e
es of Nap romatics
B
VA4P0R-lLIQUID EQUILIBRIUM DATA H. S. AIbERS C. l < .U r a u n & Co., .ilhar&m, Calif. tOhIAT1C hydrocarbons have long been knou-n to show nonideal volatility characteristics when mixed with other types of hydrocarbons. An earlier article ( 5 ) gives vapor-liquid equilibrium data for mixtures of aromatics and paraffins. 'Phi. article presents similar data for mixtures of aromatics and naphthenee. Complete vapor-liquid equilibrium data are reported for five hinary mixtures a t 760 min. of mercury- absoliite preesiirc: cyclopentane-benzene, methylcyclopentane-benzene, benzencmethylcyclohexane, cyclohexane-tolueIie, and niethylcyclopentane-toluene. The equilibrium still used for this study has h e n described previously ( 4 ) . It is of the vapor rccirculating t'gpc and uses a vapor jacket to maintain adiabatic operation. ,411 parts arc made from glass except for the Teflon sample valves. The hcatiiig elements are conipletely encased irr a borosilicate glass tube, thereby eliminating any possibility of contamination. Except for sampling, operation is completely automatic. PURIFICATION OF HYDROCARBONS
Benzene. Baker and Adamson reagent grade benzene was refractionated in a column packed x i t h l/la-inch Etainleas steel helices ( 5 ) . The column had 100 theoretical plates when tested Lyith heptane-methylcyclohesane a t total reflux. For the benzene purification, a reflux ratio of GO to 1 was used, and a 28 to 89% heartcut mas blended as pure benzene.
Toluene. The toluene wad I3aker and Adamson reagent grade, redistilled through the 100-platc packed column a t 60 to 1 reflux ratio. A 55 t o 95% cut was blended for the equilibrium studies. Cyclopentane. Phillips Petroleum Co. 9570 grade pentane was further purified b y extractive distillation in plate Oldershaw column, using aniline as the solvent. Thc impurity is chiefly 2,2-dimethylbutane. After two successive extractive distillations, about 50% of the charge was recovered as high-purity cyclopent,a.ne. Methylcyclopentane. I n Phillips 99% purc methyl pentane t,he impurity is primarily benzene. To remove the benzene, 1800 mi. of this stock \yere passed through a silica gcl column. The column was 1 inch in diameter, 82 inches high, and packed n i t h 1025 grams of 100- to 200-mesh silica gel. Methanol was used as a desorbent. ,4s a result of the extraction, thc refractive index of the methylcyclopentane dropped from 1.4104 to 1.4097 a t 20" C. For a final purification this extracted material was fractionated in the 100-plate packed column a t a reflux ratio of 50 to 1. A small amount of low refractive index impurity, probably nhexane was removed a t the front end of the distillation. A 5 to 927' heartcut was blended as pure methylcyclopentane. Methylcyclohexane. Do!\- Chemical Co. high purity methylcyclohexane was fractionatcd in t'he 100-plate packed column a t a reflux ratio of 40 t o 1. I 15 to 83% heartcut from this distillation was used for the equilibrium studies.
1
1
FIGURE 2
MOLE% CYCLOPENTPNE I N Ll9UlO
a 104
June 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
1105 FIGURE 4
ACTIVITY COEFFICIENTS FOR THE SYSTEM
1
1
METHYLCYCLOPENTANE-BENZENE
MOLE % METHYLCYCLOPENTANE
MOLE
Cyclohexane. Shell Chemical Co. cyclohexane, specified minimum purity of 98 mole Yo, was fractionated in the 100 plate column a t a reflux ratio of 40 to 1. A 30 to 95yo heartcut \vas blended as pure cyclohexane. Physical properties for all of the hydrocarbons used in this study are listed in Table I. All of the binary mixtures reported in this paper were analyzed by refractive index. There is an average spread in refractive index of about 850 points on a four-place refractometer between the pure components of these binary mixtures. It is estimated that the refractometer readings can be reproduced to =tl point. This gives an estimated accuracy for analyzing these five mixtures of ahout i O . l S % . EQUILIBRIUM MEASUREMENTS
Experimental vapor-liquid equilibrium data for the five naphthene-aromatic mixtures (Table I1 were used t o compute relative volatilities and activity coefficients. Relative volatilitiw are defined in the conventional manner:
where mole fraction vapor Y B = mole fraction vapor X A = mole fraction liquid XB = mole fraction liquid YA =
of the more volatile component in the of' the less volatile component in the
of the more volatile component in the
IN LIQUID
This equation assumes ideal-gas behavior for the vapors. Vapor pressures for the pure components are taken from values published by the National Bureau of Standards ( 1 ) . Cyclopentane-benzene. Figure 1 is the temperature-composition diagram for cyclopentane-benzene. The computed activity coefficients are plotted in Figure 2. The system shows no apparent tendency toward azeotrope formation. Methylcyclopentane-benzene. The temperature-composition diagram is shown in Figure 3, and activity coefficients are plotted in Figure 4. Grimold and Ludwig ( 3 ) reported equilibrium data for this system in 1943. Their data have heen plotted on Figure 3 along with the present data. From the temperature-composition diagram, it is apparent that a minimum boiling azeotrope is formed by this system a t about 8770 methylcyclopentane. Two fractionations were made in the 100-plate rolumn to firm up tho azeotrope composition by approaching it from both sides. Results of the two fractionations are: Fractionation I. 2
Methylcyclopentane, Reboilcr 41 .0 93.2
Mole ?$ Overhead
86,s 87.7
An average of these two overhead compositions places the azeotrope a t 87.2 mole 70methylcyclopentane. This should be reasonably close to the true azeotrope composition.
of the less volatile component in the
Activity coefficients are computed from the relation Y =
Table I. Comparison of Physical Properties of Hydrocarbons Used in This Work with NBS-API Values
(;) (y)
where
Ilydrooarbon
y = mole fraction in the vapor
x = mole fraction in the liquid P = vapor pressure of the pure component a t the equilibrium T
METHYLCYCLOPENTANE
temperature = total pressure of the system
Cyclohexane
Refractive Index at ExperiNBS-API mental (1)
c:--
Boiling Point, c. _ ~ _ _ _ ExperiNBS-API mental (2)
1.6011 1.4969 1.4065 1.4097 1.4231 1.4262
1.80110 1.49693 1 40645 1.40970 1 42312 1.42623
80.15 110.6
$9.25 (1.8 100.95 80.7
80.101 110.625 49.262 71.812 100,934 80.738
~
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1106
Vol. 48, No. 6
Table 11. Vapor-Liquid Equilibrium Data (Pressure Cyclopenlane-Benrene Mole % Cyclopentane Vapor Liquid 0 0 2.2 5.6 9.9 14.7
0.6 1.7 3.2 5.0
20.5 20.2 31.2.; :13 5 39 , 3
7.2 9.8 12.4 14.7.5 10.9
45.0 .52,9 ,??.8
21
.o
29.0 27.9 29.0 30.9
n?, 2
B6,8 59,s 03.3
Temp.,
c.
75.05 73.55 72.03 70.75 R9.Y 08.0;, 65.6
65.2
64.85 64.1
33.9 37.5 41.2 44.1 47.3
63.1 61.9 60.9 60. 15 59.25
80.2 82.3 8.5.5
50.75 50.5 61.5 08.25 72.0
58.5 57.0 56.2 55.5 64.3
87.6 89.6 91 . 0 92.8 94.4
iJ.7 7Y.0 81.8 8.5.8 88.8
5 8 .6 53.0
05.8 97.23
91.8 94.5 97.8 100.0
50.fi 50.2 49.6 49.28
00.4
68.7 71.2 73.3
77.3
--
HY.0 JOO.1)
82.3 51.7 51.1
1,iquid
Vapor 0.0 2.2 4.5
7.6
58.0
53.0 5 6.0 60. 1 63.1 07.7
72.7 72.5 72.3 72.2 72.0
83.6
68.9 74.Y 79.0 80.8 83.0
71.95 71.8 71.25 71., 71.65
84.0 87.5 92.1 96.4 100.0
84.5 87.5 92.1 96.4 100.0
1.5
3.50 5.2 8.3
20.73 29.7 3z.2 38.58
10.95 16.7 20.35 23.1 26.9
43.6
96.5 100.0
Cyclohexane-Toluene Mole % Cyclohexane Vapor Liquid 0 0 10 2 4 1 21.2 9 1 11 8 20 4 30 8 14 3
._____~ ~
28.3
3 2,3 33,B
53.3 5.5. 9 89,9 80.2 63.4
29.0 29.6 37.23 44.6 48.8
10.6 11.0 15.1 19. I 22.0
71.6.5 71.65 71.75 71.8 71.8
54.9 60.2 62.5 65.7 69.5
Temp.,
72.5 74.8 77.7 79.2 80.2
26.7 31.25 33.35 37.1 41.25 45.5 49.8 53.1
c.
96.5 94.5 93.2 92.4 91.3
94.2 93.80 92.75 91.86 90.55
88.0 87,3.i
82.7 81.1 80.7
.\Ietli>lcyclopentane -Toluene Mole Yo l I C P Temp., X'apor Iiqnid c. 0.0 2.3 4 0
100.95 100.4 99. d 98.63 97.6
Temp., C.
27,s
0.0 6.8 12.7 19.3 25.7.5
Benzene-Methylcycloliexane
7.2 10.95 16.35
81.65 81.2
87.4 96.4 100.0
73.4 73.25 73.15 72.95 72.8
2.6
82.25 88 , 3 83.05 82.55 82.1
92.6 97.3 100.0
43.0 44.8 45.8 48.9 81.4
0.0
61.7 66.5 70.5 13.9 77.7
67.2 72.7 76.3 78.0 81.4
50.0 51.4 52.3 54.8 66.8
Liquid
73.3 76.7 78.93 81.5 83.8
81.1 85.2 86.4 87.7 89.5
75.1 74.6 74.2 73.75 73.6
0.0
87.15 86.5 85.96 85.5 84.1)
36.8 37.9 41.6 45.2 50.4
27.25 31.2 34.1 39.2 40.8
70Benzene
44.8 48,:~ 51.0 53.13 57.3
69.6 59.9 63.3 RA.2 70.2 72.4 74.9 77.4 77.7 79.4
35,s 39.5 42.5 46.7 48.15
3IoIe Vapor
60.85 63.7 6 5 ,G 67.5 70.25
c.
Temp.,
77.8 27.15 ifi.65 76.1 75.6
81 , 5
90.25 89.5 88.9 88.35 87.7
30,4
9.6 13.5 16.3 19.3 23.0
71.3 76.2 79,9
30.7 33.7 36.1 38.85 42.0
?9.2 00,4 52.3 54.7 36 0
13 5 20 6 23.7 27.8 31 6
60.7 63.8 66 4 70,4
48.3 51.15 53.2 55.5 58.2
16.4 19.2 21.7 24.5 24, :3
0.0 1.25 2.5 4.5 6.95
11.3
Beneene-hlethylcyclohexene (Conld.) Mole % B e n z e n e Temp., Vapor Liquid c.
34.8 38.6 42.2 45.7 40.0
~Ietliylcyclopentane-Denzenr
_ _31olr _ _%_M C_P _ ~
760 mm. Hg absolute)
ii.35
!1 2 102 :i 102.0 99 3 96 8 9 5 , :3
55,25 56.8
83.1 85.7 88.25 91.5 93.6
62.2 67 72. I 79.R 81.6
9,5.4 96 9 98.23 100 00
89.2 92.8 9R 6 100.00
73.7 !3 (2.2 71.8
p.
