摘要:

AbstractTransport in liquid‐filled pores of molecular dimensions plays an important role in membrane separations, in various forms of chromatography, and in catalysis, to name a few examples. A frequent observation is that if the pore dimensions are of the same order as those of a solute molecule, the apparent diffusion coefficient of that solute is much lower than in bulk solution. Likewise, rates of convective transport of such solutes are generally lower than the product of bulk concentration and volume flow rate. Thus, solute transport is typically “hindered” or restricted. A key objective of research on hindered transport is to be able to predict the applicable transport coefficients from such fundamental information as the size, shape, and electrical charge of the solutes and pores. The present status of this research is rev

ISSN:0001-1541    

DOI:10.1002/aic.690330902

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

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

ISSN:0001-1541    

DOI:10.1002/aic.690330903

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractA model is developed for predicting the performance of a partially wetted trickle‐bed reactor for a gas‐limiting reaction of order less than or equal to one. The model indicates that under certain conditions the liquid reactant may affect the reaction rate due to its inability to rapidly diffuse to catalyst areas that are in direct contact with the gas. This model is the first to explain and predict on a rational basis the experimental results for the hydrogenation of diluted ć‐methylstyrene and aqueous maleic acid reported in the literature. A criterion that determines when liquid reactant effects can be expected is developed and re

ISSN:0001-1541    

DOI:10.1002/aic.690330904

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

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 rat

ISSN:0001-1541    

DOI:10.1002/aic.690330905

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractIn the analysis of countercurrent adsorption processes, an equilibrium theory in which local equilibrium between the fluid and the adsorbent phases is assumed has been used in the past to determine the composition of the pinch state that would be obtained for long columns. It is shown that this equilibrium theory is deficient and that certain mass transfer parameters, which are lost in the procedure by which the model equations for the equilibrium theory are formulated, can have a profound effect on the composition of the pinch.

ISSN:0001-1541    

DOI:10.1002/aic.690330906

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractGas holdups and volumetric mass transfer coefficientskLaare 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 erro

ISSN:0001-1541    

DOI:10.1002/aic.690330907

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractOptimal linear‐quadratic (LQ) controller design is usually associated with state space techniques. However, when one has measurements of the outputs to be controlled, there are many advantages to designing these LQ controllers using input‐output transfer function models. The design procedure leads to a discrete equivalent of the Wiener‐Hopf equation, which can be solved using a spectral factorization approach.In this paper the design procedure is presented and various interpretations of the resulting controllers are discussed. In particular, the controllers are shown to be of the internal model controller (IMC) form, and the Wiener‐Hopf procedure is shown to be a powerful way of selecting approximate model inverses and filters that yield good performance and robustness characteristics. The approach treats the problem of simultaneous disturbance rejection and set‐point tracking, and it easily handles nonsquare systems.The design approach, its performance/robustness trade‐offs, and the structure of the resulting controllers are demonstrated using models for several processes, including a two‐input/one‐output sheet forming process, a (3 × 3) multivariable level control problem, and a (2 × 2) multivariable

ISSN:0001-1541    

DOI:10.1002/aic.690330908

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractA practical application of advanced, model‐based, multivariable control to a pilot plant packed‐bed reactor carrying out highly exothermic butane hydrogenolysis reactions is presented. The system is first stabilized by using butane flow rate to control the reactor hot‐spot temperature. Propane production and butane conversion are then controlled using multivariable controllers that manipulate the hot‐spot temperature set point and hydrogen flow rate. The controller designs are based on multivariable transfer function models developed using multivariable time series and process identification methods.Two types of multivariable controllers are applied. The first is an internal model controller (IMC) utilizing a stabilized approximation of the model inverse and a tunable exponential filter. The second is a linear‐quadratic (LQ) controller design using pulse transfer function models to characterize the process dynamics and autoregressive‐moving average models to characterize the disturbances. The optimal control solution was arrived at via a spectral factorization solution to the Wiener‐Hopf equations. The results indicate that both designs, if well tuned, provide good performance and robustness over a wide range

ISSN:0001-1541    

DOI:10.1002/aic.690330909

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractGas absorption with a nonisothermal, bimolecular (1,1 order), and irreversible reaction are analyzed and approximate film theory solutions are obtained for interfacial temperature rise and enhancement factor. The model of Mann and Moyes is extended to incorporate depletion of liquid reactant concentration at the gas‐liquid interface and also the variation of dissolved gas concentration in the bulk liquid, leading to a generalized solution independent of the regime of absorption. The effect of heat generation, heat dissipation, and reaction rate parameters on enhancement factor and interfacial temperature rise is discussed. The system showed multiplicity behavior under certain conditions, but at higher values of heat dissipation parameters and for some combinations of heat generation and reaction rate parameters, unique solutions were obtained. However, even the unique solutions of enhancement factor are substantially different from the values obtained under isothermal conditions. Since depletion of liquid reactant concentration is incorporated, asymptotic values of enhancement factor (at large\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt M $\end{document}) were observed to be the same as those obtained in the instantaneous reaction regime of isothermal absorption and reaction process. The model presented does not requirea prioriassumption of the regime of absorption and hence can be useful in modeling nonisothermal reactor

ISSN:0001-1541    

DOI:10.1002/aic.690330910

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractA new method for detecting, identifying, and estimating gross errors in steady state processes is described in this paper. The generalized likelihood ratio method is based on the likelihood ratio statistical test and provides a general framework for identifying any type of gross error that can be modeled. The procedure is illustrated with gross errors caused by measurement biases and leaks. One significant advantage of the method is that the identification of gross errors is not confounded by departure from steady state conditions, which may now be accounted for by “leaks”. Also proposed is a new strategy for identifying multiple gross errors using serial compensation of gross errors, which may be applied to all types of gross errors including leaks and biases and which requires less computing time than the existing strateg

ISSN:0001-1541    

DOI:10.1002/aic.690330911

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY