摘要:

The modern petrochemical industry relies on several hydrocarbon raw materials: methane, ethylene, propylene, butene, higher olefins, and the aromatics. Some of the most important processes that such raw materials are initially subjected to are oxidation reactions[1]; for example, methane is converted to acetylene, ethylene to ethylene oxide, and propylene to acrolein, acrylic acid, or acrylonitrile. The complete oxidation of any of the hydrocarbons being favored thermodynamically, all partial oxidation reactions are kinetically limited, the nature of the products being determined mechanistically. In heterogeneous catalytic oxidations the mechanism essentially involves interaction between a hydrocarbon and surface oxygen species. In the case of the oxidation of ethylene to ethylene oxide, carbon dioxide, and water, silver is unique in giving a high selectivity to ethylene oxide. We believe it is the type of adsorbed oxygen species involved in the interaction that determines the course of the reaction and hence the selectivity.

ISSN:0161-4940    

DOI:10.1080/01614947408079624

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

For many years, it has been customary to classify catalysts as “homogeneous” or “heterogeneous.” The former commonly operate through the formation of “intermediate compounds,” and the latter, by adsorption of the reactants on the catalyst surface. The line between the two is a fine one, for the distinction between adsorption and compound formation is not at all clear, and seems to be becoming less and less clear as we learn more about adsorption. In recent years, several writers [l-7] have stressed the point that there is a good deal of overlap between homogeneous and heterogeneous catalysis. Experimental evidence supporting this point of view is accumulating, and while we are not prepared to say that there is no distinction, we can say with certainty that many homogeneous catalysts can be converted into heterogeneous ones, retaining the advantages of great activity and selectivity inherent in homogeneity and, at the same time, assuming the ready recovery which is the great advantage of heterogenity. In practice, of course, the matter is not quite that simple, for other factors must be considered. On the whole, however, many advantages have been found in the use of heterogenized homogeneous catalysts.

ISSN:0161-4940    

DOI:10.1080/01614947408079625

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The interaction of methane with metal catalysts has received less attention than that of hydrocarbons containing two or more carbon atoms [1]. Yet methane is interesting because its electronic structure resembles that of a rare gas and it possesses high symmetry and small reactivity. Also, it is the most stable of the alkanes and one of the few thermodynamically stable at room temperature. The temperature at which methane should spontaneously decompose (δG° = 0) is 570°C [2] and its reactions may give valuable information [4].

ISSN:0161-4940    

DOI:10.1080/01614947408079626

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The orthogonal collocation method is used to obtain approximate solutions to the differential equations modeling chemical reactors. There are two ways to view applications of the orthogonal collocation method. In one view it is a numerical method for which the convergence to the exact answer can be seen as the approximation is refined in successive calculations by using more collocation points, which are similar to grid points in a finite difference method. Another viewpoint considers only the first approximation, which can often be found analytically, and which gives valuable insight to the qualitative behavior of the solution. The answers, however, are of uncertain accuracy, so that the calculation must be refined to obtain useful numbers. However, with experience and appropriate caution, the first approximation is often sufficient and is easy to obtain. Thus it is very often useful in engineering work, where valid approximations are accepted. We present both viewpoints here: we use the first approximation to gain insight into a problem and we refine the calculations to obtain numerical convergence to the exact result. In this later view the method is similar to and in direct competition with finite difference methods, and some of the references listed in the next section discuss the relative advantages of the orthogonal collocation method.

ISSN:0161-4940    

DOI:10.1080/01614947408079627

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The steady-state flow method has been widely used in the kinetic study of heterogeneous catalysis. Under the conditions of steady state, all elementary steps in series are progressing at the same rate and hence the measured rates hardly tell the precise kinetic structure, or mechanism, of catalytic reactions which usually consist of several elementary steps including adsorption of reactants, surface reaction, and desorption of products. In the kinetic analyses of any given reactions, it is a common practice for the investigator to postulate a number of suspected rate models and then to assess these models to verify a optimal one which best fits observed rate data. Usually, however, there are quite a large number of plausible rate models even for a rather simple reaction, and it is not easy to determine the most adequate model among others even with the help of mathematical model indentification techniques with a electronic computer. This method is based on the assumption that there is a best model which reflects the true mechanism of the reaction sequences among the postulated models. But there is no certification which justifies this assumption. Therefore, even when a rate model is found to fit the rate data very well, the value of parameters appearing in the rate model should be further assessed in regards to their physical significance.

ISSN:0161-4940    

DOI:10.1080/01614947408079628

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A basic requirement in the analysis of catalytic reactors is a rate expression for the reaction concerned. In the design of any equipment the equations to be used contain certain basic physical-chemical coefficients whose values must be known. In the case of physical operations, these coefficients can usually be predicted from available correlations and the design of equipment is often carried out from first principles. But there is no method available by which the kinetic rate parameters of a chemical reaction can be predicted; thus experimental determination of these parameters is unavoidable.

ISSN:0161-4940    

DOI:10.1080/01614947408079629

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

With the advent of Catalysis Reviews-Science and Engineering, it would seem appropriate that a status report on catalytic reaction engineering be fashioned at this time. Rather than present a comprehensive review of the diverse aspects of the general subject, we choose to set forth a more modest and manageable commentary on key areas of the subject to indicate the level of progress, or the lack of it, in areas complementing the catalytic sciences. As such, literature citations are merely illustrative, not comprehensive. Hopefully our limited comments will inspire experts in each of the various subdisciplines of catalytic reaction engineering to create more profound commentaries for this Journal.

ISSN:0161-4940    

DOI:10.1080/01614947408079630

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Graphite reacts with a large number of substances to give lamellar compounds in which the reactant is present in the form of monolayers separated by one or more carbon layers. The compositions of some of the compounds can differ in the repeat frequency of the reactant layer, and occasionally also in the arrangement of atoms within the reactant layer. The “concentration stage” of a compound is defined as the ratio of the number of carbon layers to that of reactant layers. Thus a compound of Stage 1 is always the most concentrated one in a range of intercalation compounds of the same reactant. A survey of some graphite inclusion compounds is given in Table 1.

ISSN:0161-4940    

DOI:10.1080/01614947408079631

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0161-4940    

DOI:10.1080/01614947408079623

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor