bluuebunny/crossref_metadata_2025_split huggingface dataset:
Catalyst attrition in fluidized‐bed systems
Authors: Werther J. , Reppenhagen J. 
Published: April 2004

AbstractCatalyst attrition has often been a major obstacle in the development of new fluidized‐bed processes and it is still of concern for existing processes whenever the catalyst is changed. The main consequence of attrition is the generation of fines and the resulting loss of valuable material. In this work the attrition of FCC catalysts in a fluidized‐bed system consisting of a bubbling bed, cyclone gas cleaning, and external solids recirculation is studied. An approach developed describes the attrition‐induced overall solids loss based on the main attrition sources: grid jet attrition, bubble‐induced attrition, and attrition in the cyclone. Their respective contributions to the overall attrition rate are calculated from separately derived model equations that take into account the design of the system, the operating conditions, and the material properties of the catalysts. The solids entrainment from the bed into the cyclone is shown to have a strong effect on the attrition‐induced loss rate and must therefore be taken into account for an a‐priori prediction.
Modeling agglomeration processes in fluid‐bed granulation
Authors: Cryer Steven A. 
Published: April 2004

AbstractMany agrochemicals are formulated as water dispersive granules through agglomeration, beginning with a fine powder (∼1 μm) and ending with granules on the order of 500 μm. Powders are charged into a granulation system with a liquid binding agent, and granules are subsequently grown to an appropriate size. Granulation in fluid beds is presented using a mass conserving discretized population balance equation. Coalesce kernels governing the rate and extent of granulation are assumed dependent on the Stokes number, which is indirectly linked to important process variables (air and binder flow rate, bed charge, bed geometry) such that the physical processes governing particle coalescence and rebound are correlated to process variables. A new coalescence kernel is proposed based on physical insight, simplicity, and deterministic equivalent modeling to account for uncertainty. This kernel is based on a Stokes number method where uncertainty in the Stokes number is characterized by polynomial chaos expansions. The magnitude of the coalescence kernel is proportional to the probability of the distribution of Stokes number exceeding a critical value. This mechanistic/semiempirical approach to fluid‐bed agglomeration fosters an environment for process scaleup by eliminating specific equipment and process variable constraints to focus on the underlying mechanisms for proper scale‐up procedures. Model predictions using this new kernel are then compared to experimental pilot‐plant observations.
Modeling of particle evolution in aerosol reactors with coflowing gaseous reactants
Authors: Bensberg Andreas , Roth Paul , Brink Reinhard , Lange Helmut 
Published: April 2004

AbstractA simple model is presented for simultaneous nucleation and coagulation in combination with convective and diffusive particle transport in gas‐phase aerosol reactors over the entire particle‐size spectrum. This model is applied to a spatially inhomogeneous aerosol reactor. The flow and reaction characteristics correspond to a confined coflow diffusion flame of SiCl4 and NH3 in a wall‐heated flow. The reactor geometry and the initial and boundary conditions suggest the application of the boundary layer approximations. The reaction process is described by the flame‐sheet model. The particle‐size spectrum is approximated by a unimodal lognormal function. The characteristics of the SiN4 aerosol (concentration, polydispersity, and average particle size) calculated at every point in the reactor vary significantly in space. At the position of the reaction zone in the outlet cross section, for example, the average particle radius is small (rg ≈1 nm) and the standard deviation is large (σ > 2). At other radial positions the particles are much larger (rg
≈15 nm) and the size distribution is almost self‐preserving (σ≈1.36).
Situating the high‐density circulating fluidized bed
Authors: Grace John R. , Issangya Allan S. , Bai Dingrong , Bi Hsiaotao , Zhu Jingxu 
Published: April 2004

