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unit separate from the regular production units on account of the much larger grain size desired. A Herman mill, complete with Hummer screen, magnetic separators, conveyors, and storage bins, handles this material. The chemical laboratory ware uses the same material as the regular production. It is prepared as a slip and the shapes are formed by a combined jiggering and casting process. The ware is dried and fired in the same way as the spark-plug cores. An attempt has been made in this article to describe the thorough-going way in which control methods have been utilized in developing a program of continuous production. The process of improvement is still going on. One by one variable factors are being eliminated or restricted within increasingly narrow limits and as they are controlled new possibilities are being opened for the accurate understanding
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of the fundamentals in that hitherto very practical and but slightly fundamental industry which is devoted to the production of ceramic wares. Acknowledgment
The writers wish to express their indebtedness to J. A. Jeffery, president of the Champion Porcelain Company, for permission to present this article, and their thanks to L. E. Jeffery, who is in direct charge of the installation for the burning of ware, for valuable assistance in preparing the section on that process. Literature Cited (1) (2) (3) (4)
Bowen and Greig, J . A m . Ceram. 5'06, 7, 238 (1924). Greig, I b i d . , 8, 466 (1925). Peck, I b i d . , 8, 407 (1925). Riddle and Twells, I b i d . , 10, 281 (1927).
Studies on Production of Acetylene from Methane I-Cracking
under Vacuum1
Per K. Frolich, A. White, and H. P. Dayton DEPARTMENT OF CHEMICAL ENGINEERING, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS.
A study of the cracking of substantially pure methane tion reactions and therefore has been made at temperatures above 1000" C. and presin the economic utilizapermit a larger portion of the sures ranging from atmospheric down to 25 mm. At tion of cheap natural a c e t y l e n e to come through these high temperatures acetylene is a main primary gas available in enormous unchanged. product of the cracking but has a marked tendency It was the purpose of the quantities has led to renewed to polymerize into benzene and similar compounds, as present investigation to study attempts to convert methane well as to decompose further into carbon and hydrogen. this effect of pressure below into acetylene. Acetylene, In order to recover the acetylene as such, it becomes atmospheric on the producaside from its value as such, necessary to employ exceedingly short times of contact. tion of acetylene by cracking may be considered as a startWithin the range of conditions studied, however, it of substantially pure methane. ing material for the synthesis has not been possible to show that pressure below atof v a r i o u s o r g a n i c comExperimental Work mospheric has any appreciable effect on the acetylene Dounds, such as benzene by Methane containing from polym'erization and acetic Yield. 1.7 to 2.0 per cent et8haneand acid a n d acetaldehyde by catalytic oxidation. Of these products benzene is of particu- 0.9 to 1.0 per cent propane as impurities was passed through lar interest to the petroleum industry because as an anti- an electrically heated quartz tube in which the desired presknock for gasoline it has an almost unlimited market, pro- sure was maintained by a vacuum pump. The inlet gas rate was measured by means of a calibrated orifhe flowmeter vided it can be produced a t a sufficiently low cost. Recent patent and periodical literature has disclosed the and the exit rate with a wet gas meter. The effluent gas possibility of producing benzene from methane by a process was analyzed for acetylene by absorption in slightly ammoniaof combined cracking and polymerization a t temperatures cal cuprous chloride,2 for ethylene by absorption in saturated in the neighborhood of 1000" C. or higher. Thus, Stanley bromine water, and for hydrogen by oxidation over actiand Nash (6) report that at 1150" C. and 0.6 second time of vated cupric oxide. By combustion with oxygen the recontact a yield of 0.2 gallon of benzene per 1000 cubic feet mainder of the gas was shown to consist of methane. of methane was obtained, corresponding to a conversion of The apparatus consisted of a cylinder of methane under 4.8 per cent of the entering methane. They