bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of waste interception and allocation networks
Authors: El‐Halwagi M. M. , Hamad A. A. , Garrison G. W. 
Published: June 2004

AbstractThis article introduces the novel concept of synthesizing waste‐interception networks (WINs) and incorporates it within a mass‐integration framework for the global allocation of pollutants. The essence of this notion is to provide selective interception and rerouting of undersirable species at the heart of the process instead of dealing with the pollutants in the terminal waste streams. It also provides a unified framework for simultaneously tackling gaseous and liquid pollution. Several tools are developed to track the pollutant throughout the process and determine the optimal interception policies. The problem is formulated as an optimization program that seeks to determine the optimum locations for intercepting the pollutants, extent of separation, and separating agents to carry out the interception tasks. Furthermore, the WINs can be used within a mass‐integration scheme for the global allocation of species throughout the plant. These new concepts and associated mathematical formulation are demonstrated using a case study on the removal of a chlorinated hydrocarbon. This approach has benefits over conventional recycle/reuse (such as MEN synthesis).
Mathematical modeling of fluidized‐bed chlorination of rutile
Authors: Zhou L. , Sohn H. Y. 
Published: June 2004

AbstractA mathematical model was formulated to describe the reaction rate and the particle size distribution of solids in a fluidized bed for the chlorination of rutile by a CO/Cl2 mixture. The bubble assemblage model was applied to describe the gas behavior in the bed. The particle‐size distribution in the bed was determined by a population balance. Predictions of the model gave satisfactory agreement with experimental results. The effects of important variables such as superficial gas velocity, exchange rate between the phases, and the reaction‐rate constant were evaluated.
Optimum jet mixing in a tubular reactor
Authors: Forney Larry J. , Nafia Noureddine , Vo Hanh X. 
Published: June 2004

AbstractThe rapid mixing of two miscible fluids is a precursor to promoting fluid‐phase reactions. The configuration of a turbulent jet in a crossflow or tee‐mixer is the most efficient passive design for rapid mixing. Here the Damkohler number has been defined from available tee‐mixer data where the reactions are slow to fast compared with mixing times. For the available data the Damkohler number has been found to be of secondary importance for optimum design. The numerical simulation of jets in a tubular reactor suggests that large jet‐to‐tube momentum ratios with no backmixing are superior. Moreover, the optimum design of maximum jet entrainment is shown to be synonymous with either a minimum in the relative standard deviation or the skewness. A formula relating the optimum diameter ratio to the jet‐to‐tube flow ratio has also been derived assuming geometrically similar jet trajectories, and the result correlates both numerical and experimental data.
CEOS/AE mixing rules constrained by vdW mixing rule and second virial coefficient
Authors: Twu Chorng H. , Coon John E. 
Published: June 2004

AbstractA new class of mixing rules, with van der Waals one‐fluid mixing rule and second virial coefficient constraints, was developed for cubic equations of state (EOS) for application to various asymmetric, highly nonideal chemical systems. This approach evolved from previous research in the EOS field. The resulting mixing rule is practical in application, yet more flexible than Huron–Vidal or Wong–Sandler mixing rules and depends only on composition and temperature. It also avoids the problems associated with the Wong–Sandler mixing rules. A cubic EOS with the new mixing rules was applied successfully to complex mixtures. The new rules reduce to van der Waals mixing rules when the parameters in the nonrandom excess Helmholtz free energy are set to zero. Since many times the classic mixing rules worked very well for nonpolar systems, it is extremely desirable that the composition‐dependent mixing rules reduce to the classic mixing rules. Preserving this capability also ensures that the binary interaction parameters for the classic quadratic mixing rules in the DECHEMA Chemistry Data Series for mixtures of low boiling substances and other existing databases for systems involving hydrocarbons and gases can be used directly in the new EOS mixing rules, in addition to liquid‐activity coefficient model parameters currently reported in the Series.
Hydrodynamic model for short contact time circulating fluidized bed
Authors: Tinaburri A. 
Published: June 2004

