I&EC REPORTS & COMMENTS Abstracts for the Kinetics Symposium
Applied Kinetics and Reaction Engineering
The third summer symposium, sponsored by the I@EC Division, will be held in Washington from 13 to 15 June. The cochairmen, Dr. V . W. Weekman and Dr. R. L. Gorring of the Socony Mobil Oil Co., have divided the 79papers into six sections dealing with Fundamental Kinetics, Process Analysis, and Reaction Engineering. Abstracts f o r the individual pajers are given below in the order of their presentation. Registration information may be found on page 12 of this issue.
The Behavior of Isothermal Multicomponent Systems with Simultaneous Diffusion and First-Order Chemical Kinetics. H. L. Toor, Carnegie Institute of Technology, Pittsburgh, Pa.
The Cochairmen
VERX W. WEEKMAN JR.
ROBERT L. GORRING
Vern MI. Weekman, Jr., received his BSChE degree from Purdue, his M S from Michigan, and his PhD from Purdue. He has been with the Socony Mobil Research Department since 1954 and in 1960 was awarded the Socony Mobil Incentive Fellowship for graduate study. H e has been active in the development of hydrocracking and is currently with the Systems Research Group a t the Paulsboro Research and Development Laboratory. His research interests include applied kinetics, catalysis, and process simulation and control. Robert L. Gorring received his BA and BSChE degrees from Columbia University and the M S and PhD degrees from the University of Michigan. H e is currently with the Systems Research Group of the Applied Research and Development Division, Socony Mobil Oil Co., Paulsboro, N. J. His research interests include applied kinetics, catalysis, and chemical reaction engineering.
Equations for multicomponent, first-order, chemically reacting systems, and linearized equations for multicomponent diffusion can be uncoupled by transformation of concentration coordinates. Hoc\ ever, if reactions and diffusion occur simultaneously, there is no general transformation which will uncouple the equations. Solutions of the equations near equilibrium indicate the possibility of more oscillations than would be obtained in either pure reaction or pure diffusion systems. If the kinetics are assumed first-order in concentrations, and the reactants are dilute, then the near-equilibrium reaction-diffusion system can be shown to be stable. If the kinetics are assumed to be first-order in activities, however, the near-equilibrium system can be shown to be stable in general.
Theoretical and Experimental Analysis of Oscillating Reactions. J. Higgins, Johnson Research Foundation, University of Pennsylvania. With the experimental discovery of oscillatory kinetics in cells and cell extracts, there has been a renewed interest in the mechanism of oscillation chemical reactions. Previous theoretical results relating chemical mechanisms and oscillatory response are briefly reviewed. A generalized mechanism based on feedback pathways is presented and provides a set of necessary conditions for sustained oscillations. The oscillatory response arises as a limit cycle phenomenon in the associated phase plane, with consequent stability of frequency and amplitude and frequency. Aspects such as the projections of oscillations, filtering, and generat’on of subharmonics by chemical reactions are also discussed. Emphasis is placed on the general analysis of complex systems through the use of time scale reductions and control approximations. Such techniques, when coupled with computer studies, provide a partial basis for the understanding and analysis of complex kinetic patterns.
The Concept of Diffusion in Chemical Kinetics. T. A. Bak and E. R. Fisher, Chemistry Laboratory 111, University of Copenhagen, Denmark. T h e concept of diffusion occurs in theories of chemical kinetics in two connections. O n e is in connection with very fast bimolecular reactions in solutions where the rate determining step can be the diffusion of the reacting species toward each other. The other example is in dissociative gas phase reactions where the reaction may be considered as a diffusion in a phase space. T h e characteristic feature of both examples is that the usual hypothesis of equilibrium breaks down for either one or several degrees of freedom. A discussion will be presented of the circumstances under which diffusion theories can be expected to apply to chemical reactions. Finally, agreement with experimental evidence will be demonstrated.
Is Sophistication Really Necessary? R. Ark, University of Minnesota. Mathematical models of great sophistication have been developed for reaction engineering problems during the last decade. They are usually based on the assumption that a precise kinetic expression is available for the rate of reaction and this is rarely the case. We should, therefore, ask two related questions: “When do small errors in kinetic constants vitiate the subsequent analysis?” and “When is the effect of errors so small that a reasonably intelligent guess gives a performance almost as good as that obtained with great labor and sophistication?” These questions will be discussed in the context of optimal reactor design and associated problems, and it becomes clear that sophistication cannot be dismissed unsophisticatedly.
