i
January, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
list inevitably contains many duplications, the same material appearing under different trade names. Also some borderline materials are more properly called “assistants” for surface-active agents, rather than surface-active agents except by the broadest definition. To illustrate the multiplicity of these products, in a single patent of somewhat minor importance, nearly one hundred specific examples are discussed (6). Rarely is a patent issued in the field that does not permit of hundreds of variations. One of the longer patents (6) not only gives specific instructions for making forty-two different surface-active agents, but follows this with seven process claims and twenty-five broadly worded product claims. But however rapid the development of these products may be, it rests on the ancient foundation of soap manufacture and hardly justifies a statement recently made : “Surface-active compounds comprise a new group of organic chemicals just as do the vitamins, hormones, and dyes.”
Literature Cited (1) Campbell, G. A., in “Wetting and Detergency” (Symposium of Intern. Soc. of Leather Trades Chemists, Brit. Sect.), pp. 111-12, New York, Chem. Pub. Co., 1939.
117
(2) Ceryl, C. R., IND. ENQ.CHEM.,33, 731-7 (1941). (3) Donnan, F. G., and Potts, H. E., 2. Chem. I n d . Kolloidc, 7 , 208-14 (1911). (4) Goodwin, W., Martin, H., and Salmon, E. S., J . Agr. Sci.. 20, 18-31 (1930). (5) Guenther, Fritz, U. 8. Patent 1,932,180 (1933). (6) Harris, B. R., Zbid., 1,917,260 (1933). (7) McBain, J. W., and Spencer, W. V., J . Am. Chem. Soc., 62, 23944 (1940). (8) Mart& H:, in “Wetting and Detergency”, p. 119 (1939). (9) Ibid., p. 127. (10) Palmer, R. C., J . 900.Chem. Id., 60, 56-60 (1941). (11) Reed, R. M., and Tartar, H. V., J . Am. Chem. SOC.,58, 322-32 (1936). (12) Robinson, Conmar, in ”Wetting and Detergency”, pp. 1 1 6 1 5 (1939). (13) Ibid., P. 137. (14) Ibid., p. 142. (15) Sluhan, C. A,, Paper Trade J., Aug. 22, 1940, 26-31. (16) Van Antwerpen, F. J., IND. ENQ.CHEM.,33, 16-22 (1941). (17) Zbid., 35, 126-30 (1943). (18) Williams, E. T., Brown, C. B., and Oakley, H. B., in “Wetting and Detergency”, p. 173 (1939). PRESENTED before the Division of Colloid Chemistry at the 102nd Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantio City, N. J.
Pure Hydrocarbons from Petroleum J
Vapor-Liquid Equilibrium of Methylcyclopentane-Benzene and Other Binary Aromatic Systems JOHN GRISWOLD AND E. E. LUDWIG’ The University of Texas, Austin, Texas Atmospheric vapor-liquid equilibrium data for the system methylcyclopentane-benzeneare presented. A minimum-boiling azeotrope exists at approximately 90 mole per cent methylcyclopentane. Equilibria of binary systems containing aromatic hydrocarbons are discussed. It is evident that the presence of benzene prevents complete resolution of six-carbon petroleum fractions into their pure components by distillation, and that toluene greatly increases the difficulty of but does not prevent complete resolution of seven-carbonfractions.
I
N AN ATTEMPT to separate the constituents of a sixcarbon fraction from natural gasoline by fractional distillation, two of the last components to distill were methylcyclopentane and benzene. It was found impossible to obtain pure methylcyclopentane by repeated fractionation in a Podbielniak Heli-Grid column (1I), having an equivalent of more than sixty theoretical plates. These two hydrocarbons boil 9.3” C. apart, which is adequate for separation of normal mixtures by this column. An abnormality was apparent, and it was decided to investigate the vapor-liquid equilibrium of the binary system. 1
Present address, Dow Chemioal Company, Freeport, Texas.
Vapor-Liquid Equilibrium of MethyIcyclopentane-Benzene MATERIALS.Phillips Petroleum Company and Shell Development Company furnished samples of methylcyclopentane. The physical constants indicated both samples to be of about the same purity. Since nitrating and sulfonating mixtures destroy the compound, it was purified by fractionation in the Podbielniak column, using total reflux and intermittent take-off, The charge volume was 390 cc. After the first 10 cc. were removed, boiling points and refractive indices of further samples were constant to within 0.1” C. and 0.0001 unit, respectively. Because of a very slow increase in refractive index in the fifth decimal place before that point, only the distillate from 170 to 320 cc. was used for the studies. The benzene was The Barrett Company’s 1’ thiophenefree grade. It was fractionated through a laboratory column packed with 18 inches of glass helices, and a center cut of about 80 per cent of the original material was retained. The physical constants of the purified materials are compared with some of the modern data from the literature in Table I. While the constants of highly purified methylcyclopentane have not been established with certainty, the values for the present material are congruent with the best data from the literature. For benzene, Wojciechowski’s constants (21) are considered quite reliable. The present sample must
INDUSTRIAL AND ENGINEERING CHEMISTRY
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a a
Vol. 35, No. 1
therefore contain an impurity not easily removable by distillation, such as cyclohexane. I n this event the methylcyclopentane-benzene equilibrium will be slightly affected a t high benzene concentrations. The influence of an equivolatile impurity must fade out as the benzene concentration is decreased, and the presence of a trace of cyclohexane will tend to reduce rather than to amplify the boiling point depression observed for the methylcyclopentane azeotrope.
0
3 z W
z a
I-
z
W
n
0
9
0
TABLE
-I
> r
I.
COXSTANTS O F LIETHYLCYCLOPENTAKE AXD BENZENE
Literature Citation
B. P. a Ot 760 Xm., C.
!-
w
d:O
n
Methylcyolopentanc
r
....
1.40976 1.40972 1.4099 1.4100 1.40998 1.4100 1.4099 1,4099 1,4098 1.4096 1,4098
71.8 71.9 71-72
8 -I
....
0
71.9 71.9 72 71.8 71.9 71.8
H
M O L % METHYLCYCLOPENTANE IN LIQUID
0,7477 0,7482 0,7496
....
0.7810 ,...
0,7496 0,7494 0.7487 0.7453
....
Benzene Purified sample (21) METHYLCYCLOPENTANE-BENZENE
MOL % METHYLCYCLOPENTANE IN LIQUID
THYLCYCLOPENTANE- B E N 2
0' 0
I
W
a
3 I-
a
a W n
a
APPARATUS.Twenty-two equilibrium determinations were made in an Othmer apparatus (IO), modified by the addition of a compensating wall heater, a glass check valve and drain in the liquid return line, and an ice water condenser on the vent. Boiling points were determined on twenty-five known mixtures in the apparatus of Willard and Crabtree (do), fitted with a four-junction iron-constantan thermocouple which was calibrated against the boiling points of pure compounds. Accuracy of the boiling point determinations was approximately 0.1" C. Analysis by refractive index was obtained with a Bausch & Lomb Precision oil refractometer having an accuracy of 0.00003 refractive index unit. Compositions of the equilibrium samples were determined from a plot of refractive indices a t 20" C. of known mixtures. The data for the analytical plot are given in Table 11. RESULTS.The experimental data are summarized in Table 11. The g-x plot (Figure l) shows that the system deviates widely from ideality. The plot of relative volatility against composition (Figure 2 ) shows a definite dip below 1.0 a t approximately 90 mole per cent methylcyclopentane, indicating an azeotrope. This plot is also a rather sensitive test for consistency of the data. The experimental boiling points (Figure 3) show a definite minimum a t approximately 71.5" C. a t the azeotropic composition. To prove the azeotrope, samples on both sides of its composition were boiled under total reflux in the Podbielniak column until equilibrium was attained. A small overhead sample was then withdrawn, and the still pot m.as cooled and sampled. The results are:
r w
Sample S o .
z1
0.8775 0.87896"
Calculated from values a t 25' C. given in reference 21.
I(3
1.60015 1.60122"
80.1 80.094
1 2
dol^ Fraction llIethylcyclopentane Still pot Overhead 0.0378 0.9500
0.8795 0.9038
0
m
Behavior of Light Naphtha Hydrocarbons in Mixtures
MOL % METHYLCYCLOPENTANE
The hydrocarbon classes present in light petroleum fractions are paraffins, naphthenes, and aromatics. I n a strictly chemical sense, since these are all hydrocarbons they might be
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1943
TABLE11. SUMMARY OF EXPERIMENTAL DATAON MITHYLCYCLOPENTANEBENZENE Equilibrium Determinations Mole fraction methylcyclopentane Relative Liquid Vapor volatility, a
0.0297 0.1080 0 1751 0:3017 0.3806 0.4460 0 5031 0:5737 0.6434 0.7206 0.7855 0.8224 0.8441 0.8721 0.9030 0.9180 0.9296 0.9373 0.9450 0.9518 0.9515 0.9613
0.0526 0.1668 0 2533 013870 0.4598 0.5179 0.5673 0.6255 0.6795 0.7442 0.7986 0.8299 0.8499 0.8754 0.9034 0.9174 0.9287 0.9360 0.9442 0.9503 0.9505 0.9602
1.814 1.653 1.598 1.461 1385 1.340 1.295 1.241 1.175 1.128 1.083 1.054 1.046 1.030 1.005 0.992 0.988 0.978 0.985 0.968 0.979 0 971
Boiling Points .Mole fraction methylcycloC. a t pentane 760 mm.
0.0000
0.0297 0.1080 0.1443 0.1751 0.3017 0.3806 0.4450 0.5737 0.6434 0.7206 0,8224 0.8510 0.9030 0.9174 0.9034 0.9180 0.9360 0.9373 0.9422 0.9442 0.9450 0.9518 0.9515 1.0000
Known Mixtures Mole frsotion methylcyolopentane n v
80.10 79.64 77.62 77.15 76.62 74.85 74.00 73.43 72.84 72.06 71.97 71.54 71.53 71.47 71.50 71.39 71.53 71.60 71.65 71.56 71.62 71.68 71.80 71.84 71.80
expected to form ideal solutions. Fractions through the pentanes are separated in pure form by efficient fractional distillation. Hexane fractions have given considerable difficulty in the separation of their pure components (S), and in general the components in the pure state are not obtainable by fractionation alone. However, Bruun (6) was able to a 55-650 c* Out into isomeric reso1ve anes by distillation in 52-phte and 100-plate Columns. Tongberg, Fenske, and Sweeney (15) reported in 1938 that no true constant-boiling mixture had been found in twenty virgin aromatic-nonaromatic mixtures behaved naphthas, abnormally in distillation. It is apparent that the presence of aromatics greatly interferes with separation by fractional distillation. The cut to contaihed no During Bruun was the past few years, aromatics have been removed by nitration or azeotropic distillation before ultimate fractionation was attempted.
