T H E COMPARATIVE ACTION OF MIXED CATALYSTS WHEN USED FOR THE JOINT DEHYDRATION OF ETHYL ALCOHOL AND AMMONIA. I N. I. SHUYKIN, A. A. BALANDIN, AND Z. I. PLOTKIN Laboratory of Organic Chemistry, Section of Catalysis, State University of Moscow, Moscow, U.S . S. R. Received Januaru 7, 1936
Sabatier and Mailhe (8) were the first to indicate the possibility of obtaining alkylamines by the interaction of alcohol and ammonia in the presence of such dehydrating catalysts as thoria or alumina. Subsequently, many investigators studied quantitatively the process of the catalytic alkylation of ammonia. Eug. and Kae. Smolensky (9) passed ammonia gas and vapors of ethyl alcohol over alumina at temperatures of 330350°C. and obtained a mixture of three amines with a yield of 53 per cent, based on the ethyl alcohol that had entered the reaction, and, as by-products, ethyl ether and ethylene. When the molecular ratio NHI: C2H60H was 1 :2, the mixture consisted of 15 per cent of mono-, 70 per cent of di-, and 15 per cent of trimethylamine. Brown and Reid (3) studied the joint catalytic dehydration of ammonia and methyl, ethyl, n-propyl, and n-butyl alcohols. These authors tried not only individual catalysts, such as blue tungsten oxide and silica gel, but also mixed catalysts, such as the following: alumina on pumice, mixtures of silica gel and nickel oxide, cerium oxide on pumice, and mixtures of silica gel and thorium oxide. The best catalyst among those mentioned above proved to be a silica gel prepared in a special way. At 465"C., with this catalyst, 39.5 per cent of ethyl alcohol was converted into a mixture of amines in the ratio 2:5:3. Dorrell (4)studied the influence of temperature, contact time, and ratio of ethyl alcohol to ammonia in the presence of alumina. The best yield was obtained at 344°C. I n runs where a relatively large amount of alcohol was taken, there was an increase in the yield of the secondary amine. A decrease in the velocity of the initial products (an increase of the contact time) led to a decomposition of the amines into ammonia and ethylene. A similar investigation was carried out with methyl alcohol by Briner and Gandillon (2). The authors studied the catalytic activity of alumina, thoria, silica gel, kaolin, and blue tungsten oxide. The catalysts are re1197
1198
N . I. SHUYRIN, A. A. BALANDIN, AND 2. I. PLOTBIN
ported in the order of their decreasing activity in the reaction of the methylation of ammonia. In the presence of alumina at 405"C., with a volume ratio NHa:CHsOH = 2.25:1, a mixture of amines was obtained with a yield of 52.7 per cent. The content of the different amines in the mixture was as follows: methylamine, 43 per cent; dimethylamine, 36 per cent; and trimethylamine, 31 per cent. A decrease in the contact time led t.0 an increased yield of the primary amine and to the decomposition of the secondary and tertiary compounds. All the authors quoted above have investigated only the action of individual catalysts. Only in a few separate runs by Brown and Reid (3) have mixed catalysts been tried. The most effective one proved to be a mixture of silica gel and thoria. Up to now there have been no investigations dealing with the comparative action of mixed catalysts in the alkylation reaction of ammonia by means of alcohols. The present investigation had for its purpose the study of the dehydrating action of mixtures, consisting of alumina and of iron, chromium, tin, and zinc oxides, and the comparison of the activity of these mixtures with that of pure alumina, which has proved to be, according to former investigations, a highly active catalyst for the dehydration of the system alcoholammonia. It seemed interesting also to find out how catalysts consisting of alumina and of tin or zinc oxide would behave in this case, taking into consideration that the latter two substances in a pure state are catalysts of complex action, with a considerable predominance of dehydrogenating over dehydrating properties. In the present paper, the following catalysts were investigated? (1) alumina; (2) Al2o3(90 per cent) Fe2O3(10 per cent); (3) A1203 (80 per Cr2O3 (20 per cent) ; (4) A1208 (90 per cent) SnO (10 per cent) ; cent) (90 per cent) ZnO (10 per cent). (5) In our former investigation, dealing with the hydration of diethyl ether under pressure (l),mixtures of zinc and iron oxides with alumina proved to be more active than pure alumina.
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EXPERIMENTAL PART
A . Preparation of catalysts Aluminum hydroxide and the mixture consisting of aluminum hydroxide (90 per cent) and iron hydroxide (10 per cent) were prepared as described in a previous paper dealing with the hydrolysis of diethyl ether (1). The catalyst, consisting of A1203(80 per cent) and Cr203(20 per cent), was pre-
pared by precipitating a solution containing 750.3 g. of Al(N0&.9H20 1
All the oxides used were hydrated oxides.
