bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extraction of naphthalene by block copolymer surfactants immobilized in polymeric hydrogels
Authors: Calvert Tammy L. , Phillips Ronald J. , Dungan Stephanie R. 
Published: June 2004

AbstractGel/micelle materials, comprising hydrogels containing block copolymer micelles, have the potential to be very useful in a variety of extraction and controlled release applications. It is demonstrated that block copolymer surfactants can be immobilized in calcium alginate gels and that the resulting composite material preferentially solubilizes the model hydrophobic solute naphthalene. Five different polyethylene oxide‐polyropylene oxide‐polyethylene oxide triblock copolymer surfactants are considered, and the qualitatively different properties exhibited are interpreted in light of the properties of these surfactants in solution. Alginate gel concentrations of 22.5 and 52.5 g/L and surfactant concentrations ranging from 20.4 to 136 g/L are considered. The data indicate that micelles can be permanently immobilized for purposes of extraction or controlled release and that the extent of solute uptake or release can be altered by varying gel and surfactant concentration and the type of surfactant employed.
Instability of distillation columns
Authors: Jacobsen Elling W. , Skogestad Sigurd 
Published: June 2004

AbstractAs recently recognized, distillation columns, operating with reflux and boilup as independent inputs, may have multiple steady‐state solutions, even in the ideal binary case. Two fundamentally different sources may cause the multiplicity, and in both cases some operating points are found to be unstable. This article provides evidence for the instability and discusses the effect of operating conditions on stability. Increasing the internal flow rates increases the probability of instability; when flows other than reflux and boilup are used as independent inputs, an operating point may become unstable if the level control is not sufficiently tight. In this case, a limit cycle, usually stable, appears as the steady state goes unstable.
A continuous dilution method for phase diagram determination
Authors: Hartounian H. , Koetitz J. A. , Kaler E. W. , Sandler S. I. 
Published: June 2004

AbstractA relatively simple continuous dilution method with on‐line spectrophotometric measurement has been used to determine the phase transition boundaries of aqueous two‐phase polymer systems. The observed range of compositions over which the phase transition occurs is dominated by the polydispersity of the polymers, but also is a function of the dilution path followed. The binodal curve obtained by the continuous dilution method agrees well with the results obtained by the traditional method of phase equilibration, separation and analysis of liquid chromatography, which is slower and requires more expensive equipment.
Diffusion‐convection‐reaction in multicomponent mixtures
Authors: Guida Vincenzo , Ocone Raffaella , Astarita Gianni 
Published: June 2004

AbstractWe analyze the mathematical structure of a multicomponent reactive mixture in a plug flow reactor with axial diffusion. Quasilinearity of the kinetic equation assuming “uniformity” does not carry over to the second‐order equations when diffusion is considered and a perturbation expansion method needs to be developed. Perturbation around the limit of a CSTR is regular, which leads to nonhomogeneous second‐order differential equations containing no unknown kinetic term, so that the procedure cascades down to the solution of the CSTR problem. Perturbation around the PFR problem is singular, but the inner (boundary layer) solution is easy. The outer solution leads to a series of integro‐differential equations, which can be reduced to complete Volterra integral equations of the second kind; these are known to admit unique solutions. A formal approach to finding these solutions is discussed.
Effect of diffusion on heterogeneous ethylene propylene copolymerization
Authors: Hoel E. L. , Cozewith C. , Byrne G. D. 
Published: June 2004

AbstractIn heterogenous olefin polymerization with Ziegler catalysts, the influence of monomer mass transport in the growing granule on polymer properties has been extensively modeled, but it has not been possible to clearly establish the importance of diffusion experimentally since the multisited nature of most Ziegler catalysts can produce similar effects. In this study, ethylene‐propylene copolymers were made with single‐sited metallocene catalysts by slurry polymerization in liquid monomers. These copolymers had a relatively narrow molecular weight distribution with a composition distribution (CD) broader than expected for a single‐site catalyst. Data analysis indicates that mass‐transfer limitations in the polymer particles are the most likely explanation for the observed results. For amorphous copolymers, a diffusion/reaction model could predict CD breadth in good agreement with experimental data, but for semicrystalline polymers the model was inaccurate. We postulate that model inadequacies are due to radial gradients in monomer diffusivity during polymerization which the model does not account for.
Effect of kinetics on residue curve maps for reactive distillation
Authors: Venimadhavan Ganesh , Buzad George , Doherty Michael F. , Malone Michael F. 
Published: June 2004

AbstractA class of models is derived for studying the effects of chemical kinetics on residue curve maps for reactive distillation. Activity‐based rate and phase equilibrium expressions provide an accurate and thermodynamically consistent description of composition changes in nonideal, reacting vapor‐liquid mixtures. For certain strategies of operation, which dictate the rate of product removal, the model equations are nonautonomous, leading to unusual dynamic behavior. However, for a certain special product removal policy, the effects of kinetics can be described by a single parameter, the Damköhler number, which measures the rate of reaction relative to product removal. For small values of the Damköhler number, the nonreactive simple distillation residue curve map is recovered and the singular points are the pure components and azeotropes in the nonreactive mixture. A bifurcation analysis shows the deformation and, in some cases, the disappearance of these singular points as the Damköhler number is increased until the equilibrium reactive residue curve map is recovered at large values. This bifurcation analysis reveals the limitations of the equilibrium analysis. A model problem for the reactive distillation of methyl tertbutyl ether from isobutene and methanol is solved.
Influence of dynamic interfacial properties on droplet breakup in simple shear flow
Authors: Janssen J. J. M. , Boon A. , Agterof W. G. M. 
Published: June 2004

AbstractThe breakup of droplets in an inhomogeneous flow is the key to emulsification. Frequently, the local flow experienced by the drops is a (quasi‐) simple shear flow. The breakup of droplets in a steady, simple shear flow in the absence of emulsifiers has been studied extensively. In the presence of emulsifiers, the droplet interface may acquire viscoelastic properties, which are important in the prevention of coalescence, but their influence on droplet breakup has not been established solidly. This article reports on a phenomenological approach, which links the droplet breakup dynamics to the interfacial viscoelasticity, identifying the latter with the elasticity modulus of a deforming planar interface. Over a viscosity ratio range of three decades, the results have been found to agree with the model, which uses only independently known quantities derived from equilibrium interfacial tension properties.
Experimental study on a four‐bed PSA air separation process
Authors: Chiang A. S. T. , Chung Y. L. , Cheng Chao‐Wen , Hung Te‐Hsien , Lee T. Y. 
Published: June 2004

AbstractA 200‐s PSA cycle involving both pressure equalization and product backfill steps has been experimentally studied on a four‐bed system, where LINDE 5 A zeolites were used as the adsorbent to separate oxygen from air. This cycle is operated under a pressure ratio of 4.3. During the experiment, the pressure history and flow rates, as well as the concentration of the product stream have been continuously monitored. This is the first time detailed experimental data on a four‐bed system are presented. Under favorable conditions, this system produces better than 90% oxygen at a recovery of 17%. For the low‐pressure ratio, such a recovery could not have been achieved without the pressure equalization step and the reduced purge operation. Recovery and throughput, however, are not as high as one would expect from a linear local equilibrium model. The self‐broadening effect of the purge wave has been identified as the major cause of underperformance.
Strings of liquid beads for gas‐liquid contact operations
Authors: Hattori Kenji , Ishikawa Mitsukuni , Mori Yasuhiko H. 
Published: June 2004

AbstractA novel device for gas–liquid contact operations is proposed to feed a liquid onto wires (or threads) hanging down in a gas stream is proposed. The liquid disintegrates into beads strung on each wire at regular intervals; if the wire is moderately wettable, a thin film forms to sheathe the wire, thereby interconnecting the beads. Since the beads fall down slowly, which possibly renews the film flowing down even more slowly a sufficient gas‐liquid contact time is available even in a contactor with considerably limited height. An approximate calculation method is developed for predicting the variation in the temperature effectiveness for the liquid (the fractional approach of the liquid exit temperature to the gas inlet temperature) with the falling distance, assuming an applicability of strings‐of‐beads contactors to thermal energy recovery from hot gas streams.
Phenomenological model for dispersed bubbly flow in pipes
Authors: Nikitop Dimitris E. , Michaelides Efstathios E. 
Published: June 2004

AbstractAn analytical approach to the problem of steady‐state, axisymmetrically disperesed, bubbly flow in pipes based on a zero equation turbulence model is discussed. The formulation incorporates recent experimental observations and introduces the effect of bubble size in a rudimentary way. The two‐phase mixture is modeled as a variabledensity single fluid assuming an empirical void distribution family. The turbulent shear stress is formed from the contributions of both the velocity and density variation, and the solution of the resulting Reynolds‐type equation yields the velocity profile of the flow. Predicted void fraction and velocity distributions agree well with experimental measurements. The main objective of the model is to predict the friction multiplier with minimal computational effort. The velocity profiles of this model agree reasonably well with experiments. Predictions for the friction multiplier are compared to six known and widely used correlations, as well as to experimental data. All the correlations severely underpredict the friction multiplier in the disperesed bubbly flow regime, while the results of our model agree well with the measurements, within the range of its validity.
Three‐phase mass transfer: Improved pseudo‐homogeneous model
Authors: Nagy Endre , Moser Anton 
Published: June 2004

AbstractThis new pseudo‐homogeneous model describes the absorption rate in the presence of dispersed second liquid phase or solid catalyst particles. In contrast to previous models, it considers the diffusion process and chemical reaction inside the dispersed phase. The absorption rate is defined in the case of first‒ and zero‐order reactions for both continuous and dispersed phases. The concentration of particles from the bulk phase to the gas‐liquid boundary layer replaces the initial concentration to the balance equation for the liquid boundary layer at the gas‐liquid interface. For mass transport in the bulk phase, steady‐state film theory, while in the gas‐liquid boundary layer, unsteady‐state film‐penetration theory is applied. The effect of mass‐transfer and reaction kinetic parameters, as well as the particle size on the absorption rate, is described as well as the simulated data verified by previous experimental studies.
Production rate of an isotachic train in displacement chromatography
Authors: Zhu Jie , Guiochon Georges 
Published: June 2004

AbstractThe shock layer theory permits the derivation of an equation relating the thickness of the shock layer or mixed zone between successive bands in a fully developed isotachic train and the experimental parameters (mobile‐phase flow velocity, concentration and retention factor of the displacer, column length, and average particle size of the packing material). It also permits the calculation of the amount of each product contained in this mixed zone. The main assumptions made are the use of the competitive Langmuir isotherm, the identity of axial dispersion coefficients, and the mass‐transfer rate constants for different components. These equations make it possible to calculate the production rate and recovery yield achieved with an isotachic train, and to optimize the experimental conditions for maximum production rate. The shock layer thickness increases rapidly and the production rate decreases sharply when α‐1 tends toward 0. In agreement with previous experimental results, there are well defined optimum flow velocity and displacer concentrations which vary depending on feed components. This theory permits an easy access to the optimization of these parameters.
Use of optical probes to characterize bubble behavior in gas‐solid fluidized beds
Authors: Mainland Marlene E. , Welty James R. 
Published: June 2004

AbstractOptical probes are used to study gas‐solid fluidized‐bed hydrodynamics. The probes each consisting of a light source and photodetector separated by a gap are suitable for use at combustion‐level temperatures. The methodology to process the signal for calculation of bubble properties such as bubble frequency, local bubble residence time, bubble velocity, pierced length, bubble size, and visible bubble flow is presented. The signal processing technique is independent of bed operating conditions. The probe signal processing methodology is validated by comparing calculated bubble properties based on the probe signal with properties observed on videotapes of a 2‐D bed.
Monolith froth reactor: Development of a novel three‐phase catalytic system
Authors: Crynes Lawrence L. , Cerro Ramon L. , Abraham Martin A. 
Published: June 2004

AbstractThe monolith froth reactor, involving two‐phase flow and a monolith catalyst, is developed. The flow within monolith channels, consisting of trains of gas bubbles and liquid slugs, is produced by forming a two‐phase froth in a chamber immediately below the bottom of the monolith. The froth then flows upward into the monolith channels through pressure forces, which differs from previous methods since it may be carried out for a commercial‐scale reactor. Because the liquid film which develops between the gas phase and the surface of the catalyst is extremely thin, two‐phase flow within a monolith can provide reaction rates which are near their intrinsic values. Catalytic oxidation of aqueous phenol over copper oxide supported on γ‐Al2O3 is used as a model reaction for investigating reactor performance. Generation of a froth is confirmed by visual inspection; the average bubble size is approximately that predicted by a force balance. The effect of externally controllable process variables (liquid and gas flow rates, temperature, and pressure) on the rate of phenol oxidation was investigated. Reaction rate increases with temperature or pressure increase and decreases with gas flow rate increase, achieving a maximum with respect to liquid flow rate. The activation energy calculated from the apparent reaction rate measured in the monolith froth reactor is similar to that of intrinsic value, suggesting minimal mass‐transfer limitations.
Model for colloidal fouling of membranes
Authors: Bacchin P. , Aimar P. , Sanchez V. 
Published: June 2004

AbstractA proposed theoretical model describes colloids deposition on a membrane surface accounting for surface interactions. A mass‐transfer equation links the deposition rate to hydrodynamic conditions (permeation and tangential flow through a boundary layer thickness, δ) and to physicochemical properties of the suspension (diffusion, D, and potential barrier between particles, VB). This equation predicts the existence of a critical flux, Jcrit, for ultrafiltration, reverse osmosis, or microfiltration of large‐size colloids as:

Some of the trends observed when processing protein solutions are explained by this model. Previous experimental data for various colloids or our data with a clay suspension in the presence of electrolytes are also compared to predictions of our model. It explains the “flux anomaly” for particle sizes between 10 nm and 1 μm.
Protein transport in ultrafiltration hollow‐fiber bioreactors
Authors: Patkar Anant Y. , Koska Jürgen , Taylor David G. , Bowen Bruce D. , Piret James M. 
Published: June 2004

AbstractA 1‐D model, which neglects radial variations, describes the hydrodynamics of cell‐free ultrafiltration hollow‐fiber bioreactors (HFBRs) and the transport of highmolecular‐weight proteins trapped in the extracapillary space (ECS). The profiles of radially‐averaged protein concentrations predicted by this model are identical to those obtained using a model with radial variations. The model predictions agree well with axial profiles of bovine serum albumin (BSA) and human transferrin concentrations measured in transient and steady‐state experiments. The validated model explores the influence of cell culture operating conditions on HFBR protein transport. Increasing protein loading decreases BSA and transferrin polarization in HFBRs operated with unidirectional lumen flow. A relationship developed predicts the protein loading needed to ensure a nonzero steady‐state protein concentration throughout the ECS. This critical protein loading depends only on the lumen pressure drop and the ECS protein osmotic pressure. Periodic reversal of the lumen flow direction also decreases protein polarization. The influence of the flow‐direction switching time and membrane permeability on the ECS protein distribution is investigated.
New look at wave analogy for prediction of bubble terminal velocities
Authors: Maneri Charles C. 
Published: June 2004

AbstractThe analogy between waves on the surface of an infinite fluid and bubbles rising in low‐viscosity fluids of infinite extent, originally proposed by Mendelson for 3‐D bubbles, has been used to predict the terminal velocity of plane bubbles. In terms of its terminal velocity, a plane bubble rising in a rectangular duct of small aspect (spacing‐to‐width) ratio behaves as if it were a 3‐D bubble rising in an infinite medium as long as the end walls (the walls in the widthwise direction) are sufficiently far apart. As the end walls are moved toward each other, a wall effect is found to exist. A general expression for the terminal velocity of a bubble of any size rising in a rectangular duct including this wall effect is also developed based on the wave analogy and shown to compare well with existing data.
Agglomeration during precipitation: II. Mechanism deduction from tracer data
Authors: Ilievski D. , Hounslow M. J. 
Published: June 2004

AbstractA novel approach using a 2‐D population balance model is developed and applied to the analysis of experimental tracer crystal data. This approach is effective in discriminating among various functional forms of agglomeration kernel and enables estimation of the agglomeration kinetics. At present, the analysis is restricted to three simple agglomeration kernels and shows that the size‐independent kernel best describes the agglomeration of Al(OH)3 crystals during precipitation in caustic aluminate solutions. This agrees with the findings of Ilievski and White (1994). Estimates of the agglomeration kinetic parameters from the tracer data agree well with the experimentally observed values.
Solvent effect on adsorption phenomena in reversed‐phase liquid chromatography
Authors: Miyabe Kanji , Suzuki Motoyuki 
Published: June 2004

AbstractThe effect of solvent and mobile‐phase composition on adsorption characteristics in liquid‐phase absorption is studied. Comparing experimental adsorption data for several organics in both gas‐ and liquid‐phase systems confirms that adsorption equilibrium constant K and isosteric heat of adsorption Qst are smaller than those in corresponding gaseous systems. The logarithm of K almost linearly increases as methanol composition decreases. Solvophobic theory applied quantitatively analyzes these solvent effects. Estimation methods for three parameters influence calculation results: solvent effects on K can be quantitatively analyzed; the adsorbability of adsorbates can be estimated from the value of ΔGsolv for each homologue in a reversed‐phase liquid chromatographic system; and the solvent effect on Qst cannot be satisfactorily interpreted. It is, however, confirmed that Qst is influenced by a solvent and an apparent small value is observed in liquid‐phase adsorption.
Chromatographic study on liquid‐phase adsorption on octadecylsilyl‐Silica Gel
Authors: Miyabe Kanji , Suzuki Motoyuki 
Published: June 2004

AbstractAdsorption characteristics of reversed‐phase liquid chromatography and influence of solvent composition on the characteristics are studied by the chromatographic method and the moment analysis. Adsorption equilibrium constant increases by adding hydrophobic increments into adsorbate molecules. Contributions of fluid‐to‐particle mass transfer and intraparticle diffusion to mass‐transfer resistance in the octadecylsilyl‐silica gel (ODS) column are almost equally great. Surface diffusion is dominant for the intraparticle diffusion in ODS. The logarithm of the surface diffusion coefficient linearly increases with an increases with an increase in methanol fraction in the range from 40 to 100 vol. %. In liquid‐phase adsorption, activation energy of surface diffusion is greater than the isosteric heat of adsorption and both increase when methanol fraction decreases in the range from 40 to 100 vol. %. An empirical correlation based on experimental data proposed estimates surface diffusion coefficients from physical properties of adsorbates.
Sol‐gel preparation and properties of Alumina adsorbents for gas separation
Authors: Deng S. G. , Lin Y. S. 
Published: June 2004

AbstractThe sol‐gel method is applied to prepare Cu+ or Ag+ containing alumina adsorbents which have potential application in purification or separation of carbon monoxide or olefins containing gases. Wet impregnation and sol‐solution mixing methods are used to incorporate the active species into the sol‐gel derived γ−alumina support. These alumina adsorbents have the characteristics of large specific surface area, high dispersion of active specie on the grain surface, and mesopore size with a uniform pore size distribution. The gas chromatographic technique determines the carbon monoxide adsorption properties on these alumina adsorbents. Adsorption equilibrium constants, adsorption rate constants, axial dispersion coefficients, heat of adsorption, and adsorption activation energy are determined from GC response peaks by using the moment method. The alumina adsorbents prepared by the solgel method appear to be superior to the similar adsorbents prepared by other methods.
Process analysis in the complex domain
Authors: Sridhar L. N. , Lucia Angelo 
Published: June 2004

AbstractAnalytical support for recent numerical work in process simulation in the complex domain is discussed. In particular, the observation that nondegenerate singular points are saddle points of the two‐norm on the complex domain is proved rigorously and its numerical implications are discussed. The isothermal isobaric flash problem admits only real‐valued two‐phase solutions, provided that the feed conditions are real. Both single‐ and multivariable chemical process examples illustrate the theoretical results.