July 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
not present in skim milk in a state corresponding to that in which it is present in rennet whey. The fat globules of skim milk behave toward methanol in a manner similar to the behavior of relatively large protein particles. Thus the intercepts on the ordinate axes of the lines of Figure 2 are proportional to the fat concentration, and indicate that the fat is largely precipitated with the largest protein particles at methanol concentrations lower than that required to precipitate the main body of proteins. This phenomenon is receiving further study. LITERAlURE CITED
(1) Assoc. Offic. Agr. Chem., “Official and Tentative Methods of Analysis,” 3rd ed., Washington, D. C., 1930. (2) Deysher, E. F., and Holm, G. E., IND.ENG.CHEM., ANAL.ED. 14, 4 (1942).
1357
(3) Koenig, R. A,, and Johnson, C. R., Ibid., 14, 155 (1942). (4) Leviton, A., IND.ENG.CHEM., 35, 589 (1943). (5) Zbid., 36, 744 (1944). (6) Leviton, A., U. S.Patent 2,116,931 (May 10, 1938). (7) Zbid., 2,129,222 (Sept. 6, 1938). (8) Leviton, A., and Haller, H. S., J. Phys. CoEZoid Chem., 51, 460 (1947). (9) Leviton, A., and Leighton, A . , TND. ENG.CHEM.,30, 1305 (1938). (10) Rimington, C., Ann. Reo. Bzochem., 5, 138 (1936). (11) Rogers, L. A., Associates of, “Fundamentals of Dairy Science,” A.C.S. Monograph 41, 2nd ed., p. 48, New York, Reinhold Publishing Corp., 1935. (12) SZrensen, M., Comnt. rrnd. truu. lab. Carlsbery, 21, 123-8 (1936). (13) S$rensen, M., and SZiensen, 9. P. L., Ihid., 23,55-99 (1939). (14) SZrensen, S.P. L., Ihid., 18, 1 (1930). RBCEIVFLJ March 5 , 1948.
Hydrocarbon Azeotropes of Toluene ROBERT F. MARSCHNER AND WENDELL P. CROPPER Standard Oil Company (Indiana), Whiting, Ind. Efficient fractionation of toluene concentrates, obtained by distillation of naphthas derived from petroleum of a variety of types, showed that toluene distills from petroleum as a series of toluene-lean azeotropes of saturated hydrocarbons, including several rare cyclopen tanes. Samples of 2-methylheptane and cis-1,3-dimethylcyclohexane were distilled with toluene to form toluene-rich azeotropes. The compositions and boiling points of these toluene azeotropes have been readily correlated in the manner previously developed for benzene-saturated hydrocarbon azeotropes. Toluene shows a less broad azeotropic effect than benzene. Confirmation of predictions based upon benzene azeotrope correlationswarrants similar toluene azeotrope predictions. Hydrocarbon data obtained under the American Petroleum Institute Fundamental Research Program were of frequent use in this work.
S
T U D Y in fractionating columns of the binary systems of benzene with ten paraffins and naphthenes of neighboring boiling points conclusively demonstrated thc formation of a systematic series of azeotropes (15). It was possible from correlations bascd upon these data to predict with considerable assurance the properties of benzene-paraffin and benzene-naphthene azeotropes which had not been experimentally investigated. Toluene also has long been known t o distill in admixture with other hydrocarbons at temperatures considerably below its normal boiling point @4), but the nonaromatic hydrocarbons of boiling points near that of toluene have been unavailable and little known. A systematic study of the azeotropic behavior of toluene has, therefore, been impossible. Recent work by groups working under the American Petroleum Institute Fundamental Research Program has produced the background work that now makes i t possible to delineate the azeotropic behavior of toluene with neighboring paraffin and naphthene hydrocarbons. FRACTIONATING COLUMNS AND HYDROCARBONS
The same two fractionating columns operated in the manner previously described (15, 16) were employed in this work. Column G is constructed of stainless steel; its helix-packed section is 6 meters long and 2.6 cm. in diameter, and it has an efficiency of
something over 100 theoretical plates. Typically, 5 liters of charge are used, and 1% fractions of the distillate are removed hour, at 100 to 1 reflux ratio and at a throughput of less than alf the flooding rate. Smaller column 3 has a packed section 1.2 meters long and 1.2 cm. in diameter. Usually 200 ml. of chargc are employed, and 1% fractions are removed in half an hour a t 50 to 1 reflux ratio and at a throughput of about 250 ml. per hour. Various test mixtures showed this column to be equivalent to 60 to 90 theoretical plates a t total reflux, and with methylcyclohexane-n-heptane, 75 theoretical plates were indicated a t the usual operating conditions. Toluene was prepared from nitration-grade material, manufactured during the war, b y treatment with silica gel to remove slight coloration due t o traces of phenol, followed by refractionation. This grade of toluene, manufactured from petroleum b y the hydroforming process, proved far purer than C.P. toluene obtainable from some chemical supply houses. The methylcyclohexane was as previously described (M), By fractionation through column C of a commercial sample of solid phosphoric acid hydrocodimer, a long plateau (8) due to 2,3,4-trimethylpentane was obtained. Although the degree of purity of this hydrocarbon is not so well established as that of the others studied, the importance of this material in certain toluenerich hydrocarbon mixtures (notably aviation fuels made from hydrocodimer and catalytic cracked gasolines) made advisable the study of the best sample available. Purchased n-octane was employed without purification. Its freezing point of -56.8’ C. approximated the literature ( 1 ) value, and indicated entirely satisfactory purity; as a check, three quarters of a sample was frozen and the refractive index of the unfrozen quarter was found to be only 0.0003 higher than that of the original material. The 2-methylheptane and cis-1,3-dimethylcyclohexane were obtained from the A.P.I. Research Project 45 at the Ohio State University. They were closely fractionated portions from large batches of these hydrocarbons prepared there, and were studied without further treatment. The sources and physical property data for all hydrocarbons used are summarized in Table I. The physical properties are compared with the definitive values of A.P.I. Research Project 44 ( 1 ) . The purities as determined, reported, or estimated are given in the final column.
ger
FRACTIONATION O F PETROLEUM TOLUENE CONCENTRATE
Scrutiny of literature data on the efficient fractionation and aromatic analysis of the toluene-containing portion of peh-oleum naphthas reveals a certain regular pattern which is traced in Figure 1. I n this figure the upper and lower refractive index curves give the values obtained before and after removal of toluene from
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 41, No. 7
r T O L U E N E REFRACTIVE INDEX
98 16
x
E z
14 w
2
12
:a:
40
aw
I-
LL
VOLUME PERCENT DISTILLED
Figure 1.
Fractionation of Toluene Concentrate8
AICH, mathylcg clohexane; DMH, dirnethylhpxanrs; MS, rrLethylheptaries; solid a e a s , toluene
the fractions of distillate, the dark areas t h e r e h e repreierit toluene. Fractionation through a 70- to 75-theoretical plate column of a wide Yates naphtha (28) containing only a trace of aromatics produced a refractive index curve shoving a maximum near 100" C., due primarily to methylcyclohexane, and a subsequent broad minimum due to branched octanes. The small amount of toluene present appeared to concentrate near the methylcyclohexane. Through the same column a Pennsylvania (21J naphtha from Bradford (23) much highei in toluene, gave thrre boiling point plateaus-a 100" C. plateau coinciding with an ammatic-free refractive index peak due to methylcyclohexane, a 107" C. plateau coinciding with the highest (eoncentration of toluene, and a 117" C. plateau coinciding v,-ith a iefractive indexminimum, due evidently to rpeth, lheptaries. Toluene was found in all fractions distilling between 100" and 117" C. JTork with relatively narrower fractions of Ponra City, Okla., naphtha