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COMPARATIVE ACTION OF MIXED CATALYSTS. I
and 134.2 g. of C P ( N O ~ ) ~ . ~with H ~ aO 25 per cent solution of ammonium hydroxide, the mixture being vigorously stirred all the time. The catalyst containing AlzOs (90 per cent) and SnO (10 per cent) was prepared as follows: To a solution of 664.4 g. of A12(S04)3. 18H20 and 18.1 g. of SnS04, sodium hydroxide was added with stirring until the dissolution of the hydroxides that appeared a t first. Then sulfuric acid was added until the disappearance of the alkaline reaction to litmus. In order to obtain the catalyst consisting of A1203 (90 per cent) and ZnO (10 per cent), two separate solutions were prepared, one containing 750.3 g. of A1(N03)3.9Hz0,and the other 41.4 g. of Zn(N03)2.6H20. These two solutions were added separately to a concentrated solution of sodium hydroxide until the precipitates completely disappeared. The aluminate and zincate solutions were then mixed together and nitric acid added to the mixture until the alkaline reaction to litmus disappeared. In the preparation of all of these catalysts, the precipitates were carefully washed with hot water until a negative test for the corresponding anion was obtained, then they were dried a t 150OC. and fragments of the size of an average pea were used.
B. Expeeriments on joint dehydration of ammonia and ethyl alcohol These experiments were carried out a t temperatures of 300,330,360, and 400°C. The apparatus consisted of a glass reaction tube, having a diameter of 15 mm., and placed in an electric furnace. The catalyst, dried at 150°C.) was packed in a 30-cm. section of the tube. The alcohol was added from a graduated buret, and the ammonia (Schering-Kahlbaum) was taken from a bomb and passed first through a flask filled with lumps of sodium hydroxide for drying purposes. The rate a t which the ammonia was added was measured by a flowmeter filled with alcohol. In different runs this rate varied from 55 to 60 cc. per minute. The alcohol was added in all runs at a rate of 1.6 cc. per 10 minutes. Twenty cubic centimeters of alcohol was passed over the catalyst in each run. The molecular ratio NH3:C2H60H was about equal to 1. The condensate was collected in three consecutive receivers. The last two were provided with coils and placed in a cooling mixture. The gases, after passing the last receiver, were collected in a graduated gasometer over water, where their volume could be measured with a precision up to 5 cc. The largest amount of condensate was collected in the first receiver. Products obtained in the experiments with the catalysts A120s Cr203 and A1203 ZnO a t 360 and 4OO0C., had a characteristic odor of pyridine bases. Probably in the above experiments there was a side reaction consisting in the dehydrogenation of alcohol with the formation of the corresponding aldehyde, and this aldehyde condensed with ammonia giving
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N . I. SHUTKIN, A. A. BALANDIN, AND Z. I. PLOTKIN
a- or @-picolines. These products were obtained under similar conditions by Tschitschibabin (10).
C . T h e analysis of reaction products The analysis of the reaction products was effected by using a modification of the methods of Francois (6) and Erdmann ( 5 ) . All the condensate was neutralized with dilute (1:1) hydrochloric acid under cooling. The condensate from those receivers that had been cooled during the experiment was distilled into a flask containing dilute acid (figure l), first by heating each receiver with the hand and then by heating on a warm water bath. The liquid that did not distil under these conditions was neutralized in the receiver. The solution of amine hydrochloride was placed in a citrate bottle of 400-cc. capacity, and a mixture consisting of equal volumes of a saturated
FIQ.I soda solution and a 20 per cent sodium hydroxide solution was added in excess. Then 70 g. of ground yellow mercuric oxide was also added to the mixture. The mixture was shaken on a mechanical shaker for one hour and then was left standing for twenty hours. The solution was filtered from the precipitate and the latter was washed three times with small quantities of water. The mixture of amines was distilled and collected in a 0.2 N hydrochloric acid solution; the excess of acid was titrated with a 0.1 N sodium hydroxide solution in the presence of methyl red. In all experiments only the total amine content was determined. The catalyst was heated before the experiment to 400°C. until the elimination of water ceased, and then before every experiment ammonia was passed over the catalyst for thirty to forty minutes.
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COMPARATIVE ACTION O F MIXED CATALPSTS. I DISCUSSION O F RESULTS
The results of our experiments on the joint catalytic dehydration of ethyl alcohol and ammonia are reported in table 1. The catalysts are given in the first column in the order of their decreasing activities for this process at 400°C. In the second column the temperature of the experiments is reported. In the third the yields of the amines, expressed in cubic centiTABLE 1 Catalytic dehydration of ethyl alcohol and ammonia AMOUNT OX" TEMPERAT U R E OF THE EXPERI MENT
CATALYST
A1203.. . . . . . . . . . . . . . . . . . . . , . . . . . . , . . . . . . . . . . . . . .
0.1 N HC1 USED FOR THE NBURALIZATION OF T H E AMINES
ALCOROL )ECOMPOSED
'C.
ce.
per cent
300 330 360 400
516.7 520.9 570.3 7'27 7
8.9 12.6 15.9 23.5
I
AI2O3(90 per cent)
+ Fez08 (10 per cent). . . . . . .
300 330 360
82.0 215.5 579.0
1.8 2.6 3.9
A1203 (90 per cent)
+ Fez03 (10 per cent). . . . . . .
400
725.8
12.5
Alz08 (90 per cent)
+ ZnO (10 per cent)
,....
300 330 360 400
90.3 96.0 247'4 319.2
2.0 4.3 9.6 27 :1
Alaos (80 per cent)
+ Cr203 (20 per cent). . . . . . .
300 330 360 400
219.2 287.7 275.9 195.4
4 .O 12.3 46.6 70.2
AllOa (90 per cent)
+ SnO (10 per cent). . . . . . . .
300 330 360 400
283.7 300.9 408.6 141.6
1.5 4.0 11.6 41.1
meters of a 0.1 N hydrochloric acid solution that was used for the neutralization of these amines. In the fourth column the decomposition of the alcohol is expressed in percentage calculated on the basis of the gas collected in the gasometer. From table 1 we may see that the mixed catalysts used by us, if compared with pure alumina, do not seem to accelerate the reaction of ethyla-
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N. I. SHUYKIN, A. A. BALANDIN, AND 2. I. PLOTKIN
tion of ammonia with ethyl alcohol. The only exception is the mixture A1203 Fe203, which at 360°C. as well as at 400°C. gives practically the same yield as pure alumina. Besides, it is necessary to note the small activity of this catalyst in the decomposition of alcohol. This fact distinguishes it in the process from all other catalysts. In the case of pure alumina and a mixture of the latter with ferric oxide and zinc oxide, the yield of amines in the interval between 300 and 400°C. increases with the rise of temperature, whereas in the case of the catalyst A1203 SnO a maximum yield was obtained a t 360"C., and in the case of A1203 Cr203at 330°C. The latter catalyst showed at 360 and 400°C. an extremely high activity in the direction of alcohol decomposition, and a small activity in the ethylation of ammonia. The catalysts can be arranged as follows in order of their decreasing activity in the reaction of the decomposition of alcohol at 400°C.: A1203 + Cr203;A1203 SnO; AI2O3 ZnO; A1203; A1203 + Fe203. As we should have expected, the percentage of alcohol decomposition increases with the rise of temperature. In the case of alumina this increase is almost a linear function. According to Sabatier (8; cf. ref. 7), if we have pure alumina or pure chromium oxide and pass over them ethyl alcohol and ammonia, these catalysts will decompose ethyl alcohol only slightly with the formation of ethylene and water, because the chief reaction would be the formation of an amine. But when in our case we added to alumina 20 per cent of chromium oxide, the chief reaction was already the decomposition of the alcohol (at 360"C., 46.6 per cent; at 400"C., 70.2 per cent). Likewise, a catalyst consisting of alumina and 10 per cent of tin suboxide decreases the rate of the reaction of ethylation of ammonia fivefold at 400"C., and increases the decomposition rate of the alcohol nearly twice. Alumina to which 10 per cent of zinc oxide has been added lowers considerably the rate of both possible processes,-the ethylation of ammonia as well as the decomposition of the alcohol-particularly in the interval 300-330°C. The catalyst consisting of alumina to which 10 per cent of iron oxide has been added influences the reaction of the ethylation of ammonia in the 360400°C. range, in the same way as pure alumina, considerably decreasing the process of alcohol decomposition (at 360"C., four times; at 4OO0C., nearly twice), The catalytic action of these mixed catalysts shows that their properties are different from the properties of oxides of which these mixtures are made, and also that apparently they can even change the direction of the reaction. The results thus obtained are of interest from still another point of view.
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COMPARATIVE ACTION O F MIXED CATALYSTS. I
@2=
I
I
H O IIK;, 3
(011
(012
(013
cp2l
(0%
9 1 3
(031
(032
(033
I
I
H O U(I1 K; 1)3
I
1203
I
H O IIK:, 1
As may be seen, the difference consists only in the elements 911 (C, N, and 0),which change according to the order of their atomic numbers (the difference in p12 has only a subordinate significance). For catalysts to be compared we take the type of mixed catalysts where one of the components is aluminum hydroxide, which, as is already known, fa'cilitatesthe reaction having the index I1 K?7 3, and the other component is such a metallic oxide as catalyzes the dehydrogenation of alcohols:
0-c
I 1 H H U(II K: 2)U The latter index differs from index I1 Ki3 1 by the elements (033: in I1 Ki3 1, corresponds to an oxygen atom, and in the case of dehydrogenation (033 corresponds to a hydrogen atom.
