STUDIES I N CONTACT CATALYSIS BY CARL, J. ENGELDER
DECOMPOSITION OF ETHYL ALCOHOL Introduction A great deal of work has been done on catalysis in heterogeneous systems especially in regard to increasing the reaction velocity between gases by contact with solid catalytic agents. The phenomenon is called contact catalysis, and takes place at the surface of the oxide or finely divided metal. While catalytic action in both homogeneous and heterogeneous systems can be explained in many instances by the formation of intermediate compounds between the reacting substances and the catalyst, this theory does not explain all cases of increased reaction velocity. The catalytic decomposition of hydrogen peroxide is explained by Haber by the alternate oxidation and reduction of the metal according to the equations yHzOz Pt,Oy
+ X P t = Pt,Oy + yHzO + yH2Oz = X P t + yH2O +
~ 0 2 .
Yet the only case where the metallic oxide has been isolated is that of mercury, HgOz, and there seems to be no evidence for the existence of platinum oxides in this catalysis. Moreover, Wohlerl found that PtO and PtOz were actually less active than metallic platinum in the contact sulphuric acid process. The existence of a platinum hydride has not been definitely proven. We must therefore look to adsorption a t the interface for an explanation of increased reaction velocity. Since surface adsorption is a universal phenomenon and since gaseous reactions are catalyzed by the increased concentration of the reacting substances in the surface layer, it is natural to assume that all reactions may be catalyzed by the walls of the containing vessels. This has been shown by Bodenstein2 t o be Ber. deutsch. chem. Ges., 39, 3378 (1906); 42, 3326 (1909). Zeit. phys. Chem. (1go3-1go7).
Studies in Contact Catalysis
67 7
true in many cases. Van’t Hoff,l furthermore, showed t h a t the rate of polymerization of cyanic acid depended on the superficial area of the walls of the vessel. Bodenstein2 says that a “full explanation of all the phenomena [of heterogeneous catalysis of gas reactions] is given by the assumption that the further reaction process is retarded by the product of the reaction in those cases in which this product is more condensable and more easily adsorbed than the initial reacting substances themselves. There is, in fact, an adsorption layer, or in certain cases, an ordinary liquid or solid skin formed upon the catalyst through which the reacting substances must pass by diffusion in order to come into contact with the catalyst, where they react with practically instantaneous velocity. ” Bodenstein has overlooked the fact that the strong adsorption of the reaction products may be an important factor in causing the reaction to take place at all. If a substance may react in two ways, that reaction will predominate for which the reaction products are most strongly adsorbed by the catalytic agent. The theory of this has been explained in detail- b y Professor Bancroft3 and this paper furnishes experimental confirmation of it. There are two ways in which ethyl alcohol decomposes catalytically. The first is a dehydration, resulting in the production of ethylene. The second is one of dehydrogenation in which the alcohol breaks up into hydrogen and acetaldehyde. These reactions are represented by the following equations : CHsCH20H CH3CH20H
--+ HgO + CH2 : CHz + H2 + CHsCHO
Sabatier and Mailhe4 found that with thoria, Thoz, at a temperature of 340°-3j00 the ethylene reaction took place exclusively. Alumina, AlsO3, a t the same temperature acts practically as a dehydrating agent, the second reaction being almost negligible. With various other metallic oxides the two “$tudes,” 5 5 (1884). Zeit. phys. Chem., 60, 61 (1907). Jour. Phys. Chem., 21, 5 7 3 (1917). Sabatier and Mailhe: Ann. Chim. Phys., [ 8 ] 20, 289 (1910).
Carl J . Engelder
678
reactions take place side by side. Finely divided metals, on the other hand, such as Cu, Ni, Co and some oxides, of which manganous oxide, MnO, is best, yield almost pure hydrogen and aldehyde. This latter reaction is complicated by the fact that a t these temperatures the aldehyde is partially decomposed into methane and carbon monoxide. The catalysts studied by Sabatier and his co-workers have been arranged in a table, in the order of their function as dehydrating agents. TABLEI1 Oxide (prepared below 350')
IOO cc
Vol gas per mm.
%GH4
ThOz A1203
W203(blue) Cr203 Si02 Ti02
Be0 ZrOz
uoz
Mo205(blue)
Fez03
vzo3
ZnO MnOz SnO CdO MnaO4 MgO
cu
Ni
1
contain
% HZ
31 .o
100.0
traces
2 1 .o
98.5
57.0 4.2
98.5 91 . o 84.0 63 .o 45 .o 45 * o 24.0 23 . o 14.0 9.0
1.5 1.5 9.0 16.0 37 .o
0.9 7.0
.o .o 14.0 5.0 32 .o 14.0 6.0 3.5 45 .o I I
5 .o 0
0
traces
0 0 0
110.0
-
100.0 100.0 100.0 100.0 100.0 100.0 100.0
0
11.2 I 2 .o
55 .o 55 . O 76 .o 77.0 86.0 91 .o 95 .O
0
It was with the purpose of studying a displacement of the equilibrium in the catalytic decomposition of alcohol that the researches recorded in the following pages were undertaken. Alumina, as noted above, functions almost exclusively as a dehydrating catalyst. The question arises whether or not this Sabatier and Mailhe: Ann. Chim. Phys., [8]
20,
341 (1910).
Studies in Contact Catalysis
679
specific property can be influenced by the addition of water to the reacting vapor phase, and thus the amount of water actually adsorbed from the alcohol molecule be reduced, resulting in a corresponding lower yield of ethylene in the gaseous mixture. There would thus be a displacement of the equilibrium with a relative increase in velocity of the aldehyde reaction. Catalysts such as silica and titania, since they yield greater amounts of hydrogen, ought to show this effect more markedly. Frederiksen undertook a study of this problem using alumina as catalyst. His unpublished work shows that while the addition of water cut down the velocity it did not apparently alter the ethylene content. This, it was shown later, was due to the disturbing effect of aldehyde vapors, a difficulty which was later removed. Apparatus The general plan of procedure was to pass the heated vapors over the hot catalyst and to collect the resulting gaseous and liquid products in suitable collecting devices. A sketch of the apparatus used is shown in the accompanying diagram. The alcohol or aqueous solution was measured
from the burette A into the regulator B which served to keep the rate of flow uniform. Adjustment .could easily be
680
Carl J . Ewgelder
made by means of the capillary stopcock. The capillary tube from the regulator passed through the asbestos jacket C which was maintained at a constant temperature by means of the burner underneath. The heated vapors were led through the furnace, in which were placed two I O cm porcelain boats containing the powdered oxide. The furnace consisted of a nichrome-wound alundum tube surrounded by plumber’s packing and contained in a sheet iron shell. Fitting snugly within the alundum tube was a porcelain tube I . j cm in diameter and j o cm long. The temperature of the furnace could be well controlled by adjustment of the lamp bank resistance. A IOO volt current was used. Two large test tubes immersed in freezing mixture were inserted in the chain. One, TI, served to collect the liquid products of the decomposition and the other, TS, contained strong alkali to free the gases from aldehyde vapors. The sampling tube SIwas used when a continuous sample of the gas was desired. The gases passed on into the container E’ which was provided with a manometer, sampling capillary, Sz,outlet tube and separatory funnel for adding the confining liquid. Saturated salt solution, in which the gases are only slightly soluble, was used in the gas holder. The rate of evolution of the gas could be measured by measuring the volume of j liquid displaced in the bottle. Great care was taken to maintain conditions as uniform as possible. The rate of adding the vapors was regulated by the stopcock in the capillary. The furnace was heated for several hours before making a run to ensure constant temperature and temperatures were determined by a pyrometer inserted in the furnace. Current was read off the ammeter A. The catalysts, in general, were prepared by precipitating the hydroxide in dilute solution with ammonium hydroxide. The gelatinous or flocculent precipitates were washed thoroughly, filtered, dried over phosphorus pentoxide for about a day and then heated in an air oven to not over 2 50’.
Studies in Contact Catalysis
68 I
The dried solid was powdered in an agate mortar to a 2 0 0 mesh fineness. I n each experiment, about 0.5 g of the oxide was used in the two combustion boats.
Analysis of the Gas flixtures The methods used in analyzing the gas mixtures are here given. The sample, withdrawn either directly from the apparatus or from the gas container, was measured out in a water-jacketed Hempel burette containing mercury as the confining liquid. The various constituents contained in the mixtures mere determined as follows in the order given: I . C a h o n Dioxide-This was absorbed in I : I KOH contained in a Hempel single pipette. The pipette contained rolls of iron wire gauze t o give a greater absorption surface. 2 . Ethylene-In the earlier part of the work fuming sulphuric acid was used for determining ethylene. A threeminute passage of the gas back and forth through the acid, with a subsequent one-minute. contact in the KOH pipette to remove SOs fumes usually suficed for the absorption of all ethylene. Since, however, fuming sulphuric acid is known1 to absorb the paraffine hydrocarbons to some extent, a I percent bromine solution was substituted for the acid to remove the ethylene. Bromine fumes were removed with KOH as above. 3 . Oxygen-Alkaline pyrogallol prepared by the method of AndersonJ2i. e., dissolving 15 g of pyrogallol in IOO cc of a solution of potassium hydroxide of specific gravity I .55 , removed all the oxygen with one-minute shaking. 4. Carbon iWonoxide-The reagent for CO was ammoniacal cuprous chloride. This was made by adding 25 g of CuCl to IOO cc of strong KH40H to which had previously been added 20 g of IC'H4C1. After three-minute shaking in a double pipette, the ammonia fumes given off by the reagent were removed by passing the gas into a pipette containing 5 percent sulphuric acid. Anderson and Engelder: Jour. Ind. Eng. Chem., 6 , 989 (1914). Anderson: Ibid., 7, 587 (1915).
Carl J . Engelder
682
5 . Hydrogen-This gas was determined by fractional combustion over copper oxide heated to 2 5 0 ° - 2 7 0 0 C.I The contraction in volume gives directly the percentage of hydrogen. Before admitting the gas the air contained in the copper oxide tube must be displaced with nitrogen and a measured volume of nitrogen must be passed through the tube a t the end of the determination, to sweep out all the hydrocarbon residue for the subsequent analysis. 6. Methane and Ethane-These gases were burned with a measured volume of oxygen in a Dennis combustion pipette. From the contraction in the volume observed after the com- . bustion and the carbon dioxide formed, the percentages of methane and ethane, or methane and hydrogen can be calculated. The formulas for the former mixture are: 4C02- 2°C C2Hs = 3
COz - Z C Z H ~
CH4
and for hydrogen and methane:
Hz =
2
-
3
(TC-2202)
CHq = COz where TC represents the total contraction observed after combustion. Alumina as Catalyst Alumina was shown by Grigorieff2 and by Sabatier and Mailhe3 to be a very powerful dehydrating agent, its action upon ethyl alcohol yielding water and almost pure ethylene. The activity of the alumina depended greatly upon the conditions of its preparation; that made by precipitating the hydroxide from aluminum nitrate and drying a t 300’ C yields the best catalyst . I n the following experiments on A&O3 as catalyst, the oxide was prepared according to the above method. 50 g. of A1(N03)3were dissolved in 2 liters of hot, distilled water, the solution divided into 5 parts, each diluted to about one 1
2 3
Dennis: “Gas Analysis.” Grigorieff: Bull. SOC.chim. Paris, [ 3 ] 26, 612 (1902). Sabatier and Mailhe: Ann. Chim. Phys., [SI 20, 298 (1910).
Studies in Contact Catalysis
683
liter and I : I NH40H added to each portion until precipitation was complete. Washing by decantation six times, filtering and washing on the filter several times was considered sufficient to remove all salts. After drying over phosphorus pentoxide in a desiccator for 24 hours, the product was heated in an air oven a t 240' C for several hours. It was then ground to pass a zoo-mesh sieve. The catalyst prepared in this way proved to be a very good product. After several preliminary runs with alcohol, the oxide being heated to about jooo C, its action was studied in more detail in the following experiments. Two small combustion boats were filled with the oxide and placed in the furnace in each case. The temperature was indicated on a pyrometer inserted in the furnace. Readings of the volume of gas evolved and the cubic centimeters of alcohol admitted were made every I j minutes. In most cases the runs were of 2 hours' duration. In one experiment, however, made to determine the duration of activity of alumina, the time was extended over j hours; the catalyst showed a slight decrease in activity at the end of five hours probably due to agglomeration of the oxide particles. The table below is typical of the results obtained in these experiments. TABLEI1 Absolute alcohol over AlnOa Temperature of furnace = 490' C Readings taken every I j minutes
cc gas evolved cc total alcohol cc alcohol cc gas per cc alcohol cc gas per minute
960 2.8 2.8 342 64
cc gas evolved. cc total alcohol cc alcohol cc gas per cc alcohol cc gas per minute
1000
13.9 2.9 344 66
1000
IO10
I020
5.65 2.85 351 66
8.3 2.65 381 67
I1
920 16.5 2.6 354 61
1000
20.5 4.0 247 .66
910 23.2 2.65 343 60
.o
2.7 378 68
Carl J . Engelder
684
The gas from this experiment, calculated to an air-free basis, was 98.0 percent ethylene. The yield, obtained by reducing the gas volume to standard conditions and computing for C2H4,was 79 percent. The effect of water vapor in cutting down the rate of reaction is shown in the following table. The rate of evolution per cubic centimeter of alcohol, as well as per minute over one-hour intervals, is tabulated as shown. The rate of admitting alcohol was kept as uniform as possible, about IO cc alcohol from the regulator being added per hour. To maintain this alcohol rate for the aqueous mixtures the 50 percent solution has to be added twice as fast. That the resulting decrease in gaseous products did not occur as a result of increasing the rate of feeding was proven by a second experiment in which it was shown that the rate of admitting the alcohol did not materially affect the percentage yield. It is plausible in accordance with our theory of adsorption to account for the decreased activity on the basis of saturation of the contact surface with water vapor and hence a decreased power to take up more of the alcohol vapor.
TABLE I11 Hourly averages for A1203 Temperature of furnace 490' C ~~
First hour Experiment
Total gas
I-Absolute alcohol a-Absolute alcohol 3- 50% alcohol 4-jo7~ alcohol
1
4210 3817 2490 3000
Total alcohol
Gas per
412 383
10.2
9.95 ,
I
Gas per
"&@minute
11.2 11.1
70.1 63.6 41.5
222
Second hour I
I-Absolute alcohol a-Absolute alcohol 3-j0y0 alcohol 4-507~ alcohol
I
I
I
98.2 98.4 97.5 97.6
Studies in Coztact Catalysis
685
The yields of ethylene, at different temperatures, for both absolute and aqueous alcohol, are herewith tabulated. The higher the temperature the greater the amount of decomposition. TABLE IV Decomposition by alcohol by A1203 Absolute alcohol Sample
AI
Temperature Duration of run Total gas evolved Total alcohol used cc gas per cc alcohol Percentage decomposition
BI
A2
Ba
B2
380 15 min. 900
420 490 490 490 2 hrs. 2 hrs. 2 hrs. I j min. 8197 7812 7820 1 2 5 0 8.5 1 9 . 7 2 0 . I 19.8 426 388
94.5
11.5
78.2 81
78 Aqueous solution
Sample A3
I
1
\
Temperature Duration of run Total gas evolved Total alcohol used cc gas per cc alcohol Percentage decomposition
490 490 2 hrs. 2 hrs. 4675 5330 1 8 . 8 17.6 302 248 69 56
490 420 380 2 hrs. 15 min. 11 min. 5650 310 350 21.05 25.9 9.0 12.0 38.8 268 61
2.7
8.9
The values, except for the aqueous run at 380' C, are consistent and show clearly the effect of water on the decomposition. In studying the effect of the addition of water on the displacement of the equilibrium considerable difficulty was experienced, since the ethylene yield is so high that a relative increase in hydrogen, the other gaseous product, does not change the percentage composition of the gas mixture to any great extent, and the small residue of hydrogen is hard to determine accurately. After absorbing ethylene in I percent bromine water with subsequent removal of bromine vapors by KOH, the hydrogen was determined by combustion with
686
Carl J . Engelder
oxygen over mercury in a combustion pipette. Two sets of experiments, performed a t 380" C and 420' C, respectively, are tabulated in the following table. "cc solution" denotes the total volume of liquid added during the run, whether absolute alcohol or the aqueous mixture. The condensate ' collected in the cooled receiver showed more aldehyde in the case of the aqueous solutions. TABLE V Displacement of equilibrium with A1203
Temperature of run Duration of run in minutes cc gas evolved cc solution cc alcohol cc condensate collected cc gas per cc alcohol cc gas per minute cc absorbed in bromine cc absorbed pyrogallol cc hydrogen by combustion % C2H4
% Hz
Absolute --
Aqueous
--
Absolute -___
Aqueous
380'
310 j I .8
380' I5 900 11.5
25.9
I1.j
I47
33.0 20.6
78.2
83.3
I2
97.2
93 ' 2
420'
420'
I5
I5
1250 8.5 8.5 5 .o
.o
0.2
0.9
2.4
2.25
97.5 2.5
95.4 4.6
7.0 60.0 98 .o
I1
350
18.0 9.0 15.0
38.8 31.8
92.4
0. I I.2
I,. 2 2.1
98.7
97.7
1.3
2.3
The percentage of hydrogen is almost doubled when 50 percent alcohol is used, showing that the aldehyde reaction is greatly increased and the ethylene-water production cut down correspondingly. . Silica as Catalyst Silica as a catalytic agent in the decomposition of alcohol shows extremely variable results depending upon the origin. Sabatier and Mailhel found that finely powdered quartz as well as silica obtained from the decomposition of silicon fluoride, showed no appreciable action, whereas SiOz prepared from sodium silicate and hydrochloric acid exerted a mixed function upon primary alcohols, yielding, for ethyl alcohol, a t 380" C, a gas mixture which contained 84 percent ethylene and 16 percent hydrogen.
Studies in Contact Catalysis
-
Time in minutes
I5 30 45 60 75 90 105 I20
I35 150 165 I80
cc gas evolved
65
55 68 57 54 57 58 57 57.5 64.5 54 55.5
1
cc alcohol
used
14.5 7.6
8.7 8.9 8.4 9.6 8.6 9.8 9.2 8.9 8.I 8.8
687
cc gas per cc alcohol
cc gas per
4.5
4.3 3.7
minute
7.2 7.8
4.5
6.4 6.4 5.9 6.7 5.8 6.2 7.2 6.6 6.3
3.8 3.6 3.8 3.9 3.8 3.8 4.3 3.6 3.7
Carl J . Exgelder
688
First hour
cc gas evolved cc solution added cc alcohol added cc gas per cc alcohol cc gas per minute
75 9.7
30 11.0
5.5 145'.86 5
6.0 2
28 9.7 4.8 5.8 1.9
34 9.3 4.6 7.4 2.3
Second hour
cc gas evolved cc solution added cc alcohol added cc gas per cc alcohol cc gas per minute
* Ann.
I
I
I2
13.7 48 6.8 7.1 3.2
Chim. Phys., [ 8 ] 20, 334
(1910).
11.3 5.6 2.1
0.8
34 8.5 4.2 8.1 2.3
I
28 8.9 4.4 6.4 1.9
Studies in Cofitact Catalysis
689
minute of gas which contained 45 percent ethylene and 5 5 percent hydrogen, Experiments were undertaken in connection with t h e present work to show a shifting of the equilibrium similar to that found with alumina and silica. A sample of impure zirconium ore, finely ground, was first tried with no results. The same was true for ZrOz precipitated from the nitrate. A product, however, obtained by calcining the nitrate at a low heat, gave good results as shown in the table below. TABLE VI11 Displacement of equilibrium with ZrOz -
Absolute alcohol
Temperature Duration of run cc solution added cc alcohol cc gas evolved
con
CZH4
co
Hz CH* CzHR
380' C 25 min. 24.2 24.2 3 00
4% 63.6
507"alcohol 380'
0%
42.5
2.1
0.0
31.5 2.8
49.0 8.5
0
c
25 min. 46.4 23.2 186
0
The decrease in the percentage of ethylene as well as the increase in hydrogen shows, beyond question, that the first reaction is cut down and the second one accelerated by using aqueous alcohol. Titania as Catalyst Titania obtained by the dehydration of Ti(OH), was found by Sabatier to be a very good catalyst in the decomposition of alcohol. At 320' C he found that ethyl alcohol is decomposed into almost pure ethylene. At higher temperatures, 360" C, the evolution of gas is more rapid, when both reactions set in, the composition of the gas being 64 percent C2H4and 36 percent Hz. A t 400' C the evolution is in the neighborhood of 31 cc per minute, and contains the two gases in the same proportion as above.
Carl J . Efigelder
690
Considerable experimental work was done with Ti02 which
. will be described in the following pages. The results in most cases are at variance with those obtained by Sabatier and will be discussed in order. The first sample of TiOz, Sample A, was obtained by calcining the sulphate Ti(SO& directly in the furnace. After the evolution of SOB had ceased, a run was made a t 490' C with absolute alcohol. The evolution of gas was quite rapid. It had a very pungent, disagreeable odor and filled the receiving bottle with white fumes. The odor was that of mercaptan. The formation of mercaptan from alcohol was studied by Sabatierl who found that when H2S was led into the reacting chamber with alcohols in the presence of T h o z , ZrOz, Cr203 and other metallic oxides, high yields of mercaptan were obtained. I n the above experiment the hydrogen reduced the SOs, which was not entirely driven out, to HZS, and this in presence of TiOz reacted to form C2H5SH. The data for this run, which is typical of results obtained in further experiments, are given herewith. TABLE
Time in minutes
15 30 45
I __
i
Ix ..__
ccgas evolved
cc alcohol added
cc gas per minute
__-_____-
49
25 24
60
22
75
I9
90 105
I5
I20
15
I5
There is a gradual fall,,ig off in the gas evc,dtion with time, due to changes in the surface of the contact material. The gas contained 6 1 . 4 percent absorbable in H2SzO7. No analysis was made of the unabsorbable residue. Sabatier: "Die Katalyse in der organischen Chemie," 179-181
Studies in Contact Catalysis
691
A second sample of TiOz was prepared by dissolving 5 g of Ti(S04)2 in strong HzS04, diluting to 2 liters and adding enough strong NH40Hto precipitate the titanium as Ti(OH)4. The flocculent precipitate was washed 8 times by decantation, filtered, washed, dried over PzOj and then heated in an air oven a t about 150' C for two hours. This product was designated as B. In the following series of experiments the procedure was the same in all runs. Several hours of preliminary heating were allowed to ensure thermal equilibrium of the furnace, the temperature being read off the pyrometer and controlled with the lamp bank resistance. The reaction was allowed t o proceed long enough to sweep all air out of the apparatus before actual readings were taken. Runs with absolute, 50 percent, and 25 percent alcohol were made. The results are given in the accompanying table. The temperature was maintained at 490' C. TABLE X Sample
Total gas evolved Total alcohol cc gas per cc alcohol cc gas per minute cc ethylene cc oxygen "/c CzH4 6& unabsorhable
1 AbsPte
Absolute
Bz
2813 24.5 114 23.4 81.9
3265 32.8 99 27.2
86.2
'430 35.6 40. I 11.9 64.2
0.2
0.2
0 .j
82.7 '7.3
87.0 13 . o
66.9 33.1
The data are averaged over two-hour intervals. Readings taken in the original experiments every 1 5 minutes show the rate of decomposition to slowly and gradually decrease with time. The olefine was absorbed in HzSz07 and the oxygen of the air with which the gases were always slightly contaminated by alkaline pyrogallol. The unabsorbable residue consists chiefly of hydrogen, but contains also ethane and small amounts of methane and carbon monoxide. The percentages are calculated to an air-free basis.
Carl J . Engelder
692
The duplicates for the several runs, i t will be noted, agree quite closely. In order to bring out the effect of adding water more strikingly the following table is given in which the average is taken. TABLE XI Runs
Absolute
cc gas evolved cc solution added cc alcohol used cc gas per cc alcohol cc gas per minute
3039 28.65 28.65 I07 , 4 25.3 84.8 15.1
% CZH4 % unabsorbable
50
70
I324
77.0 38.5 34.6
I1 .o
65.9 34.0
644 126.28 31.57 26.0 5.3 48.4 51.6
By inspection of the above table it will be seen clearly that the addition of water has a great effect upon the decomposition of the alcohol. Not only is the rate of evolution cut down greatly but the amount of decomposition, or the yield of gas per cc alcohol is reduced. The greater change, however, occurs in the composition of the gas. While IOO percent alcohol gives a gas, 84.8 percent of which is absorbable in fuming sulphuric, the 50 percent water mixture yields 65.9 percent C2H4and the 2 5 percent aqueous solution 48.4 percent C2H4. There is a corresponding increase in the unabsorbable residue, which consists, not only of Hz but also CzHs and small amounts of CH4and CO. Further experiments were undertaken on the displacement of the equilibrium with TiOz. A sample of TiOz, prepared by precipitating the hydroxide from TiC14 instead of Ti (S04)2and subsequent washing, filtering and drying yielded, a t 380' C, a gas which contained as an average of several runs 59 percent CzH4. Complete analyses were made of the gas given off in several runs with absolute and aqueous alcohol. The presence of ethane was not suspected until the gaseous residue after absorbing ethylene, oxygen, carbon monoxide and removing the hydrogen by combustion over CuO showed,
Studies in Contact Catalysis
693
upon combustion, large amounts of carbon dioxide. Applying the combustion equation for C2H6 and CH4, obtained by computing from the contraction observed and the carbon dioxide formed, it was found that the reaction between CzH4 and H2 is greatly catalyzed by TiOz at the temperature of the experiment, yielding varying amounts of C2HC. The amounts of CH, formed were always small and corresponded in most cases to the CO present, both the gases re sulting from the breaking down of the aldehyde formed along with the hydrogen. Higher percentages of methane than those corresponding to CO can be accounted for on the basis of the reaction between carbon monoxide and Hz, CO
+ 3Hz
=
CH,
+ HzO,
which reaction takes place to some extent. The formation of CzHs complicated the reaction to some extent, and in order to ascertain the total ethylene and hydrogen formed, a calculation must be made to obtain the ratio between CzH4 and Hz. Carbon monoxide occurs in very small quantities, so that a recalculation can be made on a carbon monoxide-methane as well as air-free basis. Since each volume of ethane represents one volume of ethylene and one of hydrogen, the total amount of CzH4 formed will be given by the sum of C2H4and C2H6. Similarly, Hz originally formed equals Hz actually present plus the volume of C2H6 determined. Upon this basis then the ratios are found, as shown in the table. Similar sets of values were obtained from a sample of TiOz (E) made from the sulphate. Both sets are shown below. The ratio of ethylene to hydrogen agrees well in both sets, being greater for absolute than for aqueous alcohol. The two runs with absolute alcohol agree within the experimental limit even though the sample of catalyst is of different source, but in the case of the aqueous mixtures the ethane formation has taken place to a much greater extent with Sample E than with Sample D. In fact, the secondary re-
Carl J . Evtgelder
694
TABLE XI1 Displacement of equilibrium with Ti02 Temperature 380' Experiment
1
Absolute (Dr)
j4 0
1
I
::; 1,
36.0
50% (DJ
49.2 0.6 30. I 1.6 16.4
I
Absolute
(El)'
50%
-
55 2.7 8.1 4.0 30.2
(Ed
31 0.0
5.3 0
63.6 31 .o 5.3 63.6
action leading to the formation of ethane is quite variable and a hard one to control. The ethane content may vary from nothing up to about 65 percent of the gas mixture, the average of a large number of runs being about 25 percent. The presence of ethane was not suspected a t first and the disturbing factor in the gas analytical results led to considerable investigation as to the cause, vapors of aldehyde, ether and alcohol having been in turn studied. It was found that none of these vapors were present in sufficient amounts to cause any trouble. The rate of withdrawing the gases f;om the reacting tube and the temperature are the main factors influencing this reaction. In this connection it was of interest to know the behavior of mixtures of hydrogen and ethylene when passed over catalysts a t the temperature of the experiments cited above. The following experiment was performed. Ethylene and Hydrogen over TiOz A mixture of ethylene and hydrogen] analyzing 43 percent C2H4,was passed from an eight-liter bottle, provided with suitable inlet, manometer, syphon and outlet tubes, through the furnace over a layer of the catalyst. Care was taken t o adjust the rate of flow uniformly, and to keep the pressures
Stzldies in Contact Catalysis
695
equal in the delivery and receiving containers. In each run about I liter of the gas mixture was passed through. The air in the apparatus was displaced before readings were taken. Data from one run are here shown.
Duration of run cc gas passed over cc gas collected 70ethylene before
I hr. 1000 IOOj
43.0
The result shows that only slight reaction has taken place. From this we can conclude that these gases are only reactive when in the nascent state. Ethylene over TiOz It was thought desirable to study the stability of ethylene, alone and also in presence of the catalytic agents, under the conditions of the experiment. The ethylene was made by the dehydration of alcohol over A1203, and was confined over saturated salt solution. The apparatus described in the preceding section was employed. The experiment was first tried without a catalyst. The temperature was 500' C. The run extended over one and a half hours and I liter of the gas was passed through. Data are shown below.
TABLE XIV Temperature of furnace cc gas passed through cc gas collected Duration of run 70ethylene before % ethylene after
500'
C
1000
I002 I hrs.
98.9 98.5
At temperatures, therefore, below 500°, ethylene is not decomposed appreciably under the conditions of the experiment, without a catalytic agent. This substantiates the work of I,ewes,l who found that decomposition did not begin -
-
.
~
I
-
Proc. Roy. S O ~ .5,5 , 90 (1894).
Carl J . Engelder
696
below 600'. Norton and Noyesl found decomposition t o take place at a dull redness, the products being benzene, naphthalene, methylene, propylene and butylene, divinyl (CH2 = CH - CH = CH2) and CH, and CzH6. According t o Day,* the change to methane and ethane takes place only after I 7 I hours of continuous heating to 400 O C. That ethylene is not decomposed over alumina is shown by previous experiments. Two runs were made with TiOz as catalyst a t a temperature of 490 '. The data follow :
TABLE XV 1
Duration of run cc gas passed through cc gas collected yoethylene before Yo ethylene after yodecomposition
68 min. I000
I049 98.8 90.9 7.9
TiOz catalyzes the decomposition to a small extent. There is a corresponding volume increase, which can be accounted for on the basis of the following equation: z C ~ H= ~CHa
+ z H +~ 3C
The gas residue after absorption of the ethylene on combustion in the pipette showed methane and hydrogen. The catalyst is always found covered with a black deposit of free carbon. M'hile, therefore, this catalyst does exert some decomposing action on the pure ethylene it is not of appreciable extent. Displacement of Equilibi*ium with Hydrogen Thus lar the experiments on the displacement of the equilibrium with A1203,Sios, Zr02 and TiOs dealt with the reversing of the ethylene-water reaction, and it was shown t h a t the addition of water to the alcohol did cut down this Am. Chem. Jour., 8, 362 (1886) Ibid., 8, 153 (1886).
Studies in Contact Catalysis
697
reaction and that in consequence the hydrogen-aldehyde reaction was relatively increased. It was thought possible to reverse the hydrogen-aldehyde reaction by adding hydrogen to the reacting vapor. A two-holed rubber stopper was used in place of the single-holed stopper a t the inlet to the furnace tube, through one hole of which the capillary from the hydrogen container passed and through the other the tube holding the alcohol vapor. Four experiments were made with "io2, the conditions being kept as nearly uniform as possible. To get comparable data two runs were made with alcohol alone and two with hydrogen-alcohol mixtures. In computing the percentages of C2H4and H2 due allowance was, of course, made for the hydrogen added in order to get the actual amount formed in the decomposition.
TABLE XVI Displacement of the hydrogen-aldehyde reaction
I
cc alcohol added cc hydrogen added cc gas collected 7G ethylene formed % hydrogen formed Average Average
33.7
I1
38. I
I11
13.6 j 00 I 240
54.1 45.9
IV
13.6 500 1260 51.8 48.2
% C2W4 70 Hz
It is thus seen that whereas the hydrogen normally runs 53.9 percent with this sample of catalyst (C), the addition of free hydrogen to the alcohol vapors has the effect of reducing the amount formed to 47.0 percent. The equilibrium of the hydrogen-aldehyde reaction is thus displaced. This can be explained, as in the case of the displacement with water, by an approaching saturation of the surface of the catalyst with respect to hydrogen.
Carl J . Engelder
698
,
Aldehyde over TiOz
coz CZH4 co
9.6% 38.0
C2H6 CH4
3.6
22
.o
26.4
At temperatures about 400' C there is little decomposition of aldehyde. Out of 15 cc of aldehyde passed through the tube 14.5 cc were recovered unaltered in the condenser. Very little gas was given off. A sample of this, recalculated on an air-free basis, showed 57.4 percent CH, and 42.6 percent CO and no ethylene or ethane. Thus, while a t 520' the decomposition is complete and secondary reactions set in, a t 400 O the decomposition is slight and takes place practically in accordance with the equation CH3CHO
=
CH4
+ CO.
I n the presence of TiOz at the same temperature, 400°, the decomposition is likewise very slow. The gaseous products consist of equal parts of methane and carbon monoxide. That very little action is exerted by this catalyst can further be concluded from the previous work on alcohol where it was found that the percentages of CO and CH, resulting from CH3CH0 did not exceed 6.7 percent in any experiment. Ether over TiO, and Al2O3 Ether passed over AlZO3at about 380' C decomposes quantitatively into ethylene and water, in accordance with the following equation :
Studies in Contact Catalysis
+
CH3- cHz>
699
= 2CH2.CHz HzO CH3 - CH, 6 cc of ether yielded 2 2 8 0 cc gas which analyzed 98.6 percent ethylene, the remainder being air. With TiOz there is a slow dehydrating action and practically all the ether is recovered in the condenser. No aldehyde or hydrogen forms. The dehydrating action of alumina on ether is similar to that on alcohol. I n fact, ether is doubtless the intermediate product formed in the dehydration of alcohol. As shown below, a t 2 1 0 ° , ether is obtained from alcohol by dehydration with A1203. Alcohol may be considered to combine with elimination of water thus. CHs.CH2.0H CH3.CHz + HzO. CH3.CH2.0H CH3.CH2 Aldehyde results only from direct dehydrogenation of alcohol. The dehydration of alcohol by means of HzS04is the well-known method for making ether and is a classic example of catalytic acti0n.l If the temperature is allowed to reach I 60 ' 1 70 ', the ethyl sulphuric acid formed as intermediate compound will break up into ethylene and sulphuric acid. CH3.CHz.O.SO3H + HzS04 CH, = CH2 Alumina, like HzS04,will act on alcohol yielding ether or ethylene depending upon the temperature. At a temperature of about 2 1 0 ' C, 30 cc of alcohol were passed through the hot tube over A1203. Practically all the liquid was recovered in the condenser and this, subjected to fractional distillation, yielded about 7 5 percent ether. This is in accordance with the experiments of Senderens. Niekel as Catalyst The catalytic action of finely divided metals, especially platinum, nickel, cobalt and copper, is well known and the decomposition of alcohols, ketones, aldehydes, etc., in presence of these metals has been investigated by Sabatier and others.
>+
+
Williamson: Ann. Chim. Phys., [3]40, 98 (1854). Senderens: Ibid., [SI 25,449 (1912).