June 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
1107 FIGURE
6
-
A C T I V I T Y C O E F F I C I E N T S FOR T H E SYSTEM DEN2 ENE - M ET H Y LCY CLOH EX ANE
i
MOLE % BENZEHL
MOLE
9/0 BENZENE IN LlOUlD
FIGURE 8
ACTIVITY COEFFICIENTS FOR THE S Y S T E M __ CYCLOHEXANE- TOLUENE A B S O L U T E PRESSURE : 7 6 0 m m Hg
I I
15
------re-+
/
I -
I
I
'
E X P E R I M E N T A L ~ - - - ~ ~ - - I
--
-r
T INVESTIGATION
0 MOLE %CYCLOHEXANE MOLE %CYCLOHEXANE
Benzene-methylcyclohexane. Figure 5 is the temperaturecomposition diagram. and Figure 6 shows the computed activity coefficients. Sieg ( 6 ) has published data for this system in a German journal. His d a t a are plotted on the temperaturecomposition diagram along with the data from the present study. No azeotrope is indicated, although there seems to be a definite tendency toward azeotrope formation a t high benzene conrentrations.
I N Llaulo
Cyclohexane-toluene. The data are plotted as a temperatuiecomposition diagram in Figure 7 , and the activity coefficients are shown in Figure 8. Data reported by Sieg (6) for this system are also plotted on Figure 7. Agreement is excellent over the entire diagram. This system does not form an azeotrope, but there does seem to be a tendency toward azeotrope formation a t high cyclohexane concentrations.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1108
F GURE 9 TEMPERATURE COMPOSITION DIAGRAM FOR THE SYSTEM VETHYLCYCLOPENTANE T O L U E N E dbSOLUTE P R F 9 5 1 R E
1
~-
1
Vol. 48, No. 6 F I G U R E 10
760mm Pg
METHYLCYCLOPENTANE- TOLUENE
I
,
MOLE -lo METH'LCYCLOPENTPNE
M O E a/o METHYLCYCLOPENTANE IN LlQUlU
Methylcyclopentane-toluene. The temperature-composition diagram is shown in Figure 9, and t,lie computed activity coefficients are plotted in Figure 10. No azeotrope is formed. Check for Thermodynamic Consistency. A11 of t,he data were checked for thermodynamic consistency by the form of the van Laar equations given by Gilliland ( 2 ) .
niethylcyclopent,ane-toluene.Deviation8 of t,heae four systems from the van Laar equations, although riot large percentayewise, are larger than ran be explained by analyticxal errors. A3 has been mentioned earlier, two of these systems have aleo brcn reported by Sieg (6). His data show excellent' agreement with the present data, and, like the present data, do not precisely fit the van Laar curves.
c o ~LU c s o n -s
The constants €or these equations w e r e determined from the experimental points using the graphical procediire oiitlined by Gilliland (9). For each of the systems, the consistent van Laar activity coefficient ciirves are shown as broken lines on the experiniental activity-coefficient, plots. Of the five systems, only methylcyclopentane-benzene shows good agreement with the van Laar curves. This is possibly due to the fact t,hat there is only about an 8.5' C. spread between the boiling points of methylcyclopentane and benzene. The system is very nearly isothermal. T h e other four systems, however, have much larger spreads betxeen the boiling points of the pure components. About 31 O C . for cyclopentane-benzene, 20' C. for benzene-methylcyclohexane, 30" C. for cyclohexane-toliiene, arid 39" C. for
The five naphthene-aromat'ic systems studied in this work all show considerable deviations froni ideality. Terminal activity coefficients range from about 1.2 t o 1.4. Only one of the five systems, methylcyclopentane-benzene, forms an azeotrope, biit, the t'emperature-composition diagrams for all of the other four systems except cyclopentane-benzene seem t o indicate a tendency toward azeotrope formation a t the lov-boiling ends of thc diagram. LITERATURE CITED
(1) American Petroleum Institute, Research Project 44, h'ationd
Bureau of Standards, December 1952. (2) Gilliland, E. R., "Elements of Fractional Distillation," 4th c d . , LIcGraw-Hill, Sew York, 1950. (3) Griswold, J., Ludwig, E. E., IND.ENG.CHEM.35, 117 (1943). (4) Hipkin, H. G., Myers, H. S., Ibid., 46, 2524 (1964). (5) hIyers, H. S.,I b i d . (6) Sieg, L., Chem.-Ing.-Tech. 22, 322 (1950). RFOEIVED for review September 8 , 1955.
Acrer1Tr.n Fehninry 21, I D A R .