AbstractGas–solid flow in high‐density circulating fluidized‐bed risers differs significantly from that in conventional flow regimes, including fast fluidization and pneumatic conveying. It is shown that when there is no downward flux at the wall at high suspension densities, and hence no core/annulus structure, the flow corresponds to a dense suspension upflow regime. This flow regime is explained, and its key properties given. A lower boundary is also proposed for this new flow regime based on available data.
Novel mixing tank for improved gas–liquid mass transfer and solids suspension
Authors: Palmer Harvey J. , Hughes Christine M. C. , Lessen Martin , Greenleaf Jennifer , Buehler Kristen L. , Villalobos Carmen 
Published: April 2004

AbstractA novel, baffleless, mixing tank configuration presented provides greater mixing efficiency than conventional technologies under a wide variety of operating conditions. The concept uses a cylindrical tank with a contoured bottom and a shroud that surrounds an axial flow impeller and supports a set of stationary “antiswirl” fins positioned in close proximity to the impeller blades. The angle and pitch of the fins impart an angular component to the flow that is equal and opposite to the swirl induced by impeller rotation, thereby eliminating the need for wall baffles. The contoured bottom eliminates dead spaces beneath the impeller and in the corners of flat‐bottom mixing tanks. This alternative mixing system, named the ASSET system, is compared to conventional mixing configurations through experiments of power consumption, gas–liquid mass transfer, and solids suspension. Measurements of Power number vs. Reynolds number reveal that it has power requirements similar to those of high‐efficiency axial‐flow turbines in a conventional tank geometry. Unsteady‐state oxygen absorption and stripping experiments are used to determine the interphase mass‐transfer coefficient as a function of power input for each configuration at superficial gas feed velocities of 0.057 to 0.17 cm/s. With this system, KL a values are on average 30 to 50% greater than those obtained in a conventional mixing tank at the same power input. Measurements of the height of the well‐mixed region of suspended solids in a 15 wt. % mixture of 0.1‐cm‐dia. glass beads in water indicate that the ASSET system requires ∼30% less power to achieve equivalent extents of solids suspension than the conventional setup.
Modeling of liquid/liquid separation by pervaporation: Toluene from water
Authors: Meuleman Erik E. B. , Bosch Bert , Mulder Marcel H. V. , Strathmann Heiner 
Published: April 2004

AbstractThe resistances‐in‐series model, the modified solution‐diffusion model, the Flory–Rehner theory, and the film theory were used to calculate the diffusion coefficients of two components of a liquid‐feed mixture that are separated by pervaporation. The toluene and water fluxes through EPDM membranes of various thicknesses were modeled for different mass‐transfer coefficients in the feed boundary layer (kL). It is shown that the toluene flux depends strongly on the kL and the membrane resistance affects significantly the toluene flux only for very high values of kL (>10−4 m/s). The water flux increases linearly with the reciprocal value of the membrane thickness and is not affected by the boundary‐layer resistance. The small increase in the water flux, due to the toluene concentration increase in the feed, can adequately be described by this model.
Model predictive control technique combined with iterative learning for batch processes
Authors: Lee Kwang S. , Chin In‐Shik , Lee Hyuk J. , Lee Jay H. 
Published: April 2004

AbstractA novel model predictive control technique geared specifically toward batch process applications is demonstrated in an experimental batch reactor system for temperature tracking control. The technique, called Batch‐MPC (BMPC), is based on a time‐varying linear system model (representing a nonlinear system along a fixed trajectory) and utilizes not only the incoming measurements from the ongoing batch, but also the information stored from the past batches. This particular feature is shown to be essential for achieving effective tracking control performance despite model errors and disturbances. In a series of experiments performed on a bench‐scale batch reactor system, the technique was found to deliver satisfactory tracking performance, as expected, overcoming a large amount of model uncertainty and various process disturbances.
Micromixing efficiency of a novel sliding‐surface mixing device
Authors: Rousseaux Jean‐Marc , Falk Laurent , Muhr Hervé , Plasari Edouard 
Published: April 2004

AbstractA new mixing device, suitable to achieve the mixing of reactants undergoing fast chemical reactions, is studied. In the sliding‐surface mixing device, the chemical reagents are introduced in a confined mixing zone (CMZ), in which high shearing stresses are created in a very small volume to realize rapid micromixing. A system of parallel competing test reactions was used to characterize the micromixing level in the CMZ as a function of feed flow rate, rotation speed, feed pipe position, and a geometric parameter characterizing the CMZ. The influence of these parameters on micromixing efficiency was studied, and a hydrodynamic model was developed. This model successfully predicts micromixing times that were measured at two different flow regimes, two feed points, four recirculation flow rates, three geometric configurations, and various stirrer speeds.
Thermal decomposition of ethylene–comonomer mixtures under high pressure
Authors: Albert Jens , Luft Gerhard 
Published: April 2004

AbstractEthylene is unstable above certain limits of pressure and temperature decomposing into carbon, hydrogen, and methane. The influence of comonomers on this limit were studied. Vinyl acetate, acrylic acid, methyl methacrylate, 1‐butene, and 1‐hexene were added in various concentrations to ethylene and by filling the mixture into a preheated autoclave under high pressure (up to 450°C and 150 MPa). As a function of starting pressure and temperature, two reaction pathways can be distinguished: (1) stable (co‐) polymerization and (2) (co‐)polymerization with decomposition. Lowering the boundary between these two pathways seemed to be caused mainly by the thermal stability of the comonomer, for mixtures with vinyl acetate and methyl methacrylate, while an inhibition effect and increase in the limits occur in the comonomer acrylic acid, 1‐butene, and 1‐hexene. The maximum values of pressure, pressure increase, and temperature during decomposition were also influenced by comonomers. The maximum explosion pressure as a function of mixture density has a maximum for pure ethylene. As a function of ethylene concentration, the maximum explosion pressure has minimum values for pure ethylene. At a constant wall temperature and small initial pressures, the maximum rate of pressure increases reached a maximum, while, at high pressures, it decreased again. The position of this maximum depends on wall temperature and comonomer. Adding comonomers to ethylene decreases the maximum temperatures during decomposition reaction.
Distributed parameter approach to the dynamics of complex biological processes
Authors: Lee T. T. , Wang F. Y. , Newell R. B. 
Published: April 2004

AbstractModeling and simulation of a complex biological process for the removal of nutrients (nitrogen and phosphorus) from municipal wastewater are addressed. The model developed in this work employs a distributed‐parameter approach to describe the behavior of components within three different bioreaction zones and the behavior of sludge in a secondary settler. Results from a comprehensive experimental validation on an existing pilot‐scale biological‐nutrient‐removal activated‐sludge plant show that model prediction of the components' dynamics is generally good with the exception of acetate in the anaerobic zone and soluble phosphate in the aerobic zone in two experiments. Good results are achieved despite the apparent plant–model mismatch, such as uncertainties with the behavior of phosphorus‐accumulating organisms. Validation of the proposed secondary‐settler model shows that it is superior to two state‐of‐the‐art models in terms of the sum of the square relative errors.
Ligand‐grafted biomaterials for adsorptive separations of uranium in solution
Authors: Hu Michael Z.‐C. , Reeves Mark 
Published: April 2004

AbstractMany organic molecules, particularly biologicals, contain functional groups (ligands) that actively interact with metal ions in solution by adsorption, ion exchange, or chelation/coordination/complexation. Water‐soluble organics have limitations as reagents for metal‐ion separations from aqueous solutions. However, if the ligand molecule(s) are grafted on to an insoluble matrix, the resulting ligand(s)‐containing product becomes useful for separations applications related to metal recovery or remediation. It was discovered that biomolecules containing a primary amino group, secondary amino group, or hydroxyl group could be grafted into a polyurethane polymeric network via in situ polymerization reactions. With carboxyl groups, grafted material showed good selectivity among a group of divalent metal cations, and a uranium‐binding capacity of more than 10 mg/g of polymer. The material can be regenerated by sodium bicarbonate or sodium carbonate solution and reused. Data from a stirred‐tank reactor showed fast uranium‐binding kinetics, and breakthrough‐elution studies with a packed‐column reactor indicated promising process behavior.
Development of liquid‐phase agitated reactors: Synthesis, simulation, and scaleup
Authors: Samant Ketan D. , Ng Ka M. 
Published: April 2004

AbstractA systematic procedure is formulated for the development of liquid‐phase agitated reactors. The procedure has three components: synthesis, simulation, and scaleup. Synthesis leads the user to the reactor geometry, agitator type and speed, number and location of feed addition ports, feed addition or residence time, and heat‐transfer policy that would achieve the desired performance objectives. It is based on an analysis of the interplay of reaction and mixing at various length scales, and a knowledge base of the capacities of heat‐transfer equipment. Simulation assesses the performance of the reactors thus synthesized, taking into account detailed flow properties obtained through computational fluid dynamic simulations, experimental data, or a combination of both. Scaleup provides fundamentally based scaleup rules for direct development of these reactors from laboratory scale to production scale. A comparison of these derived scaleup rules with published empirical rules reveals the underlying physics, applicability, and limitations of these empirical rules. Three examples are presented to illustrate the use of this procedure.
Heat transfer from catalysts with computational fluid dynamics
Authors: McKenna Timothy F. , Spitz Roger , Cokljat Davor 
Published: April 2004

AbstractA computational fluid dynamics software package was used to study heat transfer from spherical particles of different sizes and under different heat‐transfer conditions. It was shown that although the Ranz‐Marshall and other similar correlations are valid in the case where particles do not interact, this is not true for densely packed systems such as those that we find in reactors commonly used in olefin polymerization. It was also demonstrated that convection is in fact not the only means of removing heat from small, highly active particles. Conductive heat transfer between large and small particles present in the same reactor appears to help alleviate problems of overheating and explain why earlier models of heat transfer in olefin polymerization overpredict the temperature rise during early stages of polymerization.
On‐Line runaway detection in batch reactors using chaos theory techniques
Authors: Strozzi F. , Zaldívar J. M. , Kronberg A. E. , Westerterp K. R. 
Published: April 2004

AbstractIn this work nonlinear time‐series analysis using delay coordinate embedding was applied to simulated temperature data from isoperibolic batch reactors to develop an early‐warning detection system of the runaway. In the first part of this study an early‐warning detection criterion, that is, when the divergence of the system becomes positive on a segment of the reaction path, was developed and compared with previous criteria. This criterion has the property of being preserved under phase‐space reconstruction and, hence, it is possible to calculate it when only temperature data are available. This reconstructed divergence is compared with the theoretically calculated divergence using temperature and conversion data. The comparison demonstrates the validity of such an approach finding a new path, lying between the simple use of measured variables and the complex model‐based reconstruction techniques, to assess in advance hazardous situations in chemical reactors.
Simple equation of state for hard‐sphere chains
Authors: Sadus Richard J. 
Published: April 2004

AbstractA simplified thermodynamic perturbation theory‐dimer framework is used to derive an equation of state for hard‐sphere chains. The accuracy of the equation is tested against simulation data for hard‐sphere chains containing up to 201 hard‐sphere segments. A comparison is also presented with the results of other more sophisticated hard‐sphere chain equations of state. The equation reproduces the compressibility factor of hard‐sphere chains obtained from molecular simulation with a reasonable degree of accuracy. The equation can potentially form the theoretical backbone of an equation of state for real chainlike molecules. From a practical perspective, it has the advantage of being considerably simpler than alternative hard‐sphere chain equations.
Amino‐acid extraction using D2EHPA: New description of equilibrium behavior
Authors: Tulasi G. L. , Kumar Sanjeev 
Published: April 2004

