bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mineral dissolution, precipitation, and ion exchange in surfactant flooding
Authors: Krebs R. , Sardin M. , Schweich D. 
Published: June 2004

AbstractThe transient retention of an anionic surfactant below the critical micellar concentration flowing in an argilo‐calcareous sandstone is shown to depend mainly upon: (1) the dissolution of trace amounts of calcium carbonate contained in the sandstone and (2) precipitation and redissolution of the surfactant with calcium ions due to carbonate dissolution or ion exchange on the clays. The adsorpton process on solid surfaces is secondary, due to a high pH resulting from the presence of carbonates. A predictive model is developed. It is compared with typical surfactant breakthrough curves and demonstrates that dissolution of calcite is the main process affecting the transport of surfactant close to the injection point.
Adsorption chromatography of proteins: Determination of optimum conditions
Authors: Yamamoto Shuichi , Nomura Masaki , Sano Yuji 
Published: June 2004

AbstractA simple and convenient method for predicting optimum chromatographic conditions from linear gradient elution experiments with a small column is presented and verified experimentally. The method was found to be very useful for a rapid survey of the nature of unknown proteins, for the estimation of optimum chromatographic conditions, and for scaling up the separation of proteins in ion exchange and hydrophobic interaction chromatography.Two applications were successfully carried out on the basis of the proposed method: (1) Separation of a protein mixture of ovalbumin and β‐lactoglobulins A and B with both anion and cation ion exchange columns by means of column switching technique. In this method, the sample is always subjected to the elution process until it is collected as a purified fraction through the two columns. A special valving system is devised for this method. (2) Large‐scale ion exchange chromatography separation of β‐galactosidase. Linear gradient elution of crude β‐galactosidase was carried out with a 30 L ion exchange gel column on the basis of data obtained with a small (23 mL) column.
Effectiveness enhancement and reactant depletion in a partially wetted catalyst
Authors: Harold M. P. , Ng Ka M. 
Published: June 2004

AbstractA one‐dimensional model is developed to describe reaction between a nonvolatile liquid reactant and a dissolved gas reactant in an isothermal catalytic pellet partially wetted by a flowing liquid film. The kinetics are assumed to be first order and zero order with respect to the dissolved gas and liquid reactant, respectively. The model applies to cases in which there are negligible intraparticle gradients in the direction normal to the wetted surface. A modification of the overall transport coefficients enables the model to approximate cases in which these gradients are important, for both washcoated and uniformly impregnated catalysts. The analytical solutions enable an efficient examination of the interplay between the reaction and several mass transport processes. Conditions are determined for which the catalyst effectiveness is maximized at an intermediate wetting efficiency. It is shown that the maximum is a result of two counteracting processes. As the wetting efficiency is decreased from unity the effectiveness increases if the supply of the gas reactant is more effective on the nonwetted than the wetted part; i.e., effectiveness enhancement. However, if the wetting efficiency is sufficiently reduced, the excess liquid reactant depletes within the pellet, resulting in a decreased effectiveness. A criterion is derived that predicts the minimal activity necessary to initiate depletion of the liquid reactant for a given wetting efficiency. This is useful for determining the conditions for which the common literature assumption of an excess liquid reactant is violated. The model shows good agreement with published data in which the overall rate exhibits a maximum for an intermediate liquid flow rate.
Organic liquids in a bubble column: Holdups and mass transfer coefficients
Authors: öztürk S. S. , Schumpe A. , Deckwer W.‐D. 
Published: June 2004

AbstractGas holdups and volumetric mass transfer coefficients kLa are studied in a bubble column of 0.095 m dia. with 50 different gas‐liquid systems comprising pure and mixed organic liquids and various gases. The gas holdups measured in pure organic liquids can be represented by existing correlations but the values in liquid mixtures are high. On the other hand, all mass transfer coefficients can be correlated uniformly by a new dimensionless equation, with 13.3% mean error.
Emulsion polymerization reactor stability: Simplified model analysis
Authors: Rawlings J. B. , Ray W. H. 
Published: June 2004