AbstractShort contact time circulating fluidized beds (CFBs) are high‐performance reactors with great potential of application for fast endothermic reactions. Optimal kinetic conditions require high operating temperature and very short residence time (∼0.15 s), as well as plug flow in the reaction zone, and fast and efficient solid separation before quenching effluents. Hydrodynamics of dilute CFB operated at high gas velocity was simulated in isothermal condition. The gas‐flow field is described using turbulence closure models developed for the single phase and modified to account for particle presence. Numerical computation was compared with experimental results of Arena et al. (1993) and Tinaburri et al. (1996) for two different riser configurations. A parametric analysis was performed to investigate inlet geometry influence on flow pattern along the riser. Internal tube and circumferential gas inlet produced the most promising configuration to realize optimal flow condition.
Self‐diffusion in liquids predicted by a theory of flow through granular media
Authors: Sęk Jerzy P. 
Published: June 2004

AbstractA new semiempirical model for prediction of self‐diffusion phenomena in liquids is proposed. Assuming anlogy between the concept of a free volume in liquids and a porosity of a granular medium, a capillary model of the granular bed and the Kozeny‐Carman theory was applied to determine self‐diffusion coefficients in liquids. The dimensionless free volume in liquids was evaluated using a combination of the proposed dependence and an appropriate formula available in the literature. The new model was tested for 89 sets of data concerning self‐diffusion of different chemical substances at several values of a temperature. The average error of a prediction was between ± 1% and about 3% for some data points.
Ultrasound‐modulated two‐fluid atomization of a water jet
Authors: Tsai Shirley C. , Childs Paul , Luu Patrick 
Published: June 2004

AbstractA new spray technique, called ultrasound‐modulated two‐fluid (UMTF) atomization, is based on resonance between the liquid capillary waves generated by ultrasound and those generated by high‐velocity air. The capillary waves generated by ultrasound on the cone of liquid film issuing from a coaxial two‐fluid atomizer are magnified in amplitude by air blowing around them. Atomization occurs when the amplitude of the capillary waves is too great to maintain wave stability, and the resulting drop sizes are determined by the frequency of the ultrasound. Calculations of the relative amplitude growth for the capillary waves of various wavelengths yield predictions that agree remarkably well with experimental results of drop size and size distribution. Specifically, uniform drops with diameter determined by the third harmonic frequency of the ultrasound are obtained in UMTF atomization at high air velocity and large air‐to‐water mass ratio. In contrast, drop‐size distributions with multiple peaks are obtained in UMTF atomization at low air velocity and small air‐to‐water mass ratio. The use of air also allows the liquid jet to atomize at ultrasonic power levels below and liquid flow rates above the threshold values for ultrasonic atomization without air. These new findings provide not only direct evidence of the capillary wave mechanism but also a means of controlling drop size and size distribution in two‐fluid atomization.
Mixing of granular materials in slowly rotated containers
Authors: McCarthy J. J. , Shinbrot Troy , Metcalfe Guy , Wolf J. Eduardo , Ottino Julio M. 
Published: June 2004

AbstractNoncohesive granular materials in slowly rotated containers mix by discrete avalanches; such a process can be described mathematically as a mapping of avalanching wedges. A natural decomposition is thus proposed: a geometrical part consisting of a mapping wedge → wedge, which captures large‐scale aspects of the problem; a dynamical part confined to the avalanche itself, which captures details emanating from differences in size/density/morphology. Both viewpoints are developed and comparisons with experiments are used to verify the predictions of the models. In this article, we develop a model of granular mixing and show how to extend the model in order that it may: (1) handle complicated geometries, (2) be applicable for 3‐D mixers, (3) rapidly test mixing enhancement strategies, and (4) incorporate differences in particle properties. In addition, an optimal fill level is determined for several 2‐D mixing geometries, and a novel hybrid—geometrical/dynamical—computational technique is proposed. By merging the geometrical and dynamical viewpoints, this technique reduces the computational time of a typical molecular‐dynamics‐type simulation by a factor of 15. The ultimate goal is to provide fundamental understanding and tools for the rational design and optimization of granular mixing devices.
Salt‐containing model for simulation of salt‐containing extractive distillation
Authors: Fu Jiquan 
Published: June 2004

