bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reducing NOx in diesel exhausts by SCR technique: Experiments and simulations
Authors: Andersson S. Lennart , Gabrielsson Pär L. T. , Odenbrand C. U. Ingemar 
Published: June 2004

AbstractResults of experiments are compared to simulations of the performance of V2O5/γ‐alumina SCR catalyst used to remove nitrogen oxides from diesel exhausts. The kinetic model is based on Eley‐Rideal kinetics. Temperature programmed desorption (TPD) of the ammonia is used to evaluate adsorption/desorption parameters. Stationary experiments on a 3.6‐dm3 engine with a 4.8‐dm3 honeycomb catalyst is used to evaluate kinetic rate parameters for the reduction of NO with NH3. The desorption activation energy, Ea,des, is best fitted as a function of surface coverage yielding Ea,des = 240* (I −0.44* θ) kJ/mol. A dynamic test (FTP) with a 12‐dm3 engine and24.8‐dm3 honeycomb catalyst is done with astoichiometric injection of ammonia. The NOx conversion is 52%, but during the freeway traffic the conversion reached 72%. The prediction of NOx conversion is good, but there are some deviations for temperature and ammonia slip.
Solubilization of trichloroethylene by polyelectrolyte/surfactant complexes
Authors: Uchiyama Hirotaka , Christian Sherril D. , Tucker Edwin E. , Scamehorn John F. 
Published: June 2004

AbstractAn automated vapor pressure method is used to obtain solubilization isotherms for trichloroethylene (TCE) in polyelectrolyte/surfactant complexes throughout a wide range of solute activities at 20 and 25°C. The polyelectrolyte chosen is sodium poly (styrenesulfonate), PSS, and the surfactant is cetylpyridinium chloride or N‐hexadecylpyridinium chloride, CPC. Data are fitted to the quadratic equation K = K0 (1 − αX + βX2), which correlates the solubilization equilibrium constant (K) with the mole fraction of TCE (X) in the micelles or complexes at each temperature. Activity coefficients are also obtained for TCE in the PSS/CPC complexes as a function of X. The general solubilization behavior of TCE in PSS/CPC complexes resembles that of TCE in CPC micelles, as well as that of benzene or toluene in CPC micelles, suggesting that TCE solubilizes in ionic micelles both within the hydrocarbon micellar interior and near the micellar surface. The presence of the polyelectrolyte causes a small decrease in the ability of the cationic surfactant to solubilize TCE, while greatly reducing the concentration of the surfactant present in monomeric form. PSS/CPC complexes may be useful in colloid‐enhanced ultrafiltration processes to purify organic‐contaminated water.
Control of emulsion polymerization reactors
Authors: Dimitratos John , Eliçabe Guillermo , Georgakis Christos 
Published: June 2004

AbstractThe interest in emulsion polymerization is strong because it offers the possibility of producing products with special properties not easily produced by other types of polymerization processes. Because the main reaction medium is water, not an organic solvent, its importance is steadily increasing with efforts to design environmentally benign processes. The control of emulsion polymerization is a challenging problem due to major limitations encountered in its modeling and on‐line monitoring. Although emulsion polymerization has been studied and used for several decades, progress has been slow. Industrial practice relies heavily on experience while several controversial issues are still being studied. The literature related to this issue is vast and sometimes contradictory, and most deals with experimental investigation of specific emulsion polymerization systems to improve the process understanding and develop a process model. However, universally accepted conclusions are scarce. This article reviews the major issues related to control of emulsion polymerization. The latest contributions in process understanding, mathematical modeling, sensor technology, and process control techniques for emulsion polymerization are discussed. Emphasis is on contributions, which are important in resolving the control of emulsion polymerization processes.
Oxidation of benzyl alcohol using hypochlorite ion via phase‐transfer catalysis
Authors: Asai Satoru , Nakamura Hidemi , Sumita Toshihiko 
Published: June 2004

AbstractHeterogeneous oxidation of benzyl alcohol using hypochlorite ion with phase‐transfer catalyst is carried out in an agitated vessel with a flat interface. Cetyltrimethylammonium bromide and toluene are chosen as the best catalyst and solvent, respectively. Observed reaction rates are proportional to the interfacial concentration of cetyltrimethylammonium hypochlorite in the organic phase, which is formed by ion exchange between bromide and hypochlorite ions. They are reasonably explained by the proposed theoretical model for the phase‐transfer catalysis. The reaction rate constant evaluated by fitting the rate data to the model prediction is 22.7 m3 /kmol·s at 303 K, independent of the physical properties in the aqueous solutions. The maximum yield of benzaldehyde is about 90% and the selectivity is 100% for the conversion of hypochlorite ion less than 80%.
Analysis of dispersed‐phase systems: Fresh perspective
Authors: Ramkrishna Doraiswami , Sathyagal Arun , Narsimhan G. 
Published: June 2004

AbstractDispersed‐phase systems are analyzed with a fresh perspective where the volume fraction of the dispersed phase is emphasized, not particle numbers as in population balance. Such volume fraction balances are more pertinent to engineering because they deal with the amount of the dispersed phase relative to that of the continuous phase. Although it is easy to make detailed volume fraction balances directly or from population balance, many interesting features are identified here with balance equations in terms of volume fraction, which simply characterize the dispersion process and structure the resulting equation. They lead to equivalent “single‐particle” (comprising the entire dispersed phase) processes which can be simulated with great simplicity allowing rapid calculation of quantities associated with the dispersed phase and dispersion. The techniques can solve an inverse problem for mass‐transfer coefficients of individual droplets from (simulated) measurements of the bivariate distribution of drop size and concentration of a transferring solute. Such inverse problem method is important in developing experimental techniques techniques to measure multivariate population distributions such as those of Bae and Tavlarides (1989) and of flow cytometry.
Theory of gas diffusion and permeation in inorganic molecular‐sieve membranes
Authors: Shelekhin A. B. , Dixon A. G. , Ma Y. H. 
Published: June 2004

AbstractTheoretical models of gas diffusion and permeation in microporous molecularsieve membranes are presented. The effect of the adsorbed diffusant on the total transmembrane flow is insignificant for permanent gases. For highly adsorbable gases the effect of the adsorbed molecules on the total transmembrane flux may be high at low temperatures. The activation energy of diffusion increases when the kinetic diameter of the diffusant increases. The activation energy of gas diffusion compares well with the values calculated based on the Lennard‐Jones potential. Maximum possible permeability coefficients calculated for He in the molecular‐sieve membranes do not exceed ˜30,000 Barrer at room temperature. The experimentally observed value for He permeability is ˜1,000 Barrer (T=30°C) because of the high tortuosity (τ≈︁ 25) and low porosity (θ = 0.22) of the membrane porous structure.
Nucleation, agglomeration and crystal morphology of calcium carbonate
Authors: Tai Clifford Y. , Chen Pao‐Chi 
Published: June 2004

AbstractA pH‐stat MSMPR crystallizer is used to obtain the nucleation rate equation of calcite formed in the Na2CO3‐CaCl2 reacting system. The experiments are conducted for seeded and unseeded runs. Effects of breakage and agglomeration on the crystalsize distribution are demonstrated. In a continuous operation, the agglomeration of nuclei followed by the breakage of agglomerates occurs at the transient state, while the agglomeration is significant at the steady state. Taking crystal agglomeration into account, the corrected nucleation rate and agglomeration rate are obtained simultaneously. The agglomeration rate is a function of relative supersaturation and magma density, and the corrected nucleation rate is approximately two‒ to five‐fold of the apparent nucleation rate, which is the nucleation rate without considering the agglomeration effect. Discussed also is the formation of calcium carbonate polymorphism.
Separation vector formulation for the synthesis of multicomponent separation sequences
Authors: Kao Yuen‐Koh 
Published: June 2004

