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INDUSTRIAL Ah’D EXGINEERING CHEMISTRY
carbons. The number of oxygen atoms N required for perfect combustion may be found if the average molecular weight of the gasoline is known. Suppose, for example, that the average molecular weight is 107. By subtracting 2 (for the two hydrogen atoms a t the end of the chain) and dividing the remainder by 14 (the sum of the atomic weights in the CH2 group) the number of CHZgroups in the average molecule may be obtained. Three times t.his number of oxygen atoms plus one for the two hydrogen atoms will be the number required for complete combustion. I n the above case: )%(3
f1
= N = 23.5
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The percentage composition by volume of the minimum explosive mixture and the partial pressure are then calculated as before. The vapor presure of the mixture in the region of the flash point must be known. If an unknown percentage of the members of another series is also present in the mixture, there would be no way of finding the number of oxygen atoms required for complete combustion. With mixtures it will generally be simpler to determine the flash points directly. But if the composition of the mixture is known and the vapor pressure data are available, the flash point may be calculated with an accuracy approaching that for the simple substances listed above.
Oxide Equilibria in Catalysis’ By J. M. Weiss, C. R. Downs, and R. M. Bums 50
EAST4IsT Sr., N E W YORK,N. Y.
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where c = constant for OXYIn view of the importance of vanadium oxide as a catalyst in gen 2 . 8 oxide as an oxidathe partial oxidation of benzene and naphthalene, a study was tion catalyst to made of the composition of vanadium catalysts under uarious reT = absolute temperature cause the partial oxidation action conditions. The results help to throw light on the mechaof aromatic hydrocarbons nism of fhese catalytic reactions and it is hoped that further studies Q = heat of formation is a Practical development alona these lines will be made. On the basis of the heats of comparatively recent of formation given by Mixaccomplishment. The most outstanding uses are the production of phthalic anhydride ter,4 of 28,200 calories of V20sfrom V Z Oand ~ 59,600 calories from naphthalene2 and the production of maleic acid from of VzO4 from vzo3, the following figures were obtained, exb e n ~ e n e . ~The mechanism of the action of the catalyst is of pressed in atmospheres: interest, and the present paper is a report of a few preliminary experiments which were an attempt to throw light on this question. 0 10-1s 10-40 400 0.038 10-11 A catalyst may act in several diffe’rent ways. I n the case 525 1.00 10-9 1260 ... 1.0 under consideration, one function of the catalyst appears to be that of furnishing activated oxygen. The actual Vanadium pentoxide, VaO, in equilibrium with the tetroxprocess causing this activation may involve either the adide, V204, and oxygen constitutes a univariant system. sorption and subsequent evaporation of oxygen from the catalyst surface, or, more likely in this case, an oscillation The trioxide, Vz03, may conceivably exist in equilibrium from one oxide to another, yielding activated oxygen by the with this system at one temperahre and pressure, the point dissociation of the higher oxide. The process is debatable, where the pentoxide phase just disappears. The addition of benzene vapor to the two oxide-oxygen but the actual composition of the oxides present a t the end of reacting periods constitutes a fact capable of determination, system would be expected to disturb the equilibrium a t those and it seemed likely that such knowledge might be of value temperatures above which the rate of oxidation of benzene vapor becomes appreciable, since oxygen would be removed in understanding the mechanism of the catalysis. from the system. Under given conditions of temperature The varying colors of the vanadium oxide catalyst-bluegreen to orange-when removed from the reaction zone and benzene partial pressure, this oxygen removal may be suggested that the degree of oxidation of the vanadium was fairly constant, causing as a result a definite increase in disdecidedly affected by the reaction conditions. Five oxides sociation of the pentoxide. It would be predicted, thereof vanadium have been described: VZO, brown; V202, gray; fore, that a t a given temperature the percentage of vanadium VzO3, black; VzO4, blue; and V205, reddish yellow. Under tetroxide would be proportional to the partial pressure of ordinary conditions the pentoxide is the stable form. Each benzene vapor for a given space-time velocity. It would be unsafe to attempt to predict the form which oxide naturally has a definite dissociation pressure, which, the equilibrium would take under these conditions, so exof course, is exceedingly low for the normal temperatures. Mixter4 gives data for the heats of formation of the various periments were made. oxides of vanadium, which, if reliable, serve to calculate the EXPERIMENTAL dissociation constants with a fair degree of accuracy, according to Nernst’s approximation formula:5 It was decided to hold the temperature constant a t 400” C., which is a point corresponding to that for a favorable yield of maleic anhydride, and to determine the effect on the oxide equilibrium of varying the benzene-oxygen ratio. 1 Presented before the Division of Organic Chemistry a t the 65th The catalyst was held in the reaction tube placed in an Meeting of the American Chemical Society, New Haven, Conn., April agitated bath using lead as the bath material. The gases 2 to 7, 1923. 2 Gibbs and Conover, U. S. Patent 1,285,117 (November 19, 1919). under investigation were measured by a wet drum meter and 8 Weiss and Downs, U. S. Patent 1,318,633 (October 14, 1919). dried by means of concentrated sulfuric acid. The gases 4 A m . J . Sci., [41 84, 145 (1912). used were hydrogen, nitrogen, and air. In the benzene S Nernst, “Theoretical Chemistry,” 1916, p. 758.
HE use of vanadium
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 15, No. 9
runs the air was loaded with a predetermined amount of ben- oxides will exist in equilibrium. Whether this triple point zene by passing it through a thermostatically controlled is close to the origin or not, is not known, but its accurate benzene vaporizer before it entered the catalyst tube. The determination would be of great interest. It will be seen by reference to the table that, although gain or loss in weight of the catalyst was determined by weighing the reaction tube after allowing the preliminary the composition of the catalysts used in Runs 2 and 6 conheating to proceed a t the desired temperature. When a tained no V205initially, the analyses of the catalysts upon constant weight had been reached it was known that the completion of the runs show their compositions to be praccomplex organic molecule, of which the vanadium was a part, tically the same as was found in Runs 4 and 5 where the had been decomposed. As the analysis of the mixed oxides catalysts employed contained 98.5 per cent of the pentoxide. Runs 3 and 7 were was desired, no carrier for the catalyst was used. zo A weighed sample was dissolved in dilute sulfuric acid and made with the system I 9 titrated with permanganate. The titrated solution, after a t 2 atmospheres % I* reduction by means of SO2 and boiling off the excess SOZ, pressure, a n d , a s .&7 c was again titrated with permanganate. The difference be- would be expected, $ /B tween values of the two permanganate titrations gave the show somewhat high/5 percentage of V204present in the sample. Whenever V Z O ~ er percentages of the Q 14 was present in the sample, the first titration with permanga- pentoxide owing to /s nate was greater than that after the SO2 reduction, as SO2 its decreased dissoci1.2 ation. Again, it is will not reduce V204 to V203. interesting to note kjI1 RESULTS that the catalyst used . %< IO in Run 3, which was $ 9 The results are given in the following table: originally composed Ratio of 60 per cent v203 $ 8 Weight Dura- Absoand 40 per cent Vz04, P 7 Air t o tion lute Weight of Test Pressure VzOr Catalyst Composition %6 shows practically the P No. Benzene Hrs. Atmos. % before Test same composition a t 8 5 the end of the run as c4 that shown by the $ 3 high pentoxide cata1 lyst used in Run 7. IO 10 30 40 50 bo 70 80 90 Iw fI0 The final equilibrium P e r d g4 ratio of oxides is FIQ. RELATION OF CATALYST COMPOSITION I n addition, freshly prepared catalyst was heated to 400' C. therefore approache*d TO OXYGEN-BENZENE RATIO in air a t one atmosphere pressure (absolute). The final from both directions. composition was V205, 98.5 per cent; V204, 1.5 per cent. * CONCLUSIONS No Euns were made with benzene vapor alone passing over These results show that the composition of vanadium the catalyst. I n a current of hydrogen, however, a t 400" C., the catalyst was reduced after 17 hours to the compo- oxide at a given temperature and pressure depends upon t h e sition, VZOS,86.0 per cent; v@4, 14.0 per cent. The re- air-benzene ratio employed. Although the data given in duction of the vanadium oxide catalyst below V204 is thus this paper do not include information on the conversion very slow a t this temperature in a hydrogen atmosphere, of benzene to maleic acid, they assist in throwing some light but if carried to completion with absolutely pure hydrogen, on the mechanism of catalytic processes of this type, and practically only V2O3 would result. It is of interest to note some speculation here concerning this point seems to be in here that with hydrogen containing very small amounts of order. Where the partial oxidation of organic compounds is under oxygen the rate of reduction has been found to be very maconsideration, there are evidently other important factors terially decreased. When the freshly prepared catalyst was heated to equi- besides the activation of oxygen. If the catalytic action librium a t 400" C. in a closed tube, the composition was depended entirely upon the activation of the oxygen, there V2OS, 47.0 per cent; V204, 53.0 per cent. The explanation would be no explanation of the action of different catalysts, of this composition is that the catalyst was prepared as the some of which produce only products of complete combustion, vanadium salt of an organic acid, which under decomposition while others produce mainly partially oxidized products, and by heating produced a reducing atmosphere composed of still other compounds appear to be practically inert except a t high temperatures, where their function can hardly be carbon monoxide. On the basis of the results obtained, an approximate curve called truly catalytic. The writers would differentiate, showing the relation of catalyst composition to the ratio of therefore, between active catalysts, those producing mainly oxygen to benzene has been drawn. As no results were ob- complete combustion a t temperatures where any reaction tained in the range between 3:l and 11:1, the shape of the a t all results, and productive catalysts, those which produce curve in this region is unknown, but it should lie somewhat partial oxidation products in substantial amounts, but a t to the right of a straight line connecting the determined the same time appearing always to produce products of points and take somewhat the shape of the curved line as complete combustion. The behavior of the catalyst strongly suggests that t h e shown. Above the limits of thesdresults-that is, a t greater ratios than 14:l-the curve must approach the vertical to mechanism of the catalysis involves an oscillation between correspond with the value for 0 per cent benzene, or pure VzO5 and Vz04-that is, the rate of reaction may be dependent air; consequently, the curve is extended vertically. The upon the rate a t which activated oxygen is supplied by t h e extension of the curve below the ratio of 2:l must approach dissociation of the pentoxide. At temperatures increasing above 400" C. with any given the horizontal, and a t some, probably very low, oxygen conwill procentration V205 will vanish and the equilibrium will exist ratio of air to benzene, the proportion of VZO~ between V204 and V203. At the transition point all three gressively decrease, but the writers have found that complete
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
September, 1923
combustion also increases a t the expense of the partial oxidation products. The opposite is true of the lower temperatures. Therefore, the proportion of complete combustion is not dependent upon the ratio of V ~ 0 to 6 vzo4, but upon some other factor such as the activation of the reacting substances. The reaction velocity of complete combustion apparently increases more rapidly than the reaction velocity of partial oxidation with increase in the temperature above a certain value. Again, if ratios greater than 14:l are used, with the temperature fixed, say, at 400' C., the proportion of complete combustion products to partial oxidation products is not markedly increased. With these ratios the catalyst is almost entirely VZOS, and for this reason the ratio of VZOS to Vz04 appears to have little effect upon the relative amounts of the different kinds of products. The productivity of the catalyst, whether composed of oxides of a single metal or of several metals, seems to be a function of some undetermined property other than the mere activation of the oxygen by the dissociation of the oxide. It does not seem to depend on the crystal structure of the oxides as the degree of oxidation of the catalyst does not alter its specific effect. Apparently, however, there is
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a close relation between the crystal structures and dimensions of the metal atom and those of the organic compound and this specific catalytic action, the degree of oxidation of the catalyst a t the end of the reaction being merely a result,of the conditions obtaining in the system. As the complexity and instability of the aromatic molecule increase, there appears to be a greater number of productive catalysts which yield partial oxidation products. The benzene molecule, being the most simple and stable, is partially oxidized only by oxides of vanadium, although mixtures of oxides, which alone do not give partial oxidation products of benzene, act in a similar manner. As yet there is no certain explanation of this peculiar action of mixed oxides. I n the oxidation of naphthalene, anthracene, and the methyl benzenes a progressive increase in the number of catalysts which will produce partial oxidation products is noted. It is hoped that this rather restricted resume of catalytic oxidation of aromatic compounds will excite more extended interest, and that by a combination of the study of the atomic structure of catalysts and organic compounds, together with further studies of the specific action of catalysts, a clear path may be hewn through the confusing tangle now existent.
Solubility of Nickel Sulfate by Floating Equilibrium Method' By F. C. Vilbrandt and J. A. Bender UNIVERSITY OF NORTH CAROLINA, CHAPELHILL,N. C.
given float, the weight of HE application of The paper presents the application of the floating equilibrium solute in an unknown soluthe principle of floatmethod for the determination of the solubility of the various hydrates tion can be found by bringing equilibrium to of nickel sulfate. The method consists in the determination of the ing the solution to the same the determination of the quantity of water required to bring a solution saturated with the salt density as the calibrated solubility of the various at a definite temperature to the same concentration as a gravimetrifloat at the calibration temhydrates of nickel sulfate cally standardized solution of nickel sulfate. the concentration of the perature and then multiis a modification of the latter determined by the condition of floating equilibrium of a glass plying the weight of the principle as set forth by float calibrated for the particular solution. resulting equilibrium soluRichards and Shipley12 apA description of the thermostats, thermoregulators, and solution tion by that factor which plied to precision therapparatus is set forth. Data obtained show a close agreement with has been determined from mometry. They used variresults obtained gravimetrically. The results are usually slightly the calibration of the float. ous concentrations of salts higher by the floating equilibrium method than by the gravimetric From the weight of the to affect equilibrium for methods. original solutionythe weight noting accurate temperaof the solvent added, and tures. Lamb and Lee3utilize somewhat the same principle in measuring the density of the factor for the float, the concentration for the unknown various solutions to an exceedingly high degree of accuracy, solution can be easily calculated. by measuring the weights and the amount of current sent The actual density of the float, whether greater or less through an electromagnet that will cause a 250-ml. inverted than that of the solutions to be studied, does not materially flask in which an iron rod is sealed to sink in the solution affect the calculations. When the density of the float is less being studied. The application of floating equilibrium for than the solutions to be analyzed, solvent will always necesthe determination of the solubility of lead acetate was used sarily be added to the unknown samples to bring them to by Dundon and H e n d e r ~ o n . ~ the density of the float. If the density of the float is greater The application of the principle suggested by Dundon than that of the solution to be analyzed, it becomes necessary and Henderson has been carried on in this work on the hy- to evaporate the solvent from the solution until it and the drates of nickel sulfate, and the method of application and float are in equilibrium. The value for solvent added then calculation of data are made easier by the development of becomes a negative value instead of a positive one, as in the a simple formula. I n this method is determined the weight case above. The purpose of the work herein described is to study the of solvent which will bring a solution of unknown concentration to the concentration in which a glass float calibrated applicability of the floating equilibrium method (1) to the a t an arbitrary temperature will remain in equilibrium. analysis of the concentration of solutions of nickel sulfate, Assuming the percentage of solid in equilibrium with a and (2) to the determination of the solubility of the various given solvent to be constant a t a fixed temperature for a hydrates of nickel sulfate.
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Received March 28, 1923. J, A m . Chem. Soc., 34, 599 (1912); 36, 1 (1914). Ibid.. 35. 1666 11913). Ibzd.; 44; 1197 (1922). ~I
PREPARATION OF THE PURE SALT A large quantity of the best grade of C. P. nickel sulfate was recrystallized from distilled water three times, this
