CATALYTIC ACTIVITY OF T I N BY 0 . W. BROWN AND C. 0. HENKE
lntroduetion I n our previous papers1 we have given the results of some studies on the activity of several catalysts and have shown that several metals which were not known to be catalysts were excellent catalysts. I n this paper we shall give the results of some studies with tin as catalyst and the effect of the physical condition of the tin on its activity. For this study nitrobenzene was used, a few experiments being carried out with orthonitro-toluene and ortho-nitro-anisole. Experimental Details The apparatus used, method of work and analysis was the same as in our previous papers where it has been fully described. I n all of the experiments in this paper unless otherwise noted the catalyst tube was a l/z inch glass combustion tube. The tin catalysts were prepared from C. P. Stannous Chloride crystals. Baker’s Lot No. 2322 was used,which was labeled to contain 0 . 0 0 2 ~ Fe 0 and O . O O l ~ oSOs. A test for iron indicated less than this amount. It was also tested for lead but none was detected. Previous experiments had indicated that iron was exceedingly poisonous to the tin catalyst while lead decreased its activity to a smaller extent. Stannous hydroxide was prepared by precipitation from a solution of 300 grams SnC12.2H20in 1350 cc water (the stannous chloride hydrolyzed to a certain extent) by a solution of sodium carbonate containing 150 gm Na2C08in 750 cc water. The sodium carbonate solution was added to the stannous chloride solution, both a t room temperature (about 20 O C) . The precipitated hydroxide was washed by decantation five Brown and Henke: Jour. Phys. Chem., 26,161,272,321,631,636 (1922).
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0 . W . Brown and C. 0. Helike
times using 3 to 4 liters of water each time. It was then filtered on a Buechner funnel and allowed to dry at room temperature. All the stannous hydroxide used for catalysts for this paper was prepared in this way. Unles's otherwise stated the oxide was ground to pass through a 40 mesh sieve.
'
Behavior of Stannous Hydroxide Bury and Partingtonl state that when a n excess of alkali is used to precipitate stannous hydroxide, the stannous hydroxide darkens and becomes almost black. We precipitated our stannous hydroxide in a tall cylinder, 12 cm diameter by 58 cm high, the capacity being a little over G liters. In preparing our stannous hydroxide we a t first had no trouble, the precipitate being white when filtered and remaining white during drying. After drying, the cakes of stannous hydroxide were covered with a thin coating having a slight yellow color, the inside of the cake being practically white. After making several batches in this manner we tried to prepare some from a hydrochloric acid solution of stannous chloride which contained some iron and lead. The cakes of the hydroxide after drying were black on the inside. The outside of the cake was white with a thin coating of a slight yellow color but the inside was black. The thickness of the white part varied in different attempts. Sometimes there was but a narrow streak of black while a t other times the white covering was very thin with a coiresponding increase in the thickness of the black layer. Sometimes the black was noted before filtering. After having this difficulty we tried to prepare more catalyst from stannous chloride as we had prepared it at first. But our dried cake very often contained black material. I n repeated attempts to get a satisfactory product it was noted that around the bottom of the cylinder black streaks would form in the precipitated mixture. These small black streaks corresponded to scratches in the glass 'caused by rubbing the stirrer against the side of the cylinder. Also in pouring out the suspension of Bury and Partington: Jour. Chem. SOC.,121, 1998 (1922).
Catalytic Activity of Tilt
74 1
stannous hydroxide black particles were noticed in the last part of the suspension. The cylinder was cleaned with concentrated hydrochloric acid and appeared perfectly clean. However upon again precipitating another batch of stannous hydroxide the black streaks again appeared and the dried cakes contained a black core. When a 10 cm Buechner funnel was used about 5 filter cakes would be secured from one batch. Sometimes all of these would turn black. Often only the last cake or the last two would turn black. I n filtering it was noted that the black particles seemed to be in the last portion. That is the black particles would settle more rapidly than the other particles. Likewise the last cake was usually the worst. This indicated that the black particles acted as catalysts causing the white to change to the black form which is probably the anhydrous stannous oxide. The cakes would vary from practically white to coal-black, depending upon the relative number of black and white particles. When a 19 cm Buechner funnel was used the entire precipitate would be collected in one filter cake. Upon allowing the cake to dry on drying paper it would crack in two or more pieces. Quite frequently one piece would have a black core while the other piece would be practically white throughout. The cylinder was then cleaned with a strong solution of sodium hydroxide and our difficulties disappeared. There were no black streaks around the lower part of the cylinder. The filter cake after drying would be almost perfectly white with the thin coating of a slight yellow color. These observations indicate that the black particles act as a catalyst causing the white to become black. Only an extremely small number of black particles are necessary for we have an autocatalytic process. Bury and Partington have shown in their work that moist stannous hydroxide reacts with air only slightly if a t all. From their work the dried stannous hydroxide corresponds approximately to the formula 3Sn0.2H20. Hence it might better be called a hydrated stannous oxide.