was carried out through less effective bubble plate columns before (6)and after (11) removal of toluene from the entire toluene concentrate. These data are also shown in Figure 1, where the ruled area signifies that the change in toluene conccntration with boiling point cannot be determined with this technique. Methylcyclohexane was again indicated at 101' C., but with the larger amount of material available, an additional Teak peak and valley in refractive index appeared in the toluene-containing naphtha, well below the boiling point of methylheptane,i. I n the absence of toluene, these new components occurred near 110" C., and the maximum and rriinirnum were more evident. These were later attributed (13) to trimethrlrvclopentanes and dirnethylhexancs, respectively,
bons comprising substantially all the material in petroleum normally boiling between 108" and 116" C.; 2,5-dimethylhexane, cis,tiu~s,cis-1,2,4-trimetliylcyclopentane, 2,4-dimethglhexane, cis,trans,cis- 1,2,3-trimethylcyclopentane, 3,3dimethylhexane, 1,1,2-trimethylcyclopentane, 2,3-dimethylhexane, and 2-methyl-3-et'hyl-
perit,ane. Because of this better resolution in the absence of t,oluerie many napht,ha fractionation studies have used aromatic.free niaterial. In order to clarify the perplexing distillation behavior of pvtroleuiri toluene concentrate, samples of naphthas from different crude sources were fractionated through column C. Figure 1 presents the comparative result's obtained with three of these: a mixed mid-continent naphtha lorn in toluene, and isoparaffinic riltphtha intermediate in toluene, and a W e s t Texas naphtha rich in toluene. Toluene was teinatically removed from portions of ( d i distillate fraction by rneans of silica gel (following preliminary sulfuric acid react,ion when the t,oluene concentration exceeded about, 2004) and the refractive index curves before and after rerrioval are shown as before. K i t h the adequat,e quantities of narrow-boiling niaterial used, a,nd the excellent resolut.ion obtainable in column C , it became possible to observe more closely the distillation behavior of toluene in the presence of paraffinic and naphthenic material. Methylcyclohexane distills from the midcontinent, conctxitrate entirely without, toluene, which appears first, i n low concentration near 103' C., then in moderate concent,ratiori a t 107' C., and completclg disappears just before reaching the interniediate refractive index maximum of 1.411 at 111 C. Figure 2 gives more complete data for this mid-continent napht,ha. In the isoparaffinic naphtha of intermediate toluene content, toluene givcs theappearance of distilling first at 102 C. with methylcyclohexane,, hut the low refractive index warns that only small amourit,s of methylcyclohexane can be present,. Toluene next distills in moderate amounts at, '107 C. with the prominent paraffinic O
Hydroaarbon E ~ r i ~ ~ l o y..r d Name Source ToluaIlr Standard (Indiana) Methylcyclohexane ( 1 6 ) Barrett 2,3,4-Trimethylpentane Standard (Indiana) 2-Methylheptane A.P.I. Rerearoh Projrot 45 cis-l,3-Dimetl1ylcs~clohexane' A . P . I . Revcaich Project 45 rk-Octane Colin. Hard Rubber Co. ti
b
c
3
Approximate. Lowor boiling, more *table isomer Corrected from value at 7 2 5 mm. Corrected from value a t 25.0' C.
(17)
Boiling Point, O C:. a t 760 X m . Obsvd. Lit. ( 1 ) 110.6 101.2
110.0:
120.1~
120.1 125.7
113.8 117.7 ,,.
100.9 113.5 117.6
Refractive Index, nko Obsvd. Lit. (171.4968 1.4968 1.4231
1.4231
1,4229d 1,3076
1.4229
1.4043 1.3950
1.4043 1.3950 1.3976
Indicated Purity, 70 R9.5 99 99 97.7
++
95.0-t 99.0
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1949 material, whose refractive index falls as low as 1.396, and finallv in nearly equal amounts at 110" C. with the naohthene.
1359
. TABLE11. PLATNAUS I N MID-CONTINENT TOLUENE CONCENTRATE Hydrocarbon Ethylcyclopentane l,1,3-Trimethyloyclopentane (Azeotrope)
Literature (1) B.P., ' C. n%O
103.5
Toluene Present B.P., O C. ng0
Toluene Removed C. nP a
{::::;
1 4198
.
