bluuebunny/crossref_metadata_2025_split huggingface dataset:
Restrictive diffusion in aluminas
Authors: Chantong A. , Massoth F. E. 
Published: June 2004

AbstractThe effect of the ratio of solute molecular diameter to the substrate pore diameter on the diffusion of polyaromatic compounds in four different pore sizes of amorphous gamma‐aluminas was studied at atmospheric pressure and ambient temperature. Diffusion rates of the polyaromatic compounds in the aluminas decreased as the ratio of solute molecular diameter to pore diameter increased. Empirical correlations between the apparent reduction in solute effective diffusivity and the ratio of molecular diameter to pore diameter were obtained.
Regeneration of activated carbon. Part I: Thermal decomposition of adsorbed sodium dodecylbenzene sulfonate
Authors: Umehara Tadashi , Harriott Peter , Smith J. M. 
Published: June 2004

AbstractEquilibrium adsorption isotherms and rates of thermal decomposition were measured for sodium dodecyl‐benzene sulfonate (DBS) adsorbed on powdered activation carbon. The rate data were obtained in a thermal gravimetric apparatus operated both at constant temperature (522 to 666 K) and with a constant rate of temperature increase from 298 to 1023 K.About 50% of the adsorbed material could be removed at temperatures up to 748 K and only a small amount of the remaining 50% could be eliminated by further heating to 1,023 K. The residual adsorbate at 1,023 K was considerably greater than could be accounted for by inorganic materials such as Na2SO4.The kinetics of the decomposition up to 748 K could be explained by a two‐reaction sequence, either parallel or consecutive reactions. Rates of decomposition were slower than found in earlier studies (Chihara et al., 1981) with adsorbed sucrose, and the kinetic steps were different. With sucrose, considerable decomposition occurred between 298 and 428 K. While with DBS, no decomposition was observed in this temperature range. Above 400 K, it was possible to explain the kinetics of decomposition in the case of sucrose by a single step forming residual carbon and volatile products, while with DBS, a two‐reaction sequence was required.
Studies in magnetochemical engineering. Part III: Experimental applications of a practical model for high‐gradient magnetic separation to pilot‐scale coal beneficiation
Authors: Liu Y. A. , Oak M. J. 
Published: June 2004

AbstractThe computer implementation and experimental verification of the practical model for high‐gradient magnetic separation (HGMS) based on particle buildup and feed characteristic, developed in Part II, are described. It is shown that the new model can be used to satisfactorily predict the grade, recovery and concentration breakthrough observed in pilot‐scale experimental studies of HGMS for the removal of sulfur and ash from water slurries of several pulverized Eastern coals. The experimentally verified model can be used to quantitatively identify the tradeoff of separation variables so as to optimize the magnetic removal of sulfur and ash from pulverized coal. The model can also be used to assess the technical and economical feasibility of the magnetic beneficiation of pulverized coal without extensive experimental tests.
Moving boundary problems in simple shapes solved by isotherm migration
Authors: Talmon Y. , Davis H. T. , Scriven L. E. 
Published: June 2004

AbstractThe Modified Isotherm Migration Method (MIMM) is developed for solving one‐dimensional Stefan‐type problems of multifront propagation in slabs, cylinders and spheres with a boundary condition of the third kind (radiation‐type boundary condition). The method is illustrated for all three geometries with applications to the thawing of ice and to the freezing of a 50–50 dispersion of tetradecane in water, a system in which two freezing fronts propagate simultaneously.
Kinetics of the approach to sorptional equilibrium by a foodstuff
Authors: Roman G. N. , Urbicain M. J. , Rotstein Enrique 
Published: June 2004

AbstractThe kinetics of equilibration of a vegetable foodstuff with moist air are studied on the basis of its cellular structure. The problem is modelled as a coupled heat and mass transfer phenomenon; since there is a significant shrinkage as moisture decreases, the model takes the effect into account by changing the basis for the mass and energy balances. The resulting nonlinear second‐order partial differencial equations are solved numerically; predicted values of moisture decrease and temperature gain with time are compared with experimental data. A sensitivity analysis of the solution to values of the transport properties shows that the value of effective diffusivity and heat and mass transfer coefficient may alter significantly the predicted equilibration kinetics and center temperature. The adopted value for heat of sorption has less influence. Changes in effective thermal conductivity and porosity bear little influence on predictions.
Fluidized‐bed reactor model with generalized particle balances. Part II: Coal combustion application
Authors: Overturf B. W. , Reklaitis G. V. 
Published: June 2004

AbstractThe model described in Part I is applied to study an atmospheric fluidized‐bed coal combustor. Extensive case studies are investigated on the effects of: enhanced grid region heat and mass transfer; bed void fraction; emulsion phase temperature; elutriation rates; reaction rate parameters; feed particle‐size distribution; and particle superheat. Comparison is made with experimental results reported by Babcock and Wilcox. Proper representation of the grid region and use of actual feed distributions are shown to be essential to predicting combustor performance. Better particle elutriation and single‐particle combustion submodels are found to be key requirements for improved combustor modeling.
Anomalous diffusion of vapors through solid polymers. Part II: Anomalous sorption
Authors: Neogi P. 
Published: June 2004

AbstractSorption of vapors in polymer membranes in the vicinity of and below the glass transition temperatures do not follow the Fickian (classical) diffusion. The reasons have been attributed to the molecular relaxation which affects both diffusivities and solubilities.A time‐ and memory‐dependent diffusion coefficient has been evaluated in Part I, in a form which is analogous to the treatment in the rheology of such materials. Together with a time‐dependent solubility, the conservation equation for the sorption process has been solved. Two special cases are considered, where the relaxation times are short and where they are long. The results explain the anomalous behavior observed in the experiments. Comparison with the experiments has been made.
Vapor‐liquid equilibria for NH3 and H2O in the 100 to 150°C region: Effect of low levels of phenol on partial pressure of ammonia
Authors: Pawlikowski E. M. , Newman John , Prausnitz J. M. 
Published: June 2004

AbstractExperimental results are reported for the partial pressure of ammonia in water solutions containing low concentrations of phenol. Experiments were performed in 0.6 molal phenol at 100 and 150°C. Results at 150°C indicate that the very small effect of phenol on the partial pressure of ammonia is within the limit of experimental error, 3%, and therefore could not be established from the data. However, at 100°C, the partial pressure of ammonia was decreased by nearly 10%. Computer program TIDES—a computerized thermodynamic framework for calculating vapor‐liquid equilibria for volatile weak electrolytes and other common gases—has been revised to account for the effect of low concentrations of phenol.
Influence of mixing state of carrier fluid in nonlinear equilibrium exchange systems
Authors: Schweich D. 
Published: June 2004

AbstractIt is shown that for a given residence time distribution of carrier fluid and a given nonlinear adsorption isotherm of a single solute, the breakthrough curve is not uniquely defined. The special case of a one‐dimensional dispersive flow is examined. It is shown that with a simple but realistic model for the residence time distribution, the classical self‐sharpening front becomes a continuously broadening front. Two extreme models are proposed to describe the behavior of any front in a flow system with a given residence time distribution. This study seems of crucial importance in systems for which this residence time distribution is the only available information about the flow pattern.
Pore‐diffusion model for cyclic separation: Temperature swing separation of hydrogen and methane at elevated pressures
Authors: Tsai M. C. , Wang S. S. , Yang R. T. 
Published: June 2004

AbstractA pore‐diffusion model is developed for temperature swing separation in a packed bed of sorbent. The model is applied to interpret experimental data for separation of H2 of CH4 in a packed bed of activated carbon operated in the temperature swing mode, at pressures up to 5.52 MPa. Experimental results on the effects of total pressure, particle size, adsorption temperature, and flow rate on separation efficiency compared favorably to the model predictions. The importance of pore diffusion in separation has been clearly demonstrated.
High‐temperature mutual solubilities of hydrocarbons and water. Part I: Benzene, cyclohexane andn‐hexane
Authors: Tsonopoulos Constantine , Wilson G. M. 
Published: June 2004

