INDUSTRIAL AND ENGINEERING CHEMISTRY
588
Sage, Lacey, and Schaafsma (4) examined methanepropane mixtures over an extensive temperature and pressure range. From the gas and liquid compositions given by them, X / z values for methane were calculated a t 10, 20, and 30 atmospheres. These values were also plotted in the graph; these constants seem to deviate from those calculated from butane-methane mixtures and to decrease with temperature. This abnormal behavior is due to the vicinity of the critical range of the propane-methane mixtures.. Hill and Lacey ( 2 ) determined the solubility of methane a t 30" C. and 20.4 atmospheres in n-pentane, n-hexane, and nheptane. The mole fraction of methane is recorded for the liquid phase, not for the gas, where it is approximately 1, since there is, only a little solvent in the gas phase. The mole fraction of the solvent in the gas was, however, found approximately by multiplying the mole fraction in the liquid by the equilibrium constants predicted by Souders, Selheimer, and Brown (6)for the component in question from the known vapor pressure and the compressibility as a gas. The mole fraction of methane in the gas phase was thus fairly accurately known, so that equilibrium constants for methane dissolved in n-pentane, n-hexane, and n-heptane could be determined. These were also plotted in the graph, after being corrected for the small difference between 20.4 and 20.0 atmospheres. I n the case of mixtures of methane with pentane, hexane, or heptane, the density of the liquid phase a t a given temperature and pressure is greater than for mixtures of methane with butane.
VOL. 30, NO. 5
The equilibrium constants for methane, determined from the solubility in pentane, hexane, and heptane, are nevertheless in good agreement with the curves for the equilibrium constants of methane found in the above mentioned examination of methane-butane mixtures. The influence of the greater density of the liquid phase on the equilibrium constants of methane seems therefore to be small. It is concluded, then, that the heavy lines in the graph will also give a good approximation for the equilibrium constants of methane in natural gasolines, as these are chiefly mixtures of lower paraffin hydrocarbons. From measurements by Sage, Webster, and Lacey (6) concerning the solubility of methane in n-pentane, n-hexane, cyclohexane, and benzene, it may be concluded that the equilibrium constants of methane become higher when a mixture contains many naphthenes and increase considerably when many aromatics are present.
Literature Cited (1) Dijck, W. J. D. van, J . Inst. Petroleum Tech., 18, 145 (1932). ( 2 ) Hill, E. S., and Lacey, W. N., IND.ENQ.CHEM.,26, 1324 (1934). (3) Podbielniak, W.J., IND.ENQ.CHEM.,Anal. Ed., 3, 177 (1931).
(4) Sage, B. H., Lacey, W. N., and Schaafsma, J. G., IND. ENG. CHEM.,26, 214 (1934). (5) Sage, B. H., Webster, D. C., and Lacey, W. N., Ibid., 28, 1045 (1936). (6) Souders, M.,Jr., SeIheimer, C. W., and Brown, C. G., Ibid., 24, 517 (1932). RECEIVED September 6, 1937.
Thermal Decomposition of Hexane at High Pressures J. N. PEARCE AND J. W. NEWSOME1 State University of Iowa, Iowa City, Iowa
The thermal decomposition of hexane has been studied at pressures of 14,000 to 15,000 pounds per square inch (984 to 1054 kg. per sq. ,cm.) at 10" intervals between 430" and 520" C. and for periods varying from a few minutes to 2 hours. Decomposition occurs in all cases to form compounds boiling both higher and lower than hexane : carbon is deposited in some cases. The gaseous products boiling below 100" C. are chiefly aliphatic in nature; in the products boiling above 100" C., the cycloparaffins predominate with appreciable amounts of aromatics and some olefins.
LTHOUGH a vast amount of work has been done on the thermal decomposition of paraffins at low pressures, relatively little attention has been given to similar studies a t high pressures. Huge1 and Artichevitch (6) found
A 1
Present address, Aluminum Research Laboratories, New Kensington. Pa.
that, when hexadiene is heated to 470' C. under 500 atmospheres, 60 per cent is converted t o lower boiling products. Kat6 (7) decomposed petroleum under pressures of 50 to 300 atmospheres. H e found that the loss as carbon deposit and noncondensable gases increases with the pressure, especially above 200 atmospheres. Leslie and Potthoff (8) found that the amount of olefins in the gaseous products is slightly diminished when the gas is cracked under a pressure of 500 pounds per square inch. However, the literature reveals no complete data showing the effect of very high pressures on the nature of the gaseous products. The present paper presents the results obtained in a preliminary study of the decomposition of n-hexane under very high pressures. Hexane appeared to be especially suited for such a study, since its decomposition a t low pressures was fully investigated rather recently (4). Because of mechanical restrictions the quantity of liquid products available was too small for accurate qualitative or quantitative analysis. Rice (10) assumed that the decomposition of a hydrocarbon involves the intermediate formation of free radicals and that the only stable radicals are the methyl and ethyl groups. The data of Frey and Hepp (4) on the decomposition of hexane a t low pressures agree fairly well with the predictions of Rice. The high-pressure products provide a n interesting contrast to these data.
INDUSTRIAL AND ENGINEERING CHEMISTRY
MAY, 1938
Apparatus and Materials The thermal decompositions were carried out in a molybdenum steel bomb of 148-cc. capacity. It is cylindrical in shape, with a 3-em. bore and a wall 4 cm. thick. The head is pierced. by two small holes; one opens into the thermocouple well which extends almost t o the bottom of the bomb, and the other connects with a high-pressure relief valve. The latter is, in turn, attached to a dead-weight pressure The weights were calibrated by the National Bureau of f%%dards and are accurate to * 1.0 atmosphere throughout the full permissible range of 1000 atmospheres. The liquefied gaseous products were fractionated in a Davis column ( 2 ) . The various gas cuts were analyzed in an Orsat apparatus; the hydrogen was removed by copper oxide a t 290 C., and the olefins were absorbed in bromine water. Distillation curves of the residual liquids were determined by means of a 25-cm. Hempel column of 1-cm. bore connected with a 40-cm. copper tube condenser. The Hempel column was surrounded by a heating jacket in which the temperature was maintained at 20" C. below that of distillation. Distillation temperatures were read by means of small Anschutz thermometers, readable to 0.02" C. The temperatures of the bomb and the Davis column were read by means of chromel-alumel thermocouples in conjunction with a model I Weston millivoltmeter; they are accurate to *1.0" c. The hexane was obtained from "Skellysolve" which has a boiling point of 81-69' C. It was extracted with three volumes of 98 per cent sulfuric acid and then fractionated three times in a still (9) especially suited for sharp fractionation. In the final distillation, that portion passing over at 67-88" C. at 747 mm. pressure was retained. Its refractive index was ng 1.3828.
589
data from which these curves were made were taken from two experiments in which heat was supplied continuously until the temperature reached 520" C. The temperature rises regularly with the time of heating, although less rapidly at the higher temperatures. At 497 " C. the temperature remains constant for 8 minutes. It appears that the decomposition proceeds sufficiently rapidly during this period to absorb all of the heat supplied. The possible nature of the decomposition is taken up later.
5 20
O
Procedure I n carrying out these experiments, the bomb and the tubes connecting the pressure gage were filled with hexane, and the whole system was tightly sealed. The bomb was then surrounded by an electric heater whose temperature was electrically maintained within *3.0" C. of any desired temperature. The pressure was read a t 10-minute intervals throughout the heating period. When the heating process was completed, the heater was removed and the bomb was allowed to cool to room temperature. The gas formed was collected in the usual way over a saturated salt solution. Its volume was measured and it was then passed through a condensing coil immersed in carbon dioxide snow and acetone. The liquefied portion was collected in a small flask which was subsequently connected to the Davis column for fractionation. This portion was separated into two fractions, one boiling between -80" and -38" C., and one between -38" and 25" C. Each fraction of the gaseous products was analyzed in an Orsat apparatus. I n computing the percentages of the individual gaseous hydrocarbons, it has been assumed that acetylene is absent, that the only olefin boiling below -80" is ethylene, and that propene is the only one distilling between -80" and -38" C. The distillate between -38" and 25" C. may contain the butenes, pentenes, butanes, pentanes, and other saturated and unsaturated hydrocarbons. There may be some variation in the amount of these hydrocarbons collected as gas, and the percentages reported may be somewhat in error. The distillation curves of the residual liquids were determined in the manner usually followed by petroleum chemists (1). Because of the small amount of liquids obtainable, only 30-cc. samples were used and special precautions had to be taken to avoid the loss of low-boiling liquids. The olefin and aromatic content of some of the liquid residues was determined by the method developed by Faragher, Morrell, and Levine (3).