8
742
0.W . Brown and C. 0.Hevtke Experimental Results
I n Table I are given results with four different catalysts. Catalyst F45 was prepared as above described. Catalyst F35 was prepared by soaking cleaned pumice (through 10 on 20 mesh) in 50% SnC12.2H20solution. This was placed in a vacuum desiccator and evacuated. This was for the purpose of removing the air from the pores of the pumice. Then upon admitting air the solution is forced into these pores. The pumice was then dropped into a 20% solution of sodium carbonate and filtered, washed and dried. Catalyst F15 was prepared by igniting pumice with stannous chloride at 386 O C until fumes quit coming off. The catalyst consisted of 6 grams of the ignited tin compound. Catalyst F25 was made by precipitating a 40y0 solution of SnC12.2H20with a 10% solution of (NH4)2CzO4.H2O.These catalysts were all treated alike. They were heated in hydrogen a t 294 O C for one hour and then used at this same temperature in two experiments after which one experiment was carried out a t each of the other temperatures in the order in which they are given in the table. The first experiment with each catalyst was not titrated and is not given in the table.
TABLE I Catalysts heated in hydrogen at 294' C for 1 hour Rate of flow of hydrogen-I4 liters per hour. Rate of flow of nitrobenzene-9.3 grams per hour. Excess of hydrogen-1 70%.
hydroxide
Catalyst no. F35
Catalyst no. F15
Catalyst from 3.5 gm tin hydroxide on 6 gm pumice
Catalyst from SnClz ignited on pumice
1
Catalyst no, F25 Catalyst from 12 gm of SnC204
Material yield of aniline in percent of theory
294 275 256 237
89.0 78.9 42.3 21.5
71.6 56.4 37.1 11.8
58.8 38.9 25.2 13.8
90.5 85.3 77.4 48.9
-
Catalytic Activity o j Tiw
743
The results of Table I show that the catalyst from the oxalate is the best and the one from the hydroxide a close second. The stannous hydroxide on pumice catalyst (Catalyst F35) is decidedly inferior to these two while the catalyst from the ignited stannous chloride is still worse. Catalysts similar to the two best catalysts of Table I were now tested at different rates of flow of nitrobenzene.. These results are given in Table I1 in the order in which the: experiments were carried out.
TABLE I1 All catalysts air dried.
Catalyst heated in hydrogen at 294' C for 1 hour. Rate of flow of hydrogen-14 liters per hour. Rate of flow of nitrobenzene1-5.6 grams per hour. Excess of hydrogen-3600jo. Catalyst no.
F27
I I
Catalyst no. F28
I
Cataly;t no.
Temperature Catalyst from "C 13 gm tin hydroxide 11 gm of tin from oxalate 13 gm of tin hydroxide from
294
294 275 256 237
97.9 96.0 94.2 92.0 82.3
I
I
94.6 94.6
91.6 80.8
56.9
97.5 97.4
92.7 84.9 66.6
Catalyst F37 was used with the rate of flow of nitrobenzeAe a t 4 grams per hour making the excess of hydrogen 540%. 1
On comparing the results of Table I1 with those given in Table I i t is seen that a decrease in the rate of flow of nitrobenzene from 9.3 grams per hour to 5.6 grams per hour increased the yield of aniline with both the catalyst from the hydroxide and the one from oxalate. However, the increase in yield was greater with the catalyst from the oxide than with the one from the oxalate. Thus with the rate of flow of nitrobenzene at 5.6 grams per hour the catalyst from the hydroxide is the better while with the rate at 9.3 grams per hour the catalyst from the oxalate was the better. Catalyst F37, which was like F27 and
744
0.
