INDUSTRIAL AND ENGINEERING CHEMISTRY
1406
standing flame properties, of knowledge of the actual mechanism of reaction and steady state conditions rather than of equilibrium atomic or free radical concentrations alone.
Vol. 44, No. 6
(4) Gerstein, hf.9 McDonald, G. E., and Schalla, R. L., paper PICsented a t XIIth International Congress of Pure and Applied Chemistry, New York, September 1951. ( 5 ) Henkel. M. J.. Univ. of Wisconsin Kava1 Research Lah. Rmt. CF-1385 (Jan. 31. 1950). (6) Hirschfelder, I., Henkel, ’M. J., and Spaulding, Vi-. P., Univ. of Wisconsin N a v a l Research Lab., R e p t . CF-1112 (Aug.27,1948). (7) Kitagawa, Rev. Phus. Chem. J a p a n , 12,135 (1928). (8) Kokochashvik v. I., J . PhUs. Chem. (U.S.S.B.), 23, 15, 21 -
ACKNOWLEDGMENT
The authors wish to acknowledge the assistance of Victor D. Phillips and Tom Brotherton in making the experimental measurements and of Mavis Reynolds in the numerical calculations.
>
I
(1949); 25,444 (1951). ~B., and ~ i ~G.. J , ,Chem. phus.. (9) ~ Elbe, i 2.l 537 .(1934). I (10) Manson, N, Ibid., 17,837 (1949). (11) Pease. R. N.. “Eauilibrium and Kinetics of Gas-Phase Reac~. . . , tions,” p. 112, Pr’inceton, N. J., Princeton Univ. Press, 1942. (12) Sachsse, H., andBartbolome, E., 2.Elektrochem., 53,183 (1949). (13) Tanford, C., and Pease, R. N., J . Chem. Phys., 1 5 , 8 6 1 (1947). (14) Zel’dovich, V. B., and Frank-KamenetskY, D. A., Compt. rend. m a d . & . U.R.S.S., 19,693 (1938). ~
LITERATURE CITED
(1) Anderson, R. C., Gniv. of Texas Def. Research Lab,, R e p t . 219 (Sept. 12, 1949); 220 (Sept. 15, 1949); 227 (Sept. 12, 1949); 241 (March 28, 1950). (2) Cooley, S. D., Lasater, J. A., and Anderson, R. C., J . Am. Chem. Soc., 74,739 (1952). (3) Garrison, H. R., L a s a t e l , J. 24.9 and Anderson, R.c., “Third
Symposium on Combustion, Flame, and Explosioll Phenom-
ena,” p. 155, Baltimore, Md., Killiams & Vilkins Co., 1949.
f o r review 28, 1951, ACCEPTED April 7, 1932. Presented as part of the Symposium on Combustion Chemistry before the Divisions of Petroleum Chemistry and Gas and Fuel Chemistry a t the 119th CHEMICAL SOCIETY, Cleveland, Ohio. Sponsorcd Meeting of the AXERICAN by the Bureau of Ordnance, I;.S.S a v y Department, Contract NOrd 919:.
Q
P ROBERT F. R‘IARSCHNER AND DONALD E. BURNEY Research Department, Standard Oil C o . (Indiana), Whiting, Ind. THOUGH cyclopentane was detected 50 years ago in Balakhany (8),Pennsylvania (18), and Romanian (10) petroleum, the first indication of the presence of neohexane (2,2dimethylbutane) was obtained by Chavanne (9)in 1922. By a series of fractionations of Borneo naphtha, he isolated a fraction boiling a t 49.049.6’ C., which he recognized as a mixture of 79% cyclopentane and 21 % neohexane. Twenty years later, Tooke (16)distilled from Burbank (Oklahoma) natural gasoline the cyclopentane-neohexane mixture boiling a t 49.1 C., which Serijan, Spurr, and Gibbons (14) found to contain 92% cyclopentane and 8% neohexane. From a West Virginia natural gasoline fraction, Hicks-Bruun, Bruun, and Faulconer ( 7 ) obtained cyclopentaneneohexane boiling at 49.2-49.8 a C. and apparently containing 29% cyclopentane and 71% neohexane; they --ere the first actually to isolate the neohexane present. The pronounced variation of the relative amounts of cyclopentane and neohexane with the source of the petroleum suggested investigation of cyclopentane and neohexane in other American petroleums. A preliminary study of the behavior upon fractionation of
TABLEI. APPROXIMATECoiiPowrIoiv O F CYCLOPEXTANENEOHEXANE MIXTURES Volume % CycloNeoDentane hexane
Petroleum Source East Texas (1) Greendale-Kawkawlin (Michigan) (4) Slaughter (West Texas) Salt Creek (Wyoming) Rangely Midway (California) (Colorado) (4) Bradford (Pennsylvania) (4) Ponca (Oklahoma) ( 4 ) East Texas (4) Winkler County (West Texas) Hastings (Texas Gulf Coast) Conroe (Texas Gulf Coast) ( 4 ) Turner Valley (8lberta) (8,1 7 ) Pine Island (Louisiana) West Virginia (6)
20
1 I
70
30
60
40
naphthas derived from a variety of American petroleums confirmed the wide variation in composition of the cyclopentane-ncohexane. The presence of the mixture in all the naphthas x a s revealed by the high octane number of fractions boiling ncar 50’ C. Cyclopentanewas easilydetected from its high densit yand refractive index, and the amount could often be estimated. The properties of neohexane are too much like those of neighboring alkanes for accurate determination-or even detection when the amount is small-by a single fractionation of a convenient quantity of naphtha. The approximate proportions indicated by that study and by the literature are grouped in Table I. The physical properties of cyclopentane, neohexane, and neighboring hydrocarbons are such that excellent analytical precision should be easily attained by fractionation of sufficient amounta of material. As a pair, the two hydrocarbons distill far from lower and higher boiling paraffins; individually, they are far apart in refractive index: Boiling Point,
c. ( 1 2 )
Refractive Index, ns‘ (fB) 1.3575
n-Pentane
36.1
Cyclopentane Neohexitne
49.3 49.7
1.4066
2,3-Dimethylbutane 2-Methylpentane
58.0
1.3750 1.3715
60.3
1.3688
ilccordingly, the present study consisted of fractionating selected naphthas through a large column, refractionating the cyclopentane-neohexane concentrate through a small column, and determining the refractive index of successive small fractions boiling at 49” to 50” C. EXPERIMENTAL
50 50 40
60
Naphthas representing known percentages of six petroleums of distinctly different characteristics were selected for study. Several of the naphthas were composited from two or more fields producing similar petroleum. The naphthas were produced a t petroleum refineries under conditions designed to restrict vapor losses; whatever vaporization occurred prior to sampling in-
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1952
TABLE 11. SOURCES AND INSPECTIONS OF NAPRTEAS Designation Illinois Mid-continent Wyoming Houston-Hackberry Hastings East Texas
Source (Field or Area) Several fields Many fields in Oklahoma, Kansas, and North Texas Salt Creek and Lance Creek 61% South Houston (Texas Qylf Coast) and 49% Hackberry (Louisiana Gulf Coast) Texas Gulf Coast 72% East Texas and 28% Evangeline
Specific Gravity 0.724 0 721
Boiling Range, a C. 20-170 25-180
0.722 0.705
30-150 25-140
of cyclohexane and 2,4-dimethylpentane were prepared. The experimental data for all three azeotropes are presented in Table V. AMOUNTS AND PROPORTIONS OF CYCLOPENTANE AND NEOHEXANE
The amounts of cyclopentane-neohexane present in the six petroleums studied were remarkably similar; the values in Table I11 are all 0.09 rfi 0.02 volume %. A similar value is reported for Venezuela petroleum (IS),and smaller values for Oklahoma City (16) and West Virginia (6) petroleums. Larger amounts are reported in Turner Valley ( S , l 7 ) and East Texas ( 1 ) petroleums. Other reported precise estimations (7, 16) are not comparable because the cyclopentane-neohexane was obtained from a naphtha derived from natural gas rather than from petroleum. The relative amounts of cyclopentane and neohexane present in petroleums differ widely. The percentage of cyclopentane in the mixtures shown in Table IV range from more than 90% to less than 30%. There is no discernible relation between this percentage and the amount of cyclopentane-neohexane in the various petroleums.
0.739 0 728
volved mostly butanes. Sources and inspections of the naphthas are detailed in Table 11. Five gallons of each naphtha were first fractionated a t 0.5 liter per hour and 64 to 1 reflux ratio through a large column with a helix-puked section 10 feet long and 2 inches in diameter and equivalent to about 15 theoretical plates. Light constituents were discarded from each naphtha until most of the n-pentane plateau had been traversed. Cyclopentane-neohexane concentrates were then collected between 36” and 61 ’ C. without attempting to obtain well defined boiling point plateaus. The fractionations were terminated near the middle of the 2-methylpentane plateaus. The concentrates were refractionated at 10 A,per hour into 1% cuts through a small column similar to that previously described as column 3 (9) and equivalent to a t least 60 theoretical plates. Well defined boiling point and refractive index plateaus appeared a t 49’ to 50 O C.
1407
20-160 20-150
A composite graph of the fractionation data is slmo presented in Figure 1. From the lengths of the the amounts of cycloboiling point plateaus pentane-neohexane in each naphtha were estimated with a precision of 0.01 volume %. The amounts in each petroleum were calculated by multiplying the percentages of naphtha in petroleum by the percentage of cyclopentaneneohexane in naphtha. These data are summarized in Table 111, together with the most reliable literature values for other naphthas. From the heights of the refractive-index plateaus the proportions of cyclopentane and neohexane #I were determined directly, with a precision of 2 volume %. These data are presented in Table IV, together with appropriate literature values. % DISTILLED Abnormalities in the boiling point and refractive-index data among the several naphthas sugFigure 1. Composite Graph of Fractionation Data gested that cyclopentane and neohexane form an azeotrope. This observation was confirmed by refractionation of cyclopentane-neohexane mixtures and was The empirical classification of petroleums as “paraffinic,” extended by fract2onating other alkane-cycloalkane mixtures. A “naphthenic,” and “aromatic” has long been recognized as inaderefractionation of the cyclopentane-neohexane from Mid-contiquate. I n this work, little correlation between the composition nent naphtha is shown in Figure 2. Samples of cyclohexane, of cyclopentane-neohexane and the empirical petroleum classifi2,2,3-trimethylbutane (triptane), and 2,4-dimethylpentane1 availcation was observed. The Oklahoma petroleums, ordinarily conable from an earlier study (9), were fractionated by the technique sidered paraffinic, actually are cyclopentane-rich relative to neothere described, and azeotropes of cyclohexane and triptane and hexane, whereas the naphthenic coastal and aromatic foreign
!,,=
--
8
-
TABLE111. CYCLOPENTANE-NEOHEXANE CONTENT OF
PETROLEUMS
Designation
Santa Barbara (Venezuela) Turner Valley (Alberta)
Weat Virginia
Naphtha on petroleum, Cyclopentane-Neohexane on Vol. % Naphtha Petroleum 14.0 0.56 0,078 4.6 (16) l.lS(f6) 0.053(I6) 19.0 0.51 0.102 0.50 19.7 0.093 9.8 1.16 0.113 6.5 1.22 0.068 10.8 0.94 0.102 14.51 ( f ) 1.4 ( I ) 0.21 ( I ) 0.58 (IS) 0.089 (1S) {$) 0.20 9) 9 . 9 (17) &) 0.28 {In 0.032 (6)
E:’: ....
::: ....
TABLE IV. COMPOSITION OF CYCLOPENTANE-NEOHEXANE MIXTURES
Petroleum Source
Illinois
Burbank (Okla’homa)
Plateau, n”D”
1.4033 1 ,4032(I6) 1.4029(f4)
....
Oklahoma City 1.4008 Mid-continent Borneo 1.3973 Wyoming Houston-Haokberry (Gulf Coast) 1.3970 1.3928 Hastings (Texas Gulf Coast) 1.3901 East Texas Santa Barbara (Venezuela) 1 ,380‘(i.) Clendenin (West Virginia)
Volume % CyclcNeopentane hexane
INDUSTRIAL AND ENGINEERING CHEMISTRY
1408
Vol. 44, No. 6
the S% of neohexane present (1.4) could be eliminated as the azeoOF CYCLOALKANE-ALKANE AZEOTROPES trope. TABLE V. PROPERTIES Boiling Point (760 -4related azeotrope, that of cyclohexane and triptane (2,2,3Mm.), C. Azeotrope Composition trimethylbutane), has been reported by Harrison and Berg ( 5 ) . HydroAzeoVolume % Mole % carbon 49.3 49.7
trope
80 20
85
45 Cyclohexane 80.2 65 2,4-Dimethylpentane Cyclohexane 80.8 44 2.ZI3-Trimethylbutane 80,8 Oa 56 Harrison and Berg (6) give 80.15" and 47.8% alkane.
53 47
Cyclopentane 2,2-Dimethylbutsne
49.1
15
51 49Q
'
naphthas are relatively much poorer in cyclopentane. The neohexane-rich West Virginia naphthas, however, are as paraffinic as their -1ppalachian source might suggest. CYCLOPENTANE-NEOHEXANE AZEOTROPE
From the relative boiling points and the dissimilar refractive indices of cyclopentane and neohexane, one would predict a definite decrease in the refractive index of successive fractions of the mixture boiling a t 49" to 50'. This expected behavior was observed only with mixtures containing less than SO% cyclopentane. When more than 80% cyclopentane was originally present, an increase in refractive index occurred-a behavior noted by Ray
In the present work, the existence of their azeotrope has been confirmed; its boiling point is about 0.7" C. below that of the individual components. A similar azeotrope of cyclohexane and 2,4-dimethylpentane has a boiling point 0.3 below that of 2,4dimethylpentane, the lonw boiling component. The three azeotropes shown in Table 5' are the only three cycloalkane-alkane azeotropes that have been recognized. Cycloalkanes and alkanes form azeotropes a t atmospheric pressure only if the constituents normally boil within perhaps 1'. In the familiar system methylcyclohexane-n-heptane,the components boil 2.5" apart, and, although the vapor-pressure relations are far from ideal, no azeotrope occurs. The system methylcyclopentane-n-hexane,with a 3.1 O difference in boiling points, is more nearly LLnormal." The following pairs of well known hydrocarbons boiling below 100" C. ( 1 2 ) probably form azeotropes: trans-1,3-Dimethylcyclopentane (90.8') : 2-methylhexane (90.1°) trans-1,Z-Dimethylc clopentane (91.9') :3-methylhexane (92.0') czs-1,3-Dimethylcyc6pentane (91.9') :3-methylhexane (92.0°) cis-1,2-Dimethyloyclopentane(99.5') :2,2,4-trimethylpentane (99.2')
haeotropic behavior, if it proves to occur in the first three cases, would help explain the difficulty of interpreting naphthafractionation curves in the neighborhood of 90' to 92". CONCLUSION
1.4040 I
r-l
h
3p
1.4030
c
u
X
2 z
1.4020
w
5
1s40'0
LL
E 1.4000 I
I
1.3990
L
50
A
0 0
20
40
60
100
80
PERCENT BY VOLUME Figure 2. Fractionation of CyclopentaneNeohexane Mixtures A.
B.
Fractionation of 90% cyclopentane -k 10% Neohexane (10) Refractionation of 84% cyclopentane 16% neohexane from mid-continent petroleum
+
( 1 1 and illustrated in Figure 2 . The direction of the trend was thus a function of the composition of the cyclopentane-neohesane distilled. Several cyclopentane-rich mixtures started near the same refractive index level of 1.400 but thereafter spread apart. Furthermore, the boiling points of several mixtures never reached 49.3" C., the value characteristic of cyclopentane. The explanation for these observations is the occurrence of an azeotrope of cyclopentane and neohexane boiling near 49.1" C. and approximately 80 to 20 in volume composition. The existence of this azeotrope accounts for the ease of fractionating pure neohexane from petroleum in contrast to the difficulty of obtaining pure cyclopentane. The 0.6" spread between the boiling points of the azeotrope and of neohexane permitted the isolation of neohexane ( 7 ) ; the 29% of cyclopentane was eliminated as the axotrope. The 0.2" spread between the azeotrope and cyclopentane prevented the isolation of pure cyclopentane (16); not even
The close boiling points of cyclopentane and neohexane and the occurrence of an azeotrope permit cyclopentane-neohexane mixtures to survive ordinary naphtha-distillation processes with negligible change in composition. Consequently, cyclopentaneneohexane can be used as a tracer for light naphthas from producing well to finished product, unless the naphtha is blended with streams of unknown composition. The technique of tracing by means of cyclopentane-neohexane has been employed successfully in determining the probable sources of unfamiliar aviation gasolines and solvent naphthas. Cyclopentane-neohexane can be employed as a test mixture for comparing fractionating columns, wherein the occurrence of the azeotrope may provide an advantage over nonideal pure hydrocarbon mixtures. The system azeotrope-neohexane affords a close-boiling, easily analyzed hydrocarbon pair from which vapor pressure abnormalities may have been diminished by the circumstance of azeotrope formation. The system azeotrope-cyclopentane, although closer boiling and therefore more adaptable to testing very efficient columns, is more difficult to analyze. LITERATURE CITED (1) Bell, A n a l . Chem., 22, 1005 (1950). (2) Chavanne, Bull. soc. chim. Belg., 31, 331 (1922). (3) Donald, C a n . J . Research, 18, 12 (1940). (4) Forsiati, Willingham, Mair, a n d Rossini, Proc. Am. Petroleum I n s t . , 24 (111), 34 (1943); J . Research AVatl. B u r . Standards, 32, 11 (1944). (5) Harrison a n d Berg, ISD.ENG.C H E X , 38, 117 (1946). (6) Headlee a n d hlcClelland, I b i d . , 43, 2547 (1951). (7) Hicks-Bruun, Bruun, a n d Faulconer, J . Am. C h e w Sop., 61, 3099 (1939). (8) Markownikoff, Ber., 30, 974 (1897); Ann,, 301, 154 (1898). ESG. CHEnr., 38, 262 (1946). (9) Marschner a n d Cropper, IND. (10) Poni, Chem. Zentr., 1900 11,452; 1901 I, 60. (11) R a y , 0. C., U. S.Patent2,498,928 (Feb. 28, 1950). (12) Rossini et al., "Selected Values of Properties of Hydiocarbons," Washington, D. C., Government Printing Office, 1947. (13) Schwarts, Gooding, a n d Eccleston, IND.EKG.C n E x , 40, 2166 (1948). (14) Serijan, Spurr, a n d Gibbons, J . Am. Chem. Soc., 68, 1763 (1946). (15) Tooke, IXD.ENG.CHEM.,35, 992 (1943). (16) W a r d , Gooding, a n d Eccleston, Ibsd., 39, 105 (1947). (17) Watson a n d Spinks, C a n . J . Research, 18, 388 (1940). (18) Young, J . Chem. Soc., 73, 905 (1898). RECEIVED for review June 10, 1951. ACCEPTED January 14, 1952. Presented before the Division of Petroleum Chemistry, Symposium on Composition of Petroleum and I t s Hydrocarbon Derivatives, at the 119th hleeting of the A l f E R I C A N CHEMICAL SOCIETY, Cleieland, Ohio.