B.P.,
1.418
disappearing as the fractiona104.9 1:4112} 103'4 1.424 1.412 tion approaches methylheptane 107.0 1.440 Absent at 1170 In the tolueneozs,trans,czs-l,2,4-Trimeth~lo~olo~entane 109:3 l.kib6 109.4 1.4104 109.5 1,4104 rich West Texas naphtha, methylcgclohexane is again point, the toluene is depleted before it can distill in high purity, found toluene-free. The toluene distills in increasing amounts and only saturated material boiling well above toluene remains as before, first a t 107" C. with the paraffin, then near 108" C. with the naphthene, and finally in high concentrations That this curve is typical is attested to by comparison with published crude toluene distillations (2, 19). All these characteristirs with methylheptanp a t 111', essentially the boiling point of pure of the behavior of toluene upon distillation of petroleum mixtures toluene. Refractive index curves for an unnamed naphtha interare clearly azeotropic. mediate in characteristics hetween these latter two have appeared (19) in the literature. HYDROCARBONS IN PETROLEUM TOLUENE CONCENTRATE These and many other observations are readily explained as indicating a series of toluene azeotropes. Toluene forms no azeoBy refractionation of the toluene-containing fractions of midtrope with methylcyclohexane, but when only little methylcyclocontinent naphtha, the individual toluene azeotropes were better hexane is present, it appeHrs to do so berause of gross contaminarecognized. Refractionation through column C as shown in Figtion by azeotropes containing about 10% toluene with close ure 2 had accomplished little further separation. Higher rffihigher-boiling naphthenes. With the paraffins that distill next , ciency of fractionation was, therefore, ineffective; examination of the azeotropes contain 20 to 30% toluene, and with the subsesmaller cuts was necessary. All available remaining saturated quent naphthenes, 40 to 50% toluene. The methylheptane azeoand aromatic portions from silica gel separation and analysis were trope is so rich in toluene that any toluene remaining is promptly combined in the three boiling ranges: 101" to 105", 107' to 117 ', depleted. The refractive index curve for each naphtha is characand 112" to 117" C. These portions were individually refractionterized by a precipitous drop as the toluene disappears, and the ated through column 3. The first two distillates were combined corresponding boiling point simultaneously rises sharply to that of and freed of toluene by silica gel adsorption, and the toluene-free whatever hydrocarbon remains. 9 crude toluene extracted from percolate was finally fractionated again. The results are sumpetroleum is shown in the final curve of Figure 1 to behave simimarized in Figure 3. The toluene-paraffin concentrate boiling at larly-after the disappearance of methylcyclohexane, the toluene 105" to 107 C. was not similarly studied, and the 111O to 112 O C. naphthenic fraction was examined as described later. concentration increases steadily, but because of successive conI t was scarcely possible to interpret the results of Figure 3 until tamination with saturated hydrocarbons of increasing boiling definitive data upon the physical properties of the 8I carbon cyclopentanes recently became available through A.P.I. Research Project 44 (1). I n the origiI44 nal fractionations with toluene present, the three plateaus listed in Table I1 E@ under "Toluene Present" c were observed. I n the frarI', 43 w tionation after toluene re'E INDEX n z removal) moval, the first plateau parn20 w tially divided, whereas the 2 mt hy lc y he m e Isecond plateau disappeared V 2 1.42 by drifting into the third, LL w ol which remained unchanged, 1- . as shown in the final columns TJ of Table 11. Evidently, three I naphthenes were present. I I41 -1 Two of these boil a t nearly I the same temperature, and I I form azeotropes having boilr-l ing points even closer toI 6 gether-too close for separaII ANILINE POINT z tion. The third naphthene 1 B boils much higher; it forms w z an azeotrope with toluen? =! BOILING POINT boiling sufficiently lower to 54 permit separation, and excess -n-heptane naphthene over the amount required by the azeotrope is -2 -I L I T E R S DISTILLED present. There is little doubt that these three naphthenes Figure 2. Fractionation of Mid-Continent Toluene Concentrate are the three cyclopentane Dashed refractive index curve is from original fractionation. Boiling point and solid refraotive index ourve8 a8 in Figure 1. Solid areas represent toluene. Further proaessing of recomposited portions A, B, and C is shown in Figure 3 derivatives named in Table
c.
