FIGURE 1. APPARATUS FOR STUDYING THE FORMATION OF HYDROCYANIC ACID
Alumina as a Catalvst of Hydrocyanic Acid A Formation J
J
J
catalyst was developed for the production of hydrocyanic acid from carbon monoxide and ammonia. The catalyst consists of alumina, specially prepared in splinter form and activated by zirconium oxide.
WALTER FUCHS' AND H. VERBEEK Technische Hochschule, Aachen, Germany
ARBON monoxide and ammonia, in the presence of aluminum oxide, form hydrocyanic acid. The purpose of this investigation was to develop systematically a catalyst to meet the requirements of industrial practice-cheapness, easy availability, high activity, and stability. Mailhe and Godron (4) obtained hydrocyanic acid by passing carbon monoxide and ammonia over such substances as alumina, zirconium oxide, and thorium oxide. The I. G. Farbenindustrie (3) recommends the use of a glassy aluminum oxide because it decomposes only a small amount of ammonia and carbon monoxide. Further investigations have been carried out by Simakof (6) and especially by Bredig and Elod (2) and their co-workers, who applied to the process the following equation: 2CO
+ NHI = HCN + COn + Hz
For every molecule of ammonia transformed into hydrocyanic acid, they found approximately one molecule of carbon dioxide and one molecule of hydrogen in the exhaust gases. Between 500" and 700" C. the following catalysts were used: alumina, alumina on refractory material or mixed with thorium oxide, cerium oxide, and cerium oxide on carriers. The following mechanism of the reaction was suggested: 2CO
=
C
+ COz; C + NHa
HCN
+ Hn
ammonia in amounts equivalent to from one-fourth t o onefifth of the hydrocyanic acid yield usually waq destroyed. In this investigation several catalysts were fir>t compared with a standard catalyst described in the patent of the I. G. Farbenindustrie (3) which was prepared as follom-s: A solution of 500 grams of aluminum nitrate in 3 liters of water was saturated with ammonia, the latter being introduced as a fast stream of the gas. During the operation the temperature rose to 75" to 80" C. The precipitate was filtered by suction, thoroughly washed, and dried a t 100" C. The dry lumps were heated to 600" C. During the course of the present investigation a stream of ammonia and carbon monoxide was passed over the catalysts in order to obtain hydrocyanic acid. In a series of about fifty preliminary experiments the influence of the following factors on the results was determined: ACTIVITYOF CATALYST. Using a carefully prepared, iron-free catalyst, the yield remained constant for at least 60 hours. MATERIALAND DIMENSIONS OF REACTION TUBE. Smooth, iron-free glass is necessary for the tube construction; Jena Supremax was used. The length and diameter are unimportant. VELOCITYOF GASCURRENT.The velocity of the gas current has no influence on the yield between 5 and 30 liters per minute. TEMPERATURE, A temperature of 570' C. was found t o give good results. RATIOOF CARBONMONOXIDE TO AMMONIA. This ratio proved t o be of decisive influence on the yield of hydrocyanic acid as shown in the following table: Gas Mixture, Ratio NHs:CO by Vol. 1:0.5 1:O.Q 1:1.7 1:2.6 1:5.0 l:e.o 1:6.4 1:9.2
1:1o.e
During the reaction as carried out by Bredig and Elod, * Present address, Rutgers University, New Brunswiok, N. J.
1:35.0
410
Velocity of Gas Mixture, Litera per Min. 10.4 10.3 10.7 6.0 11.0 10.4 10.4 10.4 10.0 10.0
Yield =
(
HCN loo) NHa 7.4 15.0 19.0 25.0 30.0 35.0 37.7 46.0 49.6 75.8
APRIL, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
Apparatus The apparatus used for experiments 47 to 18s is given in Figure 1: A Suprernax glass tube (inner diameter 8 mm., with heated portion of catalyst equal to 14 cc.) a a s placed in an electrically heated, quartz tube furnace; the quartz tube, 28 cm. long, was wound with nichrome wire. The thermocouple (platinum and platinum-rhodium) shown in Figure I, was later placed (experiments 100 to 188) in a protective glass tube, shown in Figure 2 . Ammonia and carbon monoxide were supplied from tanks, dried by means of soda lime (which was dry enough to retain water), and passed through rotameters (1) and a mixer, the latter being connected with the reaction tube by means of :ithree-way stopcock. Open mercury manometers leading t o overflow bottles, which incidentally served as traps, together with large g l a s stopcock; placed ahead of the rotameters, provided the means of obtaining a fairly constant flow of gas. The gas leaving the reaction tube could pass, by means of a T-connection, either into the hood or into absorption bottles. As shown in Figure 1, the latter could be emptied, washed, and filled without being removed from the apparatus. For quantitative work the gases were passed over the catalyst in a constant ratio and velocity for 15 to 20 minutes. During that time the connection to the hood and absorption bottles was alternately opened and closed. To begin the analysis, the T-connection to the hood was closed and t,he reacting gases were led to the absorption bottles. The rotameters were, if necessary, corrected and a stop watch mas started. These operations took only a few seconds. The first absorption bottle contained 40 to 60 cc. of 0.5 ili sulfuric acid and some methyl orange, the second contained 20 per cent potassium hydroxide solution. The parts between the reaction tube and the absorption bottles had to be kept scrupulously clean and dry, otherwise, by removal of ammonium salt., the determinations became inaccurate.
de.
411
-
5 = V,
Catalysts with very small grains and high
velocity of gas caused an increase in pressure up to 75 mm. of mercury, and this caused an error of about 5 per cent which was corrected by the formula. On the other hand, a rise in temperature of 1 per cent caused an error of 0.1 per cent. The ammonia gas used for the experiments was completely absorbed by sulfuric acid. The carbon monoxide contained about 1.5 per cent nitrogen and 3 per cent hydrogen. When an unusual rate of ammonia decomposition was found in an experiment (for instance, 5 to 6 per cent in the case of a zirconium oxide catalyst containing traces of iron), the results were also examined by means of the usual gas analysis. The relative accuracy was better when the authors’ own method was followed. When pure ammonia gas was passed over catalysts which, according to the results, did not destroy ammonia in the production of hydrocyanic acid, the gas leaving the furnace was completely absorbed by the sulfuric acid.
Quantitative Work In the quantitative work with the apparatus shown in Figures 1 and 2, the following conditions were kept constant: Temperature Ratio NHa:CO Velocity of gas current Amount of catalyst Tube diameter Length of tube heated
570’ C.
1:9.4
1 5 . 4 liters/hour 9 . 3 1 grams 8 mm. 280 mm.
The volume of the 9.31-gram catalyst, as taken in every experiment, varied according to grain size and conditions of production between 180 and 260 mm. of the tube length. From a theoretical point of view an arrangement providing the same contact time of the gases on the catalyst would have been correct. For practical reasons the work was always performed with the same weight - of catalysts. Catalysts prepared by h e a t i n g a l u m i n u m nitrate were compared with those produced by precipitation. The latter were much more efficient in catalytic action. Furthermore, the catalysts prepared by heating were somewhat foamy and required nearly double the space of precipitated catalysts in the reaction tube. PT,ON By examining a number of c o n d i t i o n s , the catalysts recorded in Table I were finally obtained. t These were better than all others heretofore exFIGURE2. REACTION TUBEFOR STUDYING THE FORMATION OF amined; they gave high yields of hydrocyanic acid HYDROCYANIC ACID and destroyed only minute amounts of ammonia. To obtain, for instance, catalyst 201, 100 grams of aluminum nitrate were dissolved in 1000 cc. of The operations were stopped when the methyl orange water and kept a t room temperature under constant stirring. in the first absorption bottle changed color. At this point At once 300 cc. of an aqueous solution of ammonia (specific the quantity of ammonia which had left the reaction tube gravity 0.882) were introduced, and the stirring was conduring the experiment was equivalent to the amount of the tinued for 30 minutes. Then the precipitate was allowed to sulfuric acid in the bottle. For the determination of hydrosettle, filtered by suction, and slowly and carefully dried a t cyanic acid, the major part of it was dissolved in the first looo bottle, and the combined contents of the two absorption bottles were titrated after the addition of soma potassium TABLEI. DATAON THREECATALYSTS VOl. of Ppt., iodide with 0.1 N silver nitrate according to Liebig-DenigBs. Per Cent of Timeof “sin The amount of ammonia entering the reaction tube was Total Catalyst Temperatureoof Stirring Excess Per Co!or of Precioitste VOI.~ Cedt Precipitation, C . Minute; No. recorded by a rotameter calibrated by the manufacturer 20 30 150 White 60 201 (Deutsche Rotawerke, Aachen, Germany) for a flow of 1 Bluish white 54 50 23 175 202 Bluish 52 90 15 200 203 to 30 liters per hour. The exactness of the apparatus as 5 Measured with a ruler. checked in blank experiments was *l per cent. The relative gas passage depends on the temperature and the possible Before these results were reached, the following conditions increase of pressure in the apparatus. Apparent excessive were examined: the temperature of precipitation of aluminum passage of the gas, caused by the increased pressure in the hydroxide, the application of ammonia either as gas or in apparatus, was to be corrected by means of the formula
c.
INDUSTRIAL AND ENGINEERING CHEMISTRY
412
I
I
FIGURE 3. APPARATUS FOR MAKISGHYDROCYAUIC ACID
I
of the grain size on the results, sizes under 0.5 mm. represented only inferior catalysts. Catalysts precipitated in the cold usually did not "splinter," while precipitations performed a t 100" C. or glossy products gave "splinters" which were too fine for the purpose. Precipitations produced a t 50" to 70" C. with constant stirring for 10 to 20 minutes fiiially yielded "splinters" of the desirable size and quality. The following table contains data concerning specific gravities, showing the high porosity of the catalysts: Catalyst
Y4
No.
20 1 202 200
203
t-Rh
+ -+solution, the particulars of washing and drying. Some effects brought out by the departure from the optitnum conditions are recorded in Table 11. To obtain the best results, it is necessary t o use ammonia solutions instead of gaseous ammonia and to pour the ammonia solution a t once into the aluminum solution. In htudying the influence of the further treatment of the thoroughly washed precipitate, the folloFving methods were applied : 1. Slow drying at IOO", sudden heating at 600" C. 2. Rapid heating up $I 600" C. 3. Slow drying at 100 , low heating up to 600" C. 4. Careful drying a t 100" C.
Method 4 yielded the best catalysts, provided a thoroughly washed hydroxide obtained by precipitation from an aluminum nitrate solution with an excess of aqueous ammonia solution was used.
TABLE11. INFLUENCE OF PRECIPITATION TEMPERATURE ox FINAL CATALYST
Precipitation Temperature,
c.
20 50
Stirring Time, Minutes 30 30
70
30
100 100
30
100
300
60
HCK Yield, Final Catalyst Per cent Dull, rough surface 51 3 Partly dull and rough; partly 41.6 opaque and glossy Graiiis with faintly glossy 48 9 fracture surface Smooth grains 3s. 1 Large hard grains, very faintly 3 1 . 6 lustrous Very hard dense graina
The products obtained according t o the best method developed during the present investigation shoved a peculiar property. Originally they formed hard, faintly lustrou5 lumps. These lumps shattered when moistened into smooth, lustrous grains. [Patrick (5) observed a similar phenomenon with silica acid.] These grains formed a catalyst offering a gas passage of greatest ease. As to the influence
VOL. 27, NO. 4
Specific Gravity a t 20' C. True in Apparent in benzene mercury vacuuni 3.22 0.96 3.24 1.28 3.29 1.46 3.28 1.51
Temperature of Precipitation, O C. 20 50 70 90
Refractory iiidex was about 1.65 in all cases examined. The peculiar property to shatter in water seems to be of great importance and can be utilized for the purpose of bringing small amounts of catalytically efficient substances on the active surface. Such substances might be applied in the form of dispersions, solutions, or suspensions. In this way an especially good catalyst was obtained by activation with zirconium oxide. By shattering alumina either in a suspension of zirconium hydroxide or in a solution of zirconium nitrate, splinters mere obtained which offered very little resistance to a passing gas and in the formation of hydrocyanic acid effected an excellent catalysis. The following table contains data on hydrocyanic acid formation with catalyst 103 Zr I, obtained by shattering alumina in a solution of 10 grams of zirconium nitrate in 50 cc. of Tyater: Tempera- Keight of Volume of Time of ture Catalyst Catalyet Contact C Grams Cc. Seconds 600 9 31 12 1.1 700 9 31 12 0.9
Yield
Percent 53.0 56.7
Ammonia HCN Destroyed per Hour
Percent
i-i
Grams
2.2 3.1
Attention might be called to the very short times of contact (0.9 and 1.1 seconds). Times of contact recorded in the literature vary from 10 to 12 seconds. Yields obt'ained in quantitative experiments with freshly prepared catalysts decreased about *5 to 6 per cent in the first 10 hours and then remained constant for a t least 250 hours (longer experiments were not run). The catalysts sometimes became covered with carbon; for example, catalysts 103 and 103 Zr 1, after 24 hours of reaction, were usually covered with a black layer. However, no loss of catalytic activity could be established. In an experiment lasting over 250 hours, a catalyst was used which had been precipitated in the cold and therefore, according to the authors' experience, easily caused separation of solid carbon. The latter seemed to be active also; after 10 days of reaction the catalyst still showed its original activity. During that time a frequent removal of the carbon was performed by burning the carbon layer in a current of air; thus the activity was decreased only temporarily. Also, immediately after the removal of the carbon a very definite destruction of ammonia (to nitrogen and hydrogen) occurred. In order to obtain the best results, air and steam must be excluded. Addition of inert gases, such as nitrogen, has an effect, proportional only to the diminished time of contact. Sulfur compounds were proved to have no effect upon the catalysts. Their activity, however, is destroyed by prolonged heating up t.0 1025' C. Elod and Kortum by means of Nernst's approximate formula determined the equilibrium constant of the reaction: for 2CO NHs = HCN COS HP; A H = 200 calories
+
+
+
the following constant is obtained when using 4.0 as the conventional chemical constant of hydrocyanic acid (8):
INDUSTRIAL AND ENGINEERING CHEMISTRY
APHIL, 1935
log K p X 106
=
3.444; K p X lo6 = 2806
On using 3.9 as the conventional chemical constant of hydrocyanic acid (Y),the following values are obtained: log Kp X I O 5 = 3.049; K p X lo6 = 1128
This value v a s approached frequently in the course of the precent m-ork as shown by the following figures on the constant of quilibrium at 6011” C. : Ratio NH3:CO 1:9 4 1: 10
Per Cent H C X 64 55
Loe
K p X lo5
2.7 2.09
Furtherniore, becaupe of the very small AH value of the reaction, the equilibrium shifts very little with the temperature. as shown by the following data: Temperature,
c.
575 600
700
Ratio
NHs:CO 1:10 1:lO 1:1(1
Yield, Per Cent 54.0 54.9 50.7
---Log Actual 2.67 2.68 2.70
K ~x, 105-
Theoretical 3.049 3,050 3.068
l k a l l y , in order to test the technical value of the results, a large-scale experiment was run. The apparatus used is represented in Figure 3. The large furnace contained a porcelain tube glazed on the inside, 69 mm. in diameter and 700 mm. in length. By means of nichrome wire, 480 mm. of the tube were electrically heated. A current of 9 amperes
413
and 220 volts was used in heating it to 570” C. The bottom of the oven x a s made from asbestos disks cemented with a mixture of talcum and materglass. The top of the catalytic chamber was sealed by a water-cooled rubber stopper. One thousand grams of alumina splinters were placed upon a porcelain sieve plate cemented in the oven. The mixture of carbon monoxide and ammonia passed first through special large rotameters, then through a 10liter tower filled with soda lime, and finally through a preheater before entering the apparatus. In order to produce 100 grams of hydrocyanic acid, 1500 liters of gas per hour had to pass through the oven. The oven yielded 98 grams of hydrocyanic acid per hour.
Literature Cited (1) A n o n y m o u s , Chem. Em. Fett- Harz-Ind., 18,55 (19101. (2) Bredig, G . , a n d E l o d , E., 2. Elekfrochem., 36, 1003, I 0 0 7 (1930); 37, 3 ( 1 9 3 1 ) ; G e r m a n P a t e n t s 522,253 (Del:. S, 1922i, a n d 650,909 ( M a y 24, 1924). (3) I. G . F a r b e n i n d u s t r i e = l . - G . , Ibid., 449, 730 (1926’. (4) h l a i l h e a n d Godron. A n n . o h i m . . [SI 13, 1% f l W 0 1 : H u i ; S O ( ’ . chim.,[4] 27, 737 (1920,. ( 5 ) P a t r i c k , W. A , , d i s s e r t a t i o n , Goettinceii. 1911. (6) Simakof, J . Russ. Pit -Ci,em. Sx..61: 997 ‘19291. (7) T e i c h m a n , L., 2. EZet uchena.. 28. 202 ~ 1 9 2 2 ~ . (8) K a r t e n b e r g , H. \-,, Z. anorg. Chevz.. 52, 30s (19071 RECEIVEDOctober 10, 1934. The data i n thls p a p e r rorined a part oi tile doctor’s dissertation of €1. Yerbeek a t the Chemipcli-rechnisches Inatitut 01 the Technische Hochschule, A n c h e n .
Inhibitor Dves in Cracked Gasoline J
C. D. LOWRY, JR., GUSTAV EGLOFF, J. C. MORRELL, AND C. G. DRYER
Universal Oil Products Company, Riverside, Ill.
A number of dyes are shown to have antip r e s e n c e of alkyl or tertiary HE extensive use Of in oxidant ;iction in cracked gasoline. Reamino groups, Particularly when gasoline a n d in the ortho or para position. lationships are pointed out between strucThe effects of c h r o m o p h o r i c the successful application of inhibitors to the stabilization of ture and inhibiting effectiveness* The groups on i n h i b i t i n g potency cracked motor fuel suggested a fade when they act as inhibitors and SO give had not previously been deterstudy of compounds poqsessing an indication of their depletion. mined. both coloring and i n h i b i t i n g -Azo Dyes DroDerties. A number of azo dyes derived from intermediates of pro6illet (13) clainied a parallelism between the fastness of nounced inhibiting value mere prepared and tested. Their acid wool dyes and their possession of groupings nhich he effectiveness is expressed in the tables as “cyclohexene numbelieved conferred “antioxygenic” properties. Methyl rubber,” a reproducible means of inhibitor evaluation defined ber produced during the mar was dyed yellow to prevent de(8)as the calculated increase in the induction period of cycloterioration (16). Phenylazo-0-naphthylamine and azobenhexene produced by 0.002 per cent of an inhibitor, the cyclozene are reported b> Bondy (5) to protect rubbc,r exposed to hexene number being calculated from results obtained in a ultraviolet light by virtue of their specific light, absorption; reference gasoline whose response to a-naphthol bears a azo dyes derived from diphenylamine (14)also have protective power for rubber. During the progress of this work fordefinite relationship to that of cyclohexene. The data presented were obtained by adding 0.01 per cent of each inhibiteign patents were issued to the Standard Oil Development Company (1’7) relating to dyes as inhibitors in cracked gasoing substance t o a gasoline one-fifth as responsive to a-naphtho1 as cyclohexene, and determining the induction period by line. In a study (9) on the relationship of structure to inhibiting a previously described technic (9). Each sample was diseffectiveness, it was found that the presence of primary and solved in 5 cc. of benzene or hexone (methyl isobutyl ketone) ; secondary aromatic amino and aromatic hydroxyl groups these solvents have been found not to affect the induction usually conferred antioxidant power for cracked gasoline, period before addition to a 200-cc. sample of the gasoline. and that the effect of these structures was increased by the Data on azo dyes derived from a-naphthol are as follows:
