US2934547A - Method of separating fatty acids - Google Patents

Description

April 26, 1960 R. B. RUDDICK METHOD oF SEPARATING FATTY ACIDS Filed sept. 19. 1955 IN V EN TOR.

United Se@ Patenti 2,934,547 l. l METHOD or SEPARATING FA'rrY acms Ronald B. Ruddick, Rivera, Calif., assignor, by mesne assignments, to Emery Industries, Inc., a corporation l0f Ohio Application September 19, 1955, Serial No. 535,247

17 Claims. (Cl. 260-419) i Y Organic substances particularly"contemplated by the pre'sent'invention comprise fattyacidsv havingfgat jleast six carbon atoms per molecule and generally, fromA about 1 4 to 18 carbon atoms per molecule. These materials in their natural'state are largely in the form of glycerides, although they frequently include the free fatty acids or the fattyl acid esters of the higheraliphatic alcohols. As 'used herein, the term fatty acids is intended to include synthetically derived fatty substances as well as those occurring naturally or derived from natural products, the glycerides of such fatty acids, or other fatty acid esters. ACommercially important fatty acid substances general- 1y contain both saturated and unsaturated fatty acid components inmixed form. For example,saponication of vegetable oils and animal fats (which together are a primary source of fatty acids) generally yields in addition to glycerol a mixture of saturated acids such as stearic and palmitic acids and unsaturated acids such as oleic, linoleic and linolenic acids. After separation and evaporation of the water solution of glycerol, the free fatty acids are often distilled and further separated into the commercially desirable saturated and unsaturated components.

For years, separation of the mixed free fatty acidswas accomplished by solidifying the mixture in pans and wrapping the resultant cake in burlap bags and thereafter pressing the solidified mass in large hydraulic presses to remove the normally liquid unsaturated components. Such operations were not only slow and expensive, requiring careful control, but also were incapable of-providing clear separations of the mixed components due to mechanical entrainment and collapse of the cake. Even multiple pressings were unable to effect a satisfactory separation. In recent years, somewhat more satisfactory separation has been accomplished by treatment of the mixture with a solvent which at a stated temperature is selective towards the saturated fatty acid components, that is, the solvent. dissolves the unsaturated components but not the saturated components at the stated temperature. Thereafter the saturated components, which are present in solid or undissolved form, may be readily separated from the solution of unsaturated components. This latter process is exemplified in several United States patents, namely,

Grote, No. 2,113,960; Myers et al., No. 2,293,676; and Gee, No. 2,450,235. @Successful commercial operations basedon the processes of these patents involve heating the mixed fatty acids with the solvent to a temperature at which the mixture is completely dissolved, and there- ."Heretofore solutions of .dissolved fatty acids have been cooled in such processes by the use of large banksV of double pipe refrigerant coils, with the individual sections of each coil arranged in series to provide an extended chilling surface. A typical coil may comprise as many jas 50 lengths of concentric pipe, each 20 feet or more in length. y The fatty acid solution is caused to ilow through the inner ofthe pipes anda refrigerant at low temperature -is caused to liow in the annular space between the pipes. Through resultant heat transfer, the solution is gradually cooled causing crystals of stearic and palmitic acid to be deposited in a thin layer or film on the inner pipe surface. As this layer of crystals tends to interfere with heat transfer, some means is usually provided to break up the layer and to agitate the solution so that the tiny yparticles of crystalline material continue to ow with the stream of solution. For example, one such mechanism employs a central shaft provided with Scrapers mounted for `rotation within the pipe by systems of gears at the end of `each pipe section. Besides the considerable problms of mechanical maintenance, the crystalline fragments broken and dispersed in this manner are usually not of a size susceptible to being readily filtered and washed in large scale production so that continued chilling of the solution is necessary to effect growth of the dispersed fragments to a filterable size. This fact accounts for the unusual length of therdouble pipe refrigerant coils, which insure prolonged residence time for crystal growth. Moreover, excessive amounts of solvent are generally required since it has been found that when different chemicals are employed as the circulating refrigerant, for example, a brine or ammonia, leakage of refrigerant into the inner pipe may occur and thereby spoil an entire batch of fatty acids.

The present invention is directed to a solution of these particular problems of the prior art and to many additional problems as will appear. Accordingly, one object of the invention is to provide an entirely new method of vchilling a solution of intermixed fatty acids and solvent,

lized into a readily washable lterable form in a fraction of the time required by prior processes for the purpose, 4thereby achieving economies of labor and production costs heretofore impossible. Other objects and advantages of the present invention will be apparent from the following disclosure and from the drawing which -will enable a man skilled in the art to know how the invention is to be practiced.

Briey stated, the present invention is drawn to a method of rapidly chilling asolution of intermixed fatty acids and solvent by evaporating a substantial portion of the solvent under essentially adiabatic conditions and in the presence of very low absolute pressures, say 20 to 40 mm. of Hg or less, thereby causing crystallization of the normally solid fatty acid components with sufcient `rapidity to Vcause agglomeration of the crystals into a highly ilterable washable form. While the exact mechanism of formation of such crystalline agglomerates is lnot clearly understood, it is believed they result from a unique interlocking of the individual crystals due to the unusually rapid chilling. For example, when dissolved in'fromthree to ten volumes of a polar solvent, such as acetone or methyl alcohol at normal atmospheric temperatures,V evaporation of one-half to two volumes of the solvent (by reducing the ambient atmospheric pressure to below atmospheric) will rapidly chill the fatty acid mixture to a filtration temperature between about 0 F. and 14 F., causing the crystals to form into readily flterable and granular agglomerates in about 20 to not in excess of 'o 'o `GOVminutes. VBy subsequently maintaining solution temperatures at this low level, a clear, sharp separation of the saturated agglomerates from the dissolved unsaturated components may be readily obtained. Moreoven'by re- .lying on low pressure evaporation of solvent as the sole means of reducing solution temperatures, it is possible to obtain such separations without the extensive heat exchanger surfaces, Scrapers, and long periods of crystal lgrowth required by the prior art.

aaa-ausr- 1 crystalline structures are obtained constitutes the basis of this invention.

As noted above, the fatty acid substances which may be treated in accordance with the invention may vary considerably. In particular, the process of the invention is applicable to fatty acids obtained by various saponication processes from animal fats or vegetable tallows, cotton oils, soya oiis, bone fat, palm oil and otherY such materials. With respect to mixtures of fattyacids, for example, short chain materials such as coconut oil are as susceptible to successful separation as the longer chain materials such as menhaden and whale oil.

A suitable organic solvent for practicing the invention should be capable of completely and easily dissolving the fatty substances at temperatures between about 50 F. to 120 F. and at lower temperatures, say belowabout 30 F., should be capable of dissolving the unsaturated components more easily than the saturated components.`

`fere withv ,the desiredagglomeration of crystals and should be avoided.

According to the invention, the fatty acid substance is first dissolved in a quantity of polar solvent and thereafter is rapidly chilled by evaporation of a substantial portion of the solvent. The proportions of polar solvent to fatty acid will depend'to some extent on the character of the fatty acidsubstance being treated and also the temperature at ywhich the process is to be carried out. Thus considerable variation is frequently' encountered in the concentration of -various fatty materials; cotton and tallow fatty acids containing a greater proportion of solids than soya fatty acids, Y.for example. Moreover, at very low temperatures, more` solvent may be required to prevent the normally liquid unsaturated components from dropping out of solution. It has been found, in general,

that the most satisfactory results are obtained when the u proportionl of solvent to fatty acid mixture is within the range ofabout31l .to about 6:1 although good results can be had when as much as 10 parts of solvent are mixed with `each part lof fatty acid mixture. Preferably the amount of mixed fatty acids dissolved does not eX- n ceed about 30% by weight of the solvent solution.

i .of effecting evaporationof about 15% to 25% of the The solvent must also be capable of readily evaporating Although other solvents with higher boiling points may be used, a solvent with too high a boiling point will correspondingly require too high ak vacuum to get the lowk crystallization temperatures desired. Because their properties may readily and advantageously be adapted to the requirements of the invention, acetoneand methyl alcohol are the preferred solvents, It is to be noted that the polar solvents are normally liquid (i.e. are liquid at standard temperature and pressure conditions) and the process does not require superatmospheric pressures and is not subject to the hazards attendant the use of normally gaseous materials such as propane, butane, etc.