AbstractThree binary vapor–liquid equilibrium (VLE) data were measured: tertbutanolethanediol, tertbutanol‐KAc, and ethanediol‐KAc. Experimental data were correlated with the salt‐containing local composition model (SCLCM). For the multicomponent system, VLE data predicted by SCLCM are in agreement with the data in the literature. An industrial plant (3500T/Y) of salt‐containing extractive distillation for the tertbutanol/water/ethanediol/potassium acetate system was simulated by SCLCM and improved the Rose relaxation method. Simulation results agree well with industrial data.
Nonlinear model‐predictive control: Closed‐loop stability analysis
Authors: Sistu Phani B. , Bequette B. Wayne 
Published: June 2004

AbstractA method to analyze the closed‐loop stability of a system composed of a nonlinear process and a discrete controller is developed. The closed‐loop system is described by a set of difference equations resulting from the discretization of the continuous‐time model. A commonly used method of discretization (forward difference) offers an incorrect relative order compared to exact discretization. The state and input sensitivity equations of the continuous‐time model are used in computing the nominal closed‐loop stability criteria. The nominal stability analysis is extended to the important cases of unmeasured states and uncertain model parameters. A numerical Lyapunov function is used to estimate closed‐loop regions of attraction. A simulation example (a CSTR with input multiplicity) presented illustrates the analysis methods and closed‐loop behavior.
Single‐stage fractionation of poly(ethylene‐co‐vinyl acetate) in supercritical ethylene with saft
Authors: Folie Bernard 
Published: June 2004

AbstractUsing the discrete thermodynamics approach, the single‐stage fractionation of a polydisperse poly(ethylene‐co‐vinyl acetate) in supercritical ethylene and ethylene‐vinyl acetate mixtures is modeled with an EOS rooted in statistical associating fluid theory (SAFT). The simulation results are compared to new high‐pressure coexistence data and size‐exclusion chromatography data obtained on a few selected extracts. The polymer molecular‐weight distribution is optimally represented by ten nearly‐monodisperse pseudocomponents, determined by a nonuniform lumping method. SAFT quantitatively captures the effect of pressure, temperature and solvent composition on the solvent capacity and the extract yield over a broad range of conditions. The ethylene capacity monotonically increases with increasing pressure between 200 bar and the cloud point pressure, with increasing VA concentration in the solvent mixture, and with increasing temperature above ∼ 480 bar. At intermediate pressure (200–480 bar), SAFT predicts that the ethylene capacity behaves nonmonotonically with temperature. The extract and raffinate molecular weight and polydispersity are predicted also from SAFT as a function of pressure and solvent composition for a typical bubble‐ and dew‐point‐type fractionation, thereby illustrating the underlying differences between those two phase disengagement mechanisms.
Elementary step model of ethane oxidative dehydrogenation on Pt‐coated monoliths
Authors: Huff Marylin C. , Schmidt Lanny D. 
Published: June 2004

AbstractThe oxidative dehydrogenation of ethane to ethylene over Pt‐coated foam monoliths in oxygen with varying levels of nitrogen dilution has been simulated using a 24‐stepmodel of adsorption, desorption and surface reactions. Reaction parameters for these elementary steps were obtained from surface science and catalysis literature or fit to previously reported experimental data. The model agrees with the experimental data remarkably well, mimicking the selectivity and conversion trends observed experimentally with changing operating conditions. The model shows that a purely heterogeneous mechanism can be used to simulate the experimental results collected near atmospheric pressure accurately, suggesting that the mechanism we propose is sufficiently accurate to capture the main features of this reaction system. This model can also be used to examine this reaction system under conditions experimentally inaccessible. Application of this predictive ability to operation of this type of reactor under probable industrial conditions suggests that excellent ethylene yields are possible.
Coagulation of colloids retained by porous wall
Authors: Harmant P. , Aimar P. 
Published: June 2004

AbstractThe structure of a colloidal deposit retained by a porous wall is described, accounting for surface interactions and hydrodynamic forces. The balance of forces acting over spherical, charged particles allows the calculation of the interparticular distances inside the cake according to the physicochemical conditions (ionic strength, particle potential, pH, particle size) and to the experimental parameters (flux). The model predicts that beyond a critical mass deposited on the porous wall, the structure of the layers near the membrane changes where the particles are in close contact with each other. Experimental data obtained with latex monodisperse particles filtered over various types of ultrafiltration membranes for various physicochemical and flux conditions are compared to the model predictions. These results explain the existence of irreversible colloidal deposits in filtration and suggest strategies to optimize backflush or pulsed pressure procedures often used to improve the efficiency of ultrafiltration or microfiltration.
Nonequilibrium modeling of condensed mode cooling of polyethylene reactors
Authors: Jiang Yan , McAuley Kim B. , Hsu James C. C. 
Published: June 2004

AbstractIn most industrial gas‐phase polyethylene reactors, heat is removed by cooling the recycle gas stream in an external heat exchanger, where a portion of the vapor is condensed. The condensate evaporates in the reactor to absorb heat released by polymerization reactions, thereby increasing the production capacity of the unit. Nonequilibrium methods of multicomponent condensation are applied to develop a 1‐D model to simulate the cooling unit of an industrial polyethylene reactor system operated in partial condensing mode. Finite difference approximations are used to convert the resulting set of differential equations to algebraic equations. A practical method of solving the equations is to combine the rapid local convergence of Newton's method with a globally convergent strategy. Correlation methods for estimating local heat‐transfer coefficients in the liquid film layer are discussed. Butterworth's method for shear‐stress‐controlled condensate flow gives reasonable agreement between simulation results and industrial data, while Chen et al.'s method can better describe the transition process of condensate flow from laminar to turbulent flow.
Effect of dissociation equilibria on ion‐exchange processes of weak electrolytes
Authors: Jansen Marcel L. , Houwers Joop , Straathof Adrie J. J. , Van Der Wielen Luuk A. M. , Luyben Karel Ch. A. M. , Van Den Tweel Will J. J. 
Published: June 2004

AbstractIon‐exchange processes involving weak electrolytes are influenced strongly by the pH via the occurrence of association/dissociation equilibria. This influence was investigated quantitatively through binary displacement experiments with different electrolytes to gain better insight in the role of the pH and to test a fixed‐bed ion‐exchange model used for the description of multicomponent processes. The two major factors determining the ion‐exchange behavior of weak electrolytes are the actual exchange of counterions and the sorption of neutral species. The sorption of neutral species resulted in concentration fluctuations superimposed on the normal ion‐exchange profiles, whereas pH fluctuations inherent to ion‐exchange processes in general also influenced concentration through modified ionic fractions. The relative importance of these contributions is determined by the magnitude of parameters such as resin capacity, distribution coefficients of neutral species, and selectivities of ions, as well as by operating conditions such as concentrations of all species.
Kinetic study of acrylic acid solution polymerization
Authors: Scott Robert A. , Peppas Nikolaos A. 
Published: June 2004

