CATALYTIC OXIDATION OF n-PROPYL ALCOHOL ALLAN R. DAY AND ABNER EISNER
It is a well-known fact that ceric oxide acts as a powerful oxidizing catalyst, expecially where the process is one of vapor phase oxidation. Ceric oxide is often recommended for this purpose in the combustion method for the determination of carbon and hydrogen. A better example is the great increase in light emissivity of thoria mantles when mixed with 0.9 per cent of ceric oxide. Swan' has shown that the greatest efficiency in the catalytic oxidation of electrolytic gas occurs at the same concentration of Ce02 in ThOz(i.e. 0.9 per cent). I t is probable that the CeOz by acting as an oxygen carrying promoter brings about more rapid combustion and consequently higher temperatures. I n a previous paper2 it was shown that this property was shared by the other rare oxides including the more basic Laz03. The great activity of these oxides makes it practically impossible to use them for the partial oxidation of organic compounds. Their use in small amounts with other less active oxidation catalysts should prove to be practical. A recent patent3 has made use of such a combination. The patent recommends the use of a catalyst comprised of copper mixed with not more than I per cent of ceric oxide for the preparation of acetaldehyde from ethyl alcohol. I n a recent papel-' the use of metallic silver alone and mixed with small amounts of samarium oxide as catalysts for the oxidation of ethyl alcohol was outlined, The results, while indicating that small amounts of the rare earth oxide did exert a promoter effect on the production of acetaldehyde, were scarcely definite enough to draw any general conclusions. The results presented here on the oxidation of n-propyl alcohol confirm the conclusions of the above mentioned paper. I t is shown that WmzOawhen present in small amounts with silver does act as a promoter in the partial oxidation of n-propyl alcohol to propionaldehyde.
Experimental The apparatus used was essentially the same as that used in the previous work. A wet-test meter was attached a t the end of the absorbing train to measure the total volume of outlet gases. A gas-sampling tube was also placed in line and the mixed gases were analyzed in a modified Orsat. The temperature of the preheater was so regulated that the mixture of air and alcohol left the coil at a temperature of 125'C. Preliminary runs showed that the highest 2
3 4
J. Chem. SOC., 125, 780 (1924). Lowdermilk and Day: J. Am. Chem. SOC., 52, 3j3j (1930). Brit. 344,554,Dec. 16, 1929. Day: J. Phys. Chem., 35,3272 (1931).
CATALYTIC OXIDATION OF
n-moPYL ALCOHOL
1913
aldehyde conversions were obtained a t a thermostat temperature of 7 roc., indicating this to be the optimum vaporization temperature for the formation of propionaldehyde. The oxidation process was carried out by passing measured quantities of dry, carbon dioxide free air through the vaporizer containing the n-propyl alcohol which was maintained a t constant temperature by means of a thermostat. The alcohol-air mixture was then passed through the preheater and into the catalytic chamber, the catalyst having been previously heated to 35oOC. The heat of reaction was sufficient to maintain the reaction after it had once started. The catalyst temperatures were measured by means of a thermocouple. The latter was protected by means of a quartz jacket which was imbedded in the catalyst. The catalyst chamber (length 15 mm., diameter 17 mm.) was filled with the impregnated 1 2 mesh pumice. The length of each run was carefully timed by means of a stop watch. The products of the reaction were collected in absorption flasks which were part of the cooling system. The flasks were then emptied, rinsed and the resulting solution diluted to a definite volume. Aliquots of this solution were taken for analysis. The following types of catalysts were employed: A. 2.7928 g. of silver (equivalent to 3 g. of Ag2O) deposited on g cc. of 1 2 mesh pumice. B. 2.7894 g. of silver (equivalent to 2.99625 g. of Ag2O) and 0.00375 g. of samarium oxide deposited on 9 cc. of 1 2 mesh pumice. C. 2.7858 g. of silver (equivalent to 2.9925 g. of Ag2O) and 0.0075 g. of samarium oxide deposited on 9 cc. of 1 2 mesh pumice. D. 2.7788 g. of silver (equivalent to 2.985 of AgzO) and 0.015 g. of samarium oxide deposited on 9 cc. of I 2 mesh pumice. E. 2.7648 g. of silver (equivalent to 2.97 g. of AglO) and 0.03 g. of samarium oxide deposited on 9 cc. of 12 mesh pumice. It will be noted that catalysts B, C, D and E contain 0.125,0.25, 0.5 and I per cent of samarium oxide respectively based upon Ag20:SmzOs. The catalysts were prepared in the same manner as the catalysts used in the earlier work. Before use they were activated by heating in a stream of n-propyl alcohol vapor and air for an hour. Their efficiency as catalysts did not increase over longer periods of activation. Duplicate catalyst preparations were used for many of the runs and excellent check results were obtained, indicating the uniformity of the catalysts used. Pure n-propyl alcohol (sp.g. 0.804~~~) was used for all experiments. Approximately 15 g. of alcohol was passed over the catalyst during each run. Determination of Propionaldehyde.-The aldehyde was determined by Ripper’s bisulfite method. Determination of Propionic Acid.-To a definite amount of standard sodium hydroxide solution was added a little barium chloride solution and a few drops of phenolphthalein. The resulting solution was then titrated with a portion of the condensate until the red color was discharged.