AbstractA new separation system representation uses stream separation vectors in the separation space. The characteristics of a separation sequence are clarified by its separation base vectors that form the sequence basis and those of a separation system by the geometrical properties of separation vectors. The optimal flowsheet of each sequence under separation vector formulation can be obtained as the solution of a linearly‐constrained optimization problem. A set of simple rules determines the minimum separation loads of any sharp separation sequence by inspection. A modified cost measure, which combines the separation cost with the savings due to stream bypass, can be used to select the optimal sequence without the overall cost analysis.The optimal separation sequence is obtained first by identifying the best sequence configuration according to modified cost measures and then by finding the actual costs of maximum‐bypass and its neighboring sequence configurations. For the nonlinear objective function, the exact optimal flowsheet is determined by solving a linearly‐constrained optimization problem. Since this procedure is a linearly‐constrained optimization problem, the mathematical programming solution is not likely to lead to a local minimum.
Unified excitation and performance diagnostic adaptive control framework
Authors: Hinde Ralph F. , Cooper Douglas J. 
Published: June 2004

AbstractModel‐based controllers contain two elements that must be adjusted to maintain desired performance: parameters of the process model and a tuning parameter in the controller design equation. A unified framework is presented where vector quantizing networks are used in pattern‐based methods for diagnosing process excitation and controller performance. Excitation diagnostics identify sufficiently excited dynamic process data for model updating. Performance diagnostics analyze set point response data and determine appropriate updates to the tuning parameter. Supervisory adaptation logic enables these two adaptive mechanisms to work together to maintain model accuracy and desired controller performance. The method is general to a number of model‐based control algorithms and process model forms. Demonstrations employ a FOPDT model, as well as both the PI and DMC algorithms for set point tracking and disturbance rejection in a simulation and a bench‐scale process.
Silica gels made by bicontinuous microemulsion polymerization
Authors: Burban J. H. , He Mengtao , Cussler E. L. 
Published: June 2004

AbstractMicroporous silica gels can be made by polymerizing partially hydrolyzed tetramethoxysilane sols present in the aqueous phase of bicontinuous microemulsions stabilized with didodecyldimethylammonium bromide. When vacuum‐dried, the gels made in microemulsions have about twice the specific surface area of conventional vacuum‐dried silica gels. They have 70% of the specific area of supercritically dried gels. Small‐angle X‐ray Scattering measurements in these gels show two characteristic sizes. One size, around 24Å, in the original microemulsion is retained during polymerization, but lost when the detergent is extracted. The second size grows with the square root of time during the polymerization, suggesting diffusion‐controlled gelation.
Diffusion of gases in polymer blends near the lower critical solution temperature
Authors: Li R. J. , Kwei T. K. , Myerson A. S. 
Published: June 2004

AbstractGas diffusion through miscible blends of polystyrene (PS) with poly(vinyl methyl ether) (PVME) and poly(styrene‐stat‐acrylonitrile) (PSAN) with poly(methyl methacrylate) (PMMA) is studied from temperatures below the corresponding lower critical solution temperature (LCST) to temperatures above. The Arrhenius equation describes the temperature dependence of diffusion coefficients of pure components. Diffusion coefficients of methane in the 20/80 PS/PVME blend also follow the Arrhenius equation in the temperature ranges above and below their corresponding LCST; however, discontinuity is observed in the LCST region. In contrast to the PS/PVME blend, discontinuity in the LCST region is not obvious for nitrogen and methane in the 50/50 PSAN/PMMA blend. These phenomena are discussed in terms of free volume and morphology changes in the LCST region.
Visualization and simulation of bubble growth in pore networks
Authors: Li X. , Yortsos Y. C. 
Published: June 2004

AbstractNucleation and growth of bubbles in porous media are important problems encountered in processes such as pressure depletion and boiling. Experiments and numerical simulations are studied in micromodel geometries to understand their basic aspects. Experiments of bubble growth by pressure depletion are carried out in 2‐D etched‐glass micromodels and in Hele‐Shaw cells. Nucleation of bubbles and subsequent growth of gas clusters are visualized. Contrary to the bulk or Hele‐Shaw cells, gas clusters in the micromodel have irregular and ramified shapes and share many of the features of an external invasion process (such as percolation during drainage). A pore network numerical model developed simulates the growth of multiple gas clusters under various conditions. It is based on the solution of the convection‐diffusion equation and accounts for capillary and viscous forces, which play an important role in determining growth patterns. Numerical simulation agrees well with the experimental results.
Effect of long‐range correlations on transport phenomena in disordered media
Authors: Sahimi Muhammad 
Published: June 2004

