ISSN:0001-1541    

DOI:10.1002/aic.690420102

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractDiffusion of carbon dioxide through silicone‐polycarbonate membranes containing oriented mica flakes is proportional to the square of the volume fraction of the flakes, to the square of the aspect ratio, and to the square of the cosine of the angle at which the flakes are oriented. These experiments are consistent with Monte Carlo simulations. The simulations allow investigation of more complex geometries, including other flake orientations and polydisperse flake size

ISSN:0001-1541    

DOI:10.1002/aic.690420103

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractFormation of asphalt aggregates and their deposition on the pore surfaces of a porous medium, which alter the structure of the medium and its effective properties, is a critical problem to catalytic and oil recovery and refinery processes. Extensive new experimental data for the amount of precipitated asphalt formed with crude oil and various solvents are presented. Results indicate that, contrary to the previous assumptions, asphalt formation is at best partially reversible. A thermodynamic model based on the Flory–Huggins theory of polymer solutions is used, together with the Soave equation of state, to predict the data. Critical evaluation of the model shows that its predictions do not agree well with our data. As an alternative, we propose a new model that employs a scaling equation, somewhat similar to those encountered in aggregation and gelation phenomena. The scaling function takes on a very simple form, and its predictions are in very good agreement with the data. It also predicts that the onset of precipitation may obey a simple universal equatio

ISSN:0001-1541    

DOI:10.1002/aic.690420104

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractAn integral‐spectral formulation for laminar reacting flows in tubular geometry (tubular Poiseuille flows) is introduced and performed within an operator–theoretic frame‐work where the original convective‐diffusive differential transport problem coupled with reaction is inverted to give an integral equation. This equation is of second kind and of the Volterra type with respect to the axial coordinate of the tube with a kernel given by Green's function. Green's function is identified by a methodology that gives the Mercier spectral expansion in terms of eigenvalues and eigenfunctions of the Stürm–Liouville problem in the radial variable of the tube. Eigenvalue problems for both Dirichlet and von Neumann boundary conditions are solved in terms of analytical functions (Poiseuille functions) and compared with the values found in the literature. The groundwork is set for future applications of the methodology to solving a wide variety of problems in convective–diffusive transport and reaction. Examples with wall and bulk chemical reaction are given to illustrate t

ISSN:0001-1541    

DOI:10.1002/aic.690420105

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractA laser‐Doppler velocimetry (LDV) apparatus and a computational fluid dynamic (CFD) software package (FLUENT) were used to experimentally determine and numerically predict the velocities in a baffled vessel agitated by one or two 45° pitched‐blade turbines. The flow characteristics in the impeller regions were measured by LDV and used as boundary conditions in the numerical computations. Turbulence effects were simulated using either the k‐ε model or algebraic stress model (ASM). The CFD predictions were compared to the LDV measurements in terms of average velocities in all three directions as well as turbulent kinetic energies. Predictions based on ASM were typically in closer agreement with the experimental data than those based on the k‐ε model. Flow patterns in both configurations were dominated by the axial and tangential components. The presence of the upper impeller altered the flow considerably, producing a strong vertical recirculation pattern between the impellers and significantly reducing the circulation flow below the lowe

ISSN:0001-1541    

DOI:10.1002/aic.690420106

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractThe competition between drying and reactions in a liquid coating containing precursors to a random network polymer can give rise to a variety of drying phenomena. Solidification, or gelation, of the polymer may occur before, after, or during the removal of solvents from the coating. Rates of drying and reaction are probed by solving the equations of mass transfer by diffusion along with chemical reaction in one dimension. Solutions to this system of equations are obtained by Galerkin's method with finite‐element basis functions and entail large‐scale computation. Skinning, or solidification at the surface of the coating while the bulk is still liquid, occurs in thick coatings when the diffusional resistance to drying is significant, that is, at high mass‐transfer coefficients. Homogeneous solidification occurs in thin coatings at low mass‐transfer coefficients. Drying regime maps represent these solidification phenomena as regions in paramete

ISSN:0001-1541    

DOI:10.1002/aic.690420107

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractMass transport of n‐heptane, n‐nonane, and n‐dodecane in zeolite T was studied using a gravimetric uptake technique. The sigmoidal shape of the uptake curves indicated the existence of a nondiffusional resistance in the transport process. To compute the transport parameters, an approach based on the temporal moments of the uptake curves was developed. A model involving an external resistance dependent on the local slope of the sorption isotherm best represented the data. No evidence of the “window effect” reported by Gorring was found. The measured diffusivities decrease with chain length, while the activation energies remain essentially constant. Both resistances (diffusional and nondiffusional) depend strongly on lattice loading, and their relative contributions for the transport time change as saturation is a

ISSN:0001-1541    

DOI:10.1002/aic.690420108

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractLiquid–solid fluidization characteristics of irregularly shaped Biobone particles were studied in a fluidized bioreactor column 2.35 m high and 0.1 m dia. The wet biobone particles had a density of 1,890 kg/m3. Two size ranges were studied: 1.70–2.36 mm and 1.25–2.36 mm. The Biobone is a natural cheap material composed of collagen, which is a strong protein structure, embedded with microcrystals of hydroxyapatite and calcium phosphate, and it is an excellent matrix of commercial importance used for the immobilization of enzymes, whole cells and other biocatalysts. Fluidization characteristics of Biobone particles, which include measurements of pressure drops, holdups, minimum fluidization velocities, particle entrainment, and residence time distributions at different water superficial velocities, are reported. Because of the highly irregular shape of Biobone particles, new fluidization behavior was observed, which was much different from the fluidization behavior of spherical particles reported in the literature. A new channeling index, Ic, is proposed to quantify the channeling characteristics of fluidized Biobone particles, and a new parameter, α, was developed to distinguish the transition between fixed and fluidized states of the Biobone par

ISSN:0001-1541    

DOI:10.1002/aic.690420109

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractRecent and ongoing research in the distillation of nonideal mixtures is reviewed focusing on advances in the methodologies for the synthesis, design, analysis and control of separation sequences involving homogeneous and heterogeneous azeotropic towers. Maps of residue curves and distillation lines are examined, as well as geometric methods for the synthesis and design of separation sequences, trends in the steady‐state and dynamic analysis of homogeneous and heterogeneous towers, the nonlinear behavior of these towers, and strategies for their control.Emphasis is placed on the methods of computing all of the azeotropes associated with a multicomponent mixture, on the features that distinguish azeotropic distillations from their zeotropic counterparts, on the potential for steady‐state multiplicity, and on the existence of maximum and minimum reflux bounds. Important considerations in the selection of entrainers are examined. For the synthesis of separation trains, when determining the feasible product compositions, the graphical methods are clarified, especially the conditions under which distillation boundaries can be crossed and bounding strategies under finite reflux. The application of geometric theory to locate the fixed points, at minimum reflux, is reviewed in connection with homotopy‐continuation algorithms for this purpose. The use of homotopy‐continuation algorithms, especially for the steady‐state simulation of heterogeneous azeotropic distillations, is justified. Methods for phase stability analysis are reviewed in connection with the location of real bifurcation points at phase transitions, an important feature of algorithms for the dynamic simulation of heterogeneous azeotropic dist

ISSN:0001-1541    

DOI:10.1002/aic.690420110

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractRecuperative parametric pumping in adsorptive membranes, a cyclical adsorptive separation process, can lead to two distinct mechanisms of separation: rejection and preferential transport. During rejection, the adsorptive membrane rejects an adsorbing solute while permitting the transport of nonadsorbing solutes. During preferential transport the reverse occurs; the adsorptive membrane selectively transports an adsorbing solute while preventing the transport of nonadsorbing solutes. Switching from rejection to preferential transport can be accomplished by merely decreasing the ratio of the stroke volume (cyclical volume of solution pumped into and out of the membrane) to the membrane void volume. Preferential transport, earlier called an “inverse separation,” results from the adsorbing solute crossing over from an adsorbing to a desorbing region in the interior of the membrane and is governed by the shape of the equilibrium isotherms and by process variables. In experiments with lysozyme and a membrane chromatography cartridge, selectivities obtained by preferential transport were on the order of 5 and agreed with theoretical predictions. Theoretical predictions suggest that to further improve separation by preferential transport, experiments need to be conducted on low dispersion membranes (Pe>104) and that both rejection and preferential transport can lead to continuous concentrated streams of the adsorbing solu

ISSN:0001-1541    

DOI:10.1002/aic.690420111

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY