1048 The question arises-what
INDUSTRIAL A N D ENGINEERING CHE-JlISTRY mixture ratio shall be chosen?
It seems hardly practicable to select a certain mixture ratio at random. This would require the constant use of gasanalysis apparatus or some device for measuring both air and fuel in order to make sure that the mixture ratio was properly adjusted. The procedure would become quite complicated with fuels which have different products of combustion and different physical properties. The mixture ratio for maximum power would not be suitable because power measurements are not sufficiently sensitive to changes in mixture ratio to make a satisfactory adjustment possible. There remains one outstanding and comparatively simple solution. For every fuel there is a definite mixture ratio a t which maximum knock occurs; and, if the determinations are made a t the mixture ratio for maximum knock with
Vol. 20, No. 10
each individual fuel, there is available a standard for obtaining reproducible results by different laboratories. Conclusions
1-The tendency of a fuel to knock is very sensitive to changes in mixture ratio. 2-Since the change in tendency to knock with changes in carburetor adjustment varies according to the composition of the fuel, it is necessary to choose some definite ratio mixture for knock-testing work if reproducible results are to be obtained. 3-The use of mixture ratios giving maximum knock for each fuel is suggested as a convenient means for obtaining more consistent results between different laboratories.
Action of Accelerators and Inhibitors upon the Oxidation of Liquid Hydrocarbons T. E. Layng and M. A. Youker UNIVERSITY OF ILLINOIS, URBANA, ILL.
A n apparatus has been devised and a method described for determining the effect of various inhibitors and accelerators of knock upon the slow oxidation of hydrocarbon fuels. Data are given to show the effect of various substances upon the slow oxidation of n-heptane and its normal oxygen derivatives, gasoline, and kerosene. A surprising similarity is shown between the action of lead tetraethyl and various compounds of sodium and potassium, and also a difference in the action of lead tetraethyl and these compounds of sodium and potassium upon the oxidation of hydrocarbons, in the gas or liquid phases.
HE status of the mechanism of oxidation of hydro-
T
carbons, or the cause of detonation in the internalcombustion engine, is still in an unsatisfactory state. The use of antiknock substances, notably lead tetraethyl, has added a new factor and has been the cause of increasing vastly the amount of useful information which must be obtained for the solution of this problem. I n a recent summation of our knowledge of this subject Clark1 shows that a t the present time no theory is without its defects, but the peroxide theory supported by the work of Riloureu, Dufraisse, and Chaux,2Callendar,3 and more recently of M a r d l e ~appears ,~ the most promising. This theory postulates that detonation a t high compression ratios is due to the formation of explosive peroxides by the oxidation of liquid droplets of the fuel. The above investigators and also Lewis6 studied the action of oxygen upon various hydrocarbon fuels in the presence of catalysts a t different temperatures. This method of study has also been advocated by Clark.'j The present investigation was undertaken in the hope of designing a more efficient apparatus and thus producing a means of securing more data in regard to the action of catalyst of oxidation and the causes of detonation. The results of preliminary work are presented herein. J. SOC.Aulomolloe Eng., 21 (1928). Chimre el induslne, 18, 3 (1927). 8 EngZnee7ing (London), 121 477 (1927). 1 J. Chem. SOC.(London), 1928,872. 6 Ibrd., 1927, 1556. * IND. END.CHEM., 17, 1210 (1925). 1
2
Apparatus
The experiments on which Moureu and his associates based their conclusions were conducted with the fuel to be tested and the oxygen in a small glass bulb with a manometer attached. When the bulb was immersed in a hot bath, the rise of mercury in the manometer was a measure of the oxygen absorption and hence also of the rate of peroxide formation. Lead tetraethyl and other antiknock substances, such as the aromatic amines, retarded the absorption of oxygen. Peroxides were detected in the final products when oxygen had been absorbed. The method of recording pressures in the apparatus of Lewis and Mardles was similar to that employed by Moureu. I n each case it was possible for some of the fuel to be distilled and condensed in the manometer connections. Accordingly, an apparatus (Figure 1) was designed which was extremely simple and eliminated any possibility of distillation. The Pyrex bulb is of an average volume of 160 cc. The side arm permits easy cleaning, the introduction of solid catalysts, and the withdrawal of gas samples. The mercury in the base seals off the bulb and gives a column of mercury when the bulb is heated which enables changes in the pressure 'of the enclosed system to be detected. Since the entire bulb is immersed, changes in pressure under constant-temperature conditions can only be caused by the thermal decomposition of the fuel or its chemical union with oxygen. In this apparatus there has been introduced the added factor of mercury in contact with the fuel when in the liquid phase, and with the fuel and oxygen in the case of the gaseous phase. However, no mercury compounds have been shown to have any effect upon the rate of oxidation, and since in all the tests with different accelerators and inhibitors a comparison is made with the fuel alone, any eflect of the mercury mag be assumed a constant for a given fuel a t a given temperature. Before using, the bulb was cleaned in hot sodium hydroxide solution, washed out with dilute hydrochloric acid, and rinsed several times in distilled mater. It was then washed out twice with acetone and dried. It was found to be very important to clean the bulbs very carefully.
INDUSTRIAL A N D ENGISEERISG CHEMISTRY
October, 1928
The side arm was sealed off and after evacuation the bulb was filled with dry oxygen. The fuel to be introduced was drawn up to the desired amount in the capillary pipet shown in Figure 1, and held there by closing the stopcock. Mercury was then run into the bulb above the stopcock. The capillary tube of the apparatus was then connected to the tip of the pipet with a short piece of carefully cleaned rubber tubing, and on opening the stopcock the mercury forced the material into the bulb. .A sufficiently long piece of .oft-glass capillary tubing was then connected to the capillary on the bulb by a short piece of heavy tubing. the bulb immersed in a well-stirred oil bath maintained a t the desired temperature, and the pressure in the bulb noted by t h e height of the mercury column.
-
Preliminary Experiments
Oxygen
11
Some preliminary experiments, ahowl graphically in Figure 2, were made to determine the type of data which might be ob-
pressure-still gasoline and various fractions thereof were subjected to oxygen for 8 hours a t 160" C. XOabsorption of oxygen was noted, but rather a small increase in pressure. Other 0.5-cc. samples of the same gasoline connected with a manometer of the Moureu type showed a large absorption under the same temperature conditions. It was noted also that if the bulb was not completely immersed in the bath a brown gum formed in the bulb a t the surface of the bath. While this apparatus differs from that of Moureu, especially in size, and was not to be expected to yield the same data, nevertheless these experiments indicated that variable data may be obtained if any part of the fuel was not subjected to the desired temperature. Benzaldehyde gave a rapid and smooth absorption a t 160°C. Parowax showed a preliminary absorption followed by an increase in pressure a t 160" C: Raising the temperature increased the amount of absorption. Evidences of oxidation were noted in the degree of browning and gumming, in the increase in pressure, and in the amount of carbon dioxide found in the bulbs. 0 .I
cr.
Figure 1-Apparatus
Experiments with n-Heptane and Its Normal Oxygen Derivatives
The mechanism of the oxidation of a hydrocarbon of the methane series is best expressed by the hydroxylation theory or by successive oxidation, forming the alcohol, the aldehyde, and the acid. Accordingly it was decided to determine the type of data which might be obtained on the slow oxidation of n-heptane, heptyl alcohol, heptaldehyde, and heptoic acid, when subjected to different accelerators and inhibitors a t 160" C. (Figures 3 and 4) E-HEPTANE-The pure compound is oxidized to a dark brown color in 20 hours. This oxidation was also indicated by a pressure rise of 40 to 50 mm. Inhibition or prevention of this oxidation may be obtained
1049
by 1 per cent of ethyl fluid (containing 50 to 60 per cent of lead tetraethyl), potassium lactate, potassium tartrate, potassium heptylate, potassium diphenylamine, potassium ethylate, aniline, diphenylamine, and sodium heptylate. No effect on the oxidatim was produced by small amounts of calcium lactate, sodium tartrate, and n-tributylheptyl ammonium iodide. iicceleration of the oxidation was produced by 1 per cent of butyl nitrite. Aldehydes and acids were detected in the product of the oxidation of the heptane, but none were found when the oxidation had been inhibited as by lead tetraethyl. S o positive tests for peroxides were obtained using potassium iodide and starch. 71-HEPTYL .kLcoHoL-n-Heptyl alcohol showed no tendency to oxidize when pure and when containing 1 per cent of ethyl fluid by volume. When one per cent of butyl nitrite was S which was followed added, a decrease in pressure T V ~ noted by a regular increase in pressure. If in addition to the butyl nitrite, 1 per cent of the ethyl fluid WBS added, this decrease in pressure was delayed about 4 hours, when a duplicate curve v a s obtained. HEPTALDEHYDE ASD HEPTOICAcm-oxidation progressed quite rapidly, as indicated in Figure 4. One per cent of ethyl fluid had no marked effect. If anything, ethyl fluid appeared to accelerate the oxidation. Two important results of this series are indicated. Heptane, heptaldehyde, and heptoic acid are progressively more easily oxidized. Heptyl alcohol is oxidized only with difficulty and n-heptane does not form the alcohol in its slow progressive oxidation. Lead tetraethyl has the ability to delay the oxidation of heptyl alcohol when accelerated by butyl nitrite, but when started the path of oxidation is identical with that in which no delay occurs. Experiments with Gasoline
n-Heptane offers undoubtedly the best opportunities for obtaining definite data. On account of the small quantity that the writers were able to obtain, together with the difficulty of correlating any data obtained with those from gasoline and kerosene, it was decided to determine the inhibiting and accelerating effects of different substances Samples of pressure-still gasoline and its sulfonated and
B
'*\
.
'\
A
__
1050
INDUSTRIAL AND ENGINEERING CHEMISTRY
that butyl nitrite accelerated the oxidation as it did a t the highest temperatures. At 200" C. the lead tetraethyl inhibited the oxidation. (Figure 5) The most decisive indication of these experiments with gasoline, then, was that a temperature of 200" C. must be used before definite results may be obtained. Since a t 200" C. practically all of the gasoline used was in the gas phase, for definite results the physical condition of the fuel was important.
Vol. 20, No. 10
cc. of gasoline inhibited the oxidation as well or better than the ethyl fluid. This is equivalent to almost one hundred times the engine rating of diphenylamine as compared with lead tetraethyl. Potassium ethylate in amounts of from 0.09 gram to 1.44 grams of potassium per 100 cc. gasoline was next tested. With 0.72 gram of potassium per 100 cc. the brown discoloration was prevented, with 1.08 grams per 100 cc. there was no apparent consumption of oxygen. On account of the presence of small volumes of ethyl alcohol rrith the potassium ethylate, its effect on the oxidation of the gasoline was next determined. Little effect was noted up to 10 per cent by volume. From 20 to 40 per cent of the alcohol produced little change in the final pressure. The brown discoloration always accompanying oxidation faded rapidly in percentages above 20. The substituted potassium compound of diphenylamine was next prepared. It was not soluble to any extent in gasoline unless some alcohol was added. This made it uncertain whether the potassium was in the amine or split off to form some ethylate. In any case the oxidation of the gasoline was completely stopped by a small percentage of the inhibitor. Solid potassium thiocyanate and caesium dichloro-iodide gave somewhat doubtful results, possibly inhibiting slightly.
Tj'me in N o u r s Figure 3-Oxidati o n of: A-Pure n - H e p t a n e B-n-Heptane Plus 1% E t h y l Fluid C-n-Heptane Plus 1% B u t y l Nitrite a t 160' C .
As a result of these findings it was decided to attempt a correlation of this method of study of the mechanism of oxidation in the presence of inhibitors and accelerators with their recognized evaluation which had been obtained by actual engine tests. For this purpose a gasoline from the straight-run distillation of Pennsylvania paraffin-base crude was obtained. By varying the temperature and the amount of gasoline, it was found that 0.2 cc. oxidized fairly rapidly, giving a considerable increase in pressure in 6 hours. For the comparison with engine-test evaluations of inhibitors, it was decided to use ethyl fluid and diphenylamine, and since the alkali-metal compounds in the first series of experiments gave promise of possessing inhibiting properties, potassium ethylate, ethyl alcohol, and potassium-substituted diphenylamine were also added to the list. The ethylate of potassium was chosen because it was easy to prepare, and with the addition of a little alcohol was sufficiently soluble in the gasoline. The results of these experiments are shown in Figures 6 and 7 . One indeterminate factor in the choice of lead tetraethyl for these tests a t this temperature is caused by its instability and explosive character when heated alone with oxygen. The writers nere unable to determine the effect of this factor upon the pressure changes. The gasoline alone with oxygen showed an increase in pressure of about 60 mm. The bulbs were completely coated with a uniform brown deposit. Ethyl fluid was then added in increasing amounts. Up to 1 per cent it did not affect the oxidation, but when 2 per cent was added only a small pressure rise occurred. The bulbs and the gasoline remained undiscolored by the 7 hours of heating a t 200" c. Ten per cent' or less of the ethyl fluid did not eliminate an increase in pressure of about 10 mm. The most noticeable effect of larger amounts of ethyl fluid was a small deposit on the bulbs due to the lead compounds present. Diphenylamine in amounts of from 1 to 10 grams per 100
Tlrne in H o u r s Figure 4-Oxidation of: A-Heptyl Alcohol B-Heptyl Alcohol Plus 1% B u t y l Nitrite C-B Plus 1% Ethyl Fluid D-Heptaldehyde E-Heptoic Acid a t 160' C.
The results obtained in this series of experiments indicated that there was no relation between engine-test evaluations of inhibitors and their relative values when obtained by the slow oxidation of a badly knocking gasoline in the vapor phase. The data also showed that potassium ethylate and potassium-substituted diphenylamine possessed marked inhibiting properties in the vapor-phase oxidation of gasoline. Oxidation of Kerosene
From the preceding series of experiments, it appeared that a careful study of the effect of inhibitors upon a hydrocarbon fuel in the liquid phase might lead to some important results. In fact, suchdata might showthat engine-test evaluations of inhib-
October, 1928
INDUSTRIAL AND ENGI NEERING CHEMISTRY
itors were comparable only with oxidation in the liquid phase. Ac co r ding1y, the effect of the inhibitors studied in the series of gas-phase o x i d a tions was determined in this series of experiments in which the fuel, kerosene, was almost wholly in the liquid phase. Kerosene was chosen, since z 4 6 8 t h e temperature a t T i V e i n Hours which the g a s o l i n e Figure 5-Oxidation of: Jvould be in the liquid A-0.1 CC. Cracked Gasoline COz = 8.5%, CO = 4 . 0 7 B r o b phase would give too B--A + 1% Ethyl fiuid, COZ = 5.1%, slow a rate of ox&CO = 1.5%. Clear C-A + 1% Butyl Nitrite, COZ = 13.1%, tion. The results are CO = 6 2 7 Brown shown in Figures 8 All at 20Oo'C.%r 8 Hours and 9. It was found that 0.5 cc. of kerosene could be heated for as long as 8 hours a t 180" C. without more than a slight oxidation. However, the addition of a small percentage of ethyl fluid caused a pronounced oxidation of the kerosene. An increase in the pressure was noted. The brown gummy product always indicative of oxidation was quite pronounced and instead of coating the whole inner surface of the bulb as in the case of the gasoline, was found only where the liquid kerosene had been. On removing the bulb from the bath and connecting with a buret containing air, it was found that much of the oxygen present in the bulbs had been used in the oxidation process. ,I raThe accelerating action of the lead tetraethyl reached a maximum when present in very small percentages. Increasi 12 the percentage apparently decreased its effect on the rate of oxidation. 7q As little as 0.05 cc. of ethyl fluid per 100 cc. o f kerosene (approximately 0.03 cc. lead tetraethyl per cc.) has a pronounced effect on the oxidation of the 0 . 5 ~kerosene . sample a t 180" C. About 0.3 cc. of ethyl fluid per 100 cc. of kerosene appeared to exert the maximum
1051
per 100 cc. appeared to be capable of causing the brown gummy deposit a t the base of the bulb where the liquid was in place. Sodium ethylate exhibited properties similar to those of potassium ethylate and of lead tetraethyl. 0.007 gram of sodium per 100 cc. of kerosene appeared to produce the maximum amount of oxidation. Calcium ethylate accelerated the oxidation lightly, if a t all. Aluminum ethylate had no action. The results obtained in this series of experiments indicated the surprising difference in the action of lead tetraethyl and the potassium and sodium ethylates compared with their action on gasoline. Conclusion
It is to be noted also that only extremely small percentages of these compounds are necessary. It is here, then, that the engine-test evaluations of lead tetraethyl may best be com7
I
I
I ' I
"
I
I ' l i
I
Figure 6-Effect 0; C2HsOH on Oxidation of Pennsylvania Gasoline i n Vapor Phase at 200° C.
kerosene had no tion. Aniline in percentages of from 1 to
10 by volume had no action. Alcohol in percentages of from 1 to 20 by volume had no action. Potassium ethylate exhibited catalytic properties similar to those of lead tetraethyl. Its accelerating action reached a maximum when present in very small percentages. This percentage could be increased largely without changing materially the amount of oxidation. With 0.01 gram of potassium per 100 cc. of kerosene the maximum oxidation of the kerosene took place. As little as 1 mg. of potassium
Figure 7-Effect of PbEta, CzHaOH, CrHaOK, (CaHdzNH on Oxidation of Pennsylvania Gasoline i n Vapor Phase a t 200' C.
pared with this slow oxidation method. It is unfortunnte that at this writing no engine-test evaluations are available for the potassium and sodium ethylates. Aniline and diphenylamine, two substances with which the lead tetraethyl might have been compared, failed t o have accelerating action in the liquid-phase oxidation. It appears, then, that for a compound to have properties to be classed as a suitable antiknock, it must be an inhibitor of gas-phase oxidation and an accelerator of liquid-phase oxidation. Compounds which fail to approach lead tetraethyl but which have some effect as antiknocks appear to have their effect only in one of the phases present in the gas engine a t the temperatures tested. The peculiar properties of lead tetraethyl and the aromatic amines in liquid-phase oxidation appear to be what might be expected from the work of Ormandy,' who showed by the liquid droplet method in his determination of ignition temperatures that the amines raised and lead tetraethyl lowered such temperatures. S o attempt is made at this time to correlate these data with the mechanism of combustion in the gas engine. Lead tetraethyl by engine-test evaluation is the best antiknock substance. It may be due t o its ability to delay gas-phaie oxidation and accelerate liquid-phase oxidation. 7
J . I n s t . Perroleurn Tech., 10, 335 (1924).
1052
IND USTRIAL AND ENGINEERING CHEMISTRY Summary
1-The oxidation of n-heptane in the gas phase appears not to be through its normal alcohol. 2-Heptyl alcohol may be oxidized only with diffi-
exhibit a surprising similarity of properties in affecting gasand liquid-phase oxidation. 8-While slight absorptions of oxygen were obtained in certain of the tests, owing to the known instability of peroxides and the difficulty of definite1y.determining their presence, the authors believe that these data should not be considered as conforming or rejecting the peroxide theory of oxidation of hydrocarbons.
T i m e in H o u r s
Figure 8-Effect on Catalysis of Oxidation of Kerosene b y Ethyl Fluid-3 Hours at 180° C.
culty in the gas phase. Lead tetraethyl has the ability to delay the accelerating action of butyl nitrite, but if once started the path of oxidation is the same as when not delayed. 3-Aniline, diphenylamine, lead tetraethyl, and potassium ethylate are all inhibitors of gas-phase oxidation. 4-There is no relation between the engine-test evaluation of inhibitors and the values obtained in their slow oxidation data for gas-phase oxidation. 5-Ethyl alcohol, aniline, diphenylamine, aluminum ethylate are not accelerators of liquid-phase oxidation. 6-Lead tetraethyl, and potassium and sodium ethylate are accelerators of liquid-phase oxidation when present in extremely small percentages. 7-Lead tetraethyl and potassium and sodium ethylate
Vol. 20, KO.10
F i g u r e 9-Effect of KOCzHa, NaOCxHa, PbEtd, etc., on Onidation of a Kerosene at 180° C. All amounts of catalysts are per 100 cc. of kerosene.
9-From the data presented it appears that an ideal antiknock substance might be obtained by incorporating a powerful inhibitor of only vapor-phase oxidation with a powerful accelerator of only liquid-phase oxidation. Acknowledgment The authors are indebted to the Ethyl Gasoline Corporation for the n-heptane and ethyl fluid; to E. B. Philips, of the Sinclair Refining Company, for the straight-run gasoline; and to Professors G. L. Clark and D. B. Keyes, of the University of Illinois, for their suggestions and interest in this investigation.
Partial Oxidation of Methane and Ethane in the Presence of Catalysts T. E. Layng and Roy Soukupl UNIVERSITY OF ILLINOIS,URBANA, ILL.
The catalytic partial oxidation of various mixtures of methane and ethane with oxygen has been studied by the dynamic method a t atmospheric pressure within the temperature range 100" to 700" C. Some experiments have also been made with a natural gas under similar conditions. For t h e production of alcoholic or aldehydic intermediates, catalysts of copper and silver, oxides of these metals, activated charcoal, platinum oxide, and barium peroxide proved unsatisfactory on the basis of hydrocarbon consumed and products obtained. Small amounts of nitrogen dioxide, when added to hydrocarbon-oxygen mixtures and passed through heated capillary tubes, were found to promote the oxidation materially. Yields of oxygenated derivatives varying from 15 t o 30 per cent by volume of the amount of hydrocarbon used were obtained. As much as 38 per cent of the hydrocarbon has been decomposed in a single pass through the catalytic chamber. Auxiliary catalysts used in conjunction with nitrogen dioxide activated the decomposition of intermediate oxidation products without materially increasing the a m o u n t of hydrocarbon decomposed.
Methyl nitrite has been shown to exert a promoting action in partial oxidation reactions of hydrocarbons. An explanation is offered of the effect of small amounts of nitrogen dioxide and methyl nitrite on the partial oxidation of aliphatic hydrocarbons. The hydroxylation theory of the combustion of hydrocarbons has been further confirmed by thermodynamic considerations as well as by experimental evidence.
N T H E basis of the hydroxylation theory of the com-
0
bustion of hydrocarbons, some attempts have been made in the past to isolate alcohols, aldehydes, and acids by the partial combustion of a mixture of the hydrocarbon and oxygen or air. Natural gas is a prolific source of raw material for such processes, although other hydrocarboncontaining gases are also available. The products formed are extremely valuable for many purposes, either in the pure state or as mixtures. Numerous patents have appeared in the literature, claiming the production of substantial amounts of these oxygenated derivatives, usually by a process comprising the passage of a mixture of hydrocarbon and air over a solid catalyst a t a n 1
Present address, Dupont Rayon Co.,Buffalo, N. Y.
T a b l e I-Data
400
C.
co,
0%
HZ
co
CzHs CHI N2
Rate of flow of gas, cm. per second Time of heating, secondsb Effluent gas:
co2
CnHzn
0 29.0 0 0.2 15.0 47.6 8.2 161 0.09
0
500
0.3 4.4 0.1
0.4
0.2 21.9 5.8
67.3
121.2 0.12
46.6 10.2
198.7 197.6 1.1
200.0 196.3 3.7
0.5 14.7
Contraction : Influent gas, cc. Effluent gas, cc. Contraction, cc. “n-Factor :”c Influent gas Effluent gas
570
1.4 0 1.8 0 0.2 21.5 66.1 9.0
0 28.0 0
for Solid C a t a l y s t s : Single-Pass A.~ pparatus COPPER OXIDE
COPPER
Catalyst Temperature, Influent gas+
1053
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
October, 1928
28.8 0 0.2 15.6 45.6 9.4 28.9 0.52
SILVER OXIDS
605 0.2 23.4 0 0.1 17.2 52.9 6.1 30.5 0.49
BARIUM PEROXIDE
PLATINUM OXIDE
520
400
520
410
610
0.5 18.1 0 0.1 18.2 58.4 4.7 27.6
0 18.4
0 18.4
0.2
18.2 0
18.6
0.3 18.2 0 0.3
18.6 58.8 4.0
7.9 1.90
57.5 4.5 3.4 4.41
0 0.2
0.54
58.8 4.0 8.3 1.81
11.8 0
0.3
n
0.1
200.0
197.8 2.2
200.0 198.6 0.4
4CTIVATED CHARCOAL
199.1 196.1 3.0
0
19.2
1.8
11.7
0 15.0 0.1 0.8
0 0.3
o
0
0.3
0.3 19.2
57.5
4.5 2.5 6.00
9.8
0.3 0.5 0.7 7.2
15.6 65.5
15.9
6.6
15.9 65.0 7.1
61.8 4.6
18.7 57.1 5.7
199.9 176.5 23.4
200.0 175.4 24.6
200.0 198.3 1.7
200.0
1.245 1.180
1.245
1.197
1.250 1.205
190.4 9.6
1.250
1,250
All gas analyses are reported on the dry basis. Both initial and final gases, however, were saturated with moisture while in the single-Pass apparatus. b B y “heating time” is understood the time required for one molecule of the influent gas to pass in a straight line from one end of the heatlng zone of the catalyjjc chamber to the other. c n-factor” is a n index of the relative amounts of ethane and methane in a mixture of these two gases, a s determined by gas analysis. 0
elevated temperature. A few2 specify the use of gaseous catalysts. Published data are much more meager in quantity. It has been shown conclusively by Bone,3 Wheeler and Blair,‘ Medvedev,6 and Berl and Fischer,6 among others, that oxygenated derivatives could be formed by partial oxidation of gaseous hydrocarbons, although only traces of alcohols and acids were obtained. However, yields of aldehydes were too small to warrant the application of these processes to an industrial operation. This investigation had for its object a study of the partial oxidation of mixtures of methane, ethane, and natural gas with oxygen under conditions which would yield the greatest amount of oxygenated derivatives, preferably the alcohols. A thermodynamic analysis of the partial oxidation of met,hane and ethane, and hence natural gas in which these two hydrocarbons predominate, on the basis of Nernst’s thermodynamic theorem, as well as by integration of available specific heat data, indicates that formaldehyde is the most probable product or reaction if the oxidation process is considered from a kinetic as well as a static aspect. This analysis, however, does not take into consideration the effect of catalysts in altering the reaction velocities of equilibria involved in partial oxidation, so that isolation of alcohols by direct oxidation of hydrocarbons is not impossible, though apparently difficult. Experimental Procedure In this investigation the catalytic partial oxidation of various mixtures of natural gas, methane, and ethane with oxygen was studied by the dynamic metshod a t atmospheric pressure withi? the temperature range 100” to 700” C. The flow sheet of operation consisted essentially of the passage of an analyzed and measured quantity of a gas mixture through a heated reaction zone of small cross section, the times of heating being of the order of 0.1 to 1.0 second. Solid catalysts 2 Bibb, U. S. Patent 1,392,886 (October 4, 1922); U. S. Reissue 15,789 (March 11, 1924). a Bone and Collaborators, J . Chem. SOC.(London), 81, 5.75 (1902); 83, 1074 (1903); 85, 693 (1904): 86, 1637 (1904); 87, 1232 (1905); 89, 660 (1906); Proc. Chem. SOL, 21, 220 (1905). 4 - 7 . SOC.Chem. I n d . , 41, 303T (1022); 42, 81” (1923); 42, 260T (1923); 42, 491T (1923). 6 Trans. Karpow Inst. Ciiem., No. 3, 54 (1924); C . A , , 21, 2457 (1927); 2 0 , 2273 (1926). 6 Z . a n g e v . Chem., 36, 297 (1923).
were mounted in the heated portion of the system, while gaseous catalysts were mixed with the influent gas before its admission into the reaction chamber. After passage through this chamber, the effluent gas was rapidly cooled, intermediate products were removed by condensation and scrubbing, and the gas was then passed into a reservoir where it was accurately measured and analyzed. Initial and final gas compositions were determined by analysis in a modified Orsat apparatus. In the analysis of intermediate product7 from methane oxidation, formic acid was determined by a permanganate titration’ of residual liquors after removal of formaldehyde and methanol by distillation. N o quantitative analyses were made of the condensate and wash water obtained by the Oxidation of natural gas and ethane, since the amounts of eWuent gases utilized were too small to permit quantitative methods to be applied. When acidic gaseous catalysts were used, it became necessary to effect the removal of inorganic acids formed by partial solution of these catalysts in the condensates and scrubbing liquors before analyzing for alcohols, aldehydes, etc. Formaldehyde was determined separately in an aliquot part of the distillate obtained by neutralizing the combined condensate and wash water and removing formaldehyde and methanol by distillation. The aldehyde was determined either by the iodometric8 or hydroxylamine hydrochlorideg titration methods. Methanol was estimated from the amount of standard permanganate solution required for the oxidation of both methanol and formaldehyde in another similar portion of the distillate.’o Results with Solid Catalysts Catalysts consisting of copper and silver films which were mounted in a narrow annular space in such a manner as to provide an intimate contact between the influent gas stream and the catalyst, as well as to obviate the difficulties of heat transfer which are involved in the case of catalysts supported in the usual manner on pumice, asbestos, etc., did not promote the oxidation to intermediate products successfully in single passes through the catalytic chamber. Oxides of copper and silver, supported as in the case of the Treadwell and Hall, “Analytical Chemistry,” Vol. I, p. 626, John \Tiley and Sons 1919. 8 Romljn, z a n d Chem , 36, 19 (1897). 9 Brocket and Cambier, Compl. r e n d , 120, 449 (1895). ‘0 Lockemann and Croner, Z. anal. Chem., 64, 21 (1914).
I S D USTRIAL A N D EiVGI,VEERI;VG CHEMISTRY
1054
metals, exhibited better promoting action than the latter, but the reaction was still slight under conditions which favored the production of intermediates. Barium peroxide a t 450” C., supported on asbestos, proved to be an unsatisfactory promoter of the partial oxidation reaction for single-pass operations. A platinum oxide catalyst, supported on asbestos, caused appreciable oxidation of natural gas to occur a t temperatures in excess of 400” C., but this oxidation proceeded completely toward the production of carbon dioxide and water. Practically all of the oxygen present when using a mixture of oxygen, ethane, and methane in the proportions by volume of 1:1:3 was utilized in a single pass through the catalytic chamber in a heating time of about 2 seconds. By “heating time” is meant the time required for one molecule of the influent gas to pass in a straight line from one end of the heating zone of the catalytic chamber to the other. Activated charcoal gave results which mere of about the same order as those obtained by the use of copper and silver. However, a t the temperatures required for appreciable reaction to occur, the charcoal was itself oxidized to carbon monoxide and carbon dioxide. T a b l e 11-Data
for G a s e o u s Catalysis: S i n e l e - P a s s ADDaratus _-
Temperature, Influent gas:
NO? (PYREX CATALYTIC CHAMBER)
SO3
Catalyst O
C.
cot 0 2
H2
co
CzHa CHk Nz Rate of flow of gas, cm. per second Time of heating, seconds Effluent gas: COzb CnHtn 0 2
H2
co
C2Hs CH4 N2
Contraction, C C . ~ Per cent hydrocarbon decomposed : Ethane Methane Per cent of total hydrocarbon converted to oxygenated derivatives Per cent of cata. lyst present, by volume
440
635
0.5 18.4 0 0.2 16.9 52.1 11.9
0.5 18.4 0 0.2 16.9 52.1 11.9
11.7
12.3
1.28
1.22
3.1
3.2
17:i 0 0.1 14.1 51.0 13.8 1.4
17:3 0.2 0.3 14.0 51.5 13.5 0.1
600
635
133%~700
620
620
0.2 0.2 0.2 0 0 0 20.6 48.0 27.5 26.2 10.0 30.6 0 0 0 0 0 0 0.1 0.2 0.2 0.2 0 0 18.3 10.9 17.4 56.3 34.0 52.1 61.2 38.4 20.4 4.5 6 . 7 2 . 8 1 2 . 4 51.6 4 9 . 0 4.7 3.2 2.0 0.5 0.6 4.4 15.0 7 5 5S.5 11.5 32.1
8.3
8.66 8 . 5 5 8 . 6 4 8.49
1.81 1 . 7 4 1.76
1.74
L77
5.1
0.3
0.8
...
0.9
...
1.4
5.5 25.0 2 . 2 6.0 7.8 0.3 7.5 @,9 3 9 . 3 0 . 9 18.7 1.8 2.6 15.9 2 5 . 3 50.2 50.0 3 4 . 4 14.4 6 . 8 20.0 56.6 64.4 2.6 32.0 11.8
20.2 0.8 7.0 13.7 57.5 26.3
were obtained by recirculation of gases through the catalytic chamber, oxygen being added to maintain a suitable hydrocarbon-oxygen ratio. A single pass through the heated zone of the system resulted in a decomposition of the hydrocarbons in natural gas to the extent of 35 to 84 per cent in the case of ethane and 0.2 to 50.5 per cent in the case of methane, while the yield of oxygenated derivatives varied from 0.6 to 20.3 per cent of the total hydrocarbon, depending on the experimental conditions. It was found that a temperature of a t least 600’ C. and a heating time of about 0.5 second were necessary to obtain satisfactory yields. Effect of Auxiliary Catalysts with Nitrogen Dioxide
Some experiments, in which an activated charcoal and a platinum oxide catalyst were employed in conjunction with nitrogen dioxide, indicated that the use of these materials resulted in a decrease in the amount of oxygenated derivatives formed and an increase in yield of hydrogen, oxides of carbon, and steam. These auxiliary catalysts evidently activated the oxidation (or decomposition) of intermediate products of partial combustion under the experimental conditions used. At temperatures of 600” to 700” C. and a heating time of about 1.5 seconds the oxidation of pure methane and ethane was also materially promoted by the presence of small amounts of nitrogen dioxide in the influent gas. Yields of oxygenated derivatives were increased about thirty-fold in a single pass by the addition of 1 per cent of nitrogen dioxide to a gas mixture containing 27.5 per cent oxygen, 17.4 per cent ethane, and 52.1 per cent methane. I n all cases where nitrogen dioxide was employed as a catalyst the amounts of carbon dioxide obtained in the effluent gases were uniformly muchsmallerthan the corresponding amounts of carbon monoxide and hydrogen, indicating that the oxidation proceeded only to a small extent to the carbon dioxide-wder stage. Although an increase in the rate of gas flow resulted in the formation of greater amounts of oxygenated derivatives in relation to the yield of carbon monoxide and hydrogen, yet the total oxidation was less, thus necessitating recirculation. Table 111-Data for G a s e o u s C a t a l y s t s : S e m i - C o n t i n u o u s Apparatus A-02 (PYREX CATALYTIC CHAMBER)
Catalyst
.. .. .. ... ...
35.6 21.2 67.0 84.0 14.0 50.5
42.0
9.8 5.7
Temperature, Influent gas:
C.
C02 0 2
Hz
... ... 0.6
co 20.3
1.25
1.4
12.0
0.6
0.35 0
9 . 9 12.7
0.6
1.2
9.0 1.2
a NOS absent from influent gas.
b Includes any of gaseous catalysts which remained in effluent gas after scrubbing and was therefore removed as “Cot” in KOH absorption pipet. c Resulting from passing influent gas through catalytic chamber.
CHI
h-2
CHd:O? Time of heating, seconds Effluent gas: COP 0 2
Hz
co
CHI
Results with Gaseous Catalysts
Catalysts employed in the vapor phase gave varying degrees of success in pronioting the partial oxidation of gaseous hydrocarbons of the paraffin group. Sulfur trioxide in amounts of about 1.0 per cent by volume failed to accelerate the oxidation reaction in single-pass operation. Nitrogen dioxide, when present in amounts of from 0.3 to 5.0 per cent by volume, exerted considerable promoting action in the oxidation of mixtures of the hydrocarbon and oxygen when passed through a capillary tube of Pyrex glass or fused quartz heated to 600-700” C. The acceleratingeffect of nitrogen dioxide increased as the amounts of that gas in the initial gas mixture were increased, yields of oxygenated derivatives varying from 15 per cent to 30 per cent by volume of the hydrocarbon used were obtained. The higher yields
Vol. 20, No. 10
Iit
Volumes: Influent gas, cc. Effluent gas, cc. Contraction, cc. Per cent methane decomposed Per cent methane converted to oxygenated derivatives: Per experiment Total Yields of oxygenated derivatives per liter of methane decomposed, by analysis: Methanol, mg. Formaldehyde, mg. Formic acid, mg.
690
690
690
690
1.5 4.2 8.2 0.4 19.7 25.2 16.5 9.2 8.9 10.4 6.0 0 18.0 29.4 39.2 0.4 69.5 46.0 30.0 20.3 12.7 4.5 8 . 8 11.0 1.82 2 . 2 1 2.76 2.34 1.90 1.90 1.81 1.88 2.0 0 11.2 20.9 55.4 10.5
5.4 0 14.7 32.4 34.5 13.0
9.5 0.1 15.5 40.0 21.5 13.4
8.2 4.9 11.2 42.0 19.4 14.3
690 8.2 7.6 10.2 44.9 18.6 10.5 2.45 1.81
12.4 0.2 15.8 44.0 11.4 16.2
14270 12530 12290 10340 10183 11:059 11:319 10:181 10:032 91505 310 678 3,210 1,211 2,112 38.2 32.2 40.7 7.3 42.6 13.1
0.2
7.0
0.12
11.3
25 205 76
Addition of about 5.0 per cent by volume of hydrogen chloride to the influent gas caused some activation of the partial combustion reaction, but to a less degree than nitrogen dioxide. I n every case the promoting action of hydrogen
October, 1928
ISDUSTRIAL AA-D ESGIIYEERISG CHEIIfISTRY
chloride was less than that obtained by hledvedev, . a condition which probably is explained by the additional contact catalysts employed by hledvedev. Methyl Nitrite as Catalyst
.
