Liquid-Vapor Equilibrium Relations in the Ethane-Cyclohexane System R‘EBSTER B . IeI
EXPERIMEXTAL METIIODS AND APPARATUS
The P-T’-l’-x relatioris of the ethane-cyclohexane system at the liquid-vapor phase boundaries were obtained by the detrrniination of the pressure-temperat~ireborder curves and temperutriredensity mrves of a series of mixture3 of k n o w i composition*. The relatiom between any combinntion of the variable,q n ’ e w then derived by the contrrictioit of the appropriatp ('revs plot of these ciirves. The app:ifiitus and esperimenrd ~ ~ i , o w d u rfoi, e s the drtwiiiitation of the pressure, volume, temperature, and composition of a mixture were the same as those employed in the earlier studiw and recrritl>-dwcribed in detail ( S i . The procedure, verx I)r.iefl?-. was as follow: .A small air-free s:iniple of the h~-drocarl)onmi\-ture Tvss confirled over merciiry i i i :i thick-walled g1rt.s t r i l w which w i s siirrorintled l)y a coiiit:triT temperature bath. TIM, tube was fastened in 5 n i ~ ~ i ~ c i i i ~ ~ ~ compressor -fiIlcd with m e a t i s provided for controlling the prcwirp on the Paniple. .\ftei, t l w presetire h:id l~eenproperly adjusted and equilibrjum :ittiiinc~l by means of a magnetic stirrer, the volume of the samplca W : I S determined h y measuring the length of the column of ,-:ini1ile, this length having \weti t,elated t o thr volume tiy a prior ( ~ t t I i l ~ i , : i tion of the tiihe. The temperature of the sample was measured t o within 0.05” I’. by means of a copp‘r-coiistantari thermocouple and a rrnrir ivr potentiomc.irr. For the pressure, :I dead weight gape, 3imil:Lr t o that Iii,eriou.ly dewribetl ( 8 ) , \KI$ ii%xl. ITS seri.itivity \v:i*
,
C
-_LA-
13
20 DEIvSITY L B
3c FER
40
0
C- F ‘
Figure 2. Temperature-density horder curves of mixtiires of ethane and r\rIohexane
Figure 1. Pressure-temperature border curves of tuixtirres of ethane and cyclohexane
422
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1956
423
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-
2006
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P &
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'
I
2
,
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I
,
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4
6
PWPT LB. /WIN
COMFOSITIOU
MOLE
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ETIANC
Figure t . Iitely 2.0-11111~bow. It IWP carefr:lly calibrated n-ith merciiry. 13)- thc IISC of a catlictometer, reading t o 0.05 xiiiii. :rnd v i t h a s:iiiiple occiip>.iirg a length never less t h a n 15 mm.
1400
1
Figure 5 .
I
COMPOSITION M O L E % ETHANE Pressure-cornpositioll relations, ethane-cyclohexane system
PREl'.\H4T10\
Of' \ I t ' I ' k X l . t L S
Bot11 t l i ( , c't liane and cyrlohexn~ic\vcre fiirriishd hy the l'liillipci l'etrolcllnl co. Thc c t h n c n-as stated to br 99.9 niolr% ethsnr. It wiyfiirrlier Iiurificti 1)). repeat r:d distillatioil :it low temperature and iinder
COMPOSITION
Figure 6 .
MOLE % E T H A N E
l'emperatrlre-cotnposition relations, ethanec>-clohexanesystem
INDUSTRIAL AND ENGINEERING CHEMISTRY
424
voi. 48, N ~ 3.
Table 1. Summary of Temperature, Pressitre, a n d Density Data a t l'hase Ho~rndariesof Etharle-Cjclohexane S\stem Pleusliir.
LII. 'Sq.I l l .
Liquid _____~___ Temp., 0 F.
Density. lb./cu. f t .
--
Vapor
'r3elliFp.,
Preaarlri.,
Density,
lb.
'CII.
fr.
1.b 4 q . 1 1 1 .
13.78 Mole 7% 1:tiiane
Temp
F.
Liquid Density. lb , l e u . f t
~~
Te1np. 0
I:.
T'srior _
_ ~ -
Density, l b ;cu i t .
50.20 l I o l e YEEt!iane
100
I50
200 250 300 350 400 460 500 550 600 650
700
750 ii2
100 150
200 250 300 350 400 430 500
550 600 650 700 750
800 850 900 (4
io
ino
150
200 do0 330 300 450
500 550
BO0 650 700 730 800 830 900 Y 50
1000 1050 1100 1140 1160
mal boiling point of cyclohexane reported in the literat i r e ( I ) is 80.138" C. Prior to their we, the ethane arid cyclohexane were tested for contamination by measuring, in the experimental apparatus, the differ-
..-" 0
13.78 28.93 42 84 50.20 57 85 70 99 72 48 86 17 100
535.64 507 66 468.27 421.36 393.10 370.51 298.58 281 89 193 It! 89 .54
591.5 7Bi.0 $431 0 1184.0 1218.(j 1271 8 17811.1
I32i.i
iia n 707.2
15:14
1s 8.'1 14.59 19 18 ...
IKiS 17.02
..
511..2
483 n 451 8 4 2 4 . .i
...
14 7 I2 0 11 1 10 0
7': (13
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INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1956
425
R E S U L T S .ASD I)I SCU S SIOh
For the determination of the P- L'-T-.r relations of the ethane-cyclohexane system, the vapor pressure ciirve of p m c c3yclohesarie antl the ~)rc.ssure-trni~,erat w e and tleiisity-temperatiire ('i~rvcs of six different, rnistiires of ethane and t~yclohcsarie \yere determined. Sinii1;tr cl:tta on two additional mixturc~s \vert: determined over :t limited tcirii)cr:itiire rangc, in order t o lot.:ite tlir compoFition possessing the highcpt c-ritical pressure. The?(? d a t a are shown by the ciirvrs in Figures 1 :tiid 2 . The vapor pressurc ciirve of rthane was drawn using (lata reportotl by Kay and Brice (6). T h e broken-line portion in the low pressure region of the vapor pressure curves antl the pressure-teniperature border curves are extrapolations of the data, obtained hy extending the straight linr that 7 . Pressure-equilibrium ratio curves a t constant teniuerature ethane-cyclohexane system rebults when the logarithm of thc presSuie is plotted against the rrcipiocal of t h e a b s o l u t e temperature. T h e densitv data of Rotinjanz and Sagornow for cyclohexane (9), and those reported in International Critical Tables ( 2 ) for ethane, were used for the construction of the densit) -tPrnperatnie curves of the piire components. Table I gives a summary of
Figure
1000
a oo Table 111. Temperature-Composition Relations of Ethane-Cyclohexane System a t Constant Pressure
600
z
Cnmpn., 1\lole % Ethane
Telnperature,
F.
Vapor 100 Lb./Sn. Inch Abs.
a400 \
m
0
-I
5 10 20 80
W
E
-10
200
50
no
Id
70
(L
a
80 90 95 100
IO0
-___
ETHANE IN IN ~ETIiANE IN ..- .- -. ..ETHANE IN
_ _ -ETHANE
1
I
BUTANE HEPTANE CYC-OHEXANE BENZENE
2 4 6 8 IO E Q U L I B R IUM CONSTANT K =Y/X
Ethane
322 5 214.0 335.0 49 4 17.9 - 1 8 -17.8 -28.4 -35 J -40.7 -43.3 -43.9 -44 0
0 2 10 20 30 40 50 A0 70 80 90 95 100
400 Lb., S q . Inch Abs. 471 3 416.1 366.8 10 266.8 20 1% 3 30 140.0 40 111.2 50 92 0 60 76 5 70 63.9 80 53.1 90 47.9 95 42 8 100
0
I
20
~
Fignre 8. Comparison of pressure-equilibriuni ratio curves at constant temperature for ethane
800 Lb.iSq. Inch Abs.
ence between the bubble and den- point pressures a t some elevated temperature. The pressure change was 0.17 pound per square inch a t 32.0" F. for the ethane and 0.22 ponnd per square inch at 489.06" F. for the cyclohexane Mixtures of ethane and cyclohexane were prepared by loading the experimental tube a i t h a sample of pure cyclohexane, calculating its weight from the meawred volume and density, and then adding a measured volume of ethane gas at a knoNn temperature and pressure t o make a mixture of known composition. The procedures employed in loading the experimental tube Yith the cyclohexane and ethane were those employed in earlier fitudies (6, 8 ) .