-
ct
INDUSTRIAL AND ENGINEERING CHEMISTRY
1360
,4403
REFRACTIVE INDEX (before toluene rernavall
4300
1
A
1.1.2- trirnethylcyclopentane
+
sa c x
D W
5
f
. 4 200
ethylcyclopentane
w
'1
7 ,l,3- irimethylcyclopentanr/-
BOILING POINT [after toluene removal)
> c
U
a
o z LL w: D
i'_t_
4 100
.4000 rf'
--/- 2,4-dimethylhexane 12.5-dimethylhexane
terial is mainly paraffinic. An attempt to fractionate more closely a mid-continent naphtha containing one third more toluene than the material in Figure 2 gave little additional information. The cis,trans,cis- l ,2,3-trimethylcyclopentane did appear to give an azeotrope with a refractive index peak a t n%' 1.446 which would indicate 39y0 toluene. The relatively smaller proportion of naphthenes in the isoparaffinic naphtha prevented ready recognition of this azeotrope. The presence in quantity of the azeotropes of close higherboiling paraffinic material in the West ,Texas naphtha likewise made recognition difficult. The best values obtained for these several cyclopentane azeotropes are collected in Table 111. It is not surprising that the azeotropic behavior of toluene in petroleum distillates and the identity of the saturated material in this boiling range of petroleum 'remained so long unrecognized. The first two azeotropes described above boil within 3' of methylcyclohexane, from which they can be separated only with modern efficient fractionating equipment. I n both cases also, the toluene contents of the azeotropes happen to be just sufficient to give mixtures which resemble methylcyclohexanc in refractiveindex. Moreover, 1,1,3trimethylcyclopentane itself was until 1 ecenlly unknown (1.9). TOLUENE AZEOTROPES
S YNTHETlC
+2,2-dimethyhexane I
Vol. 41, No. 1
With the toluene-poor hydrocarbon azeotropes thus oriented, determination of the boiling range of the hydrocarbons yieldFigure 3. Refractionatiori of Portions of Nlid-Continen t Toluene Concentrate ing toluene-rich azeotropes was Recomqosited portions A and B of Figure 2 were refractionated separately, then combined, freed of toluene undertaken. Of the two recogand again fractionated. Dotted boiling point curve is after toluene removal, with about 50% recovery, and i; plotted accordingly at double scale u i t h intersection at 110' as zero point as indicated in parenthesis nized methods of establishing the presence of an azeotrope, fractionation through an efficient wlumn is f a r simpler than the lengthy alternative liquid11. The first two toluene azeotrope-forming hydrocarbons-ethylvapor equilibrium procedure. T o eliminate any question cyclopentane and l,l,a-trimethyl cyclopentane-have recentlv as to the validity of the favored fractionation technique for been isolated in 1 to 2 ratio from the 102 O to 108" C. fraction of isolating close-boiling azeotropes, the boiling point of the bentoluene-free Ponca City naphtha ( 7 ) . Some 230 ml. of the third zcnc-2,4-dimcthylpentane azeotrope (16) was redetermined naphthene-cis,tmns,cis - 1,2,4trimethylcyclopentane-probably using an ebulliometer instead of a fractionating column and contaminated with some of the higher-boiling cis,trans,cis-l,2,3 employing new and carefully prepared samples of the components. isomer, were available from the original fractionation. This 111 * The benzene was successively fractionated through both column to 3 12' cut had a n aniline point of 60.2 arid a CFR-M clear octane C and column 3. The 2,4-dimethylpentane, obtained in quantity number of 80.2, the highest value which has been observed for an from an alkylate by fractionation through column C, was refracaromatic-free petroleum cut containing more than 6 carbon atoms. tionated and its purity was determined in connection with other It is evident from Figure 3 that the hydrocarbons boiling immework by A.P.I. Research Project 6 at the National Bureau of diately above the toluene azeotropes in mid-continent naphtha Standards. The high purity of both hydrocarbons mas well esrepresent a complicated and not plentiful mixture. After removal tablished, as shown in Table JV. After running both hydrocarby distillation of small amounts of ds,truns,cis-lJ2,3-trimethylbons alone in the equipment and by the technique described by cvclopentane and probably 1,1,2-trimet~hylcyclopentane, the maIO)
2 00
I
I
I
400
c2m1
I
tlOOl MILLILITERS DISTILLED
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1949
2 m 0
1. Ethylcyclopentane 2. 1,1,3-Trimethylcyolopentane 3. cis, trans, cis-1.2,4-Trimetbylcyclopentane 4. 2,3,4-Trimethylpentane 5. 2-Methylheptane 6. cis-l,3-Dimethylcye10hexane Paraffins Naphthenes
2 110 0 0
n 2. I
,100 W
5 Q I3
'
,
Figure 5. Azeotropes of Toluene with Saturated Hydro. carbons
120
1361
90-
lL 0
MOL P E R C E N T AROMATIC HYDROCARBON
Figure 4.
Comparison of Azeotropic Behavior-of Benzene and of Toluene 0 Paraffins
H Naphthenes
Swietoslawski (20), the azeotropic mixture was similarly run. The resulting boiling point presented in Table IV is in excellent agreement with the previous values (15). Accordingly, the simpler fractionation procedure for toluene azeotropic identification was undertaken with this additional assurance as to its reliability. The described samples of methylcyclohexane,' 2,3,4-trimethylpentane, 2-methylheptane, cis-1,3-dimethylcyclohexane, and noctane were fractionated with selected varying amounts of toluene through column 3. The plateaus obtained corresponding to the azeotropic mixtures of toluene with three of these hydrocarbons had the properties summarized in Table 111. I n agreement with previously reported work ( d ) , no azeotrope was observed with n-octane or with methylcyclohexane. Nor does toluene form an azeotrope with n-heptane a t atmospheric pressure, although benzene forms an azeotrope with n-hexane, and very nearly if not actually with n-heptane (16). As shown in Figure 4, toluene thus forms azeotropes through only an 18" boiling range
as compared withabout 30" in the case of benzene. Olefins also form azeotropes with toluene. A close-boiling octene plateau from "solid phosphoric acid" mixed butene polymer, which form the prop0 50 erties indicated in MOL PERCENT TOLUENE Table I11 was mainly 2,3,4-trimethyl- 2 - pentene ( I ) , was fractionated through column 3 with a deficiency o f toluene, and an azeotrope containing about 82 volume yotoluene resulted. PREDICTION OF UNKNOWN TOLUENE AZEOTROPE PROPERTIES
The boiling point and aromatic hydrocarbon content of unknown benzene azeotropes were found t o be predictable from data upon available benzene-paraffin and benzene-naphthene azeotropes. For example, the experimental azeotrope of benzene with 2,2-dimethylpentane has been reported (3)to boil a t 75.85'C. as compared with the authors' predicted value of 75.7" C.; its composition was 52.5 mole yo benzene, in fair agreement with the authors' predicted value of 48%. Likewise as predicted, the cyclohexene-benzene azeotrope contains less benzene (9) than formerly believed. The same means of predicting data upon unknown toluene-saturated hydrocarbons, therefore, appeared warranted. Thus by plotting the data of Table I11 as in Figure 3, compositions may be estimated, then from Figure 5, the corresponding boiling points can b e derived, and a plot of hydrocarbon boiling points against, OB TOLUENE-SATURATED HYDROCARBON AZEOTROPES TABLE111. PROPERTIES azeotropic lowering utilized to Boiling Point, ' C . Refractive Index, check these values, at 760 Mm. nso
HydroToluene Azeotrope carbon Ethylcyclopentane 103.5 1 1 3-Trimethylcyclopentane 104.9 Pkiaffin (2,5-dimethylhexane?) 109a cia,trans,cis-l,2,4-Trimethylcyolopentane 109.3 cis,trans,c~s-l,2,3-Trimethylcyclopentane110.4 2 3,4-Trimethylpentane 113.5 dlefin (mainly 2,3,4-trimethyl-2-pentene)116" 2-Meth lheptane 117.6 120.1 ois-1,3-6imethylcyclohexane a Approximate.
