摘要:

AbstractFor the first time, a macroscopic method was used to measure directly diffusivity of fast diffusing species such as methane in silicalite. A form of Wicke–Kallenbach technique was applied to measure intracrystalline diffusivity. The technique uses a single embedded zeolite crystal as a membrane and a mass‐selective detector to determine the transient mass response and hence the diffusion flux passing through the membranne. A concentration‐difference driving force is used rather than a pressure‐difference driving force. The diffusivities calculated from both adsorption and desorption transients were in excellent agreement, thus providing a check for the self‐consistency of the data. The diffusivities of carbon dioxide, methane, ethane, propane and butane in silicalite between 30 and 70°C have been compared with those from the literature. The diffusivities reported here are between those measured with microscopic methods and those measured with other macroscop

ISSN:0001-1541    

DOI:10.1002/aic.690421102

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractA two‐phase model of a nonisothermal fluidized‐bed catalytic reactor with consecutive exothermic reactions makes it possible to control the chaotic behavior by small parametric perturbations of an input variable with suitable frequency and amplitude. By periodic forcing of the feed temperature the chaotic behavior of the autonomous system can be controlled and become periodic even for small amplitudes of forcing. For constant frequency with change in forcing amplitudes the behavior of the system alternates between periodic and chaotic regimes via period doubling and period adding bifurcation mechanisms. When the amplitude is fixed, regular patterns also appear with small changes in the forcing frequency. Appropriate selection of the forcing frequency can improve the yield of the desired intermediate component in the consecutive reactions network A →

ISSN:0001-1541    

DOI:10.1002/aic.690421103

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractAn oriented submicron silicalite membrane has been prepared by growing a layer of oriented silicalite crystals on a composite precursor nanocrystalline silicalite/alumina film using controlled secondary growth. The orientation of the crystals at the surface was such that both straight and sinusoidal channel networks run nearly parallel to the membrane surface. The membrane exhibits ideal selectivities for H2over N2as high as 60 at 150°C and O2over N2as high as 3.6 at 185°C. H2, N2and O2permeances are 2.13, 0.05 and 0.17 cm3(STP)/(cm2·min·atm) at 185°C, respectively, and the corresponding apparent activation energies are 11, 26 and 32 kJ/mol. The permeation characteristics are attributed to the preferred orientation of the molecular sieving l

ISSN:0001-1541    

DOI:10.1002/aic.690421104

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractDesign and operational performance of convective industrial dryers are an important field of chemical engineering, which is still governed by empiricism. This article addresses the design vs. operation problem for three basic types of continuous convective industrial dryers: conveyor‐belt, fluidized bed, and rotary. Design procedures determined the optimal construction and operational characteristics in terms of total annual cost for each type involved and for a given production capacity through appropriate mathematical modeling. All dryer were compared by evaluating optimum configurations for a wide range of product characteristics and production capacity values. Once the dryer configuration was specified, its operational performance was evaluated by comparing the optimum operational cost vs. production capacity for predefined optimum designed structures. Rotary dryers were more expensive to design than fluidized bed dryers. Operationally, however, it is the other way around due to the favored heat transfer achieved in rotary dryers. Conveyor‐belt dryers lie somewhere between producing satisfactory results in terms of both design and operation. Case studies on foods and inorganics are included to demonstrate the performance of each process as well as the effectiveness of the proposed appro

ISSN:0001-1541    

DOI:10.1002/aic.690421105

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractThe axial and transverse apparent dispersion coefficients of three solvents in two packed chromatographic columns were determined by pulsed‐field‐gradient nuclear‐magnetic resonance in a range of mobile phase velocity. The column beds were packed with 5‐ μm particles of porous C18 silica or 30‐μm particles of silica. The solvents used were methanol and acetonitrile (in an 80:20 ACN/water solution) in the former case and acetone in the latter. The coefficients were determined over a range of particle Peclet numbers from less than 0.1 to approximately 10 in the former case and 40 in the latter. The data obtained with short dispersion times were fitted to the correlations suggested by Giddings, Horvath and Lin, Huber, and Knox. These data agreed well only with the Giddin

