US2571663A - Refining of fatty acids - Google Patents

Description

Patented Get. 16, 1951 l'iED STATES PATENT OFFICE.

REFINING 0F FATTY. ACIDS Ward J. Bloomer, Westfield, N. J assignor to The Lumrnus Company, New York, N. Y., a corporation of Delaware Application April 26, 1946, Serial No. 665,083

3 Claims.

This invention relates to the refining of fatty acids and particularly to an improved method of obtaining fractions of fatty acids having different characteristics. It is a continuation-in-part of my copending application Serial No. 402,363, filed July 14, 1941, entitled Solvent Fractionation of Fatty Acids, which is now abandoned.

Mixtures of fatty acids are generally comprised of both saturated and unsaturated members in varying proportions. The several acids present, in such a mixture of higher fatty acids derived from a vegetable, animal, or synthetic source usually include palmitic, stearic, oleic, linoleic, and linolenic; Other acids, both saturated and unsaturated, may also be present, however.

Fatty acids find a use in the manufacture of many products. For example, the metallic salts of palmitic, stearic, and oleic acids, particularly the sodium and potassium salts, form the various soaps. The unsaturated acids may be used in the preparation of synthetic resins and plastics. These acids also have many other important applications.

The fatty acids, when esterified with glycerine, form the corresponding glycerides, which are valuable either as food products or as drying oils according to the degree of saturation of the particular glyceride. The glycerides of palmitic and stearic acids, both of which are saturated, are

valuable as edible oils and are non-drying in nature. Although oleic acid contains a single double bond and, hence is unsaturated, its glyceride is also non-drying; this glyceride also finds use as an edible oil. The glycerides of linoleic acid and of linolenic acid, which respectively contain two and three nonconjugate double bonds, are good drying oils because of the increased activity of the double bonds. Elaeo-stearic and licanic acid glycerides contain several double bonds in conjugate relationship, in which positionthe double bonds are extremely active, and are very fastdrying oils.

In order to take full advantage of the different individual properties of the various acids present, it is highly desirable to separate such a mixture into fractions which are respectively relatively more saturated and relatively more unsaturated in nature. Heretofore, such a separation has been accomplished principally by distillation; but in this procedure there are the disadvantages that decomposition of some of the fatty acids usually occurs at the high temperatures necessary even though the distillation is effected under vacuum and that the fractionation accomplished may. not be so sharp as desired. Thense of -sol-;

vents to effect a separation of the saturated from the unsaturated fatty acids by a liquid-liquid phase separation as well as by a liquid-solid phase separation has also been proposed. Attempts in this respect have not been entirely satisfactory, however, because of certain operating or other disadvantages in each particular instance.

A specific object of my invention is to separate soybean fatty acid mixtures into fractions-comprising the relatively more saturated and the relatively more unsaturated constituentssothat the respective acids may be moreadvantageously utilized.

Other objects and advantages of my invention will appear from the following description thereof taken in connection with the accompanying drawing in which the single figure is-a diagrammatic flow sheet of a process embodying m invention.

In carrying out my invention, I bring the mixture of fatty acids and the solvent into intimate contact to produce a solution of fattyacids. This solution is gradually cooled and chilled until the desired amount of the relatively more-saturated acids precipitates or separates out. This insoluble material is then separated from the remaining liquid by filtration or the like. The solvent retained in the filter cake and the filtrate is suitably recovered as by distillation, and the separated fatty acid fractions may then be utilized for their respective purposes.

In the following description reference is made to the solvent fractionation of soybean fatty acids. Soybean fatty acids may be derived from soybean oil, which in turn has been extracted from the soybean, by splitting the oil, which consists of glycerides of the fatty acids, into glycerine and the free fatty acids by hydrolysis in the presence of steam. For convenience, the approximate composition of soybean fatty acids is given below (see- Chemical engineering advances in soybean processing by Gordon W. McBride in Chemical and Metallurgical Engineering, vol. XLVII, No. 9 (September 1940), pp. 614, 618) As shown. in the accompanying drawing, the

, mixture of fatty acids. is introduced into the system at In. Inasmuch as these fatty acids will be substantially liquid at the usual atmospheric temperature, they can be readily pumped through line by pump l I. A suitable solvent from line [2 is added to the fatty acids, and the resulting mixture is thoroughly agitated in mixer I4 to insure that the fatty acids are completely dissolved in the solvent. If desirable or necessary, the mixture of fatty acids and solvent may be slightly heated in order to effect complete solution. In such case, mixer l4 may be dispensed with, and the mixture may be circulated through a heat exchanger (not shown), wherein the desired heat is provided and the turbulent flow insures complete solution.

