IMD USTRIAL A S D ESGINEERING CHEMISTRY
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VOl. 16, N o . 9
T h e Potentialities of Catalytic Research in t h e Chemical Industry By Hugh S. Taylor PRIYCETOY
UNIVERSITY,PRINCETON, i Y J
HE potentialities of catalytic research constitute a problem which must continuously confront the executive officer of any large chemical organization.
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How prepared for developments along catalytic lines should such an organization be? Is it worth while to carry on the payroll a specialist in such a particular branch of the subject? The answers to such questions are most important in any well-ordered concern. A resume of some problems and a brief record of some progress may help towards such answers. LOWEROPERATIKG TEMPERATURE OF CATALYSTS Sabatier, in his text on “Catalysis in Organis Chemistry,” states that ethylene and hydrogen begin to combine rapidly in presence of active copper above 160” C. A recent article by Pease’ calls attention to the fact that by reducing copper oxide under controlled conditions a copper of such activity may be obtained that immeasurably rapid reaction of the same two gases is obtainable at 0” C., with the vessel containing the copper in an ice bath. The hydrogenation of ethylene is not likely to be of commercial interest in the near future, but one cannot be blind to the potentialities which would result from a reduction of 150 degrees HUGHS. in the operating temperature of all Catalytic agents. -For example, in ammonia synthesis, operation a t 350” C. instead of the usual 5 0 0 ” t o 600” C. would enormously increase the possible yield per gas passage as a result of the more favorable equilibrium conditions; or, what w7ould amount to the same thing in the end, the lower working temperature would make possible the use of lower working pressures than are now required for a given yield a t the higher temperatures. Simplification of operation and less risk and danger might thereby be achieved. That such an eventuality is realizable seems to be indicated by the results recently communicated a t the spring meeting of the AMERICAN CHEMICAL SOCIETYon the ammonia equilibrium a t 30 atmospheres pressure. It is hard to believe that such studies were made unless operation a t 30 atmospheres pressure were within the realm of practical achievement. COXTROL OF “POISONING” Everyone interested in the problem of catalysis is familiar with the ‘(poisoning”of catalytic agents. This factor of poisoning still constitutes one of the bugbears of the industrialist and it is the subject of anxious queries put to anyone desiring to initiate new catalytic processes. It is refreshing, therefore, to be able to record that “poisoning” is now being brought so under control by the scientific investigator as to be susceptible of use for desired ends. The recent researches of Rosenmund, Zetsche, and Heise2 have demonstrated that 1 2
J . A m . Chem. SOL, 45, 1190 (1923). Be?., 54, 425, 638, 1092, 2033, 2038 (1921).
reactions which may not go when the utmost purity of reagents is secured, may be carried out by the addition of mitable impurities to the reaction system. Palladium, for example, may be partially poisoned by a variety of substances in such a manner that the chief reaction product of the reduction of benzoyl chloride ma$ be one or other of the substances benzaldehyde, benzyl alcohol, benzyl benzoate, dibenzyl ether, or toluene, the produ et obtained being determined by the nature and amount of the added substance. As typical of such substances, quinoline, quinoline heated with sulfur, xanthone, and dimethylaniline may be cited. This constitutes a new method of preparation of aldehydes hitherto unprepared. Zetsche has extended the work to dehydrogenation of alcohols with accompanying oxidation. I n this case aldehydes, acids, and esters may result. Aldehyde is the preferred product if to a copper catalyst small amounts of quinoline are added. Nitro bodies further assist. Added t o nickel,‘ however, quinoline promotes acid and ester formation. It is not possible to give the details of this fascinating work, which is now quite extensive. Its implications, however, cannot be overlooked by either the theoretical or the practical student. TAYLOR Controlled oxidation is of the greatest importance in technology. Especially in the field ofYhydrocarbon oxidation would the application of Rosenmund and Zetsche’s principles lead to most fruitful industrial results. Oxidation of methane, ethylene, and other simple hydrocarbons to yield formaldehyde is always accompanied by a variety of other undesired oxidation products. A catalyst, modified to produce formaldehyde alone, would be a most useful discovery. The same holds true also of such oxidations as those of naphthalene to phthalic anhydride, of anthraceqe to anthraquinone, and of benzene to maleic acid. In all these cases the danger of producing undesired oxidation products necessitates a most rigid, narrow, and inflexible set of experimental conditions. How far it is possible to obviate such limitations by controlled catalyst poisoning is worthy of study. Our knowledge of the underlying causes of catalyst poisoning is growing steadily. Maxted’s3 researches have demonstrated that poisons for platinum and palladium hydrogenation catalysts cut down the adsorption of hydrogen by the catalyst. Peasel has shown the same to be true as regards the adsorption of hydrogen, ethylene, and carbon monoxide (private communication) for a copper catalyst poisoned with mercury. Taylor and Burns and Gauger‘ have shown that diminished adsorption by a nickel catalyst may be secured by controlled heat treatment of the metal. 8 J . Chem. SOG.(London), 116, 1050 (1919); 117, 1280, 1501 (1920); 119 225, 1280 (1921). 4 J . A m . Chem Soc., 43, 1277 (1921); 46, 920 (1923).