Azeotrope 103.0 103.8 107" 107.0 108.0 109.5 11oa 110.3 110.6
Lowering 0.5 1.1 25 2.3 2.4 4.0 5a 7.3
Hydrocarbon 1.4198 1.4112 1.3935 1.4106 1.4144 1.4043 1.4270 1.3950 1.4229
Azeotrope 1.4240 1.4235 1.432a 1.4410 1.4485 1.4550 1.4840 1.4748 1.4941
% Toluene
But the interesting recent treatment of the authors' benzene azeotrope data by Skolnik (18)provides new means of pre39 43 diction which is in certain re.. 85 .. 60 spects more precise than that .. just outlined. Plotting semi82 85 9.5 logarithmically the molar tolu90 97 ene concentration against the boiling point of these azeo~tropes as in Figure 6 indicates TABLEIV. COMPARISON OF AZEOTROPE DETERMINATION PROCEDURES that the trimethylcyclo enComtanes fall somewhat apart Boiling Point Refractive Freeziag position, the other saturated hydrocarO c. a t 760 Mm. Materials Procedures Index, Point, C. Mole % bons studied. If either the boilSammie used Benzene 80.13 * 0.02 1.5011a 5.40 ing point or the composition of LiteGature (I) 80.10 1.5011 5.53 2,4-Dimethylpentane Sample used 80.51 * 0 . 0 2 1.3816 -119.57 the toluene azeotrope of a satuLiterature ( f ) 80.51 1.3816 -119.5 rated hydrocarbon is known, Azeotrope Ebulliometric 76.68 A 0.02 1.4309 ... the other property can be deter76.6 0.2 Fractionation ( f 6 ) C 1.4312 ... Fractionation I 6 ) d 76.7 * 0 . 2 1.4309 mined from Figure 6, provided ... Ebulliometric IS) 76.45 ... the correlation line has been Determined on calibrated Pulfrich refractometer. Obtained with excess benzene. developed for the proper subPer cent benzene. d Obtained with excess 2,4-dimethylpentane. class of hydrocarbon. T h e boiling point can be predicted 6 14 3Sa 35 39a 55 82 79 96
7 16
7 19 .
I
80,
...
1362
INDUSTRIAL AND ENGINEERING CHEMISTRY
IO0 w
00
’2 5
60 40
5 8
20
&
LL W
;IO z 5
104 106 IO8 BOILING POINT OF AZEOTROPE,
Figure 6.
110
”C.
Correlation of A\zeotropeProperties
Vol. 41, No. 7
from two other plots. First, as in Figure 7, i t is shown that t>helocus of the points obtained by plott,ing hydrocarbon boiling points against azeotro e boiling points, is asymptotic to a line somewhat above the {oiling point, of toluene. Second, plotting as in Figure 8 of the logarithm of t’he difference between the asymptotic tempemture and the azeotrope boiling point, against the hydrocarbon boiling point, develops a curvi which is most nearly linear when the asymptotic temperature is taken as 111.6” C., or 1.0” above the boiling point of toluene. To predict toluene azeotrope propert’ics, the boiling point lowering is first determined from Figure 8, then the composition derived from t’heboiling point through Figure 6. Predictions of the compositions and boiling points of unknown toluene azeotropes of alkanes and cycloalkanes boiling below 120 C. are present’edin Table V as determined through both the Mnir-GlaRgo~~-Rossini (14) and Skolnilc (18) correlations. The two treatments give values which show close agreement in many instances, but differ in the extreme cases by as much as 0.6” in boiling point and 10% in t,oluene concentration. An interesting test, case is afforded by 2,%dimethylhexane, sincc Lecat (10) anticipated 30 years ago that this hydrocarbon would form an azeotrope with toluene. ACKNO W LEDGM EYT
The authors thank C. E. Boord and K. It’, Greenlee of the B.P.I. Research Project 45 at Ohio State University for the gift of sampirs of 2-methylheptane and cis-1,3-dimethylcyclohexane, and F. D. Rossini of A.P.I. Research Project 6 a t the National Bureau of Standards for final purification and determination of propel ties of the 2,4-dimethylpentane. The interest and assistance of A. P. Lien of this laboratory and W. B. Kay, formerly of this laboratory, are appreciated. LITERKITRE CITED
(1) Ani. Petroleum Inst. Research Project 44, tabulated selected values. (2) Berl, Chem. Eng. .Vews, 19,636 (1941). (3) Birch. Collis, and Lowry, -Vatwe, 158, BO
(Aug. 13, 1946). 104
112
I08
(4)Bromily and Quiggle, IND.E m s .
