1364
I n d . Eng. Chem. Res. 1989, 28, 1364-1369
matography. Chem. Eng. Commun. 1987, 58, 273. Helfferich, F. Sorption of Solutes. In Ion Exchange; McGraw-Hill: New York, 1962. Jarrett, H. W.; Cooksy, K. D.; Ellis, B.; Anderson, J. M. The Separation of o-Phthalaldehyde Derivatives of Amino Acids by Reversed-Phase Chromatography on Octylsilica Columns. Anal. Biochem. 1986, 152(1), 189-198. Lapidus, L.; Amundson, N. R. Mathematics of Adsorption in Beds. VI. The Effect of Longitudinal Diffusion in Ion Exchange and Chromatographic Columns. J. Phys. Chem. 1952, 56, 984. Lightfoot, E. N.; Sanchez-Palma, R. J.; Edwards, D. 0. Chromatography and Allied Fixed Bed Separations Processes. In New Chemical Engineering Separation Techniques; Schoen, H. M., Ed.; Interscience: New York, 1962. Liu, P. D. Equilibria and Mass Transfer in Ion Exchange/Sorption Biochemical Separation. MS.ChE. Dissertation, University of Delaware, Newark, DE, 1985. Miller, G. H.; Wankat, P. C. Moving Port Chromatography: A Method of Improving Preparative Chromatography. Chem. Eng. Commun. 1984,31, 21-43. Rhee, H. R.; Aris, R.; Amundson, N. R. On the Theory of Multi-
component Chromatography. Phil. Trans. R. SOC.London, A. 1970,267, 419. Sherwood, T. K.; Pigford, R. L.; Wilke, C. R. The Resistance to Mass Transfer Between Phases for Ion Exchange and Sorption. In Mass Transfer; McGraw-Hill: New York, 1975; Chaper 10.8. Snyder, L. R.; Kirkland, J. J. Basic Concepts and Control of Separation. In Introduction to Modern Liquid Chromatography, 2nd ed.; John Wiley; New York, 1979; Chapter 2. Spackman, D. H.; Stein, W. H.; Moore, S. Automatic Recording Apparatus for Use in the Chromatography of Amino Acids. Anal. Chem. 1958, 30(7), 1190. Wankat, P. C. Improved Preparative Chromatography: Moving-Port Chromatography. Ind. Eng. Chem. Fundam. 1984, 23, 256. Wankat, P. C. Large-Scale Adsorption and Chromatography; CRC Press: Boca Raton, FL, 1986; Vol. 2. Yu, Q.; Yang, J.; Wang, N.-H. L. Multicomponent Ion-Exchange Chromatography for Separating Amino Acid Mixtures. Reactive Polym. 1987, 6 , 33-44.
Received for review December 28, 1988 Accepted May 29, 1989
Selective Extraction of Oleic, Linoleic, and Linolenic Acid Methyl Esters from Their Mixture with Supercritical Carbon Dioxide-Entrainer Systems and a Correlation of the Extraction Efficiency with a Solubility Parameter Yutaka Ikushima,* Norio Saito, and Tomio Goto Government Industrial Research Institute, Tohoku, Nigatake 4-chome, Miyagino-ku, Sendai 983, Japan
Oleic, linoleic, and linolenic acid methyl esters were able to be well extracted and separated from their mixture by supercritical carbon dioxide (SC-C02) with an entrainer. We used several entrainers, some paraffins, and some esters, and these were alternately added to the C02. T h e SC-C02 with a single entrainer flowed over the mixture and then through a separation chamber packed with AgN03-doped silica gel. T h e use of the chamber and the entrainer made it possible t o effectively extract and separate the desired component from the mixture. T h e amount of each substance extracted was estimated by a model including the solubility parameter. The affinity of the substance for the mobile (SC-C02or SC-C02and an entrainer) and stationary (AgN0,-doped silica gel) phases was regarded as the ratio of the activity coefficient of the substance in the two phases. An approximately linear relationship exists between the variation in the ratio of the activity coefficient and the amount of substances extracted. In the fields of food and pharmacy, supercritical carbon dioxide (SC-C02) extraction is noted to be a useful method for extracting valuable materials such as docosahexenoic acid (DHA), eicosapentenoic acid (EPA), linoleic acid, linolenic acid, and others contained in natural resources (Yamaguchi and Murakami, 1986; Sako et al., 1986). The utility of these acids is described elsewhere (Lossonczy, 1978; Hirao et al., 1980; Sanders and Younger, 1981). However, it is difficult to extract selectively a specific component from the mixture of such higher fatty acids because these are similar in chemical and physical properties. We (Ikushima et al., 1988) previously reported that the selective extraction of stearic (clw) and linolenic (c18-3) acid methyl esters from a equimolar mixture of stearic, oleic (CIB-J, linoleic (CIB-J,and linolenic acid methyl esters becomes feasible by means of a chamber packed with both AgN0,-doped silica gel and ethyl acetate as the entrainer. (In the subscripts, the first and second figures refer to the number of carbon atoms and the degree of unsaturation in the molecule, respectively.) When flowing out the extractor and then passing through the AgN0,-doped silica gel chamber, fatty acid methyl esters having a higher deOSSS-5885/89/2628-1364$01.50/0
gree of unsaturation, such as C18-2and Clgg methyl esters, were found to be held in the chamber, probably because these two might form some adducts with AgNO,. It was possible to isolate C18-3 methyl ester in adequate purity from the chamber by the addition of entrainer to the COz. However, c18-1 and c18-2 acid methyl esters could not be separated well from the mixture. The property of the solvent for the extraction can be easily changed according to an entrainer added to the COz (Ikushima et al., 1988), and the amounts of Clgl and Clg2 methyl esters extracted through the chamber might be adjustable with several entrainers, which are alternately added to the COz. The first objective of this work is to present a method to extract and isolate a desired component in high purity from a mixture of oleic (Clgl), linoleic (Clg2), and linolenic acid methyl esters by the alternate addition of suitable entrainers to COz for a given extraction system in which AgN0,-doped silica gel is used. The gradual variations in the solvent polarity may occur by means of the alternate addition of entrainers. The second objective is to apply chromatographic analysis to the estimation of the amount of each fatty acid methyl ester extracted through the chamber. The amount 6 1989 American Chemical Society
Ind. Eng. Chem. Res., Vol. 28, No. 9, 1989 1365
**Air
Table I. Compositions of Extracts on Extraction with SC-C02 and SC-C02-Ester Entrainer System at 9.3 MPa and 313 K amt of extract, concn, 106Y, wt % mol/nL mg I nL 0.42
(1)sc-co,
ClS-1 c18-2 c18-3
U Figure 1. Schematic diagram of supercritical extraction apparatus. (1)COz cylinder, (2) high-pressure pump, (3) high-pressure pump for an entrainer, (4) cooling circulator, (5) preheater, (6) extractor, (7) back-pressure regulator, (8) separation chamber, (9) heating tape, (10) temperature controller, (11)receiver, (12) thermocouples, (13) pressure gauge, (14) wet gas meter, (15) constant-temperature bath, (16) gas sampler, (17) gas chromatograph, (18) FID detector, and (19) pen recorder.
of extract is correlated to the variations in affinities of fatty acid methyl esters for mobile (SC-C02or SC-C02 and an entrainer) and stationary (AgN0,-doped silica gel) phases. The affinities will be represented by a model including the solubility parameter with the assumption of the regular mixing rule.
Experimental Section Materials. Oleic, linoleic, and linolenic acid methyl esters were obtained from Kanto Chemical Co. Inc. Commercial-grade carbon dioxide was used. All chemicals were used without further purification. Silica gel (Silbead N) was obtained from Mizusawa Ind. Chemicals, Ltd. It was powdered to 65-100 mesh, the BET surface area being 513 m2/g. AgNO, was supported on the silica gel by impregnating the support powder with silver nitrate aqueous solution to the 7% level by weight and drying under vacuum at 413 K for 4 h. Apparatus and Procedures. A schematic diagram of the apparatus used in this study is presented in Figure 1. With a 0.1-L extractor maintained at 305 or 313 K, a weighed sample was extracted by SC-COz with or without an entrainer at pressures of 9.3 and 10.8 MPa. Liquid carbon dioxide and/or an entrainer was charged into a Hitachi Model 6358 high-pressure liquid pump through a 1/16-in.tube and a check valve, compressed to the desired pressure and then fed into the extractor. The concentration of the entrainer in SC-C02 was about 4% by weight. The pump delivered the COz at a constant flow rate of 1 nL/min (1 nL = 1 L of gas a t 293 K and 101.3 kPa). The pressure inside the extractor was controlled with a heated back-pressure regulator. The extraction pressure is measured with a Bourdon-type pressure gauge. Fluctuations in pressure due to the pump were less than f O . O 1 MPa below 19.6 MPa. The temperature was controlled to within *0.1 K. The apparatus was equipped with a chamber between the extractor and the back-pressure regulator for the selective removal of dissolved material from the loaded supercritical phase. The chamber was a stainless steel tube 80 cm long and 0.5-cm i.d. and was filled with glass wool at both the bottom and top outlets. It was packed with AgN0, supported on silica gel. The temperature of the chamber was kept at the same temperature as that of the extractor. The solution extracted was flashed to atmospheric pressure across the heated back-pressure regulator, and then the component was collected in receivers, which consisted of two-stage traps maintained at 273 K with ice-cold water. The amount of solutes collected was determined by weighing, and the total flow volume of COz
60.6 28.3 11.1
2.11 0.97 0.39
(2) C0,-Ethyl Valerate 1.99 c1S-1
Cle-2 CIS-3
30.2 40.5 29.3
4.91 6.62 4.79
(3) C0,-Ethyl Butyrate 0.15 Cle-1 Cle-2 clS-3
30.9 31.7 37.4
0.37 0.39 0.46
(4) COz-Ethyl Propionate
0.17 CIS-1 Cle-2 CIS-,
11.7 31.3 57.0
0.16 0.43 0.79
(5) C0,-Ethyl Acetate 0.18
CE-1 ClS-2 c18-3
5.2 17.7 77.1
0.08 0.26 1.10
used was measured with a wet gas meter. The composition of methyl esters was determined by a Shimadzu Model GC-7A gas chromatograph. Each run in the present experiments was conducted first with SC-COzalone until some degree of extraction occurred and then together with entrainer. The fractions were taken every 10-100 nL of COz. We sampled and analyzed more than 50 fractions for each run. Here, the degree of extraction is defined as the total amount of materials extracted divided by the initial amount of materials fed into the extractor.
Results and Discussion Selective Extraction of Clgl, ClS2, and C18-3 Acids. Effects of Ester Entrainers. The extraction of a mixture of Clel, Clg2, and Cis3 methyl esters was carried out with SC-COz alone at 313 K and 9.3 MPa. The total weight of the mixture charged was 3.7 g, and the concentrations of the feed materials, Clgl, Clgz, and Clg3 methyl esters, are 34.0, 36.3, and 29.7 w t %, respectively. It is seen that methyl ester can selectively be separated with a concentration above 50% during this extraction process. In contrast, C1g3 methyl ester is scarcely extracted before a degree of extraction of 40%. The average concentrations of ClS1, Clgz, and Clg3 methyl esters in this run are shown in Table I. Unless the AgN0,-doped silica gel was used, the composition of the mixture extracted was almost identical with that of the feed material (Ikushima et al., 1988). It is thought that, when flowing out of the extractor and then passing through the AgN0,-doped silica gel chamber, fatty acid methyl esters having a higher degree of unsaturation, such as C18-3 methyl ester, may form some adducts or complexes with AgNO,. Then, it may be possible to isolate Clg2 and Clg3 methyl esters in adequate purity from the mixture held in the chamber by a subsequent treatment. The total amount of the esters extracted increases immediately after the outset of the extraction, but it decreases rapidly after the degree of extraction near 10%.
1366 Ind. Eng. Chem. Res., Vol. 28, No. 9, 1989 Table 11. Composition of Extracts on Extraction with SC-CO, and SC-C0,-Alkane Entrainer System at 10.8 MPa and 305 K concn, 105~, amt of extract, wt % mol/nL me/nL (1) sc-co2
0.87 Cl8-1 CIS-2 c18-3
79.1 20.3 0.6
11.13 2.87 0.09
(2) C0,-Hexane 0.34 C18-I
Cl8-2 C18-3
15.1 73.1 11.8
1.83 2.03 0.20
(3) C0,-Heptane 1.33 ClS-1 Cl8-2 c18-3
34.8 62.9 2.3
3.71 6.85 0.25
40.9 57.7 1.4
4.72 6.69 0.22
(4) C0,-Octane
1.42 C18-1
Cl8-2 c18-3
(5) CO,-Ethyl Acetate 1.90 ClS-1 C18-2 C18-3
6.4 11.6 82.0
0.99 1.80 11.50
When the above-mentioned run was made up to a degree of extraction of about 40%, a small amount of the extract could be obtained. Thus, SC-C02 was further flowed with ethyl valerate. The concentration of Clgl methyl ester decreased, whereas those of cla-2 and Clg3 methyl esters increased. The composition of the extract is shown to be almost the same as that of the feed material, as shown in Table I. When the above-described extraction reached a degree of ca. 8O%, SC-C02 was alternately flowed with ethyl butyrate, ethyl propionate, or ethyl acetate instead of ethyl valerate. One entrainer was switched to the other a t a certain degree of extraction where the extract could not be obtained. The concentrations of Clgl and Clg2 methyl esters in the extract decreased and that of C1&3 methyl ester increased for all the entrainers, especially ethyl acetate, which enhanced the concentration of Clg3 methyl ester to about 90 w t 70. Effects of Hydrocarbon Entrainers. Next, we examine the entrainer effects of hexane, heptane, and octane. The weight of the feed charged was 5.8 g, and the initial concentrations of CIg1, ClS2, and Cis3 methyl esters are 32.5,36.3, and 31.2 wt 9’0,respectively. When SC-C02was flowed with one of the entrainers in the order of hexane, heptane, octane, and ethyl acetate, esters were extracted, and their compositions are shown in Table 11. It was found that Clgl methyl ester could selectively be separated with SC-C02 alone at 10.8 MPa, while C18-3 methyl ester was scarcely extracted with SC-C02 alone. The total amount of the esters extracted is significantly enhanced compared to that with SC-COP alone at 9.3 MPa shown in Table I because of an increase in the pressure to 10.8 MPa and a decrease in the temperature to 305 K. Table I1 also shows that the concentration of C18-2 methyl ester is increased by the addition of the hydrocarbon entrainers to the COP,reaching a maximum above 70 wt. 70.Although the Concentration of the CIg3 methyl ester is enhanced, it cannot be obtained in adequate purity. The addition of ethyl acetate instead of a series of‘ al-
kanes can selectively isolate C1a-3 methyl ester with a concentration over 80 wt % as shown in Table 11. Especially, its concentration maximally reaches above 95 w t 70 a t a degree of extraction near 75%. It is noted that the amount of the extract reaches a maximum, ca. 7.0 mg/nL, at a degree of extraction near 75%. Thus, the Clg3 methyl ester can be separated and concentrated in high purity and large solubility from the mixture of the fatty acid methyl esters used. Although it has often been said that a large solubility counters a low selectivity (Brunner et al., 1979), the present work shows that the desired fatty acid can be separated well from the mixture by employing suitable entrainers such as the hydrocarbons and ethyl acetate as well as the AgN0,-doped silica gel. Correlation of the Extraction with a Solubility Parameter. We regard the extraction behavior of fatty acid methyl esters through the AgNO,-doped silica gel chamber as a chromatographic mechanism. That is, the amount of each acid eluted from the separation chamber strongly depends upon the differnece in affinities of the solute with mobile (SC-C02 or SC-C02-entrainer) and stationary (AgNOB-dopedsilica gel) phases. We attempt to represent the affinities of solutes with the two phases by a model including the solubility parameter with the assumption of the regular mixing rule. The connection of solubility parameter and chromatographic retention parameters will be established through the activity coefficient. Since the variation in volume by mixing a solute with a pure liquid is generally negligible, the total freeenergy change is considered to result only from the enthalpy difference before and after the mixing. If we regard the pure liquid as the standard state, the regular mixing rule describes the activity coefficient (7) of a solute (1) in a phase ( 2 ) as In y1 = VI(&, - 6 J 2 / R T
(1)
where 6 is the solubility parameter, R is the gas constant, and V is the molar volume. The capacity factor (Schoermakers et al., 1978), k , used as the basic retention parameter is applied to represent the chromatographic separation power. It can be expressed as the ratio of the activity coefficients of the solute in two chromatographic phases as follows:
h = (ym/nm)/(+Y,/ns) = (Ym/Ys)(ns/nm)
(2)
where n is the number of moles in the separation chamber and the subscripts m and s indicate the mobile and stationary phases, respectively. From eq 1and 2, the capacity factor (ki) of the solute (i) extracted with SC-C02 alone is given as In ki = Vi(6, + 6, - 26,)(6, - 6,)/RT + In (n,/n,) (3) Since one kind of stationary phase is used in this work, the addition of the entrainer would vary the properties of mobile phase only. The variation in the capacity factor can be clarified by differentiating eq 3 toward 6, for a given system, where the solubility parameter of the stationary phase (6,) is constant. Namely, we obtain A h i / k , = (2Vi/RT)16, - 6iIA6, (4) Lam =
6ec - ~ C O ~
(5)
where 6,, is the solubility parameter of the COz with an entrainer. The 6, is determined with a simple mixing rule (Barton, 1975) as 6ec
= 4 ~ 0 ~+ 6 4~e 60e ~
(6)
where 4 is the volume fraction and subscript e refers to an entrainer. The solubility parameter of SC-C02 (6c,$
Ind. Eng. Chem. Res., Vol. 28, No. 9, 1989 1367 Table 111. Solubility Parameters of Substances Used substance alkane octane heptane hexane ester ethyl valerate ethyl butyrate ethyl propionate ethyl acetate fatty acid methyl ester oleic linoleic linolenic
sc-co,
a t 9.3 MPa and 313 K at 10.8 MPa and 305 K
molar vol, cm3/mol
6,
~al'/~/cm~/~
163.5 147.4 131.6
7.53 7.48 7.30
148.2 132.0 115.5 98.5
8.48 8.55 8.66 8.95
344.4 337.1 330.5
8.03 7.98 7.94
89.9 59.0
4.02 5.91
can be determined by the method presented previously (Ikushima et al., 1987). Furthermore, we estimate the solubility parameters of the unsaturated higher fatty acid methyl esters with a multicomponent solubility parameter model (Hansen, 1967a,b, 1969). Table I11 shows the solubility parameters determined for the fatty acid methyl esters used in the present work. From eq 4, the separation power of a solute held in the chamber is strongly dependent upon the variation in 6,. Assuming that the fatty acid methyl esters in the chamber have no mutual influence and independently interact with the AgN0,-doped silica gel, an increase of the capacity factor (Aki/ki) due to the addition of suitable entrainers can be related to an increase in the affinity of the mobile phase for solute adsorbing on the AgN0,-doped silica gel. We estimate, by calculating Aki/ki, that the longer the aliphatic chain of the ester entrainer added to the C 0 2 is, the weaker the affinity of the solvent for fatty acid methyl ester gets. Therefore, the ester entrainers were alternately added to the C 0 2 in the order described above. The order of the addition of the alkane entrainers was also determined in a similar manner. Figures 2 and 3 show the relationships between Aki/ki and the amount of each fatty acid methyl ester extracted through the chamber for C02-ester entrainer systems and C02-alkane entrainer systems, respectively. In the extraction of Clgl and ClgZ methyl esters, we have obtained an approximately linear relationship between Aki/ki and the amount of the extract. For a given fatty acid methyl ester, Aki/ki can correlate the amount extracted. It is thought that the variation in ,6 depending upon the addition of entrainers varies the capacity factor in such a way that eq 4 is obeyed and Clgl and Clg2 methyl esters held in the chamber have been extracted gradually with an increase in the capacity factor. However, with regard to the extraction of Clga acid methyl ester having a higher degree of unsaturation, nonlinear relationships in Figures 2c and 3c indicate that the amount of c18-3 methyl ester extracted through the chamber is small before the addition of ethyl acetate to the COP,and the affinity of ClS3 methyl ester for the AgN0,-doped silica gel is stronger than that predicted by eq 3. If molar volumes of the higher fatty acid methyl esters are regarded as being equal, the following expression for the relative capacity factor of two acid methyl esters can be derived: In aid= In (ki/kj) = 2Vi(6j- 6i)(6co, - 6,)/RT (7) Since the relative retention (aij)represents the separation power of the solute (i) against that of the solute 6 ) in the chamber, the concentration of each fatty acid methyl ester
1
.75
AMOUNT
OF
I
I
C18-,
ESTER EXTRACTED, M O L / N L x 1 0 5
(b) .90
0
6.6
6.8
AMOUNT OF C,8-2
.70
7.4
7.6
7.8
ESTER EXTRACTED. M O L / N L x 1 0 5
t
.85
75
7.2
1.0
0
L
I
4.7
I
I
5.2 AMOUNT OF C18-3
5.7
6.2
6.1
J
ESTER EXTRACTED, M O L / N L x 1 0 5
Figure 2. Relationship between Aki/ki and the amount of fatty acid methyl ester extracted on the addition of ester entrainers to the CO,. (a) Clgl, (b) C1g2, and (c) C1g3.
on the extraction with SC-C02 alone could be estimated
by eq 7. According to eq 7, the larger the difference in the solubility parameter between the mobile and stationary phases, the more powerful the separation ability gets. As
1368 Ind. Eng. Chem. Res., Vol. 28, No. 9, 1989 Table IV. Concentrations of Cls-l, CL8-2,and C18-3Methyl Esters on the Extraction with SC-CO, Alone at 10.8 MPa and at 9.3 MPa and 313 K 305 K exptl, model, exptl, model, mol % mol '70 mol % mol % CIS-1
60.8
ClS-2
27.9 11.3
cl&3
4MO!!NT
9
CF CiY_,
15
10
78.9 20.4 0.7
61.6 25.7 12.7
The concentration of each fatty acid methyl ester calculated by eq 7 is shown in Table IV. The calculation has shown the strong retention ability that the AgN0,-doped silica gel possesses for unsaturated higher fatty acid.
ESTER EXTRACTED. MGL:'iLulC5
5
61.3 25.8 12.9
2@
AMG'JNT OF C,H_2 ESTE? EXTRACTED. FlOL NLxiO3
(C)
i
Conclusions CISl, Cl&z, and Clga acid methyl esters were selectively extracted from their mixture in high purity and large solubility by SC-C02 and a proper entrainer with a flow system with a separation chamber packed with AgN03doped silica gel. The alternate addition of alkanes and ethyl acetate as an entrainer to the COz was markedly effective for the extraction. The amount of the fatty acid methyl esters extracted through the chamber could be estimated with a model including the solubility parameter. In the extraction of CISl and C18-2acid methyl esters with SC-C02 and the entrainers, we have obtained a good relationship between the variation in capacity factor, Aki/ki, and the degree of extraction. This model could not represent the affinity of the C I S 3 acid methyl ester with the AgN0,-doped silica gel because fatty acids having higher degrees of unsaturation would interact more strongly with the silica gel than expected by this model. We think, however, that the present model may be useful for other extraction systems where the interactions are not so strong between the substances used. Nomenclature k = capacity factor n = number of moles in the chamber R = gas constant T = absolute temperature V = molar volume
i
D
Greek Symbols a = relative retention parameter, eq 7 y = activity coefficient
J
6 = solubility parameter 4 = volume fraction ci
IC
'5
c,8-3 E S T E R E X T R A C T E D , MOL N L ~ I C ~ Figure 3. Relationship between A k , / k , and the amount of fatty acid methyl ester extracted on the addition of alkane entrainers to the ~ M O I I * , TOF
CO,. (a) C l ~ - l (b) , C1&2, and (c) C1&3.
Subscripts e = entrainer ec = C 0 2 with entrainer i, j = solute i, j m = mobile phase s = stationary phase 1, 2 = component 1, 2 Registry No. AgNOB,7761-88-8;COz, 124-38-9; octane, 11165-9;heptane, 142-82-5;hexane, 110-54-3;ethyl valerate, 539-82-2; ethyl butyrate, 105-54-4;ethyl propionate, 105-37-3;ethyl acetate, 141-78-6;methyl oleate, 112-62-9; methyl linoleate, 112-63-0; methyl linolenate, 301-00-8.
shown in Table 111, the solubility parameters of each fatty acid methyl ester are similar, and these fatty acid methyl esters must be separated due to the difference in affinities of each fatty acid methyl ester for the stationary and mobile phases. It was reported that the solubility parameter of the uncoated silica gel is close to that of alumina Literature Cited and its value is about 16 ~ m - (Karger ~ / ~ et al., 1978), Barton, Allan F. M. Chem. Reu. 1975, 75, 731. while that of Ag is ca. 82 ~ m - (Lawson, ~ / ~ 1978). We Brunner, G.; Peter, S.; Retzlaff, B.; Riha, R. High Pressure Science presume that the solubility parameter of the stationary and Technology. Sixth AIRART Conference 1979; Vol. 1, p 565. phase, 7 wt % AgN03 supported on silica gel, is ca. 20 ~ a l ' / ~ Hansen, C. M. Ind. Eng. Chem. Process Des. Deu. 1969,2,8. Han~ m - with ~ / the ~ assumption that the 6, is nearly proporsen, C. M. J . Paint Technol. 1967a, 39, 104. Hansen, C. M. J . Paint Technol. 1969, 39, 505. tional to the mole fractions of uncoated silica gel and Ag.
1369
I n d . Eng. Chem. Res. 1989,28, 1369-1374 Hirao, A.; Hamazaki, T.; Terano, T.; Nishikawa, T.; Tamura, A.; Kumagai, A.; Sajiki, J. Lacent 1980, 11, 1132. Ikushima, Y.; Goto, T.; Arai, M. Bull. Chem. SOC. Jpn. 1987, 60, 4145. Ikushima, Y.; Hatakeda, K.; Ito, S.; Saito, N.; Asano, T.; Goto, T. Ind. Eng. Chem. Res. 1988,27, 818. Karger, B. L.; Eon, C.; Synder, L. R. J . Chromatogr. 1978,125, 71. Lawson, D. D. Proceedings of the DOE Chemical/Hydrogen Energy Contractor Review Systems, National Technical Information Service, Springfield, 1978.
Lossonczy, T. 0. Am. J . Clin. Nutr. 1978, 31, 1340. Sako, T.; Yokochi, T.; Sugeta, T.; Nakazawa, N.; Hakuta, T.; Suzuki, 0.; Sato, S.; Yoshitome, H. J . Jpn. Oil Chem. SOC. 1986,35, 463. Sanders, T. A. B.; Younger, K. M. Br. J . Nutr. 1981,45, 613. Schoermakers, P. J.; Billiet, H. A. H.; Tijssen, R.; de Galan, L. J . Chromatogr. 1978, 149, 519. Yamaguchi, K.; Murakami, M. J. Jpn. Oil Chem. SOC.1986,35,260.
Received for review December 28, 1988 Accepted J u n e 12, 1989
Liquid-Liquid Equilibrium of Sulfolane-Benzene-Pentane and Sulfolane-Toluene-Pentane George W. Cassell,+ Nilufer Dural, and Anthony L. Hines* Chemical Engineering Department, University of Missouri, Columbia, Missouri 6521I
Ternary liquid-liquid equilibrium data for the systems sulfolane-toluene-pentane and sulfolanebenzene-pentane were obtained a t 17, 25, and 50 "C. Experimental tie line data were measured by gas chromtographic analyses and correlated with the nonrandom two liquid (NRTL) and universal quasi-chemical (UNIQUAC) equations. Ternary liquid-liquid equilibrium data are essential for the design of liquid-liquid extraction processes and for the selection of solvents. Sulfolane (tetramethylene sulfone) is widely used as a solvent in the recovery of high-purity aromatics, such as benzene, toluene, and xylenes, from refinery process streams (Deal et al., 1959; Voetter and Kosters, 1966; Broughton and Asselin, 1967). Although relatively little quantitative phase equilibrium data on sulfolane have been published (Hartwig et al., 1955; Hanson et al., 1969; Tripathi et al., 1975; De Fre and Verhoeye, 1976; Rawat and Gulati, 1976; Ashcroft et al., 1982; Mukhopadyay and Dongaonkar, 1983; Hassan et al., 1988),some ternary systems containing sulfolane have been reported in the data collection of Sorensen and Arlt (1980), including tables of experimental tie lines, diagrams of these tie lines with corresponding predictions of phase envelopes, and distribution coefficients. In the present work, two new systems involving sulfolane have been investigated: sulfolane-toluene-pentane and sulfolane-benzene-pentane. The experimental equilibrium data were collected at 17, 25, and 50 "C.
Experimental Section Materials. Benzene and toluene were obtained from the J. T. Baker Chemical Co., and pentane and sulfolane were obtained from Burdick & Jackson Laboratory and from Alfa Products, respectively. Different purification methods were utilized to purify the chemicals used. Recrystallization was used exclusively for sulfolane since its melting point is 27 "C and because heating for distillation caused a discoloration. Recrystallization was carried out three times by heating the sulfolane to a temperature of 50 "C and then allowing it to cool slowly until approximately 90% had solidified; the remaining 10% was discarded. The other chemicals were purified with a Bughi Rotavapor-R rotary evaporator operated a t atmospheric pressure. The water bath used to heat the rotary evaporator was controlled to produce a slow evaporation rate, generating 400 mL/h of final product. A heart cut was
* To whom correspondence should be directed. 'Current address: Conoco Oil Co., Ponca City, OK 74602.
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collected by discarding approximately the first 10% of the distillate and the last 10% residual. The chemicals were injected into the packed column gas chromatograph before and after purification to determine their purities. All of the chemicals used in this study had purities greater than 99.9% after the purification process. Data Collection. The ternary LLE data for the systems investigated were obtained by using a gas chromatograph, and the size of the binodal curves was predicted by a cloud point determination (Tripathi et al., 1975). In order to analyze the sample mixtures with the gas chromatograph, it was necessary to dilute the mixtures with an appropriate solvent. Among the several solvents examined (methanol, butanol, methylene chloride, acetone, carbon tetrachloride, carbon disulfide, freon, and pyridine), carbon disulfide was selected for several reasons. First, the flame ionization detector sensitivity to carbon disulfide is very low, and if the concentration ranges were carefully controlled, carbon disulfide does not cause peak interference with most of the chemicals studied. Second, carbon disulfide is inexpensive and easy to handle compared with other solvents. It is available in a relatively pure form and can be further purified quite easily by distillation. Since detector sensitivity to some components was nonlinear, standards were prepared over the same concentration ranges as the samples. The first standard concentration was estimated by using an area analysis produced from the gas chromatographic test analysis. Once a few points on the binodal curve were determined, a new standard concentration was calculated from the trends present. Sample mixtures were prepared within the two-phase region using Supelco sample bottles with Teflon-lined septum caps. The samples were then placed in a shaker bath and brought to equilibrium a t the specified temperature (f0.2 "C, as indicated by a digital thermometer). Batch studies carried out in this work and by others (Tripathi et al., 1975) indicated that the equilibrium was reached within 30-45 min. However, the mixtures were left in the shaker bath about 24 h before sampling in order to ensure that equilibrium was obtained. After attainment of equilibrium, the agitation of the samples were stopped to allow proper phase separation prior to sampling. Both 0 1989 American Chemical Society
