bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrogenation of butynediol to cis‐butenediol catalyzed by Pd‐Zn‐CaCO3: Reaction kinetics and modeling of a batch slurry reactor
Authors: Chaudhari R. V. , Parande M. G. , Ramachandran P. A. , Brahme P. H. , Vadgaonkar H. G. , Jaganathan R. 
Published: June 2004

AbstractAn experimental study of the kinetics of hydrogenation of butynediol has been reported using Pd‐Zn‐Ca3 catalyst in a slurry reactor. The effects of catalyst loading, butynediol concentration, H2 partial pressure, butenediol (product concentration, temperature, and agitation speed on the rate of hydrogenation have been studied using a stirred pressure reactor). The initial rate data shwoed that the rate is proportional to the square root of H2 pressure, while increase in butynediol concentration inhibited the reaction. A Langmuir‐Hinshelwood‐type rate model has been proposed based on these data and the kinetic parameters evaluated. The values of the activation energy E and the heat of adsorption of butynediol (−ΔH) evaluated were 38.30 kJ/mol and –9.87 kJ/mol, respectively.Batch reactor models were derived based on the rate expression obtained from the initial rate data for variable pressure as well as constant pressure conditions. The prediction of the model were compared with experimental data obtained over a wide range of conditions. The predictions of the model were compared with experimental data obtained over a wide range of conditions. The results agreed well within 5–7% error. Use of the pressure vs. time data for evaluation of kinetic and mass transfer parameters is also demonstrated.
A nonequilibrium stage model of multicomponent separation processes. Part III: The influence of unequal component‐efficiencies in process design problems
Authors: Krishnamurthy R. , Taylor R. 
Published: June 2004

AbstractThe conventional equilibrium‐stage model that uses a component‐independent stage efficiency and a nonequilibrium‐stage model, in which mass transfer rate equations are solved simultaneously with the stage conservation equations, are employed to solve four representative distillation design problems. There are large differences between the number of stages predicted by the two models for a specific separation of the more volatile component. The differences arise from two causes: the way in which the liquid phase resistances and equilibrium equations are used in the models, and the consequences of diffusional interaction effects. Neglect of the latter may lead to an underdesigned column; there is between a 9 and 15% difference in the stage requirements predicted by the nonequilibrium model with a rigorous mass transfer model and a nonequilibrium model which ignores interaction effects.
Regeneration of activated carbons used in waste‐water treatment by a moving‐bed regenerator
Authors: Hashimoto Kenji , Miura Kouichi , Kyotani Susumu 
Published: June 2004

AbstractA method was developed for calculating the distributions of weight loss and temperature of spent activated carbon in a moving‐bed regenerator in which the solid flow was regarded as being plug flow. A kinetic model developed earlier, which was based on regeneration consisting of many first‐order reactions each with different frequency factors and different activation energies, was successfully applied to a design method for the regenerator. The flow pattern of the solid particles and heat transfer characteristics in a small moving bed were clarified experimentally, and the information obtained was used to calculate the distributions of weight loss of the spent carbon and temperature in the moving‐bed regenerator by means of the design method. The calculated results were in fairly good agreement with the experimental data obtained in a small moving‐bed regenerator. The adsorption capacity of the regenerated carbon was comparable to or greater than that of the virigin carbon.
Analytic reduced‐order dynamic models for large equilibrium staged cascades
Authors: Celebi Caglayan , Chimowitz E. H. 
Published: June 2004

AbstractA model reduction technique based upon modal analysis is presented for modeling the dynamics of general, large equilibrium staged cascades encountered in chemical processes. The analysis is general enough to encompass quite complex cascades involving multiple fee and/or product streams with nonideal thermodynamic behavior. The low‐order models proposed have a number of desirable features: the state variables have physical significance and model parameters are clearly related to the fundamental process parameters which are easily obtainable from steady‐state plant data. Quantitatively it is shown that the low‐order models proposed are in excellent agreement with the complete (high‐order) dynamic models on a range of problems some of which involve complex, nonideal cascades.
Zero‐gravity distillation utilizing the heat pipe principle (micro‐distillation)
Authors: Seok D. R. , Hwang Sun‐Tak 
Published: June 2004

AbstractSeparation of ethanol‐water and methanol‐water mixtures has been accomplished experimentally using a horizontal zero‐gravity distillation column. A countercurrent flow between liquid and vapor phases was established utilizing the principle of the heat pipe. The concentration profile along the column has been investigated with various product rates. A high degree of separation was achieved in a relatively short column lined with capillary wicks. The flexible column orientation can also be a tremendous advantage as compared to the necessarily vertical operation of the conventional distillation columns.
The vacancy solution model of adsorption—improvements and recommendations
Authors: Cochran T. W. , Kabel R. L. , Danner R. P. 
Published: June 2004

AbstractThe vacancy solution model of adsorption which uses an activity coefficient equation of the Wilson form has been improved (1) by incorporating temperature dependency into the model, and (2) by development of a functional relationship between the adsorbate‐adsorbate binary interaction parameters. This reduces the number of regression parameters and improves the predictive capabilities of the model. Comparisons of this improved model with the Flory‐Huggins activity coefficient form of the vacancy solution model are presented for binary and ternary systems. For a priori predictions from pure‐component data, the Flory‐Huggins form is recommended. If experimental binary data are available for all pairs, the form that most accurately correlates the binary data should be used to predict higher‐order systems.
Study of coal gasification in an experimental fluidized bed reactor
Authors: Neogi D. , Chang C. C. , Walawender W. P. , Fan L. T. 
Published: June 2004

AbstractThermal gasification has been proposed as one technical option for the conversion of coal to gaseous fuels and/or chemicals to supplement supplies presently derived from petroleum and natural gas. In the present study, a bench‐scale fluidized bed reactor was used for the gasification of coal with steam as the fluidizing medium. A mixture of sand and limestone used as the bed material made it possible to gasify a caking coal without the problem of agglomeration. The gas composition and yield of the hydrogen‐rich product gas were studied as a function of temperature.To study the heterogeneous reactions taking place in the reactor and also the transient behavior of the system, a mathematical model was developed. The model assumed a reaction mechanism that accounted for the devolatilization of coal, cracking of volatiles, char gasification, and the water‐gas shift reaction. Both the dynamic behavior and steady state performance of the gasifier were simulated based on the model. The steady state results of the simulation were compared with the experimental data. This comparison enabled us to ascertain that the proposed reaction mechanism and dynamic model predicted the correct trends.
Experimental study on the separability of reaction‐deactivation kinetics: Thermal desorption of alcohols from fresh and Na‐poisoned γ–Al2O3
Authors: Forzatti Pio , Borghesi Massimo , Pasquon Italo , Tronconi Enrico 
Published: June 2004

AbstractTemperature programmed desorption (TPD) of methanol and ethanol from fresh and Na‐poisoned γ–Al2O3 has been employed to investigate experimentally the separability of reaction‐deactivation kinetics. The analysis of the TPD spectra has provided both an energetic characterization of the nonhomogeneous catalytic surface and the kinetic parameters of the desorption reaction, and has allowed quantitative discussion of the separability of the expression for the rate of desorption. The results obtained have been related to the chemical causes of nonseparability of reaction‐deactivation kinetics; they also demonstrate the influence of catalyst decay on selectivity. For the systems considered, it appears that the assumption of separable deactivation kinetics is generally not a satisfactory approximation.
A radioisotopic tracer method for measurement of solids concentration in a settling bed of solids
Authors: Watson J. S. , Brown C. H. , Byers C. H. , Clinton S. D. , Perona J. J. 
Published: June 2004

AbstractA new and improved radiotracer technique provides information on both the particulate concentration and the movement during sedimentation of monodispersed and binary mixtures. In studies of sedimentation with 44 and 62 μm ion exchange particles, several solids concentrations, three fluid viscosities, and three mixtures with different ratios of the two size particles, the results all lie close to a correlation proposed by Richardson and Zaki.
A new model for entrainment from fluidized beds
Authors: Briens C. L. , Bergougnou M. A. 
Published: June 2004

AbstractA model describing the entrainment of solid particles from gas‐fluidized beds of mixed‐size particles is proposed. It was tested with the limited experimental data published to date and was shown to be superior to existing models and correlations. The model demonstrates that the concentration of very fine particles in the bed can have a significant effect on entrainment.
Reconciliation of process data with process simulation
Authors: Stephenson G. R. , Shewchuk C. F. 
Published: June 2004

AbstractThe SACDA group at the University of Western Ontario has developed an equations‐oriented modular process simulation program called MASSBAL. A model of a process is constructed by selecting and flowsheeting standard building blocks describing fundamental operations such as the mixing and separating of streams. Building blocks are also provided by which equipment operating or design equations may be incorporated into the model. Reconciliation of the inconsistency and redundancy of process measurements is an optional feature of the program. The measurements are reconciled by minimizing a weighted least‐squares criterion while satisfying the model equations and any modeling constraints. The minimum is obtained directly, avoiding the need for laborious searching techniques.
Parametric sensitivity in fixed‐bed catalytic reactors: The role of interparticle transfer resistances
Authors: Morbidelli Massimo , Varma Arvind 
Published: June 2004

AbstractThe parameteric sensitivity behavior of a plug‐flow catalytic fixed‐bed reactor with negligible intraparticle mass and heat transfer resistances is examined for any positive‐order irreversible reaction. By combining information about multiplicity and runaway, a complete picture of the steady state reactor behavior is obtained. Calculations of the parametrically sensitive region for various values of the involved dimensionless parameters are reported.
The hydrodynamics of trickling flow in packed beds. Part II: Experimental observations
Authors: Levec J. , Sáez A. E. , Carbonell R. G. 
Published: June 2004

AbstractThe liquid holdup and the pressure drop for two‐phase trickling flow in a packed bed were measured experimentally. Different values of those parameters were obtained as the liquid flow rate was increased and then decreased, indicating a multiplicity in hydrodynamic states. This behavior was observed even when the gas flow rate was zero in the bed. It was determined that the hysteresis exhibited by the process is due to imperfect wetting of the packing and to the difference between advancing and receding contact angles at the gas‐liquid‐solid contact lines. The reduced wetting conditions are also the cause of the increase in liquid holdup observed when the surface tension of the liquid is decreased. In this case, the amount of liquid retained in the bed is controlled by the extension of the wetted regions due to the more favorable contact angles as the surface tension decreases. The transition from the trickling to the pulsing flow regime was also dependent on the history of the process.A new correlation for predicting liquid holdups and pressure drops for trickling flow in packed beds is proposed for the decreasing liquid flow rate operating mode. This correlation is based on the experimental determination of the liquid phase relative permeability as a function of the the liquid phase reduced saturation and the determination of the gas phase relative permeability as a function of the gas phase saturation and the gas phase Reynolds number. The new data are analyzed in the light of the theory developed in the first part of this paper.
Effect of recycle structure on distillation tower time constants
Authors: Kapoor Naveen , McAvoy T. J. , Marlin T. E. 
Published: June 2004

AbstractRecycle of material or energy can change the effective dynamic behavior of a process. Distillation towers are inherently recycle processes. Published tower time constants based on linear analysis have been substantially in error when compared to actual responses for many cases. The reason for this error is shown to be the recycle nature of distillation towers. An improved method of estimating time constants, which can be extended to industrial towers, is presented.
Effect of radial velocities on laminar flow, tubular reactor models
Authors: McLaughlin H. S. , Mallikarjun Ramesh , Nauman E. B. 
Published: June 2004

AbstractExisting models for laminar flow in tubular reactors neglect radial velocities in the momentum transport equation. The axial velocity distribution is calculated assuming fully developed flow wherein axial velocities are in local equilibrium with the radial viscosity profile. A test of this assumption has been devised using a representative model of the Newtonian viscosity, μ(r, z), and by reconstructing the radial velocity components using the continuity equation. The assumption of fully developed flow is shown to be a valid approximation for typical polymerization reactions. However, the fact that radial velocities are negligible with respect to momentum transport does not mean they are negligible with respect to convective diffusion of heat and mass. Radial convection is shown to be important for typical polymerization and heat transfer examples.
Dynamic interfacial tensions in acidic crude oil/caustic systems. Part I: A chemical diffusion‐kinetic model
Authors: Borwankar R. P. , Wasan D. T. 
Published: June 2004

AbstractA chemical diffusion‐kinetic model is developed for the acidic oil/caustic system of alkaline flooding by proposing a set of interfacial reactions leading to in situ generation of surfactants. The rate constants of interfacial reactions are independent of aqueous phase compositions. In Part I, the model is applied for determining these rate constants from its correlation with dynamic interfacial tension data obtained using the spinning drop tensiometer. The relative magnitudes of the rate constants characterizing the adsorption/desorption barriers are shown to govern the extent of dynamic interfacial tension minimum.
Aerobic coupling of aqueous phenols catalyzed by binuclear copper: Ring substituent effect and the kinetics of the coupling of o‐methylphenol
Authors: Cha J. A. , Berry K. B. , Lim P. K. 
Published: June 2004

AbstractThe substituent effect on the aerobic and catalytic coupling of aqueous phenols conforms to a Hammett correlation in which the reaction constant is −2.16; the results are very similar to that of the enzymatic coupling reaction, in which the reaction constant is −2.4. Deviations from the Hammett correlation are attributed to steric factor, product inhibition, and the blocking of coupling sites on phenoxy radicals. Available evidence indicates that catalytic and enzymatic coupling reactions are strikingly similar in many respects. The striking resemblance suggests a common reaction mechanism in which binuclear metal (copper or iron) plays a key role. The common mechanistic features of the coupling reactions are suggested, and the implications of the findings are discussed with reference to (1) the design of a novel dephenolization scheme, (2) the elucidation of the widely occurring but poorly understood enzymatic coupling reactions, and (3) the synthesis of active polymer‐bound coupling catalysts.
Dynamic contact angles on moving plates
Authors: Ishimi Kosaku , Hikita Haruo , Esmail M. N. 
Published: June 2004

AbstractA simple model for advancing dynamic menisci of the interface between two immiscible fluids is proposed on the hypothesis that there is a monomolecular film which precedes an apparent contact line and that a frictional force due to the solid surface is balanced with the interfacial tension forces on the film. An analytical solution for dynamic contact angles on vertical and inclined solid surfaces of plates is obtained as a function of the interfacial capillary number, the static contact angle, and the parameters of Langumuir's duplex film model. An analytical solution for dynamic meniscus heights is also derived. The analytical solutions are compared with previous experimental data. The agreement between the theoretical and experimental results is found to be fairly good, average deviations being 3.8 and 12%, respectively, for dynamic contact angles and dynamic meniscus heights at the solid surface.
Cocurrent flow of gas‐particulate mixtures through helical tubular colis: Particle velocity measurement and prediction
Authors: Shu Ming‐Tsai , Hamshar J. A. , Weinberger C. B. 
Published: June 2004

AbstractParticle velocities are measured for the cocurrent flow of air and coal particles through helical colis. The ratio of average particle velocity to gas velocity, Vg, is nearly independent of Vg at 0.25 ± 0.1. This ratio would be above 0.95 for similar flow conditions in straight, horizontal tubes. The particle velocities also depend slightly on other variables, decreasing with larger particles, larger solids feed rate, and smaller helix diameters. Visual observations reveal that the particles slide along the outer periphery of the coil, in a fashion similar to the sliding action at saltation conditions in horizontal flow. A model that permits prediction of particle velocity in helical geometries is proposed; this model is based on the modification of existing saltation velocity correlations by substituting centripetal acceleration for gravitational acceleration. Approximate agreement between experiment and prediction is obtained.
The effective diffusivity of fibrous media
Authors: Koch D. L. , Brady J. F. 
Published: June 2004

