Effects of High-Voltage Discharge on Thermal Decomposition of Ethane IRWIN H. PARRILL' AND W. G. EVERSOLE The State University of Iowa, Iowa City, Iowa
T
HE effects of high-voltage discharge on chemical reactions have been observed and recorded since ancient times. References to the sulfurlike odors accompanying strokes of lightning by Homer in the Illiad and Odyssey are among the earliest. The use of the varied and controlled forms of electrical discharges as activating agents for chemical phenomena opens an immense field for study of both theoretical and practical interest. The purpose of this investigation was to determine the effect of the ozonizer type of glow discharge on ethane a t lower temperatures than those a t which ethane shows definite decomposition as the result of thermal action alone. The results of the decomposition by the combined thermal and electrical action are compared with the results obtained by thermal and electrical treatment separately. Apparatus The reaction chember was the annular space between two concentric Pyrex tubes with outlets sealed into the outer tube. The thickness of the annular space was about 2 mm.
n
Rmtm Tube or3 Here! Hrsembly
Ethane is decomposed to ethylene and hydrogen in the glow discharges. Methane production becomes greater at higher temperatures and higher energy input. Decomposition of ethane occurs in the glow discharge, yielding decomposition products corresponding to those obtained by thermal action at 300' C. higher temperature. Decomposition proceeds at temperatures as low as 100' C.
serted in an electrically heated and manually controlled furnace (Figure l). The temperatures below 380" C. were measured with a mercury thermometer. Higher temperatures were measured by a copper-constantan thermocouple and a potentiometer. Temperature measurements were made on the inner tube a t one-minute intervals. A roll of brass plate, 0.015 cm. thick, wrapped tightly on the outside of the outer concentric tube and another roll inside the inner tube served as electrodes. The discharge was produced in two ways: (a) by an induction coil operating on 6 volts a t about 8 amDeres and develoDing 75,000 volts; (b) a Jefferson 15,000-volt transformer operating on 110 volts, 25 cycles. The reaction chamber was filled with ethane by displacing mercury. At the temperature desired the discharge current was turned on for 15 minutes. The gaseous product was passed directly to the gas analysis apparatus. The gases collected were analyzed by a modified Orsat apparatus. Check runs analyzed in the Podbielniak model A apparatus indicated that the Orsat method was satisfactory for our purpose.
m
Results The decomposition of ethane in the glow A . To gas analysis discharge for a 15-minute period is shown B . T o water-jacketed buret in Figure 2 in which the percentage of C. T o rheostat ethane in the final gaseous mixture is plotted against the temperatures a t which the runs were made. The data are given in Table I. These The outside diameter of the outer tube was 3 cm. The tubes curves are practically straight lines showing that the amount were 40 om. long and were made of Pyrex glass 1 mm. thick. of ethane decomposed increased regularly and linearly with The reaction chamber capacity was about 100 cc. It was inincrease in temperature. The rate of decomposition was 1 Present address, Panama Canal Testing Laboratory, Pedro Miguel, greater with the transformer discharge than with the inducCanal Zone. 1316 FIGURE 1. HEATER ASSEMBLY
INDUSTRIAL A N D ENGINEERING CHEMISTRY
October, 1941
1317
7 hours a t the temperatures indicated on the graphs plus 300" C. Their results at the higher temperatures correspond remarkably well with the results reported here for the electric discharges. A line through their points on Figure 2 would show a somewhat greater change of decomposition rate with increase of temperature than for either type of electrical discharge.
FIGURE2. ETHANE REMAININQ AT ENDOF RUNSUSING INDUCTION COIL( 0 )AND TRANSFORMER (0 ) V Williams and Qardner (4, continuous circulation for 4-7 hours a t temperature indicated plus 300' C. Egloff et al. ( I ) , minimum decomposition temperature for ethane. p Frey and Smith (Sl, ethane decomposition in a 400-cc., round silica flask. Q Williams and Gardner ( 4 ) , 60 00. per minute for 7 hours in a porcelain glazed tube. V Williams and Gardner ( 4 ) , continuous static runs. A
tion coil discharge. A small but undetermined amount of free carbon was present in the reaction tube after each run. The percentage of hydrogen formed is plotted against the temperature for the two types of discharge in Figure 3A. Hydrogen production in the transformer glow discharges reaches a maximum a t about 300' C. The decrease in hydrogen produced may be due to the consumption of hydrogen in forming the increased quantity of methane. I n the case of the induction coil discharge, there was a continued increase in the amount of hydrogen produced and little increase in the percentage of methane with increase in temperature (Figure 3B).
20
w
z W
-I
>-
O F ETHANE FOR TABLEI. DECOMPOSITION DISCHARGEO
Tzrng.,
Ethane,
%
80.2 78.9 73.3 68.5 67.6 62.0 63.0
56.6
61.2
130
175 230 320 350
74.8 66.0 60.0 46.0
Hydrogen, %
Methane, %
1.8
12.6
4.2 6.1 8.0 12.4
12.6
2.3
15.2
12.4
...
14.4 17.6
...
16.8 22.2 36.1
21.6
8.3 19.0 15.9
6.8 8.0 19.6 34.5 41.0 61.6
...
...
...
THE
TWO TYPESO F
I O
r I-
w o
5.5
Discharge6 I
...
I
11.6 12.7 14.0
I
Ethylene, % 5.9
... 9.4 10.4
I
I I I
200
300 400 500 TEMPERATURE "C,
600
FIQURE 3. HYDROGEN, METHANE, AND ETHYLENE BY ACTION OF INDUCTION COIL( 0 ) AND FORMED TRANSFORMER ( 0 )DISCHARGE ON ETHANE
I
I
17.0
I
10.1
T T
10.5 11.9 12.2 10.8 10.8
100
T T
... 14.3 T 450 17.6 10.0 T Results are averages of two to seven runs at the temperatures specified; partial analyses are included in the averages. b I induction coil discharge; T = transformer discharge.
-
Decomposition of ethane has been accomplished at 100' C. in the electric discharges. This may be compared to the slower but definite decomposition of ethane by Lind and Glockler (3) a t room temperature. These temperatures are considerably lower than the minimum of 485" C. for thermal decomposition of ethane reported by Egloff (1). Literature Cited
With the transformer discharge the percentage of ethylene reached a maximum a t about 300' C. (Figure 3C). A second series of reactions became effective a t this temperature and resulted in methane production (Figure 3B). Data from the work of Williams and Gardner (4) are included in Figures 2 and 3 in the form of inverted triangles ('7). They were obtained by circulating the ethane from 4 to
(1) Egloff, Schaad, and Lowry, J. Phys. Chem., 34, 1673 (1930). (2) Frey and Smith, IND. ENG.CHEM., 2 0 , 9 4 8 (1928). (3) Lind and Glockler, J . A m . Chem. SOC.,52, 4450-61 (1930); Trans. A m . Electrochem. Soc., 52, 37-46 (1927). (4) Williams and Gardner, Fuel, 4, 430 (1925). ABSTRACTED from a dissertation submitted in partial fulfillment of the requirements for the degree of doctor of philosophy in the Department of Chemistry, Graduate College, State University of Iowa.