AbstractThree different flow and transport phenomena considered here are hydrodynamic dispersion in heterogeneous porous media and aquifers, transport of passive particles in an oscillating flow field, and miscible displacement processes in heterogeneous reservoirs. At microscales all three phenomena are described by the classical convective‐diffusion equation (CDE). The presence of long‐range correlations at macroscales gives rise to a rich variety of phenomena that cannot be predicted by analyzing the CDE by classical methods. In particular, a new percolation model with long‐range correlations provides a rational explanation for the hitherto unexplained field‐scale experimental data for hydrodynamic dispersion in porous media and aquifers. Moreover, for transport in oscillating flow in convection cells percolation provides a novel relation between the dispersion coefficient and the Péclet number that cannot be predicted by other methods.
Linear eddy modeling of reactant conversion and selectivity in turbulent flows
Authors: Frankel S. H. , McMurtry P. A. , Givi P. 
Published: June 2004

AbstractThe linear eddy model (LEM) is used for statistical predictions of stationary, homogeneous turbulent flows under the influence of isothermal chemical reactions. Nonpremixed reacting systems are considered with two reaction mechanisms: a binary, irreversible single‐step reaction A + B ↦ P; the series‐parallel reaction A + B ↦ R, A + R ↦ P. In both systems, the influence of various flow parameters on the reactant conversion rate is elucidated. For the second reaction scheme, effects of the flow parameters on the “selectivity” are also investigated. The trends predicted by the LEM agree with those produced previously by direct numerical simulation (DNS) at moderate values of the Reynolds number, Schmidt number and Damköhler number. An important feature of the LEM is its capability to extend the parameter range well beyond that currently attainable by DNS. The LEM generated results for a wide range of Schmidt and Damköhler numbers are discussed as well as their effects on the selectivity. These results assess the performance of some of the existing closures for modeling of the selectivity. None of the closures are capable of reproducing the LEM results.
Analysis and shape inequalities for gas‐solid reactions with changing volume
Authors: Cao Giacomo , Strieder William , Varma Arvind 
Published: June 2004

AbstractFor gas‐solid noncatalytic reactions following the sharp‐interface model, some fundamental aspects, not discussed previously in the literature, are presented for particle shapes where diffusion processes are described by a single space dimension. A detailed structure analysis of the solution for monotone nonlinear kinetics reveals interesting differences in the dynamics of the interfacial reaction front, including local maxima and minima in the rate of reaction interface motion, depending on particle shape and expanding or shrinking particle size. Rigorous shape inequalities on the interfacial reactant concentration, the motion of the reaction front and the particle conversion for the sphere and slab, and cylinder and slab geometries are obtained for any nonlinear monotonically increasing reaction kinetics and a wide range of parameter values. By taking advantage of these inequalities, the fraction of original solids of spherical or cylindrical shape, which remains unconverted at the exit of a fluidized‐bed reactor, is bounded by the corresponding quantities related to the slab shape. As an example, a first‐order reaction of the gaseous reactant is considered, where expressions for the reactor are obtained analytically, without any assumptions about possible controlling regimes. These analytical bounds for reactor conversion closely approximate the numerical solutions for design purposes.
Detailed kinetics of titanium nitride synthesis
Authors: Rode Hilmar , Hlavacek Vladimir 
Published: June 2004

AbstractA thermogravimetric analyzer is used to study the synthesis of TiN from Ti powder over a wide range of temperature, conversion and heating rate, and for two Ti precursor powders with different morphologies. Conversions to TiN up to 99% are obtained with negligible oxygen contamination. Nonisothermal initial rate and isothermal data are used in a nonlinear least‐squares minimization to determine the most appropriate rate law. The logarithmic rate law offers an excellent agreement between the experimental and calculated conversions to TiN and can predict afterburning, which is an important experimentally observed phenomenon. Due to the form of the logarithmic rate law, the observed activation energy is a function of effective particle size, extent of conversion, and temperature even when the intrinsic activation energy remains constant. This aspect explains discrepancies among activation energies obtained in previous studies. The frequently used sedimentation particle size is a poor measure of the powder reactivity. The BET surface area indicates the powder reactivity much better.
Phase transition extraction using solvent mixtures with critical point of miscibility
Authors: Ullmann Amos , Ludmer Zvi , Shinnar Reuel 
Published: June 2004

