bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identifiability of kinetic parameters of methanol synthesis in plug‐flow tracing
Authors: Otarod Masood , Happel John 
Published: April 2004

AbstractThe identifability of the fundamental kinetic parameters of a model of a plug‐flow isotope transient tracing of methanol over PdNO/Al was investigated. The values of the parameters were estimated by securing a least‐squares fit between the tracer data and the partial differential equations describing the reaction response in a plug‐flow mode. The results demonstrate that modeling and identifiability of isotope transient tracing data provide for a meaningful assessment of heterogeneous catalytic reaction systems.
Dynamic NMR microscopy of chromatographic columns
Authors: Tallarek Ulrich , Bayer Ernst , Van Dusschoten Dagmar , Scheenen Tom , Van As Henk , Guiochon Georges , Neue Uwe D. 
Published: April 2004

AbstractPulsed magnetic field gradients encoded a discrete spatial and temporal motion of the molecules of a fluid percolating through the packed bed of a dynamic radial compression column for liquid chromatography. Two packing materials of porous, chemically bonded C18 silica were used: large irregularly shaped particles (55 – 105 μm) and small spherical particles (6 μm). By combining pulsed field gradient NMR and NMR imaging the distribution of the fluid dynamic displacement probability was determined quantitatively at each point of the static image space. The local axial dispersion coefficient, fluid velocity, and external porosity of the bed were also estimated. The resolution achieved was 250 μm × 250 μm × 2,500 μm per voxel, corresponding to a 250 μm × 250 μm pixel in a 2.5‐mm‐thick slice. Irregularly shaped particles showed slight external porosity heterogeneities over the column cross section, causing a dramatic loss of performance. Spherically shaped particles offered a nearly planar distribution of the transport characteristics across the packed bed, making radial compression of the bed enhance the performance.
Acoustic force distribution in resonators for ultrasonic particle separation
Authors: Woodside Steven M. , Piret James M. , Gröschl Martin , Benes Ewald , Bowen Bruce D. 
Published: April 2004

AbstractThe effectiveness of particle–liquid separation by ultrasonic radiation forces depends on the acoustic energy density distribution in the standing‐wavefield. The energy distribution in an ultrasonic particle‐separation device was analyzed to assist continued optimization and design efforts. Measurements of the energy‐density distribution in the liquid using a microscope‐based imaging system were compared to laser interferometer measurements of the velocity‐amplitude distribution on the transducer and reflector surfaces of the ultrasonic separator. The energy density followed the same trend as the surface velocity, being highest near the resonator center and approaching zero near the walls. The energy density gradients and local gridlike reflector‐amplitude variation had characteristic lengths of 1.4 mm. These results suggest that the energy‐density distribution in the liquid is a defined function of the dimensions, imposed boundary conditions and physical properties of the reflector and transducer. This understanding provides a practical basis for developing a mathematical model of cell aggregation and retention, potentially enabling the design of resonators with predetermined energy density distributions for specific particle aggregation, separation, and fractionation applications.
Robustness metrics for dynamic optimization models under parameter uncertainty
Authors: Samsatli Nouri J. , Papageorgiou Lazaros G. , Shah Nilay 
Published: April 2004

AbstractRecent research in process systems engineering has focused mostly on the issue of making decisions under uncertainty. Various approaches used over the years include optimizing the expected and worst cases, maximizing the feasibility of operation, and constraining variances of performance measures. The consideration of robustness, that is, guaranteeing a reasonable performance over a wide range of uncertainty, is either implicit or explicit in these approaches, and is certainly receiving more attention. In this article, we argue that mathematical techniques for robust optimization must be capable of capturing different perspectives on risk of different users. We define some general robustness metrics that can represent significantly different robustness objectives simply by modifying functions and parameters. We also describe a solution procedure along with two illustrative examples.
Application of a neural network to evaluation of interactions in a MIMO process
Authors: Ohba Takehiro , Ishida Masaru 
Published: April 2004

