DIVISION OF INDUSTRIAL AND ENGINEERING CHEMISTRY
THE ROLE OF THE DIVISION
CHAIRMAN R. L. HERSHEY Du Pant Co. Du Pone Bldg. Wilmington, 98, Del.
CHAIRMAN-ELECT M. R. FENSKE Dept. of Chemical Eng. Pennsylvania State Univ. University Park, Pa. SECRETARY FRANCESCO DE MARIA American Machine & Foundry 689 Hope St. Springdale, Conn. TREASURER R. N. MADDOX Dept. of Chemical Eng. Oklahoma State Univ. Stillwater, Okla. PROGRAM SECRETARY V. A. FAUVER E. C. Britton Lab. Dow Chemical Go. Midland, Mich. COUNCILORS JOSEPH STEWART Esso Research & Eng. P. 0. Box 51 Linden, N. J. NORBERT PLATZER Hydrocarbons & Polymers Division Monsanto Go. Springfield, Mass.
I n this Division Newsletter, the last to appear over my signature as chairman, I want to conlment on certain aspects of the Division’s work and problems which have impressed me with their importance during my two years as Chairman-Elect and Chairman. The most critical current problem of the Division is the establishment of a better definition of its objectives. Fundamentally, this problem has its roots in the history of the changes through which the Division has passed since its formation in 1908. As interests in specialized areas of the Division’s general field have developed, they have, in a number of cases, led finally to the creation of new, independent ACS Divisions. As each such specialized area has found another home, the parent Division (I&EC) has inevitably lost some scope. The cumulative effect has perhaps been greater than just the simple sum of all the losses. The consequence is that today a generally accepted definition of the area or aspect of science and technology upon which the Division should place its primary emphasis does not exist. A 1961 study by a group of former chairmen led to a statement on this matter, which the Executive Committee approved at the time; but some recent comments of active and concerned members suggest that perhaps revisions in that statement are desirable. There are other aspects of the problem of objectives than just the delineation of appropriate technological fields; for example, what role, if any, should the Division attempt to play in the matter of the academic-industrial interface, or again, what activities should the Division attempt with the Local Sections. Fortunately, there are members of the Division with stimulating ideas in all these areas, and Dr. Fenske has recently appointed a committee to study this whole matter. There are ample reasons to expect the formulation of sound policy and the creation of some vigorous new Division programs in the not too distant future. A second matter of concern is the recruitment of young chemists and engineers into the work of the Division. Perhaps the best first step for such young men is participation in, or assistance to, the program committees of the Division. The administrative structure of the program committees has recently been improved, and a note to the Division’s program secretary expressing interest in such work, either for symposia at national meetings or for the annual Chemical Engineering Symposium, is the way to learn of specific current opportunities to assist. This matter of enlisting younger men into Division activities will be always with us. As a personal parenthetical aside, I must note that it hardly seems sound general policy to have as chairman one who has been retired for age from the daily hurly-burly, as has been the case in 1967. Finally, the Division has had administrative problems. I n substance these are less significant than the others already discussed ; but effective achievement of those more important objectives can be greatly aided by good administrative procedures. This problem is by no means peculiar to this Division. Any organization having a frequent change in officers, who are usually widely separated geographically, and all of whom have other full-time jobs of first importance to them personally, will have the same administrative difficulties. I n essence, the problem is to familiarize each new officer with the whole scope of his duties practically immediately upon his election. Too often in the past, an officer or committee chairman has spent his term in learning his duties. The Division has recently taken steps to extend the terms of the secretary, the program secretary, and the treasurer from one to two years for greater continuity. I n addition, there is in preparation a handbook for officers and committee chairmen which, it is hoped, will provide means for comprehensive indoctrination and authoritative reference. I t has been a stimulating experience to serve the Division, and I leave office with confidence that the new officers and committees will lead it to new high levels of accomplishment.
VOL. 5 9
NO. 1 2
DECEMBER 1967
17
ne very important aspect of the heterogeneous 0 catalytic oxidation of hydrocarbons is the question of selectivity. What is ideally required in the petrochemical industry is, of course, the means of oxidizing a given hydrocarbon (or a group of selected hydrocarbons) rapidly and cleanly to one particular product. As far as gas-phase reactions are concerned, oxidation over a heterogeneous catalyst almost certainly represents, at the present time, the most successful method for bringing about such conversions. Nevertheless, the development of suitable heterogeneous catalysts for effecting the partial oxidation of hydrocarbons has hitherto tended to take place largely on a trial-and-error basis and the mechanisms of oxidation are still very far from completely understood. It is, therefore, important first to try to rationalize the subject by dealing with the general principles governing the mechanisms of the heterogeneous catalytic oxidation ofhydrocarbons.
Comparison of Homogeneous and Homogeneous Oxidation Reactions
It is perhaps helpful to begin by comparing briefly heterogeneous catalytic oxidation with homogeneous oxidation. Competition between concurrent and consecutive steps. The broader features of the homogeneous oxidation of hydrocarbons are now established. These oxidations are-both in the gas-phase and in the liquidphase--generally free radical chain reactions, the kinetics of which are dependent upon the interplay of four groups of elementary stepsuiz., initiation, propagation, branching, and termination. What makes real systems especially complex, however, is that the molecular species produced by oxidation of a given hydrocarbon are frequently as reactive, or more so, than the hydrocarbon itself. Thus, attack begins to take place on the intermediate products-as well as on the hydmcarbon-as soon as a s m a l l proportion of the original fuel has reacted, and reaction soon consists of a large number 18
INDUSTRIAL A N D ENGINEERING CHEMISTRY
of concurrent and consecutive elementary steps, the relative importance of which changes constantly. Now in reactions over heterogeneous catalysts, it is envisaged that old bonds are broken and new bonds are formed only in species sorbed on the surface of the catalyst. Nevertheless, the complications resulting from the occurrence of consecutive and concurrent reactions are still present. Whereas in homogeneous oxidation, free radicals attack both reactants and partial products, so in heterogeneous systems there is a competition between reactants, partial oxidation products, and indeed final oxidation products for active sites on the surface of the catalyst. Sequence of reactivities of hydrocarbons. Another broad similarity between homogeneous and heterogeneous oxidation lies in the fact that the reactivities of different hydrocarbons normally fall in the same sequence. Thus, in both types of systems, paraffins are less
reactive than olefins, and benzene is less reactive than polycyclic aromatics, such as naphthalene, which in turn are less reactive than aromatic hydrocarbons with alkyl side-chains. As an example, a study of the reactions of various olefins over a Bi/Mo catalyst (7) shows that reactivity is determined largely by the number and type of allylic hydrogen atoms and that, furthermore, substitution on either vinyl group increases reactivity (Table I). These effects are very similar to those found for hydrogen abstraction by free radicals in solution (7) (Figure l), and thii suggests that the rate-determining step in oxidation is abstraction of an allylic hydrogen atom by chemisorbed oxygen. The products of hydrocarbon oxidation which can be obtained in high yield are those which possess a stability (in terms of C-H bond dissociation energy) at least comparable with that of the parent hydrocarbon. Hydrogen atoms at allyl and benzyl positions (where the C-H bond strength = 75-80 kcal.) appear to be readily attacked, whereas those at vinyl positions (where the