1200 Lb./Sq. Inch Abs. 315 3 399.9 337.9 399.8 280.3 384.1 239.5 353.7 214.0 304.0 84 211.1 274.5
49 50 60 70 80
%ztnfi
Liquid
T e m p e r a t u r e . 1,'. Liquid Yapor-
200 I.b./So. I n r h Ah9 . 395.7 395.7 307.4 388.4 236.8 381.3 139.8 365.9 67.8 349.9 57 9 333.4 39.1 316.3 25.1 297.5 14 8 264.2 1.2 242.5 - 0.8 184.4 - 4.1 131.2 - 7.4 - 7.4 ~~
600 Lb.,'Sa. Inrii Abs. 1.0 530.0 5 517.0 10 508.9 20 488. D 30 459. 8 40 434,s 50 408.7 60 379.0 70 344.5 80 302.0 90 246.5 95 201.0 100 76.4 1000 I.b./Sq. Inch Abs. 457.1 454.0 429.7 397.5 362. I 318.6 256 2 236 7
1300 Lb./Sq. Inch 319.1 65 293.2 70 272.0 75 254.6 80 250.0 60
Abs. 354.9 346.9 331.0 311.1 276.8
i 352 3.6, _
1
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1 2
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Vol. 48, No. 3
INDUSTRIAL AND ENGINEERING CHEMISTRY
426
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....
30
100 200 400
4 78 2.22
1.07
0.0370 0.0180 0.0290
100 200
7.50 3.60 1.77 1.20
0 0718 0.0410 0.0320 0.0187
100
ti00
.
150
100 YJO 400 (in0 800
Figiirc
9.
?00
MOLE % ETHANE
Specific \-oliinie-c.ornposition r e l a t i o n s ethane-c?-cl~liexane syteni
the presstires, temperatures, and densities of t lie $:it iir:it c,tl liquid and vapor states for each of thci sis iiiistiirrs stadirtl. T h e tabulated values were read from Inrge scale plot: of Figiires 1 and 2. The vapor pressure of r>-clohesaiie was Incwurrtl :it I7 t emperatiires from the standard boiling point t o the (2ritir:il lioitit, T h e resulta hsvr been erpreswti liy means of the rqiiatioit: -
283 9,875
T7p(a~H.i
100 200
400 600 800
in
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COPw'POSITION
I'I.FSSIIIP,
Kc: Kch 2 60 0 0 l f i S
I
'30 3c3
7
I
__
430 500 630
Table I V . Eqiiili1,riuiu Ratios for Ethane and Cyclohexane
100 200
,400 600
800 1000 1200 1300
10.1 0 126 5 . 0 8 0.0795 2 . 6 0 0.0542 1 74 n 0415 1 . 3 1 0.115 13 6 0 228 6.75 0.138 3 . 3 6 0.093 2.28 0 083 1 . 7 0 0.137 1 . 3 7 0 183
17.7 8 65 3.98 2.75 2.06 1.62 1.29 1.03
0.430 0.241 0.167 0 157 0.190 0.208 0.400 0 860
330
Lb. i 5 , In. , A h . 100 200
400
4.S2
600 800 1000 1200 1300
3.07 2.31 1.82 1 43 1.20
200 400
12.3 5.00 3.28 2 43 1.80 1. 4 5 1.09
600 800 1000 1200 1300
mo
4x1
300
Kc2 22.8 10.6
400 600 800 io00 1200
5.77 3.32 2 40 1 76 1.00
Ki 0,7!9lJ 0.43; 0 290 0 265 0 275 0.301 0 442 0.b3U
0.720 0.4tiii
0.398 0.393 0.440 0 5lj0 0 880
0.665 0.3130 0 550 0 615 1 00
600 800 1000
7.70 3 10 2.10 1 37
0 863 0 7-13 0.728
600 800
2.53 1.00
1 (IO 0 91
1-00
0 822
c.al tempei,at ire ( 7', = 89.j4O F.,I>nrwrtheless the diflrreiicc in the slopes of t h e curves of loiwi, temperatures is such as t o iridicute that the nature of the cyc,lohesarie molecaule Iius some effect. thoiirh not nearly :is much iis the benzene molecule. It seems t,cmoiial)lr to suppose, therrforc, thiit if the light paraffiri hydrocuriioti?: are dissolved in n n p h t henic base liquids, thcir h' i,atios at i i giveii temperature m i l pressure xi11 be someq-hat higher than they Rould be if tiismlvrd i r i :L paraffinic hase liqiiid. The relations among the pressure, volume, temperature, :rnd roniposition for the system are ciupresred in a somewhat diffwerit manner in Figure 9, xhere the variation of the specific volume of the liyiiid and vapor phases with composition is shon-ii nitli temperatiire as :L parameter. By t h e addition of the cwnntant pressure tir line. t h e diagram givri a rornpletr picturr of thP relation~hipe hetween the vnriablw :ir the Ijqriid-vapor ~ i l i i i e I~nuntlai~ies of t h r system. ~