AbstractA class of simplified emulsion polymerization models is developed. These models include the distribution of particle sizes and radical numbers, and the coupling of the particle initiation rate to the particle size distribution. An analytical solution to the modeling equations is found from contraction mapping. In addition, necessary and sufficient conditions for local stability are derived. These result in a simple criterion for the onset of oscillations in terms of kinetic rate constants and reactor operating conditions. The results clearly show that radical desorption, chain transfer agents, and certain types of impurities should have a strong influence on reactor stability.
Partial oxidation of CH4 to HCHO over a MoO3‐SiO2 catalyst: A kinetic study
Authors: Spencer N. D. , Pereira C. J. 
Published: June 2004

AbstractThere is considerable economic incentive to convert methane into formaldehyde, which is used in the manufacture of insulating materials and adhesives. This paper discusses the kinetics of a one‐step oxidation of methane with molecular oxygen over a MoO3‐SiO2 catalyst. The space velocity was varied between 2,500 and 10,000 h−1 (at NTP) over a range of temperatures from 848 to 923 K.Selectivities to formaldehyde between 30 and 89% were observed in the 0–5% methane conversion range, the other principal products being CO, CO2, and H2O. Kinetic analysis indicates that methane is directly oxidized to CO2 and HCHO, with HCHO being further oxidized to CO. The reactions were all found to be zero order in oxygen concentration, with methane and formaldehyde oxidation following overall first‐order rate laws. Kinetic rate constants have been determined and there is good agreement between model predictions and experimental data.
Equilibrium properties of liquids containing supercritical substances
Authors: Campanella E. A. , Mathias P. M. , O'Connell J. P. 
Published: June 2004

AbstractA two‐parameter, corresponding‐states form for direct correlation function integrals in liquids is applied to many types of systems with one substance being supercritical. This gives a quantitative correlation for volumetric behavior, pure and mixed solvent Henry's constants, and Henry's Law deviations over wide ranges of conditions using only pure‐component information and a single binary parameter. Details of the method and results are given for H2, N2, CO, CH4, and other gases in pure and mixed simple, polar, and aqueous solvents and coal oils. Because of its reliable predictive capability, the present approach can serve as a generator of data for parameter estimation by other models such as equations of state.
Hindered settling of semidilute monodisperse and polydisperse suspensions
Authors: Davis R. H. , Birdsell K. H. 
Published: June 2004

AbstractA light‐extinction principle was used to measure the fall speeds of the interfaces that develop during gravity sedimentation of monodisperse, bidisperse, and tridisperse suspensions of noncolloidal particles with small particle Reynolds numbers in the semidilute total particle volume fraction range 0.0003 ⩽ c0 ⩽ 0.15. For monodisperse suspensions, the hindered settling velocity of the interface at the top of the suspension was found to be well represented by the correlation of Richardson and Zaki, provided that the isolated particle fall speed was chosen by linear extrapolation of the data to c0 = 0, with 90% confidence intervals on the exponent of n = 5.0 ± 0.1. For dilute monodisperse, bidisperse, and tridisperse suspensions, the hindered settling velocities of the interfaces showed agreement within experimental uncertainty with the theory of Batchelor, which predicts that the settling velocity decreases linearly with increasing particle concentration and which is based upon pairwise particle interactions.
Dispersion‐free solvent extraction with microporous hollow‐fiber modules
Authors: Prasad R. , Sirkar K. K. 
Published: June 2004

AbstractExtensive studies on dispersion‐free solvent extraction have been carried out using modules made with either hydrophobic or hydrophilic microporous hollow‐fiber membranes. Membrane and boundary layer resistances have been characterized for both kinds of hollow fiber using solvent extraction systems with a wide variation of distribution coefficients and interfacial tensions. It has been found that the Graetz solution for a constant wall concentration describes satisfactorily mass transfer on the lumen side of a hollow‐fiber device. A correlation of the form NSh = [Dh(1 − ϕ)/L]NN appears to provide a close fit to the shell‐side mass transfer coefficient data. The perforamnce characteristics of dispersion‐free extraction in hollow‐fiber modules have been considered against those of commercial packed‐bed extractors. A perspective has been provided on comparative utilities of hydrophobic or hydrophilic hollow fibers for a given solvent extraction problem.
Oxygen transfer between metals and oxygen‐ion conducting supports
Authors: Metcalfe I. S. , Sundaresan S. 
Published: June 2004