AbstractThe mutual solubilities at the three‐phase equilibrium pressure of three C6hydrocarbons (benzene, cyclohexane andn‐hexane) and water have been experimentally investigated up to 482 K. A thermodynamic analysis of these new measurements and of critically selected literature data has been carried out to the three‐phase critical end point. Information is also provided on the two‐phase critical locus. The solubility of hydrocarbons in water has been used to calculate Henry's constants, while the solubility of water in the hydrocarbons has been correlated with a modified version of the Redlich‐Kwong equation of state. Consideration is also given to the effect of pressure on the mutual solubilities.
Hydrogenation reactions of model titanium compounds under coal liquefaction conditions
Authors: Treblow M. , Spitler C. A. , Brown F. R. 
Published: June 2004

AbstractUsed catalyst and reactor deposits from a fixed‐bed coal liquefaction unit show high concentrations of titanium and boron. The titanium was present as anatase, a titania polymorph. Hydrogenation reactions with and without catalyst were performed with model titanium and boron compounds under liquefaction conditions. The catalyst used was Harshaw 0402T 3% CoO – 15% MoO3 on an alumina‐silica support. Rutile remained unchanged by reactor conditions. In all other runs the titanium starting material, whether organic or inorganic in nature, converted to anatase. When the deposition of the reaction products was monitored, only that anatase derived from organic titanium compounds accumulated on and in the catalyst pellets to an appreciable extent.
Bubble formation at vibrated orifices: Medium‐chamber‐volume region
Authors: Baker C. T. , de Nevers Noel 
Published: June 2004

AbstractThe bubble formation process at small, single, circular orifices at low gas flow rates is modified when the system is vertically vibrated in a sinusoidal fashion.For systems with significant gas chamber volume, bubble volume in the vibrated case is smaller than in the nonvibrated case. The vibrations increase the amount of liquid weeping through the orifice into the gas chamber. A simple inviscid model adequately predicts bubble formation in the medium‐chamber‐volume region at low values of amplitude and frequency of vibration and low viscosities. The boundaries of the transition from the FR ≫ 1 to the FR = 1 regions are described in terms of “the acceleration number/Eötvös number”.
Effects of radially nonuniform distributions of catalytic activity on performance of spherical catalyst pellets
Authors: Johnson D. L. , Verykios X. E. 
Published: June 2004

AbstractThe performance of spherical catalyst pellets with radially nonuniform distributions of activity is simulated under parallel reaction networks closely resembling hydrocarbon oxidation reactions. Both reaction paths are assumed to be exothermic with the desired path exhibiting lower activation energy requirements than the undesired one. It is shown that nonuniform activity distributions enhance effectiveness and selectivity over a large range of values of the Thiele modulus. Multiple steady states in effectiveness and selectivity are observed for certain values of the heat of reaction parameter.
Antimisting action of polymeric additives in jet fuels
Authors: Chao K. K. , Child C. A. , Grens E. A. , Williams M. C. 
Published: June 2004

AbstractPolymeric solutes in jet fuel can serve to increase greatly the droplet size and reduce flammability in fuel sprays created by high‐velocity wind shear. Photographic and spark‐ignition studies show that high molecular weight polyisobutylenes can be effective at levels below 100 ppm, where they cause only slight increases in fuel viscosity. The effectiveness of the polymers increases with molecular weight and is very well correlated by the elongational viscosity of the solution, as measured by the ductless siphon height.
Characterization of mixing in reactor systems through analysis of regional tracer dilution data obtained with a gamma camera
Authors: Castellana F. S. , Friedman M. I. , Spencer J. L. 
Published: June 2004

AbstractA new approach to the characterization of flow patterns and mixing through analysis of regional tracer dilution data obtained with a gamma camera is presented. Studies performed in a small, two‐dimensional, multiple‐inlet vessel demonstrate the experimental technique and how data are analyzed to determine the intravessel spatial distribution of fluid deriving from the traced stream. Good agreement is shown between calculated values of the flow distribution and visually observed flow patterns.
Hydrodynamics and mass transfer in non‐Newtonian solutions in a bubble column
Authors: Godbole S. P. , Schumpe A. , Shah Y. T. , Carr N. L. 
Published: June 2004

