INDUSTRIAL AND ENGINEERING CHEMISTRY
754
composition of the fuel-air mixtures. Furthermore, if the Aamestability limits of propane and of ethylene are known, the behavior of any mixture of these two fuels can be predicted. These findings are in accord Kith other studies in this laboratory of the flame speeds of propane-ethylene mixtures ( 2 ) , and the stability of propane-ethylene flames on vortex-type burners (4). Isobutane-ethylene mixtures are compatible a t lean blowoff and at the two flash-back limits. The data for these stability criteria show that the behavior of the mixtures is in agreement with an empirical combustion equation which requires that I;V,/V$ = 1. Accordingly, it is possible to predict the behavior of these mixtures a t lean blowoff or at flash back, provided the behavior of the component fuels is known. Furthermore, if the behavior of one component and of typical binary isobutane-ethylene mixtures is k n o m , the behavior of the other fuel component may be obtained by extrapolation or calculation. The results of rich-limit studies with the divergent Smithells tube and with an inert gas shield are in good agreement and point to the conclusion that the deviations of the behavior of isobutane-ethylene mixtures a t rich blowoff from the requirements that zV,/V: = 1, though small, are real.
A study of the laminar flames of other binary mixtures and with ternary mixtures is continuing. It is believed that this work will lead to a better understanding of the behavior of multicomponent fuel mixtures.
Vol. 46,No. 4
ACKNOWLEDGMENT
This work was done under the sponsorship of the Flight Research Laboratory, Wright Air Development Center. WrightPatterson ,4ir Force Base, Ohio. The author wishes to express his thanks to R. E, Poling and W. B. Thompson for their able and faithful assistance in carrying out the experimental vork, and to J. F. Foster, division chief at Battelle, for his helpful interest and consideration. LITERATURE CITED
(1) Coward, H. F., and Greenwald, H. P., U. S. Bur. Mines, Tech. Paper 427 (1928). (2) Kurz, P. F., Battelle Technical Rept. 15036-2, to TTright Air Development Center, Wright-Patterson Air Force Base, Contract AF 33(038)-12656 (Sept. 28, 1951). (3) Ibid., 15036-3(April 30,1952). (4) Ibid., 15036-9 (Aug. 25, 1952). (5) Kurz, P. F., ISD.ENC.CHEXI.,45,2361 (1953). (6) LeChatelier, H., Ann. mines, 19 ( 8 ) ,388 (1891). (7) Payman, W., J . Chem. Soc., 115,1436 (1919). (8) Smithells, A,, and Ingle, H., Trans. Chem. Soc. (London), 61, 204 (1892). RECEIVED for review August 19, 1963. ACCEPTED December 21, 1953. Presented before the Division of Gas and Fuel Chemistry at the 124th Meeting of the AYERICAK CHEMICAL SOCIBTY.Chicago, Ill.
Vapor-Liquid Equili m- and p-Xylenes in Different Solvents JU CHIN CHU AND 0.P. KIlARBANDA Polytechnic Institute of Brooklyn, Brooklyn, N. Y .
R. F, BROQBS'
AND S. L. WANG2 Washington University, St. Louis, Mo.
T
HE production of xylenes, which were mainly obtained from coal tar prior t o World War 11,has been greatly increased by
catalytic hydroforming. The separation of a mixture of the p and m-xylenes has presented a difficult problem because of the closeness of the boiling points. A number of methods have been reported ( 1 , 2, 4, 5, 9,13, 14, 16-19, 21-25) for the separation of these two xylene isomers. The original objective of the work reported here 'was t o investigate the possibility of employing extractive distillation for the separation of m- and p-xylenes by determining vapor-liquid equilibrium data of the isomers with different solvents. Two different experimental approaches have been used in this investigation. One is to determine the relative volatility of two xylene isomere directly in the presence of an optimum amount of a solvent. The other is t o determine vapor-liquid equilibrium data of each isomer with a solvent in the complete range of concentration, as suggested by Othmer et al. (31). Vapor-liquid equilibrium data of some systems are represented analytically by the thermodynamic correlations proposed ( 7 , 16, SS, 40). From the results of this study it appears that the extractive distillation is not feasible for the xylene separation. CHOICE OF SOLVENTS
The choice of solvent is affected by both practical consideratione, such as its cost, availability, stability, corrosion characteristics, and toxicity, and by the technical feasibility, which includes 1
Present address, Xfonsanto Chemical C o t Et. Louis, Mo.
a Present address, Kansas State College, Manhattan, Kan.
volatility, solubility, azeotropic formation, and selectivity. The eolvent must be appreciably less volatile than the xylene, in order to save the reboiler duty and to facilitate the subsequent recovery of the solvent. Normally, a difference in boiling points of 20" C. is sufficient. The solvent to be uaed, therefore, should boil above 160' C . The solvent should be a t least completely miscible with the xylene isomere, without the formation of an azeotrope. Empirical correlation ( d 6 ) and experimental investigations (6), as well as literature data, are used to guide the selection in this respect. The selectivity of the solvent is believed to be due to some type of molecular association with one of the isomers to form nonideal solutions in a seIective degree (I, fd). One type of association is so-called hydrogen bonding ( I d ) , the association of two molecules with a hydrogen atom as bridge. If the xylene isomers could be considered t o contain the active hydrogen atom as electron acceptor, compounds classified by Ewe11 et al. (12) as class I1 (alcohols, acids, phenols, primary and secondary amines, oxides, etc.) and Class I11 (ethers, ketones, aldehydes, esters, tertiary amines, nitro compounds, etc.) would be more likely to be promising selective solvents. The second type of association is attributable to the intermolecular forces of attraction due t o electrical moment of the molecules, whether permanent or temporary (94). The dipole moment of p-xylene is 0 (28); that of m-xylene is 0.37 Debye (28). The published correlations of the dipole moment with selectivity, however, are not conclusive enough t o predict or rule out the choice of the solvent. Although a method of preliminary solvent selection by boiling point observation has been reported (14),
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1954 0.45
I
I
I
I
755
Their purity and pertinent physical properties have been described (6,SQ).
I
MATERIALS 0.3s
-
0.30
-
0.26
-
0.20
-
0.15
-
0.10
-
0.06
-
STANDARDS AND REAGBA-TS. National Bureau of Standards samples of No. 213 o-xylene (impurity 0.06 f 0.04%), No. 215 p-xylene (impurity 0.06 f- 0.03%), and No. 212 ethylbenzene (impurity 0.04 =k 0.02%) were used in calibrating the ultraviolet analytical method. All the purities are given in weight per cent. An ultraviolet absorption spectrum of this solvent has been given (6). XYLENES.The m- and p-xylenes used during most of this work were taken from the 5-gallon samples donated by the Oronite Chemical Co., which kindly furnished the following analyses of these xylenes.
W
3 e v) Q
0.00 2550
I
I
I
I
2600
2600
2700
2150
yp:p
2800
2850
WAVE LENOTH, ANOSTROMS
Figure 1. Ultraviolet Absorption Spectra of Xylenes Beckman Instrument, 1.00-cm. cell, slit width
1.000 mm.
the search for a selective solvent is still mainly a task of trial and error in nature, relying somewhat on the experimental investigations. Solvents used in this work are all available commercially. 2-Heptanol 2-E thylhexanol Propylene glycol Hexylene glycol Octylene glycol Diethylene glycol Butyl Cellosolve Monoethanolamine 2-Ethylhexylamine Nonylamine Aniline o-Chloroaniline m-Chloroaniline pchloroaniline o-Phenetidine p-Phenetidine Phenol o-Chlorophenol pChloropheno1 2,4-Dichlorophenol
Purity, isomer, % w. Ilistillation ' C. Roiling ranhe 0 C. a t 60/60° F. 01 wash color Color Saybolt ~ o p p k corrosion r Water by separation Sulfur compounds such as IhS or 902 Cloud point a t 30' C. Sediment Acidity
o-Ni trophenol p-Nitrophenol Catechol Resorcinol o-Phenylphenol p-Chloro-mcresol Methylsalicylate Nonanoic acid Sulfolane Dichloroethyl ether 2-Ethylhexaldehyde Diisobutyl ketone Tetrahydrofurfuryl alcohol (3.3) p-Toluidine m-Nitrochlorobenzene pNitrochlorobenzene p-Nitrotoluene Dimethyl sulfolane (96) Nonyl alcohol
m-Xylene, 95%, Sample 50276-R 95.5% 138.1-138.9
...
.....
0.5 0.865 1 to 2 Plns 30 Nil Nil None None Trace Nil
0.8684 2 to 3 Plus 30 Nil Nil h'one None Trace Nil
Ultraviolet absorption spectra of these materials, as determined by the Beckman Model DU and Cary Recording Model 11, Series 11, ultraviolet spectrophotometers, are given in Figures 1 to 3. The spectra of the National Bureau of Standards samples, as determined with these instruments for reference, have been measured (6). Based on the data obtained with the Cary recording ultraviolet spectrophotometers, the compositions of these xylenes were calculated to be: Immer m-Xylene % p-xylens ' % EthylbeAene, %
m-Xylene, Sample 50276-R 97.0
p-Xylene Sample 337il-R 1.3 98.6
..
3:4
During the initial experiments a second series of xylene samples was used for the equilibrium still charge. This second series consisted of m-xylene from the Eastman Kodak Co. (boiling point 138"-139 O C.) and p-xylene from the Fisher Scientific Co. (c.P.grade), which were used without further purification. APPARATUS
I n the determination of the relative volatility of xylene isomers in the presence of solvents, two groups of apparatus were used. I
COHC. 1,018 QM.IL1TER
L
CONC. I 7 2 2 OM /LITER INSTRUMENT CELL 0.6 CM.
omr
CARI INSTRUMENT CELL 0 . 8 CM. WAVE LENQTH,
p-Xylene, 95%, Sample 33721-R 97.9%
WAVE LENQTH,
ANQSTROMS
ANQSTROMS
4
2600
Figure 2.
Ultraviolet Absorption Spectra of p-Xylene
Figure 3.
I
Ultraviolet Absorption Spectra of m-Xylene
I N D U S T R I A L A N D E N G I N E E R IN G C HE hi I S T R Y
756
The first group consisted of a vapor-liquid equilibrium still and two stripping columns fabricated of borosilicate glass ( 6 ) , which were used for evaluating the solvents; the second group TVBKu-ed t o analyze the various still Famples.
Figure 4.
Equilibrium Still
The equilibrium still, illustrated in Figure 4, is a modification of the Othmer still (WQ. 30) by Munch (3). It is made of borosilicate glass and composed of three parts: the still body, the ?till head and condenser, and the condensate receiver. Not shown in the drawing are the external heating coil and insulation. Bbout 10 feet of Nichrome wire (0.782 ohm per foot) is wound around the outer surface of the still and connected across a Variac. The still is insulated with L'insulationcement" about 1 inch in thiclrness. The still has a capacity of about 120 ml. of liquid charge. The two stripping columns were used t o separate the bulk of the solvent from the xylenes in the vapor and liquid samples obtained from the equilibrium still. This stripping was carried out in order to simplify the subsequent chemical washing of the samples preparatory to analyzing the samples on a solvent-fi ee basis. A Beckman quartz spectrophotometer (Model DU, Xatioiihl Technical Laboratories, Pasadena, Calif.) and a Gary recording spectrophotometer (Model 11, Serial 11, Applied Physics Corp , Pasadena, Calif.) were used for analyzing the equilibrium still vapor and liquid samples. The former instrument is a continuous-recording, variable-speed ultraviolet spectrophotometer located at the Research Department, SIonsanto Chemical Co., St. Louis, Mo. I n the second part of the experimental investigations the Othmer still of the latest revision (29) m s used to obtain the vapor-liquid equilibrium samples of the systems formed by each isomer of xylene with the solvent. The samples are analyzed by means of an Abbe refractometer, the ecale of which can be estimated to =!=0.0002. During the measurements the lens of the refractometer was maintained constant a t 30 i 0.01' C. 5y circulating water from a thermoregulator.
Vol. 46, No. 4
EXPERIMENTAL PROCEDURES
EQUILIBRIUM EVALUATIONS. Two experiment,ai procedures Kere available for the evaluation of solvents for the extractive distillation of m- and p-xylenes. Both mere based upon the uie of the equilibrium still to obtain the necessary data from which the relative volatility of the xylenes in the preRence of the tliini component could be calculated. Method I. The first method of determining the relative volatility of a third component is more direct than the second. It is based upon determining the relative volatilit,y of the binzry system on a solvent-free basis, and is dependent upon evaluating all of the solvents under the same conditions of concentration. It is the method used by the previous investigators (3, 11, 13, 38) in the studies of extractive distillation. This method canlitit predict the formation of an azeotrope. The alteration of the relative volatility of a binary system iq :I function of t'he solvent concentration in an extractive dktillation (10, 11, $20)-The maximum improvement in relative volatility would be obtained at' a solvent concentration approaching 100%. Eighty mole per cent, economical limit of solvent concent'ratioa, v a s chosen for the present n-ork. Approximat'ely 115 ml. of the solution containing 80 mole 70 of solvent and 10 mole % of each of the xylenes was charged t o the still. The charge \vas heated until the attainment of equilibrium, which was judged by the constancy of the vapor and liquid temperatures. The relative volatility is determined and reported on a solvcntfree basis t o simplify the analytical procedure and to have all the data on a comparable basis. The entire liquid sample IVRS charged t o a stripping column and fractionated batchivise a t a reflux ratio of about 20 or 25 t o 1, t o a head temperature of approximately 146' C. The vapor samples in a second stripping column mere distilled t o a head temperature of approximately 145" C. The actua! distillation diflered for each sample: depwding upon the boiling point, amount, and stabilit,y of the solvent', etc. Because of the neressity of a further purification, not all of the vapor samples were put through this stripping operation. The partially purified xylenes were further treated t o remove the last trace of the solvent. This treatment consisted of w a ~ h ing the samples three times with 5% sodium hydroxide or 5% hydrochloric acid, followed by an equal number of water washes. The xylenes were then dried over 8-mesh Drierite for a t least 2 1 hours before being analyzed by the spectrophotometer. Method II. The second method consists of the measurement of vapor-liquid equilibrium data for the binary mixturcs of each individual xylene isomer v i t h the solvent as a second component. A recent'ly improved Othmer still (28) was used for this purpose. Analyses were in every caee made by the measurement of refractive index by an Abbe refractometer indead of the spectropliotometer. Calibration curves n-hich were used to translate the readings of refractive index into the values of the compositions were prepared from the measurements of the refractive indexes of nine or more synthetic mixtuiw of each binary or k n o m compositions. If the individual xylenes how difi'erent x-y di:ig?ams with the added solvent, that compound can be uscd as a sokent f o r yeparsting p- and m-xylenes by extractive distillation. The application of radiant energy to separating a vapor rnivrure of close boiling components in a partial condenser was disclovd by Schlessmnn (95). The compounds having identical boiling point may differ n-idely in their rate of absorbing radiant energy of certain frequency. As the vapor mixture p a m s through t'he condenser on which the radiant energy is projecting, the molecules of one component may absorb the radiant energy to increase its free path and remain in the vapor phase, whereas the other component shows no response t o that frequency and condenses into liquid. It appears that Schlessman's claim may be valid only if mean
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1954
TABLE I. OPERATING DATAOF EQUILIBRIUM STILL Xylene=
Solvent Control, no solvent
2-Heptanol 2-Ethylhexanol Propylene glycol Hexylene glycol Octylene glycol Butyl Cellosolve Diacetone alcohol Phenol o-Chlorophenol p-Chlorophenol 2,4-Dichlorophenol o-?Y-itrophenol o-Phenvlwhenol
-.m-SourcepE
F
E
F
0 0 0
0 0 0 0
0 0
0
0
0
F F
E
F
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 E
0 E 0 0 0 0
0
E E
E
p-Chlorortniline o-Phenetidine n-Phenetidine
0 0 0
0 0 0 0 0 0 0 0 0 0
F
0 0 0 0 0
F 0
F
0 0 0
Charge, Mole % Xylene Solvent mp.. 50 50 .. 50 50 25 75 25 75 si:s 9.1 9.1 10 10 80 80 10 10 10 10 80 10 10 80 9,25 9.25 81.5 9.15 9.15 81.7 10 10 80 9.0 9.0 82.0 10 10 80 10 10 80 10 10 80 10 10 80 10 10 80 10 10 80 10 10 80 10 10 80 10 10 80 10 10 80 9.0 9.1 81.9 10 10 80 10 10 80 10 80 10 80 10 10 10 80 10 9.2 81.6 9.2 10 10 80 9.2 9.2 81.6 10 10 80 10 10 80 10 80 10
..
Equilibrium Temp., O C. Vapor Liquid 138 138 138 138 137 140 140 140 153 153 167 167 134 143 176 176 207 221 160 160 142 142 167 167 165 165 163 163 166 166 193 193 193 192 190 190 190 189 240 240 200 200 161 157 169 169 167 167 190 179 199 199 199 199 205 205 213 213 150 152 155 155 162 161 220 219 213 213
..
E = Eastman Kodak m-xylene. F = Fisher Scientific p-xylene. 0 = Oronite m- and p-xylene.
free paths between gaseous molecules are sufficiently large. Otherwise the collision between molecules will equalize the energy distribution between molecules of two compounds, and the separation of isomers becomes impossible. The infrared technique was used to test the experimental basis of the Schlessman claim, especially under atmospheric pressure, a t which the mean free path between molecules is relatively short. The infrared lamps were used for the systems of individual xylene with tetrahydrofurfuryl alcohol, diisobutyl ketone, and nonyl alcohol. The boiling liquid was subjected to the radiation from infrared heating bulbs of various power output and for different durations. SPECTROPHOTOMETRIC ANALYSIS. A Beckman Model DU ultraviolet spectrophotometer was available and the ultraviolet method of analysis ( I S ) was claimed to be effective for this type of compound, with slight modification (6). The fused silica cell used in this instrument is 1.00 em. thick. Because of the failure of the Beckman instrument during the latter part of the work, it was necessary to use the Cary recording instrument a t the Monsanto Chemical Co. The same procedure was used with this instrument, the only differences being in the cell thickness used and the characteristic wave lengths chosen. A cell thickness of 2 em. was necessary because of the greater resolving power in the instrument. The characteristic bands were: para 2743 A. and meta 2724 A. p-Xylene does not follow Beer’s law, and the above analytical method of determining the composition of a mixture cannot be used. A method of successive approximations, as illustrated in Brooks’ report ( 6 ) ,must be used. 1. Determine the absorbance a t all the characteristic wave lengths. 2. Assuming the absorption to be due only to the component a t the characteristic wave length being considered, read the corresponding component concentration from the calibration curve. 3. Determine the absorbance of this concentration a t the other wave lengths. Enter this as a correction under the appropriate wave length. 4. Repeat steps 2 and 3 for each component.
Press Relative Mm. l& Volatility 749 I9 1.05 1.02 749.5 1.02 746,s 1.03 754.1 748.1 0: 99 740.1 1.03 745.4 1.02 751,l 1.04 745.6 1.04 745.2 747.1 l;h5 738.5 0.92 746.0 1.07 755.6 1.07 741.0 1.01 741.8 0.97 755.0 1.01 757.4 0.98 746.4 1.03 746.4 1.00 745.2 1.01 745.7 755.0 0:93 745 7 1.06 742.6 1.05 748.1 1.00 754.0 1.08 748.3 740.3 0.98 749 5 745.0 747.4 1: i 3 740.3 1 03 754.0 0.97
752 5. Subtract the sum of the corrections at each wave length from its original absorbance. The difference is the new or corrected absorbance, which is used for repeating steps 2, 3,4, and 5. The correction is always subtracted from the original absorbance. 6. Repeat the o p e r a t i o n until the absorbance measured equals the sum of the absorbances for all components a t the wave length being considered. Determine the true composition from the calibration curve a t these corrected absorbances.
The fact that p-xylene did not follow Beer’s law (6) is not consistent with the data given in the literature (8,I3). However, the fact that such a deviation might exist under the experimental conditions was substantiated by the data ob.... tained with the more powerfuI resolving Cary recording spectrophotometer. A very defi.. .... nite curvature of the ?I-xvlene curve was obtained when the concentration was high enough to give the most accurate absorbance readings. The small amount of ethylbenzene in the Oronite m-xylene did not interfere with the treatment of the system as a binary mixture. EXPERIiMENTAL DATA
Equilibrium still data for the xylene isomers in the presence of various solvent8 by the first method are given in Table I. The theoretical relative volatility of the xylenes was calculated from the vapor pressure data given in the literature (20, 27, 87) to be 1.02, which is constant over the whole range of concentration. In the unsuccessful trial of using ethylhexaldehyde as a solvent, the equilibrium temperature of 155 o C. was noted. During the stripping operation the possibility of an azeotrope formation was noted. Using Meissner’s method ( 2 6 ) a minimum boiling point azeotrope containing 96 mole % xylene and boiling a t 135 O C. was estimated as forming in this system. A check of this point was made using Oronite xylene. The calculated composition was charged to the still. The similarity of the analysis of the vapor and liquid samples, deviating only by experimental error, shows the formation of the azeotrope of the following composition: Xylene 2-Ethylhexaldehyde
Mole % Vapor 96.1 3.9
Mole % Liquid 95.8 4.2
The boiling point determined experimentally was 13Y0 C. (under 745 mm. of mercury). The vapor and liquid samples obtained were analyzed according to the regular procedure, because it was found that 2-ethyl hexaldehyde in 2,2,4-trimethylpentane solution did not absorb in the portion of the ultraviofet region under consideration. The 2-ethylhexaldehyde content was obtained by difference. The data obtained during the run, in which propylene glycollJ2-propanediol was evaluated as a solvent, show a possible minimum boiling azeotrope formed between the glycol and xylenes. This would explain the low vapor temperature (134” C.) as compared to that obtained during the control runs. This might be expected from the similarity in the structures of ethylene
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46,No. 4
IO0
IO0
100
80
80
80
60
60
60
40
40
40
40
20
20
20
20
20
40
60
80
I00
0
IO0
100
EO
80
60
60
40
40
20
20
20
40
60
80
100
0
20
40
60
80
20
100
40
60
80
0
100
20
40
60
80
100
I
20
40
60
80
100
0
IO0
X, MOLE PERCENT XYLENE IN LIQUID
0 X, MOLE PERCENT XYLENE IN LIQUID
80 60
A. B. C. D.
40
E.
F. G. H.
20
I.
K.
0
20 40 60 80 X, MOLE PERCENT XYLENE IN LIQUID
100 0
20
40
60
80
I n diisobutvl ketone I n methyl salicylate I n tetrahydrofurfural alcohol I n dimethyl sulfolane I n nonyl alcohol I n o-chlorophenol I n aniline In nonyl alcohol exposed t o infrared light for 1 hour In nonyl alcohol exposed t o infrared light for 2 hours I n diisobutyl ketone exposed t o infrared light for 1.5 hours
100
X, MOLE PERCENT
XYLENE IN LIQUID
Figure 5. Equilibrium Curves of p-Xylene and rn-Xylene 0 p-Xylene A m-Xylene and propylene glycols-Le., both have hydroxyl groups on adjacent carbons and the ethylene derivative is known t o form xylene azeotropes. Meissner's correlation does not cover the formation of these two azeotropes. The relative volatilities of p - and m-xylene determined by the authors compare very well with the theoretical value of 1.02. The data obtained in the first part of the work in the presence of the third components tested are given in Table I. In all cases the results are within 1 0 . 1 of the theoretical value of relative volatility of 1.02. Thus, these components may be considered to have exerted no effect on the separability of the xylene isomers. The vapor-liquid equilibrium data obtained in the second part of the investigation are graphically piesented in Figures 5 and 6. Figure 5 represents the data obtained in the presence of infrared radiation. I n locating the experimental points on the graph, the precision is no better than 0.5 mole %. Therefore, the data obtained are not of sufficient precision to compare shapes of, or relations between, the two curves in Figures 5 and 6. A single average curve should be the most probable representation, The detailed data (Table IV) are filed with the American Documentation Institute. The second experimental approach for determining solvent suitability from binary data depends upon the validity of activity coefficient correlations between binaries and the ternary. For the mixture of xylene isomers in a solvent, the ternary effect is not present. Although some solvents display an effect in increasing the relative volatility of xylene isomers, the effect is not
large enough t o make the extractive distillation economically feasible. Where a nearly ideal binary is added to a solvent, ternary- effects are negligible. This was found in the present case. THERMODYNARIIC CORRELATION
The thermodynamic treatment of experimental data of vaporliquid equilibrium has two main objectives: to test the consistency and reliability of the data and to summarize the bulky amount of data in a convenient form. Numerous methods of correlation have been repeated in the literature. The most convenient and flexible methods of correlation are due t o Wohl (40), Redlich and Kister (SS), and Gilmont e l al. ( 1 5 ) . By choosing the pure coniponents at the pressure of the solution as the standard states, the activity coefficient of a component in aoIution of miscible liquids is represented by
At moderate pressure the effect of pressure on fugacity is negligible. .fy may be taken as the fugacity of pure component 1 under its own vapor pressure. Meantime, the fugacity can be replaced by pressure under low pressure, such as 1 atmosphere as used in the present investigation. Equation 1 can be transformed into
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1954
759
~~~
TABLE11. COXPARISON
CALCULATED
BETWEEN
Temp.,
c.
System p-Xylene-aniline P = 745 mm.
p-Xylene-dimethylsulfolane P = 746 mm.
p-Xylene-methyl salicylate P = 755 mm.
p-Xylene-nonyl alcohol P = 753 mm.
p-Xylene- tetrahydrofurfural alcohol P = 746 mm.
m-Xylene-aniline P = 745 mm.
m-Xylene-nonyl alcohol P = 753 mm.
n-Xylene-methyl salicylate P = 755 mm.
m-Xylene-tetrahydrofurfural alcohol
m-Xylene-dimethylsulfolane P = 746 mm.
171 165 156 148 142 140 244 196 177 159 149 142 204 185 169 157 148 143 178 168 160 151 146 141 169.5 158.8 151.1 144 141.2 139 167 160 153 146 143 141 179 168 159 151.5 146 142 197 182 171 158 150 143 169 158 151 145 141.8 139.5 232 171 150 143
AND EXPERIMENTAL
Liquid Mole Fraction, XI
0.075 0.140 0.265 0.485 0.725 0.830 0.075 0.175 0.285 0.440 0.620 0.840 0.060 0.195 0.350 0.525 0.715 0.850 0.160 0.280 0.420 0.590 0.725 0.880 0.045 0.177 0.212 0.464 0.633 0.800 0.100 0.195 0.340 0.530 0.715 0.820 0.135 0.245 0.410 0.570 0.710 0.870 0.110 0.215 0.340 0.520 0.685 0.855 0.077 0.150 0.310 0.484 0.670 0.850 0.100 0.325 0.610 0.820
V.4POR COMPOSITION
Equilibrium Vapor Mole Fraction, Y RedlichKister Gilmont Van Laar Margules 0.370 0.371 0.349 0.342 0.370 0.574 0.525 0.496 0.483 0.500 0.739 0,672 0.650 0.649 0.675 0.852 0.792 0.775 0.783 0.800 0.870 0.887 0.877 0.886 0.890 0.900 0.905 0.922 0.926 0,920 0.705 0.860 0.545 0.870 0.468 0.862 0.900 0.940 0.750 0.890 0.937 0.958 0.960 0.965 0.940 0.928 0.950 0.977 0.985 0.970 0.935 0.990 0.985 0.982 0.980 0.965 0.990 0.990 0.995 0.985 0.555 0.425 0.425 0.379 0.415 0.872 0.832 0.714 0.699 0.720 0.885 0.810 0.851 0.853 0.850 0.892 0.880 0.914 0.929 0.930 0.880 0.920 0.958 0.973 0.965 0.930 0.953 0.980 0.989 0.985 0.452 0.457 0.665 ' 0.716 0.420 0.637 0.635 0.800 0.794 0.655 0.779 0.780 0.878 0.840 0.770 0.890 0.910 0.933 0.880 0.865 0.902 0.930 0,920 0.964 0.902 0.940 0.967 0.987 0.940 0.970 0.192 0.276 0.177 0.182 0. I98 0.541 0.645 0.552 0.530 0.587 0.628 0.603 0.610 0.590 0.658 0.791 0.778 0.764 0.755 0.770 0.836 0.819 0.791 0.792 0.800 0.885 0.868 0.845 0.857 0.864 0.424 0.423 0.388 0.432 0.455 0.565 0.565 0.560 0.582 0.580 0.679 0.686 0.700 0.707 0.715 0.786 0.797 0.805 0.817 0.830 0.864 0.876 0.880 0.886 0.890 0.915 0.921 0.918 0.926 0.930 0.465 0.478 0.285 0.681 0.370 0.610 0.592 0.511 0.775 0 600 0.748 0.735 0.755 0.815 0.750 0.807 0.805 0.880 0.822 0.855 0.850 0.850 0.953 0.822 0.915 0.960 0.948 0.985 0.843 0.960 0.522 0,529 0.504 0.529 0.520 0.711 0.719 0.735 0.719 0.710 0.811 0.821 0.840 0.821 0.840 0.901 0.910 0.915 0.909 0.925 0.946 0.952 0.945 0.950 0.950 0.970 0.980 0.979 0.981 0.980 0.303 0.270 0.300 0,455 0.343 0.446 0.440 0.582 0.440 0.596 0.727 0.852 0.604 0.670 0.670 0.886 0.765 0.740 0.798 0.680 0.906 0.780 0.815 0.810 0.855 0.924 0.925 0.890 0.890 0.910 Data for this system insufficient to 0.685 obtain correlation 0.960 1.000 1.000
. .Exptl.
I
Wohl pointed out (40) that the empirical equations commonly used for the correlation of activity coefficients represent special caaes of the following general expression:
If q1 is assumed to beequal t o p2, the general equation of 4 can be reduced into Margules equation: log
y, =
the
+
X2; [ A 2(B - A)Xd ( 6 4
The vapor-liquid equilibrium composition data of each xylene isomer and different solvent collected in the second part of the work are correlated by both Equations 5 and 6. The following systems are correlated well by Equation 5 of Van Laar form: p-Xylene-aniline p-Xylene-methyl salicylate p-Xylene-non 1 alcohol m-X ylene-anigne m-Xylene-nonyl alcohol m-Xylene-methyl salicylate The following systems are correlated well by Equation 6 of Margules form: p-Xy lene-aniline p-Xylene-nonyl alcohol p-Xylene-tetrahydrofurfuryl alcohol m-Xylene-aniline m-Xylene-methyl salicylate m-Xylene-dimethyldf olane m-Xylene-nonyl alcohol
The values of constants in both the Van Laar and Margules equations are calculated and given in Table I1 for all these systems. The equilibrium vapor composition calculated by the Van Laar and Margules equations are listed in comparison with the experimental data in Table IV. Redlich and Kister (33) defined a term Q by the following expression:
Q = ZXi log
yi
(7)
For a binary system the expansion of Equation 7 gives For a binary system of components 1 and 2, a three-suffix equation can be expanded and simplified into
[.+ 2(B: - A)&] = 2," p 3 + 2 ( 4 5 - 23)z2]
log y1 = 2; log
y*
where A and B are constant characteristics of temperature and nature of the system. If n_l is assumed to be equal t o A / B , the 912
general form of Equation 4 is reduced to the Van Laar equation:
AX; log
=
($x,+ XZ)l
Q
= XI log YI
+ ( 1 - Xi) log YZ
(8)
To satisfy the necessary condition that Q = O a t XI = O and X I = 1, according to Equation 8, the 6j function has been developed (99) in the following form:
Q
= Xi(1
- Xi)B + C(2X1 - 1) f D(2X1 - 1)' + . . .
(9)
The constants B, C, and D can be solved by the relations given by Redlich and E s t e r . y, and y, are then calculated to give the vapor compositions in equilibrium with liquids a t different compositions. The calculated values of constants B, C, and D for different binary systems are given in Table 111. Both the calculated and experimental vapor compositions are listed in Table 11. The following systems are well correlated by this method:
INDUSTRIAL A N D ENGINEERING CHEMISTRY
160
TABLE 111. CONSTANTS IN VARIOUBEQUATIONS OF CORRELATIOSS Systems p-Xylene Aniline Dimethylsulfolane hIethy1salicylat.e Xonyl alcohol Tetrahydrofurfural alcohol m-Xylene Aniline Methyl salicylate Nonylaloohol
Redlich-Kister
B
C
D 0 0.100 0 0
0.348 0.600 0.170 0.162
0.023 -0.130 0.057
0.493
0.133
-0,193
0.326 0.390 -0.700 0.388
0.019 0.130 0.780 0.132
-0.526 -0,092
-0.056
0 0
Values of Constants Gilmont 8'
8"
0.303 -0.220 -0.280 1.000
0
1.265
B
0.493 0.180
0.400 0.035
0
0.400 0.115 o,383 0,147
0.493
0.030
0.493 0.317 o,05j ~ 0.500
-2.77
0.500
0.485
0.506
0.312
0 0 0 -1.31
0.478 0.356 0.200 0.652
0.245 0.160 0.100 0.585
0 , 5 2 0 0.245 0.356 0,160 0 . 2 0 0 0.100 0,380 0.243
-3.40
0
-0.53 0 0 0 1.683
p-Xylene-aniline p-Xylene-methyl salicylate p-ylene-tetrahydrofurfury 1 alcohol m- ylene-aniline m-Xylene-methyl salicylate
A new method of correlating vapor-liquid equilibria was proposed recently by Gilmont et al. ( 1 5 ) . The correlation is made through relative volatility, which is expressed in terms of a symmetrical composition variable as follows: n
log
as1
= log
+ sc- 1
4%
= log ai1 i g'al
+ 8:
8Sh
Margules A B
A
o
3.18 0 0
0.250 0.170 1.600 -0.150
~___ Van Lam
gIII
o,055
o
,
~
Vol. 46,No. 4 The equilibrium vapor compositions calculatcd by four methods of correlations and the experimental dat'a are plotted in Figure 7 for coniparkon. The agreement be~tween the experimental data and the calculated values is well within the limits of error. ACKNOWLEDGMEA-T
G r a t e f u l acknowledgment is made t o thc following for their comments or assistance during the investigation or the preparation of the manuscript: R. H. Munch; R. Rose and 6. W.Ashworth, Rlonsanto Chemical Co ; L. Hart, J. Pegan, F. A. Frick, and J. R.Couper, formerly of Washington University; H. W. Wang, H. T. Welch, R. R. Calaceto, Alexander Sommers, and J. W. Ericson, formerly of the Polytechnic Institute of Brooklyn; and RIrs. RI. Resternhagen, Polytechnic Institute of Brooklyn. The Oronite Chemical, Carbide and Carbon, Monsanto Chemical, Phillips Petroleum, Shell Chemical, and Tennessee Eastman Companies donated the materials used in this work. The authors are grateful for their cooperation.
17 ,"
8,+ gzP E
hQ3PESCEATLRE
f g*P*2; f
..
e
(10)
R.,
R,
ie a coefficient of the term in the power series which can be evaluated from the experimental data by a graphical method n-hich not only determines the number of coefficients but also g
evaluates these coefficients with a degree of precision corresponding with that of the data. With the use of only two parameters in Equation 15, the authors treated their data and found good correlations for the following systems: p-Xylene-aniline p-Xylene-methyl salicylate p-Xylene-tetrahydrofurfuryl alcohol m-Xylene-aniline m-Xylene-methyl Palicylate The constants in Equation 15 for different systems have been computed and presented in Table IV. The calculated and experimental vapor compositions are listed in Table I1 for comparison.
empirical constants corresponding to indicated groups of Components C, D = constants characteristic of sy&m = fugacity of a component = fugacity of a component a t temperature and pressure of the solution = vapor pressure of a pure component = effective molal volume = mole fraction in liquid phase = mole fraction in vapor phase
A s h l Ash,, A t h j l =
f
f" Po q
X Y
x:,
19 = 1 / 1 Z = effective volume fraction T = total pressure of a system a = relative volatility = relative volatility of solution containing equal moles of two components y = activity coefficient in liquid phase Subscripts 1, 2, i, h, 1, I refer to each individual component. LITERATURE CITED
(1) dndrews, L. J., and Keefer, R. M., J. Am. Chem. Soc., 71, 3644 (1949) *
100
58
i3
80
60
az y s 40 By $ 5 20 20 40 60 8 X, MOLE PERCENT XYLENE IN LIQUIR
0 X, MOLE PERCENT XYLENE IN LIQUID
X, MOLE PERCENT XYLENE IN LIQUID
Figure 6. Equilibrium Curves of p-Xylene and m-Xylene
0 p-Xylene
A A. B. C. C.
m-Xylene
In tetrahydrofuurfural alcohol exposed to infrared light for 1 hour In diisohutyl ketone exposed t o infrared light for 1.5 hour8 In nonyl alcohol expomed to infrared light for 1 hour In nonyl alcohol exposed to infrared light for 2 hours
X , MOLE PERCENT XYLENE IN LIQUID
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1954
X
MARGULES
P-
M.F.M-XYLENE IN LIQUID
o
2
li
6
8
16 1
- GlLMONT ,2
-
1 . 0 0
MEPXYLENE IN L i a u i ~
2
4
6
8
1.00
Arnold, J. C., Brit. Patent 585,076 (January 1945). Renedict, M,, and Rubin, L. C., Trans. Am. Inst. Chem. Engrs., 41, 353 (1945). Bonauguri, E., Bicelli, I,.,and Spiller, G., Chim. i n d . (Milan), 33, 81 (1951). Brooke, L. F., Gordon, E. L., and Sfrickland, A. E., U.S Patent 2,521,444 (Sept. 5, 1950). Brooks, R. F., chemical engineering thesis, Washington University, St. Louis, Mo., 1949. Carlson, H. C., and Colburn, A. P., IXD.EKG.CIIEM.,34, 581 (1942). Charlampowicz, R., Bull. intern. acad. polan. sci., Classe sci. math. nut., 19298,335. Clarke, H. T., and Taylor, E. R., J . Am. Chem. Soc., 45, 830 (1923). Colburn, A. P., and Schoenborn, E. M., Trans. ,4m. Inst. Chem. Engrs., 44,421 (1945). Dunn, C. L., Miller, R. W., Pierotti, G. J., Shiras, R. E., and Saunders, bI., Jr., Ibid., 41,631 (1945). Ewell, R. H., Harrison, J. bl., and Berg, L., IND.ENG.CHEM., 36,871 (1944). Fulton, S. C., and Heigl, J. J., Instruments, 20, 35 (1947). Garner. F. H.. and Ellis. S. R. M., Trans. Inst. Chem. Engrs. (London),29,45 (1951). Gilniont, R., Weinman, E. A., Kramer, F., lIiller, E., Hashmall, F., and Othmer, D. F., IWD. ENG.CHEM.,42, 120 (1950). Greenberg, R. B., U. S. Patent 2,398,526 (April 1946). Griswold, J., Andres, D., Van Berg, C. F., and Kasch, J. E., ISD.ENG.CHEW,38, 65 (1946). Iletzner, H. P., U. S. Patent 2,511,711 (June 1950). Hieffer, W.F., and Gabriel, C. F., IND.ENG. CHEY., 43, 973 (1961). Kremman. R..J . Chem. Soc.. 110. 11. 4 i l (1916). LeFerre, R. J. IT.,J . Am. Chem. hoc., 60,3095 (1938). Linn, C. B., U. S Patent 2,630,406 (Oct. 2, 1950). Mcdrdle, E. H., and Mason, D. bl., U. S. Patent 2,435,792 (February 1945).
2
4
.6
8
IO
(24) hlcCaulay, D. A., Shoemaker, B. H., and Lien, A. P., IXD. ENG.CHEM.,42,2103 (1950). (25) hlair, B. J., Glasgow, A. R., and Rossini, F. D., J . Research Natl. Bur. Standards, 27, 39 (1941). (26) bIeissner, H. P.. and Greenfield, S. M., IND.ENG.CHEY..40.438 (1948). (27) National Bureau of Standards, Am. Petroleum Institute, Research Project 44 (December 1945). (28) Oronite Chemical Co., San Francisco, Calif., “Xylene Technical Review,” 1943. (29) Othmer, D. F., Anal. Chem., 20, 763 (1948). (30) Othmer, D. F., IND.ENG.CHEM.,35, 614 (1943). (31) Othmer, D. F., Savitt, S. A., Krasner, A., Goldberg, A. AI,, and Markowitz, D., Ibid., 41, 572 (1949). (32) Quaker Oats Chemical Co., “Tetrahydrofurfuryl Alcohol,” Tech. Div. Bull. 87A (1948). (33) Redlich, O., and Kister, A. T., IXD.ENG.CHEM.,40,345 (1948). (34) Resnick, A. E., “Electronic Interpretation of Organic Chemistry,” p. 271, New York, John Wiley & Sons, 1949. (35) Schlessman, C. H., U.S. Patent 2,455,812 (December 1948) (36) Shell Development Co., Emeryville, Calif., “Dimethyl Sulfonate,” Rept. 5-9868 (1946). (37) Stull, F. R., IND.ENG.CHEM.,39, 517 (1947). (38) Updike, 0. L., Jr., Langdom, W. M., and Keyes, D. B., Trans. Am. Inst. Chem. Engrs., 42,215 (1946) (39) Wang, S. L., chemical engineering thesis, Washington University, St. Louis, Mo., 1950. (40) Wohl, K., Trans. Am. Inst. Chem. Engrs., 42,215 (1946). RECEIVED for review September 22, 1951. A C C E ~ E December D 21, 1953. Rlaterial supplementary to this article has been deposited as Document S o 4170 with the AD1 Auxiliary Publications Project, Photoduplication Service, Library of Congress, Washington 25, D. C. A copy may be secured by citing the document number and by remitting $1.25 for photoprints or $1.25 for 35-mm. microfilm. Advance payment is required. Make checks or money orders payable to Chief, Photoduplication Service, Library of Congress