Binary Systems Containing Aromatics It has long been established that benzene-toluene form nearly ideal solutions. Toluene-xylene and the ternary mixtures with benzene do also (9). Beatty and Calingaert (1) reported that the toluene-ethylbenzene system is nearly ideal. On the other hand, all reported that aromatic-naphthene and aromatic-paraffin systems deviate widely from regularity of solution. The existence of a benzene azeotrope with methylcyclopentane is established in this paper. Scatchard, Wood, and Mochel (IS) took accurate isothermal data on the benzenecyclohexane system, which shows an azeotrope having a composition of approximately 50 mole per cent benzene a t 70’ C. Quiggle and Fenske reported data on the methylcyclohexane-toluene system (12). While it deviates greatly from ideality, it does not form an azeotrope. Tongberg and Johhston (16), studying the equilibrium of n-hexane-benzene, reported no separation obtainable a t concentrations above 97 mole per cent hexane. Although a minimum-boiling -ture was not observed, the presentauthors are of the opinion that one exists having a boiling point &hin 0.10 c. of pure n-hexane, which thereby escaped detection. Otherwise this is the first pseudo-azeotrope to be established with modern fractionating equipment. Bromiley and Quiggle
0.0547 0.1343 0.1616 0.2096 0.3857 0.4851 0.6159 0.7486 0.7871 0.8316 0.8435 0.9366
1.49333 1.48432 1.48120 1.47553 1.45794 1 44896 1.43820 1.42749 1.42486 1.42175 1.42138 1.41452
119
(9) studied n-heptane and n-octane with t o l u e n e . No a z e o t r o p e s formed, but the shape of both 9-x curves was similar to that of methylcyclohexane-toluene, in that the r el a t i v e volatility decreased abnormally as the aomposition approached the pure low-boiling component. The existence of benzene azeotropes and the abnormally low relative volatility of toluene in certain concentrations with both lower and higher boiling compounds is considered an adequate explanation for the failure of good fractionation equipment to resolve six- and sevencarbon petroleum fractions into their pure components when aromatics are present.
Acknowledgment E. P. Schoch, of the Bureau of Industrial Chemistry, University of Texas, generously loaned the distillation equipment and encouraged the work. Thanks are due George Scatchard for review and criticism of the manuscript.
Literature Cited (1) Beatty and Calingaert, IND.ENQ.CHEM.,26, 504,904 (1934). (2) Bromiley and Quiggle, Ibid., 25, 1136 (1933). (3) Bruun and Hicks-Bruun, Bur. Standards J . Research, 5, 933 (1930). (4) Ibid., 6,577 (1931). (5) Bruun, HicbBruun, and Faulconer, J . Am. Chem. Sot., 59, 2355 (1937); 61,3099 (1939). (6) Evans, J . Inet. Petroleum Tech., 24, 332 (1938). (7) Fenske, M. R.,in “Physical Constants of the Principal Hydrocarbons”, 2nd ed., p. 73,Texas Co., 1939. (8) Garner and Evans, J. Inst. Petroleum Tech., 18,761 (1932). (9) Griswold, J., Sc.D. thesis, Mass. Inst. Tech., 1931. (10) Othmer, D.F., IND. ENQ.CHEM.,ANAL.ED., 4, 232 (1932). (11) Podbielniak, W. J., Ibid., 13, 639 (1941). (12) Quiggle and Fenske, J . Am. Chem. SOC.,59, 1829 (1937). (13) Scatchard, Wood, and Mochel, J . Phys. Chem., 43,119 (1939). (14) Smittenberg, Hoog, and Henkes, J. Am. Chem. SOC.,60, 17 (1938), (15) Tongberg, Fenske, and Sweeney, IND.ENQ. CHEY.,30, 169 Tongberg (1938). and Johnston, Ibid., 25, 733 (1933). (17) vogei, A. I., J . Chem. SOC., 153, 1323 (1938). (18) Vondracek, Collection Czechoszav. Chem. Commun., 9,521 (1937). (19) Wibaut et al., Rec. trav. chim., 58, 329 (1939). (20) Willard and Crabtree, IND.ENG. CHEM.,ANAL. ED., 8, 79, (1936). (21) Wojciechowski, M.,J . Research Natl. Bur. Standards, 19, 347 (1937). (22) Zelinsky and PoUak, Ber., 65, 1171 (1932).
Infrared Radiant Heating-Correction It has been pointed out to the writers that a mistake in calculation arises in connection with Figure 8 on page 778 of the July, 194% issue. The ordinate of Performance should be multiplied by the factor 0.86. It should also Liavebeen specifically pointed out that the initial stock temperature was 80’ F. F.
TILLER
Vanderbilt University Nashville, Tenn.
H. J. GARBER University of Cincinnati Cincinnati, Ohio