AbstractA new reaction mechanism to explain the equilibrium behavior of amino‐acid extraction using di(2‐ethylhexyl)phosphoric acid (D2EHPA) is proposed. This mechanism represents the interaction between amino acid and D2EHPA through a set of two reactions, one at the aqueous–organic interface and the other in the bulk of the organic phase. It quantitatively predicts the hitherto unexplained dependence of apparent equilibrium constant on a single parameter—loading ratio (ratio of concentration of amino acid in the organic phase at equilibrium to initial concentration of carrier). At low loading ratios, reaction in the bulk plays an insignificant role, and interfacial reaction alone can explain the equilibrium behavior. At high loading ratios, both reactions need to be considered. The new mechanism is tested for the extraction of two amino acids, phenylalanine and tryptophan, for which the equilibrium data have been published. New data were also obtained for phenylalanine to test it over a much wider range of parameter values. The proposed mechanism can predict all the data very well.
On‐line estimation of the specific growth rate in the bacitracin fermentation process
Authors: Golobič Iztok , Gjerkeš Henrik , Malenšek Jože 
Published: April 2004

AbstractAn on‐line estimation of the specific growth rate of an aerobic fermentation batch process was conducted based on measurements of oxygen or carbon dioxide concentrations in exhaust gas, or the concentrations of dissolved oxygen in the liquid phase in the fermentor. A simple linear model used was upgraded with a mechanism for a time‐varying forgetting factor to enable good tracking of estimated parameters as well during rapid and large changes in the process. Because the measuring methods used are independent of each other and can identify the process well, mutual control of individual sensors is also possible in industrial reactors. The results from the model agree well with experimentally obtained values for bacitracin fermentation in an 80‐m3 and 1.5‐m3 batch bioreactor. The model provides a good basis for robust adaptive regulation of aerobic batch processes.
Bubble nucleation during devolatilization of polymer melts
Authors: Yarin A. L. , Lastochkin D. , Talmon Y. , Tadmor Z. 
Published: April 2004

AbstractDevolatilization of different types of polymer melts was studied experimentally and theoretically. The experimental work was carried out in a “falling‐strand”‐type apparatus built especially for this study. Polymer samples after devolatilization were examined by scanning electron microscopy. The micrographs obtained showed that strong nucleation of bubble nuclei occurs first in the vicinity of existing primary microbubbles. These bubble nuclei (secondary nuclei) form blisters (microbubbles) growing under appropriate conditions. The growth is controlled by momentum transfer and diffusion. The microbubbles then coalesce leading to formation of large voids and foaming of the polymer strands. The key parameter, the critical bubble radius triggering the process of growth, was assessed from the micrographs. The time dependence of the concentration of the residual styrene (dissolved gas) in polystyrene melt was determined by gas chromatography. A theoretical model of stress‐enhanced secondary nucleation in polymer melts during their devolatilization was developed. It shows that nucleation proceeds due to the growth of initially existing gas bubbles, when a sample is exposed to vacuum. In the vicinity of the bubbles homogeneous nucleation proceeds at an accelerated rate, because it is strongly enhanced by mechanical degradation of polymer macromolecules. The rate of devolatilization was calculated and compared with the experimental data. Theoretical results agreed with the experimental data rather good, although no adjustable parameters characteristic of some of the existing nucleation models were involved.
Raman spectroscopic determination of hydration number of methane hydrates
Authors: Uchida Tsutomu , Hirano Takashi , Ebinuma Takao , Narita Hideo , Gohara Kazutoshi , Mae Shinji , Matsumoto Ryo 
Published: April 2004

AbstractHydration numbers of methane hydrates with various water/gas ratios of the sample were measured by Raman spectroscopy. Artificial methane hydrates were formed at temperatures ranging from 273.2 to 278.4 K, and pressures from 3.0 to 7.0 MPa, with a stirring rate of approximately 500 rpm. Under such nonequilibrium conditions, the obtained hydrate samples had a water/gas ratio ranging from 6.4 to 17.4, which was determined by mass measurements. The spectroscopic analysis revealed, however, that the crystallographic hydration number was almost constant at 6.2±0.2, which corresponds to the hydration number estimated from the thermodynamic model. The same measurements were carried out on natural gas hydrate samples obtained from the deep‐sea floor of Blake Ridge. The coincidence of the hydration numbers between natural and artificial samples indicated that the crystallographic hydration number is independent of the formation conditions and the large variation in the water/gas ratio of samples is described by the ratio between pure hydrate and free water.