INDUSTRIAL A N D ENGINEERING CHEMISTRY
1396
Vol. 23, No. 12
Gaseous Products from Action of Cathode Rays on Hydrocarbons’ C. S. Schoepfle and C. H. Fellows UNIVERSITY OF MICHIGAN,
‘
ANN ARBOR,M I C H . ,
AND
THEDETROIT EDISONCOXPANY,
DETROIT,
MICH.
A number of hydrocarbons have been subjected to URING the operation operated a t 170,000 volts and cathode-ray bombardment and the volume and comof oil-impregnated, 0.3 milliampere, in order to position of the gaseous products determined. Satupaper-insulated, leadprevent u n d u e h e a t i n g of covered cables a t high volrated hydrocarbons give large amounts and unsaturated the window which might rehydrocarbons small amounts of gas consisting of hydrotage, there is deposited in the sult in pyrogenic cracking of gen and saturated hydrocarbons; aromatic hydrocable an i n s o l u b l e , flaky, the h y d r o c a r b o n v a p o r . carbons give practically no gaseous products; branchedwax-like substance, called The actual distance of the chain compounds give more methane and other gaseous ‘(X” c o m p o u n d or “wax.” surface of the sample from saturated hydrocarbons than straight-chain comThis wax is a condensation the window of the tube was pounds. The reaction is shown to be similar to that product of the hydrocarbon 72 mm. By standardizing of hydrocarbons under the influence of the corona oils used in the immemathe conditions of the test in tion, and can be produced exdischarge or of particles. this manner, a quantitative perimentally by subjecting comparison of the results with the oil to a gaseous electric discharge. The formation of wax various hydrocarbons could be made, since the energy input in is accompanied by the liberation of a gas, consisting principally the reaction was the same in each case, even though its exact of hydrogen, and this production of gas in the cable is un- value was unknown. doubtedly of importance in connection with the deterioration With two exceptions, the hydrocarbons used in this work of cable with use. were obtained from the Eastman Kodak Company in the best I n a previous paper (6) the effect of cathode rays upon grade available, and were used without further purification. hydrocarbon oils of known history was investigated, particu- Phenanthrene was a chemically pure Kahlbaum sample and larly in regard to the volume and constitution of the gas 2,5-dimethyl hexane was synthesized. which was formed. The reaction of the oils under the A partial analysis of the gas produced in each raying period bombardment with cathode rays was found to be the same as was obtained by transferring it to a bulb immersed in liquid that obtained by means of the corona discharge2 (and also by air and pumping off the volatile portion, consisting of hydrocr particles) and therefore it was concluded that the results gen and methane, to a buret where the volume was measured. obtained in the cathode-ray experiments would give reliable The hydrogen in this mixture was then determined by cominformation concerning the behavior of the oils when used as bustion with cupric oxide, and the methane by combustion impregnating compounds in cable. Since there was a marked with a hot platinum spiral after admixture with oxygen. The difference in the nature of the reaction with different oils, the portion of gas which was nonvolatile in liquid air was probsaturated oils producing large volumes of gas in comparison ably a mixture of ethane, propane, butane, etc. It was shown with those volumes produced by the unsaturated oils, it was to be saturated in character, as it did not add bromine, but decided to extend the investigation to pure hydrocarbons was not studied further. where the results could be definitely correlated. In the The formation of complex compounds of high molecular present work a study has been made of the effect of cathode weight was observed when the hydrocarbons were subjected rays upon a large number of hydrocarbons, in order to deter- to longer periods of bombardment. For example, n-tetraq i n e in particular the relationship which exists between the decane, after being rayed for 16 hours, deposited about 0.15 structure of the compound and the volume and constitution gram of an insoluble solid product which was unsaturated of the gas which is evolved in the reaction. in character inasmuch as it absorbed oxygen from the air. The apparatus and the procedure used in the present raying In appearance and properties it resembled wax obtained from experiments were essentially the same as those described in cable or from the action of the corona discharge on hydrothe previous work on oils. A sample of 25 cc. of the hydro- carbon oils. carbon, which was more than sufficient to absorb all of the The data for the gaseous products obtained in the raying cathode rays, was placed in a flat-bottom, glass reaction experiments with hydrocarbons are given in Table I. The chamber, 70 mm. inside diameter, which was connected by volume of gas given in the table has been reduced to normal means of a side arm to a vacuum pump and t o a buret. The temperature and pressure and has been corrected by subreaction chamber with the sample was sealed to the bottom of tracting the volume of vapor of the hydrocarbon under test the Coolidge tube which was mounted in a vertical position. in those cases where the correction was appreciable-i. e., for The reaction chamber and its contents were immersed in ice Compounds