AbstractThe kinetics of acrylic acid (AA) solution polymerizations were characterized under various polymerization conditions using differential scanning calorimetry. The AA polymerization rate Rp decreased with increasing pH over all pH values due to the decreased reactivity of ionized AA relative to the unionized monomer. The rate behavior above pH 6 was suggestive of diffusion‐controlled termination kinetics. The degree of ionization thus impacted not only the reactivity of species in solution but also the diffusive characteristics of propagating macroradicals. As the AA concentration was increased, the change in polymerization rate with pH was substantially less. The temperature dependence of Rp indicated that the overall activation energy for polymerization varied with temperature, due to diffusion‐controlled termination kinetics. The polymerization rate was significantly higher when a multifunctional cross‐linking agent was added, because of the gel effect, even while maintaining a constant double bond concentration.
Dynamics of semibatch polymerization reactors: II. Pilot‐plant study
Authors: Chylla R. W. , Campbell J. David , Teymour F. 
Published: June 2004

AbstractA semibatch flow scheduling strategy proposed by Teymour and Ray (1989, 1996) is evaluated for a polymerization reaction conducted in a pilot‐plant reactor. The reaction used is the free radical terpolymerization of styrene, α‐methyl styrene, and acrylic acid monomers initiated by an organic peroxide initiator and carried out in the presence of a reactive glycol ether solvent. This strategy was tested in both single batch and sequential semibatch modes. The process was shown to produce polymer of constant molecular weight properties and composition as inferred from acid number and monomer conversion measurements. This process could be used for obtaining polymer products from a semibatch reactor that are of comparable quality to CSTR products. Results indicate success of this process at meeting this objective; however, practical considerations relating to agitation and temperature control need to be properly addressed to ensure this success.
Phase equilibria for the mean‐force potential of globular protein solutions
Authors: Tavares Frederico W. , Sandler Stanley I. 
Published: June 2004

AbstractWhen polymers are added to a solution containing proteins, the protein may deposit as an amorphous precipitate or as crystals. Experimental evidence indicates that from a thermodynamic viewpoint, an amorphous precipitate should be treated as a liquid phase dense in the protein and crystals as true solids. To understand the conditions under which protein precipitation or crystallization may occur, Gibbs‐ensemble Monte Carlo simulation and Gibbs–Duhem integration techniques are used to calculate the liquid–liquid and liquid–solid phase boundaries for protein precipitation induced by polymers. In these simulations, the system is modeled using the pseudo‐one‐component approximation with an appropriate potential of mean force. The critical point for fluid–fluid phase equilibrium disappears as the attractive part of the mean‐force potential becomes very short ranged. The accuracy of the second‐order Barker and Henderson perturbation theory is examined by comparing the phase diagram predicted using this method with the simulation results. Perturbation theory is able to predict the general trends observed in the simulations but not with quantitative accuracy. Perturbation theory is then used to examine a broader range of conditions for protein deposition.
Recovery and purification of paclitaxel using low‐pressure liquid chromatography
Authors: Wu D.‐J. , Ma Z. , Au B. W. , Wang N.‐H. L. 
Published: June 2004

AbstractAn efficient and economical low‐pressure liquid chromatography process has been developed for paclitaxel recovery and purification directly from plant‐tissue culture (PTC) broth. PTC broth is first diluted with ethanol to ensure padlitaxel dissolution and then passed through a column packed with a high‐capacity polystyrene divinyl‐benzene sorbent. A step increase in ethanol concentration in the mobile phase (ethanol:water) is used to concentrate and compress the taxane bands to as high as 29‐fold of influent concentrations (about 1 mg/L). A recycle technique is then used to separate the concentrated paclitaxel band from other taxane bands, achieving 95% purity with more than 90% recovery and 99% purity with more than 80% recovery. In this process, the same low‐pressure columns are used to capture, concentrate and purify paclitaxel. Theoretical predictions agree closely with the stepwise elution and recycle chromatography data. After validation, simulations are used to explore various design and operating alternatives. Analysis of the alternatives shows that the process cost can be further reduced by using higher feed concentration, larger loading volume, smaller particle size, and optimal gradient and recycle strategies.