also state that pressure, a reducing valve to bleed the methane down to 8.8 per cent of the methane appeared in the product as acety- atmospheric pressure, a calibrated orifice flowmeter, a malene and ethylene. Results obtained in this laboratory on nometer, a second reducing valve through which the methane the production of aromatics from methane at atmospheric was let into the electrically-heated quartz tube, a waterpressure in electrically-heated tubes substantially agree with cooled condenser, and glass wool trap, followed by a vacuum the data published by these investigators and others work- pump and finally a wet meter. The pressure in the cracking ing in the same field (3, 7), pointing to the possibility of tube was measured by means of a manometer and was reguacetylene as an intermediate product when operating a t lated by the speed of the vacuum pump or by a by-pass temperatures of the order of magnitude of 1000" C. arrangement. Two types of pumps were employed, one of Jones (5) states that in passing methane through a hot the oil-vacuum and the other of the ejector type. The first quartz tube the yield of acetylene reaches a maximum a t contained only a very small quantity of oil and blank exa pressure of 30 to 40 cm. of mercury. That a reduction periments showed that the amount of gaseous products in pressure should actually favor the process might be antici- absorbed in the pump was only a negligible fraction of the pated, because the lower partial pressures in a system operat2 This method is satisfactory for the determination of acetylene in the ing under vacuum would tend to decrease the polymeriza- presence of ethylene over the concentration range covered by the present
HE widespread interest
T
1
Received October 31, 1929.
experiments.
INDUSTRIAL A h D ENGIh'EERING CHEMISTRY
January, 1930
total gas resulting from the cracking. The ejector was connected to recirculate a saturated zinc sulfate solution in order to minimize the absorption of gas. It appeared that the results obtained with both these pumps were essentially the same. The condenser and trap were kept under vacuum, 80
3 c 40
30
L
1 b
2 0 IW
:: 10
D.
0
TLMPERATURE 'Ca
21
Results and Discussion
The results of a series of experiments made to study the effect of temperature on the cracking of methane under vacuum are shown in Figure 1. While it was intended t o maintain all other conditions constant, the pressure fluctuated between 33 and 102 mm. of mercury and the time of contact between 0.8 and 1.0 second in these runs. However, it is apparent from the data reported that variations within these limits have only a negligible effect upon the composition of the cracking products. Hence Figure 1 may be considered as representing the effect of temperature on cracking of methane under otherwise parallel conditions. The acetylene content of the exit gas increases with temperature until a t the highest temperature studied, 1150' C., it reaches a concentration of slightly less than 2 per cent, corresponding to about 4 per cent conversion on the basis of methane reacting. Above 1120" C., however, the cracking to carbon and hydrogen is so rapid that the reactor becomes clogged shortly after an experiment has been started, thereby limiting the temperature which can conveniently be employed in operation under these conditions. Figures 2 and 3 show the effect of pressures below atmospheric on the cracking of methane a t a constant temperature of 1120" C. and a time of contact of 0.60.1 seconda3 From
Figure I-Effect of Temperature on Cracking of M e t h a n e under Vacuum Absolute pressure = 33-102 mm. mercury; time of contact = 0.8-1.0 second
the condenser to cool the gas and to remove any nonvolatile polymers and the trap to filter out any carbon and tar before the gas entered the pump. Effluent gas samples were taken after the gas had left the pump. The temperatures reported were measured by means of a thermocouple in the gas stream in the center of the reaction tube, but because of radiation from the wall of the tube the readings of the thermocouple were undoubtedly somewhat higher than the actual gas temperatures. Both the reactor and the thermocouple well were of quartz, which seems to have little catalytic action on the cracking of methane. 3.0
30 w z 0 0
sog
2.0
g2 kt
1055
110
YZ a
w O Q
0
0
0.2
0.4 0.6 0.b 1.0 1.2 TIME OF CONTACT IN SECONDS
Figure 4-Effect of Time of Contact on Cracking of Methane under Vacuum Absolute pressure = 33-64 mm. mercury; temperature = 1120" C.