with boiling points below 150’ C. The vapor water and evacuated, after which the sample was rayed for a pressure data when not given in the literature were obtained period of 30 minutes. The gas produced in the reaction was by the simple procedure described by Francis ( I ) , which gave transferred by means of a Toepler pump to a buret where the results sufficiently accurate for this purpose. The values volume was measured, and then the sample was rayed for a given for the volume of gas are usually the average of three second 30-minute period and finally for a third period, the 30-minute raying periods on a single sample, but in many gas being pumped off and measured in each case. The tube, cases several experiments with the same hydrocarbon were although rated a t 350,000 volts and several milliamperes, was made. The results checked reasonably well considering the 1 Received August 13, 1931. minor variations possible in the operation of the tube, and are 9 The reaction of hydrocarbons in the electric discharge at low pressures considered to be accurate to about 10 per cent, except in the and with high current density is quite different from that in the corona case of the aromatic compounds where very limited quantities discharge inasmuch, as in the former case, the products are often similar to of gas were obtained. With these compounds the error may those resulting from thermal reactions (3).
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December, 1931
I X D I ‘ S T R I A L A.VD ENGINEERING CHEMISTRY
be quite large, since there is a small amount of gas (usually about 0.5 cc.) obtained from the reaction chamber itself for which no correction has been made. The results obtained in the present investigation therefore substantiate the conclusion drawn from previous work that the reaction of hydrocarbons under bombardment of cathode rays is analogous to that produced by a rays or by the corona discharge. The saturated hydrocarbons react with elimination of hydrogen to give condensation and perhaps polymerization products of higher molecular weight, and methane and saturated hydrocarbons of lower molecular weight than the original compound are also formed in varying amounts. The unsaturated aliphatic hydrocarbons behave similarly except that much less gas is formed, and the aromatic compounds give practically no gas a t all. Five straight-chain and two branched-chain members of the paraffin series were studied. The volume of gas was largest with hexane, 57 cc., and decreased with increase in molecular weight to 35 cc. for n-tetradecane. The three isomeric octanes gave approximately the same volume, indicating that the amount of gas was not appreciably different with straight-chain and branched-chain compounds of the same molecular weight. The varying quantity of gas obtained with different members of the paraffin series may be due to a different rate of reaction in the gaseous and liquid phase, since both vapor and liquid are being bombarded under the conditions used. If the reaction is more rapid in the gaseous phase, then we should expect to obtain larger volumes of gas with the compounds of lower molecular weights and higher vapor pressures, since the amount of the reaction taking place in the gaseous phase depends upon the vapor pressure. The cycloparaffins, cyclohexane and methyl cyclohexane, which are saturated, also gave large volumes of gas, although the amounts were somewhat less than with the corresponding open-chain paraffins, hexane and heptane. Two unsaturated hydrocarbons containing eight carbon atoms and one double bond were studied-namely, caprylene, which is probably a mixture of 1-octene and 2-octene, and diisobutylene, which is probably a mixture of 2,4,4,-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene. These olefins gave 16 and 21 cc., respectively, in comparison with the three saturated octanes which gave approximately 50 cc. Two cyclo-olefins, cyclohexene and 1-methyl cyclohexene, gave 19 cc. and 14 cc., compared with 46 cc. and 40 cc. for the corresponding saturated cycloparaffins. That is, the presence of one double bond in the molecule was sufficient to decrease the volume of gas to considerably less than one-half the amount obtained from the saturated compound. The unsaturated hydrocarbons, pinene and limonene, also gave small volumes of gas-namely, 5.5 cc. and 7.5 cc., respectively. The difference is even more marked with the aromatic compounds, which in most cases gave less than 1 cc. of gas. Only when the number or size of the side chains becomes of importance does the volume of gas rise appreciably, as in the cases of hexamethylbenzene and p-cymene. These results are in agreement with those obtained with hydrocarbon oils, where, for example, a highly refined and therefore highly saturated wax and oil mixture gave 40 cc. of gas, whereas certain highly unsaturated oils gave as little as 2 cc. of gas per 30-minute raying period.3 An interesting comparison is found in the case of naphthalene, an aromatic hydrocarbon, decahydronaphthalene, a saturated derivative belonging to the cycloparaffin series, and tetrahydronaphthalene, which is intermediate between the two, being partly saturated and partly benzenoid in character, The volumes of gas obtained from the three compounds were 8 Correction: Sample 2 in Table 111, p. 533, in the previous article ( 5 ) should read “saturated wax” instead of “unslturated.”