Results The rate at which the pressure and temperature increase with time of heating is shown graphically in Figure 1. The
v D l 420 w
16000
U
I
3
-l
320
a
U
9
w
a
5 c
q
-
12000 u
a000
220
2'011Y !kkl 20
50
100
!E
d
150
200
250
4000 OT 300 a
TI M E - MI NUT ES FIGURE1. INCREASE IN PRESSURE AND TEMPERATUR~ WITH TIME
The pressure rises rapidly as the bomb is heated until the relief valve opens at about 14,600 pounds per square inch (1025 kg. per sq. cm.). This limiting pressure remains nearly constant until the temperature reaches 500" C. Thereafter the pressure falls even with rising temperature. It is possible that there is some obstruction by carbon in the relief valve which does not allow it to seat properly. Table IA gives the data from the first series of experiments in which heat was supplied continuously until a certain temperature was reached, after which the bomb was immediately cooled. The amount of gas collected is approximately doubled for each 10" C. rise in temperature. Gas is lost from the relief valve after about 15 liters are formed, so that the amount collected no longer represents the total amount of gaseous products formed. The proportions of the saturated hydrocarbons in the gas remain reasonably constant up to 490" C. Although the percentage of hydrogen and of olefins is low a t all temperatures, it decreases with rising temperature. Above 490" C. there is an abrupt change in the proportions of the saturated hydrocarbons, and the voluminous deposition of carbon begins. The percentages of paraffins above ethane decrease, while the proportion of methane increases rapidly. The temperature a t which this shift in gas composition occurs is coincident with the level place in the heating curve. It is possible that the rapid decomposition of the paraffins above ethane a t this temperature absorbs enough heat to account for the break in the curve. These reactions-as with propane, for example-probably start with a scission of the carbon chain to produce a methyl and an ethyl radical. By collision with another molecule, the methyl radical may appropriate hydrogen to form methane. By the same process the ethyl radical may form ethane, or i t may lose a hydrogen atom to form ethylene. Although some of this ethylene undoubtedly polymerizes to higher olefins or aromatic compounds, some of it must decompose into methylene radicals. Some of these, in turn, decompose to hydrogen and free carbon; others may gain
INDUSTRIAL AND ENGINEERING CHEMISTRY
590
VOL. 30, NO. 5
TABLEI. PRODUCTS REMAINING AFTER HEATING FOR VARIOUS PERIODS A. Temp.,
C.
-
460
Mean ressure: Lb.Lq. in. Kg./sq. in. Liquidresidue, cc. Carbon, grams Gaa, liters Analysis, mole yo: Hydrogen Methane Ethylene Ethane Propene Propane Butenes, etc. Butanes, etc.
B. After Maintaining Temp. for
After Heating t o Temp. Indicated and Cooling Immediately 470
480
-
490
as Indicated A
497
510
520
14,200 14,500 14,750 14,800 14,700 14,700 14,500 998 1,019 1,037 1,040 1,032 1,032 1,019 3 32 13 110 102 75 123 0.01 0.01 1.4 4.0 5.5 0.01 0.01 22.0 25.8 7.8 15.0 25.9 3.9 1.7 2.5 26.0 1.4 45.0 1.5 14.5 2.1 7.0
1.4 25.0 1.1 48.0 1.2 15.0 1.7 6.6
hydrogen to form methane. represented as follows:
0.8 24.5 0.7 47.5 0.7 16.0 1.1 8.7
0.1 24.5 0.15 47.0 0.35 16.0 0.5 11.4
0 36.0 54.; 0.04 5.5 0.16 4.0
0 49.5 0 45.0 0.04 4.0 0.04 1.4
n 51.0 0 44.5 0.02 3.0 0.04 1.44
The possible reactions are
+
CHaCH2CH3 + CHsCHzCHaRH CHI R CHaCHXCH9RH + CHxCH, R
+ + + + CH;CH~-L C H ~ = C H ~ - +H --L
The production of carbon a t this temperature may be the result of the catalytic action of the steel wall of the bomb. Walker (11)found that ethylene is decomposed a t 425" C. in the presence of an iron catalyst with the voluminous decomposition of carbon. H e believes that iron promotes the scission of the double bond to form methylene radicals which by loss of hydrogen form carbon or by gain of hydrogen form methane.