w.Brcwvi and C. 0.Henkc
F45, was used with the rate of flow of nitrobenzene at 4 grams per hour. When these results (of F37) are compared with those of the other two catalysts (F27 and F45) i t will be seen that the highest yields were obtained with F27 where the nitrobenzene flow was 5.6 grams per hour. This would indicate that a catalyst made b y heating stannous hydroxide in hydrogen is better than one made from the oxalate. I n order to compare catalysts made from stannous and stannic chlorides a solution of stannic chloride was precipitated by sodium carbonate. The precipitated hydroxide dried to a very hard mass. When this was heated in hydrogen and then used as a catalyst the yields of aniline secured were less than '/3 the yields secured (under the same conditions) with a catalyst made from the hydroxide which had been prepared by precipitation from stannous chloride by sodium carbonate. Of all these catalysts the catalyst from the stannous hydroxide, with the rate of flow of nitrobenzene a t 5.6 grams per hour, was the best. The effect of various conditions on the activity of catalysts from stannous hydroxide was next determined. The stannous hydroxide was in each case prepared as described above and allowed to dry a t room temperature. After drying the filter cake, the hydroxide was white throughout with a thin outer coating of a slightly yellow color. As noted above the work of Bury and Partington indicates that the r e a c t h , if any, is slight between the moist stannous hydroxide and the ai:, and the composition of the dried material is probably 3Sn0.2Yz0. In Table I11 are given the results with three catalysts prepared from the hydroxide which had been ignited in different ways. Each was ignited in a small porcelain dish a t 300" C in a muffle for one hour. For catalyst F16; the stannous hydroxide was in the form of lumps during the ignition and a current of air was drawn through the muffle. After ignition this was ground to pass a 40 mesh sieve. For catalyst F36, the lumps of stannous hydroxide in the evaporating dish wer? covered with a watch glass and no air was drawn through the muffle during ignition. I n making catalyst F46, the stannous
Catalytic Activity of Tin
745
hydroxide was powdered to pass a 40 mesh sieve before ignition. During ignition the dish was kept covered with a watch glass as in catalyst F46. Upon ignition the stannous hydroxide burns t o the SnOzwith an evolution of heat. This makes i t difficult t o regulate the temperature during the first part of the ignition. Also when the stannous hydroxide burns to Sn02 it becomes incandescent for a moment at the point where the oxidation takes place. The experiments are given in the table in the order in which they were carried out. After heating in hydrogen at 294 O C two experiments were carried out at this temperature and then one experiment at each of the other temperatures. The first experiment with each catalyst was not titrated and is not given in the table.
Temperature "C
I/ 294
275 236 23'7
Catalyst no. F16
Catalyst no. F36
Catalyst no.
Grams used 17.5
Grams used 14
Grams used
F46 15
Material yield of aniline in percent of theory
9G.O 96.4 94.0
93.7 89.0
S9.0
G0.S
9G.O
92.7 94.9 84.6 53.4
These results show that Catalyst F16 was the best. This was the one in which a current of air was drawn through the muffle during ignition. Also the stannous hydroxide in lump form was in an open dish. This would indicate that a catalyst prepared from SnOz made by oxidizing stannous hydroxide is better than one made from stannous hydroxide directly. In the succeeding tables all the ignited catalysts were ignited in this manner.
746
0.W . Brown and C. 0.Henke
The effect of temperature of ignition was next studied. The method of ignition was that which gave the best results in Table 111. The results with catalysts ignited at different temperatures are given in Table IV. For convenience in comparison the results of F16 of Table I11 and F27 of Table I1 are included. The first experiment with Catalysts F16 and F26 were not titrated. The experiments are given in the order in which they were carried out.
. Temperature
"C
294 294 275 256 237
Catalyst no. F27
Catalyst no. F26
Catalyst no. F16
Grams used 13
Grams used 16.5
Grams used 17.5
Ignited a t air dried
Ignited a t 150" C
Ignited a t 300' C
--
-
97.1 96.0 94.2 90.5
96.0 96.4 94.9 80.0
07.9 96.0 ' 04.2 92.0 52.3
I
'
94.5 95.2 96.4 92.4 86.8
On comparing the results of Table IV the differences are seen to be very small. The results for F26 and F16 are a little higher than for the other two Catalysts, F26 being a little higher than F16, although this latter difference is well within experimental error. These results show that the lower the temperature of ignition, within the limits studied, the better the resulting catalyst. However, within relatively wide limits the difference due t o temperature of ignition is small. Catalyst F27 which was merely air dried and not ignited gave lower results than those that were ignited. To determine the effect of temperature of reduction a temperature of ignition of 300" C was chosen. Each catalyst in
Activity of Tin
Catal+
747
lump form in an open dish was ignited at this temperature for one hour with a current of air through the muffle. They were then reduced for one hour a t the temperatures indicated in Table V. To show the effect of length of time of reduction Catalyst F310 was reduced a t 350" C for 33/4hours. Catalysts F39 and F4S are duplicates and show how different catalysts, when made in the same way and treated alike check. These two catalysts were even used in different sets of apparatus. Catalysts F38 and F49 are likewise duplicates. For convenience in comparison the results with Catalyst F1G of Table I11 are included. The experiments are given in the order in which they were carried out.
TABLE V Catalysts ignited at 300' C for one hour. Rate of flow of hydrogen-14 liters per hour. Rate of flow of nitrobenzene--5.6 grams per hour. Excess of hydrogen-360%. F29 Temterature
C
294 294 275 256 237
15.5
97.1 96.4 95.3 95.3 92.0
I
F16
I
I 17.5 I
-
F38
Catalyst no. I FA9 1 F3101 1 F3D
Grams used 14 I 15.5 I 15.5
95.7 96.0 97.1 96.4 95.3 94.9 __ 89.0 -
94.2 96.1 94.9 92.7 81.6
94.2 96.8
95.7 88.7 71.0
I
15.5
97.5 97.5 94.6
92.4 74.2
I
F48
I
14.0
96.8 96.4 96.4 92.7 72.7
Catalyst F310 was reduced for 3'/4 hours instead of one how.
The experiments of Table V show that the lower the temperature of reduction the better the catalyst (within the limits studied). However, this difference is not great and at the two higher temperatures the results are practically the same within experimental error. Also the length of time of reduction a t 350" C has but a small effect upon the activity of the
748
0.W . Brown
aiid
C. 0.Heizke
catalyst. Thus Catalyst F310 gave practically the same yields as F49 at the higher temperatures, although at the lower temperatures the results with F310 are lower, indicating a slight loss in activity due to prolonged reduction at 350" C. Catalyst F410 was used t o determine the effect of length of time of ignition. The results with this catalyst are given in Table VI. It was ignited at 300" C for three hours while Catalyst F49 of Table V was ignited but for one hour at this temperature. The results with Catalyst F49 of Table Vare included in Table VI for purposes of comparison.
TABLE VI Catalysts ignited in air a t 300" C. Catalysts heated in hydrogen at 350" C for one hour. Rate of flow of hydrogen--14 liters per hour. Rate of flow of nitrobenzene--5.6 grams per hour. Excess of hydrogen-360%.
I Temperature " C
F-110
I
F49 no.
Grams used 15.5
Grams used 15.5
Time of ignition 3 hours
Time of ignition 1 hour
Material yield of ani!ine in percent of theory
294 294 275 256 237
-02.4 93.1 94.6 84.6
'
94.2 96.1 94.9 02.7 S1.G
.
,
Catalytic Activity of Tivz
740
I n all the foregoing experiments the catalysts (except those on pumice) were put through a 40 mesh sieve. The effect of mesh size of the catalyst on its activity is shown in Table VII. The last column, F210X, shows the effect of oxidation and reduction. After using Catalyst F210, in the experiments given in the first column it was oxidized a t 300' C for one hour by a current of air and then reduced a t 29.1' C for one hour. It was then used in the experiments listed under F210X. The results with Catalyst FA8 of Table V are included for convenience in comparison. The experiments are given in the order in which they were carried out.
