bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymeric materials formed by precipitation with a compressed fluid antisolvent
Authors: Dixon David J. , Johnston Keith P. , Bodmeier Roland A. 
Published: June 2004

AbstractPolymer microspheres and fibers are formed with a versatile new process, precipitation with a compressed fluid antisolvent. By spraying a 1 wt. % polystyrene in toluene solution into CO2 through a 100‐μm nozzle, microspheres are formed with diameters from 0.1 to 20 μm as the CO2 density decreases from 0.86 to 0.13 g/cm3. The uniform submicron spheres produced at high CO2 density are due in part to the rapid atomization produced by the large intertial and low interfacial forces. Fibers, with and without microporosity, are obtained at higher polymer concentrations where viscous forces stabilize the jet. The effect of CO2 density and temperature on the size, morphology and porosity of the resulting polymeric materials is explained in terms of the phase behavior, spray characteristics, and the depression in the glass transition temperature.
Stability of multislit devolatilization of polymers
Authors: Ianniruberto Giovanni , Maffettone Pier Luca , Astarita Gianni 
Published: June 2004

AbstractSlit devolatilization of polymers has been considered in a recent work by Maffettone et al. (1991), who have presented a successful model for single slit devolatilization. In this article, the stability of operation of a realistic multislit process is considered. It is shown that the flow rate per slit which can be stably operated may be significantly less than the optimal one for single slit operation. Stability improves as the concentration of volatiles in the feed solution decreases. The non‐Newtonian character of the feed solution at high shear rates is discussed in qualitative terms.
2‐Chlorophenol oxidation in supercritical water: Global kinetics and reaction products
Authors: Li Ruokang , Savage Phillip E. , Szmukler David 
Published: June 2004

Abstract2‐Chlorophenol (2CP) was oxidized in near‐critical and supercritical water in a high‐pressure plug‐flow reactor. The global kinetics for 2CP disappearance were described by a rate law that was 0.88±0.06 order in 2CP, 0.41±0.12 order in O2, and 0.34±0.17 order in water. The activation energy was 11.0±3.8 kcal/mol, and the Arrhenius pre‐exponential factor was 102.0±1.2 M−0.63 S−1. The uncertainties represent 95% confidence intervals. The products of 2CP oxidation included CO, CO2, HCl, other chlorophenols, chlorohydroxybenzaldehydes, dichlorophenoxyphenols, dichlorobiphenols, and chlorinated dibenzodioxins and dibenzofuran. The molar yields of the organic products were determined for a set of experiments at 380°C and 278 atm. The most abundant products were 2CP dimers such as dichlorophenoxyphenols and dichlorobiphenols, and the highest yield observed for any individual product was 0.6%. Although the yields of these products were low, their selectivities were high. For example, at 3.6 s, the shortest residence time studied under these conditions, about 50% of the carbon in the 2CP that reacted appeared in 2CP dimers, 18% appeared as CO2, and the balance (32%) was presumably in single‐ring and ring‐opening products. A reaction pathway analysis using the Delplot methodology revealed that the evolution of products from 2CP oxidation in supercritical water was consistent with a reaction network comprising two parallel primary reactions. One primary reaction path led to dichlorophenoxyphenols and dichlorobiphenols whereas the second primary reaction led to single‐ring and ring‐opening products. The 2CP dimers were convereted to single‐ring and ring‐opening products, which were, in turn, ultimately oxidized to CO2.
Fractionation of suspensions using synchronized ultrasonic and flow fields
Authors: Mandralis Zenon I. , Feke Donald L. 
Published: June 2004