In accordance with my invention, the solution of fatty acids is then passed through heat exchanger [6 wherein its temperature is considerably lowered. The cooled solution then flows through line [1 to chiller l8, through which ammonia is preferably circulated as by line l9 as the heat-removing medium in indirect contact with the solution. In chiller I8 the temperature of the solution is lowered sufiiciently to precipitate out the portion of the fatty acids which it is desired to separate from the original mixture.

The portion of the acids which separates out from the soybean fatty acids comprises the relatively more saturated fatty acids and consists of palmitic and stearic acids as well as some oleic acid whereas the fatty acids remaining dissolved comprise oleic, linoleic, and linolenic.

The chilled mixture containing the precipitated fatty acids is accumulated in surge tank 20,

from which it is continuously passed to rotary that used to form the initial solution, serves to displace the greater portion of the relatively more unsaturated fatty acids which are retained in the filter cake. The wash solvent filtrate may be removed from the filter through line 3| into receiver 32. The filter cake may be continuously removed from the filter surface as by a, scraper knife (not shown) and may be discharged by screw conveyors 34 into hopper 35. This hopper is preferably provided with a steam coil 36 or the like so that the filter cake may be melted down for convenient disposal.

It will be appreciated that the application of my invention is not limited to the use of a rotary or other special type filter. Furthermore, either pressure or vacuum filtration may be used; the choice of the particular system used will depend primarily on the amount of acids precipitated and on the efliciency of the washing step. It may also be found desirable to use a flue gas system (not shown) to blanket the surge tank 20, wash solvent tank 29, filter 22, receivers 26 and 32, and hopper 35 in order to make the apparatus fireproof and explosion-proof.

For recovery of the solvent, the filtrates collected in receivers 26 and 32 may be combined, and the resulting mixture may be passed through A line 38 as by pump 39 to exchanger l6 wherein it serves to lower the temperature of the incomins solution of fatty acids.

The combined ill-- trate is then heated in heater 4!! to a temperature above the boiling point of the solvent and is introduced into the upper part of distillation tower 4| wherein the greater portion of the solvent is separated from the relatively more unsaturated fatty acids. This distillation may be accomplished at atmospheric pressure or under vacuum produced by vacuum pump 42 as desired. Dry solvent is removed overhead and is condensed in condenser 43. The net condensate is discharged through line 44 into receiver 46, from which solvent is withdrawn through line 41 as by pump 48 and passed through line I2 to be mixed with the incoming fatty acids in line In. The relatively more unsaturated fatty acids are preferably introduced by means of trapped line into the lower part of distillation tower 4|, which may also be operated under vacuum. Imperforate plate 50 serves to separate the two parts of the tower from each other. Stripping steam may be introduced through line 51 to aid in the removal of the remainder of the solvent from the unsaturated fatty acids, which may be removed as a bottoms product through line 52. The wet solvent vapors may be removed from the lower part of tower 4| through line 53 for introduction into a system (not shown) for dehydration of the solvent.

The melted filter cake of relatively more saturated fatty acids may be pumped through line 55 and heater 56 as by pump 51 and is introduced into the upper part of distillation tower 58 for separation of the greater portion of the solvent therefrom. This distillation may likewise be carried out at atmospheric pressure or under vacuum produced by vacuum pump 42. Dry solvent is taken off overhead and condensed in condenser 60 the net condensate is discharged through line 6| into receiver 46. The relatively more saturated fatty acids are preferably introduced by means of trapped line 62 into the lower part of tower 58 wherein the remaining solvent is separated therefrom. This part of the tower may also be operated under vacuum and is also separated from the upper part of the tower by imperforate plate 64. Stripping steam may also be introduced at 65 to aid in the removal of the remainder of the solvent from the relatively more saturated fatty acids, which are removed as a bottoms product through line 56. The wet solvent vapors may be discharged through line 68 into the solvent dehydration system (not shown). It will be appreciated that, in place of heaters 40 and 56, heat exchangers utilizing steam as the heating medium may be employed.

Wash solvent is provided by withdrawing a portion of the solvent from receiver 46 and passing it through lines 41 and 10 as by pump 48 into tank 29, from which it is discharged through line 28 into filter 22 for washing of the fatty acid filter cake. This wash solvent is preferably cooled in exchanger 'H by indirect contact with a cooling medium circulated through line 12.

In the solvent fractionation of soybean fatty acids, melting point 65 F., iodine number (Wijs) 137.3, I have found that ethyl alcohol is particularly eifective as a selective solvent. With a solvent ratio of 3:1 and a wash ratio of 2:1 at a filtering temperature of -l0 F., 84.3% filtrate of unsaturated fatty acids having an iodine number of 157.4 and a pour point of 5 F., and 15.7% filter cake of saturated fatty acids having an iodine number of 8.2 and a melting point of 122 R, were obtained in a single pass.

It will be appreciated that the ultimate yields and efiiciencies of separation will depend to a large extent on the solvent ratio (ratio of solvent to fatty acid feed) and the wash solvent ratio (ratio of wash solvent to fatty acid feed) used. In operating my improved process, I prefer to use a solvent ratio of 3:1 although the range of solvent ratio may extend from 0.5:1 to 6:1. The ratio of wash solvent is preferably 2:1, but ratios ranging from 0.5:1 to 4:1 may also be used. The solvent ratio and the wash ratio used will depend primarily on the balance of the fatty acid separation obtained against the cost of recovery and refrigeration of the solvent used. In addition, the solvent ratio used will depend on the concentration of saturated acids in the feed and the filtering temperature.

I also find it desirable in some cases to recycle chilled filtrate solution, as by line 38a to the feed to increase the ratio of liquids to solids to improve the liquid solid separation and provide a more efficient cake thickness and more effective crystallization.

Although I have shown and described a preferred manner of carrying out my invention, I am aware that modifications may be made thereto; therefore, only such limitations as appear in the claims appended hereinafter should be applied.

I claim:

1. The method of resolving a mixture of the fatty acids derived from soy bean oil into a fraction containing substantially only unsaturated acids and a second fraction containing substantially only saturated acid which comprises feeding a mixture of the fatty acids having an iodine number of approximately 137 (Wijs) to a mixing device and mixing said acids With non-toxic ethyl alcohol, reducing the temperature of said mixture to below F., continuously filtering said mixture, washing the filter cake and separating as a filtrate approximately 85% of the charge as unsaturated acids having an iodine number in excess of 160 from the remainder of the charge as saturated acids having an iodine number less than 10.

2. A process for the separation of fractions of saturated acids from fractions of unsaturated fatty acids in a mixture of soybean fatty acid, which comprises dissolving the mixture in 95% ethyl alcohol with a solvent ratio of three parts of alcohol to fatty acid, cooling the solution to below 0 F. to efiect precipitation of the saturated acid fraction, making a liquid solid separation to separate the saturated acid fraction from the remaining liquid containing the unsaturated acid fraction, separately recovering the solvent from said fractions and washing said relatively saturated acid fraction with said recovered solvents, said wash ratio being at least 2:1 whereby a saturated fatty acid fraction of 8.2 iodine number and an unsaturated fatty acid fraction of 157.4 iodine number are recovered in one pass.

3. The method of making a fractional cut in the oleic acid range of a soya fatty acid to separate completely all higher unsaturated components from all saturated components, said acid having a general range of 13% saturated components and higher unsaturated components whereby a high yield of a product having an iodine number of nearly and the balance of a product having an iodine number of less than 10 may be simultaneously obtained in a once through operation, which comprises mixing from between two and four parts of ethyl alcohol with the fatty acid at temperatures at which the mixture is fluid, thereafter sub-cooling said mixture to a temperature in the range of from 20 F. to below 0 F. whereby saturated components of the mixture are precipitated, continuously filtering the precipitated constituents from the liquid unsaturated components and the solvent, Washing the cake formed with additional solvent in the ratio of at least two parts of solvent to one of cake to liberate any retained unsaturated component, heating the filter cake to remove the solvent therefrom, separately heating the filtrate to recover the solvent therein, returning such solvents for primary use, and thereafter independently steam stripping the filtrate and filter cake to produce the desired end products and I wet solvent.

WARD J. BLOOMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,045,727 Rider June 30, 1936 2,113,960 Grote et a1. Apr. 12, 1938 2,291,461 Freeman July 28, 1942 2,293,676 Myers et al. Aug. 18, 1942 2,340,104 Brown Jan. 25, 1944

Claims (1)

1. THE METHOD OF RESOLVING A MIXTURE OF THE FATTY ACIDS DERIVED FROM SOY BEAN OIL INTO A FRACTION CONTAINING SUBSTANTIALLY ONLY UNSATURATED ACIDS AND A SECOND FRACTION CONTAINING SUBSTANTIALLY ONLY SATURATED ACIDS WHICH COMPRISES FEEDING A MIXTURE OF THE FATTY ACIDS HAVING AN IODINE NUMBER OF APPROXIMATELY 137 (WIJS) TO A MIXING DEVICE AND MIXING SAID ACIDS WITH NON-TOXIC ETHYL ALCOHOL, REDUCING THE TEMPERATURE OF SAID MIXTURE TO BELOW -10* F., CONTINUOUSLY FILTERING SAID MIXTURE, WASHING THE FILTER CAKE AND SEPARATING AS A FILTRATE APPROXIMATELY 85% OF THE CHARGE AS UNSATURATED ACIDS HAVING AN IODINE NUMBER IN EXCESS OF 160 FROM THE REMAINDER OF THE CHARGE AS SATURATED ACIDS HAVING AN IODINE NUMBER LESS THAN 10.

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