bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of Buckingham potentials in engineering approximations for chemical kinetics
Authors: Blowers Paul , Masel Richard I. 
Published: April 2004

AbstractPrevious investigators have often used the Polanyi relationship to correlate activation barriers for series of reactions. The correlations often work, but a different Polanyi relationship is needed for each class of reactions. As a result, the correlations are difficult to extrapolate to new situations. In this article, we suggest new correlations that show greater capability to correlate rate data. Quantum mechanical calculations are done which indicate that the main barriers to ligand exchange reactions are associated with getting the reactants close enough to react. The energy to get the reactants close enough to react can be calculated from a united‐atom Buckingham potential and correlated to rate data. The additional correlating parameter allows the activation energies for a series of hydrocarbon reactions to be collapsed onto a single line. The root‐mean‐square error of the line is 2 kcal/mol compared to 7 kcal/mol with the Polanyi relationship alone. This shows that our new correlating parameter will be useful in engineering approximations in kinetics.
Kinetics of the aqueous‐phase reaction between ozone and 2,4,6‐trichlorophenol
Authors: Rinker Edward B. , Ashour Sami S. , Johnson Michael C. , Kott Gregory J. , Rinker Robert G. , Sandall Orville C. 
Published: April 2004

AbstractA wetted‐sphere absorber was used to measure absorption rates of ozone into aqueous‐buffered solutions of 2,4,6‐trichlorophenol (TCP). Gas consisting of approximately 2.5% ozone in oxygen was contacted with aqueous‐buffered TCP solution flowing over a sphere in a laminar liquid film. Absorption data were obtained by measuring the change in the liquid‐phase concentration of TCP from the inlet to the outlet of the absorber. A rigorous numerical model for this diffusion/reaction process was used to analyze the absorption data to determine the second‐order rate constant of the reaction between ozone and TCP at 15–35°C and pH 2 and 7. The kinetic data indicate that the rate‐limiting step for the reaction of aqueous TCP with ozone is the same at pH 2 and 7. Four reaction products that occur early in the reaction of ozone with aqueous TCP were identified by GCMS, including: 2,3,4,6‐tetrachlorophenol (TRCP), 4,6‐dichlorocatechol (DCC), 2,6‐dichlorohydroquinone (DCHQ), and 2,6‐dichloroquinone (DCQ). Only DCHQ and DCQ occurred in significant concentrations. Over the pH range of 2 to 5, both DCHQ and DCQ were detected in the reacted solutions, while for pH 6 and 7 only DCHQ was detected. Carbon‐13 NMR analysis shows that over longer ozone exposure times short‐chain carboxylic acids are the dominant species in the reacted TCP solutions.
Synthesis of prepolymerization stage in polycondensation processes
Authors: Samant Ketan D. , Ng Ka M. 
Published: April 2004

AbstractA systematic design procedure of the prepolymerization stage of a polycondensation process is presented. This procedure treats polycondensation processes as reactive separation processes and offers an alternative to design through simulations. Feasible flowsheets and operating conditions are developed by analyzing the phase behavior of polycondensation systems at thermodynamic equilibrium. Functional end groups and apparent mole fractions are used to represent reaction kinetics and equilibrium, and real mole fractions are used to represent phase equilibrium. Reactive phase diagrams are plotted in transformed mole‐fraction space to facilitate visualization of the phase behavior. Three examples are presented: manufacture of polyethylene terephthalate (PET) from dimethyl terephthalate (DMT) and ethylene glycol (EG), from terephthalic acid (TPA) and EG, and manufacture of nylon‐6,6. For these processes, the results of the approach agree excellently with detailed iterative performance simulations. The approach also reveals additional feasible process alternatives and corresponding operating conditions.
Flow and dispersion in porous media: Lattice‐Boltzmann and NMR studies
Authors: Manz B. , Gladden L. F. , Warren P. B. 
Published: April 2004