AbstractA novel separation process, phase transition extraction, proposed in this article uses solvents that have a critical point of miscibility with the feed liquid to be extracted. Alternate heating and cooling across the coexistence curve leads alternatively to a homogeneous phase or two separate phases. The formation of a homogeneous phase in the mixing stage eliminates the need for intense agitation. Coalescence on cooling in the settling stage is rapid in the presence of impurities that in conventional extraction lead to emulsions. A fermentation broth is extracted without a centrifuge with improved recovery of the antibiotic extracted. The process may have a significant advantage for cases in which extraction is difficult either due to formation of stable emulsions and dispersions or shear sensitivity.
Adjustable discretized population balance for growth and aggregation
Authors: Lister J. D. , Smit D. J. , Hounslow M. J. 
Published: June 2004

AbstractThe discretized population balance (DPB) of Hounslow et al. (1988) is extended to allow the use of an adjustable discretization of the size domain of the form νi+/ν1=2 1/q (where q ≥ 1 and is an integer). All the advantages of Hounslow et al.'s original work are retained: the zeroth and third moments of the particle‐size distribution are correctly predicted, and the DPB is simple to solve with no integration within each size interval. The predicted and analytical particle size distributions are in excellent agreement for the cases of nucleation and growth and aggregation alone in batch and in continuous vessels. High‐order moments and self‐preserving particle‐size distributions are accurately predicted when q ≥ 4.
High‐temperature kinetic study for the reactive ion etching of InP in BCl3/Ar/O2
Authors: Demos Alex T. , Fogler H. Scott , Fournier Jeffrey , Elta Michael E. 
Published: June 2004

AbstractThe reactive ion etching kinetics of InP studied uses BCl3/Ar and BCl3/Ar/O2 as etchants. High‐temperature etching using BCl3 and Ar increases the etch rate negligibly. However, the addition of 30% oxygen in the gas feed increases etch rates by a factor of 10,000 up to 1.5 micron/min at wafer temperatures of 250°C. X‐ray photoelectron spectroscopy analysis reveals that oxygen removes the boron species adsorbing on the InP surface by scavenging the boron to form volatile boron oxides. To study the gas‐phase chemistry, optical emission spectroscopy is used to monitor atomic chlorine intensity at different gas mixtures. The chlorine intensity shows a Gaussian‐type dependence with oxygen addition, which is similar to the etch rate dependence. Two regimes of etching found are: at temperatures below 150°C, the etching is limited by the removal of indium chlorides; above 180°C, the etching is reaction‐limited. The surface morphology shows that the etch profile becomes rougher as a result of increased chemical etching. At high power densities (0.21 W/cm2) and intermediate temperatures (150°C), near vertical wall shapes are obtained. A kinetic model for the high‐temperature etching is developed, as well as a rate law based on the InCl formation reaction. The rate law compares favorably with experimental etch rate results.
Measurement of protein diffusion in Dextran solutions by holographic interferometry
Authors: Kosar T. Fettah , Phillips Ronald J. 
Published: June 2004

AbstractTheories and experimental measurements related to the diffusion of globular macromolecules and small spheres in polymer solutions are discussed. It is shown that the Kirkwood‐Riseman point scatterer and Brinkman models, two theoretical approaches that lead to hydrodynamic screening, are equivalent. Holographic interferometry is presented as a new method for measuring gradient diffusion of proteins in transparent polymer solutions and gels. This method is used to examine the effect of ionic strength, polymer concentration and polymer molecular weight on the diffusion of bovine serum albumin (BSA) in dextran solutions. The data are interpreted in light of the hydrodynamic screening and Stokes‐Einstein models of diffusion. In particular, it is shown that while the Stokes‐Einstein equation may be appropriate for the diffusion of relatively large latex spheres in polymer solutions, it is inappropriate for predicting diffusion coefficients of BSA and comparable proteins in such solutions.