ISSN:0001-1541    

DOI:10.1002/aic.690421106

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractThe inverse probability theorem of Bayes is used, along with sampling theory, to obtain objective criteria for choosing among rival models. Formulas are given for the relative posterior probabilities of candidate models and for their goodness of fit, when the models are fitted to a common data set with Normally distributed errors. Cases of full, partial and minimal variance information are treated. The formulas are demonstrated with three examples, including a kinetic study of a catalytic reaction.

ISSN:0001-1541    

DOI:10.1002/aic.690421107

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractThis article deals with distributed parameter systems described by first‐order hyperbolic partial differential equations (PDEs), for which the manipulated input, the controlled output, and the measured output are distributed in space. For these systems, a general output‐feedback control methodology is developed employing a combination of theory of PDEs and concepts from geometric control. A concept of characteristic index is introduced and used for the synthesis of distributed state‐feedback laws that guarantee output tracking in the closed‐loop system. Analytical formulas of distributed output‐feedback controllers are derived through combination of appropriate distributed state observers with the developed state‐feedback controllers. Theoretical analogies between our approach and available results on stabilization of linear hyperbolic PDEs are also identified. The developed control methodology is implemented on a nonisothermal plug‐flow reactor and its performance is evaluated throug

ISSN:0001-1541    

DOI:10.1002/aic.690421108

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractThis article introduces the novel concept of synthesizing waste‐interception networks (WINs) and incorporates it within a mass‐integration framework for the global allocation of pollutants. The essence of this notion is to provide selective interception and rerouting of undersirable species at the heart of the process instead of dealing with the pollutants in the terminal waste streams. It also provides a unified framework for simultaneously tackling gaseous and liquid pollution. Several tools are developed to track the pollutant throughout the process and determine the optimal interception policies. The problem is formulated as an optimization program that seeks to determine the optimum locations for intercepting the pollutants, extent of separation, and separating agents to carry out the interception tasks. Furthermore, the WINs can be used within a mass‐integration scheme for the global allocation of species throughout the plant. These new concepts and associated mathematical formulation are demonstrated using a case study on the removal of a chlorinated hydrocarbon. This approach has benefits over conventional recycle/reuse (such as MEN synth

ISSN:0001-1541    

DOI:10.1002/aic.690421109

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractA mathematical model was formulated to describe the reaction rate and the particle size distribution of solids in a fluidized bed for the chlorination of rutile by a CO/Cl2mixture. The bubble assemblage model was applied to describe the gas behavior in the bed. The particle‐size distribution in the bed was determined by a population balance. Predictions of the model gave satisfactory agreement with experimental results. The effects of important variables such as superficial gas velocity, exchange rate between the phases, and the reaction‐rate constant were evalua

ISSN:0001-1541    

DOI:10.1002/aic.690421110

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractThe rapid mixing of two miscible fluids is a precursor to promoting fluid‐phase reactions. The configuration of a turbulent jet in a crossflow or tee‐mixer is the most efficient passive design for rapid mixing. Here the Damkohler number has been defined from available tee‐mixer data where the reactions are slow to fast compared with mixing times. For the available data the Damkohler number has been found to be of secondary importance for optimum design. The numerical simulation of jets in a tubular reactor suggests that large jet‐to‐tube momentum ratios with no backmixing are superior. Moreover, the optimum design of maximum jet entrainment is shown to be synonymous with either a minimum in the relative standard deviation or the skewness. A formula relating the optimum diameter ratio to the jet‐to‐tube flow ratio has also been derived assuming geometrically similar jet trajectories, and the result correlates both numerical and expe

ISSN:0001-1541    

DOI:10.1002/aic.690421111

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY