INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 23, No. 12
SYMPOSIUM O N NEW RESEARCH TOOLS (Continued) Presented before the Division of Industrial and Engineering Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo, N. Y., August 31 to September 4, 1931
Catalysis’ Per K. Frolich &ANDARD
OILDEVELOPMENT Co., ELIZABBTH, N. J.
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N GOING about his daily routine, the chemist as a rule does not give much thought to the part played by catalysis in modern industrial chemistry. And yet a great many of the most important articles of chemical manufacture are the outcome of catalytic processes. Examples of such operations are the manufacture of sulfuric acid by both the lead-chamber and contact processes, the oxidation of ammonia to nitric acid, and the production of quantities of hydrogen; these in turn are consumed in other catalytic reactions, such as the now so widely employed hydrogenation of vegetable and animal oils and the synthesis of ammonia. Other illustrations are the manufacture of all kinds of rubber articles, the hydrolysis of starch to dextrin and sugars, the splitting of fats and oils to fatty acids and glycerol, and a variety of organic chemical processes, such as many of those met with in the manufacture of dyes and medicinals. If enzyme action is included, there may also be added the manufacture of leather, as well as the fermentation processes in use for making vinegar, ethyl alcohol, and certain solvents. While, in the cases enumerated, a catalyst is employed to speed up an otherwise slow and stubborn, or even impossible, reaction, there are other instances where it is desired to retard or inhibit a chemical process. The materials used for this purpose are called “negative” catalysts or, more frequently, “inhibitors,” and the study of their action has now almost become a science in itself. The efforts in this field are directed primarily toward combating the natural processes of deterioration so commonly experienced when materials are exposed to shifting atmospheric conditions. Certain types of inhibitors are used in specific cases to prevent rusting of iron and steel, and, more extehsively, to prolong the life of rubber articles: others are employed to prevent the formation of gum in gasoline as well a.a to retard the deterioration of transformer and lubricating oils. It may be expected that further studies will lead to inhibitors which will improve the durability of protective coatings of the paint and lacquer type, and it is to be hoped that materials may be found which will increase the life of cellulose, so as to aid in the preservation of written and printed records and to make clothes survive a larger number of laundering operations. Mechanism of Catalysis
In spite of the extensive fundamental studies of the subject being conducted by both universities and industrial concerns, present knowledge of the mechanism of catalysis is rather limited. While it is now generally agreed that the formation of intermediate compounds of one type or another play an important part in catalytic phenomena, it is still largely a matter of speculation just why platinum, for example, should combine with elementary oxygen in such a manner as to render it available for oxidation of sulfur dioxide to trioxide. A satisfactory answer to this fundamentally important question of the true mechanism of activation would be of far-reaching 1 Received
October 10, 19311
consequence and might eventually make it possible to choose the proper catalyst for any chemical process, much in the same manner in which the free-energy change of chemical reactions can now be calculated. It would seem reasonable to turn to the students of atomic and molecular physics for aid in the solution of this problem. Although x-ray analysis has shown some promise in the study of heterogeneous catalysis, this method has the disadvantage of being concerned chiefly with the interior structure of matter, whereas the process of activation is distinctly a surface phenomenon. A solid catalyst must be pictured as possessing a highly developed surface structure, composed of partly unsaturated atoms or molecules whose free valences are capable of interacting with the constituents of a given chemical system. It is to this surface layer, which constitutes only a small fraction of the total material, that the catalyst owes its activity. Apparently the function of certain promoters is to maintain the proper physical condition of the catalyst by preventing these unstable surface atoms from gradually rearranging themselves into their normal state of saturation with accompanying loss in activity. Recent Developments
As for the practical side of the subject, it is evident that, besides numerous major and minor improvements in existing industries, the most striking developments of the last decade are in the field of hydrogenation catalysts and processes concerned with their use. The important contribution here is the discovery of the hydrogenating power of a great variety of metallic oxides. Heretofore a limited number of metallic catalysts, such as nickel, platinum, and palladium, were available for hydrogenation purposes, but the oxides offer certain decided advantages, such as a greater degree of selectivity with respect to the chemical reactions they cause to take place, and a marked resistance to the ordinary catalyst poisons as well as to changes in temperature. The exploitation of this new type of catalysts has led to some extremely promisink results, the full significance of which can hardly be properly gaged a t this early date. However, the general situation in this field is of such interest to the industrial chemist that it deserves considerable attention. Synthesis of Aliphatic Compounds The first point to be noted is that it is possible to synthesize aliphatic compounds of a great variety of types by a series of stepwise reduction and condensation reactions, starting with as insignificant a raw material as the oxides of carbon. Now so much has been said and written about these processes that there is no justification in devoting much time to the subject. It will be sufficient to mention that by the proper choice of metallic oxides one may synthesize methanol and higher alcohols from a mixture of carbon monoxide and hydrogen, and that methanol may also be produced from carbon dioxide, available as a by-product from many indus-
December, 1931
I N D U S T R I A L A N D ENGINEERING CIIEMISTRY
trial operations. Likewise, lower ; h h u l s nioy be converted into higher ones which are more valualde for use as solvents arid for other purposes, or the process may be directed toward the formation of aldehydes, ketones, acids, and esters, which all have their specific uses in industry. Saturated and unsat.urated hydrocarbons are other possible products, but admittedly of lesser commercial importance. .4lthougti it is gratifying to note that some of these reactions already have been exploited successfully on a commercial scnle, as evidenced for example, by the manufacture in this country of methanol in quant.ities equivalent to, or perhaps even exceeding, that of the production of wood alcohol, tlie real value of this recent contribution to catalysis does not lie in such iiriniedinte industrial applications, hut far more in tlic fact that it is gradually bringing about a profound change in t.he concept of aliphatic orpanic chemistry. Changes in Structure of Hydrocarbon8 ~
The second observation relates to changes which may be brought about in the structure of hydrocarbons. Until a short time ago the chemist looked upon coal tar as tho very foundation of aromatic chemistry, while petroleum and its products were supposed to belong in the realm of paraffins and the more obscure naphthenes. Very few bridges existed hetween these various mourn of hvdrocarbons. one of the most
another almost at will. That this is not a wholly thkiretieal deduction is proved by the formation of an essentially nonaromatic tar in the low-temperature carbonization of coal, while petroleum yields
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creasing hydrogen-carbon ratio. The ultimate products of petroleum cracking are, therefore, on the one hand, gaseousproducts high in hydrogen, and on the other hand, tar and coke of very low hydrogen content. To reduce the forniation of these undesirable products to a minimum, the petroleum engineer is obliged to crack with the shortest possible time of contact at any given temperature, and thia leaves him only a limited opportunity to regulate t,he structure of his liquid products. The introduction of high-pressure hydrogenation has now solved this difficultv by bringing the hydrogen-carbon ratio under control. In this process, hydrogen, activated by means of the previously mentioned metallic oxide catalysts, is foisted upon the hydrocarbon structure in such a manner that the molecules may rearrange tliemselves without serious interference from the progressive dehydrogenation reactions which lead to losses in the form of constituents deficient in hydrogen. By operation under hydrogenating conditions, the flexibility of the system is therefore increased to such an extent that aliphatic-type hydrocarbons may be transformed into naphthenes and aromatics, and vice versa, with high efioiency. It is possible in commercial operation to convert heavy refinery residues into distillate oils, to produce remarkably high yields of aromatic-type gasoline from paraffinic stock, and to improve the quality of lubricating and burning oils bv chanitina the molecular structure. The semistent
Danger of Too Many New Synthetic Methods Truly it may he said that supplementing the previously known technic of or-
New High-Pressure Hydrogen8ition Plant a t Baton Rouge, La. ing, gowever, that devent market. But if st r u c t i v e operations, there is sueh an ex= consisting of an endless number of simultaneous arid consecu- capacity for production in this field that the solvent industry is tivereactionsare beingdealt with here, it is by no means a sim- expected to be in a quandary long after the general depression ple matter to vary the stmcture and composition of the prod- is over, may it not be hoped that this situation will rectify itself ucts according to d e s i r e a t least not without sacrifice in yield. by giving the impetus to new researches leading out of the presOne serious handicap is that the hydrogen-carbon ratio of the ent difficulties? If the industry is equipped to produce twice or system is fixed. What this means is readily illustrated by what three times as much methanol and acetone as the country needs, takes place in the cracking 6f petroleum: While the original and if there is a large potential excess ofethyl and higher a h feed stock has a ratio of hydrogen t u earbon of about 1.8, or hob, acetic acid, and esters, why should not a healthful applicasomewhat lower than that of the oaraffim and nanhthenes. tion of the same research methods. which originallv led to their there is a rapid production of ga&ous products (Gydrogen; synthesis,inthenext round result in theutilizationof thesevery methane, ethane etc.) of much higher hydrogen content, and products for the manufacture of other commodities which can consequently there is left behind a material of gradually de- he ahmrbed by the market? Bearing in mind that glucose, Y
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artificial silk, butyl alc&ol, acetolie, furfural, and other distinbwish from nature's product. A long time has passed materials are being derired froin farm prodiicts, rrrny one riot since the colonies' sugar monopoly was destroyed hy h'apobe justified in going a step farther arid suggesting that chem- leon's successfiil efforts to stimulate beet growing in Europe. istry he called upon to find oublcts for the eriunbry's agricultural Today the synthesis of sugar from cellulose and coal is being surplus in the manufacture of new synthetics and thus aid in considered seriously by lieet-growing countries desirous of releasing the soil for other purposes. the solution of one of the most pressing cconomic prol)lems? Until recently, uphok?ry leather was made elchIsively Although such reasoning may be perfectly sound from a chemical point of view, these prol,lems are not a matter of from hides, which to a large extent came from foreign markets. research alone. One cannot fielo but ask how ICJIIE the chemist Today millions of a.utomobiles in this country are upholstered can continue succe&$fullyto develop new mctliods of manu- with a durable substitute made from native cellulose. These facturing new and old products in a world which even in same automobiles were formerly coated with materials obnormal times seems to be ridden by overproduction in most tained, at least in part, from foreign countries. Today a far better result is realized fields. Can he keeu on . .. with a cellulose produet indefinitely cr eat'i n g by the aid of synthetic d e m a n d s for his new products at the present I s o l v e n t s , plasticizers, and resins. Precious rate? In the case of stones a n d so-called e xis t i n g commodities, ivory are now products it may also j u s t l y he of the chemical indusasked whether the t r y . P e o p l e a r e no hardships w o r k e d on longer dependent upon established industries t h e Far E a s t a n d do not frequently more France for silk, for the than outweigh the adartificial eellulove prodvantages of new synuct wdl s e r v e admirthetic methods. While ablywelluntilamethod it would be beyond the is found for making a scope of this paper t i i true protein fiber. One go into a detailed discan even visualize syncussion of such questhetic wool or new textions, the fact remains tile materials superior that t h e i n d u s t r i a l . . . to any that nature has chemist will continue to Panormma of Baton Rouge Plant f r ~ m Oven Sfalle to G a s Plant provided, and to these i n t r o d u c e new synmieht be added numerthetic processes, if for no other reason than as a hgical consequence of the struggle uus otber products which recent progress suggests. While such achievements may justly be taken as proof of among nations for industrial independence and self-support. the chemist's unt.iring effort to produce new materials, to Role of Synthetic Methods in Breaking Monopoliea lower the cost of existing commodities, or t,o improve on nature's products, the origin and success of the processes People have become accustomed to think that the rest of enlimerated can in a majority of cases be t,raced to industry's the world has to get its rubber from a limited number of endeavor to Eid itself of monopolies created by restrictions in points in the tropics; its cotton, wool, and silk from certain the geographic distribution of conventional raw materials. other localities; its motor fuel and lubricants from others; its Some of these developments would never have materialized drying oils and edible vegetable oils from still others-just to had they not, at least in their infancy, been suhsidizd by mention a few of the more important articles on which present tariff protection or direct government contributions. It can civilization is dependent. But this does not necessarily have safely be concluded that this efEnrt on the part of the indito remain so forever, for, in dealing with its SUPP~Yof raw vidual nation to attain industrial independence will continue mat~erialn,industry is striying zealously to rid itself Of rest,& t,o Rtimulate tlic introduction of new synthetic methods, in tions imposed by geographw locations. A noteworthy ilhst,ra- spite of overproduct.ion arid an unfortunate dupliration of tion is that the synthetic-ammonia process has broken Chile's effort as far as the world a t large is concerned. monopoly so thoroughly that the plants erected in most Conclusion civilized countries during t,he past decade would be capable today of supplying the world's entire demand for fixed Although the products discussed in the previous paragTdphs nitrogen. The same urge for iiidustrial independence which with only one or two exceptions are the outcome of typical created the ammonia process during the Great War in turn led eatalybir operatioils, it is by no means intended to stake the to the solution of the probleni of liquefying coal to produce future of synthetic chemistry on catalysis alone. The old, motor fuel and lubricants in countries lacking natural petro- established methods of organic as well as inorganic chemistry leum resources. It hasalso been claimed that rubber, glycerol, play an etjually important part, and the new high-pressure and fatty acids were synthesized in Germany under the pres- technic is now aiding the chemist in carrying out operat,ions sure of the war, and it is not inconceivable that such processes which forniorly appeared entirely impossible. The fact is, may reappear a t some future date, suffii:iently improved to lioacver, that the recent progress in catalytic reactions more compete even in a normal marlcet. One of the war measures than over before has turned the attention of the chemical which has survived is the substitution of whale oil for butter fraternity to the endless possibilities of the organic field, and and edible fats. When first introduced in Norway some particularly to that of the aliphatic compounds. After havfifteen years ago as a matter of bare necessity, the material ing taken stock of the situation in this admittedly sketchy was hardly fit to eat, but now people use artificial butter manner, should not the chemical engineer feel justified therecontaining some 60 per cent of expertly hardened and reEned fore in looking upon catalysis as a most promising research whale oil which even the connoisseur frequently cannot tool of the future? ~
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