0
Figure 2 it will be seen that the concentration of acetyb n e in the exit gas increases slightly with increasing pressure. The upward trend of the acetylene curve, however, is the result of an increase in the amount of methane cracked, for by recalculating the data to a basis of entering methane, as illustrated in Figure 3, it appears that the conversion to acetylene remains practically constant for pressures ranging from 25 mm. up to 1 atmosphere. Furthermore, as the percentage of methane going to carbon and polymerization products increases continuously with increasing pressure (Figure 3), it follows that there actually is a decrease in acetylene yield on the basis of methane reacting. This is not in agreement with Jones (5), who states that the maximum yield of acetylene occurred in his experiments a t pressures of 30 to 40 cm. As no experimental data are given to support
Figure 3-Effect of Pressure below Atmospheric on Conversion of Methane to Cracked Products Temperature = 1120' C.:time of contact = 0.6-1.0 second
8 By time of contact is meant the actual time required for a gas molecule to travel through the reaction zone. By determining the temperature distribution through the quartz reactor, this time may be estimated with fair accuracy.
0
100
200
300
400
500
600
700
LOO
ABSOLUTE PRESSURE IN MILLIMETERS OF MERWRY
of Pressure below Atmospheric on Cracking of Methane Temperature = 1120° C.: time of contact = 0.6-1.0 second
Figure 2-Effect
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0 0
100 200 300 400 500 600 700 ABSOLUTE PRESSURE IN MILLIMETERS OF MERCURY
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this conclusion, however, it is not possible to ascertain the reason for the apparent discrepancy. Also, the conversion to carbon and polymerization products parallels the total increase in cracking with rising pressure. The fact that the amount of methane cracked increases with increasing pressure for constant time of contact may be due to variations in the gas temperature, as it may be assumed 20
10
0 0
0.2
0.4 0.6 0.6 10 . TIME OF CONTACT IN SECONDS
1.2
Figure 5-Effect of T i m e of Contact on Conversion of Methane under Vacuum to Cracked Products Absolute pressure = 33-64 mm. of mercury; temperature 11200 c.
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polymers by stepwise reaction when methane is cracked at this high temperature level. That times of contact above 1 second have little effect upon the yield of acetylene, but markedly increase the formation of carbon and polymers, is shown by Figures 6 and 7. The irregularity of the experimental points in these diagrams, as compared with those previously given, is due to the heavy deposition of carbon in the reactor and, to a certain extent, to the formation of polymers (9). This deposition of carbon, which in some cases exceeds 30 per cent on the basis of entering methane, made it difficult to niaintain constant conditions in the apparatus. Although the methane used contained a small amount of ethane and propane, these higher hydrocarbons were not present in quantities sufficient to account for the acetylene produced. Thus, the highest yield of acetylene reported in
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that the thermocouple receives more heat by radiation and less by conduction and convection the lower the pressure on the system. Hence, for constant thermocouple readings, it is not impossible that the true gas temperature increases somewhat as the pressure rises and thereby accounts for the increased cracking. It might also be inferred that the increased pressure favors polymerization of the acetylene, thus removing it from the reaction zone and permitting further cracking to take place. I n the latter case it would be necessary to assume approach to equilibrium conditions in the cracking reactions. However, in the light of the admittedly very qualitative data on the methane-acetylene TIME OF CONTACT IN SECONDS
3
Figure 7-Effect of T i m e of Contact on Conversion of Methane under Vacuum to Crarked Products Absolute pressure P 203-241 mm. mercury; temperature = 1120' C.
t W
z W W
Figure 4 corresponds to 4 times that which could possibly have been obtained by quantitative conversion of the ethane and propane. On the basis of other experimental work ( I ) , it is improbable that the small amounts of propane and ethane account for more than an insignificant fraction of the total acetylene produced, as there is reason to believe that these higher hydrocarbons are quantitatively converted into propylene and ethylene in the preheating zone-i. e., before the gas mixture reaches the temperature required for acetylene production. It may further be assumed that the resulting olefins are partly polymerized into aromatics ( I ) , while the remainder accounts for the rather constant value for ethylene shown by all the diagrams.
1 0