-___
I
Catalyst no. F210 Grams used
Temperature " C
1
I
294 294 27-5 256 237
,
15.5
'
Catalyst no. FllO
Catalyst no. F49
Catalyst no. F2 1OX
Grams used 15.5
Grams used 15.5
Grams used 15.5
Mesh size Mesh size through 4 on 6 through 10 on 20
08.3 95.7 96.1 94.0 90.9
94.2 95.7 . 94.6 95.3 91.2
Mesh size through 40
94.2 96.1 94.0 02.7 S1.G
__ 0G.S 94.G 03.4 81.0
On comparing the results of the first three columns of Table VI1 i t will be seen that the results in the third column are lower than those in the other two columns, especially a t the lower temperatures. That is the catalyst from the finest material was the poorest. Catalysts F210 and FllO gave practically the same results, the yields with Catalyst F210 averaging slightly higher although the difference is well within experimental error. These results show that a catalyst from
0.W . Brown avzd C.0.Hciake
750
a rather coarse material is the better although the difference is not large. The results of P210X compared with F210 show that oxidation and reduction decreased the yields somewhat, especially a t the lowest temperature, indicating that after oxidation and reduction its activity is not quite as high as it originally was.
TABLE VI11 Catalysts ignited in air at 300" C for one hour. Catalysts heated in hydrogen at 350' C for one hour. Mesh size-through 40 mesh. Rate of flow of hydrogen--14 liters per hour. Rate of flow of nitrobenzene-5.6 grams per hour. Excesslof hydrogen-360%.
I Temperature "C
294 294 275
556 237 394 312 331
F49 no.
I
F19 no'
Grams used 15.5
Grams used 15.5
Catalyst tube Glass
Catalyst tube Iron
94.2 96.1 94.9 92.7 81.6 99.0 99.4 98.3
53.1 54.2 57.2 90.1
91.6
.
87.2 85.0 79.3
All the foregoing exper-ments have Uden carried out w t 1 the catalyst in a glass combustion tube. I n Table VI11 are given comparative values for catalysts in glass and iron tubes. The two catalysts for Table VI11 were prepared exactly alike and used under the same conditions. The stannous hydroxide was ignited in a current of air a t 300" C for one hour. It was in the form of lumps in an open dish. After ignition it was ground to pass through a 40 mesh sieve. The results of Table VI11 are plotted in Figure 1. The average of the three results at 294" C for each catalyst is used
Catalytic Activity of Tin
751
in plotting the curves. The experiments of Table VI11 are given in the order in which they were carried out. It will be noted that this is first with decreasing temperature and then with increasing temperature. The curve with the catalyst in an iron tube is the opposite of that with the catalyst in a glass tube. Thus in an iron tube the highest yield was secured a t the lowest temperature while with the glass tube the lowest yield was secured a t this temperature. As the temperature was increased the yield with the catalyst in a glass tube increased while with the catalyst in an iron tube the yield decreased. We are unable to account for this difference in Fig. 1 behavior in iron and glass. I n the foregoing tables i t will be noted that each catalyst was first used in two experiments a t 294" C and then in one experiment a t 275", 256" and 237" C, respective1y.l Thiswas the method that was chosen as a means of studying a catalyst. The catalyst giving the highest yields of aniline has been called the best catalyst. Por convenience it has often been styled the most active. The results of the first two tables show that of all thetin catalysts studied, the one prepared from the stannous hydroxide was the best. All the catalysts in the succeeding tables were then prepared from this material which had been precipitated and dried as described in the first part of this paper. Table I11 showed that the best way to ignite the stannous hydroxide was by placing it, in the form of lumps, in an open dish and drawing a current of air through the muffle during ignition. All 1
above.
Catalysts F19 and F49 were usetfurther but were first used as outlined
752
0. W . Brown and C. 0. Henke
of the subsequently ignited catalysts were ignited in this way. In Table IV i t was found that temperature of ignition did not have, within the limits studied, a great importance. However, catalysts ignited at 150" and 300" C were slightly better than the other catalysts, the difference between these two catalysts being well within experimental error. The catalysts in the later tables were prepared from the oxide which had been ignited at 300" C by the method which gave the highest yields in Table 111. Table B showed that the lower the temperature of reduction the better the catalyst, although within rather wide limits the difference was not great. Prolonged ignition, according to Table VI is injurious. In the later tables the ignition period was in each case one hour. Catalyst F310 of Table V had likewise shown that prolonged heating in hydrogen at 350 O C was slightly injurious. So the catalysts in the later tables were heated in hydrogen for one hour. I n Table VI1 it was seen that a catalyst in the lump form was somewhat better than when in the powdered state. However all the other catalysts were put through a 40 mesh sieve. Table VI11 shows that a glass tube is better than an iron tube. I n all the tables except Table VI11 a glass tube was used. From these results the best tin catalyst is prepared by ignition of the stannous hydroxide a t 150" to 300" C for one hour and heating the resulting oxide in hydrogen at a low temperature (237" C) for one hour. The lump form is preferable to the powdered condition and a glass catalyst tube is iuperior to an iron one. I n the previous tables no thorough study has been made of the effect of temperature although all of the catalysts have been used at several different temperatures, which was the method chosen of studying a particular catalyst. The effect of temperature was now studied with a catalyst prepared and used under the best conditions as outlined in the latter part of the last paragraph, with the exception that the catalyst was powdered instead of in the lump form. The results are given in Table I X . Catalyst F211 was prepared from an oxide ignited a t 300 " C for one hour. Results under F211X are with this same catalyst after i t had been used in the experiments
753
Catalytic Activity of Tim
listed in the first column. The experiments are given in the order in which they were carried out. Catalyst F413 was prepared like F211 and shows how different catalysts used in different apparatus check. Results with Catalyst F111 are also given. This catalyst was not ignited.
Temperature "C
-1 337 256 275 294 311 330 350 368
Catalyst no. F211 Grams used 16
Catalyst no. F211X Grams used 16
Catalyst no. F413
Catalyst no. F1111
_ _ . -
Grams used 16
Grams used 15.5
Material yield of aniline in percent. of theory
90.9 90.4 98.6 98.3 98.6 98.3 97.5 90.2
90.9 95.3 96.8 94.6 96.. 1 9G.S 9G.4 87.5
73.9 92.0 97.5 98.6 97.5 07.9 97.5 95.7
71.3 93.s 04.9 95.7
--
-_
Catalyst F l l l was not ignited but was merely air dried.
The yields with the catalyst which was not ignited (F111) are much lower than with the other catalysts. This is in accord with the results.of Table IV although the order of carrying out the experiments was different. The results with Catalyst F413 (except at the highest and lowest temperatures) compare very well with the results with Catalyst p211. The results under F211X are lower than under F211. This would indicate that use at the higher temperatures decreased to a small extent the activity of the catalyst. The results with Catalyst F211 are shown graphically in curve Sn of Figure 2. It will be noted that high yields are
0. W . Bqowqz and C. 0. Henke
754
secured within a rather wide range o f ' temperature. This will be especially noted upon comparing this curve with the curves for nickel and copper which have been redrawn from the data of a previous paper.l These high yields within the wide range of temperature would be distinctly advantageous commercially as i t would not be necessary to control temperature within such narrow limits. The .best temperature for carrying out the reaction in a glass tube is probably 275" to 294" C. The effect of rates of flow of hydrogen and nitrobenzene was now studied. I n all the previous experiments except in Tables I and I1 the rate of flow of nitrobenzene was 5.6 grams Fig. 2 per hour and the rate of flow of hydrogen was 14 liters per hour. The results with different rates of flow of nitrobenzene and the flow of hydrogen at 14 TABLE X Catalysts ignited a t 300' C for one hour. Catalysts heated in hydrogen a t 237" C for one hour. Mesh size-through 40 mesh. C. Temperature of catalyst-294' Rate of flow' of hydrogen--14 liters per hour. Rate Of flow Of nitrobenzene in grams per hour
5.6 5.6 3.8 7.3 9.3 13.9 5.6 1
Excess of hydrogen in percent
Material yield of aniline in percent of ,theory
360 360 580 250 170 80 360
Brown and Henke: Jour. Phys. Chem., 26,161 (1922).
95.7 97.1 96.1 95.3 93.8 90.1 96.8
.
Catalytic Activity of Tin
e- r
I
aa
liters per hour are given in Table X. The catalyst for these experiments was prepared and used under the best conditions as previously determined with the exception that it was put through a 40-mesh sieve and not used in the lump form. It weighed 16 grams. The experiments are given in the table in the order in which they were carried out. The results of Table X are plotted in Curve Sn of Figure 3. The first experiment is not used as this is frequently irregular. It will be noted that the last experiment was carried out under the same conditions as the first two. It checks well with the second showing that the catalyst did not change appreciably during use. I n plotting, the average of the second and last experiments is used for that point. For purposes of comparison the curves for P ffl. nickel and copper (from the precipitated oxide) are reFig. 3 drawn from the data of a previous paper. Only a t one point is the curve for tin below that for copper and here the difference is within experimental error. In fact in most places the values for tin are above those for copper. Tin is likewise superior to nickel a t all but the highest rates while a t the lower rates the yields with tin are far superior to those for nickel. The effect of flow of hydrogen with the rate of flow of nitrobenzene a t 5.6 grams per hour is shown in Table XI. The catalyst for these experiments was prepared exactly like the catalyst for the experiments of Table X, 16 grams of catalyst being used.
* Brown and Henke:
Jour. Phys. Chem., 26,161,715 (1922).
0. W . Brown and C. 0. Henke
756
'
The results of Table XI are shown graphically i n c u r v e Sn of Figure 4. It will be noted that the last experiment was carried out under the same conditions as the first two. The average of the second and last experiments is used in plotting the curve, the first being, as usual, not considered. The curves for nickel and copper (from the precipitated oxide) are redrawn from the data of previous papers. The curve for tin has a different shape than the other two curves. Thus the decrease in yield with too much or too little hydrogen is more rapid However, the region within which high yields are secured is as wide or wider with tin than with the other catalysts. On comparing the curves for tin with those for copper and
TABLE XI Catalysts ignited in air a t 300' C for one hour. Catalysts heated in hydrogen at 237 for one hour. O
Mesh size-through 40 mesh. Temperature of catalysts 294" C. Rate of flow of nitrobenzene-5.6 grams per hour. Rate of flow of hydrogel in liters per hour
14 14 24 3s -cm 8 4.5 14
Excess of hydrogen in percent
Material yield of anilline in percent of theory
360 360 700 1160 1730 200 50 360
95.7 96.8 96.1 S1.G 73.9 97.5 93.s 97.9
Catalytic Activity of Tin
757
nickel (in Figures 2, 3 and 4) one is led to believe that for producing aniline a tin catalyst from stannous hydroxide would be better than one from precipitated copper oxide or ignited nickel oxide. Thus in Figure 2 the curves show that tin will give high yields over a wider range of temperature than either nickel or copper. As a result a tin catalyst would not necessitate such close temperature control as copper or nickel, which would be a distinct advantage commercially. I n Figure 3 the curves for tin and copper are very close together, both being higher than nickel except a t extremely high rates. I n Figure 4 tin and copper are again close together both being higher than nickel. But here again tin gives high yields over a little wider range in rate of hydrogen flow than copper. I n using tin as a catalyst quite frequently small amounts of a white solid was observed a t the exit end of the catalyst tube. Not enough of the material was secured to determine what it was. It was only slightly volatile as i t would condense in the catalyst tube before reaching the condenser. We never secured more than a small amount of it and do not know what conditions are the most favorable for its preparation. When ortho-nitro-toluene was used instead of nitrobenzene a 94.1% yield of ortho-toluidine was secured. The rate of flow of ortho-nitro-toluene was 5.6 grams per hour, and of the hydrogen '7 liters per hour. The temperature of the catalyst was 275" C. The catalyst had been prepared under the best conditions as determined above except i t was in the powdered form instead of in lumps. When ortho-nitro-anisole was used under the same conditions that the ortho-nitro-toluene was used, a 9370 yield of anisidine was secured. A few experiments were carried out in an iron tube with a catalyst of stannous hydroxide which had been dried a t 100" C. Twenty-three grams of catalyst was used which is about 50% more than was used in the previous experiments of this paper. This catalyst was heated in hydrogen a t 288" C for 11/2 hours and then used a t this temperature. The results are given in Table XII. The experiments are given in the order in which they were carried out.
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TABLE XI1 Rate of flow of hydrogen--14 liters per hour. Rate of flow of nitrobenzene--.$ grams per hour. Excess of hydrogen-640%. Tempoerature
C
287 269 264 245 227 215 196 232 25 1
I
Material yield of aniline in percent of theory
77.3 85.1
84.8 96.5 97.5 90.6 55.0 99.1 91.3
The results of Table XI1 are plotted in Curve X of Figure 1. It will be noted that this curve is similar to the Curve Fe. The highest yield on Curve X is at 232" C, while in Curve Fe the highest yield is at 237" C which was the lowest temperature used. The shape of Curve Fe indicates that a still lower temperature would have increased the yield but slightly if a t all. However, much higher yields are secured in Curve X ' t h a n i n Curve Fe. The higher yields cannot be due to the difference in the method of preparing the catalysts. Thus the catalyst for Curve Fe was ignited while the one for Curve X was not, which would make the catalyst of Curve Fe the better instead of the worse. The difference in reduction temperatures would not have much effect. However, 50% more catalyst was used for Curve X than for Curve Fe which probably is the cause for the higher yields of Curve X. Also the rate of flow of nitrobenzene was lower in Curve X than in Curve Fe. At 287" C, Curve X is lower than Curve Fe. The low yield at 287" C is due to the reduction being carried too far, the odor of ammonia being pronounced. These results show that the best temperature for the reaction with tin as catalyst in an iron tube is 232" to 237" C. Also a greater amount of catalyst in a given space (within the above limits) increased the yield of amine.
Catalytic Activity of Tin
759
Tin was then tried in furnaces of larger capacity and different design. Using a catalyst from 100 grams of the oxide in a vertical furnace (iron catalyst tube), 99% yields of aniline were secured at 232" C with the rate of flow of nitrobenzene a t 29 grams per hour, and the rate of flow of hydrogen at 10 liters per hour. I n this experiment excess of hydrogen was only 20%. Larger excesses of hydrogen gave similar high yields. After carrying out several experiments with nitrobenzene ortho-nitro-toluene was used. With the rate of flow of ortho-nitro-toluene at 20 grams per hour and that of the hydrogen at 14 liters per hour (40yo excess hydrogen) 98 to 09% yields of ortho-toluidine were secured with the catalyst a t 250' C. With the hydrogen flow at 23 liters per hour (130% excess hydrogen) similar high yields of ortho-toluidine were secured. This indicates that the process may have commercial possibilities.
Summary of Results
1. Tin has been shown to be an excellent catalyst for the reduction of nitrobenzene to aniline by hydrogen. 2. Of all the tin catalysts studied the one made from the hydroxide, prepared by precipitation with sodium carbonate from a stannous chloride solution, was the best. 3. Oxidation of the hydroxide, prior to reduction, increased the efficiency of the resulting catalyst, the lower the temperature of oxidation, within the limits studied, the better the resulting catalyst. 4. The lower the temperature of reduction of the oxide within the limits studied, the better the resulting catalyst. 5. A tin catalyst in the form of rather coarse lumps is better than in the powdered form. 6. The behavior of a catalyst in glass and iron catalyst tubes is very different, a higher temperature being necessary in glass than in iron. 7. A larger temperature variation is permissible with tin than with many other catalysts. Probably 2 i 5 " to 294" C
7 GO
0. W . Brown and C. 0. Henlze
is the best temperature for the production of aniline when a glass catalyst tube is used. 8. The best rates of flow of nitrobenzene and hydrogen with the tin catalyst compare rather closely with those for copper. 9. When ortho-nitro-toluene and ortho-nitro-anisole were used instead of nitrobenzene, 94.1 and 93% yields were secured of ortho-toluidine and ortho-anisidine, respectively. 10. Experiments carried out in apparatus of larger capacity and different design gave yields of 9970 aniline and 98 to 99% yields of ortho-toluidine, indicating that the process may have commercial possibilities. Laboratory of Physical Chemistry Indiana University Bloomiitgfon
