CATALYTIC ACTIVITY OF TITAKIA I N T H E REDGCTION O F NITROCOMPOUXDS BY G. ETZEL
Introduction The first systematic investigation of the problem of hydrogenation was made by Sabatier’ and his co-workers, principally Senderens and hiailhe at the close of the nineteenth century. Earlier investigators* however, had already shown the catalytic action of finely divided metals. The work done by Sabatier and his assistants practically opened the field of research in hydrogenation, showing its application to the industry. The catalysts used were nickel, cobalt, iron, copper, platinum, and palladium. He found that by using nickel and cobalt in the hydrogenation of nitrobenzene by hydrogen, aniline, cyclohexylamine, ammonia, benzene, cyclohexane, dicyclohexylamine, cyclohexylaniline, and diphenylamine were obtained. Sabatier made an extensive study of catalytic reduction of several types of organic compounds. A very complete and quantitative study on the reduction of nitrobenzene has been carried on since 1920 by 0. W. Brown and his co-workers, principally C. 0. Henke. The following catalysts were used: nickel, copper, silver, cobalt, iron, antimony, molybdenum oxide, manganese, chromium, vanadium oxide, uranium oxide, tungstic acid, cerium oxide, calcium oxide, barium oxide, tellurium, silica, alumina, lead, thallium, and bismuth. They showed that lead, bismuth, and thallium were the only catalysts to give high yields of azobenzene. The only case known by the writer in which titania was used as a catalyst on reduction of nitrobenzene, is that of a few preliminary experiments made by 0. W. Brown and Dr. F. A. Madenwald in this laboratory. Purpose of Investigation The purpose of this investigation was to make a thorough study of titania as a catalyst on the reduction of nitrobenzene. Conditions which were most favorable for the production of different compounds and their identification were sought. I n order to obtain the maximum activity of the cbtalysts, efforts were made to find the most efficient temperature of ignition of the catalyst, temperature of reduction of the catalyst, rate of flow of hydrogen, rate of flow of nitrobenzene, and the temperature of reduction of nitrobenzene. The length of life of the catalyst, action of asbestos as a support, and the action of traces of manganese were also studied. Sabatier: “Catalysis in Organic Chemistry,” 341-583 (1922). 1107 (1838);Debus: Ann., 128, zoo (1863);von Wilde: Ber., 7, 352 (1874).
* Kuhlmann: Compt. rend., 7,
CATALYTIC ACTIVITY O F TITANIA
853
Apparatus and Method of Procedure The apparatus as well as the method of procedure were the same as that followed by Brown and Henke.l The advantages of this apparatus are that it gives an accurate method of determining the temperature of the gaseous mixture while in contact with the catalyst, an easily regulated and accurately known rate of flow of nitrobenzene, and a means of quantitatively receiving the products. The rate a t which the hydrogen was passed into the furnace was measured by means of a flowmeter. A copper-constantan thermocouple was used to measure the temperature, and the voltage was read by a high resistance millivoltmeter. Material used I n order to purify the material used, it was shaken with sodium carbonate solution and then distilled with steam. The distillate was dried with calcium chloride and redistilled twice. The hydrogen used was commercial hydrogen. It was purified by passing over red-hot scrap copper, caustic soda, through concentrated sulfuric acid, and then through a U-tube containing glass wool. Estimation of Reduced Products The product in the condenser was washed into a one liter flask, containing 2 5 cc. of concentrated hydrochloric acid, and then diluted to the mark. A portion of it was analysed for aniline in the same manner employed by Henke and Brown.2 When azobenzene or hydrazobenzene was produced, it was filtered, dried and weighed. The method used by Sabatier and Senderens3 was followed to identify the cyclo compounds. Preparation of the Catalyst The catalyst was prepared by reducing titanium hydroxide in hydrogen. The titanium hydroxide was prepared by diluting I 50 cc. of a I 5 % solution of titanium trichloride to one liter. After the solution had reached the boil, an excess of ammonium hydroxide was added. The precipitated titanium hydroxide was then filtered] washed free from chloride, and dried at IOO'C. I n most cases 14 g. of the catalyst was used. It was reduced at 3 0 2 O C unless otherwise stated. The reduction was performed by passing hydrogen at the rate of 14liters per hour during a period of one hour. Effect of the Amount of Catalyst used I n order to determine the effects of different amounts of catalyst on the production of aniline, two furnaces were charged. One contained 6.8 g. of titanium hydroxide] and the other 14 g. The rate of flow of hydrogen, temperature of reduction, and all the other conditions were kept the same throughout a large number of experiments. It required about 16 experiments to obtain constant results, after which all the results were tabulated, as shown in Table I. The yields given are averages of from z to 4 experiments. Brown and Henke: J. Phys. Chem., 26, 161-190(1922). Henke and Brown: J. Phys. Chem., 26, 161-190(1922). Sabatier and Senderens: Ann. Chim. Phys., (S), 4,319 (1905).
854
G. ETZEL
TABLE I Temperature of reduction of catalyst-30z'C. Rate of flow of hydrogen-14 liters per hour. Hydrogen passed in per cent of theory-573. Rate of flow of nitrobenzene-4.05 g. per hour. Yields in
70 of amines calculated as aniline
Te,mp. C
Catalyst '4 g.
264 275 282 291 302
50.I
-
82.85 85.43 88.86 89.83
42.8 62.08 63.74 88.1
Catalyst 6.8 g.
Temp. "C
310 320 358 395
431
Catalyst I4 g.
84.31 75.98 60. I 28.9 11.8
Catalyst 6.8 g.
89.93
75.91
58.15 31.34
It is evident from the results obtained that a broader curve is secured by using larger amounts of catalyst. I n this manner higher yields are the result] a t a wider range of temperature. At a temperature ranging from 273 to 302' C high yields are obtained with 14 g. of catalyst] while with 6.8 g. of catalysts, the high yields lay between 302 and 31o'C showing a sudden drop when these limits are passed. Effect of Rate of Flow of Hydrogen on the Production of Aniline In studying the effect of the rate of flow of hydrogen, the best temperature for the production of aniline was selected] and the rate of flow of nitrobenzene, as well as all the other conditions, were kept constant. The results are given in Table 11. The percents are averages of two experiments.
TABLE I1 Weight of catalyst-14 g. Temperature of reduction of catalyst-3oz'C. Rate of flow of nitrobenzene-4.05 g. per hour. Temperature of reduction of nitrobenaene--~oa C. Flow of hydroegn liters per hour = A. Hydrogen passed in 7 0 of theory = B. Yields in of amines calculated as aniline = C. A
B
C
A
I4 18
537 737
89.49 88.30 86.70 80.56 82.97
7 5
43.3
901 I778
30
1229
22
B 2 86
C
4
204 163
83.90 77.84 48.75
I4
537
77.90
It is evident from the results shown here that the best yields of aniline are obtained with the rate of flow of hydrogen a t 14 liters per hour.
855
CATALYTIC ACTIVITY OF TITANIA
The Effect of Rate of Flow of Nitrobenzene on the Production of Aniline The catalyst used t o determine the best rate of flow of nitrobenzene was reduced at 302OC. The temperature was kept constant, while the rate of flow of hydrogen varies with the rate of flow of nitrobenzene, maintaining the same excess of hydrogen throughout the different experiments. Results are tabulated in Table 111. TABLE I11 Weight of catalyst-14 g. Temperature of reduction of the catalyst-3oz"C. Temperature of reduction of nitrobenzene-30~~C. Hydrogen passed in per cent of theory-573. Flow of hydrogen liters per hour = A. G. nitrobenzene per hour = G. Yields in yo of amines calculated as aniline = C. A
G
C
A
G
C
8.8 9.6
2.36 66.16 15. 4.37 19.5 26. 7.13 78.75 2.8 66.26 9.7 3.15 74.59 32. 9.4 76. I O 85.30 49. 14.2 63.45 14. 4.05 It is obvious from these results that the rate of flow of nitrobenzene which produced the best yield of aniline was from 2.08 g. to 4.05 g. per hour. The highest yield was secured with a rate of flow of 4.05 g. per hour.
Effect of Temperature of Ignition of Titanium Hydroxide on the Reduction of Nitrobenzene To determine the best temperature of ignition of the catalyst, three furnaces were charged, the first with titanium hydroxide dried at IOOOC., the second ignited at 245OC, and the third at 412'C.. All the conditions influencing the experiments were kept constant. The results became constant only after the sixteenth experiment, and those following this experiment are tabulated in Table IV. They are averages of from 2 to 4 experiments. The results show that higher yields of aniline are obtained with the catalyst which was not previously ignited. I n comparing the yields of aniline at any definite temperature a decrease is shown as the temperature of ignition increases. The only exception to this general rule was the temperature of 302'C, which gave a higher yield with the catalyst ignited at 245OC. The best yield was 93.570 aniline secured a t 282OC with the non-ignited catalyst. The catalyst ignited a t 415'C gave, a t temperatures of 245 and 266"C, traces of azobenzene and hydrazobenzene. At higher temperature such as 340 to 430°C considerable amounts of ammonia and cyclo-compounds were produced. The production of ammonia and cyclo-compounds, as well as azobenzene and hydrazobenzene, was noticeably less with the catalyst ignited a t 245OC. With the non-ignited catalyst no azobenzene and hydrazobenzene were produced. The production of ammonia and cyclo-compounds was also less with the non-ignited catalyst.
8j6
G . ETZEL
TABLE IV Weight of the catalyst-14 g. Temperature of reduction of the catalyst-30~"C. Rate of flow of nitrobenzene-4.05 g. per hour. Rate of flow of hydrogen-14 liters per hour. Hydrogen passed in per cent of theory-573. Temperature in degrees centigrade
Yields in % of amines calculated as aniline Catalyst not ignited
Catalyst ignited a t 245°C
226 245
264 282
302 3 40
360 395 43 0
75.86 84.54 91.40 93 ' 50 85.35 60.45 -
16.80 6.61
71.04 80.41 82.87
86.80 66.55 19.18 8.60 6.51
Catalyst ignited a t 4'5OC
60.4 79.50 78.03 82.21 52.94
38.38 14.88 3.30 I
.32
Effect of Temperature of Reduction on the Production of Amines The effect of temperature of reduction of the catalyst was studied. Four catalysts were reduced; the first a t 260, the second at 203, the third at 360, and the fourth at 41zOC.. The rate of flow of hydrogen was 14 liters per hour, allowing an excess of 634YGof hydrogen. The rate of flow of nitrobenzene was 4.05 g. per hour. The results obtained showed: (a) The best yield of aniline was 93.73% a t a temperature of 282'C, with the catalyst reduced a t 302OC. (b) The maximum yield with every catalyst was secured at z8z°C. (c) Catalysts reduced a t 360 and 412OC produced from 2 to 4y0 of azobenzene and hydrazobenzene a t 206OC, and traces of them a t z8z°C, while with catalysts reduced at 360 and 302OC no azobenzene or hydrazobenzene were produced. (d) With catalysts reduced a t 26ooC the amount of aniline produced a t 32oOC was 39.09% as compared to 64-8670 and 72.0870 which were the yields obtained by the catalysts reduced a t 360 and 41zoC respectively, although the amount of ammonia and cyclo-compounds was considerably higher in the case of the catalyst reduced at 260'C than with the ones reduced a t higher temperatures. (e) The aniline obtained with the catalyst reduced a t 260'C had a yellowish color, while with the other catalyst i t was cherry red. It is obvious from these results that the best temperature of reduction of the catalyst for the production of aniline is 3oz0C, while for the production of cyclo-compounds it is 26ooC.
857
CATALYTIC ACTIVITY O F TITAKIA
Durability of the Catalyst and the Effect of Continuous and Intermittent Feeding of Nitrobenzene A study was undertaken t o determine the length of life of the catalyst. For this purpose experiments were carried on for several weeks, discontinuing only a t night. I n the first 58 experiments nitrobenzene was fed intermittently, leaving only 2 5 minutes after each 2 cc. to allow the hydrogen to wash any product from the furnace. After the 58th experiment from 8 to I O cc. nitrobenzene was fed continuously each day for I I days. Intermittent feeding was then resorted to again. The results secured are given in the following table.