Methyl nitrite in amounts of 1.0 to 2.0 per cent by volume were also shown to exert a promoting action less vigorous than that of nitrogen dioxide but more pronounced than that of other catalysts investigated under approximately similar operating conditions. The action of methyl nitrite was probably based on ii s spontaneous decomposition a t elevated temperatures into nitrogen dioxide or nitric oxide and a carbon-hydrogen-oxygen residue, the former acting as the catalyst. Explanation of Promoting Action of Nitrogen Dioxide and Methyl Nitrite
In order to obtain data on the character of oxygenated deiivatives formed in these reactions, experiments on a larger scale were necessary, utilizing a semi-continuous apparatus as mentioned previously. In a typical series of experiments, using pure methane as the hydrocarbon source, four passes of the gas through the system, adding oxygen before each pass in order, to maintain a constant oxygen-hydrocarbon ratio, resulted in a yield of oxygenated derivatives amounting to 25 mg. methanol, 205 mg. formaldehyde, and 76 mg. formic acid per liter (standard conditions) of methane decomposed. This was equivalent to 0.0093 atom carbon per liter of methane decomposed. Of the original amount of methane present. 80.3 per cent was decomposed in four passes, while 27.1 per cent appeared as oxygenated derivatives. Calculations indicated that 0.0151 atom of carbon per liter of methane decomposed should have been obtained, whereas only 0.0093 atom, or 61.5 per cent, was experimentally determined to have been present. The actual yield of oxygenated derivatives was probably decreased by decomposition reactions which took place in the condensate and scrubber during the run, since nitric acid was continuously present on account of the partial solution of nitrogen dioxide in water. I n fact, if the condensate temperature was allowed to rise to room temperature, it was observed
1055
that an ebullition occurred within the liquid, iridicatirig a decomposition reaction which resulted in the formation of a gas. Among these oxidations may have been those of formaldehyde and methanol to formic acid, as well. It is improbable that the pronounced action of small amounts of nitrogen dioxide in accelerating the partial oxidation of gaseous hydrocarbon-oxygen mixtures was a result of the formation of unstable intermediates by chemical reaction of the hydrocarbon and nitrogen dioxide. A more satisfactory explanation n-as sought in the readiness with which nitrogen in its oxides changes its valence, thus giving an opportunity for the accomplishment of adsorption phenomena of some character. In any case, the action of nitrogen dioxide appeared to be an additional example of homogeneous catalysis in the gaseous phase, for changing the composition of the chamber in which the catalysis occurred had apparently no effect on the nature of the reaction. hloreover. the rate of oxidation obtained in the small single-pass unit agreed closely with rates and degrees of oxidation obtained in the larger semi-continuous apparatus. For the purposes of this investigation it suffices to indicate that the promoting action of small amounts of nitrogen dioxide in partial oxidation of hydrocarbon-oxygen mixtures is far superior to that of the other solid and gaseous catalysts which were investigated. hloreover, the yields of oxygenated derivatives obtained were about double the amounts which the best5 of previous investigations on the basis of singlepass oxidation was able to indicate, and were many times larger than the yields secured by Wheeler and Blair4 in a circulation apparatus. Tabulated Results
Tables I to I11 show representative results obtained with variable gas-oxygen mixtures a t different temperatures under the influence of different catalysts. One hundred and fourteen tests were made in all. These results are most easily considered by noting the changes in percentages of carbon monoxide, the contraction in volume, tile “n-factor,” and the percentage of total hydrocarbons con\-erted to oxygenated derivatives under the varying conditions.
Relative Rates of Reaction of Olefins in Combustion with Oxygen and in Oxidation with Aqueous Potassium Permanganate’” Harold S. Davis3 LIASSACHUSETTS
ISSTITUTEOF TECHNOLOGY, CAMBRIDGE, hfASS.
With a view to investigating the relative rates of combustion of the olefins, known mixtures of ethylene and propene and of ethylene and isobutene were exploded with oxygen, and the proportion of each olefin remaining unburned was found by analysis of the products. One slow combustion was also made of a mixture of ethylene and isobutene. In every case propene or isobutene burned faster than ethylene. To test their relative ease of oxidation by potassium 1 Contribution No. 34 from the Research Laboratory of Organic Chemistry, Massachusetts Institute of Technology. 2 This paper contains results obtained in an investigation o n the “Relative Rates of Reaction of the Olefins” listed as Project No. 19 of American Petroleum Institute Research. Financial assistance in this work has been received from a research fund of the American Petroleum Institute donated by John D. Rockefeller. This fund is being administered by the Institute with the cooperation of the Central Petroleum Committee of the National Research Council. Director and research associate, Project N o . 19.
permanganate, known mixtures of ethylene and isobutene were dissolved in water and oxidized by a deficiency of permanganate. Then the proportion of each olefin unoxidized was found by boiling out the gases and analyzing them. Here again isobutene reacted faster than ethylene. Calculations of the relative rates of reaction based on a formula developed by Francis, Hill, and Johnston are given. Relative Rates of Combustion with Oxygen
A
PPARATUS-Fifty cubic centimeter samples of the gas mixtures were exploded over lmter in upright thick’ walled Carius tubes (or similar ones of Pyrex glass). The upper end of the tube mas closed by a rubber stopper (wired in) through which passed two glass tubes carrying platinum or tungsten electrodes and an exit tube with a glass stopper. The inner surface of rubber exposed was small and was