AbstractA neural‐net controller for multivariable systems is presented. The neural network for this controller has a structure in which small neural‐net controllers for SISO systems are assembled and offers a unique path from the controlled variable to the manipulated variable. By using such a structured assembly, the interactions among the controlled and manipulated variables can be evaluated. The simulation results for both a linear three‐input and three‐output system and a crystal‐growth process indicate that the proposed controller has the ability to learn the interactions between the control variables and to disclose the features of the interactions.
Stability calculations for nonequilibrium separation processes
Authors: Sridhar Lakshmi N. , Torres Monica 
Published: April 2004

AbstractTwo of the most significant contributions in the last two decades to separation process are the numerical implementation of the tangent‐plane criterion to check the stability of any given mixture and the use of mass‐transfer models to solve separation‐process problems. This work combines the use of the tangent‐plane analysis with mass‐transfer models to solve problems with multiple liquid phases. As in equilibrium‐stage problems, the tangent‐plane analysis works effectively with nonequilibrium‐stage separation‐process problems. An example is presented where the nonequilibrium model, when used in conjunction with the tangent‐plane criterion, predicts the correct number of phases, while the equilibrium model predicts the incorrect number of phases.
Finite‐element methods for steady‐state population balance equations
Authors: Nicmanis M. , Hounslow M. J. 
Published: April 2004

AbstractA finite‐element algorithm is developed to solve the population balance equation that governs steady‐state behavior of well‐mixed particulate systems. Collocation and Galerkin methods are used to solve several test problems in which aggregation, breakage, nucleation and growth (and combinations of these phenomena) occur. It is shown that the Galerkin method must be used in growth problems to obtain a well‐conditioned system. In all the cases investigated, density distributions and their moments are accurately predicted by the method. In a direct comparison with the discretized population balance (DPB) of Litster et al. (1995) the finite‐element method proves capable of predictions that are typically two orders of magnitude more accurate than those of the DPB. These results were obtained using smaller systems of equations and with considerably less computational power.
Catalytic liquid‐phase nitrite reduction: Kinetics and catalyst deactivation
Authors: Pintar Albin , Berčič Gorazd , Levec Janez 
Published: April 2004

AbstractLiquid‐phase reduction using a solid catalyst provides a potential technique for the removal of nitrites from waters. Activity and selectivity measurements were performed for a wide range of reactant concentrations and reaction conditions in an isothermal semi‐batch slurry reactor, which was operated at temperatures below 298 K and atmospheric pressure. The effects of catalyst loading and initial nitrite concentration on the reaction rate were also investigated. The Pd monometallic catalysts were found to be advantageous over the Pd‐Cu bimetallic catalyst with respect to either reaction activity or selectivity. Among the catalysts tested, minimum ammonia formation was observed for the Pd(l wt. %)/γ‐Al2O3 catalyst. The proposed intrinsic rate expression for nitrite disappearance over the most selective catalyst is based on the steady‐state adsorption model of Hinshelwood, which accounts for a dissociative hydrogen adsorption step on the catalyst surface and an irreversible surface reaction step between adsorbed hydrogen species and nitrite ions in the Helmholtz layer. Both processes occur at comparable rates. An exponential decay in the activity of Pd(l wt. %)/γ‐Al2O3 catalyst has been observed during the liquid‐phase nitrite reduction. This is attributed to the catalyst surface deprotonation, which occurs due to the partial neutralization of stoichiometrically produced hydroxide ions with carbon dioxide.
Radiation perpendicular to the symmetry axis of prolate and oblate cavities
Authors: Fitzgerald Sean P. , Strieder William 
Published: April 2004

AbstractThermal radiation heat transport within prolate and oblate ellipsoidal cavities was examined. The axisymmetric anisotropy of the cavity shape gives rise to a thermal radiation conductivity tensor with principal axes components parallel (λr, ‖) and perpendicular (λr, ⊥) to the symmetry axis. The prolate (λr, ⊥) and oblate (λr, ⊥) transverse components are calculated and compared with well‐known results from the kinetic theory of transport across cylindrical and within slit void geometries. The use of λr, ⊥ and λr, ⊥, along with earlier results for λr, ‖ and λr, ‖, in well‐known effective conductivity equations for spheroidal inclusions within a solid matrix, provides a means to rigorously treat cavity orientation and shape in high‐temperature heat transport across porous materials. To facilitate the calculations and produce readily usable equations, a variational principle is used.
Liquid backmixing in bubble columns and the axial dispersion coefficient
Authors: Degaleesan Sujatha , Duduković Milorad P. 
Published: April 2004

AbstractLiquid backmixing in bubble columns is commonly described using the 1‐D axial dispersion model, wherein all the contributing mechanisms leading to liquid macromixing are lumped into a single axial dispersion coefficient. No relationship has been reported that allows the quantification of various fluid‐dynamic contributions to the axial dispersion coefficient in bubble columns. In this study, a Taylor‐type analysis was performed to arrive at an expression for the axial dispersion coefficient in terms of the two dominant fluid‐dynamic factors, convective recirculation and eddy diffusion. Experimental measurements of the relevant fluid‐dynamic parameters are used to study the effects of operating conditions on the axial dispersion coefficient and its contributing factors.
Practical model for compressive cake filtration including fine particle invasion
Authors: Civan Faruk 
Published: April 2004

AbstractPractical and improved ordinary differential models for compressible filter cake buildup involving small particle invasion and deposition inside the cake at static and dynamic conditions are developed by averaging particle and carrier fluid transport equations over the filter cake thickness. The models are simplified by considering that the panicles and carrier fluids involving many practical applications are incompressible. The results of radial and linear filtration cases are compared for constant rate and constant pressure drive filtrations. This thickness‐averaged ordinary differential model reproduces the predictions of the Tien et al. (1997) partial differential model rapidly with less computational effort. Parametric studies indicate that the particle screening efficiency of the filter is an important factor on the filter cake properties and filtration rate, and differences between linear and radial cake filtration performances are more pronounced, and the cake thickness and filtrate volume are smaller for constant pressure filtration than constant rate filtration. The equations of the thickness‐averaged linear and radial filter cake formation models are simple requiring less computational effort over the reported partial differential models for the analysis, design and optimization of the industrial cake filtration processes involving plate and drum filters.
FTIR measurements of acid‐gas–methyldiethanolamine systems
Authors: Rogers William J. , Bullin Jerry A. , Davison Richard R. 
Published: April 2004

AbstractThe standard industrial process for the purification of natural gas is to remove acid gases, mainly hydrogen sulfide and carbon dioxide, by the absorption and reaction of these gases with alkanolamines, but the lack of reliable and accurate vapor–liquid equilibrium (VLB) data impedes the commercial application of more efficient alkanolamine systems. A novel Fourier‐transform infrared (FTIR) technique was developed to make in‐situ VLE measurements of acid‐gas‐aqueous alkanolamine systems and to improve the accuracy of VLE measurements at low hydrogen sulfide and carbon dioxide concentrations. VLE measurements of low carbon dioxide and hydrogen sulfide concentrations in aqueous mixtures of methyldiethanolamine (MDEA) are reported using the new FTIR technique.
Influence of H2O2 on a chloride‐dependent reaction path to chlorine dioxide
Authors: Crump Brian , Ernst William R. , Neumann H. M. 
Published: April 2004

AbstractReaction paths governing chlorine dioxide formation from solutions of sodium chlorate, sulfuric acid, hydrogen peroxide and sodium chloride at 25°C were examined. Chlorine dioxide was formed by two paths: the reduction of chlorate by hydrogen peroxide and the reduction of chlorate by chloride. At conditions of this study, the rate of the chloride‐chlorate path predominated and was enhanced by hydrogen peroxide, reaching an upper limit as hydrogen peroxide concentration was increased. A mechanism was proposed that explains the observed behavior. It is based on existing theory, but includes a new step: the rapid reaction of hydrogen peroxide with an intermediate, Cl2O2. It was shown also that chloride was not required to sustain chlorine dioxide formation in the hydrogen peroxide‐chlorate path.
Evaluation of dialysis membranes using a tortuous pore model
Authors: Kokubo Ken‐ichi , Sakai Kiyotaka 
Published: April 2004

AbstractThe pore‐size distribution and diffusive permeability of homogeneous cellulosic dialysis membranes were measured by thermoporometry and by radioisotope and photoabsorption techniques, respectively. A tortuous pore model incorporating membrane pore‐size distribution, in which tortuosity differs with pore size, can predict diffusive permeability for a wide range of solute molecular weights. The tortuosity obtained using the tortuous pore model by fitting the experimentally obtained diffusive permeability varied with molecular weight (Stokes radius). To evaluate the physical meaning of the tortuosity varied with solute Stokes radius, the tortuosity of the tortuous pore model was correlated to permeability parameters of the friction model. Tortuosity is represented by a ratio of intramembrane friction coefficients for solute and water between actual and hypothetical membrane having isodiametric pores for which the straight pore model is valid. The change in the ratio with the solute is attributable to the pore‐size distribution.
Stability and multiplicity approach to the design of heat‐integrated PFR
Authors: Bildea Costin S. , Dimian Alexandra C. 
Published: April 2004

AbstractThe nonlinear behavior of the heat‐integrated plug‐flow reactor, consisting of a feed‐effluent heat exchanger (FEHE), furnace, adiabatic tubular reactor, and steam generator is studied, considering a first‐order, irreversible, exothermic, adiabatic reaction. Bifurcation theory is used to analyze the relationships among design, reaction thermodynamics and kinetics, and state multiplicity and stability. Hysteresis, isola and boundary‐limit varieties are computed, and the influence of the activation energy, reaction heat and FEHE efficiency on the multiplicity region is studied. The double‐Hopf and double‐zero bifurcation points divide parameter space in regions with different dynamic behavior. State multiplicity, isolated branches, and oscillatory behavior may occur for realistic values of model parameters. A design procedure is proposed to ensure a desired multiplicity pattern and a stable point of operation and to avoid high sensitivity. The procedure was applied to three reaction systems with different kinetic and thermodynamic characteristics.
3‐D modeling of SCR of NOx by NH3 on vanadia honeycomb catalysts
Authors: Roduit B. , Baiker A. , Bettoni F. , Baldyga J. , Wokaun A. 
Published: April 2004

AbstractA novel scheme for simulating the selective catalytic reduction of NO with NH3 on a honeycomb‐type catalyst was developed based on a 3‐D model. New insight was gained by considering such modeling aspects as: correct geometry (square ducts); hydrodynamic entrance effects; occurrence of adsorption phenomena and side reactions; NH3/NO ratio in the feed; influence of the reactant (NO, NH3, O2, H2O) concentrations; interphase diffusion and interphase mass‐transfer processes; and a large range of operating conditions (temperature 140–475°C and gas hourly space velocity 14,800–73,900 h−1). These aspects proved to be crucial for interpreting and quantifying the experimental results and optimizing the catalytic reactor processes. The 3‐D model was validated by comparing manufacturer's set point and experimental data to calculated data, and the external mass‐transfer coefficients derived from the concentration gradients to the mass‐transfer correlations available in the literature.
Radiation heat transfer in catalytic monoliths
Authors: Boehman André L. 
Published: April 2004

AbstractNumerical simulations of heat‐ and mass‐transfer and heterogeneous reactions in catalytic monoliths are reported with the focus on the influence of radiation heat transfer on the thermal behavior of the monolith. Appropriate heterogeneous kinetics and boundary conditions were calculated for two cases including: an automobile catalytic converter in which carbon monoxide is oxidized over a platinum (Pt) catalyst and a catalytic combustor for gas turbine power generation in which methane is oxidized over a palladium oxide (PdO) catalyst. Surface oxidation rates of carbon monoxide are based on measurements of Pt catalyst activity in a catalytic flow reactor, and rates for methane oxidation are based on reaction kinetics for a supported PdO catalyst assigned from differential reactor measurements. These simulations show that in the high aspect ratio passageways (length to diameter) in catalytic monoliths, radiation heat transfer can play a major role in the energy balance on the catalytic surfaces, which determines the transient warm‐up behavior and the steady‐state location of catalyst light‐off. For gray surfaces, however, the predicted steady‐state and transient behaviors are not sensitive to the emissivity of the monolith walls.
Effect of a nonionic surfactant on the flow dynamics of a model HASE associative polymer
Authors: Tirtaatmadja Viyada , Tam Kam C. , Jenkins Richard D. 
Published: April 2004

AbstractThe interaction between a model hydrophobically modified alkali soluble emulsion polymer and a nonionic surfactant C12EO4 is investigated. A huge synergistic increase in the viscosity over 10,000‐fold is demonstrated when the surfactant concentration is increased to 0.1 M, due to the formation of mixed micelles of surfactant hydrophobic tails and polymer hydrophobic groups. Incorporating surfactant molecules increases the number of mechanically active junctions in the polymer network and thus reduces the functionality of the hydrophobic groups. In the intermediate range of surfactant concentrations (0.001–0.01 M), the parallel superposition of steady shear and dynamic testings reveal that the microstructure of the network is affected by stress even in the low‐shear plateau region of the flow curves. The number of network junctions increases substantially with applied shear stress within the low‐shear viscosity region, although the longest relaxation time of the polymer–surfactant systems is greatly reduced. At very high surfactant concentrations ( > 0.01 M), polymer hydrophobes interact with the surfactant to form a stiff gel‐like structure. Surfactant molecules form a mixed bilayer structure with the polymer hydrophobes. These stronger network junctions cause a larger increase in both the viscosity and longest relaxation time of the system. Thus, adding a nonionic surfactant can effectively enhance flow properties of the associative polymer depending on the amount of surfactant used.
Micromixing in a single‐feed semi‐batch precipitation process
Authors: Phillips R. , Rohani S. , Baldyga J. 
Published: April 2004

AbstractA mixing‐precipitation model (based on engulfment, the E‐model by Baldyga and Rohani, 1987) is applied to a single‐feed semi‐batch precipitation process to describe the mixing effects on the final particle‐size distribution (PSD) and particle morphology. The model describes mixing on two scales: the microscale (at which the flow directly affects nucleation and growth phenomena in the mixed‐precipitation (MP) zone) and a macroscale (which controls the environment for the MP‐zone). Application of the model is limited to 1≪Sc<4,000 and slow feed addition rates. When the model was applied to experimental results of BaSO4 precipitation, satisfactory agreement between predicted and observed results was obtained. Experiments were carried out in a single‐feed 18‐L Rushton reactor, whereby the effects of various operating conditions such as feed rate, intensity of mixing, mean initial reactant concentration and reactant volume ratio on barium sulfate precipitation process were investigated.
Influence of hydrodynamics on the upper explosion limit of ethene–air–nitrogen mixtures
Authors: Bolk Jeroen W. , Westerterp K. Roel 
Published: April 2004

AbstractA large pilot plant was constructed to study the upper explosion limit of ethene–air–nitrogen mixtures under conditions of flow in a tube. Experiments were performed at pressures of 0.5, 1.0, and 1.5 MPa, gas temperatures between 298 and 573 K, and with ethene concentrations between 20 and 40 vol. %. A cylinder‐symmetrical 2‐D model developed simulated the experimentally obtained ignition and flame propagation phenomena. The commercial computational fluid dynamics code AEA‐CFX 4.1 was used to solve this model, to which reaction kinetics for a scheme of two consecutive reactions were added. The model predicts the experimental explosion points within 0.5 vol. %. The explosion limit is influenced by the gas velocity: it becomes smaller and shifts to higher oxygen concentrations at increasing flow rates. In practice this means that partial oxidation reactions can safely be operated at high oxygen concentrations, provided the gas is kept flowing at high flow rates.