T H E CATALYTIC DEHYDRATION OF ALCOHOLS1 BY A . B. BROWN AND E. EMMET REID
It has long been known that alcohols undergo thermal decomposition in two waysz: RCHzCHZOH-RCH :CH2+Hz0 RCH2CHzOH+RCH2CHO Hz Both of these reactions are greatly accelerated by catalysts as has been shown in comprehensive studies by Sabatier and Senderens3 and Sabatier and Mailhe4. Sabatier5 divides the catalysts into 3 classes : ( I ) dehydrating, ( 2 ) mixed and (3) dehydrogenating, placing the oxides of thorium, tungsten, and aluminum in the first class and silica in the second. Kramer and Reid6 have reported the formation of a large amount aldehyde when butyl alcohol and hydrogen sulphide are passed over thoria and Brown and Reid7 observed considerable aldehyde formation in the case of butyl alcohol and ammonia over the same catalyst. The question arose whether the aldehyde formation is influenced by the presence of the hydrogen sulphide and ammonia or whether thoria is more of a dehydrogenation catalyst than has been suspected. The recent work of Adkinss shows that the method of preparation of a catalyst influences the kind of its action as well as its activity. As a search of the literature did not reveal complete analysis of the gases evolved in the passage of an alcohol over catalysts for an extended temperature range, it was decided to make a careful study of two alcohols, ethyl and butyl, over the dehydrating catalysts, thoria, alumina, blue oxide of tungsten and silica gel at various temperatures. In all cases carbon dioxide was found: the amounts are small except with thoria with which it is IO% of the reaction product at high temperatures. Its origin is not apparent : perhaps the aldehyde first formed polymerizes to the ester which decomposes to give carbon dioxide in the known manner, or perhaps the carbon monoxide resulting from the breaking up of the aldehyde yields carbon and carbon dioxide. From ethyl alcohol both ethane and methane are formed and from butyl alcohol, both butane and propane, the amounts of the ethane and butane being particularly large with silica gel as catalyst. The methane and propane doubtless come from the decomposition of the aldehydes yielding CO as the other product, while the ethane and butane must be produced by the hydrogenation of ethylene and butylene by the hydrogen present,
+
Contribution from the Chemical Laboratory of Johns Hopkins University Berthelot and Jungfleisch: Trait6 616m. de chimie org. 1, z j 6 (1886). 3Ann. chim. phys. [ 8 ] 4, 458 (1905). Ibid [SI 20, 289 (1910). 6 “Catalysis in Organic Chemistry,” p. 252 (1922) 6 J. Am. Chem. SOC.43, 880 (1921). J. Phys. Chem. 28, 1067 (1924). J. Am. Chem. SOC.44, 2175 (1922).
A. B. BROWN AND E. EMMET REID
1078
After our work was finished an article appeared by Gilfillanl in which the dehydration of ethyl alcohol by some of the same catalysts is described. His reaction tube was nearly the same size as ours but contained more catalyst and he passed the alcohol more rapidly. Our results agree in a general way with his, in so far as comparisons can be made. He does not give complete analyses of the gases produced. We find that butyl alcohol is decomposed at a lower temperature than ethyl, the differences for 60% decomposition being 78' with Wz06, 104' with alumina, 54' with thoria and 78' with silica gel. Comparing the catalysts, we find the following order with the two alcohols, the figures interposed representing the difference in temperatures a t which the catalysts effect 6 0 7 ~ decomposition, Le. alumina decomposes 6 0 7 ~of butyl alcohol 27' lower than blue oxide of tungsten : Ethyl alumina I' W z 0 5 92' thoria 33' s. gel- s. gel com'l. I, Butyl 27' ,' 16" ') 9' ', 81' ,' The curves for alumina and blue oxide of tungsten cross for both alcohols. These are the best