1574
I n d . Eng. C h e m . Res. 1994, 33, 1574-1579
Phase Equilibria of Urea-Fractionated Fish Oil Fatty Acid Ethyl Esters and Supercritical Carbon Dioxide Christina Borch-Jensen, Arne Staby, and Jerrgen M. Mollerup' Department of Chemical Engineering, Technical University of Denmark, D T H , Building 229, 2800 Lyngby, Denmark
Measurements of phase equilibria of urea-fractionated fish oil fatty acid ethyl esters (FAEEs) in supercritical carbon dioxide were performed a t pressures from 8 to 26 M P a and temperatures of 313.2 and 343.2 K. Experimental temperatures, pressures, and mass fractions are reported in tabular form. T h e equilibrium ratios of the esters depend strongly on the system pressure and temperature, and a comparison with previous equilibrium measurements on the fatty acid ethyl ester mixture before the urea fractionation shows that they also depend on the composition of the ester mixture. The data show that high selectivity and low solubility are obtained a t low operating pressures, while a t high operating pressures the selectivity is low but the solubility is high. Twenty-nine components corresponding t o more than 90% of the natural mixture are identified. The three polyunsaturated C20:bn3, and C22:Gn3, correspond t o more than 80 % ' of the urea-fractionated mixture. FAEEs, C18:4n3,
Introduction Fish oils and derived products are important raw materials in the chemical and food industry with 20% for industrial uses and 80% for edible uses (Bimbo and Crowther, 1992). Fish oils consist for the major part of triglycerides with molecular weights from 500 to 1200 Da, but they also contain other important compounds like free fatty acids, cholesterol and cholesterol esters, vitamins A, D, and E (retinol, cholecalciferol, and tocopherol), squalene, phospolipids, and wax esters. Some of the compounds can be separated by fractional crystallization processes,vacuum distillation, liquid chromatography, and extraction processes. The conventional vacuum distillation process has the disadvantage of requiring elevated processing temperature, often resulting in undesired degradation and poiymerization of the highly unsaturated compounds. With a proper choice of solvent, however, supercritical fluid fractionation (SFF) can be carried out at temperatures less than 100 "C. At present, SFF is more expensive than the conventional methods, but when developed properly we believe it to be compatible or even superior to some of the conventional methods, because SFF allows for separation in nearly as many fractions as on a nonpolar supercritical fluid chromatographic column, making large-scale production of many specialized chemicals possible. What makes SFF techniques different from other separation techniques are the properties of the solvent(s) used in these techniques. When applied at a temperature slightly above its critical temperature, the properties of the solvent can be varied from gaslike to liquidlike by minor changes in temperature and pressure, causing large changes in solubility and selectivity. In principle, any substance from helium to water can be used as a supercritical solvent. The solvent selection depends on the particular application and the choice of operating temperature. The choice of solvents for supercritical extraction of coal or wood will be different from the choice of solvents for SFF applied to chemicals in the food and pharmaceutical industry. The design of supercritical countercurrent fractionation processes of fish oils and derived products requires knowledge of the phase equilibria with supercritical solvents and pilot-plant operation data (Krukonis, 1988). A review on experimental solubility, extraction, and OSS8-5885/94/2633-1574$04.50/0
chromatographic data on fish oil and derived products (Staby and Mollerup, 1993a)covers data published before 1993. Recently, we have studied phase equilibrium measurements of carbon dioxide and a natural mixture of FAEEs (fatty acid ethyl esters) derived from fish oil of sand eel (Ammodytes l a n c e a ) (Staby and Mollerup, 1993b; Staby et al., 1993). In this paper we publish the results obtained by measuring similar phase equilibria of a urea-fractionated FAEE mixture prepared from the same sand eel FAEE mixture as employed in the previous work. The ureafractionated FAEE mixture contains mainly the unsaturated portion of the natural FAEE mixture and has a higher average molecular weight than the natural FAEE mixture. The reason for choosinga urea-fractionated FAEE mixture is that it could be the feed to a SFF process. The ureafractionated FAEE mixture could either be performed conventionally in organic solvents or preferably in supercritical carbon dioxide (Arai and Saito, 1986).
Experimental Section Equipment. A combined gravimetric and volumetric method was used to determine the phase equilibria of ureafractionated fish oil ethyl esters and carbon dioxide. The apparatus has previously been described in detail elsewhere (Staby and Mollerup, 1991). The equipment consists of a phase equilibrium view cell, an airbath, a displacement pump, pycnometers, a rocking mechanism, filling,cleaning, and sampling lines, and a gasometer. The phase equilibrium cell is of the variable-volume static cell type rated to 70 MPa with a working temperature range from 278 to 453 K. The pressure transducer has an accuracy better than *20 kPa, and the temperature setpoint resolution is 0.1 K. The gasometer has a capacity of 10 L and was used to degas the high-pressure sample at ambient temperature and pressure in order to measure the amount of gas dissolved in the sample. The composition of the liquid part of the degassed sample was determined using a HP-5880A chromatograph (Hewlett-Packard Co., Avondale, PA). The chromatograph is equipped with a flame ionization detector (FID) and a manual split injection port connected to a HP-FFAP (Hewlett-Packard Co., Avondale, PA) fused-silica capillary column (25 m X 0.2 mm X 0.33 pm). Phase Equilibrium Measurements. The experimental procedure has been described in detail elsewhere (Staby 0 1994 American Chemical Society
Ind. Eng. Chem. Res., Vol. 33, No. 6, 1994 1575 and Mollerup, 1991;Staby, 1993). In a typicalexperiment, 10-15 g of sample was withdrawn from the cell into an evacuated and weighed high-pressure pycnometer. The pycnometer was weighed before and after the sample was degassed in the gasometer to atmospheric conditions and the volume of liberated gas was measured. The remaining liquid fraction in the pycnometer was diluted with n-heptane and analyzed by gas chromatography (GC). A computer program was used to verify the mass balance of the sample and calculate the mass fractions. Single runs were performed at each pressure due to the limited amount of raw material available for the urea fractionation. The relative uncertainty of the measured mass fractions is estimated to be within 3-5 % . The relative uncertainty in the fish oil ester solubility at low densities may be larger because of the very small amount of solute in the sample, often less than 0.1 g in 10-15 g of sample. The uncertainty of the cell pressure is less than f30 kPa, and the cell temperatures are known within f0.2 K. The gas and liquid phase densities were determined from the mass displaced to the pycnometer divided by the volume displaced. The uncertainty in the densities is rather high due to the uncertainty in the sample line volume correction which has to be made in order to estimate the true volume displaced to the pycnometer. Chromatographic Analysis. The FAEE composition of the fish oil fractions was determined by GC. The collected liquid fraction of a sample was diluted to approximately 25 % with n-heptane to make detection of low-concentration FAEEs possible. A sample of 1.0 pL of the n-heptane solution was injected quickly onto the column through the split injection port with a split ratio of 1:lOO. The analyses were performed with the injection temperature and FID temperature set at 250 "C and the flow at 1mL/min. The initial oven temperature of 140 "C was held for 1min and then increased at a rate of 3 "C/min to 200 "C, where it was held for 1 min, followed by an increase of 3 "C/min to 22OoC,where it was held constant for 15 min. The resultant chromatographic peaks were identified by comparing their retention times to those of injected standards and by confirmation analyses done by The Technological Laboratory, Danish Ministry of Fisheries. A computer program converts the chromatographic peak areas into relative amounts of each FAEE and calculates the mass fractions of each of the 29 components identified using theoretical response factors (Staby, 1993). The relative standard deviation of the major components (>1% ) may be as large as 2 5% but generally it is less than 1?4 , while for minor components it may range between 1 and 10%. Each chromatographic analysis was performed three times. Materials. The carbon dioxide was supplied by Linde AG (Munchen, Germany) having a stated purity of 99.995 % +. The ethyl esters from the fish oil of the sand eel were supplied by Grindsted Products A/S (Arhus, Denmark) with a stated purity of 98%. The urea fractionation of the fish oil FAEEs was performed by The Technological Laboratory, Danish Ministry of Fisheries (Lyngby, Denmark) using a method similar to that described by Haagsma et al. (1982). Gases for the chromatographic analyses, helium, hydrogen, and air, were obtained from Hede Nielsen A/S (Ballerup, Denmark). The stated purities were >99.996 % for helium and >99.8 % for hydrogen. n-Heptane LiChrosolvsolvent was obtained from Merck (Darmstadt, Germany). All materials were used without further purification.
Results Urea-Fractionated FAEE Mixture and Carbon Dioxide. The results of the phase equilibrium measure-
25i
-= 1I
cd 20
a
W
-
8
0
20
40
80
80
100
Xcoo (Mass Percent) Figure 1. Pressure-composition diagram for a urea-fractionated fish oil FAEE mixture and carbon dioxide at the temperatures of 313.2 and 343.2 K. Table 1. Equilibrium Phase Pressures and Compositions (mass '3%) of the Carbon Dioxide + Urea-Fractionated Fish Oil Ester System at the Temperature of 313.2 K run no.
P (MPa)
1 1 2 2 3 3 4 4 5 5 6 6 7
8.02 8.03 9.00 9.05 10.08 10.08 12.55 12.54 15.01 15.00 17.54 17.55 19.00
yco.
(mass % )
TCO.
(mass % )
99.93 34.48 98.11 40.37 95.74 42.46 92.83 46.58 87.86 52.42 83.67 56.62 73.90
Table 2. Equilibrium Phase Pressures and Compositions (mass W )of the Carbon Dioxide + Urea-Fractionated Fish Oil Ester System at the Temperature of 343.2 K run no.
P (MPa)
yco2 (mass % )
8 8 9 9 10 10 11 11 12 12 13 13 13
10.08 10.07 12.58 12.56 15.00 14.98 17.56 17.59 19.95 19.95 22.57 22.58 25.54
99.82
TCO,
(mass % 23.53
98.82 29.38 97.62 35.78 95.61 41.22 93.81 43.17 87.58 52.07 68.82
ments of the system performed at 313.2 and 343.2 K are given in Tables 1and 2, respectively. The phase diagram of this system shown in Figure 1is very similar to that of the original FAEE mixture with carbon dioxide (Staby et al., 1993). The location of the phase boundaries is affected by the inevitable variations in the overall composition of the mixture in the cell from charge to charge. This emerges as ripples on the phase boundary curves looking like experimental uncertainty. The overall compositionvaried from 60 to 80 wt % carbon dioxide. The influence on the results was, however,limited as the ratio of all components in the feed except carbon dioxide was constant.
1576 Ind. Eng. Chem. Res., Vol. 33, No. 6, 1994 -
L/F = 0.534
o T = 313.2 K O T = 343.2 K
R
W
i
14 14 14 15 16 16 16 16 16 18 1 8 16 18 18 16 20 20 2 0 20 20 2 0 22 22 2 1 22 22 22 0 '0 ' 1 1 1 0 : 2 .3 4 -0 1 : 2 :3 .3 4 1 :2 '4 . 3 4 : 5 1 1 5 :5 : 5 6 MI Me
F a t t y Acid Ethyl Ester
Figure 4. Calculated phase ratio, LIF, of the individual FAEEs for run no. 13. The mean value of the phase ratio is 0.534.
Fzi = Lxi + ( F - L)yi
Density of C 0 2 ( kg/m3)
/
n
$
/
600-
a (d
L=-
400-
0
h
$
200-
/
/
d Q,
n "
I
0
200
400
600
800
1000
Density of C 0 2 ( kg/m3) Figure 3. Vapor phase density at 343.2 K as a function of the pure carbon dioxide density. The solid curve is the calculated density of the vapor phase if the dissolved FAEEs do not contribute to any volume change.
The solubility of the FAEEs in the carbon dioxide rich phase is plotted in Figure 2 as a function of the pure carbon dioxide density, and Figure 3 presents the measured phase density at 343.2 K as a function of the pure carbon dioxide density. As expected, all the measured vapor phase densities are higher than the pure carbon dioxide densities because of the dissolved FAEEs. The solid line is the calculated density of the vapor phases if the FAEEs were dissolved in the pure carbon dioxide with no change in the carbon dioxide phase volume. Because the vapor phase densities are situated above this line, the dissolution of the fish oil FAEEs occurs through volume contraction indicating that the partial molar volumes are less than the pure component volumes. The partial molar volumes of the FAEEs are probably negative. The phase ratio, LIF, in the cell can be calculated from a mass balance if the overall composition of the mixture and the phase compositions are measured. A mass balance of species, i, gives
(1)
where F is the overall mass in the cell, L is the mass of the liquid phase, zi is the overall mass fraction of component i, and yi and xi are the mass fractions of component i in the vapor and liquid phases, respectively. This may be rearranged to give
If the compositional analyses of the overall composition and of the coexisting phases are correct, a constant phase ratio should be obtained. Due to the limited amount of raw material the overall composition was only measured in one particular case. At run no. 13we prepared a mixture suitable for determination of the maximum pressure on the phase boundary curve, determined the pressure to be 25.54 MPa, increased the pressure to 30 MPa to avoid precipitation during sampling, and drew a sample from the single phase system. The pressure was then lowered to 22.6 MPa, and the phase compositions were determined. The calculated phase ratios plotted for each component in Figure 4 show a good consistency. The phase ratio deviates the most from the mean value for the components C18:0,CZoln9, C202n6, and C203n3, which are only present as minor components (see Table 3). Composition of the Urea-Fractionated Mixture. The urea fractionation of the original fish oil FAEE mixture resulted in a 3-fold increase in the concentration of the polyunsaturated FAEEs and an almost complete removal of saturated and monounsaturated FAEEs. The color of the urea-fractionated mixture was somewhat more intense yellow toward orange compared to the original oil. The composition determined from six chromatographic analyses of the urea-fractionated FAEE mixture is given in Table 3 along with the overall composition on a COzfree basis at the pressure maxima on the phase boundary at runs no. 7 and 13. As expected, there is a good concordance between the three compositions. The three polyunsaturated FAEEs, C184n3, C205n3, and C226n3, correspond to more than 80% of urea-fractionated mixture. One should notice that analysesperformed using a different chromatographic column than the FFAP column showed that approximately one-third of the component labeled as CIS:^ actually is phytanic acid ethyl ester. The Phase Compositions. The compositions of the coexisting phases are reported on a COz-free basis in Tables 4 and 5. More than 90% of the total peak area of each sample is identified. The mass fractions on a C02-free basis in Tables 3-5 have been normalized to 100%. The
Ind. Eng. Chem. Res., Vol. 33, No. 6,1994 1577 Table 3. Composition (mass 70)of the Urea-Fractionated Fish Oil Ester Mixture and Composition of the Two "Critical- Phases on a COz-Free Basis urea-fractionated P = 19.00 MPa P = 25.54 MPa ester mixture T = 313.2 K T = 343.2 K component i c140
12-Me-C11:o C14ln.5 C16:lnS C160 C16ln7 I4-Me-Cle:o Cl6:2* c163
C164n3 Cleo C18:lnS Cl82n6 Cl63n6 C18:3n3 C164n3 C201n9 C20:2n6 C204n6 C203n3 C204n3 CZ05n3 C22:lnll C22:Ing C21:5n3 C226n6 C225n3 C226n3 identified
Xi
xi
0.8 0.1 0.2 0.1
0.9 0.1 0.2 0.1
nda
0.01
0.5 0.3 2.3 1.6 2.9 0.03 0.6 1.2 0.8 0.9 12.7 0.6 0.5 0.9 0.1
0.5 0.3 2.4 1.7 3.1 0.0~ 0.6 1.3 0.8 1.0 13.0 0.6 0.5 0.9 0.1
1.0
1.0
35.9 0.3 0.1 1.5 0.4 1.1 33.2
35.6 0.3 0.1 1.5 0.4 1.1 32.6
0.4 1.1 33.4
91.9
91.4
91.9
Xi
0.8
0.1 0.2
0.1 nd 0.5 0.3 2.3 1.6 2.9
9.0 MPa 10.2 MPa a 12.5 MPa 0 15.0 MPa A
0.03 0.6 1.2 0.8 0.9 12.7 0.6 0.4 0.9
0.1 1.0
Figure 6. Comparison of K-values of the FAEEs of C14:0, C16:4~3, C18:4n3, C205n3, and C22:6n3 from the urea-fractionated mixture with the K-values from the original mixture (Staby et al., 1993) for several pressures at 313.2 K.
35.8 0.3
0.1 1.5
n
i
/
*
nd, not detected. Approximately one-third of this peak is phytanic acid ethyl ester. W
b/
,
2e:
, I
kz
, ,, 10
,
12.5 15.0 17.5 020.0 A
0
MPa MPa MPa MPa
-3&'
I
I
10
10
L E E
I
-I
10 -'
(mass)
Figure 7. Comparison of K-values of the FAEEs of C14:0, C16:4n3, C18:4n3, C20:5n3, and C22Bn3 from the urea-fractionated mixture with the K-values from the original mixture (Staby et al., 1993) for several pressures at 343.2 K.
10
i f
-3
I
5.0
I
10.0
I
15.0
I
20.0
Pressure P (MPa) Figure 5. K-values of docosahexaenoic acid ethyl ester, C22:6n3, at (0) 313.2 and (m) 343.2 Kin carbon dioxide. Solid line, originalFAEE mixture (Staby et al., 1993); dashed line, urea-fractionated FAEE mixture.
equilibrium ratios, K-values, are calculated from the mass fractions
Ki= y i / x i
(3) Figure 5 displays the influence of the system pressure on the equilibrium ratios of docosahexaenoic acid ethyl ester, C22:6n3,measured from the original and the urea-fractionated FAEE mixtures at 313.2 K for the nominal pressures of 9.0, 10.0, 12.5, and 15.0 MPa, and a t 343.2 K for the nominal pressures of 12.5, 15.0, 17.5, and 20.0 MPa. Figures 6 and 7 compare the K-values of the FAEEs of
Ci4:0, C164n3, C184n3, CZ05n3, and Czmn3 measured for the urea-fractionated mixture and the original mixture at 313.2 and 343.2 K, respectively. The diagonal indicates equal sizes of the K-values. The figures show that the K-values in the urea-fractionated mixture are increased by one decade at the lowest pressures when compared to the K-values for the original mixture, while a t the highest pressure they are lower due to the higher critical pressure of the urea-fractionated mixture. Further, the relative difference between the K-values is seen to be larger at the lower pressures, indicating that the best selectivity is achieved here. Similar trends are obtained for the other components. The K-values on a COz-free basis are related to the equilibrium ratios through (4)
where sy and s x are the solubility of the FAEEs in carbon dioxide in the vaporlsupercritical and liquid phases,
1578 Ind. Eng. Chem. Res., Vol. 33, No. 6, 1994 Table 4. Composition (mass % ) of the Urea-Fractionated Fish Oil Ester Mixture of the Vapor and Liquid Phases on a COz-Free Basis at the Temperature of 313.2 K
P = 8.03 MPa component i c140
12-Me-C140 C14ln5 C15ln5 C160 C16ln7 14-Me-Cleo Cl62b c163
yi
Xi
P = 9.03 MPa Yi
xi
P = 12.25 MPa
Yi
Xi
Yi
0.8 0.1 0.2 0.1
1.7 0.1 0.3 0.1
0.8 0.1 0.2 0.1
0.7
xi
P = 15.01 MPa xi
Yi
0.05 0.1 0.1
1.1 0.1 0.2 0.1
0.7 0.1 0.2 0.1
nd
nd
0.4 0.3 2.1 1.4 2.6
0.5 0.4 2.7 1.9 3.5
P = 17.55 MPa Yi
Xi
nda
nd
nd
nd
0.01
0.01
0.8 0.5 3.5 2.8 5.0
0.5 0.3 2.4 1.6 3.0
0.8 0.5 3.5 2.6 4.8
0.5 0.3 2.3 1.6 2.9
0.7 0.5 3.4 2.5 4.6
0.4 0.3 2.2 1.5 2.8
1.3 0.1 0.3 0.1 0.02 0.6 0.4 3.0 2.1 3.9
nd
0.03 0.6 1.2 0.8 1.0 12.9 0.6 0.5 0.9 0.1 1.0 35.8 0.2 0.1 1.5 0.4
0.04
0.03
0.04
0.03
0.03
0.03
0.03
0.03
0.03
0.03
1.1 32.9
0.7 1.5 1.0 1.1 15.8 0.7 0.5 0.9 0.1 1.0 34.8 0.2 0.1 1.3 0.4 0.9 25.4
0.6 1.2 0.8 0.9 12.7 0.6 0.5 0.9 0.1 1.0 36.0 0.3 0.1 1.5 0.4 1.1 33.2
0.7 1.5 1.0 1.1 15.8 0.7 0.5 0.9 0.1 0.9 34.9 0.2 0.1 1.3 0.3 0.9 25.9
0.6 1.2 0.8 0.9 12.6 0.6 0.5 0.9 0.1 1.0 35.9 0.3 0.1 1.5 0.5 1.1 33.6
0.7 1.4 0.9 1.1 14.6 0.7 0.5 1.0 0.1 1.0 35.7 0.2 0.1 1.4 0.4 1.0 28.4
0.5 1.2 0.8 0.9 12.2 0.6 0.5 0.9 0.1 1.0 35.8 0.2 0.1 1.5 0.5 1.2 34.8
0.6 1.3 0.9 1.0 13.9 0.6 0.5 0.9 0.1 1.0 36.0 0.3 0.1 1.4 0.4 1.0 29.9
0.6 1.2 0.8 0.9 12.4 0.6 0.5 0.9 0.1 1.0 36.4 0.3 0.1 1.5 0.5 1.2 33.5
0.6 1.3 0.9 1.0 13.4 0.6 0.5 0.9 0.1 1.0 35.8 0.3 0.1 1.4 0.4 1.1 31.6
0.5 1.2 0.8 0.9 12.0 0.5 0.5 0.9 0.1 1.0 35.8 0.3 0.1 1.5 0.5 1.2 34.9
92.0
90.9
92.0
90.1
92.0
91.8
91.6
92.0
90.5
91.5
91.7
2.1 0.1 0.4 0.1
C164n3 Cleo C181n9 Cl82n6 C183n6 C183n3 Cl84n3 CZ0ln9 C202n6 C204n6 C203n3 C204n3 C205n3 C22:lnll C22ln9 C21:5n3 C225n6 C225n3 C22:6n3
1.2 0.3 0.8 25.5
identified
94.7
0.6 1.5
1.0 1.1 15.9 0.7 0.4 0.9
nd 1.1 34.6 0.1
nd
0.9 0.1 0.2 0.1
1.9 0.1 0.4 0.1
P = 10.08 MPa
1.0 0.1 0.2 0.1
0.7
nd
nd
nd
0.4 0.3 2.1 1.5 2.7
0.5 0.3 2.5 1.8 3.2
0.4 0.3 2.1 1.4 2.6
0.05 0.1 0.1
nd, not detected. * Phytanic acid ethyl ester coincides with CIB:~. Table 5. Composition (mass %) of the Urea-Fractionated Fish Oil Ester Mixture of the Vapor and Liquid Phases on a COz-Free Basis at the Temperature of 343.2 K
P = 10.08 MPa component i c140
12-Me-Clr:o C14ln5 C15ln5 C160 C16:lnl 14-Me-Cle:o C162b c16:3
C164n3 Cl80 C181ns Cl82n6 C183n6 C183n3 C184n3 C20ln9 C202n6 C204n6 C203n3 C20:4n3 C205n3 C221n11 C22:lng C21:5n3 C22:5n6 c225n3
C226n3 identified (I
xi
yi
P = 12.57 MPa Yi
Xi
P = 14.99 MPa Yi
xi
P = 17.58 MPa Yi
Xi
P = 19.95 MPa Yi
3.2 0.2 0.6 0.1
0.9 0.1 0.2 0.1
3.3 0.2 0.6 0.2
0.8 0.1 0.2 0.1
2.1 0.1 0.4 0.1
0.8 0.1 0.2 0.1
1.8 0.1 0.3 0.1
0.7 0.1 0.2 0.1
1.2 0.1 0.2 0.1
nda
nd
nd
nd
0.01
nd
nd
nd
nd
1.0 0.7 4.2 3.4 6.0
0.5 0.3 2.4 1.7 3.1
1.1 0.7 4.7 3.7 6.7
0.5 0.3 2.3 1.6 2.9
0.8 0.6 3.8 2.8 5.1
0.4 0.3 2.3 1.5 2.8
0.8 0.5 3.6 2.5 4.5
0.4 0.3 2.2 1.5 2.7
0.6 0.4 2.9 2.1 3.8
nd
0.03
0.0~
0.03
0.04
0.03
0.04
0.0~
0.03
0.7 1.6 1.1 1.2 16.0 0.7 0.4 0.9 0.1 1.1 32.3 0.1 0.02 1.1 0.3 0.8 23.7
0.6 1.3 0.8 1.0 13.1 0.6 0.5 0.9 0.1 1.0 35.7 0.3 0.1 1.5 0.4 1.1 32.3
0.8 1.7 1.2 1.3 17.9 0.8 0.4 0.9 0.1 0.8 32.5 0.2
0.7 1.6 1.1 1.2 16.2 0.7 0.5 0.9 0.1 0.9 34.2 0.3 0.1 1.2 0.3 0.9 24.3
0.6 1.2 0.8 0.9 12.6 0.6 0.5 0.9 0.1 1.0 35.9 0.2 0.1 1.5 0.4 1.1 33.6
0.7 1.6
20.4
0.6 1.2 0.8 0.9 12.7 0.6 0.5 0.9 0.1 1.0 35.9 0.3 0.1 1.5 0.5 1.1 33.3
1.0 1.1 15.7 0.7 0.5 0.9 0.1 1.0 35.1 0.2 0.1 1.3 0.3 0.9 25.8
0.6 1.2 0.8 0.9 12.4 0.6 0.5 0.9 0.1 1.1 35.9 0.3 0.1 1.5 0.4 1.1 34.1
90.6
91.6
90.7
91.7
90.2
91.9
91.3
91.0
0.0~ 1.1 0.2
0.7
Xi
0.6 1.4 0.9 1.1 14.5 0.6 0.5 0.9 0.1 1.0 35.7 0.3 0.1 1.4 0.4 1.0 28.9
0.6 0.04 0.1 0.1 0.02 0.4 0.3 2.0 1.3 2.4 0.02 0.5 1.1 0.8 0.9 11.8 0.5 0.4 0.9 0.1 1.1 35.9 0.3 0.1 1.5 0.5 1.2 35.5
91.2
91.8
P = 22.58 MPa Yi 1.1 0.1 0.2 0.1
xi 0.7 0.1 0.2
nd
0.06 nd
0.6 0.4 2.8 1.9 3.5
0.4 0.3 2.2 1.5 2.7
0.0~
0.0~
0.6 1.4 0.9 1.0 13.9 0.6 0.5 0.9 0.1 1.0 35.7 0.2 0.1 1.4 0.4 1.0 30.2
0.5 1.2 0.8 0.9 12.2 0.5 0.5 0.9 0.1 1.0 35.9 0.3 0.1 1.5 0.5 1.2 34.4
91.9
91.7
nd, not detected. Phytanic acid ethyl ester coincides with C16:~.
respectively, given as the mass dissolved divided by the mass of carbon dioxide. The K-values on a C02-free basis at 343.2 K of C14:0,C164n3, C18:4~3,C20:5n3, and C22:cn3from the original and the urea-fractionated mixtures are plotted against the system pressure in Figures 8 and 9. The figures show how the various FAEEs separate depending on the
composition of the mixture. In the original mixture C,,,, is roughly speaking equally distributed between the two phases, while C20:bn3is predominantly in the liquid phase. In the urea-fractionated mixture, however, C18:4n3will be concentrated in the vapor phase, and the distribution of C205n3 is now nearly equal between the two phases.
Ind. Eng. Chem. Res., Vol. 33, No. 6, 1994 1579
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Pressure P (MPa) Figure 8. K-values on a COz-free basis from the original FAEE C14..0,(0) Cle:4,,3, (Q) C18:4n3, mixture (Staby, 1993)at 343.2 Kfor (0) (0) C20:6n3, and (A) C22:6"3 as a function of pressure.
eel has been measured. The experimental conditions ranged from 8 to 26 MPa a t the temperatures of 313.2 and 343.2 K. Single runs were performed a t each pressure, but a calculation of the phase ratio at 22.5 MPa from the overall composition of the feed and the phase compositions showed good consistency. The compounds C18:dn3,C20:5n3, and C22:6,-,3account for more than 80 5% of the urea-fractionated mixture; however, 29 components including phytanic acid ethyl ester were identified. The mass-based equilibrium ratios displayed a strong dependence on the system pressure and on the composition of the FAEE mixture. The data show that better selectivities are obtained at 343.2 K, than a t 313.2 K and the solubility measurements show that the solubility increases as the temperature increases. This makes 343.2 K a more favorable separation temperature than 313.2 K. The optimal separation conditions in respect to both selectivity and solubility lie in the range of 16-18 MPa corresponding to carbon dioxide densities from 550 to 615 kg/m3.
Acknowledgment This work was supported by a grant from the Danish Research Council (STVF). We thank Grindsted Products for the supply of the original fish oil ethyl ester mixture and Steen Balchen and Benny Jensen of The Technological Laboratory, Danish Ministry of Fisheries, for the urea fractionation of the esters and for the chromatographic confirmation analysis. Literature Cited
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Pressure P (MPa) Figure 9. K-values on a CO2-free basis from the urea-fractionated Ci4:0, (0) C164n31 (6)C184n3, (0) FAEE mixture at 343.2 K for (0) C~0:5~3, and (A) C22:en3as a function of pressure.
The equilibrium ratios have changed significantly from the original mixture to the urea-fractionated mixture, demonstrating the dependence of the K-values on the composition of the feed material. The highest selectivity in both systems is at approximately 12.5 MPa, where the solubility of the FAEEs is low. Thus, optimal separation conditions must be chosen in respect to both solubility (Figure 2) and selectivity (Figure 9).
Arai, K.; Saito, S. Fractionation of Fatty Acids and Their Derivatives by Extractive Crystallization Using Gas as a Solvent. Paper Dresented at the World Congress - I11 of Chemical Engineering, Tokyo, 1986. Bimbo, A. P.; Crowther, J. B. Marine Oils: Fishing for Industrial Uses. Inform 1992, 3, 988. Haagsma, N.; van Gent, C. M.; Luten, J. B.; de Jong, R. W.; van Doorn, E. Preparation of an w3 Fatty Acid Concentrate from Cod Liver Oil. J. Am. Oil Chem. Soc. 1982,59, 117. Krukonis, V. J. Processing with Supercritical Fluids. Overview and Applications. In Supercritical Fluid Extraction and Chromatography, Techniques and Applications;ACS Symposium Series 366; Charpentier, B. A., Sevenants, M. R., Eds.; American Chemical Society: Washington DC, 1988. Staby, A. Application of Supercritical Fluid Techniques on Fish Oil and Alcohols. Ph.D. Thesis, Technical University of Denmark, Lyngby, Denmark, 1993. Staby, A,; Mollerup, J. Measurement of Solubilities of 1-Pentanol in Supercritical Ethene. J. Supercrit. Fluids 1991, 4 , 233. Staby, A,; Mollerup, J. Separation of Constituents of Fish Oil Using Supercritical Fluids: A Review of Experimental Solubility, Extraction, and Chromatographic Data. Fluid Phase Equilib. 1993a, 91, 349. Staby, A.; Mollerup, J. Solubility of Fish Oil Fatty Acid Ethyl Esters in Sub- and Supercritical Carbon Dioxide. J.Am. Oil Chem. SOC. 199313, 70, 583. Staby, A.; Forskov, T.; Mollerup, J. Phase Equilibria of Fish Oil Fatty Acid Ethyl Esters and Sub- and Supercritical COz. Fluid Phase Equilib. 1993,87, 309. Received f o r review October 26, 1993 Revised manuscript received March 21, 1994 Accepted March 29, 1994'
Conclusion The phase equilibrium behavior of supercritical carbon dioxide and urea-fractionated fish oil FAEEs from sand
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Abstractpublished in Advance ACS Abstracts, May 1,1994.