AbstractThe results of lattice‐Boltzmann simulations of the flow field through a random packing of spheres are compared with NMR velocimetry and propagator measurements. Flows are investigated for Péclet (Pe) and Reynolds (Re) numbers in the range 182<Pe<350 and 0.4<Re<0.77, respectively. An MRI visualization of the 3‐D packing of spheres for which NMR data are obtained is used as the matrix for the simulation, thereby enabling a direct assessment of the ability of the lattice‐Boltzmann method to quantitatively predict flow phenomena within porous media of complex geometry. By introducing normalized parameters, hydrodynamical dispersion over normalized displacement lengthscales extending over nearly four orders of magnitude is investigated and is shown to be dominated by mechanical dispersion over most of this range. At the largest lengthscales studied holdup may play a significant role in the hydrodynamics characteristic of the porous medium. Quantitative agreement between NMR measurements and the predictions of the lattice‐Boltzmann simulation is obtained in all cases.
New effective‐nuclei concept for simplified analysis of batch crystallization
Authors: Yokota Masaaki , Sato Akira , Kubota Noriaki 
Published: April 2004

AbstractA new “effective nuclei” concept for a simplified approach to the analysis of batch crystallization with agglomeration is proposed. The new effective‐nuclei concept comes from agglomeration characteristics observed experimentally in a batch crystallizer. Small‐sized crystals could combine with both large‐sized crystals and each other. Agglomeration among large‐sized crystals can be neglected. From these experimental results, new effective nuclei are defined as crystals at a size‐boundary between small‐sized crystals and large‐4sized crystals. By taking into account only large‐sized crystals in formulating population balance equation, the agglomeration term can be omitted. The analytical solution of the population balance equation is induced for an ideal batch‐cooling case (constant supersaturation and constant effective growth rate of crystal). The solution explains measured data well.
Adsorption kinetics of light paraffins in AC by a constant molar flow‐rate method
Authors: Prasetyo I. , Do D. D. 
Published: April 2004

AbstractA semibatch constant molar flow‐rate technique developed earlier by Do was applied to a series of light paraffins adsorbing onto a number of adsorbents. The adsorption and diffusion of methane, ethane, propane and n‐butane on activated carbon at different temperatures were studied to determine the diffusivity of surface diffusion and its activation energy. It was found that the surface diffusivity decreases with the molecular weight in an exponential manner and increases with temperature according to the Arrhenius law. The ratio of the activation energy for surface diffusion to the heat of adsorption increases with the carbon number. A mechanism for surface diffusion is suggested to explain this increase.
Modeling capillary condensation hysteresis cycles in reconstructed porous media
Authors: Štěpánek František , Marek Miloš , Adler Pierre M. 
Published: April 2004

AbstractA computational algorithm for tracking liquid–vapor interfaces moving with curvature‐dependent velocity, based on the Gibbs energy formulation and the level‐set approach, is described. The algorithm is used for finding equilibrium distributions of condensate in several samples of 3‐D reconstructed porous media under varying relative saturation of the surrounding atmosphere. Primary and higher‐order hysteresis cycles are calculated and their dependence on various physico‐chemical parameters (temperature, wetting angle) as well as on geometrical properties of the porous medium is investigated. An explanation of the influence of the morphology of a porous medium on the character of corresponding hysteresis loops is provided.
Viscosity effects on Dean vortex membrane microfiltration
Authors: Kluge Tanja , Kalra Amrit , Belfort Georges 
Published: April 2004

AbstractThe influence of changing viscosity by adding polyethylene glycol (PEG) during microfiltration of silica suspensions in the presence and absence of Dean vortices was determined. A new microfiltration membrane module design containing helically wound hollow fibers (with Dean vortices) was compared with a standard commercial cross‐flow module (without Dean vortices) containing linear hollow fibers during filtration of poly(ethylene) glycol solutions and silica suspensions. The influence of solution viscosity on permeation flux behavior was evident through two separate effects. First, increased viscosity effected the formation and stability of vortices and, hence, wall shear rate and convective back‐flow. Second, permeation flux was reduced with increasing fluid viscosity. Flux improvements (linear vs. helical membranes) of up to 45% were observed for all value of the silica suspensions with and without PEG. The energy required to obtain these improvements, however, was considerable. Flux advantages of the helical design decreased and eventually disappeared as the viscosity of the solution increased up to 12 times that of water at 27°C. New mass‐transfer correlations for microfiltration of poly(ethylene) glycol solutions containing silica concentrations for laminar flow in a helical and a linear module were obtained with respect to the solution viscosity, for a silica particle concentration of 0.1 wt. %.
Design and upgrade of nonredundant and redundant linear sensor networks
Authors: Bagajewicz Miguel J. , Sánchez Mabel C. 
Published: April 2004