catalysts for making ethylene and butylene, both on account of high yield and purity of products. The ratio of unsaturated hydrocarbon to aldehyde decreases with rise of temperature with all of the catalysts, It is greatest with alumina and least with thoria. Comparing the two alcohols, we find the ratio of butylene to aldehyde to be considerably higher than that of ethylene to aldehyde with the same catalyst. Catalysts The preparations of catalysts were similar to those in our study of the alkylation of ammonia2. The tube was filled with 75 g. of the special silica gel. The thoria ( 2 5 g.) on asbestos was similar to "catalyst A". The blue oxide of tungsten was 75 g. of the commercial oxide made into a paste and suspended on asbestos, otherwise similar to "catalyst F". The alumina catalyst was made by suspending 2 5 g. of the well washed hydroxide as a paste on asbestos fibre, drying at 100' till crumbly and finally heating in the tube for an hour at 3 7 5-400'. Apparatus The apparatus used was essentially that described by Kramer and Reid3 and used by us in previous work4. The alcohol fed in through a calibrated dropper a t a known rate, approximately 0 . 2 mole per hour, passed through a vaporizing bulb, over the catalyst and through an air condenser to the receiver, a constant level trap being used to avoid correction for volume of liquid condensed. The air condenser was used to minimize the solubility of the hydrocarbons in the condensate. 1
*
J. Am. Chem. SOC.,44, 1323 (1922). J. Phys. Chem. 28, 1067 (1924). J. Am. Chem. SOC.43, 880 (1921). J. Phys. Chem. 28, 1067 ( 1 9 2 ~ ) .
I079
CATALYTIC DEHYDRATION
Analysis The gases were collected in a burette over water saturated with ethylene (or butylene) and analyzed in a modified Orsat apparatus. The steps were: (A) shaking with water saturated with the hydrocarbon to remove alcohol and ether vapors, (B) shaking with caustic potash solution which had been saturated with the hydrocarbon, C,H,,, (C) shaking with fuming sulphuric acid followed by caustic potash solution containing no C,H,,, (while the gas sample was in the acid pipette, the burette was filled with water free from the hydrocarbons), (D) shaking with nmmonical cuprous chloride, (E) burning the residual gas in a combustion pipette with an oxygen-air mixture, (F) measurement of the contraction due to the combustion, (G) determining the carbon dioxide thus formed. The Alcohols Both alcohols were refluxed over lime until thoroughly anhydrous and distilled.
Results The results are given in Tables I and 11. The figures in column 3 are the yield of ethylene or butylene based on the total alcohol passed in while those in the rest of the columns are figured on the amount of alcohol, decomposed as given in column 2 . The methane or butane formed is the same as the carbon monoxide. The figures in the last column give the ratio of the ethylene or butylene to the aldehyde found. The percentages of carbon dioxide given are double the percentages found by analysis since two molecules of alcohol are required to give one of the dioxide. The percentages of aldehyde and of aldehyde decomposed have been calculated from data in columns 7 to IO.
TABLE I-ETHYL ALCOHOL Alumina Temp.
%Dee. YoCzH~% C Z H %Aid. ~ %Ald.dec. %H2 70C0 %CO, %CzHs Ratio
275
21.1
325 400 500
70.9 86.5 86.0
19.9 69.0 83.4
80.9
94.7 97.2 96.5 94.0
1 . 7 9 4 8 . 0 1.32 0.85 1.31 40.0 0 . 2 7 0.53 2.49 16.2 1.04 0.40 4.18 8.0 3.42 0 . 3 4
3 . 2 9 0 . 3 9 52.3 1 . 0 6 1.05 7 8 . 2 0.93 1.45 38.6 1.99 0 . 7 7 2 2 . 5
Thoria 350 400 450 500
s1.8 57.9 79.2 86.8
8.4 36.2 41.2 39.9
71.7
0.98
2.68
62.6
0.98
2.11
1.25
1.42
2.38
1.12
26.7 3 . 5 23.8 0.87 3.7 29.7 5 . 7 2 8 , 7 1.69 8 . 9 52.1 3 7 . 6 5.1 34.7 1.95 15.5 4 6 . 0 41.1 3 . 2 3 8 . 9 1.32 19.7 (Table I continued o n page 1080)
.