(:HEM.,
25,
1136 (1933). ( 5 ) Bruun, Leslie, and Schicktanx, J . Research ;LTatE. B u r . Standards, 6, 363 (1931). Figure 7. Determination of Azeotrope Figure 8. Linear Boiling Point Asymptote Relationship ( 6 ) Glasgow, Willingham, and Rossini, “Hydiucaibons in the 108’ t o 116OC. Fractionof Petroleum,” publication in progress. (7) Glasgow, Willingham and Rossini, J.Research S a t l . B u r . Standards, 38,621 (1947). TABLEv. PREDICTED P R o P s R T I s b o b ~ Z ~ K N O W UT0r.r EN^ (8) Glasgow, Streiff, Willingham, and Hosaini, I b i d . , 38, 537 (1947). AZEOTROPES (9) Harrison and Berg. IXD. ENG.CHEM., 38, 117 (1946). (10) Lecat, “La tension de vapeur des m6langes de liquides. L’ Hvdi ocirbon SzQotropisme,”p. 167, Brussels, Henri Lamertin, 1918. Toluenc Alaeotroix ... B. P., C. (11) Leslie, J . Research ”Vatl. R7rr. Standards, 15,41,2 1 1 (1935). at B. P., C . z t hIole 9 Paraffin3 760 Mni. 760 M m . toluene (12) I h i d . , 22, 153 (1939). (13) McKinley, St,evens, and Baldwin, J . Am. Chem. SOC.,67, 1455 18 28 105.7 105.1 106.8 2 %Dimethylhexane 31 41 107.3 106.8 109. 1 (1945). 2’5-Dimethvlhexane 34 43 107.5 109.4 107.0 2’4-Dimeth:,lhexane (14) Mair, GlaJgow, and Rossini, J . Research iVat2. Bur. Standards, 36 46 107.7 107.2 109.8 2’5 3-Trimekhylpentana 27, 39 (1941). 51 57 l08,7 112.0 108.6 3’3:Dirnethylhexane 6.5 71 109.4 110.0 114.8 (15) Marschner and Cropper, IKD. ENG.CHCM.,38, 262 (1948). 2’3 3-Trimethylpentana 74 7 5 109.8 110.1 115.6 2’3iDimethylhexsne (16) Marschner and Cropper, Proc. Am. Petroleum, Inst., 26, 111, 41 76 76 109.9 115.7 110.1 zi.Methyl-3-ethylpentane ( 1946). 88 86 110.3 110.3 117.7 4-Methylheptane 68 86 110.3 110.3 117.7 (17) ICossini and Pitaer, Science, 105, 647 (1947). 3 4-Dimethvlhexane 92 88 110.4 110.4 118.3 31~’I~thvl-3Iethslpentanr (18) Skolnik, IND.EBG.C H m f . , 40,442 (1948). 93 89 110.5 110.4 118.6 3-Ethyihexane 96 (19) Sweeney aud Mciirdle, I h i d . , 33,787 (1941). 91 110.5 110.5 118.9 3-Methylheytane (20) Swietoslamski, “Ebulliomietric Measurements,” p. 6,’New York, Reinhold Publishing Gorp., 1945. Naphthenes (21) Tongberg and Fenske, IND.ESG.CHEaf., 24, 814 (1932). 113.7 109.6 109.3 66 72 1 1,2-Trimethylcycl ouentsne :hylcz!s,~is,t~ans-1,2,3-T~~imel (22) Tongberg, Fenske, and Nickels, Ihid., 29,70 (1937). 117.7 110.3 110.3 86 92 cyclopentane (23) Tongberg, Quiggle, Fenske, and Fry, Oil Gas clohexane 119 4 99 BOILING POINT OF AZEOTROPE,
1 ,1-Dll;lethylcyclohexane
119 5
C.
110.5
LOG (1ii.6.B. P. AZEOTROPE,
110.6
94
First column lists predictions derived through correlations ba.sed 1 1 ~ 0 1 1 Rossini ( 1 4 ) ; second column lists predictions using correlation method presented b y Skolnlk (18). a
C.)
I ~ W E I Y E UJune 9, 1948. Presented in part a t the Joint Meeting of the Chicago Section of the AWERICAX CHEMICAL SOCIETY and Section C (Chemistry) of t h e American rissociation for the Advancement of Science, Chicago, December 26, 1947.
