DRYING OILS FROM LIQUID FATS Fractionation by Solvent Extractions A. W. ICLEINSMITH AND H. R. ICRAYBILL Purdue University Agricultural Experiment Station, Lafayette, Ind.
Corn, cottonseed, soybean, and linseed oils have been separated into fractions of widely different degrees of unsaturation by liquidliquid extraction with methanol. The more unsaturated fractions of soybean oil are better suited for use as drying oils than the original oils. No evidence could be found for the presence of any completely saturated glycerides in soybean oil. The fractionation of fats by solvent extraction is a valuable tool in the study of glyceride composition of fats. Fatty acids of soybean oil arenot distributedin truerandom fashion or in true maximum even distribution.
they laid the groundwork for solvent extraction of liquid fats. Yamada (84) sepmated a rather highly unsaturated fraction from soybean oil by crystallizing the latter from acetone at -20” C. Edeleanu ( 5 ) procured a drying oil from soybean oil by extracting this material with liquid sulfur dioxide. Freeman (7) employed many different types of organic solvents to fractionate the glycerides of liquid fats. Kraybill, Thornton, and Eldridge (15) separated sterols from soybean oil by extracting the latter with methanol. I n so doing, they separated the oil into two portions, an extract and a residue. The data presented in this paper represent the results of an investigation of the chemical make-up of these fractions. EXTRACTION AND ANALYSIS
All oils were first subjected to the refining method developed by Xraybill et al. ( 1 5 ) to remove the “break” material. This consists essentially of atering the oil through a sodium aluminum silicate gel which adsorbs the phosphatides and part of the sterols. An ordinary liquid type extractor was used which is designed for extracting a liquid with a solvent lighter than the liquid to be extracted. In each case a sample of oil weighing approximately 1.5 kg. was separated at 25” C. into seven or eight fractions. After removal of the solvent, each fraction was analyzed. Iodine numbers were determined according to the method of Wijs ( 3 ) . Refractive index determinations were made at 25’ C. in the Abbe refractometer (5). Saturated fatty acids were determined both by the crystallization method of Milner and Earle ( 1 6 ) and the oxidation procedure of Bertram (16, 18). The methods of the American Oil Chemists’ Society ( 8 ) were followed in determining unsaponifiable matter and thiocyanogen number; the procedure developed by Hilditch (11) was used in analyzing for fully saturated glycerides. From the iodine number, thiocyanogen number, and saturated fatty acid value of the acids separated from each fraction, the percentage of oleic, linoleic, and linolenic acids in each was determined. In these calculations the iodine and thiocyanogen numbers of linoleic and linolenic acids as given by Iiass et al. (12, IS) were employed. For the drying time tests 5 grams of oil were weighed into a 50ml. beaker. Then 0.0833 gram of Nuodex manganese drier (equivalent to 0.10 per cent manganese) was stirred into the oil, and 0.0521 gram of Nuodex lead drier (equivalent to 0.25 per cent lead) was added with stirring. The oil-drier mixture was applied t o a smooth glass plate (3 X 4 inches) by means of a Park’s filmograph calibrated to yield a film 0.003 inch thick. The plate was then placed in a sloping position (approximately 45’ angle) in a cabinet at 80” F. in which the humidity mas maintained approximately constant (about 55 per cent) by a saturated solution of magnesium nitrate. An electric fan clrculated the air over the latter solution. After 2 hours the films were checked at half-hour intervals until they were dry t o the touch.