(033
1 The terminology in the present paper is taken from the article referred t o (see Balandin: J. Phys. Chem. U. S. S. R . 6, 679-706 (1934). Below the index its symbol is given; when multiplied by matrix
Li
=
1;
the index does not change, but only turns.
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N. I. SHUYKIN, A. A. BALANDIN, AND Z. I. PLOTKIN
Experiments (1) have shown that such mixed catalysts accelerate considerably reactions belonging to class I1 Kd31 (ether hydrolysis). The reaction I1 Kq, 3 (alcohol dehydration), it seems, is not sensitive towards the addition of dehydrogenating oxides to alumina. The reaction studied in the present paper, the joint dehydration of ethyl alcohol and ammonia, is one of the cases of index U(I K! 1), which occupies a middle position in the above-mentioned series. This applies not only to the first stage, the formation of a primary amine, but also to subsequent reactions,-to the formation of a secondary and tertiary amine:
H H2
H O H
H O H
In order that such a reaction may take place upon the same active tenters of the catalysts on which the alcohol dehydration reaction took place, it is necessary for the alcohol molecule to turn somewhat, i.e., to be oriented C in a different way, so that the places previously occupied by atoms 1
H
and now left free in the left part of the index, should be occupied by the
N group
1
H'
It appears that in such a case the addition of dehydrogenating
oxides to alumina decreases the rate of the reaction, in contrast to the case of ether hydrolysis. I n that instance we can see how profoundly specific is the action of a catalyst, even when the reactions are very similar. The introduction of a nitrogen atom instead of oxygen into the index already produces a perturbation in the catalytic activity. According to previous theories, the reactions of ether hydrolysis as well as of the amination of an alcohol were considered as representing one and the same type of reaction, namely, the reaction of addition or removal of water. It was considered that only the elements of water come into a temporary contact with the catalyst. From the point of view of these old theories it was not possible to expect a difference in the catalyst action. From the point of view of the new theory, where the interaction of all the atoms participating in the reaction is taken into consideration, such a difference cannot readily be unexpected. We should remark still further that the addition of iron oxide decreases the rate not only of reactions I1 K;7 3, but also of an analogous reaction,the splitting of the amine that was formed,
COMPARATIVE ACTION O F MIXED CATALYSTS. I
c-c 1
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1
H N which differs from the former reaction only by ‘p33 (‘p33corresponds to an oxygen atom in I1 K&3, and to a nitrogen atom in I1 K;6 4). The specific action of the catalyst in this case is manifested just as sharply as in previous cases. CONCLUSIONS
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1. Mixed catalysts studied by us (except A1203 Fez03 at 360OC. and 4OO0C.),when compared to pure alumina, under the conditions of our experiments, decrease the reaction rate of the formation of amines from ethyl alcohol and ammonia. 2. Among the mixed catalysts that we tried, the most effective one proved to be a catalyst consisting of 90 per cent A1203 and 10 per cent Fe203. The advantage of this catalyst over pure alumina consists in a smaller decomposition of the alcohol in its presence. 3. The action of mixed catalysts in this case is not an additive one. 4. The facts observed are interpreted from the point of view of the multiplet theory. a
REFERENCES (1) BALANDIN, A. A., SHUYKIN, N. I., NESVIJSKY, M. P., AND KOZMINSKAYA, T. K.:
J. Gen. Chem. U. S.S.R . 2,601 (1932);Ber. 66,1557 (1932). (2) BRINERAND GANDILLON: Helv. Chim. Acta 14, 1283 (1931). (3) BROWNAND REID:J. Phys. Chem. 28, 1067 (1924). J. Chem. SOC.127, 2399 (1925). (4) DORRELL: (5) ERDMANN: J. Biol. Chem. 8,41 (1910);Chem. Zentr. 19lO,II,761. (6) FRANCOIS: Compt. rend. 144, 857 (1907). Die Katalyse, p. 223. Leipzig (1927). (7) SABATIER: (8) SABATIER AND MAILHE:Compt. rend. 148,898 (1909);160,823 (1910). EuG., AND SMOLENSKY, KAZ.:Roczniki Chemji 1, 232 (1923); (9) SMOLENSKY, Chem. Zentr. 1923, 111, 204. (10) TSCHITSCHIBABIN: J. Russ. Phys. Chem. SOC.47,703 (1915).