AbstractThe design of sensor networks featuring minimum cost, while satisfying constraints of redundancy only, is examined. For this purpose, the concept of degree of redundancy for measurements and degree of observability for unmeasured variables are merged into one single property, the degree of estimability of a variable. In addition, the concept of estimation efficiency is introduced. Based on these concepts, mathematical programming procedures are presented that allow the design of sensor networks for different degrees of estimability of key variables.
Detection, identification, and reconstruction of faulty sensors with maximized sensitivity
Authors: Qin S. Joe , Li Weihua 
Published: April 2004

AbstractA new method proposed here detects, reconstructs, and identifies faulty sensors using a normal process model, which can be built from first principles or statistical methods such as partial least squares or principal component analysis. The model residual is used to detect sensor faults that demonstrate a deviation from the normal process model. To identify which sensor is faulty, a structured residual approach with maximized sensitivity is proposed to make one residual insensitive to one subset of faults but most sensitive to other faults. The structured residuals are subject to exponentially weighted moving average filtering to reduce the effect of noise and dynamic transients. The confidence limits for these filtered structured residuals are determined using statistical inferential techniques. In addition, other indices including generalized likelihood ratio test, cumulative sum, and cumulative variance of the structured residuals are compared to identify faulty sensors. The fault magnitude is then estimated based on the model and faulty data. Four types of sensor faults, including bias, precision degradation, drifting and complete failure, are simulated to test this method. Data from an industrial boiler process are used to test its effectiveness. Both single faults and simultaneous double faults are detected and uniquely identified with the method.
Scoping and screening complex reaction networks using stochastic optimization
Authors: Marcoulaki E. C. , Kokossis A. C. 
Published: April 2004

AbstractA systematic methodology to target the performance of chemical reactors with the use of stochastic optimization is presented. The approach employs a two‐level strategy where targets are followed by the proposition of reactor configurations that match or are near the desired performance. The targets can be used for synthesis and retrofit problems, as they can provide the incentives to modify the operation, and ideas in developing the reactor design. The application of stochastic optimization enables confidence in the optimization results, can afford particularly nonlinear reactor models, and is not restricted by the dimensionality or the size of the problem.
Formation of microgel beads by electric dispersion of polymer solutions
Authors: Poncelet D. , Neufeld R. J. , Goosen M. F. A. , Burgarski B. , Babak V. 
Published: April 2004

AbstractMicrocapsules are produced by a dropwise addition of one solution into a solidifying bath. By applying an electrostatic potential between the droplet formation device and the collecting solution, it is possible to obtain smaller droplets which are desirable for many applications. Droplet formation may be divided into two phases. Under a certain critical value of the electric potential Uc, liquid exits the nozzle as droplets. The surface tension decreases with increasing electric potential resulting in a reduction of droplet diameter to approximately 200 μm. At higher electric potential, liquid exits the nozzle as a jet which subsequently breaks into droplets, which are smaller than 200 μm. In this case, droplet size is mainly determined by the jet instability (theory of Rayleigh).
Vapor‐liquid and chemical equilibria of formaldehyde‐water mixtures
Authors: Albert Michael , García Baudilio Coto , Kreiter Cornelius , Maurer Gerd 
Published: April 2004