URING the past decade the paint and varnish industry has encountered serious raw material shortages due to interruptions in the flow of drying oils from foreign sources of supply. Chemists have sought to make the industry less dependent upon these liquid fats by finding methods for converting available oils into products usable in protective coatings. The many lines of attack may be classified under two general headings-chemical and physical. Chemical procedures include halogenation and dehalogenation, dehydration, introduction into the liquid fat of hypochlorous acid followed by dehydration and dehalogenation, and separation of fatty acids into nondrying and drying fractions followed by conversion of the latter into drying oils. Physical means include molecular distillation and solvent extraction. Gardner and Bielouss (9) used chlorination in conjunction with dechlorination to produce a n improved drying oil from soybean oil. Scheiber (21), Schwarcman (26), and many others dehydrated castor oil catalytically to obtain a drying oil. Munzel(4,17) treated dehydrated castor oil with hypochlorous acid. By removing water and hydrogen chloride from the resulting product, he obtained a material resembling tung oil in physical and chemical properties. Stingley (W) converted liquid fats into glycerol and fatty acids; he then separated the acids by distillation into drying and nondrying METHANOL EXTRACTIONS fractions, and resynthesized the latter into drying oils. SOYBEANOIL. For a long time the idea prevailed that Rawlings (29) subjected corn and soybean oils to molecular natural fats are mixtures of simple triglycerides; this notion distillation but failed to fractionate the glycerides to any great has been discarded. It has been replaced by the more modern extent. Using the same technique, Fawcett (6) likewise was view that these materials are mixtures of mixed triglycerides unable to separate appreciably the glycerides of cottonseed oil. and that the fatty acids of seed fats are distributed among the On the other hand, Riemenschneider, Swift, and Sando (20) glycerides as widely and evenly as possible. Because of this effected a marked separation of the latter oil by molecular latter idea, attempts to separate by physical means the condistillation. stituents of natural fats have not been considered promising, Heise (IO), Fritzweiler (8), Klimont ( I d ) , Amberger ( I ) , even though early workers isolated various glycerides from and others showed by crystallization methods that fats can fats by crystallization methods. be more or less separated into their components. Thus, 674
D
OF CRUDEAND REFINED EXPELLER SOYTABLE I. PROPERTIES BEAN OIL AND OF FRACTIONS FROM THE REFINED OIL
%.of
Weight Grams'
Bample Crude Refined Extract Residue
Or%?'
..
iiio
235 895
26:s 79.2
Iodine Number 131.7 132.1 139.5 128.9
Dryin Time,
&.
9.25 8.25
5
9.5
TABLE11. PROPERT~ES OF EXTRACTS AND RESIDUESFROM METHANOL EXTRACTIOK OF REFINEDEXPELLER SOYBEAN OIL f , Orig&;lOil
Weight, Grams 968 36
Sample Oil Extract 1 Residue 1 Extract 2 Residue2 Extract3 Residue3 Extract4 Residue4 Extract5 Residue5 Extract6 Residue6
....
3.7
..
....
127
13.1
, ,
..
.... 24.5 ....
237
... 141 . .. 286 .. . .27. .
.. ....
14.6 29.5
2.8 ....
Iodine Number 132.6 139,Q 132.3 141.5 131.4 138.2 126.9 128.7 119.4 123.4 99.8 103.5 94.3
Saturated Acids.
%
14.1 9.77 1.
9.99
... .. 12.55 .. 13.97 ..
11.02
18.40 26.55
Table I shows that soybean oil can be partially separated into its constituents by physical means. A refined expeller soybean oil with an iodine number of 132.1 was divided by methanol extraction into two portions, an extract and residue, which had iodine numbers of 139.5 and 128.9, respectively. The difference in the degree of unsaturation of these oils showed up clearly in drying tests. The extract dried within 5 hours to a film relatively free from tack. On the other hand, the residue and refined oil required 9.5 and 8.25 hours, respectively, to yield tacky films. Table I1 presents the results of an experiment designed to follow the decrease in unsaturation of the liquid fat when the latter is subjected to continuous methanol extraction. From a refined expeller soybean oil were separated six extracts which showed