bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractExperimental 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

AbstractElliptical 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

AbstractA 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

AbstractWhile 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

AbstractRecurrent 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

AbstractThe 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

AbstractThe 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

AbstractIn 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

AbstractThe 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

AbstractRules 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

AbstractThe 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

AbstractExperimental 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

AbstractGas‐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.
Isomerization of 1‐butene on silica‐alumina: Kinetic modeling and catalyst deactivation
Authors: Garcia‐Ochoa F. , Santos A. 
Published: June 2004

AbstractIn the study of 1‐butene isomerization on a silica‐alumina catalyst 448‐523 K, cis‐2‐butene and trans‐2‐butene are detected. Based on BSTR experimental data and zero‐time prediction kinetic models using the Langmuir‐Hinshelwood mechanism are assumed to develop kinetic equations for which a triangular reaction scheme is used. In four different mechanisms, one and two active sites take part in the surface reaction as the controlling step and then the deactivation rate determined considering two types of experimental data from BSTR and by measuring weight changes of a catalyst particle from coke deposition in an electrobalance. A coke precursor is assumed formed by reaction of adsorbed molecules (of any butene isomer) and gas‐phase molecules. Activity‐ and coke‐content‐time data allow us to choose a model whose activation energies of the deactivation kinetic parameter are closer in value. Coke is assumed deposited in a monolayer. The model chosen shows a triangular scheme, kinetic equations of the reaction for fresh catalyst with two active sites in the surface reaction, and the deactivation rate according to a coke formation mechanism in which a precursor is formed by reaction of 3 adsorbed molecules and 1 molecule in the gas phase. It accurately fits both BSTR conversion‐time data and electrobalance coke‐content data. The coke formation mechanism establishes relationships of activity vs. coke content and catalyst acidity which are supported by experimental results.
Nucleation and growth in microcellular materials: Supercritical CO2 as foaming agent
Authors: Goel Satish K. , Beckman Eric J. 
Published: June 2004

AbstractBubble growth is a phenomenon encountered in several commercially important processes. A mathematical model presented here describes the growth of bubbles during phase separation of an initially homogeneous polymer‐supercritical fluid mixture, triggered by a sudden pressure drop at constant temperature. It is a modification of the viscoelastic model of Arefmanesh and Advani (1991) in which the polymer is treated as a single relaxation‐time Maxwell fluid. Since properties of the polymer‐fluid mixture vary with the amount of fluid absorbed in the polymer (as a function of fluid pressure), the model needs to be used evaluating system properties as functions of temperature and pressure. The viscosity of polymer/fluid mixture, density of the mixture, diffusivity of CO2 in the mixture, and relaxation time for poly (methyl methacrylate) swollen by supercritical carbon dioxide are, therefore, predicted as functions of CO2 pressure and temperature using appropriate model equations at each step of the bubble growth simulation. The model predicts well the trends in equilibrium cell size vs. saturation pressure and temperature.
Cross‐flow microfiltration with high‐frequency reverse filtration
Authors: Redkar Sanjeev G. , Davis Robert H. 
Published: June 2004

AbstractA primary method of reducing membrane fouling during cross‐flow microfiltration is periodic reverse filtration. This in situ method of cleaning the membrane forces clear fluid in the reverse direction through the membrane and readjusts the particle or solute accumulation on the retentate side of the membrane. This work focuses on the design of a high‐frequency, reverse‐filtration strategy to maximize the flux for washed yeast suspensions through 0.2‐ μm cellulose acetate flat sheet membranes. Several experiments were conducted with reverse‐filtration times ranging from 0.5–4 s and forward‐filtration times ranging from 1–40 s. For every back‐filtration time, there exists an optimum forward‐filtration time that gives the maximum global average flux. The optimum average flux increases with decreasing back filtration times and feed concentrations, but shows little dependence on cross‐flow velocity and reverse filtration transmembrane pressure. The optimum flux with rapid backflushing is 20 to 30 times higher than the long‐term flux in the absence of backflushing. A theory presented assumes that cake formation during forward filtration follows dead‐end filtration theory and the cake is instantly removed during reverse filtration. The measured average flux per cycle follows the trends predicted by the theory, but the measured values exceed the predictions, presumably due to brief delays in cake removal and cake formation at the start of reverse and forward filtration, respectively, during each cycle.
Habituating control strategies for process control
Authors: Henson Michael A. , Ogunnaike Babatunde A. , Schwaber James S. 
Published: June 2004

AbstractBy “reverse engineering” the functions of a specific biological system, habituating control strategies are developed for process control applications. A habituating control system has the distinguishing property of more more manipulated inputs than controlled outputs; with the inputs differing significantly in their dynamic effect on the outputs and in the relative costs of manipulating each one. A habituating controller coordinates the use of all the available inputs to achieve high‐performance output objectives while simulatneously minimizing the cost of taking control action.The “baroreceptor reflex,” the control system responsible for short‐term blood pressure regulation, provides the biological paradigm for the analysis and design of the habituating control structure. Its main characteristics are discussed from a process control perspective, indicating that the robust, high‐performance control, characteristic of biological systems is partly due to such habituating control architectures. The broad range of potential process applications is illustrated with two examples. Two basic strategies are presented for the design of habituating controllers for linear systems with two inputs and one output: the direct synthesis approach and the model predictive approach. Compared to previous techniques for multiple‐input, single‐output systems, the direct synthesis strategy is straightforward and systematic. Simulation results demonstrate the superior performance of habituating control compared to conventional techniques for which the number of inputs and outputs are equal.
Shear thinning in ternary bicontinuous and water‐in‐oil microemulsions
Authors: Anklam Mark R. , Prud'Homme Robert K. , Warr Gregory G. 
Published: June 2004

AbstractShear thinning of ternary microemulsions of didodecyldimethylammonium bromide (DDAB), water, and dodecane in the range 103 to 106 s−1 is documented over a wide range of compositions. A marked transition in the characteristic shear rate is observed accompanying the structural transition from bicontinuous to water‐in‐oil (w/o) droplets as previously reported from diffusion and small‐angle scattering techniques. Results in the w/o region are consistent with those for a dispersion of hard spheres. The shear thinning of the bicontinuous structure, however, occurs at much higher shear rates, implying a shorter time and length scale for disruption of the equilibrium liquid structure by the flow field.