AbstractA physicochemical model of the thermodynamic properties of formaldehyde‐containing mixtures was revised and extended using new experimental data for vapor–liquid and chemical equilibria. The new vapor–liquid equilibrium data of the formaldehyde–water system were taken for very diluted (formaldehyde concentrations as low as 0.07 mass %) and very concentrated (up to 71 mass %) formaldehyde solutions at temperatures between 363 and 423 K and pressures up to about 650 kPa. The new chemical equilibrium data were obtained applying 13 C‐NMR spectroscopy to the same system at temperatures between 338 and 383 K at formaldehyde concentrations of up to about 62 mass %. Results from both investigations were used simultaneously—together with data from the literature—to improve a physicochemical model of the thermodynamic properties of aqueous solutions of formaldehyde.
Intermolecular forces in phase‐change heat transfer: 1998 Kern award review
Authors: Wayner Peter C. 
Published: April 2004

AbstractThe variation of long‐range intermolecular forces near interfaces profoundly affects the performance of change‐of‐phase heat exchangers. Starting with the fundamental electromagnetic force between molecules (dielectric properties), the effects of shape (Kelvin effect), temperature (Clapeyron effect) and concentration on the heat‐transfer characteristics of thin films and larger systems are reviewed and connected. A judicious selection of literature gives a consistent set of models of particular use in heat transfer. Examples of experimental verification of these interfacial models in this rapidly developing field are also presented.
Mass‐transfer enhancement in single‐drop extraction experiments
Authors: Henschke Martin , Pfennig Andreas 
Published: April 2004

AbstractTo reduce costs, engineers in the industry wish to substitute laboratory‐scale experiments for pilot‐scale investigations. Thus mass‐transfer experiments with single drops seem to be a first step toward the design of liquid–liquid extraction columns, along with other experiments needed, for example, for the estimation of coalescence parameters. In this article it is shown that it is possible to describe nonstationary mass transfer between single drops and a continuous phase with a single parameter, the instability constant CIP. The instability constant is independent of both drop diameter and contact time between drop and continuous phase. Thus in principle a single laboratory experiment allows the determination of CIP for a given combination of components. When mass transfer in an extraction column is calculated using the estimated value of CIP, an increase in mass transfer due to the concentration gradient in the continuous phase of the column has to be accounted for appropriately.
Characterizing growth‐rate dispersion of NaNO3 secondary nuclei
Authors: Jones Christopher M. , Larson Maurice A. 
Published: April 2004

AbstractPrevious work on growth‐rate dispersion has shown how to calculate crystal‐size distributions when the growth‐rate distribution is known and how to calculate the growth rate distribution when the crystal‐size distribution is known. There is a significant lack of information, however, on how growth‐rate dispersion is affected by changes in system conditions like supersaturation, stirring speed, slurry density, or temperature. In this work, the growth‐rate distributions of sodium nitrate secondary nuclei are characterized as a function of the nucleation and growing supersaturations. Growth‐rate dispersion is characterized by analyzing the mean, spread, and shape of the growth‐rate distribution. This provides a means of determining the factors that cause and control growth‐rate dispersion. The analysis of this experimental work provides valuable insight into the relationships among supersaturation conditions, strain, and dislocation density. The average growth rates of secondary nuclei are dislocation controlled at low growing supersaturations and strain controlled at high growing supersaturations, where increasing the nucleation supersaturation causes an increase in both dislocation density and strain. Increasing strain by itself will decrease growth rates, while increasing dislocation density by itself will increase growth rates. This work also suggests that harsh system conditions can affect growth rates adversely.
Modeling Au(CN) extraction by mixtures of primene JMT and cyanex 925 reagents
Authors: Alguacil Francisco José 
Published: April 2004

AbstractA chemically based thermodynamic model to predict the distribution coefficient has been developed for the Au(CN)‐Primene JMT‐Cyanex 925 system. The predictive model makes use of the extraction mechanism, speciation in the organic phase, and the equilibrium constant for the extraction reaction. The distribution coefficient of gold can be predicted by the equation DAu = K′[H+], where K′ is an effective extraction constant and [H+] is the proton concentration of the aqueous phase at equilibrium. Excellent agreement between the experimental data and the predicted value was obtained. Furthermore, for the present extraction system, the equilibrium isotherm was determined at 20°C.
Air separation by integrally asymmetric hollow‐fiber membranes
Authors: Feng Xianshe , Ivory John , Rajan Varagur S. V. 
Published: April 2004

AbstractIntegrally asymmetric hollow‐fiber membranes each with an outer skin layer and a porous substrate were studied for air separation to produce nitrogen and oxygen enriched air. The test on both bore‐side feed and shell‐side feed with cocurrent and countercurrent flow arrangements for a wide range of stage cuts shows that the bore‐side feed countercurrent flow was the most advantageous configuration in the permeator design. When operated in the bore‐side feed countercurrent configuration, the permeator performance compared favorably with the commercial systems available for nitrogen production. A mathematical model was developed for this configuration. Since the concentration polarization in the substrate was a major concern for the bore‐side feed configuration, especially for high stage‐cut operations, a theoretical approach was pursued to formulate the concentration polarization. This allows for the diagnosis of the significance of concentration polarization in a specific permeation process, although it is difficult to predict concentration polarization accurately due to limited knowledge of the detailed membrane structure.
Geographic and process information for chemical plant layout problems
Authors: Özyurt Derya B. , Realff Matthew J. 
Published: April 2004

AbstractGeographic information systems (GIS) introduced here offer a source of information for problems with a geographic dimension, such as layout and environmental decision making. A mixed‐integer linear‐programming formulation of a chemical‐plant layout problem was developed, and is presented along with an existing formulation. The effectiveness of these formulations is highly problem‐ and data‐specific, and a combination of the two formulations can be derived that is more effective on certain problems than either formulation alone. The formulations are ineffective for some problems due to the highly redundant search space engendered by symmetries in the layout—symmetries that can be eliminated by a more careful analysis of the situation using location‐specific information such as existing units and facilities, geographic constraints, wind, elevation, and soil conditions. Different classes of such information can be captured from a GIS and represented within the mixed‐integer linear‐programming formulation. Two cases studies presented illustrate the formulations and the use of geographic information for chemical‐plant layout.
New analysis and design tool for achieving low variability process designs
Authors: Tseng J. L. , Cluett W. R. , Bialkowski W. L. 
Published: April 2004

AbstractA new process analysis and design tool was developed. The analysis tool consists of a systematic algorithm for analyzing a block diagram representation of a process flowsheet and identifying different paths between a given input and output variable. Transfer function representations of different paths are calculated to determine the contribution of each path to the overall attenuation characteristics of the process. To improve these attenuation characteristics, the paths that contribute the most to the overall variability must be identified and addressed. The design tool consists of a set of guidelines that the engineer can use to develop alternate process designs or control strategies to eliminate these identified paths, reduce their contribution to overall variability, or negate their effects by adding new paths. Although the ingenuity of the design engineer is critical, this tool provides the engineer with a means to identify problems in a process design, to help develop design alternatives, and a quantitative basis for comparing and evaluating these alternatives. This new tool was applied to a standard design for a stock preparation system in a pulp and paper mill.
Impinging jets confined by a conical wall: Laminar flow predictions
Authors: Miranda João M. , Campos João B. L. M. 
Published: April 2004

AbstractA laminar jet flow confined by a conical wall and an impinging plate was investigated. The Navier‐Stokes equations were numerically solved by a finite difference technique and the results compared with laser Doppler anemometry data, the latter also covering the transition and turbulent flow regimes. Transition was found to start in the impingement region at a jet Reynolds number of around 1,600. The investigation concentrated on assessing the effects of nozzle‐to‐plate distance (always less than one nozzle diameter), jet Reynolds number, and nozzle outlet conditions. The shape of the velocity profile at the nozzle outlet determines the entire cell flow field, whereas nozzle‐to‐plate distance affects the flow in the expansion region. Under certain flow and geometric conditions a recirculation zone appears in the expansion region, in the vicinity of the plate.