AbstractA fractionation method for fine‐particle suspensions using resonant ultrasonic fields coordinated with bidirectional fluid flow fields is described. The basis for the separation is differences in the speed of response of particles to the imposition of a resonant acoustic field. As such, the method is sensitive to the particle size and the acoustic contrast between the solid particles and their suspending fluid. Both batch and continuous fractionation processes can be developed from a two‐step acoustic‐flow cycle. An analytical model was constructed from equations that describe the trajectories of particles as they respond to the acoustic and flow fields. Model predictions indicate how the fractionation can be controlled through choice of cycle parameters. The method was implemented experimentally. Results for the fractionation of 325‐mesh polystyrene spheres indicate that sharp fractionations can be achieved. The experimental results are generally in agreement with the model predictions.
Liquid‐liquid phase separations in aqueous solutions of globular proteins
Authors: Vlachy V. , Blanch H. W. , Prausnitz J. M. 
Published: June 2004

AbstractA simple statistical‐mechanical theory, known as the random‐phase approximation, is applied to study liquid‐liquid phase separations in solutions of globular proteins. Phase separation may be induced by addition of nonionic polymer or/and ordinary electrolytes. In this analysis, the osmotic‐attraction mechanism, whereby the depletion of “solvent” particles between two proteins causes an attractive force, is primarily responsible for phase separation. For one‐component models of protein solutions, the theory yields simple algebraic expressions for the equation of state and for the chemical potential of the protein. This analytical theory describes the observed solubility behavior of proteins, including the effect of protein and polymer size, protein charge and concentration, and concentration of simple electrolytes.
Modeling of reverse osmosis in the presence of strong solute‐membrane affinity
Authors: Mehdizadeh H. , Dickson J. M. 
Published: June 2004

AbstractModeling of reverse osmosis in the presence of strong solute‐membrane affinity has always been a challenge due to the complexity of the solute‐solvent‐membrane interactions and the resultant effect on membrane performance. Most transport models, including all models treating membranes as nonporous and those based on irreversible thermodynamics, are unable to describe or to predict all of the phenomena associated with this case. Recently, the modified surface force‐pore flow model has been derived and used to describe the performance of reverse osmosis membranes for solutes which are rejected from the membrane. In the present work, this model is extended to a more general form which can describe the solute‐membrane affinity case. For illustration, the extended model, with five adjustable parameters, is used to describe the performance for cellulose acetate membranes and dilute aqueous solutions of toluene, cumene, and p‐chlorophenol (data from literature). The model is reasonably consistent with the data. Simulation results of the extended model are also shown.
Process simulation in the complex domain
Authors: Lucia Angelo , Guo Xinzhou , Wang Xiaofeng 
Published: June 2004

AbstractThe asymptotic behavior of fixed‐point methods in the complex domain is studied. Both direct substitution and Newton's method exhibit stable periodic and aperiodic behavior from real‐ or complex‐valued starting points. Moreover, multiple stable periodic orbits can exist for direct substitution. Traditional trust region (or dogleg) methods, on the other hand, often terminate at singular points, which correspond to nonzero‐valued saddlepoints in the least‐squares function that can be arbitrarily far from a solution. Furthermore, the basins of attraction of these singular points are usually dispersed throughout the basin boundaries in the complex domain, clearly illustrating that singular points (via the dogleg strategy) also attract either real‐ or complex‐valued starting points.In light of this, an extension of the dogleg strategy to the complex domain, based on a simple norm‐reducing, singular point perturbation, is proposed. This extended trust region method removes all forms of nonconvergent behavior and always terminates at a fixed point, even from critical point (worst‐case) initial values. Many numerical results and geometric illustrations using chemical process simulation examples are presented.
Reactions between calcium oxide and flue gas containing sulfur dioxide at lower temperatures
Authors: Hartman M. , Trnka O. 
Published: June 2004

AbstractAn experimental study has been performed of the reactions occurring when the reactive particles of calcium oxide are exposed to sulfur dioxide bearing flue gas. Using a differential, fixed‐bed reactor, kinetic measurements have been made in the temperature range of 170 and 580°C. A relatively simple correlation based on the amassed data has been proposed. This correlation allows the estimation of the reaction rate as a function of temperature, conversion of the solids and concentration of sulfur dioxide in the gas phase. The proposed rate law equation makes it possible to predict in a straightforward manner the rate of sorption which would be required to design the performance of a desulfurization unit.
Computer simulation of molecular fluid mixtures: Results and two new one‐fluid models
Authors: Sowers Gary M. , Sandler Stanley I. 
Published: June 2004