TABLE V Weight of the catalyst-14 g. Temperature of reduction of the catalyst-302~C. Temperature of reduction of nitrobenzene-302~C. Hydrogen passed in per cent of theory-573. Temperature in degrees centigrade = A. Rate of flow nitrobenzene g. per hour = G. Yields of amines in % calculated as aniline = C. Number of cc. nitrobenzene fed = D. Nitrobenzene fed intermittently A G C D
282
4.05
302 320
”
360 39s
lf
” ))
43 2
>)
282
’l
302 302 302 302 302
14.2
302
9.4
302
2.36
”
4.37 7.13 4.05
.
51.31 31.37
8
302
2
25.41 11.11
4 4
3.75
2
2.42
2
80.50 85.62 79.50 78.75 86.69 63.45 76.10 66.16
2
302 302 302 302 282 264 302
36 2 2
8
9.5 4.05 11
j1
”
3*0
11
395 43 2
1,
80.74
2
74 59
2
66.1
2
80.08
2
89.38 93.74 91.42 84.35 60.45 16.80
2
6.11
2
4
4
2
228 245
”
87.02 75.89
4
245
l’
82.05
l1
2
4 4 4 2 2
4
”
93.07
8
I’
85.55
IO
93.07 91.40 90.43
8 8
Sitrobenzene fed continuously during each day 282 4.05 88.02 4 7, 282 85.55 I4 282 ” 85.42 8 11 282 93‘07 2 11 282 90.43 8
8
282
94.64
8
” 11
,l
”
Nitrobenzene fed intermittently 4.05 90.69 8
282
4.37 2.8 2.36
11
2
Nitrobenzene fed continuously during each day 282 4.05 90.43 8
282 282 282 282 282 282
Sitrobenaene fed intermittently A G C D
l1
88.02
6
858
G. ETZEL
Results showed that a t the end of I 1 2 experiments, which were performed during a period of several weeks, the catalyst was still giving its maximum yield of aniline. There was practically no difference in the results obtained when nitrobenzene was fed continuously or intermittently. However, slightly higher results were secured when it was fed continuously. With every catalyst used, the first 16 experiments gave percent yields that were low and somewhat irregular. But it was found that by feeding nitrobenzene a t the temperature of q,o°C or by passing hydrogen a t the same temperature for one hour, the activity of the catalyst was increased for the production of aniline and was decreased for the production of ammonia and cyclo-compounds. The color of the aniline produced was in most experiments cherry red. But after passing nitrobenzene a t q,o°C the color changed for a few experiments to a light yellow, later returning to a cherry red when a low temperature waa used. This seems to indicate that the color is probably due to small traces of azobenzene in solution. By heating the catalyst to a high temperature the azobenzene in the furnace was entirely washed out. As the azobenzene was reformed slowly, the aniline turned red again.
Identification of Cyclo-compounds I n all the experiments performed it was noted that not only ammonia but also cyclo-compounds were being produced. I n order to identify cyclo-compounds a large vertical furnace containing 30 g. of reduced catalyst was set up. About 70 cc. of nitrobenzene was introduced into the furnace. The temperature was q,o°C while the other conditions were the same as those in previous experiments. The product obtained was dried over calcium chloride and submitted to fractional distillation. Three fractions were obtained: one boiling below I ~ o O C ,another boiling from 1 5 0 to 18o'C, and the other was the residue left in the distilling flask. The first two fractions were mixed and submitted again to fractional distillation. At a temperature of about IOOOC, white crystals were deposited i n the condenser tube. They were recrystallized and appeared to correspond to cyclohexylamine carbonate. The fraction which remained in the distilling flask was fractionally distilled under a 5 in. reduced pressure to avoid any decomposition of the compounds. Two fractions were secured; one boiling a t 19ooC, and the other was a residue which was solid. The residue corresponded to diphenylamine. The portion which was distilled under rogOC was redistilled a t atmospheric pressure. Most of the solution boiled a t 182'C, which is the boiling point of aniline. It is evident from this that cyclo-compounds are obtained, cyclohexylamine and diphenylamine being formed in large amounts.