variations in iodine number and saturated acid content from 139.9 to 103.5 and from 9.77 to 18.40 per cent, respectively. Iodine number determinations on small samples of the residue taken after the separation of each extract revealed a continuous decrease in the unmturation of the oil, the iodine number falling from 132.6 for the original oil to 94.3 for the h a 1 residue. A saturated fatty acid determination showed this final residue to contain 26.55 per cent saturated fatty acids. A sample of refined expeller soybean oil was resolved into eight fractions (Table 111). The iodine numbers showed a maximum of 140.9 and a minimum of 108.4; the refractive indices showed a corresponding change from 1.4751 to 1.4710. The unsaponifiable matter amounted t o 2.21 per cent of the first extract and 0.64 per cent of the second. The average value of this material for the next five fractions was 0.4 per
TABLE 111. r
Sample
675
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June, 1943
Weight, grams 1600
Oil Fraction No. 1 231 2 181 3 190 4 201 5 220 6 210 7 193 8 174
cent; for the final residue it was 0.60 per cent. In the case of the mixed fatty acids isolated from each fraction, the saturated acids ranged from 12.38to 23.19 per cent, the oleic from 20.27 to 30.64, the linoleic from 60.28 to 43.49 per cent, and the linolenic from 8.93 to 2.67 per cent. The results of re-extracting the more highly unsaturated and saturated fractions isolated from a refined solvent soybean oil are given in Table IV. From a refined oil were separated an extract l-E and a residue l-R; re-extraction of l-E yielded a second extract, 2-E, and this in turn gave a third extract, 3-E. From residue 1-R was isolated fraction 2-R. This oil did not contain any fully saturated glycerides. OTHERVEGETABLE OILS.Table V presents experimental data on the methanol extraction of three other vegetable oils. From samples of refined linseed, corn, and cottonseed oils were isolated fractions varying in iodine number from 189.6 to 134.6, 134.3 to 112.2, and 110.8 to 81.3, respectively. The refractive indices of the corn and cottonseed fractions in changing from 1.4738 to 1.4713 and from 1.4714 to 1.4680, respectively, varied in a linear manner with iodine number. The refractive indices of the first seven linseed oil fractions dropped from 1.4834 to 1.4815 and likewise changed linearly with iodine number. However, the refractive index of the eighth fraction rose to 1.4851, greater than that of the most highly unsaturated extract. This peculiar behavior may have been due to the concentration of impurities in this residue during extraction. SOYBEAN OIL EXTRACTION WITH OTHER SOLVENTS
To separate the components of a liquid fat effectively, a solvent must be substantially immiscible with the oil. This immiscibility depends largely on the number of polar groups in the solvent molecule and on the temperature of extraction. The relative effectiveness of several different types of organic solvents in partially separating the glycerides of a sample of solvent soybean oil is indicated by Table VI. I n addition to furfural, the lower aliphatic nitriles, esters, nitro compounds, aldehydes, ketones, and alcohols were found useful. Of the compounds tested, nitroethane, acetonitrile, and methyl formate proved particularly effective; 1- and 2-propanol failed to produce any appreciable fractionation of the oil. DISTRIBUTION OF SOYBEAN FATTY ACIDS
Ordinary soybean oil contains about 14 per cent saturated fatty acids. If these acids were distributed in a random manner, this oil should contain about 0.25 per cent fully saturated glycerides. In any extraction of the oil with methanol, these compounds should be concentrated in the more highly saturated fractions in which they should be easily detected. Thus, since none of this type of glycerides was found in residue 2-R (Table IV) we may be reasonably sure of the absence of fully saturated glycerides in soybean oil and may conclude that the acids of soybean oil are not distributed in true random fashion.
PROPERTIES OF FRACTIONS FROM REFINED EXPELLER SOYBEAN OIL AND
Fractions from Refined Oil b .of Refractive original Iodine index Unsaponioil number (25O C.) fiable. % 132.5 1.4733 0.68
..
14.4 11.3 11.9 12.6 13.7 13.1 12.1 10.9
140.2 140.9 139.7 137.4 134.3 131.2 123.0 108.4
1.4751 1.4744 1.4746 1.4740 1.4733 1.4729 1.4722 1.4710
2.21 0.64 0.43 0.35 0.36 0.41 0.44 0.60
Iodine number 136.3 146.7 146.1 144.7 142.6 139.5 135.0 127.7 113.6
DISTRIBUTION OF FATTY ACIDS
Fatty Acids Isolated from Fractions ThioEatd. Unsatd. Oleic cyanogen acids, acids, acid, number % % % 84.1 14.54 85.46 25.07 88.1 88.8 87.1 86.7 85.5 82.6 80.1 73.9
12.38 12.93 13.06 13.79 14.25 15.66 17.37 23.19
87.62 87.07 86.94 86.21 85.75 84.44 82.63 76.81
20.27 21.73 20.65 22.05 23.62 23.60 27.27 30.64
Linoleio acid, 70
Linolenic acid,
%
55.08
4.81
60.28 56.41 59.66 56.97 55.88 56.89 52.14 43.49
7.07 8.93 6.62 7.16 6.25 3.94 3.21 2.67
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
676
Vol. 35, No. 6
3. The residues separated from soybean oil by methanol CHEMICAL STUDIES ON MOREHIGHLY UNSATURATED extraction are more highly saturated and more resistant to AND SATURATED FRACTIONS FROM REFINED SOLVENT SOYBE.4N oxidative and similar changes than is ordinary soybean oil. OIL These fractions may be better suited for edible purposes than Weight, Iodine F a t t y Acids from the original soybean oil since they may be made more stable t o Sample Grams No. Residue 2 reversion. 130.2 Iodine No. 9000 90.6 Oil 138.2 Thiocyanogen No. 1392 Extract 1-E 64.0 4. Extraction w&h methanol fractionates the unsaponifi32.2 Satd. acids, yo 142.6 684 Extract 2-E able matter from the glycerides of soybean oil. Unsatd. acids, % 145.8 67.8 Extract 3-E 136 Oleic acid, % 1078 106.4 36.82 Residue 1-R 5. Extraction with lower aliphatic alcohols, aldehydes, Linoleic acid 70 86.8 208 29.48 Residue 2-R Linolenic acid, % 1.50 ketones, nitriles, esters, and nitro compounds, as well as with furfural, preferentially separates the more highly unsaturated portions of soybean oil. 6. No evidence can be found for the presence of any comOn the other hand, if the fatty acids of this oil were displetely saturated glycerides in soybean oil. tributed according t o the rule of maximum even distribution, 7 . The fatty acids of soybean oil are not distributed in it should be impossible to separate fractions containing a true random fashion or in true maximum even distribution. higher percentage of oleic than linoleic acid. This becomes 8. Liquid extraction of fats is a valuable tool in the study clear when one realizes that this oil consists of about 55 per cent linoleic and only about 28 per cent oleic. With this of glyceride composition of fats and may be of practical value composition there is enough of the former acid for each glycerin separating fats into fractions for specific industrial uses. TABLE IV.
TABLEv. Sample Oil Fraction No. 1 2 3 4
5
6 7 8
Weight, grams 1833
PROPERTIES O F
REFINEDOILS
Linseed Oil % of original Iodine oil number 176.3
369 328 193 226 220 239 125 132
..
20.0 17.9 10.5 12.3 12.0 13.0 6.8 7.2
189.3 189.0 188.7 184.3 176.5 169.9 153.9 134.6
AND OF
Refractive index (25' C . ) 1.4832
Weight, grams 1500
1.4834 1.4831 1.4829 1.4828 1.4826 1.4822 1.4815 1.4851
181 197 168 248 211 262 230
...
FRACTIOR'S OBTAIXED %,of original oil
..
Weight, grams 1060
12.1 13.1 11.2 16.5 14.1 17.5 15.3
134.3 132.9 131.3 130.2 127.6 122.0 112.2
1.4738 1.4734 1.4731 1.4728 1.4728 1.4724 1.4713
181 170 172 180 174 158 24
SUMMARY
TABLEVI. EXTRACTION OF REFINED EXPELLER SOYBEAN OIL^ WITH ORGANIC SOLVENTS
Q
Iodine Number 136.1 132.3 130.4 133.4 134.0 138.2 136.9 135.5 135.1 144.2 142.6 139.8 141.4 135.1
Extn. Temp.,
c.
25 5 5
5 -15 25 15 5 25 5
-
25
..
...
.,..
Cottonseed Oil %,of original Iodine oil number 106.5
7 -
Refractive index (25' C.) 1.4728
1. Extraction with methanol separates preferentially the more highly unsaturated portions of soybean, corn, cottonseed, and linseed oils. 2. The extracts separated from soybean oil by methanol extraction are more highly unsaturated and have better drying properties than the original soybean oil. These fractions are better suited for use as drying oils than the original soybean oil.
Grams Extd. per 100 G Solvent 1.3 12.7 6.7 12.0 22.0 6.3 19.7 11.3 1.0 8.3 1.0 10.0 4.0 21.7
-
FROM THE11 B Y METHSNOL EXTRACTION
Iodine number 127.0
ide to hold a linoleic acid radical and for part of the glycerides to hold two linoleic radicals; there is not even enough oleic acid for each glyceride to hold one of the latter acids. Since the fatty acids isolated from residue 2-R contained more oleic than linoleic acid, we may conclude that the acids of soybean oil are not distributed according to the rule of true maximum even distribution.
Solvent 95% ethanol 1-Propanol 2-Propanol Acetaldehyde Crotonaldehvde Furfural Acetone Diaoetone Nitromethane Nitroethane Acetonitrile Propionitrile Methyl formate E t h y l formate Iodine number, 132.5.
Corn Oil--
...
..
17.1 16.0 16.2 17.0 16.4 14.9 2.3
Refractive index (25O C.) 1.4701
110.8 110.8 110.5 108.7 104.4 96.4 81.3 I
.
.
1.4714 1,4705 1.4696 1.4698 1.4697 1.4694 1.4680
....
LITERATURE CITED
(1) Amberger, C., 2. Untersuch. Nahr. u. Genussm., 40, 192-201
(1920). (2) Am. Oil Chem. SOC.,Official and Tentative Methods, 1938. (3) Assoo. of Official -4gr. Chem., Official and Tentative Methods of Analysis, 4th ed., 1935. (4) Blom, 9.V., Paint Oil Chem. Rev.,101,No.15, 9 (1939). (5) Edeleanu G. m. b. H., German Patent 669,620 (Dec. 30, 1938). (6) Fawcett, E. W. M., J . SOC.Chem. I n d . , 58, 43-50 (1939). (7) Freeman, S. E., U. S. Patents 2,200,390-1 (May 14, 1940). (8) Friteweiler, R., Arb. kaiserl. Gesundh., A18, 371-7 (1902). (9) Gardner, H. A., and Bielouss, E., J. IND. ENC.CHEIII., 14,619-21 (1922). (10) Heise, R., Arb. kaiserl. Gesundh., A12,540-6 (1896). (11) Hilditch, T . P., and Lea, C . H., J . Chem. SOC.,1927,3106-17. (12) Kass, J. P., Loeb, H. G., Norris, F. A., and Burr, G. O., Oil & Soap, 17, 118-19 (1940). (13) Kass, J. P., Lundberg, W. O., and Burr, G. O., Ibid., 17, 50-3 (1940). (14) Klimont, J. I., 2. Untersuch. Nahr. u. Genussm., 12,359 (1906). (15) Kraybill, H. R., Thornton, M. H., and Eldridge, K. E., IND. EXG.CHEDI., 32, 1138-9 (1940). (16) Milner, R.T., and Earle, F. R., Oil & Soap, 17,106-8 (1940). (17) Muneel, F., Swiss Patent 193,931 (April 1, 1.938); French Patent 830,494 (Aug. 1, 1938). (18) Pelikan, K. A., and Mikusch, J. D. von, Oil & Soup, 15, 14950 (1938). (19) Rawlings, H. W., Ibid., 16,231-2 (1939). (20) Riemensohneider, R. W., Swift, C . E., and Sando, C . E., Ibid.. 17,145-8 (1940). (21) Scheiber, J., German Patent 55,496 (Dee. 17, 1929); U. S. Patent 1,942,778 (Jan. 9, 1934). (22) Schwarcman, A., U. S. Patent 2,140,271 (Dec. 13, 1938). (23) Stingley, D. V., IND. ENG.CHEN.,32, 1217-20 (1940). (24) Yamada, T., J . SOC.Chem. Ind. J a p a n , 37, Suppl. Binding 190-2 (1934).
5
- 155 FROXthe Ph.D. thesis of A. 7' . ICleinsmith, Purdue University. Paper 33, Purdue University Agricultural Experiment Station.
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