,
I080
A . B. BROWN AND E. EMMET REID
Blue oxide of Tungsten 2 50
16.2 58.9
300 375 475
65.0
360 400 450 500
16.2 47.9 66.8 71.9
70.0
---
-0.54 -0.39
2.04
. --
-
0.52
__
-
2.23 17.7 8.43 4 . 0
1.06 0.36 5.24 0.34
0.48 0.64
1.18 43.3 3.19 10.8
15.6 57.8 62.8 63.5
96.1 98.1 96.6 90.8
13.7 39.5
84.5 14.3 0.0 8 2 . 6 15.2 4 . 8 7 8 . 1 - __ 73.5 2 3 . 6 4.2
Silica gel, special
52.2
52.9
7.42 0 . 0 6 . 5 5 0.73 -0.93 12.28 0 . 9 9
1.31 6.84 5.92 1.46 8 . 7 2 5.43 1.86 - 1 . 9 9 11.34 3 . 1 1
TABLE II-BVTYL ALCOHOL Temp.
175 255 345 450
%Dee. %C4Hs %C4Hs %Aid. %Ald.dec.%HZ %CO %COZ %CIHI~ Ratio 4 8 . 3 47.7 9 9 . 1 71.9 70.8 98.5 79.1 77.3 97.7 91.5 88.8 97.1
-
- -0.23 - -0.35
-
- -0.49
1.31 32.9
0.87
0.43
1 . 1 9 - -0 . 9 8 - __ 1 . 9 4 __ 1 . 4 5 0 , 4 3 74.1
4.3 2.9 4.3 29.5
0.35 0.30 0.43 1.33
1 . 3 1 0.66 1 8 . 9 0.74 2 5 . 7 4.27 1.11 1 7 . 1 16.82 0.26 1.9
Thoria 325 370 415 45 5
24.9 78.8 84.7 100.9
23.3 74.6 77.6 57.3
93.6 94.6 91.7 56.8
4.9 3.7 5.4 29.8
7.1 8.0 7.9 4.5
2.07
Blue oxide of Tungsten 225
278 333 400
4 5 . 9 45.6 87.7 85,3 85.9 84.4 88.4 83.2
9 9 . 3 - __ - 0.18 0 . 5 3 9 8 . 4 - __ - - 0 . 8 9 9 8 . 3 __ __ -- 0.42 0 . 8 4 94.1 5 . 4 5 . 2 3.82 0 . 2 7 0.29
- - __
1.47
17.5
Silica gel, special 325 355 405 475
17.4 17.6 56.1 54.3 85.2 8 2 . 5 84.2 76.0
101.3 96.8 96.9 90.3
- - __ 0.32 __ __
__ -__ __
3.31
5.5
1.26 __
-
0.50
0.72
0.41 0.41
0,79 - 1.05 3 . 2 2 2 7 . 3
12.0
0.78 1.21
17.5
2.27
2.34 7 . 0 1.90 8 . 9 2.41 10.9
4.20
Silica gel, com’l 400 440 48 5
21.3 59.9 90.2
19.4 90.9 45.5 76.0 59.5 66.0
16.3 20.9 28.3
4.8 5.8 8.0
9.3
5.56 3.64 2.34
The results above were plotted and smooth curves drawn. From these the temperatures a t which even percentages of the alcohols are decomposed by the various catalysts were taken off. These are given in Table 111.
CATALYTIC DEHYDRATION
108 I
TABLE I11 Temperatures at which various percentages of the alcohols are decomposed. Ethyl Alcohol % W20s Alto3 Tho2 Silica gel 20
30 40 50 60
70 80
253 260 269
275 283 292 282 302 313 312 480 325 - 447
359 369 380 392 405 423 448
364 376 389 409 438 490
-
Summary The catalytic decomposition of ethyl and butyl alcohols by blue oxide of tungsten, alumina, thoria and silica gel has been studied between 220' and 500'. The first two named are the best catalysts for producing ethylene and butylene both for yields and absence of side reactions. For 60y0 decomposition the temperature is about 76' lower for butyl than for ethyl alcohol. Baltimore. M d .