I914
ALLAS R. DAY A S D ABNER EISSER
Gas Analysis.-The gas sample was transferred from the sampling tube to the Orsat and the usual methods employed for the determination of carbon dioxide, oxygen, alkenes and carbon monoxide. The following table includes the results for the more important runs. Duplicate runs checked within 0.5 - 0.6 per cent (based on the aldehyde yields) and they are therefore not included in the table.
TABLE I Thermostat Temp. 71OC Molar Conversions Acid
602
72.8
3.5 3.5 3.3 3.4
4.2 4.0 3.4 4.1
445 3 90 365
73.9 75.4 76.4
3.5 3.4 3.2
4.0
0.94 0.77 0.65
495 455 420
71.5 72.6 74.3
0.52
380
75.5
3.8 3.6 34 3.4
0.94 0.77 0.65
498
70.0
445
385 350
71.3 74.0 74.3
491
69.0
460
71.4
395 345
72.4 73.1
Air Rate Liter/min.
A
0.94 0.77 0.65 0 . 52
B
0.77 0.65 0 . 52
C
D
0.52
E
0.94 Q.77 0.65 0.52
Catalyst Temp. "C
Aldehyde
505 450 395 355
% 71.5 72.3 72.1
%
4.1 3.6 3.6 4.2 3.4 3.3 3.4 3.6
%
2.7
4.0
3.2 4.1
4.1 4.2 2 .O
3.2 2.7
3.5 5.0
3.8 3.8 4.5
Discussion of Results There does not appear t o be a careful study on the oxidation of n-propyl alcohol in the literature since the work of Orlov.' Orlov using metallic copper as the catalyst reported j o per cent as his highest yield of propiona!dehyde. The results recorded in Table I show that the maximum conversions to aldehyde were obtained where the lower air rates were used. The results recorded for catalysts B and C show definite increases in the conversion to aldehyde. Even with catalyst D an increase in yield is shown where the lower 1
J. Russ. Phys.-Chem. SOC.,40,203 (1908).
V
CATALYTIC OXIDATION O F
n-PROPYL
ALCOHOL
'915
air rates were used (0.65 - 0 . 5 2 L/min.). It will be noted that while the yields of aldehyde were definitely higher, the amount of carbon dioxide formed did not appear to increase. This would indicate that small amounts of Sm203 do not promote complete oxidation under the conditions recorded in Table I, in spite of the fact that an excess of oxygen was present during the runs. At the thermostat temperature of 71OC. the ratio mols alcohol/mols O2 was approximately 1/0.57-0.58 (theoretical I / o . ~ ) . At higher catalyst temperatures (higher air rate used) the samarium oxide did exert a promoter effect toward complete combustion. The amount of carbon dioxide increased with increase in temperature much more rapidly than in the cases where pure silver was used. However, one would not work at such temperatures if propionaldehyde were the desired product. The results in the table show that within certain catalyst temperatures (350-500') the small amounts of Sm2Oa present did not enhance or produce any undesirable side reactions. The amounts of carbon monoxide and alkenes formed were not included in the table as they were in every case negligible quantities. summary
The optimum conditions for the oxidation of n-propyl alcohol to propionaldehyde, using metallic silver on I 2-mesh pumice, have been determined. 2. It has been shown that the presence of small amounts of samarium oxide increases the yields of propionaldehyde. 3. Higher yields of propionaldehyde have been obtained by a one-step vapor phase oxidation of n-propyl alcohol than have been previously reported from similar methods. I.
Harrison Laboratory of Chemistry, University of Pennsylvania, Philadelphia, Pa.