AbstractUntil now the oxygen transfer in viscous non‐Newtonian solutions has been studied only in bubble columns of about 0.14‐m diameter. Recently Godbole et al. (1982) reported much smaller gas holdups in Carboxy Methyl Cellulose solutions (CMC) for a large‐diameter column. Therefore, the gas holdups, volumetric mass transfer coefficients, and specific gas‐liquid interfacial areas are measured in CMC solutions using a bubble column of diameter 0.305 m and height 3.4 m. The transition from churn‐turbulent to slug flow regime occured at higher viscosities and the gas holdups and volumetric mass transfer coefficients were lower in both flow regimes than reported for smaller column diameters. Empirical correlations are presented for the gas holdup, volumetric mass transfer coefficient, and specific gas‐liquid interfacial area which would be suitable for the design of fermentors.
Optimal operation of integrated processing systems: Part II: Closed‐loop on‐line optimizing control
Authors: Garcia C. E. , Morari Manfred 
Published: June 2004

AbstractA method for tracking the economically optimal operating conditions of a chemical process in the presence of constraints is developed. The technique is based on an on‐line search rather than a fundamental model. The most profitable operating point is found by fitting a dynamic model of the process based on data obtained from experimental moves on the plant.This model is used to compute gradients of the economic objective and of the constraints so that a direction of economic improvement inside the allowed operating region of the plant is always obtained. Constraint violations during the transients are prevented by a multivariable regulator. A new regulation method (Internal Model Control) is used which permits explicit handling of constraints and which can be made robust against modelling errors. This combined optimization/regulation approach is tested in a demonstrative simulation example and shown to be reliable for following a moving optimum and safely handling complex constraint moves.
Critical point measurements on nearly polydisperse fluids
Authors: Morrison G. , Kincaid J. M. 
Published: June 2004

AbstractThe critical temperatures, pressures and volumes of several mixtures containing CO2, C2H6, C3H8, and C4H10 have been measured using a heavy walled, variable volume, cylindrical glass vessel. In each mixturre the relative proportions of the three hydrocarbon solutes to one another were changed; total solute mole fraction never exceeded 0.1. A detailed study of the mixture CO2 + C3H8 shows that the critical temperature exhibits a minimum at a C3H8 mole fraction of 0.0265. Our mixture data are analyzed using a polydisperse model of dilute solutions.
Precipitation and dissolution of solids attending flow through porous media
Authors: Walsh M. P. , Bryant S. L. , Schechter R. S. , Lake L. W. 
Published: June 2004

AbstractA model is developed that calculates the chemical equilibrium that exists between a flowing electrolyte solution and mineral assemblages. The development computes the mineral and aqueous compositions as a function of time and position in a one‐dimensional porous medium. The model considers the dissolution of solids as well as their precipitation. The application of the model to various problems has revealed that characteristic aqueous and solid phase concentration waves develop and propagate through the system in a chromatographic manner. Example calculations are presented that illustrate the widespread applicability of the model. Specifically, a calculation is presented that reproduces the genetic mineralization features that are found in sandstone‐type uranium deposits.
Stratified turbulent‐turbulent gas‐liquid flow in horizontal and inclined pipes
Authors: Shoham Ovadia , Taitel Yehuda 
Published: June 2004

AbstractA two‐dimensional model for stratified turbulent‐turbulent gas‐liquid flow in inclined pipes is proposed. The gas phase is treated as bulk flow, but an exact solution is carried out for the liquid phase, applying the eddy viscosity theory to model the turbulent viscosity. The interfacial structure is taken into consideration using appropriate correlations for the interfacial shear stress. The model is capable of predicting the liquid velocity field, holdup and pressure drop given gas and liquid flow rates, physical properties, pipe size, and angle of inclination. The results are substantially better than the prediction of Lockhart and Martinelli (1949) correlation and better than the Taitel and Dukler (1976) model for stratified flow.
Complex nature of the sulfation reaction of limestones and dolomites
Authors: Chang E. Y. , Thodos George 
Published: June 2004

AbstractExperimental information available in the literature for the sulfation of a wide variety of calcined limestones and dolomites has been used to establish rates of reaction over their entire range of conversion. The reaction rate was found to decay exponentially with extent of conversion and implicated parameters related to two factors, each factor representing a diffusional resistance. These factors define two generalized constants which permit the prediction of the decaying parameters associated with the sorptive capacity of the sorbent.The sorptive capacity, x∞, which represents the ultimate conversion of the solid sorbent, has been found to depend on the pore size distribution, the chemical composition of the limestone and/or dolomite and its accessible pore surface area. The combined contribution of x∞ along with predicted parameters permit the calculation of conversion vs. time relationships that are found in close agreement with experimental measurements for the ten sorbents investigated, with the exception of one.
Breakage functions for droplets in agitated liquid‐liquid dispersions
Authors: Narsimhan Ganesan , Nejfelt Gregory , Ramkrishna Doraiswami 
Published: June 2004

AbstractPhotographic measurements of transient drop‐size distributions from stirred liquid‐liquid systems of low dispersed phase fraction in a batch vessel confirm consistency with a similarity behavior from population balance established earlier by Narsimhan et al. (1980). Moreover, breakage functions are presented in generalized dimensionless form accounting for dependence on physical properties of the system and power input through stirring. This information is essential for predicting drop‐size distributions in stirred liquid‐liquid systems. Experimental measurements of steady‐state drip‐size distributions obtained from stirred, continuous flow systems with known inlet drop sizes compare very favorably with theoretical predictions based on population balance analysis using the breakage functions obtained from batch experiments.
Kinetics of hydration‐dehydration reactions considered as solid transformations
Authors: Stanish M. A. , Perlmutter D. D. 
Published: June 2004

AbstractA mechanism is proposed for the dehydration‐rehydration process in solid inorganic salts, and model rate equations are derived and applied to the observed behavior of potassium carbonate. Quantitative expressions for the effect of pressure on the reaction rates are derived using basic principles from nucleation and heterogeneous phase transformation theory. Model equation predictions agree with experimental dehydration and rehydration rate data at all but extreme pressures. The basic rate equation is also used to interpret the data of Eckhardt and Flanagan (1964) for the effect of pressure on the dehydration of manganous formate dihydrate. The mechanism on which the model equations are based is also consistent with the observed effects of cycling and of high temperature pretreatment on the K2CO3 rehydration rate.
Analytical solution using a pore diffusion model for a pseudoirreversible isotherm for the adsorption of basic dye on silica
Authors: McKay Gordon 
Published: June 2004

AbstractAn analytical solution for a two resistance mass transfer model explaining the adsorption of Astrazone Blue dye (Basic Blue 69) onto Sorbsil silica has been developed. The model includes a film mass transfer coefficient, kf1 = 80 × 10−6cm·s−1, and an internal effective diffusivity, Deff = 18×10−9cm2·s−1 which controls the internal mass transport processes based on a pore diffusion mechanism.
High‐pressure phase equilibria for the water/methane system
Authors: Larsen E. R. , Prausnitz J. M. 
Published: June 2004

AbstractA semitheoretical method has been established for superimposing the residual thermodynamic properties of pure methane and of pure water over wide ranges of pressure (0.01 to 1,000 MPa) and temperature (triple point to twice the critical temperature). Using reasonable mixing rules with two binary parameters, this superposition also gives mixture properties, including high‐pressure vapor‐liquid equilibria.
Deactivation of hydrodesulfurization catalysts by metals deposition
Authors: Ahn Bum‐Jong , Smith J. M. 
Published: June 2004

AbstractPrimary causes of deactivation of hydrodesulfurization catalysts are partial poisoning of the interior pore surface and pore‐mouth plugging by deposition of metals from organo‐metallic compounds in the reactor feed. A model is developed to account for both causes of deactivation. It can be used to predict which occurs first: complete surface poisoning or pore‐mouth plugging. Equations are formulated for catalyst activity as a function of time for demetallization and also for desulfurization. The results depend upon particle geometry and geometry of deposited species, Thiele moduli for demetallization and desulfurization, and relative rates of desulfurization on fresh and partially poisoned catalytic surfaces. The treatment is for a single, isothermal catalyst particle.