Miao P. , Watson A. T. , Pepin G. P. , Moss R. M. , Semmelbeck M.
Published: June 2004

Devonian shales and other unconventional resources can be highly fractured and may have significant amounts of gas stored by adsorption. Conventional experiments are not well suited for characterizing the properties important for describing gas storage and transport in these media. Here, X‐ray computed tomography scanning is used to determine gas storage in dynamic gas flow experiments on Devonian shale samples. Several important properties are obtained from these experiments, including fracture widths, adsorption isotherms, and matrix porosities and permeabilities.
Computer‐aided molecular design of solvents for separation processes
Authors: Pretel Eduardo J. , López Patricio Araya , Bottini Susana B. , Brignole Esteban A.
Published: June 2004

The search for potential solvents for liquid extraction and extractive distillation is carried out through a group contribution molecular design of solvents (MOLDES) approach. A set of submolecular groups (UNIFAC) is used for the synthesis of molecular structures with desired solvent properties. Submolecular group combination (linking) properties are characterized to ensure the chemical feasibility of the MOLDES generated molecular structures. The size of the combinatorial problem posed by the molecular synthesis procedure is reduced by group selection and by imposing physical and molecular constraints at different stages. Criteria are developed for solvent evaluation and the reliability of the VLE and the LLE UNIFAC parameter tables for solvent screening are compared with experimental data for the recovery of oxychemicals by liquid extraction from dilute aqueous solutions.
Salt effects in extraction of ethanol, 1‐butanol and acetone from aqueous solutions
Authors: Malinowski Janusz J. , Daugulis Andrew J.
Published: June 2004

Experimental studies were performed to assess the effect of salt addition on the extraction of 1‐butanol, ethanol and acetone from dilute aqueous solutions using cyclopentanol, n‐valeraldehyde, tert‐amyl alcohol, and Adol 85NF as extractants. The liquid‐liquid partitioning was examined for a few strong electrolytes in a broad range of concentrations. Results demonstrate that the distribution coefficient and selectivity in systems with reduced water activity resulting from salt addition were markedly increased. These observations can be qualitatively explained on the basis of the hydration theory. It was also determined that strong electrolytes added to the aqueous feed reduced extractant solubility in the aqueous phase, thus contributing to lower solvent losses. The results showed that the extraction efficiency was not significantly affected by increasing salt content beyond a level that reduces the water activity to a value of 0.92.
Probability density estimation using elliptical basis functions
Authors: Johnston Lloyd P. M. , Kramer Mark A.
Published: June 2004

Elliptical basis function (EBF) networks are introduced as a new nonparametric method of estimating probability density functions for process data. Unlike Parzen window density estimators that use identical hyperspherical basis functions, the EBF method uses elliptical basis functions adapted to the local character of the data. This technique overcomes the spikiness problem associated with Parzen windows, where in high dimension, they can fail to produce smooth probability density estimates. The EBF estimator produces valid density functions that converage to the underlying distribution of the data in the limit of an infinite number of training examples. A technique based on statistical cross validation is introduced for evaluating different density estimators. The criterion is a measure of how well the density estimator estimates the density of data not used in the training. The EBF density estimation method and the evaluation technique are demonstrated using several examples of fault diagnosis.
New group contribution method for estimating properties of pure compounds
Authors: Constantinou Leonidas , Gani Rafiqul
Published: June 2004

A new group contribution method for the estimation of properties of pure organic compounds is presented. Estimation is performed at two levels: the basic level uses contributions from first‐order groups, while the next higher level uses a small set of second‐order groups having the first‐order groups as building blocks. Thus, the method provides both a first‐order approximation (first‐order group contributions) and a more accurate second‐order prediction (first‐ and second‐order group contributions). This article discusses methods for prediction of normal boiling point, normal melting point, critical pressure, critical temperature, critical volume, standard enthalpy of vaporization at 298 K, standard Gibbs energy, and standard enthalpy of formation at 298 K. The predictions are based exclusively on the molecular structure of the compound, and the method is able to distinguish among isomers. Compared to the currently‐used methods, this technique demonstrates significant improvements in accuracy and applicability.
Characterizing patterns in plant somatic embryo cultures: Its morphology and development
Authors: Vits Hugo , Chi Chung‐Ming , Hu Wei‐Shou , Staba E. John , Cooke Todd J.
Published: June 2004

While being developed, plant somatic embryos change shape and increase size. An effective kinetic description of growth and development of somatic embryos is important for process scale‐up and optimization. An essential component of such a kinetic description is the developmental characterization of the individual embryos present in culture. Embryo morphological data obtained by image processing techniques were transformed into sizeand size‐independent morphological descriptors. Qualitative relations between the descriptors and geometric properties of the embryos were established to interpret the results. For training, a branch‐and‐bound search technique was used to search for optimal subsets of descriptors, as determined by member clustering and class separability properties evaluated from within‐class and between‐class scatter matrices. In the classification mode, individuals were identified using a voting nearest neighbor classifier. This nonparametric nearest‐neighbor classifier was trained on optimal projections of the feature space established from developmental stage discrimination (branch‐and‐bound algorithm). Using a test population, normal and abnormal embryos and callus were assigned to six morphological classes. The image‐analysis‐based classification was in 80–90% agreement compared to the results obtained through visual classification by an experienced operator.
Dynamic data rectification by recurrent neural networks vs. Traditional methods
Authors: Karjala Thomas W. , Himmelblau David M.
Published: June 2004

Recurrent neural networks are used to demonstrate the dynamic data rectification of process measurements containing Gaussin noise. The performance of these networks is compared to the traditional extended Kalman filtering approach and to published results for model‐based nonlinear programming techniques for data reconciliation. The recurrent network architecture is shown to provide comparable, if not superior, results when compared to traditional methods. The networks used were trained using conventional nonlinear programming techniques in a batch fashion.
Colloidal gel filtration: Experiment and theory
Authors: Shen Charlton , Russel William B. , Auzerais François M.
Published: June 2004

The filtration of colloidal gels, consisting of octadecyl‐coated silica spheres in hexadecane, is examined experimentally using CAT scanning. A number of interparticle strengths are explored, with significant differences in qualitative behavior relative to the filtration of stable dispersions. For stiff gels, the transmission of stresses from the cell wall to the dispersion results in a fracturing phenomenon during consolidation on a length scale substantially larger than the particle size. For more pliant gels, the radial propagation of stress is more local to the wall region and gravitational effects play a prominent role. The existing theory of network consolidation is compared against our experimental results for pliant gels, independent of the form of the constitutive functions for the sedimentation velocity and yield stress. Though our measurements seem consistent with the theory at early times, deviations at later moments question whether a compressive yield stress is actually present.
Computation of phase and chemical equilibria in flue‐gas/water systems
Authors: Luckas Michael , Lucas Klaus , Roth Hans
Published: June 2004

The phase and chemical equilibria of flue‐gas/water systems containing sour gases such as HCl, HF, SO2, SO3, NOx and volatile heavy metal compounds such as Hg, HgCl2, and SeO2 are calculated from thermodynamic standard data using the Gibbs free energy minimization method. The Pitzer/Debye/Hückel equation is used for the activity coefficients of the ions in the aqueous solution. The inhibition of certain oxidation reactions is considered by a proper formulation of the atom matrix. The comparison of the calculated equilibrium values to experimental data from a coalfired power plant show that concentrations of most pollutants at the outlet of the absorbers are close to the equilibrium values of one single theoretical stage. The extension of the Gibbs free energy minimization to multistage countercurrent absorbers gives the concentration profiles of various components.
Mass‐transfer mechanisms for zeolite ion exchange in wastewater treatment
Authors: Robinson S. M. , Arnold W. D. , Byers C. H.
Published: June 2004

In spite of the increasing commercial use of zeolites for binary and multicomponent ion exchange, understanding of the basic mass‐transfer processes associated with multicomponent zeolite systems is quite limited. This study evaluates Na‐Ca‐Mg‐Cs‐Sr ion exchange from an aqueous solution using a chabazite zeolite. Mass‐transfer coefficients are determined from experimental batch‐reactor data for binary and multicomponent systems. The experimental data indicate that diffusion through the microporous zeolite crystals is the primary diffusional resistance. Macropore diffusion also significantly contributes to the mass‐transfer resistance. Various mass‐transfer models are compared with the experimental data to determine values for intraparticle diffusivities. Effective diffusivities obtained accurately predict experimental data using a variety of models. Only the model accounting for micropore and macropore diffusion occurring in series accurately predict multicomponent data using diffusivities from the binary system. Liquid and surface diffusion both contribute to macropore diffusion. Surface and micropore diffusivities are concentration‐dependent for the system of interest.
Mean velocity field relative to a Rushton turbine blade
Authors: Stoots Carl M. , Calabrese Richard V.
Published: June 2004

The 3‐D flow field relative to a rotating Rushton turbine blade is acquired for fully turbulent tank conditions by synchronizing LDA measurements with the output of a shaft‐mounted encoder. This makes it possible to capture the impeller stream velocity field, including the details of the voritices behind the blades. Mean velocity data at three impeller speeds show the extent of periodicity and the axes and structure of the vortices. Pumping capacities are determined and it is shown that the radial jet is a consequence of fluid entrainment into the vortices. Deformation rates based on gradients of mean velocity are calculated. Close to the blade they can exceed impeller rotational frequency by as much as two orders of magnitude. To a first approximation, the normalized mean flow field is independent of impeller speed.
Reactor operating procedures for startup of continuously‐operated chemical plants
Authors: Verwijs J. W. , Kösters P. H. , Van Den Berg H. , Westerterp K. R.
Published: June 2004

Rules are presented for the startup of an adiabatic tubular reactor, based on a qualitative analysis of the dynamic behavior of continuously‐operated vapor‒ and liquid‐phase processes. The relationships between the process dynamics, operating criteria, and operating constraints are investigated, since a reactor startup cannot be isolated from an entire plant startup. Composition control of the process material is critical to speed up plant startup operations and to minimize the amount of offgrade materials. The initial reactor conditions are normally critical for a successful startup. For process conditioning, a plant should have an operating mode at which the reactor can be included in a recycle loop together with its feed system and downstream process section. Experimental data of an adiabatic tubular reactor startup and thermal runaway demonstrate some operational problems when such an intermediate operating stage is missing. The derived rules are applied to an industrial, highly heat‐integrated reactor section, and the resulting startup strategy is summarized in an elementary‐step diagram.
Experimental measurements of pressure waves generated by impulsive heating of a surface
Authors: Brown Matthew A. , Churchill Stuart W.
Published: June 2004

The first quantitative, reproducible experimental results are presented for the compressive wave generated in a gas by a rapid rise in the temperature of a bounding solid surface. When a resistive‐capacitive electrical circuit rapidly heats a thin foil constituting one end of a closed polyacetal cylindrical tube to a high temperature, the amplitude of the initial traveling peak in pressure is proportional to the maximum rise in temperature of the heated surface and depends critically on the heating rate. This amplitude is twice as high for argon as for helium, and is intermediate and essentially the same for nitrogen and air. For all conditions, the wave celerity is slightly greater than the adiabatic acoustic velocity. The waves have a very sharp front and a long region of decay, which is contradictory to the sinusoidal waves postulated by Rayleigh and the nearly symmetrical ones predicted by all prior numerical solutions as well as by the asymptotic solution of Trilling. Such compressive waves and their reflections increase the transient heating rate of a confined gas, may produce unsuspected and unwanted disturbances in otherwise static systems, and offer a possible means of remote detection of excursions in the temperature of a surface.
Direct‐contact steam condensation with simultaneous noncondensable gas absorption
Authors: Bontozoglou Vasilis , Karabelas Anastasios J.
Published: June 2004

Experimental results are reported on simulataneous heat transfer and gas dissolution during the direct‐contact condensation of steam on water in the presence of CO2. A column filled with structured packing is used as condenser with the water in counterflow with the steam/CO2 mixture. The region along the column where the bulk of condensation takes place is controllable by suitable choice of the steam/water ratio. Measured local heat‐transfer coefficients change by roughly an order of magnitude from the bottom to the top of the column. The extent of CO2 dissolution in the water/condensate under most conditions is unexpectedly high and depends strongly on the exit liquid temperature. A driving force based on the interfacial CO2 concentration, not the overall concentration difference used in conventional absorption operations, is suggested as more appropriate to describe the phenomenon. The data are complemented with preliminary results from a computational model based on the integration along the column of local heat‐ and mass‐transfer rates.
Flow regimes of the three‐phase circulating fluidized bed
Authors: Liang W. G. , Wu Q. W. , Yu Z. Q. , Jin Y. , Bi H. T.
Published: June 2004

Gas‐solids circulating fluidized beds have been successfully used in catalytic cracking of heavy oil, coal combustion, and some metallurgical and physical processes (Grace, 1990). Gas‐liquid‐solids fluidized beds are operated mainly in conventional fluidization regimes without solids circulation or in the transport regime with low solids holdups (less than 5%) (Fan, 1989). A circulating/fast fluidization regime, however, has not been studied. A three‐phase circulating fluidized bed has several potential applications in biochemical and chemical processes. Three‐phase fluidized‐bed bioreactors generally use light and small particles (Berk et al., 1984). Circulating operation can promote solids mixing and increase product throughput per unit bed cross section, while high shear stress can promote biofilm renewal (Pirozzi et al., 1990). In three‐phase hydrotreating reactors, solids catalysts lose their activity due to the deposit of metal and coke on the surface. Circulating operation not only regenerates deactivated catalyst continuously using accompanying downcomers but also transfers heat to and from the reactor. This article discusses the flow regimes of the three‐phase circulating fluidized bed.