50
FIGURE 2.
1
GASEOUSPRODUCTS DECOMPOSITION OF HEXANE
PERCENTAGE OF
products predicted by Rice (IO) __ _ - - Theoretical Mrtintained a t 425O C. for 1.5 hours a t 140 mm. from data of Frey and Hep ( 4 )
FROM
pressure,
- - Maintained a t 430° C. for 2 gours a t 14.250 . .pounds per square inch (1002 kg. per sq. om.) -- - Heated t o 510' C. a t 14,700 pounds per square inch (1032 --
kg. per sq. om.)
Table IB gives the data from the series of experiments in which the temperature was raised to a certain value, maintained there for 1 hour, and then cooled. AS in the previous case the amount of gas collected approximately doubles for each 10' C. rise in temperature. The gas composition is almost identically the same for the same amount of gas collected as was obtained in the first series of experiments. The sudden shift in gas composition with the appearance of car-
440
450
480
470
1 Hr.
(7.
- -
480
14,000 14,100 14,250 14,450 14,650 984 991 1,002 1,016 1,023 124 110 102 74 37 0.01 0.01 0.01 0.01 1.7 1.6 7.9 15,4 22.3 4.3 2.5 24.0 1.5 47.0 1.5 16.0 2.0 6.5
1.5 22.0 1.0 46.0 1.1 18.0 1.4 9.0
1.0 23.0 0.5 50.0 0.4 16.0 0.6 8.5
26.0 0.2 48.0 0.3 15.5 0.5 9.0
0 37.0 54.6
0.06
7.0 0.15 1.8
After Maintaining Temp. for 2 Hr.as Indicated A
430
441
460
460
-
471
14,250 14,000 14,100 14,400 14,400 1,002 984 991 1,012 1,012 124 . 110 102 72 35 0.01 0.01 0.01 0.01 1.8 1.9 7.7 15.6 22.5 4.5 2.5 25.0 1.6 43.0 1.5 15.0 1.9 9.5
1.6 25.0 1.2 43.5 1.0 14.0 1.3 12.5
0.8 24.0 0.6 44.0 0.7 19.0 1.2 9.7
0.5 25.0 0.3 44.0 0.5 18.0 0.7 11.0
0 39.0 0.1 52.0 0.2 6.5 0.2 2.0
bon, which occurs a t 497" C. for short heating periods, now appears between 470" and 480" C. for the 1-hour period. Table IC gives similar data for experiments in which the temperature was raised to a certain value, maintained for 2 hours, and then cooled. Again the amount of gas collected approximately doubles for each 10" C. rise in temperature and again the composition of the gas for the same amount produced is nearly the same as that formed in shorter heating periods. Under these conditions the deposition of carbon, with the marked shift in gas composition, occurs between 460" and 470" C. I n general, the composition of the gaseous products depends primarily on the amount of gas formed-in other words, on the extent of the decomposition. The nature of the gaseous products depends on the time and temperature of decomposition only in so far as these factors determine the stage of the decomposition process. In Figure 2 the gaseous products obtained in two of these experiments are compared graphically with those obtained a t low pressures by Frey and Hepp (4), and with those predicted by Rice (10). All olefins containing four or five carbon atoms are grouped and designated as C4Hs while the paraffins with four or five carbon atoms are designated as CdH,,. At high pressures the nature of the products is totally changed. Although the olefins appear a t the peaks of the curve for low-pressure decomposition, the paraffins predominate a t high pressures and the olefins appear only in very small amounts, if a t all. The wide divergence of these pyrolysis products from those predicted by Rice probably results from the fact that Rice considers the primary decomposition, whereas a t high pressures secondary reactions follow closely on the heels of the primary decomposition. Thus some of the products of the primary reactions may not appear in the final products. Some of the olefins have been removed by polymerization to form more complex compounds, in most cases with the liberation of hydrogen. For example, benzene might be formed from ethylene thus:
+
+
CHz=CHz HZC=CHz + CH2=CH-CH=CHa Hz CHz=CH--CH=CH* HzC=CH% + CHz=CH-CH=CHCH=CHz H C
+
CH~=CH-CH=CH-CH=CH~-+
H-c H-
/ \
C-H
I
d
C-H
+ HI
+ Hz
H The hydrogen set free in these reactions is taken up by other olefins to form the corresponding paraffins. Thus:
MAY, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
If Rice's theory is correct, this is the only means by which the paraffins higher than ethane found in this experiment can be formed. The distillation curves of the residual liquids are shown in Figure 3. The dotted lines in these curves represent liquid residue and the blank spaces a t the ends of the curves represent distillation losses. A check determination on the 460" C. curve of Figure 3B is shown by the points marked by triangles. Since the original hexane boils a t 67" to 68" C., that portion of the liquid boiling in this range may be considered to be unchanged hexane. As the temperature of decomposition rises, less of the original hexane remains and the range of boiling points of the liquids increases considerably. All of the curves show a slight predominance of compounds boiling around 150" C. The number of hydrocarbons which might produce this effect is so great that it is impossible, in a study of this type, to determine what they are. Figure 3B shows that the liquid remaining after heating a t 440' C. for 1 hour contains compounds of nearly the same boiling point range as the liquid remaining upon heating to 460" C. with immediate cooling. The same is true for the liquid remaining upon heating a t 430" C. for 2 hours as shown by Figure'3C. For the longer heating periods the same shift in the nature of the liquid is observed with rising temperature of decomposition as was found in the short heating periods. Again, there is a slight predominance of compounds boiling around 150" C. The olefin and aromatic contents of some of the liquids remaining upon heating to a given temperature with immediate cooling are shown in Table 11. The liquid remaining upon heating t o 490" C. was separated into the fractions indicated, and each fraction was studied separately, both with respect to olefin and aromatic content and to refractive index. The latter data are shown in Table 111.
: I 0
0
I
I
25
0 TABLE 11.
Residue,
490
.)
TABLE111. Boiling Point, a
c.
< 100 100-200 > 200
-
I
50
75
I
OLEFINAND ARONATIC CONTENTS OF RESIDUAL LIQUORS Olefin,
c.
460 470 480
591
< 100
100-200
>200
Aromatic,
%
%
3.0 4~. . 00 4.5 3.0 3.5 21 .o
6.5 R 8 . O0 10.5 11.5 14.5 27.0
REFRACTIVE INDICESOF FRACTIONS OF LIQUID AT 490" C. FORMED
-
-
Orieinal 1.3958 1.4320 1.4854
Refractive Index With With olefins olefins and aromatics out ~~.
1.3951 1.4336 1.4697
- __
"llt,
1.3873 1.4241 1.4518
The percentage of olefins and aromatics increases as the temperature of decomposition increases. The compounds boiling higher than hexane have been formed necessarily by polymerization. According to the theories of Hague and Wheeler (5) and of Wheeler and Wood ( l a ) ,these compounds should conskt entirely of cycloolefins and of aromatic compounds. Table I1 shows that this is not the case. The liquid boiling from 100" to 200" C. contains 82 per cent of hydrocarbons which are neither olefins nor aromatics, and that boiling above 200" C. contains 52 per cent of these compounds. They must be paraffins of either aliphatic or cyclic
0
I
I
25
I
I
50
75
I
PERCENTAGE OF DISTILLATE FIGURE3.
DISTILLATION CURVES
OF
RESIDUAL LIQUIDS
A . Liquids remaining after heating to temperature indicated and cooling immediately.
B.
Liquids remaining after heating to temperature indicated for 1 hour.
C. Liquids remaining after heating to temperature indicated for 2 hour.
INDUSTRIAL AND ENGINEERING CHEMISTRY
592
structure. From their refractive indices they appear t o be chiefly cycloparaffins. Any cycloolefins which may exist as intermediates are apparently hydrogenated by the hydrogen set free in their formation from simple olefins to yield the corresponding cycloparaffins.
Literature Cited (1) Cross, R., Handbook of Petroleum, Asphalt and Natural Gas,
Kansas City, Mo., Kansas City Testing Lab., 1931. (2) Davis, H. El., and Daugherty, J. P., IND.ENQ.CREM., Anal. Ed.,
( 5 ) Hague, E. N., and Wheeler, R. V., Fuel, 8,560 (1929).