Effect of Asbestos as a Support on the Titania Catalyst Tbe effect of asbestos as a support for titania was determined. The catalyst was prepared in the following manner. Clean asbestos was boiled with concentrated hydrochloric acid, washed free from chloride, and dried in an electric muffle. It was then soaked in a boiling solution of IOO cc. of 15% titanium
CATALYTIC ACTIVITY O F TITANIA
859
trichloride diluted to 500 cc., treated with ammonium hydroxide, filtered, and dried a t IOOOC. Since the weight of asbestos was known, from the total weight the percent of titanium hydroxide was calculated. The catalyst used contained j g. of asbestos and 7 g. of titanium hydroxide. It was reduced at 302OC and the rate of flow of hydrogen used was 14liters per hour, while the rate of flow of nitrobenzene was 4.05 g. per hour. The results obtained showed that there is no advantage in using asbestos as a support for the catalyst. The yields obtained were practically the same as those of the catalyst consisting of the same weight of titanium alone. Also the color of aniline was not improved. The average yields secured were: 79.79% a t 282OC, and 76.6% a t 32oOC. Although asbestos did not improve the yields, its presence did not reduce the activity.
Effect of Traces of Manganese on Titania The catalyst used to determine the effect of traces of manganese on titania was prepared by dissolving a calculated amount of manganese chloride in water mixed with IOO cc. of a 15% solution of titanium trichloride diluted to one liter and precipitated with ammonium hydroxide. The manganese and titanium precipitates were filtered and washed free from chloride, then dried a t room temperature. Fourteen grams of the catalyst was used. It contained 5% of manganese and 95% of titania, and was reduced a t 302OC. The rate of flow of hydrogen used was 14liters per hour, and the rate of flow of nitrobenzene 4.05 g. per hour. The best yields obtained were 89.96% a t 282'C., 8 2 . 3 ~ a7 t~246OC. The yields of aniline did not improve but the presence of manganese prevented the formation of azobenzene. The color of aniline was improved. At first it was light yellow, then it turned to a very light red, after having been used for several experiments. This problem was suggested by Prof. 0. W. Brown. I wish to thank him for his suggestions and interest throughout this investigation. Cpnclusion Titania was shown to be a very active catalyst of the nickel and cobalt type. It produced, on the reduction of nitrobenzene, the following compounds : aniline, azobenzene, hydrazobenzene, ammonia, and cyclo-compounds. 2. The catalyst used in this study was made from titanium hydroxide which was prepared by precipitation with ammonium hydroxide from a 157~ solution of titanium trichloride. 3. I n making a comparison of the weight of the catalyst on the reduction of nitrobenzene, i t was found that higher yields were obtained with 14g. catalyst than with 6.8 g. This shows that the yield of amines increases with the amount of catalyst. 4. The best temperature for carrying out reduction of nitrobenzene to aniline was about 2 8 2 O C . 5. The best yield of aniline was 94.4Yc or an average of 93.570 obtained a t about 282OC with catalyst reduced a t 3 0 2 O C . I
860
(3.
ETZEL
6. The most favorable temperature of ignition of titanium hydroxide for the reduction of nitrobenzene to aniline was IOOOC.Those ignited a t 302 and 412'C were the best for the production of azobenzene and hydrazobenzene. 7. The rate of flow of hydrogen which gave the highest yield of aniline was 14 liters per hour, with 14 g. of catalyst. A gradual drop occurred as the volume of hydrogen increased, and a more sudden drop when it decreased. 8. The rate of flow of nitrobenzene giving the best results with a 14 g. catalyst was found to be from 2 . 0 2 to 4.05 g. per hour, the best being 4.05 g. per hour. 9. Practically no difference was found in the yields of aniline when nitrobenzene was fed continuously or intermittently. IO. The activity of the catalyst was poor and gave results that were somewhat irregular up to the 16th experiment. After that it became constant. I I. After heating the reduced catalyst for one hour in hydrogen a t a temperature of 41ooC,or by passing nitrobenzene at that temperature for one or two experiments, its activity was increased for the production of aniline. I 2 . The temperature of reduction of the catalyst that was most successful was 302OC.. Although the catalyst reduced a t 260'c did not give maximum yields, they were high, and the color of aniline was improved. 13. The color of aniline produced was slightly yellow with the catalyst reduced a t 260°C, while with those reduced a t a higher temperature it was cherry red. I 4. Identification of cyclo-compounds showed the presence of cyclohexylamine and diphenylamine. 15. Although asbestos did not produce higher yields of aniline, its presence did not reduce the activity of the catalyst. 16. Traces of manganese did not improve the yields of aniline, but gave a product of better color. Labordory of Physical Chemistry, Indiana University, Bloomington.