Determination of Reaction Mech anisms for Reactor Design. H. M. Hulbert and Y . G . Kim, Northwestern University. When reactors are designed to produce a specific dist ibution of products, a more detailed mechanism must be established than when only a n overall conversion of a reactant is controlled. I n particular, when reactor scale-up involves significant change in the distribution of temperature, concentration, and residence time, mechanisms must be known to predict the effect of scale-up on yields and product distributions. Though chemical theory may postulate a number of reaction sequences, any one of which may account equally well for a specific set of observations, the engineer must select only those steps which account for his stoichiometric and kinetic observations, omitting those steps which have no kinetic consequences. Methods of kinetic experimentation are reviewed with emphasis on their suitability for identifying the significant steps of a reaction mechanism. I n addition to traditional, batch, and steady flow analysis, recent developments in the use of frequency response, relaxation methods, and parametric perturbation methods are discussed. Analogies between the process identification problems in general proces, control theory and mechanism identification in reaction kinetics are developed
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M A Y 1966
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I&EC R E P O R T S
Reaction Rate Modeling in Heterogeneous Catalysis. J. R. Kittrell, R. Mezaki, and C. C. Watson, University of Wisconsin. T h e model of a chemically reacting system should involve only that amount of insight into the reaction mechanism that can be justified by economics of the plant. Therefore, methods must be available which are applicable to a number of model types. A review of recently developed techniques for reaction rate modeling will be presented, with emphasis on their application to specific experimental systems. These techniques include model building methodology in which a n adequate model is constructed by modification of a n existing inadequate model. T h e catalytic oxidation of methane will be used to typify the procedure. Also included are model discrimination methods. Mention will be made of a recently developed technique for the estimation of reaction order, to be used when above methods are uneconomical.
be completely insensitive to wide variations in the Reynolds number and Prandtl number when the Lewis number is fixed. As the Lewis number is changed, significant variations in the results are noted; these variations are discussed in detail. Finally, the general theoretical results obtained in the present study are compared with a recently set of data for heat transfer to decomposing nitrogen dioxide gas in the turbulent boundary layer on the surface of a rotating cylinder.
On the Maximum Temperature Inside a Porous Catalyst. J. Wei, Socony Mobil Oil Co.
Numerical solutions have been obtained for heat transfer to a reversibly reacting gas in the turbulent boundary layer on the surface of a rotating cylinder. By restricting the study to cases of a small temperature gradient, general results are obtained in terms of a n arbitrary reaction rate expression. When these results are presented in dimensionless form, they are found to
During a chemical reaction, the inside temperature of a porous catalyst may be considerably higher than the ambient temperature. T h e maximum temperature under steady-state conditions was given by Prater and is valid for any conceivable kinetics. Under transient conditions, the maximum Prater temperature may be exceeded. Although the average temperature inside the catalyst may not exceed the Prater temperature or the adiabatic flame temperature, whichever is larger, individual hot spots may attain temperatures much higher than these two. I n fact, if we adhere to the convention that matter is a continuum, one can suggest a n arbitrary kinetics that results in a hot spot of infinite temperature. Such a spot must be, of course, infinitesimal. Fortunately matter is not continuous but is an aggregate of molecules. We are not concerned with hot spots smaller than individual molecules. We have developed a convenient upper boundary to the maximum temperature of any hot spot, and the value given is valid for any conceivable kinetics.
Registration Information
Hotels
If a t all possible, please use the preregistration form below and return it as soon as possible. T h e earlier forms are received, the more rapidly and accurately they may be processed. There will be no preprints of papers available.
Hotel reservations must be made by the individuals attending the symposium. In the immediate vicinity of ACS Headquarters are several good hotels and motels, such as: T h e Mayflower (Connecticut Ave. at De Sales St.), T h e Madison (15th and M Sts.), the StatlerHilton and Carlton Hotels (16th and K Sts.), the Executive House Motor Inn (16th St. and Rhode Island Ave.), T h e Holiday Inn (17th St. and Rhode Island Ave.), and T h e Gramercy Inn (across from the Holiday Inn). In view of the large influx of visitors in the late spring and early summer, hotel space should be booked as far in advance as possible.