AbstractThe charge‐transfer reactions in the three‐phase interfacial region, between a platinum catalyst, an yttria‐stabilized zirconia (YSZ) support, and the gas phase, were studied electrochemically during carbon monoxide oxidation. From electrochemical and reaction‐rate measurements, it appeared that oxygen was being removed from the support by carbon monoxide adsorbed on the platinum, while being supplied to the support by atomic oxygen adsorbed on either the platinum or the YSZ.Highly disperse Pt/YSZ catalyst outperformed a Pt/Al2O3 catalyst, the rate difference being explained in terms of interfacial reactions. Even in the presence of species such as water and sulfur dioxide, catalysts with YSZ supports outperformed those with alumina supports.
Influence of secondary flows on the stability of chemically reacting systems
Authors: Gatica J. E. , Viljoen H. J. , Hlavacek Vladimir 
Published: June 2004

AbstractA model is presented for convection and chemical reacton in porous media. An irreversible chemical reaction of arbitrary order is considered. Reactant depletion allows for basic solutions in either the kinetic or the diffusion regime. The cases of forced flow parallel to the lateral walls of the cavity and a closed system are addressed. A linear stability analysis of the basic states is performed and critical values of the thermal Rayleigh number for the onset of natural convection are determined. A dispersion relation is derived and a graphical representation of the linear stability analysis results is provided for typical values of the system parameters. Analytical predictions are verified by results obtained by numerical integration of the complete set of nonlinear partial differential equations. The effect of natural convection is discussed when the basic state is either in the kinetic or in the diffusion regime. For large gradients, associated with the diffusion regime, chemical reaction can drive free convection even for low values of the Rayleigh number. In forced flow systems, natural convection can change substantially the flow pattern of the system.
Effect of nonuniform activity on hydrodemetallation catalyst
Authors: Limbach K. W. , Wei James 
Published: June 2004

AbstractA model is developed to qualitatively predict the effect of a nonuniform activity distribution on the total quantity of metal deposited in hydrodemetallation catalysts. A fixed catalyst support system is assumed and no restrictions are placed on local or overall catalytic activity in seeking an optimal solution that maximizes the amount of contaminant metal deposition over the useful catalyst life. Results indicate that deposition capacity could be substantially increased by a nonuniform activity profile in which the activity at the catalyst center is higher than that at the outer edge. The shape of the optimum activity profile is presented along with practical design improvements.
Bifurcation behavior of a catalytic reaction due to a slowly varying parameter
Authors: Tsotsis T. T. , Sane R. C. , Lindstrom T. H. 
Published: June 2004

AbstractBifurcation problems with slowly varying control parameters are of interest in several research areas, including catalyst deactivation, combustion, and lasers and other nonlinear optical devices. Significant theoretical work has been devoted to the study of these dynamic phenomena, but very little directly relevant experimental information is currently available. Results are presented here from an experimental study of the dynamic behavior of a catalytic reaction system due to a deliberately slowly varied control parameter. Attention is focused on the dynamics due to slow passage through simple limit and Hopf points.
Countercurrent gas‐liquid annular flow, including the flooding state
Authors: Zabaras G. J. , Dukler A. E. 
Published: June 2004

AbstractThe structure of the wavy interface on a falling liquid film is studied for conditions of countercurrent gas flow in order to investigate mechanisms for flooding. Measurements taken just below the liquid feed and at 1.7 m down the tube show that under all conditions, including flooding, the waves propagate only downward and are never of such amplitude as to bridge the tube. These observations are in contrast to speculations in the literature that upward flow of waves or bridging of liquid due to waves cause flooding. In the mechanism suggested, flooding is due to flow reversal in the film just at the liquid entry.
Recovery of uranium from seawater using amidoxime hollow fibers
Authors: Saito Kyoichi , Uezu Kazuya , Hori Takahiro , Furusaki Shintaro , Sugo Takanobu , Okamoto Jiro 
Published: June 2004

