bluuebunny/crossref_metadata_2025_split huggingface dataset:
Asphalt flocculation and deposition: II. Formation and growth of fractal aggregates
Authors: Rassamdana Hossein , Sahimi Muhammad 
Published: June 2004

AbstractExtensive small‐angle X‐ray and neutron‐scattering data, as well as results of precipitation measurements, are analyzed to delineate the structure of the asphalt and asphaltene aggregates that are formed when a solvent is injected into a system containing crude oil. The two types of data strongly suggest that both small and large aggregates have a fractal structure, with well‐defined fractal dimensions. If the system is aged long enough at low enough temperature, large asphalt particles will have the structure of diffusion‐limited cluster–cluster aggregates with a fractal dimension Df ≃ 1.8, while the small ones are similar to diffusion‐limited particle aggregates with a fractal dimension df ≃ 2.5. High temperatures increase the rotational motion of the particles, disturb the structure and mechanical stability of the aggregates, and decrease their fractal dimension. Aging and concentration effects of the asphalts in the solution, and the type of the solvent on the structure of the aggregates are also investigated. Implications of these results for the structure, mechanical stability, and molecular‐weight distribution of asphalts and asphaltenes are detailed. A new molecular‐weight distribution for asphalt aggregates predicts the experimental data excellently.
Strategy for dynamic process modeling based on neural networks in macroscopic balances
Authors: Van Can Henricus J. L. , Hellinga Chris , Luyben Karel Ch. A. M. , Heijnen Joseph J. , Te Braake Hubert A. B. 
Published: June 2004

AbstractGray box models combine the short development time of data‐driven black box models with extrapolation properties of knowledge‐driven first principles models (white box), which in (bio)chemical engineering are always based on macroscopic balances. By modeling the inaccurately known terms in a macroscopic balance with a black box model, one naturally obtains a so‐called serial gray box model configuration. The identification data must cover only the input‐output space of the inaccurately known terms, and the accurately known terms can be used for reliable extrapolation. In this way, the serial gray box configuration results in accurate models with known extrapolation properties with a limited experimental effort. This strategy is demonstrated for the modeling and control of a pressure vessel using real‐time experiments. For this case, the strategy is superior to a black box modeling approach that requires much more data and to a parallel gray box approach that results in a model with poor extrapolation properties. Moreover, neural networks are an accurate and convenient modeling tool for the black part in gray box model configurations, because a very fast noniterative training algorithm is used for training neural networks.
Homogeneous multicomponent azeotropic batch distillation
Authors: Ahmad Berit S. , Barton Paul I. 
Published: June 2004

AbstractMixed waste‐solvent streams generated in pharmaceutical and specialty chemical manufacturing typically form multicomponent azeotropic mixtures. This highly nonideal behavior often prevents separation and recovery of the solvents. Batch distillation remains an important separation technology for these industries. The sequence of pure component and azeotropic cuts produced in batch distillation depends strongly on the feed composition. For ternary‐ and four‐component mixtures the separation behavior can be studied graphically in residue‐curve maps. For mixtures with more components, this approach is infeasible. Other tools are therefore required. Deficiencies in earlier work on ternary systems are demonstrated and addressed as well as a complete set of concepts to describe batch distillation of an azeotropic mixture with an arbitrary number of components. The body of theory is derived from the fields of nonlinear dynamics and topology.
Model for SrCsCaMgNa ion‐exchange uptake kinetics on chabazite
Authors: Depaoli Susan M. , Perona Joseph J. 
Published: June 2004

AbstractMany nuclear facilities throughout the world must separate strontium‐90 and cesium‐137 from natural waters containing calcium, magnesium, and sodium. Our research showed that chabazite, a zeolite with a hexagonal ring structure, is cost‐effective for this purpose. A batch kinetic uptake model for this five‐component ion‐exchange system was developed and tested against experimental data. The pore‐diffusion model of Yao and Tien is used with the equilibrium model of Perona. The resulting model is fast and stable, and represents the experimental data well.
Modeling of phase separation in PEG–salt aqueous two‐phase systems
Authors: Kenkare Paresh U. , Hall Carol K. 
Published: June 2004

AbstractA molecular model based on the integral equation theory of statistical thermodynamics is used to study phase separation in PEG–salt aqueous two‐phase systems. PEG molecules are modeled as hard spheres that attract each other through a temperaturedependent Yukawa potential, which mimics the effect of PEG–water hydrogen bonding on the attraction between PEG molecules. The salt ions are modeled as charged hard spheres interacting through a Coulombic potential. Excess thermodynamic properties due to Coulombic and Yukawa interactions are calculated by analytical solutions to the Ornstein–Zernike equation for the mean spherical approximation closure. Yukawa parameters for PEG–PEG interactions are determined by fitting the theoretical phase diagram for a pure Yukawa fluid to the experimental phase diagram for a PEG–water mixture. The model predicts experimentally observed trends: increasing the temperature increases the slope and length of the tie lines; increasing the PEG molecular weight increases the miscibility gap; and increasing the anion charge lowers the salt concentration at which phase separation occurs. Theoretical results allow us to infer the relative importance of ion–PEG interactions, ion–solvent interactions, and the interpenetrable nature of PEG molecules on the phase separation in PEG–salt aqueous two‐phase systems.
Molar mass distribution and solubility modeling of asphaltenes
Authors: Yarranton Harvey W. , Masliyah Jocob H. 
Published: June 2004

AbstractAttempts to model asphaltene solubility with Scatchard‐Hildebrand theory were hampered by uncertainty in molar volume and solubility parameter distribution within the asphaltenes. By considering asphaltenes as a series of polyaromatic hydrocarbons with randomly distributed associated functional groups, molar volume and solubility parameter distributions are calculated from experimental measurements of molar mass and density. The molar mass distribution of Athabasca asphaltenes is determined from interfacial tension and vapor pressure osmometry measurements together with plasma desorption mass spectrometry determinations from the literature. Asphaltene desnities are calculated indirectly from mixtures of known concentration of asphaltene in toluene. Asphaltene density, molar volume, and solubility parameter are correlated with molar mass. Solid‐liquid equilibrium calculations based on solubility theory and the asphaltene property correlations successfully predict experimental data for both the precipitation point and the amount of precipitated asphaltenes in toluene‐hexane solvent mixtures.
Characteristics of high‐pressure liquid–solid fluidization
Authors: Lin Tsao‐Jen , Fan Liang‐Shih 
Published: June 2004

AbstractFundamental characteristics of liquid–solid fluidization at high pressures (up to 21 MPa) and moderate temperatures (up to 89°C) are investigated. Properties under study include minimum fluidization velocity (umf), bed voidage at minimum fluidization, and bed expansion. Devices for in‐situ measurements of physical properties of the liquid in the bed are developed, and measurements are carried out to quantify the pressure and temperature effects on the fluidization behavior. The results indicate that under high pressures and moderate temperatures, liquid–solid fluidization behavior is affected significantly by the variation of liquid density and viscosity with pressure. As the pressure increases, the liquid viscosity and density increase, yielding an increased drag force and buoyancy force on the particles, and hence a decreasing umf and an increasing bed expansion for a given liquid flow rate. An increase in temperature has an opposite effect on the physical properties of the liquid, increasing umf and decreasing the bed expansion for a given liquid flow rate. Various correlations proposed in the literature for umf and bed expansion, including those by Richardson and Zaki (1954) and Chitester et al. (1984), are applicable to high‐pressure and high‐temperature conditions when proper account is made of the liquid physical properties under bed operating conditions.
Permeation studies on oriented single‐crystal ferrierite membranes
Authors: Lewis John E. , Gavalas George R. , Davis Mark E. 
Published: June 2004

AbstractLarge, high‐quality, single crystals of pure‐silica ferrierite are synthesized, and the structure is described. Selected individual crystals (approximately 600 μm X 500 μm X 20 μm) are mounted in a membrane configuration so that only the 10‐membered‐ring channels (5.4 Å X 5.4 Å X 4.2 Å) or the 8‐membered‐ring channels (4.6 Å X 3.7 Å X 3.0 Å) are accessible for gas‐molecule permeation. The first examples of transport exclusively through 8‐ or 10‐membered‐ring channel systems are reported and obtained through crystal orientation in the membrane. A series. of adsorption experiments are conducted to help select suitable probe molecules and evaluate the role of adsorption in the permeation process for single‐crystal membranes. Methane, n‐butane, isobutane and nitrogen probe molecules are used to study intracrystalline sorption and transport effects for different crystal orientations, pressures and temperatures. Both pure‐gas selectivities and mixed‐gas separation factors are reported. A mixed‐gas separation factor of n‐butane/isobutane = 116 for the 10‐membered‐ring orientation of the crystal at 383 K and a transmembrane pressure difference of 1.01 X 105 Pa are found using this technique. In addition, molecular sieving is observed for the 8‐membered‐ring orientation of the crystal since methane, but not butane, transport is observed for this crystal orientation.
Simulations of a LDPE reactor using computational fluid dynamics
Authors: Read Nolan K. , Zhang Simon X. , Ray W. Harmon 
Published: June 2004

AbstractComputational fluid dynamics methods are used to provide three‐dimensional simulations of a low‐density polyethylene (LDPE) autoclave reactor under normal operating conditions. For the conditions used, the reactor is not very well mixed; thus, the common model approximation of a perfectly stirred reactor is not warranted. The simulations verify the sensitive nature of the polymerization reactors and indicate a need for optimizing operating parameters.
Simulation of decoking of thermal cracking coils by steam/air‐mixtures
Authors: Schools Evy M. , Froment Gilbert F. 
Published: June 2004

AbstractA rigorous approach was developed for the simulation of the decoking of an industrial cracking furnace. A one‐dimensional heterogeneous reactor model, which accounts for the interfacial gradients between the process gas and the coke surface, was used to simulate reactor coils. Both the combustion and steam gasification of the coke layer were taken into account. The reactor model for the decoking was coupled with a detailed firebox simulation model. The initial profile of the coke layer thickness, required for the decoking calculations, was obtained by a run‐length simulation. The evolution with time of the temperature distribution inside the cracking coil and in the furnace was generated simultaneously, which made it possible to understand the decoking operation in detail and to predict its duration accurately.
Dynamics of semibatch polymerization reactors: I. Theoretical analysis
Authors: Teymour F. 
Published: June 2004

AbstractThe dynamics of semibatch reactors is often neglected in the literature despite their industrial importance. This article analyzes the stability and dynamic behavior of semibatch polymerization reactors operated according to a flow scheduling strategy designed to impart a steady‐state nature to the dynamics of these essentially transient reactors. It can also improve the operation of these reactors, especially the quality of the polymer produced (such as molecular weight distribution and polymer composition). In the proposed strategy of flow rate scheduling, the intensive states of the reactor can be made to reach steady‐state values. A comparison of the dynamics of the proposed and classical operating strategies illustrates this possibility. Further dynamic analysis reveals the emergence of phenomena characteristic of continuous operation in a CSTR. Examples are multiplicity of the trajectories, limit cycle oscillations, as well as nonhomogeneous oscillations belonging to a period doubling cascade. Operation in a sequential semibatch mode is discussed, as well as the importance of selecting parameters for the fillup and discharge operation. In this mode of operation either periodic or chaotic behavior is obtained. The effect of both on polymer properties is studied in detail.
Enhanced SO2 abatement with water‐hydrated dolomitic particles
Authors: Al‐Shawabkeh Ali , Matsuda Hitoki , Hasatani Masanobu 
Published: June 2004

AbstractA dolomitic calcine was hydrated with liquid water and then recalcined as an effective sorbent toward SO2 removal. The hydrated/recalcined sorbent was tested for SO2 removal in a thermogravimetric analyzer under conditions applicable to an atmospheric fluidized‐bed combustor: 1,123 K, 20 vol. % excess air, and 3,000 ppmv SO2. Specific pore surface areas and volumes of hydrated/recalcined dolomites, hydrated at 80°C for 1 h, increased by four and five times, respectively, compared to unhydrated dolomitic calcines. Due to these improved pore characteristics, the SO2 capture achieved by the hydrated/recalcined calcine, was 1.3–1.6 times higher than that of the unhydrated one after a 1‐h exposure to SO2 concentrations of 0.11–0.31 vol. % at 1,073–1,173 K. In the hydrated/recalcined calcine CaO utilization was enhanced due to the absence of significant pore diffusional limitations, at least during the early reaction times, evidenced by the high apparent activation energy of 198 kJ/mol. On the contrary, the lower CaO utilization in the unhydrated calcine was presumably due to severe pore diffusional limitations, which dropped the apparent activation energy from 149 to 85 kJ/mol at > 1,123 K.
Recent advances in modeling thermodynamic properties of aqueous strong electrolyte systems
Authors: Loehe Joseph R. , Donohue Marc D. 
Published: June 2004

AbstractTheoretical and engineering models for the thermodynamic properties of strong electrolyte solutions have advanced significantly since 1985. This progress is notable in the ability to calculate selected properties of single and mixed strong electrolyte solutions over a wide range of temperatures and compositions, including effects of various nonelectrolytes, solvents and supercritical components. Theoretical studies have begun to consider more realistic fundamental interactions between various components in these systems. There have been several successful conversions of theories based on the mean spherical approximation and perturbation methods into engineering equations, without large numbers of empirical parameters. Other theoretical models seem almost ready for application to real systems. The capability to estimate a wide variety of thermodynamic properties accurately with a consistent set of equations and a small number of adjustable parameters has been achieved by several groups over limited temperature and composition ranges. Much work remains to be done, however, to understand completely the interplay and relative importance of various contributing energy effects.
Molecular interactions in chloroform‐diluent mixtures
Authors: Choi K. , Tedder D. W. 
Published: June 2004

AbstractPlausible stoichiometries for solvation and association complexes in binary mixtures of chloroform and one of six organic diluents (n‐hexane, p‐dioxane, acetone, diethyl ether, tri‐n‐butyl phosphate, or triethylamine) are examined parametrically. A range of stoichiometric assumptions based on hydrogen bonding are examined, but only a few such combinations yield statistically significant fits to the experimental vapor–liquid equilibria and NMR chemical shift data. Hydrogen bonding considerations and the “true” chemical species are much more important than nonspecific physical factors such as molecular sizes, shape differences, and regular solution terms. Thermodynamic equilibrium constants are presented for the most significant chloroform solvation complexes. Nonspecific dilution shift is important and more helpful in fitting NMR data than the assumption of a chloroform dimer. Physical effects and an orientation factor are used to predict excess enthalpy in chloroform/n‐hexane mixtures where no solvation or association reactions occur. Model parameters are used to predict excess molar volumes and enthalpies. Commonly reported stability constants are concentration dependent.
Removal of oil films from stainless steel tubes
Authors: Yan Jenn‐Feng , Sáez A. Eduardo , Grant Christine S. 
Published: June 2004

AbstractThe removal of oil films from the inner surface of a stainless steel tube cell using aqueous cleaning solutions was studied. The two oils used in the cleaning experiments, Sunquench 1042 and heavy mineral oil, contained P32 labeled tributyl phosphate (TBP) as a radioactive tracer. The β‐ particles emitted from the radioactive TBP were detected by a CaF2 scintillator and used as a measure of the amount of oil remaining in the tube cell. Cleaning experiments performed at different flow rates, surface treatment, and surfactant concentrations indicated that initially the oil films were removed rapidly. At the end of the experiments, the oil removal rate reduced significantly, eventually becoming negligible. The stainless steel morphology affected oil removal significantly, and the rougher tube tended to retard the oil removal. The rate and extent of the decontamination were significantly increased in the presence of sodium dodecyl sulfate, a nonionic surfactant. Experimental data were compared to a hydrodynamic model based on the removal of a liquid contaminant from a solid surface by an immiscible fluid. The model deviated from the experimental data due to the presence of instabilities at the oil‐water interface.
Digital particle imaging velocimetry of viscoelastic fluids
Authors: Pakdel Peyman , McKinley Gareth H. 
Published: June 2004

AbstractWe investigate the utility of digital particle imaging velocimetry (DPIV) for performing kinematic measurements in non‐Newtonian flows. With the advances in numerical techniques for simulation of viscoelastic flows, acquisition of spatially dense 2‐D kinematic data in steady and time‐dependent deformations can be useful in verifying predictions of the corresponding computational studies. Furthermore, kinematic measurements of the velocity field and rate of deformation in prototypical industrial processes can significantly enhance the rational design and optimization of polymer processing unit operations. Application of a high seeding density DPIV technique in viscoelastic media is discussed, and quantitative data are obtained in a number of industrially relevant flow geometries. The issues of velocity‐position assignment and the effects of a velocity gradient across DPIV correlation regions are discussed. A simple yet effective averaging technique preserves the order of accuracy and assigns the velocity vectors to their appropriate positions using an overlapping discretization scheme. The examples studied experimentally include steady flow in circular pipes, flow past obstructions, flow in a lid‐driven cavity, and time‐dependent free‐surface extensional flows in a liquid filament. With the exception of the first example, these flow geometries constitute an important collection of configurations in which quantitative experimental data for non‐Newtonian fluids are scarce or nonexistent.
Turbulence in flocculators: Effects of tank size and impeller type
Authors: Ducoste Joel J. , Clark Mark M. , Weetman Ronald J. 
Published: June 2004

AbstractPast research shows that for the same power per unit volume, flocculation performance varies with tank size and impeller type. This study was performed to characterize effects of scale and impeller design on turbulence produced in the flocculation process. The study was performed with a Rushton turbine and an A310 foil impeller in three square tanks of 5‐, 28‐ and 560‐L volume. Fluid velocities were measured using a dual‐channel laser Doppler velocimeter with an enhanced burst spectrum analyzer. Flocculation tanks were operated at a constant average unit‐mass energy‐dissipation rate of 0.0016 m2/s3. The results show that the turbulence intensity and local turbulent energy‐dissipation rate were higher for the Rushton turbine than for the A310 impeller. The turbulence intensity was found to increase with increasing tank size regardless of impeller type. The local turbulent energy dissipation rate decreased for the Rushton turbine and remained constant for the A310 impeller with increasing tank size.
Efficient sampling technique for optimization under uncertainty
Authors: Diwekar Urmila M. , Kalagnanam Jayant R. 
Published: June 2004

AbstractThe concept of robust design involves identification of design settings that make the product performance less sensitive to the effects of seasonal and environmental variations. This concept is discussed in this article in the context of batch distillation column design with feed stock variations, and internal and external uncertainties. Stochastic optimization methods provide a general approach to robust/parameter design as compared to conventional techniques. However, the computational burden of these approaches can be extreme and depends on the sample size used for characterizing the parametric variations and uncertainties. A novel sampling technique is presented that generates and inverts the Hammersley points (an optimal design for placing n points uniformly on a k‐dimensional cube) to provide a representative sample for multivariate probability distributions. The example of robust batch‐distillation column design illustrates that the new sampling technique offers significant computational savings and better accuracy.
Simulation and design of fluid catalytic‐cracking riser‐type reactors
Authors: Theologos K. N. , Nikou I. D. , Lygeros A. I. , Markatos N. C. 
Published: June 2004

AbstractTwo‐phase flow, heat transfer, and reaction in fluid catalytic‐cracking riser‐type reactors are studied using a 3‐D mathematical model. This study was carried out based on the model of Theologos and Markatos, which incorporates a detailed ten‐lump reaction kinetics scheme and accounts for gradual feedstock vaporization inside the reactor. Predictions obtained using the new model are compared against industrial reactor operating data. A design study was also carried out to illustrate that the model developed is capable of predicting feed‐injector geometry effects on overall reactor performance. It shows that by increasing the number of feed‐injection operating nozzles at the bottom of the reactor, selectivity of primary products is improved.