Turbulent Heat Transfer to a Nonequilibrium Chemically Reacting Gas. P. L. T. Brian and S. W. Bodman, Massachusetts Institute of Technology.
Fees T h e schedule of fees is as follows : I & E C Division Members ACS members who are not I&EC Division members All others
$5 .OO $9.00 $18.00
Preregistration Form Symposium on Applied Kinetics and Chemical Reaction Engineering ACS Division of Industrial and Engineering Chemistry Washington, D . C., June 13-15, 1966 Name Address Business or Professional Affiliation I & E C Division Member
$5
ACS Member, Nonmember of I & E C Division Other
0
0
$9
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Make check payable to INDUSTRIAL A N D ENGINEERING CHEMISTRY and send with completed form to the Editor, I&EC, 1155 16th St., N.W., Washington, D. C. 20036.
Surface Chemical Kinetics and Gas Phase Diffusion in the Germanium Iodide Reaction. D. R. Olander, University of California, Berkeley, T h e reaction of gaseous iodine and a rotating disk of germanium has been studied in the temperature range 280' to 460' C. A clear demarcation between reaction-limited and diffusion-limited regions was observed. I n the diffusion limited regime, the rate was independent of temperature. I n the reaction limited regime, processes with activation energies of 31 and 215 kcal./mole were observed. These have been tentatively attributed to iodine reaction with grain boundary and crystal surface germanium, respectively. For analysis of the diffusion-limited transfer rate, the momentum, overall continuity, and two diffusion equations governing rotating disk mass transfer in a ternary mixture with a reaction boundary condition were applied. T h e effects of variable density, interfacial velocity, and multicomponent diffusion were included, and the theory was compared with experimental data for the I$GeIl dilute system. Absolute prediction of the transfer rates in the dilute iodine region was within 15% of the experimental results. I n the concentrated reactant gas region, the conservation equations were solved by an approximate method which permitted the effects of density variation in the flow equations, interfacial velocity, and density variations and multicomponent effects in the diffusion equations to be evaluated independently. Theory and experiment were compared by examining the variation of the ratio of the mass transfer coefficients in the coordinated and dilute reactant gas region as a function of the iodine concentration. For iodine mole fractions between zero and unity, and helium and argon diluents, the theory was consistently 7-1070 below the experimental data.
Mixing and Contacting in Chemical Reactors. K. B. Bischoff, University of Texas. Mixing and contacting behavior for singlephase flow in cylindrical open and packed tubes is reasonably \vel1 understood, a t least to order of magnitude. Other geometries need more investigation, but general correlations would be difficult to envision. However, the situation for general two-phase fiow is quite different since the effects are larger and there are more variables to consider. The three areas of gas-liquid flow in empty and packed tubes and aggregatively fluidized beds are representative of commercially important but not completely understood processes of this type. Recent \vork in mixing and contacting in these areas will be discussed with particular emphasis on the two-phase system.
Stochastic Mixing Models for Chemical Reactors. F. Krambeck, R. Shinnar, and s. Katz, City University of New York. Turbulent chemical reactors are modeled by networks of stirred tanks, with the stochastic nature of the mixing introduced by taking interstage flows to be stationary Markov processes. Some general features of tracer experiments in these quasi-steady flows are discussed together with their relation to residence time distributions in steady flows. The statistics of tracer experiments are analyzed and related on the one hand to the estimation of mixing parameters and on the other hand to the forecast of yield from the reactor system under first order-kinetics. T h e study of more complicated kinetic mechanisms is deferred.
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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I&EC REPORTS Photochemical Reaction Engineering. A. Cassano, P. L. Silveston, and J. M. Smith, University of California, Davis. T h e design problems for photochemical reactors are discussed in relation to convention reactors with particular emphasis on wall deposits and radiant energy distributions. General conservation equations are developed for chain kinetics. Solutions can be obtained numerically for special cases. Examples are given for appropriate values of the pertinent parameters. Of particular interest is the influence of heterogeneous termination steps on the radial gradients in tubular reactors. T h e effects of reactor shape and reactor-lamp geometry are illustrated quantitatively for several designs. Scale-up problems are particularly challenging in photoreactors and these are discussed in relation to mixing effects and wall reactions. A summary is also given for the accumulated experience in laboratory work of an engineering nature.
