T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
2 28
ORIGINAL PAPERS
Vol.
12,
No. 3
1
CATALYTIC OXIDATION. I-BENZENE’ By John Morris Weiss and Charles R. Downs
fied products from petroleum oils. The work of Walter, however, was largely qualitative and the control of conditions such t h a t , except for the hints of RESEARCH DEPARTMENT, THE BARRETT COMPANY, 17 BATTERY PLACE, possibilities, the articles and patents are of little pracNEWYORK,N. Y. tical value. PRELIMINARY COMMUNICATION Zinckel obtained dichloromaleic acid by the action The present communication is for the most part of chlorine on $-aminophenol in alkaline solution. Derivatives of heterocyclic ring compounds such as preliminary and i s essentially an announcement of furfurane, thiophene and pyrrole, according t o Ciamiresults obtained in a new and hitherto substantially cian and Silber,2 and Ciamician and Angeli,3 likeuntouched field of organic chemistry involving novel reactions and t h e production commercially of products wise yield derivatives of maleic acid. A British patent4 which have previously been considered as laboratory t o Wedge claims the production of phenol from liquid curiosities of purely theoretical interest. The facts benzene by oxidation with ozone or ozonized air in established also seem t o throw some doubt on t h e t h e presence of catalysts such as platinum black, theories of catalytic action which have been accepted Kempfs in a paper dealing largely with theoretical in t h e past, but it is not our intention t o enter into a consideration of t h e constitution of t h e benzene molediscussion of this aspect a t t h e present time b u t t o cule notes the formation of maleic acid by t h e liquid reserve these considerations for a later communica- phase oxidation of benzoquinone with peroxide of tion when certain experimental work on the theo- silver. I n 1907, however, t h e most important and most retical side of catalytic oxidation has been completed. thorough researches on catalytic oxidation of organic The literature regarding catalytic oxidation in general compounds began t o appear. The work of OrloffG is very extensive, b u t t h a t portion bearing specifically on t h e oxidation of benzene short of complete com- is of extreme value both for t h e data given and for the theoretical considerations presented. He also bustion is quite meagre. I n 1870, Carius2 formed the so-called ‘(trichloro- published a very valuable theoretical article in 1909.7 phenomalonic acid” (chloromaleic‘ acid) by treat- Most of this work has been collected into two books.8 ing benzene with “hydrated chloric acid” (free per- The work of Orloff covered very thoroughly the oxidachloric acid generated by t h e treatment of potassium tion of alcohols. His work on hydrocarbons was chlorate with sulfuric acid). Coquillon,3 in 1875, merely preliminary. He worked mainly on Baku stated t h a t both benzene and toluene gave benzalde- petroleum, but gave some study t o benzene and tolhyde and benzoic acid when the vapor of t h e hydro- uene. He produced benzaldehyde from t h e latter carbon and air were passed through a tube contain- and a number of unidentified products from t h e former ing incandescent platinum wire. These products using a copper sieve contact mass. He also oxidized noted from benzene were possibly due t o toluene turpentine in this manner, b u t obtained no definite present as an impurity in t h e benzene. A little later products. About the same time WOOgg reports the production Kekul6 and Strecker4 repeated the experiments of Carius5 in connection with their classic work on t h e of benzaldehyde from toluene in the vapor phase constitution of t h e benzene molecule and found t h a t by the action of platinum and other catalysts. I n t h e trichlorophenomalonic acid was converted by 1908 patents were taken out by the Farbenfabrik v. F. Bayer & Co.,l0 covering t h e production of methylwarm baryta water into maleic acid. The first really important article in this field was adipic acid by the liquid phase oxidation, with nitric t h a t of Walter,+j in which was described the air oxida- acid and alkaline potassium permanganate succestion of toluene t o benzoic acid and benLaldehyde and sively, of methylcyclohexanol or methylcyclohexanone, of anthracene t o anthraquinone using vanadium oxide giving another instance of t h e splitting of t h e benzene as a catalyzer. Later, in 1904 and Igoj, German, ring without complete oxidation. A later patentll t o A. French and British patents’ were taken out covering Lowenthal covers t h e oxidation of aromatic hydrocarthe processes disclosed in t h e paper. I n the patents bons or alcohols t o aldehydes in the presence of chroma whole series of catalyzers were listed and besides t h e 1 Ber., 24 (1891), 912. 2 Ibzd., 20 (1887), 698, 2594. reactions mentioned above, Walter claimed the pro3 I b i d . , 24 (1891), 77, 1347. duction of acetic acid and aldehyde from alcohol, 4 Brit. Patent 2,010, April 20, 1901. 6 Ber., 39 (1906), 3715-27. carbazol from diphenylamine, diphenyl from benzene, J. Russ. Phys. Chem. S O L ,39 (1907), 855, 1023, 1414: 40 (1908), /3-naphthol from naphthalene, and various unidenti- 652, 8659, 796, 799, 1590, 1596. I Read before the New York Section of the American Chemical Society, Chemists’ Club, New York, N. Y., January 9, 1920. 2 J
‘
Ann., 166, 217-233. Compt. rend., 80, 1089-90. Ann., 223 (1884), 170-197; 239, 176.
6 LOG.
Lit.
J . PYakt. Chem., 1892, 107-111. 7 D. R . P. 168,291, Class 120, Oct. 28, 1904; French Patent 360,785, Oct. 11, 1905; Brit. Patent 21,941, Oct. 27, 1905.
2. physik. Chem., 69, 499-505. “Der bisherige Stand der wissenshaftlichen Erkentniss und der technischen Verwendung sowie neue fintersuchungen hber seine Herstellung und ixber pyrogenetische Kontactreaktionen,” trans, into German, C. Kietaibl Barth, Leipzig, 1909; “Formaldehyd,” Barth, Leipzig, 1909. 9 Compt. vend., 146, 124-6. 10 D. R . P. 221,849, Oct. 12, 1908; French Patent 409,083, Nov. 15, 3908; Brit. Patent 24,298, Oct. 22, 1909. 11 D. R. P. 239,651, June 25, 1909. 7
8
Mar.,
1920
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
ium catalyzers. The patent is very vague and lacking in detail. Kempfl gives a very long and interesting article regarding the liquid phase oxidation of quinone by means of the electric current t o form maleic acid. The work is largely theoretical but is of extreme interest in this connection. A German patent2 t o Farbenfabrik v. F. Bayer covers the production of erythrene by the incomplete combustion of many organic substances, among which are mentioned benzene, toluene, and naphthalene. Willstatter and Sonnenfelt3 describe the production of adipic acid and aldehyde by oxidation of cyclohexanol in the liquid phase in the presence of metals of the platinum group. Finally, we would mention the work of H. D. Gibbs and his associates a t the Bureau of Chemistry on the catalytic oxidation of organic compounds. This work to a great extent paralleled our own and in some instances duplicated it. The Bureau has published little detail of the work but American and foreign patents have appeared on the production of phthalic anhydride from naphthalene, anthraquinone from anthracene, phenanthraquinone from phenanthrene, and benzaldehyde from toluene, using various catalyzers and temperature ranges in t h e specific processes.4 Of our own work in this field which has been carried on over a n extended period of time, five U. S. patents and a number of various foreign patents have so far appeared, four of the U. S. patents dealing with the oxidation of benzene in the vapor phase in the presence of a catalyzer. Under varying conditions diphenyl, benzoquinone, or maleic acid have been obt ained. Because of our long standing interest in t h e disinfectant field we had speculated considerably upon the cause of the formation of the relatively large proportions of t a r acids in the so-called Scotch blastfurnace tars. I n these furnaces coal, iron ore and air are present and this combination appears t o be responsible for the peculiar high tar-acid content of these tars. I n this country coke is used almost exclusively in blast furnaces with consequently little or no t a r formation. We, therefore, decided t o attempt t o duplicate these supposed conditionsnamely, t h e contact of hydrocarbons, iron oxide and air-by passing t a r oil vapors admixed with air through heated tubes filled with iron oxide. A very short time, however, convinced us of the uselessness of working with such complex mixtures and we turned our attention entirely t o benzene, which could readily be obtained in t h e pure state. Later, because of the outbreak of the war, the demand for phenol became very insistent and the problem viewed from the production of this material became of more practical importance t h a n the theoretical considerations concerning the formation of the complex Scotch acids. , 83 (191 I ) , 329-94. D. R. P. 278,647, Class 120, Aug. 5 , 1912. 8 Bm., 46 (1913), 2952-8. * Brit. Patents 14,150, Oct. 1, 1917; 14,151, Oct. 1, 1917. Canadian Patents 186,444, Sept. 10, 1918; 186,445, Sept. 10, 1918. U. S. Patents 1,284,887, Nov 12, 1918; 1,284,888, NOV. 12, 1918; 1,285,117, Nov. 19, 1918; 1,288,431, Dec. 1 7 , 1918; 1,303,168, May 6, 1919. J . puakl. Chem
229
For an investigation of the mechanism of the oxidation of benzene t o phenol in the vapor phase a study of temperature effects was first in order and we soon found t h a t a t the higher temperatures, diphenyl, t a r r y products and complete combustion were the only results. From these experiments, however, we learned t h a t the presence of steam in moderate amount aided t h e production of high yields of diphenyl of good quality and, moreover, that increased pressure was f avorable t o the course of the reaction. These developments are covered in a recent patent' taken out by the authors I n some of the work a t temperatures below diphenyl formation we had obtained traces of phenols with certain catalysts, so we decided t o make a n exhaustive investigation of these possibilities. We reviewed the periodic system and determined t o t r y every metal and metallic oxide which would be stable under the conditions of experiment, t o determine which, if any, exerted catalytic action. We may say here t h a t we completed this program and in addition tried many mixtures although, of course, we could not exhaust all the possible permutations and combinations of materials and conditions. Wherever a trace of product was formed we went thoroughly into the various combinations with t h a t particular catalyst in attempts t o enlarge the observations to commercial possibilities. Tn no case did we secure yields of phenol a t all approaching anything commercial, although in the cases of a few catalysts we obtained conversions of from 0 . 2 t o 0.3 per cent. We did, however, a t a very early stage of our investigation produce benzoquinone with a number of catalysts and discovered further t h a t with certain catalysts, notably vanadium oxide, there was a considerable formation (in the initial experiments about 4 per cent) of a highly water-soluble acid which was readily identified as maleic acid. This result was so remarkable t h a t we split our inve8tigation a t once into two phases and, continuing one group of men on the general subject of catalytic oxidation, formed another group t o take up the production of maleic acid and improve the yields and develop technical apparatus t o a point where a commercial process might be possible. The processes involved have been covered in three U. S. patents taken out by the authors.2 The investigation of vapor-phase oxidation is exceedingly complex because of the number of factors affecting the reactions, for example, variations in ratio ol oxygen t o hydrocarbon, catalyst form, pressure conditions, effect of water vapor and fixed gases, catalyst deterioration and revivification, temperature control, time of contact, secondary and by-reactions, etc. Several of these factors, such as temperature control, may be subdivided into a number of problems, each of which may be very difficult of solution especially if it is desired t o construct large scale apparatus for the commercial production of the oxidation products. The number of experiments involved was U. S. Patent 1,322,983, Nov. 25, 1919.
* U. 1919.
S . Patents 1,318,631. 1,318,632, and 1,318 633, all issued Oct 14,
I
T H E J O U R N A L OF I N D U S T R I A L A X D ENGIMEERING C H E M I S T R Y
230
enormous and has required very extended careful work over a long period of time. Our laboratory work has been carried on with the direct object of solving the problems of commercial application simultaneously with the theoretical aspect of the problem as a whole. We have from the first attempted t o perfect a laboratory apparatus which would allow of uniform temperature control, and a description of such a n apparatus is given later in this paper. This was absolutely essential as we have found t h a t the problem of temperature control is the most important single difficulty t o be solved. T h k is evident from the following considerations in connection with the oxidation of benzene. T h e reactions which we have identified as taking place with such catalysts as molybdenum and vanadium we will consider in step-wise form and are mainly as follows:
Vol.
12,
No. 5
during condensation. Small amounts of fumaric acid are usually present in the products because of rearrangement during; condensation. Another side reaction is responsible for the formation of definite amounts of formaldehyde but we will not consider the genesis of this compound in the present paper. The total amount of oxygen needed t o completely burn one molecule of benzene is fifteen atoms. It is conceivable t h a t the intermediate products previously mentioned are formed and immediately burned to the more highly oxidized form even in the ordinary combustion of benzene but t h a t they cannot be isolated as such because of the extreme velocity of t h e combustion reaction. The function of a catalyst, which b y its use allows t h e separation of the intermediate products of combustion, is, of course, problematical, but i t would appear t h a t by its presence t h e range of temperature between the formation of one 0 intermediate product and its combustion t o a higher H II degree of oxidation is broadened, and that, b y a close temperature regulation within th's range throughout which t h e intermediate is stable, i t may be isolated. HC CH HC CH Another contact substance which either shows no reaction or produces complete combustion a t a higher temperature does not provide this sufficiently broad \/ \/ temperature range and the only products of reaction C are those of complete combustion. An example of H 0 the former contact substance is vanadium oxide, and examples of the latter are cerium oxide, platinum, a n d 0 0 numerous others. Even with these it is possible t h a t II II sufficiently close regulation will result in the isolation C C of intermediate products and i t is further possible /\ HC CH HC and even probable t h a t in other cases suitable control I1 I1 + b o II 0 HzO 2C02 would make possible the isolation of other products, Hc;" such as phenol. It has been mentioned above t h a t the question of C C temperature control is of extreme importance, and for It I1 purposes of comparison we are giving the amount of 0 0 heat developed during the oxidation of benzene, sulfur 0 dioxide, and ammonia. I n Table I we have collected data from the literaL ture bearing on the subject of benzene oxidation. The values given for the heat of combustion for HC\'/ quinone and maleic acid are for the solid form of t h e 0 6 0 4 Con Hz0 II compound. The heats of combustion in vapor form C /" are therefore somewhat greater since heat must b e C absorbed in melting and volatilizing the compounds. From this it is evident t h a t the heat developed in II 0 the formation of maleic acid from benzene is nearly T h a t is, during catalytic oxidation of benzene, quin- 60 per cent of t h a t developed by a benzene flame. These are, of course, the theoretical values, but as one is first formed, then oxidized t o maleic anhydride, and this in turn burned completely t o COZ we have not succeeded as yet in producing simple reand H20. The preferred reaction involves a splitting actions as represented by any of the single equations without the simultaneous production of other reacof the benzene nucleus without complete oxidation. There are, of course, two acids, maleic and fumaric, tions, the amount of heat formed is a composite of which are isomeric, but from our experience maleic all the values given above. An inspection of these acid is the primary product obtained during the re- values reveals the accelerating character of the heat action, This is explainable in t h a t only maleic acid formation which takes place with the increasing deforms an anhydride and this appears t o be the stable gree of oxidation and since the tendency t o higher form a t the temperature of the reaction. Some maleic oxidation increases with the temperature for a given acid ts probably always formed as a secondary reac- set of conditions i t is evident t h a t the temperature tion product due t o the hydration of the anhydride control must be most refined.
A
A i
\
HcvcH
+
*
+
+
+
Mar.,
1920
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y TABLEI-OXIDATION
OF BENZENE B. t. u. per B. t u. per
Lb. of Substance X-HEATS OF COMBUSTION (1) Benzene: 785.1 kg. cal. per mol.; 10.06 kg. cal. p e r g (2) Quinone: 654.8 kg. cal. per mol.; 6.06 kg. cal. per g. (3) Maleic Acid: 327.0 kg. cal. per mol.; 2.81 kg. cal. per g II-HEATS OP FORMATION (calculated) From Benzene (1) t o Quinone: 130.3 kg. cal. per mol.; 1.21 kg. cal. per g . . (2) t o Maleic Acid: 458.1 kg. cal. per mol.; 3.95 kg. cal. per g . From Quinone (3) to Maleic Acid: 327.8 kg. cal. per mol.; 2.82 kg. cal. per g . .
...............................
.............................. ............................
......................... ......................
.....................
Lb. of &Ha
18,108
18.108
10,908
15,102
5,058
7,542
2,178
3,006
7,110
10,566
5.076
7,560 B. t. u. per Lb. CoH6
SUMMARY
................................ ............................. ................. TOTAL. ...........................
Benzene t o quinone.. Quinone to maleic acid.. Maleic acid t o complete combustion..
3,006 7,560 7,542 18,108
Benzene: Landolt, p. 910; Berthelot, Ana. chim. phys., [ 5 ] 23 (1881),
If we are t o consider temperature control for the production of maleic acid, nitric oxide and sulfur trioxide we must also calculate the amount of heat which can be carried away from the zone of reaction by the products. We will assume t h a t a 9 per cent ammonia-air mixture is used for the oxidation of ammonia (Landis), t h a t the theoretical amount of oxygen as air is used for the oxidation of benzene t o maleic acid and t h a t in the oxidation of sulfur dioxide three molecules of oxygen are present for every two molecules of sulfur dioxide' and t h a t the courses of the reactions are simple and not accompanied by side reactions. We will also assume t h a t t h e reaction mixtures enter the converters a t 25' C. and leave the catalytic zone a t the temperature of the properly functioning catalyst which temperatures are assumed t o be: 750' C. (Landis) Ammonia oxidation, ..................... Benzene oxidation., 400' C. Sulfur dioxide oxidation. . . . . . . . . . . . . . . . . . 400' C. (Knietsch)
.....................
Without burdening you with our calculations, we arrive roughly a t the following results:
188. Quinone: Landolt, p. 919; Berthelot and Luginin, A n n . chim. phys., j6] 13 (1888), 328. Maleic: Landolt, p. 925; Luginin, I b i d . , [6] 1891, 179.
This question of temperature control has been given considerable study in the past in connection with the oxidation of sulfur dioxide t o sulfur trioxide, since too high a temperature results in the dissociation of t h e trioxide with a consequent loss in efficiency. I n this case, however, the resulting dissociation products, SO2 and 0 2 ,may be recombined in a second catalytic zone a t a lower temperature. I n the case of maleic acid, when once burned i t is safe t o say t h a t i t cannot be regenerated from its combustion products. The oxidation of ammonia t o nitrogen oxides is a reaction which is more closely comparable t o the oxidation of benzene in t h a t without proper precautions undesirable reactions take place with a great heat evolution. Calculation shows t h a t the comparative exotherms per pound of starting substance are:
......................... ...................................... ................................... ................
Benzene to maleic acid.. SOzto SO3 NHa to NO.. Benzene t o complete combustion.. NHa to complete combustion..
...................
B. t. u.
5 10,560 5 635.6 5 5,660 If: 18 100
k 7 :930
I n these calculations the following figures have been used as heats of formation: SO2
+ 69.26 kg. cal. per mol.
sos
f 91.90 kg. cal. per mol.
Hz0
+ 58 kg. cal. per mol.
NO 1"
- 21.6 kg. cal. per mol. + 12 kg. cal. per mol.
Berthelot, Ann. chim. p h r s . , [5] 22 (1881), 428; Landolt, p. 853.. Berthelot Thermo-chimie, 2 (1897), 91; Landod, p. 853. Berthelot and Matignon, Ann. chim. @p 161., SO (1893), 553; Landolt, p. 82.U.
Berthelot Ann. chim. phys., [51 20 (ISSO), 260; LAndolt, p. 854. Berthelot, A n n . chzm. phrs., 151 20 (1880), 252; Landolt, p. 851.
The ammonia oxidation is assumed t o proceed by t h e equation given by Landis.' 4NHa 5 0 2 = 4NO 6Hz0 4NH3 3 0 2 = 2N2 6H20
+ +
1
+
+
Chem. b Met. Eng., 20 (1919), 473, 474.
REACTION
12Nz 32Na 36Nz
++ 4NH3 2502 + 3 0 --+SO8 4- 802 +nitropen 4- 2CeHe + 90a -CaHaOa
HEAT CAPACITY OF HEAT ENTERINO DEVELOPED GASES 635 661 oxides 5660 6264 10560 1620
The calculations are based on the following values for specific heats: MATERIAL SPECIFIC HEAT REFERENCE so2 0.154 Regnault, Mem. de Z'Acad., 26 (1862), 1. Na 0.249 Schell and Heiise, Tdtigkeitsber. d. P.-T. 0 2
0.230
NHs C6He
0.65 0.375
Reichsanst. i. J . , 1911.
Holborn and Austin, Sitzb. A k a d . W i s s . , Berlin, 1905, 175. Nernst, 2. Elektrochem., 16 (1910). 96. Regnault, Mem. de Z'Acad., 26 (1862), 1.
We inevitably found t h a t even the refined apparatus developed for the control of these older reactions was unsuitable for such a "hair trigger" reaction as t h a t of benzene t o maleic acid. Our laboratory apparatus for study of the reaction consists essentially of a combined vaporizer and mixer, a contact tube and condensing system. The vaporizer consists of a vessel containing benzene held a t a n exact temperature through which is passed a stream of air heated t o the same temperature. The temperature of t h e vaporizer controls the benzene-air ratio used. The mixture then passes t o a U-tube containing the catalyst immersed in a regulated metal bath. The products of reaction are passed through a series of absorbers-first water t o remove maleic acid, then ice-cooled receivers t o remove the bulk of the unreacted benzene, and finally oil scrubbers t o remove the last traces of benzene. This is a mere skeleton outline of the set-up and we do not mean t o burden you with a minute description of the meters, pressure and temperature regulators, special gas sampling devices, and numerous automatic condition recording devices, which make the apparatus when fully set up seem indeed formidable. Our experience, however, led us t o add one device after another and t h e general 1 Knietsch-Lunge,
4th Ed., 131 1, 1306.
23 2
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
set-up now in use for investigations is the result of two years) continuous development and application. With our laboratory contact tube a great mass of d a t a has been collected in connection with the catalytic oxidation of such reactions as anthracene t o anthraquinone, naphthalene t o phthalic acid and naphthoquinone, benzene t o maleic acid, and toluene t o benzaldehyde and benzoic acid, in addition t o similar reactions of numerous other hydrocarbons and their derivatives. It possesses the distinct advantage of a close approach t o absolute temperature control which is so vital for the duplication of results under fixed conditions and the establishment of reliable data. It is, moreover, simple t o manipulate, which is of importance in problems where a very large number of runs are necessary in order t o accumulate a large mass of data before conclusions can be drawn safely. Advances are moreover being continually recorded toward improvement of design. Of course, a special vaporizer and a different form of condenser must be adopted for each raw material under investigation. The reaction velocity of these partial oxidations appears t o be without doubt much less t h a n in the case of the oxidation of sulfur dioxide t o sulfur trioxide and of ammonia t o nitric oxide in the presence of platinum as a catalyst, and therefore the productive capacity of a converter of equal size is relatively small. This is an important factor in the design of large scale apparacus and coupled with the necessity for rapid heat removal t o maintain a constant temperature, without being cumbrous and impracticable, makes the problem doubly difficuli. Definite progress has been made in our experimental manufacturing plant so t h a t the problem of tempe,ature control has been solved and large scale production now depends on the development of suitable tonnage uses for the products. We are able t o furnish either maleic acid or its isomer, fumaric acid, in sample lots t o those who may have an interest in their utilization. Many such possible uses are evident and are being thoroughly investigated. When you consider the very reactive nature of maleic acid, its anhydride and amide, the possibilities in pure chemical synthesis are unlimited. I t opens up the possibility of the commercial production of many of the straightchain acids such as fumaric, malic, succinic, aspartic, tartaric, propionic, lactic, acrylic, malonic, and hydracrylic acids. The use of these acids t o replace those previously obtainable only from natural sources (mainly fruit juices) is receiving attention and has very decided possibilities. I n conclusion, we wish t o express our sincere thanks t o our Messrs. G. C Bailey, F. A. Canon, A. E. Craver, L. A. Helfrich, W. J. Huff, J. F. W. Schulze, C. G. Stupp, and their some ten t o a dozen assistants engaged on this problem, all of whom have contributed t o the success of the undertaking and have by their earnest effort and teamwork made possible the development of the original discovery t o a completed manufacturing process.
Vol.
12,
NO. 3
THE GENERATION OF HYDROGEN BY THE REACTION BETWEEN FERROSILJCON AND A SOLUTION OF SODIUM HYDROXIDE' By E. R. Weaver BUREAUOF
STINDARDS,
DEPARTMBNT OF
COMMERCE, WASHINGTON,
D.
c.
Received May 16, 1919
D E S C R I P T I O N O F THE F E R R O S I L I C O N P R O C E S S
The generation of hydrogen by the reaction between ferrosilicon and a solution of sodium hydroxide is, in itself, an interesting process which has been, extensively employed in recent years for filling military and naval balloons. The cost of materials makes the method expensive, but i t has several great advantages, especially for use aboard ship and in portable units for field service. A very rapid rate of production of hydrogen can be secured from a comparatively small and inexpensive plant with very little labor and only sufficient power t o operate the water pumps and stirring machinery. None of the materials used are combustible; they do not give off hydrogen until mixed, even when wet; and they are easily and safely transported and handled. T h e principal reaction involved may be represented by the equation: 2NaOH Si HzO = NazSiOs 2H2 (I) This equation probably represents the reaction taking place a t the beginning of a run. However, sodium silicate in solution hydrolyzes, giving sodium hydroxide and hydrated silicic acid as indicated by the equation: NazSi03 (x: 4- I ) H ~ O= zNaOH SiOz.xHZ0 ( 2 ) If we combine Equations I and 2 , we have
+ +
+
+ + Si + (x: + 2)H20 = SiOz.xHzO + 2Hz
(3) While these equations may not represent all the complex compounds occurring in the solution, they probably represent the general course of the reaction, which thus appears t o be in effect one between silicon a n d water, the sodium hydroxide serving as a catalyst. This viewpoint is important, since it shows t h a t t h e relative amounts of alkali and ferrosilicon t o be used in practice should be determined by the speed of reaction and the relative cost of the materials, rather t h a n by computing the proportions corresponding t o a definite equation. T h e plant required for the production of hydrogen consists of three principal parts: ( I ) the solution tank in which the sodium hydroxide is dissolved, ( 2 ) the generator in which the react'on takes place, and (3) the washer, or condenser, in which the evolved gas is washed and cooled with water before being stored or put into the balloon. T h e generator controls should permit the operator t o regulate the supply of sodium hydroxide solution, ferrosilicon, and water. 1 Publisiied by permission of the Director of the Bureau of Standards. This work was done in connection with the use of the process for military purposes. I t was shown that certain changes in the methods used b y at least one of the allied nations would result in greatly facilitating generator operation with a saving of two-thirds of the sodium hydroxide and some of the ferrosilicon The experiments, computations, and results, including specific operating directions for field generators, are given in considerable detail in the Fourth Annual Report of the National Advisory Committee for Aeronautics. This paper is intended only to present the method of investigation employed.