supplemented xitli the (1evi:itioii ciirve shown i n 1;igiir.c :i.T h e confitants i n the equation were evaluated using the esperinieiit:il values of the teiiiperstiii,e arid prrssiire at the critic*:rl I i o i i i t : ~ t r t l the riornial boiling point. Table I1 gives a mnimai~yof the characteristic p i i n t s of ttic various niistures in the critical rrgion. T h e criticul poiltts \vihrr determined visnally, whereas t h r teniperature, pressiit'r, :tiid t i c b i i sit) at the iiiiisinirini presslire poiiits arid niasiniiini twip(Ji,:ttii1.t' points on the pressure teniperatiiw tiorder curve n w e ~.c\:iti froni the large scale plotr. T h e wlatiorip of these points witli this (.miposition are sho~vtigraphically tiy the r i m w in F i g l m 4, As n-ill be rioted, the maximum pressure on the critical locus amoiuitr t ( 1 1338 poundr per square ir1i.h ahsoliite a t 298.3" F. for :I n i i \ - t r i i , c a ACKROW LEDGMEYT of 71 mole 7. ethane. The pre.sure-conipositioii di:igr:iniz at rotist:Ltit t ~ m p c ~ r : i t i i i ~ ~ Grateful acknowledgment is made to the Phillips Pct r o l i - i i t i i are shown in Figure 5 . The upper vilrvr or b u l h l r point i.twvc> Co. for fiirnishing t h e aamples of ethane an11cycIo1ic~~:~ric. in each of the diagrams gives t h r relation hetween tlir total p i w sure arid the solubility of ethane in ryclohes:~tic~c3sp1~c3swd it1 LITERATtiRE (:ITE:D niolr fi,:tctioti of etliaiir. T h e w C I I ~ V ~ F are ne:ii,iy lirirar over a wide range of coricrntratioii, indicating good sgwrmcwt wit li (1) .\NI. Petroleiiiii Imt,, "Selerted 1-alues of P r o p e r t i e s of Hydrocarbons," .lPI lteurarch Project 44, S a t i o r i a l Bureau of IIenry's IBW. Standards, IVashingturi. D. r..Table 23a, P a r t I. Sept. 30, III Table 111 the relations between ten1per:iturr :md compo-i1951. tioii of the coesisting liquid and vapor phases at c.orist:irit p r w f2) Ititet~~iationalCritical Tables. vol. I, p. 55. lIcGr:~\v-lIill, sure are given for a serirs of pressures ranging from 100 t o 1300 Y-ev York, 1928. poiiiids per square inch. These relations arc shomi grspiiioally ( 3 ) Kay. JT-. B.. ISu. E:S.,f'herti. Eiig. Prngr. Sun!~iosiiimS e r . . S o . 3 . 48, 108 (1952). 0 x 1 the, basis of thr l:i\v> of pcrfect solutions, tlic, Zi ratio:: f o ~ . ( 8 ) l i a ~ - .TY, B., Hamhoxek. ( ; , 11..ISD. ESG. CHEM. 45, 2221 ethane should be the u n i t ' regardless of the liquid with which (1953. ethane is misrd. That this is not the case for binary f % liotitr,jntiz, I,,, S a a i r t i u i v , S . . %. p h y s . C ' h e r n A169, 20 s y s t erns, in which ethane is a cbonirnon conipolierit, (1934). (I0) S\rictoslarvski, W., "Ebullionieti~iclleasurements," p. 2 2 , Iteirithe curves of log P L ' S . log K , in Figure 8, for ethane iii n-I)l1tarie, hold, S e w York. 1945. n-heptane, cycloiiexan~,and Iiriizene. The curve for i,yi:loliexaiie lies betn-eeri thr c ~ i r v efor ~ the paraffin compound$ and lienR E C L I V Kfor I I rer.ie\v July 1. 1Y.i.7. ACCEPTEUOctober 17, 1955. zerie. While some of the spread betxccti the ~ I I I ' V C Ris tlrw ti) l l i r i s i o n of Petroleum Chemistry, 1 2 7 t h l I e e t i n g , ACS, Cincinnati. Ohio, llarcli--.\ijril 1953. the fact that, at tile trnipersturr sliowri, ethntir is :rliovi~its ci,iti-