AbstractA novel amidoxime‐group‐containing adsorbent of hollow‐fiber form (AO‐H fiber) was prepared by radiation‐induced graft polymerization of acrylonitrile onto a polyethylene hollow fiber, followed by chemical conversion of the produced cyano group to an amidoxime group. Distribution of the amidoxime group was uniform throughout the hollow‐fiber membrane. The fixed‐bed adsorption column, 30 cm in length and charged with the bundle of AO‐H fibers, was found to adsorb uranium from natural seawater at a sufficiently high rate: 0.66 mg uranium per g of adsorbent in 25 days.
Analytical and preparative electrophoresis in a nonuniform electric field
Authors: Rolchigo P. M. , Graves D. J. 
Published: June 2004

AbstractA nonuniform electric field is proposed as the basis for the batch and continuous electrophoretic separation of biomolecules. A theoretical analysis shows the advantages of these techniques over conventional separation processes that use a uniform electric field. The mathematical modeling of such processes and its implications for the experimental design of a nonuniform field separator are presented.
Effect of favorable pressure gradients on turbulent boundary layers
Authors: Finnicum D. S. , Hanratty T. J. 
Published: June 2004

AbstractLarge favorable pressure gradients can cause the drag of a turbulent boundary layer on a solid surface to decrease; if large enough, such gradients can cause a return to laminar flow. Scaling relations and a computational model for the viscous wall layer, recently developed in this laboratory are used to interpret this phenomenon.
On nonlinear doubly‐diffusive marangoni instability
Authors: Ho Kwok‐Lun , Chang Hsueh‐Chia 
Published: June 2004

AbstractEnhancement of simultaneous heat and mass transfer due to surface tension gradient‐induced Marangoni convection is studied. The geometry considered is a thin liquid film between a solid phase and a gas phase. In regions where the two Marangoni numbers are of opposite signs (quadrants II and IV), Orr‐Sommerfeld analysis reveals the possibility of oscillatory roll cells. A nonlinear bifurcation study of the amplitude equations indicates that the finite‐amplitude oscillatory rolls are annihilated by steady rolls slightly beyond the oscillatory stability boundary in a heteroclinic bifurcation. Oscillatory rolls are hence restricted to quadrants II and IV. Finite‐amplitude instability due to subcritical bifurcation of the steady rolls is also shown to be limited to these quadrants. In addition to classifying the bifurcations, the numerical study also provides a useful correlation for single‐component flux enhancement, Nh* = 1 + 0.001324 Nu0.23Pr0.16(NT − N), which is compared to available experimental data.
Analysis of the effect of internal phase leakage on liquid membrane separations
Authors: Borwankar R. P. , Chan C. C. , Wasan D. T. , Kurzeja R. M. , Gu Z. M. , Li N. N. 
Published: June 2004

AbstractA general physical model of a typical batch extraction system employing liquid surfactant membranes is developed. The model takes into account the continuous‐phase resistance and the interfacial resistance along with permeation through a composite emulsion globule. It also quantifies the loss in extraction efficiencies by leakage of the encapsulated phase due to membrane breakage. The physical model is easily adapted to apply to the case of transport facilitation wherein the solute is reacted in the internal phase to yield products incapable of permeating through the membrane phase. Experimental data on o‐chlorophenol extraction are satisfactorily correlated with the model.
Rapid coal devolatilization as an equilibrium flash distillation
Authors: Niksa Stephen 
Published: June 2004

AbstractA model for the rapid devolatilization of individual coal particles is developed by analogy with a single‐stage equilibrium flash distillation. In the theory, thermal depolymerization of the coal generates aromatic fragments that are widely distributed in size. Conditions for phase equilibrium determine the partitioning of these fragments into intermediates in the condensed phase, which ultimately form char and light gas, and into tar vapor, which escapes in a stream of light gases. Comparison with data shows that the model accurately correlates the yields of noncondensible gas and tar from bituminous coals over wide ranges of temperature and pressure. The predicted molecular weight distributions of tar are also in agreement with measured distributions, and the model yields a mechanistic basis for their observed insensitivity to temperature. The tendency to form lighter tar at higher pressures is also explained.
A model for molecular weights in vinyl acetate emulsion polymerization
Authors: Lee Chan H. , Mallinson Richard G. 
Published: June 2004