Yield in Chemical Reactor Engineering. J. J. Carberry, University of Notre Dame. Both local and overall yield in complex reaction networks are discussed in terms of mixing, diffusion, and temperature influences, with particular emphasis being devoted to solid catalyzed reaction systems.
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A Study of Molecular Mixing in a Continuous Stirred Tank Reactor by Means of the Kinetics of the Ethylene Oxide Phenoxyethanol Polymerization. J, M. Ross, G. J. O'Brien, D. E. Jost, and L. C. Eagleton, University of Pennsylvania. T h e extremes in mixing on a molecular scale in a continuous flow reactor have been termed maximum mixedness and complete segregation by Danckwerts and Zwietering. Previous studies have some evidence of segregation in a CSTR by means of the conversion obtained from a relatively slow second-order liquid phase reaction. This technique is not suitable \\hen the time for molecular mixing is very short compared with the nominal residence time in the reactor. T h e major objective of this study was to develop a method to measure the time required for a liquid to be completely mixed on a molecular scale that would be suitable for the 0.1- to 10-second range of mixing times. T h e method was based on the measurement of product distributions which results from a series of second-order reactions in a continuous stirred reactor.
Experimental Studies of an Industrial Reactor. J. 0.Hougen,G. H. Quentin, and 0.R. Martin, Monsanto Co. This paper presents, in a general n a y , results of a n experimental study of an industrial reactor made to determine the operating conditions for improved conversion and to produce information useful in the design of appropriate control systems. After instrumentation, the plant tests were made to study the dynamic characteristics of the plant and its subsystems. T h e information obtained indicated simple methods for controlling the reactor and useful operating guides for maintaining conditions necessary to improve the conversion.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Pyrolysis of Methane for Production of Acetylene and Hydrogen. J. Happel and L. Kramer, New York University. Kinetic studies are reported for the pyrolysis of methane in the temperature range 1400O to 1900' C. This range is substantially higher than that employed in present thermal and combustion processes for acetylene production, but is about 1000° C. lower than temperatures used in the arc processes. These studies indicate that methane, either alone or diluted with hydrogen, can be pyrolyzed in this temperature range to give high yields of relatively uncontaminated mixtures of acetylene and hydrogen. Pilot plant studies are now in progress and indicate good agreement with laboratory data.
Kinetic Studies of Complex Heterogeneous Catalytic Reactions. C. D. Prater, Socony Mobil Oil Co. Xew theoretical techniques have been developed for the study of heterogeneous catalytic reactions. These techniques provide the experimenter with criteria for the selection of experimental procedures to provide maximum amounts of information for a given amount of effort. They also provide powerful methods for analysis of data and for the development of kinetic and mechanistic models of the reaction system. Results obtained from the application of these techniques in laboratory experiments are discussed.
Kinetics Effects of Surface Diffusion. M. Boudart, Stanford University. Reactants must diffuse through the boundary layer, into the pores, along the surface to the acrive centers. T h e last stage of this transport is usually neglected although it is kno\vn that surface diffusion can change apparent activation energies and orders of reaction. Examples of such behavior will be reviewed and discussed. They include the recombinarion of hydrogen atoms o n glass, chemisorption of hydrogen on platinized carbon, the oxidation of pure carbon and of platinized carbon, and the reduction at room temperature by molecular hydrogen of tungsten trioxide catalyzed by platinum and water.
Kinetics Considerations in Surface Catalysis-Some Applications to Typical Catalyst Systems. J. H. Fnfelt, Esso Research and Engineering co. This paper will consider certain types of rate laws encountered in surface catalysis, with particular emphasis on applications to hydrogenation and hydrogenolysis reactions and to reactions occurring over bifunctional catalysts. A discussion will be given of some recent work on the kinetics of ethylene hydrogenation and of ethane hydrogenolysis over dilute platinum catalysts. T h e studies of ethane hydrogenolysis serve as good examples of the applicability of simple power rate laws as simplifications of more complex rate expressions. Some discussion will also be given of rhe kinetics of reactions over acidic oxide catalysts. T h e kinetics of hydrocracking reactions over such catalysts will be compared with the kinetics of hydrogenolysis reactions of hydrocarbons over metals, and points of contrast will be emphasized. Finally, the combination of properties of acidic and metallic catalysts in bifunctional systems will be considered, as well as the consequences with regard to the kinetics.