AbstractMonte Carlo simulation results for binary mixtures of diatomic molecules with spheres, diatomic molecules of different bond lengths, and triatomic molecules with spheres, all interacting with the site‐site Lennard‐Jones potential, were obtained at three different volume ratios and a range of densities and compositions. We report the configurational internal energy of the mixture and of the 1‐1, 1‐2 and 2‐2 pairs, and the compressibility factors at 195 state points. The site‐site correlation functions also computed are available from the authors. Equations of state derived previously (Sowers and Sandler, 1991, 1992) for pure site‐site Lennard‐Jones fluids from a combination of perturbation theory and a three‐parameter corresponding states principle are extended to mixtures using simple one‐fluid mixing rules. These simple mixing rules allow us to make satisfactory predictions of the compressibilities computed from simulation without the use of binary interaction parameters. We also show that the effect of composition on the perturbation free energy βAp/N not accounted for by one‐fluid mixing rules is quite small, and therefore a more complicated mixing rule is not necessary in our equations of state for the mixtures studied.
Solute retention in electrochromatography by electrically induced sorption
Authors: Rudge S. R. , Basak S. K. , Ladisch M. R. 
Published: June 2004

AbstractColumn chromatography and electrophoresis are combined in electrochromatography, where an electric potential is applied to a chromatography column in the axial direction. These studies utilized a dextran gel stationary phase and an eluent of low ionic strength, which were chosen to minimize electric current and therefore column heating and undesirable dispersion effects. The gel, with a small ion exchange capacity of several microequivalents per mL, turned out to be more conductive than the eluent and was able to concentrate macromolecules in the presence of combined electric and flow fields. The model presented describes solute retention due to electrically induced concentration polarization of solute on the resin surfaces, as well as electrophoresis in the mobile and stationary phases. The polarization effect explains differences between retention of high‐molecular‐weight solutes with exclusion coefficients of less than 1 and that of a charged low‐molecular‐weight solute, which is hypothesized to pass through the gel matrix in the presence of an electric field and does not experience concentration polarization. It also shows the application of this effect for protein separation in a liquid chromatography system with a superimposed electric potential.
Continuous electrochemically modulated complexation separations process
Authors: Jemaa N. , Walls H. J. , Noble R. D. , Wedman D. E. , Koval C. A. 
Published: June 2004

AbstractA continuous electrochemically modulated complexation (EMC) process was devised to extract and concentrate a class of heterocyclic nitrogen compounds. This design is composed of flow‐through electrolysis cells for redox modulation and cycling of the complexing agent and hollow‐fiber membrane modules for phase contacting. The extent of both extraction and concentration was found to depend mainly on the magnitude of the distribution coefficients for both steps. Experimental results and modeling of this continuous EMC process are reported, as well as potential applications for this process for other separations.
Dense‐gas solvent‐solute clusters at near‐infinite dilution: EPR spectroscopic evidence
Authors: Carlier Claude , Randolph Theodore W. 
Published: June 2004

AbstractThe nitrogen hyperfine splitting constant of ditertbutyl nitroxide radicals was measured with electron paramagnetic resonance spectroscopy at near‐infinite dilution in near‐critical and supercritical ethane, as well as in liquid propane, liquid isobutane, and several nonhydrogen bonding liquid solvents. While the measurements in the liquids are described well by the theory of McRae, large deviations from the liquid behavior are observed in supercritical ethane. The deviations are used as a measure of the effective local density of the solvent around the solute. At the two temperatures investigated, Tr = 1.009 and Tr = 1.084, the local density enhancement, defined as the ratio of local to bulk densities, exhibits a maximum of about 3 occurring around 1/2 the critical density. The maximum is removed well from the critical density, where the maximum of the isothermal compressibility is observed. Local density enhancements are short‐range effects and do not correlate well with the development of long‐range critical phenomena. Local density enhancement data in ethane are compared with the prewetting transition that has been observed in nearcritical ultrapure argon.
Eddy viscosity and velocity distribution in turbulent pipe flow revisited
Authors: Datta Ravindra 
Published: June 2004

AbstractAn algebraic expression involving three universal constants is proposed for the eddy momentum diffusivity in fully developed turbulent pipe flow that adequately simulates its variation throughout the pipe cross‐section. The model permits analytical integration to provide a single universal correlation that, unlike other available expressions, smoothly and accurately describes the entire turbulent velocity distribution from the inner region in the immediate vicinity of the wall all the way to the core region near the pipe axis and compares well with the existing correlations and experimental data. Accurate values of the maximum velocity and other flow variables of engineering interest can also be calculated from the velocity profile expression.
Solid‐State film diffusion for the production of integrated optical waveguides
Authors: Kapila D. , Plawsky J. L. 
Published: June 2004

AbstractSolid‐state film ion exchange (Ag+‐Na+) in glass substrates has been investigated for the fabrication of passive, integrated, optical waveguides. A new ion exchange mechanism is proposed which couples the oxidation of silver metal to silver oxide and the diffusion of silver ions into the glass substrate. At high electric fields and/or high temperatures, the growth rate of a silver oxide film limits the formation of mobile silver ions and constrains the diffusion of silver into the glass. This new mechanism is able to predict the dopant distribution profile under those conditions and under conditions where a constant surface concentration is appropriate (infinitely thick oxide film). It also explains the characteristics of the current vs. time curve measured during the ion exchange process. The formation and growth of the silver oxide film were confirmed by X‐ray photoelectron spectroscopy and X‐ray diffraction analysis.
Feasibility of separations for distillation of nonideal ternary mixtures
Authors: Fidkowski Z. T. , Doherty M. F. , Malone M. F. 
Published: June 2004

AbstractThe product compositions in single‐feed distillation columns can be specified only in certain regions of the composition space, which depend only on the pressure, feed, and vapor‐liquid equilibrium for the mixture. In nonideal mixtures, even without azeotropes, the regions may allow unusual product distributions. For example, the distillate in a “direct split” is composed primarily of the lightest component. Intuition and experience with relatively ideal mixtures suggest that the next most plentiful component is the intermediate boiler. In nonideal mixtures, however, with or without azeotropes, the next most plentiful component may be the highestboiling species with only trace amounts of the intermediate boiler. For azeotropic mixtures, distillation boundaries may give rise to additional restrictions on the product compositions. We describe how simple distillation boundaries deform into continuous distillation boundaries and, in a limited number of cases, how the simple distillation boundaries can be crossed in continuous columns for certain ranges of the design variables. Unfortunately, such designs may be quite sensitive to model uncertainties or to disturbances in the parameters.
Homogeneous nitrous oxide formation and destruction under combustion conditions
Authors: Hulgaard Tore , Dam‐Johansen Kim 
Published: June 2004

AbstractN2O decomposition and formation during the oxidation of NH3 and HCN were studied in a quartz flow reactor in the presence of CO, NO and other gases. The emphasis is on the influence of CO and NO. In addition, the homogeneous nitrogen chemistry of fluidized bed combustion and the selective noncatalytic reduction of NO (SNR) are discussed. The rate of N2O decomposition in N2 agrees with a first‐order rate expression. The presence of CO or H2 increases the decomposition rate regardless of the additional presence of O2For the formation of N2O, HCN oxidation is more efficient than NH3 oxidation. The presence of NO increases the amount of N2O formed during the oxidation of HCN or NH3.CO moves the N2O formation toward lower temperatures. H2O increases the reaction rate where few components are present, whereas H2O has little influence in the presence of large amounts of a combustible component such as CO. There are indications that NO is a necessary intermediate for any significant formation of N2O during the oxidation of NH3 and HCN. NO reduction is obtained when NO is initially present during oxidation of both NH3 and HCN. These results are comparable to the respective SNR results with reductant ammonia and urea.
Partial derivative quantities from phase equilibria relationships for mixtures
Authors: Mullins James A. , Rawlings James B. , Johnston Keith P. 
Published: June 2004

AbstractA systematic formulation of multicomponent/multiphase phase equilibria as a linear algebra problem in the fugacities, mole fractions, partial molar volumes, and partial molar enthalpies is given. The algorithm takes advantage of the Gibbs‐Duhem relationships for each phase and a modified Gaussian elimination technique to reduce the system of equations. These algorithmic steps allow current symbolic manipulation packages to generate useful partial derivative relationships in terms of measurable thermodynamic quantities. Features of the algorithm are demonstrated by applying a computer implementation of the method to a simple two‐phase/two‐component system and to the more complicated examples of a two‐phase/three‐component supercritical fluid chromatography experiment and a mass‐conserving closed system.
Effect of rheological properties on power consumption with helical ribbon agitators
Authors: Carreau P. J. , Chhabra R. P. , Cheng J. 
Published: June 2004

AbstractThe influence of shear thinning and viscoelasticity on the power required for the mixing of viscous liquids using six different helical ribbon agitators has been investigated. Four Newtonian and 12 non‐Newtonian fluids prepared using several polymers dissolved in varying concentrations in different solvents cover a wide range of rheological properties. By a careful choice of test media, the specific and combined effects of shear thinning and viscoelasticity on the power requirement have been examined. Simple models are proposed to predict the effective shear rate in the tank from the knowledge of the torque or power number. The effective shear rate predictions compared with the effective shear rate estimated using the scheme of Metzner and Otto (1957) show that they slightly depend on the shear thinning properties. Fluid's elasticity increases appreciably the power requirement, and departures from the generalized Newtonian power curve in the laminar regime are observed at smaller Reynolds numbers for viscoelastic fluids. Bottom wall resistance of the mixing vessel makes a negligible contribution to the power consumption.
Simulation of a three‐step one‐column pressure swing adsorption process
Authors: Lu Z. P. , Loureiro J. M. , Rodrigues A. E. , Levan M. D. 
Published: June 2004

AbstractSeparation of a binary mixture by a three‐step one‐column pressure swing adsorption process in isothermal and adiabatic cases has been studied. The separation performance of the process is characterized by three parameters: enrichment, recovery and productivity. It has been compared at various operating conditions. The evolution of the bed performance from cycle to cycle and the bed dynamics at cyclic steady state have also been addressed.
Application of the LCPT model to solid‐liquid equilibria for binary compound‐forming alloys
Authors: Howell Wayne J. , Alger Montgomery M. , Eckert Charles A. 
Published: June 2004

AbstractThe linear chemical‐physical theory (LCPT) model for liquid metal solution thermodynamics has been extended to the determination of the liquidus curves for binary intermetallic compound‐forming systems. The equations developed include corrections to the observed melting point temperature and heat of fusion for compounds that dissociate partially on melting. The primary advantages of the LCPT model for solid‐liquid equilibria are the small number of physically realistic parameters required, ease of implementation, and wide applicability. In addition, the model also permits the incorporation of compounds in modeling the liquidus curves that are not necessary for representing the liquid‐phase thermodynamic properties. For the seven systems studied, the agreement between calculated and experimentally measured liquidus curves is quite good.
Measurements of mass flux in a turbulent liquid flow with a chemical reaction
Authors: Komori Satoru , Nagata Kouji , Kanzaki Takao , Murakami Yasuhiro 
Published: June 2004

AbstractAn original technique for simultaneous measurements of concentration and velocity in a turbulent liquid flow with and without a chemical reaction is developed by combining a two‐component He‐Ne laser Doppler velocimeter with a Ar+ laserinduced fluorescence technique. The mass flux and eddy diffusivity of mass are estimated from the simultaneous measurements of concentration and velocity in a liquid shear‐free mixing layer downstream of a turbulence grid. The results show that the present measuring technique enables us to simultaneously measure velocity and concentration with high resolutions and that the approximation of the mean gradient diffusion causes about 10% error in estimating the mass flux in a reacting liquid flow.