VOL. 30, NO. 5
J. Ckem. Soc., 1929,378;
( 6 ) Hugel and Artichevitch, Ann. combustibles liquides, 3, 985 (1928). (7) KatB, T., J. Soc. Chem. I n d . Japan, 36, Suppl. Binding, 228 (1933). (8) Leslie, E. H., and Potthoff, E. H., IND. ENG.CHEM.,18, 776 (1926). (9) Loveless, A. W. T., Ibid., 18,826 (1926). (10) Rice, F. O., J. Am. Chem. SOC.,55, 3035 (1933). (11) Walker, H. j. p h y s . Chem., 31,961 (1927). (12) Wheeler, R. V., and Wood, W. L., J. Chem. Soc., 1930, 1819.
w.,
4. 193 (1932).
(3) Faragher,’ W. F., Morrell, J. C., and Levine, I. M., IND.ENQ. CHEM., Anal. Ed., 2, 18 (1930). (4) Frey, F. E., and Hepp, H. J., IND.ENG.CHEM., 25, 441 (1933).
RECEIVED November 6, 1938. 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, in June, 1934.
Toxicological Studies of Derris Chronic Toxicity of Derris’ ANTHONY M. AMBROSEa AND HARVEY B. HAAG Food Research Division, Bureau of Chemistry a n d Soils, United States Department of Agriculture, and Department of Pharmacology, Medical College of Virginia, Richmond, Va.
Studies are reported upon the chronic toxicity of derris (Derris elliptica) for rabbits, dogs, and rats. For rabbits, 60 mg. per kg. and above showed signs of cumulative toxicity. I n adult dogs on diets containing 0.04 per cent derris, no symptoms of toxicity were observed. I n young growing dogs on the same diet, the most pronounced effect was the stunting of growth. Derris diets containing less than 0.0312 per cent derris had no demonstrable effect on growth of rats. As the concentration of derris in the diet was increased, the inhibition in growth was more marked. Pathologic studies on the tissues of dogs and rats indicated that derris in all concentrations studied was somewhat injurious, the liver being the only organ consistently affected.
D
URIKG the last decade a vast amount of information on the toxicity of derris (Derris elliptica) for various insects has been published. Roark ( I S ) published an extensive bibliography on the subject which was consulted by the authors in the preparation of this and previous papers from this laboratory. Derris and derris preparations in one form or another have gained widespread use as an insecticide
in the control of various plant insects (4-8, 11, 16); as a remedial agent for combating mites, fleas, and body lice on animals (3, 6, 11, I d , 17); and as a killing agent for roaches. and house flies (3,6, 10, 11, l a ) . I n all these studies derris and derris preparations were found toxic to both sucking and chewing insects. The literature on the toxicology and pharmacology of derris was discussed in previous papers of this series ( 1 ) . In considering the usefulness of a n insecticide, it is most important t h a t due attention be given to the question of whether or not prolonged ingestion of the material in minute is, i n amounts approaching those which quantities-that might be present on sprayed fruits or vegetables-will have any untoward or deleterious effect upon the animal economy. While it is the general opinion that derris would be noninjurious in the quantities that might be present upon sprayed foods, no experimental evidence has come to the authors’ attention bearing out this belief. I n an attempt to throw some light upon this problem, rabbits, dogs, and white rats have been maintained on small daily doses of derris for periods of 1 t o 8 months. The sample of Devris elliptica root used in these studies contained 9.6 per cent rotenone and 28.6 per cent total carbon tetrachloride extractives. The average powdered derris root on the American market contains about 4.5 per cent rotenone and from 14 to 18 per cent total extractives. A sample unusually high in active principles was selected for these studies. The sample and analysis were furnished by the Bureau of Entomology and Plant Quarantine, United States Department of Agriculture. 1 This is the fourth of a series of papers on the toxicology of Derris elltptzca and its constltuents. The others rtppeared in J. Pharmacol., 43, 193 (1931), and in IND. ENQ.CHEM.,28. 815 (1936), and 29, 429 (1937). 2 Present address, United States Department of Agriculture, Stanfordi University Medical School, Ban Francisco, Calif.