AbstractA procedure based on averaging the conservation equations in a homogeneous, disordered fibrous medium is used to demonstrate that in the limit of long times, macroscopic versions of Fick's and Fourier's laws may be used to relate the average flux to the average gradient in driving force. The asymptotic behavior in the limit of low volume fraction of the effective diffusivity (or conductivity) in such a medium is determined for all values of the Peclet number, P = Ua/Df, where U is the average velocity through the bed, a is the fiber radius, and Df is the molecular diffusivity of the solute in the fluid. The convective disturbance caused by the fibers is found to have a large influence on the rate of mass transfer even at moderate Peclet numbers and low volume fraction.
Kerogen decomposition at subpyrolysis temperatures
Authors: Yucelen Fusun , Smith J. M. , Wakao N. 
Published: June 2004

AbstractThe thermal decomposition of Colorado oil shale was studied at subpyrolysis temperatures, 533 to 611 K, as part of an investigation of rates of supercritical extraction. Thermal degradation followed by solution in the solvent is a possible, partial explanation for the enhanced solubility at supercritical conditions for a complex mixture such as kerogen.In the region of the critical temperature of toluene, up to 26% of the kerogen in the original shale was converted by thermal reactions to gases and soluble (in toluene at 298 K and 101 kPa) products. The kinetics of the decomposition of the insoluble organics in shale could be explained by a combination of series and parallel reactions.
Effective heat transfer parameters for transient packed‐bed models
Authors: Dixon A. G. , Cresswell D. L. 
Published: June 2004

AbstractA general theory is presented for the prediction of effective axial conductivity and overall radial heat transfer coefficient for fluid flow through packed beds, under either transient or steady state conditions. The parameters to be used in each case may be quite different, depending on the dominant phase for heat transfer. The theory unifies all previous results and explains conflicting conclusions arrived at by different workers. The ability of a pseudohomogeneous model to reproduce packedbed transients is shown to depend upon the choice of effective parameters.
NMR Measurements of chemical theory equilibrium constants for hydrogen‐bonded solutions
Authors: Eckert C. A. , McNiel M. M. , Scott B. A. , Halas L. A. 
Published: June 2004

AbstractAlthough various chemical theories have often been used to characterize hydrogen‐bonded systems with some success, they have been limited by the fact that the equilibrium constants were adjustable parameters. This paper reports a method to measure directly these constants by proton nuclear magnetic resonance spectroscopy. Results are reported for several systems and are used with a chemical‐physical theory to predict vapor‐liquid equilibria.
Exploiting the Gibbs‐Duhem equation in separation calculations
Authors: Venkataraman S. , Lucia Angelo 
Published: June 2004

AbstractVarious ways of building quasi‐Newton matrix approximations that satisfy the special form of the Gibbs‐Duhem equation are studied. Partition symmetry, the separability of the functions in γ and in ϕ, and the method of iterated projections are used in order to develop thermodynamically consistent matrix approximations with good secant information. Many examples are presented which show that exploiting the special form of the Gibbs‐Duhem equation results in improved numerical performance. Ways of exploiting the Gibbs‐Helmholtz equation in addition to the special form of Gibbs‐Duhem equation, and thus the isobaric form of the Gibbs‐Duhem equation, are also discussed.
Particle size improvement by a countercurrent tower crystallizer
Authors: Farmer R. W. , Beckman J. R. 
Published: June 2004

AbstractA continuous, staged‐feed column crystallizer was investigated to obtain enlarged product size distribution in precipitation from solution. Stage population balances, in moment form, were solved analytically for several single‐feed configurations. It was found that internal staging permits control of the solids concentration profile, and if collision nucleation is unimportant then countercurrent operation yields the greatest product size enlargement. Nucleation kinetic parameters for a given salt indicate the potential product size improvement, compared to product from an MSMPR crystallizer of equal volume.