AbstractThe continuous stirred tank emulsion polymerization of vinyl acetate has shown oscillatory behavior in conversion, particle size, molecular weight, and polydispersity during polymerization. The kinetics in vinyl acetate emulsion polymerization are especially complex because of chain transfer to polymer and monomer and the terminal double bond reaction. A nonsteady‐state model to predict the average molecular weights is developed for this polymerization system. Improved results are achieved by inclusion of the effects of polymer chain initiation and termination by absorbed radicals. It is found that the observed oscillations are closely related to the radical diffusion and desorption rates that are involved in a heterogeneous initiation mechanism. The molecular weights and polydispersities are successfully predicted by the model. The nature of the oscillations in these properties is examined.
Combined surface and pore volume diffusion in porous media
Authors: Bhatia S. K. 
Published: June 2004

AbstractThe recent theory for pore volume diffusion in porous media (Bhatia, 1985, 1986) is further extended to include surface diffusion with adsorption‐desorption phenomena proceeding at finite rates. The short‐range memory effects, previously discussed in terms of a correlation between successive pores traversed, are included here and are found to be important for surface diffusion as well. A tortuosity for surface diffusion is defined and found to be larger than 3, in the range of 5 to 7, because of internal correlation effects in the random network structure examined. Under conditions of gradients in pore surface area it is shown that the surface transport equation is

and the relation between the effective surface diffusivity Dse and the pore structure parameters is derived. The equation for pore volume diffusion requires further justification when adsorption‐desorption occurs at finite rates, and is also derived here.
Effect of iron impurity in zinc sulfide concentrates on the rate of dissolution
Authors: Crundwell Frank K. 
Published: June 2004

AbstractThe rate of dissolution of sphalerite is shown to be directly proportional to the concentration of substitutional iron impurity in the solid. This is attributed to the formation of a narrow impurity band within the forbidden band gap of the sphalerite. The impurity band is of iron d‐orbital origin. The transfer of electrons between this d‐orbital band and the oxidant is energetically more favorable than the transfer of electrons between the valence band and the oxidant. A fundamental model combining the electronic structure of sphalerite and semiconductor electrochemistry is presented. An equation is derived that describes the rate of dissolution as being first order for the concentration of iron in the solid and half‐order for the concentration of the oxidant. This is in agreement with the experimental evidence.
Modeling catalytic gauze reactors: HCN synthesis
Authors: Waletzko N. , Schmidt L. D. 
Published: June 2004

AbstractThe performance of the industrial HCN synthesis Andrussow reactor on a Pt gauze catalyst is simulated using rate equations for 13 simultaneous unimolecular and bimolecular surface reactions. Individual rates have been determined experimentally for reactants, intermediates, and products on polycrystalline Pt, and the model therefore contains no adjustable parameters except for reactant flux limits. Predicted selectivities of HCN formation agree quite well with those observed in commercial reactors, and a distinct optimum with feed composition is obtained near that observed experimentally. In addition, behaviors are predicted at compositions, pressures, and temperatures inaccessible to the commercial reactors. Both isothermal and nonisothermal situations are examined. Questions concerning the validity of models, reactant flux limits, and the decoupling of simultaneous surface reactions are considered.
Thermodynamics of solutions with solvent and solute in different pure states
Authors: Kopatsis A. , Salinger A. , Myers A. L. 
Published: June 2004

AbstractIsoactive‐solvent (ISAC) theory is a thermodynamic framework for the case where the components of a solution exist in different pure states: liquid solvent and gaseous solutes (absorption of gases); solid solvent and liquid solutes (sorption of liquids); and liquid solvent and solid solutes (solubility of mixed electrolytes). Properties of mixed solutes are predicted from known activities of single solutes by assuming that solute‐solute (but not solute‐solvent) molecular interactions are ideal. Equations for an ISAC ideal solution are exact in the limiting case of a solution of identical solutes. The thermodynamic potential is a Legendre transformation of the Gibbs free energy: Ψ = G − μ1n1, where the solvent is component number 1. The ISAC standard state is the real single‐solute mixture.