1397
0.5 cc. from naphthalene, 37.2 cc. from decahydronaphthalene, and 2.6 cc. from tetrahydronaphthalene. The last compound gave only a few cubic centimeters of gas in spite of the fact that part of the molecule is saturated. Phenyl cyclohexane, of which one half of the molecule is saturated and the other benzenoid, shows a similar behavior in that only about 2 cc. of gas were obtained. Again, a mixture of 90 per cent benzene and 10 per cent cyclohexane, which should give (0.9 X 2.2) (0.1 x 45.8) = 6.6 cc. of gas if the two components reacted in proportion to the percentage of each present, actually gave about half this amount-namely, 3.2 cc. It appears, therefore, that the hydrogen which is produced in the condensation may be taken up by unsaturated compounds with which it is in contact a t the moment when it is liberated and in an active form. If the molecule is partly or wholly unsaturated in character, the conditions are most favorable for the hydrogen to be completely taken up-that is, the hydrogen is simply transferred to the new molecule resulting from the condensation. The amount of gas obtained with various classes of hydrocarbons is therefore not a measure of the extent of condensation.
+
Table I-Data
f r o m Raying Experiments with Hydrocarbons
T6-N
HYDRO-
%
%
POR-
METAANE HYIN DRO- METE30- VOLA- VOLA- IN MIN. TILE TILE VOLA-VOLA-DEN A N E PERIOD IN IN TILE TILE IN IN (N. T. LIQUIDLIQUIDPOR- POR- TOTALTOTAL P.) AIR AIR TION n o N GAS GAS GAS PER
HYDROCARBON
cc. Paraffins: n-Hexane n-Heptane n-Octane n-Decane n-Tetradecane 2,5-Dimethylhexane 2,2,4-Trimethylpentane Olefins: Caprylene Diisobutvlene Cycloparaffins: Cyclohexane Methylcyclohexane Decahydronaphthalene Cyclo-olefins: Cyclohexene 1-Methylcyclohexene Pinene Limonene Aromatics: Benzene Toluene Hexamethylbenzene p-Cymene Naphthalene a-Methylnaphthalene @-Methylnaphthalene Anthracene
Phenyicyclohexane 90% benzene 10% cyclohexane
+
PORTION
%
NON-GEN
%
%
%
66.3 5.3 76.9 3.9 78.8 2.8 78.9 2 . 1 91.1 1.6 42.1 11.6 35.1 1 5 . 2 1 6 . 4 75.0 2 5 . 0 92.3 20.8 5 5 . 3 44.7 70.5
6 . 5 69.2 29.2 39.0
4.8 16.1
45.8 91.0 39.2 8 7 . 0 37.2 98.8
9 . 0 97.7 13.0 9 5 . 2 1 . 2 99.5
1 . 4 88.9 3.6 82.8 98.3
1.3 3.1
18.8 14.0 5.5 7.6
39.0 93.0 19.3 92.0 25.1 21.1
6 . 0 66.7 6 . 5 74.2
3.7 6.3
61.0 80.7 74.9 78.9
..,.
..
..
..
,.
..
..
.. ..
2.2 2.7 7.5 3.5