September, 1923
INDUSTRIAL A N D ENGINEEBING CHEiWISTRY
This is verified also in the work of Pease and in that of Benton6 for oxide catalysts. The effect of the heat treatment parallels roughly the effect of controlled poisoning. That such manipulation of a catalyst may lead to useful results is to be expected, since by such means the relative concentrations of reacting materials can be in part controlled. Benton’s researches have shown that the preferential catalytic oxidation of carbon monoxide in presence of hydrogen, a t oxide catalyst surfaces, is to be associated with the relative adsorptions of the two gases by the catalyst. When such concentrations ’ ce of adsorbed materials can be manipulated a t will, the prosm of preferential reactions mill be enormously extended.
THEORY OF INHIBITION OR NEGATIVE CATALYSIS
It is twenty-five years since Bigelow studied the peculiar property exercised by a variety of organic compounds such as benzyl alcohol, benzaldehyde, glycerol, mannite, and phenol in arresting the oxidation of sodium sulfite solutions. Young6 extended Bigelow’s study showing that such substances as nicotine and other alkaloids, ammonium salts, and potassium cyanide behaved similarly towards sodium sulfite solutions. He also showed that the oxidation of stannous chloride solutions could be similarly inhibited. Lumihre and Seyewetz’ also showed that the inhibitory substances of sulfite solutions included hydroquinone, pyrocatechin, pyrogallol, paraminophenol, paraphenylenediamine, glycine, etc. This is of importance in view of more recent results. Somewhat earlier than this Titoff,* attempting to elucidate the mechanism of the action of such inhibitors, demonstrated that the oxidation of sulfite solutions was accelerated markedly by the most minute traces of positive catalysts, notably copper salts. A solution of copper sulfate as dilute as 0.113 molar was shown to produce perceptible acceleration of the rate of oxidation of the sodium sulfite solution. Parenthetically, it may be observed that it was this activity of copper which was utilized recently by Mack, Osterhof, and Kramerg in their determinations of the vapor pressure of copper and copper oxide a t relatively low temperatures. This study of Titoff, demonstrating the enormously sensitive nature of sulfite solutions to positive catalysts, led him to suggest that negative catalysts act by suppression of minute traces of powerful positive catalysts. In this way the small amounts of negative catalyst sometimes adequate to inhibit a reaction almost completely found a ready explanation. In considering such a situation it might suggest itself to the critic to inquire why it is more difficult to comprehend negative catalysis by substances in minute concentrations than it is to accept positive catalysis in such marked dilutions as those discussed above; why, for example, one gram mol of copper in 55 million million mols of water should speed up a reaction if one gram mol of a substance in ten thousand mols of water should lead to doubt and disbelief when acting as a negative catalyst. It is nevertheless true that Titoff’s work has colored most of the subsequent work on the subject of negative catalysis; it is still the most quoted “explanation)) of negative catalysis. It may be argued, with a considerable degree of confidence in vieq of recent history, that the general acceptance of Titoff’s viewpoint has retarded the development of this fascinating and increasingly important branch of the subject. A few other cases of inhibitory power are known. The luminescence of phosphorus in air or dilute oxygen gas mixtures is suppressed by sulfurous gases, as observed by Berthollet in 1797 and studied continuously since that time 6
J. A m . Chem. SOL.,45, 887, 900 (1923).
B I b z d . , 23, 119, 450 (1901); 24, 297 (1902). 7 Bull. SOL. chzm., 81, 672 (1922). P h y s . Chem., 45, 641 (1903). * J . A m Chem. SOL.,45,617 (1023). 8Z.
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until the present day. It has long been known that a variety of substances inhibit the decomposition, both thermal and photochemical, of hydrogen peroxide. Water, famous as a necessary positive catalyst to a large number of reactions ever since the researches of Mrs. Fulhame in the last decade of the 18th century, is now known as the inhibitor in a variety of reactions in nonaqueous liquid media, notably of the decomposition of oxalic acid in concentrated sulfuric acid solutions.lO The more observant have frequently noted that benzaldehyde occasionally oxidizes quite readily; a t other times it has seemed remarkably resistant to oxidation. Essential oils have shown similar variability. It has been known that the natural essential oils preserve their qualities on keeping better than the chemically pure materials. Many of these and other observations have been collected by Moureu and Dufraissell in a literature study accompanying their recent important contributions to the problem of inhibition of autoxidation processes. Their earliest work showed that the prevention of autoxidation of a variety of substances-for example, benzaldehyde and acroleinwas possessed by phenolic compounds. The efficiency of such compounds was remarkable. One molecule of hydroquinone suppressed the oxidation of 40,000 molecules of acrolein. Analogous results were obtained with such autoxidizable substances as acetaldehyde, chloral, propionic aldehyde, acrolein, anisic aldehyde, cinnamic aldehyde, hydrocinnamic aldehyde, furfurol, styrolene, turpentine, linseed oil, nut oil, and butter. Furthermore, various secondary phenomena which often accompany autoxidation processes, generally related to molecular condensations and manifested by changes of color, precipitates, change in viscosity, rancidity, etc., are also inhibited by such additions. Thus, furfural, instead of turning deep black, remains almost colorless; acrolein no longer yields dis-acryl, a polymerized product; styrolene remains fluid, no longer giving the soluble resin known as m-styrolene; linseed oil can be exposed to the air in thin layers without losing its fluidity (observations lasting three years) ; butter preserves its organoleptic properties; and, in general, fatty bodies do not become rancid. Further afield, Moureu and Dufraisse have noted the French patent to the Societa Anonyma Cooperativa (1905) which claims the protection of silks against light, heat, and atmospheric action by means of thiourea, hydroquinone, and their derivatives, this patent being a product of the investigations of Sisley and Seyewetz;12also a German patent (1918) to the Badische Anilin und Soda Fabrik claiming the protection of synthetic rubber against autoxidation by the presence of phenolic compounds. I n a recent paper communicated by Professor Moureu, Gillet and G i o P have noted that materials dyed with azo dyes and eosin dyes are protected against color change by such inhibitors as Moureu and Dufraisse have studied. Rubber oxidation is inhibited by tanning and hydroquinone.l4 It is very evident, therefore, that there is here a rich field of study, both for the industrialist and the scientist-for the technical man in the applications possible, and for the theoretical chemist in the problems of mechanism which thereby arise. Moureu and Dufraisse, ’rejecting the Titoff concept of suppression of a positive catalyst, have formulated a theory of mechanism which seeks the theoretical solution of the problem of autoxidation in the ‘(per-oxidation” of both autoxidant and of inhibitor followed by interaction of the two oxidized agents, to regenerate both initial substances 10 Bredig and Lichty, Z. Elektrochem., 12, 450 (1906); Lichty, J . Phys. Chem., 11, 255 (1907). 11 Compt. rend., 174,268 (1922); 176, 127 (1922), 17’6, 624, 797 (1923). Bull. SOL. chzm., 31,672 (1922). 1 8 Compt. r e n d , 176, 1402 (1923). I r I b i d , 177, 204 (1923); French Patent 509,667 (1919).
IND UXTRIAL AND ENGIAVEERIhTGCHEMISTRY
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and elementary oxygen. Thus, if A be the autoxidizable substance and B be the inhibitor, the sequence of reactions would be A 0 2 = A ( 0 z ) ; A(02) B = A(O) B(O); A(0) B(0) = A B 0 2
+
+
++ + +
or alternatively
Certain data already accumulated lend a degree of credence to this formulation. It is doubtful, however, whether it is applicable in more than a few cases; it would need entirely recasting to cover the general case of negative catalysis, which, as we have seen, includes reactions not autoxidant in nature. -4n attempt to formulate a more general theory of negative catalysis has recently been made by the writer
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independently of the work of the French a ~ t h 0 r s . I ~ The theory accounts for inhibitory power by assuming interaction between one of the reactants and inhibitor to form a molecular compound, as an alternative to reaction between the two or more reactants. The extent of the inhibition is determined by the degree and velocity of compound formation. The mechanism of Moureu and Dufraisse would be a special case of this more general formulation. The general theory would suggest other possibilities of inhibitory mechanism and thereby a wider range of reactions sensitive to negative catalysis and a more extended series of inhibitory materials. It should be very evident, therefore, that catalysis, both positive and negative, is a subject that the chemical organization cannot ignore; the theoretical chemist can surely find therein problems that will delight his soul. 1:
J. P h y s . Chem., 27, 322 (1923).
T h e Mechanism of Corrosion By John Johnston YAJ,E
UNIVERSITY,
h’EW
HAVEN,C O N N .
F T H E great number of publicathat in discussing this problem it is almost tions dealing with the general impossible to avoid dogmatic statements, topic of corrosion, few add much unsupported by convincing evidence, or to the reader’s positive knowledge. Ingeneralizations too broad to be useful. Points of similarity in the diverse condeed, by their lack of agreement, many ditions have led different writers t o atof the observations recorded in the literature are likely to confuse and weary tribute the effects to various factors. Adequate emphasis has not been given to one him. This appears to arise in part from of these, namely, that in all cases of corthe desire of an author to show that other rosion we are dealing with effects a t a surproducts are worse than the one whose face between at least two, and possibly merits he is championing and in part three, phases. Therefore more attention from the fact that many investigations should be directed to what may be exhave been limited to a specific set of pected to happen at such a surface of conditions which have not been defined and controlled with sufficient care. The separation, and the formation and behavior of a film or layer (using these words most important cause, however, is an in a general sense) a t a metal surface oversimplification of the problem in an under various conditions should be atterhpt to discover a single primary studied. It has long been recognized that factor to the operation of which all phein a general way the character of the nomena of corrosion may be ascribed. metal surface is of importance. For inThe protagonists of several such factors, Harris and Ewine stance, polishing lessens the rate of corassumed to be primary, bring forward JOHN JOHNSTON rosion. and txotection from corrosion is evidence in favor of their particular beliefs and give reasons why any other explanation is un- achieved if the surface layer be impervious to the corrodsatisfactory. This does not mean that evidence has been ing agent. But little is known definitely as to why there deliberately manufactured or ignored, brit rather indicates should be such large differences in the protection afforded that the problem is more complex than many have assumed by such coatings, even when formed under conditions which it to be. In other words, a complete description of the proc- appear to be nearly identical. A clue to the cause of these differences in some cases may be esses of corrosion necessitates the consideration of several factors, any one of which may under some circumstances given by the following considerations. When a metal oxide be dominant,. ThaLit could not well be otherwise is evident or Eydroxide is shaken with water in the presence of carbon from the wide range of conditions under which the term dioxide until the system is in equilibrium, the stable solid “corrosion” is applied-in water, in salt or acid solutions, phase will be hydroxide or carbonate (excluding, for the cold and hot, in the atmosphere, dry and moist, clean and moment, the possibility of a basic carbonate) , according t o dirty, in air or gases a t high temperature. And the medium whether the partial pressure of carbon dioxide a t equilibrium may be stagnant or in rapid relative motion. Further- is below or above a certain limiting value. This limiting more, we may be dealing with a single*metalfrom any part value, or transition pressure, characteristic of the particular of the electrochemical series, pure or impure, with a metal metal, is determined largely by the relative solubility of its made up substantially of a single kind of crystal or containing hydroxide and carbonate, so that it depends upon temperaseveral kinds of crystal, and the metal may be acting as ture. At present it is not known for any metal except magelectrode and under electrical or mechanical stress produced nesium, for which it is about 0.0005 atmosphere of carbon by external causes or internal strains. It is clear, therefore, dioxide, a concentration slightly greater than that in outside
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