700
Temperature of furnace Duration of run Gas evolved Alcohol used Condensate
Carl J . Engelder
380' C
15 min. 950 cc 1.4 cc Kone
Composition of gas mixture
coz
= 3.870 C2H4 = o = 3.8 Hz = 12.6 CH4 = 79.8 CzHs- = o
co
Studies in Contact Catalysis
701
A third reaction may also occur between some of the carbon dioxide formed above and the hydrogen: COz
+ 4Hz = z H ~ O+ CH4
This reaction is likewise facilitated by nickel and goes on readily below 400' C. These reactions between the gases account for the high percentage of methane and corresponding lower values for Hz and CO. Niekel and Alumina as Catalyst Since metallic nickel functions as a dehydrogenating catalyst and A&O3 as a dehydrating agent, it was thought desirable to try mixtures of the two catalysts and thus study the combined effect of the two. The following experiment was performed with this object in view. Equal parts by weight of Al(NO& and Ni(N03), were dissolved in distilled water and enough I : I NH40H added to precipitate both salts as the hydroxides. The gelatinous mass was then washed, filtered, dried, and ground to 2 0 0 mesh. Reduction of the nickel to the pulverulent state was accomplished in a stream of hydrogen as before. A run with alcohol was made keeping conditions as uniform as possible. The data are shown in the table. TABLEXIX Temperature of furnace Duration of run Gas evolved Alcohol used up
380' C
min. 3 j o cc 0 . 5 cc IO
Composition of gas mixture
CO,
=
0
CzHs
=
0.6
Hz CH4
= 1.8 = 13.4 = 84.2 = 0
co
CzHs
The evolved gas does not differ much in composition from that obtained with nickel alone. It is known that nickel catalyzes the reaction a t much lower temperatures than does alumina and the above result bears out this observation. All the alcohol is broken up by the nickel before the less active alumina has a chance to function. As a modification of the above, another experiment was performed in which the catalyst consisted of a mechanical
Carl J . Engelder
702
mixture of powdered alumina and reduced nickel. From the results obtained, A1203in this form seems to be more active and exerts a retarding effect upon the secondary reactions taking place. Some ethylene and ethane were formed and the CO and Hz have partially resisted transformation. The data for this experiment are shown in Col. 3 of the summarized table. TABLE XX ~
Summary for nickel Gas
Reduced nickel
3.8 0.0
3.8 12.6 79.8
Precipitated mixture
A1203
+ Ni
0
0.6 1.8 13.4 84.2
0
0
Mechanical mixture
AlzOs
+ Ni
1.4 2.0
29.0 29.0 35.2 3.4
The action of nickel is so much greater than alumina that it masks the latter’s action almost entirely, yet the mechanical mixture is more effective as a dehydrant than the chemically precipitated mixture.
Conelusions The following conclusions can be drawn from this work: I . It has been shown that in the catalytic decomposition of alcohol the water-ethylene equilibrium can be displaced with A1203,Sios, Zr02, and TiO, as catalysts by adding water vapor to the system. 2 . The hydrogen-aldehyde equilibrium can be displaced with Ti02 as catalytic agent by adding hydrogen to the system. 3. The presence of water vapor furthermore greatly decreases the rate of decomposition, as shown by the decreased gas evolution for the aqueous mixtures; this applies to the volume of gas per cc of alcohol as well as the volume of gas per minute.
Studies in Contact Catalysis
703
4. The rate of decomposition increases with rise in temperature. With A1203a t 380" C the rate is 78.2 cc gas per minute while a t 490' C it is 426 for absolute alcohol. The corresponding percentage decomposition is I 8 percent a t 380" C and 94.5 percent a t 490' C. 5. Alumina prepared from A1(N03)3 retains its activity indefinitely, its action after five hours' use being only slightly reduced. 6. When equal volumes of alcohol and water vapor are passed over A1203,the amount of hydrogen formed is almost double that formed from the absolute alcohol. 7. Silica is a poor catalyst for the decomposition of alcohol. At 490" it yields 4 cc gas per minute. 8. It was found possible t o reduce the ethylene content from 84.2 percent to 68.6 percent by adding water to the alcohol over SiOz. 9. Zirconia, obtained by calcining the nitrate, is an active catalyst. With absolute alcohol it yields a gas containing 63.6 percent C2H4 and 3.5 percent Hz. With aqueous alcohol mixtures the composition changes to 42.5 percent C2H4and 49.0 percent Hz. IO. The decomposition of alcohol over TiOz has been studied in detail. The activity decreases with time and increases with temperature rise. 11. The displacement of the equilibrium by the addition of water is marked with this catalyst. 12. When hydrogen is mixed with the alcohol vapors and passed over Ti02, the amount of hydrogen formed decreases from 53.9 percent to 47.0 percent. 13. Ethane forms from ethylene and hydrogen when alcohol is decomposed over Ti02. 14. The decomposition of aldehyde into methane and carbon monoxide does not take place to any great extent with TiOz. 15. Ethyl ether results from the dehydration of ethyl alcohol with Al2O3at 210" C. 16. Finely divided nickel decomposes alcohol into hy-
Carl J . Engelder
704
drogen and aldehyde. Acetaldehyde is easily broken up by this catalyst into CH4 and CO and the reaction between Hz and CO accounts for the high values for CH4 obtained in the experiments. The author takes this opportunity of expressing his appreciation and thanks to Professor Wilder D. Bancroft under whose cheerful guidance this work was carried out. Cornell University i.