It is to be noted Vthat the present invention contemplates the use of solvent in substantially anhydrous form (i.e., containing less than about 1% water), as the presence of water is not a prerequisite to the formation of lterable crystalline agglomerates, In certain prior art processes, and particularly in the process set forth in the aforementioned patent to Myers et al., No. 2,293,676, substantial amounts of water must be present in the solvent or crystal growth in theV conventionalmanner will not occur. In the present process the formation of interlocked crystal agglomerates is entirely independent of the presence of water. may be present in the solvent without harmful effects;

in fact, under certain conditions, the presence of water in amounts up to 5%l of the volume of thersolvent may actually tend to assist in the separation of the saturated and unsaturated fatty acid components. 0n ,the other hand, `amounts of water above about 5% tend to inter.-I

Examples of suitable solvents include any of solvent, the temperature Vof the solution may be lowered with sufcient rapidity to achieve the desired interlocking of crystals into agglomerates of the saturated c ornponents. For example, by reducing absolute pressure to 20 mm. of Hg, evaporation of approximately 1/5 of the acetone presentin a mixed solution of 5 parts acetone and ltpart tallow fatty acids will achieve a filtration temperature of about 0 F. in no more than 15 to 25 minutes. Evaporation of a less amount of solvent will of course lessen thedegree of temperature lowering and prolong somewhat the period ofy crystallization. Generally, within the indicated range of subatmospheric pressures, chilling to filtration temperatures may be accomplished within from l0 to 40 minutes and in no event longer than 60 minutes andthereby achieve the desired formation and interlocking of the crystals.

Microphoto studies of the flterable agglomerates of the invention have revealed crystalline structures of much lgreater size although of less definition than is customary in the prior art. Thus, instead of relatively large, sharply defined individual crystals, the agglomerates appear to be formed of large numbers of tiny interlocked crystalline particles arranged in clusters of generally irregular or roughly ovoidal shape. Comparatively, the rapidly formed agglomerates approach a size approximately 3 to l0 times the size of individual crystals produced in the conventional manner by'prolonged crystal growth. For example, crystalline agglomerates ranging in dimension from about'l mm. to 1.5 mm. or larger are produced with regularity by the process of the invention, whereas growth of individual crystals to lengths (measured along the long axis) greater than about 0.2 mm. to 0.5 mm. is achieved by prior techniques only with considerable difficulty.

The operation of the process in producing satisfactorily filterable crystalline agglomerates will be clearly understood from the accompanying drawing and the following description thereof.` Polar, normally liquid sol- However, small amounts of water I vent for the process is fed by charge pump 10 through `line 12 toa suitable mixing tank 14. vSimultaneously a desired amount of fatty oil to be separated is charged through line 16 and proportioning pump 18 to the mixing tank, where the -solution is partially cooled. The cooled solution, preferably containing about ve volumes of polar solvent to eachy volume of mixed fatty acids, is pumped through line 20 and valves 21 and 23 into one .of `the crystallizers. .or .chilling tanks .22. These tanks.

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which Aarethoroughly insulated, are alternately filled at normal atmospheric pressures to approximately twothirds capacity-with the solution. Thereafter the inlet valvey is closed and exhaust valve 25 or 27 opened to subject the intermixed solvent and fatty acid to very low absolute pressures being pulled through line 24 by aV suitable source of vacuum 26. In the illustrated apparatus a multistage steam ejector and surface condenser system is employed to gradually reduce absolute pressures above the surface of the solution in the chiller to 20 to 40 mm.A of Hg or less, causing rapid evaporation of solvent. A refrigerated condenser 28 is preferably positioned before the evacuating means to recover vthe evaporated solvent for further use in the process, as will appear. Within the crystallizer continued evaporation of the solvent at theI low absolute pressure causes the solution temperature to be lowered in about 20 to 40 minutes to a temperature approaching equilibrium conditions at the absolute pressure withinvthe tank.. For example, at an absolute pressure of 20 mm. of Hg, acetone will rapidly cool to a temperature ofabout F. and, at 40 mm. of Hg, will cool at substantially the same rate to about 14 F. The resultant rapid chilling causes the formation of clusters or agglomerations of the normally solid fatty acid components in a highly filterable, washable form. Of course, the exact conditions of pressure, temperature and time will vary to some extent with the character of the feed, the solvent employed and the particular circumstances under which the system is operated.

lIn tank 22, the crystalline agglomerates of stearic acid, palmitic acid or other relatively high melting substances are maintained in suspension by the gentle agitation, as by stirrers 30, until the crystallization process has been completed. Thereafter, the chilled fatty acidl solvent solution containing the separated'solid components in suspension is discharged from the tank 22 by compressed air (passing from compressor 27a through line 29 and drier 31 to one of the valves 33 or 35). After crystallization has proceeded to completion, the fatty acid solution (containing about 8% to 12% solids) is fed by gravity ilow through one of the lines 32 to a hold tank 34 maintained at substantially the chilling temperatures in the crystallizer. Any suitable means may be employed for this purpose, such as ammonia refrigerant in coils or a jacket about the tank or by effective insulation. As desired, the mixture of dissolved unsaturated acids and agglomerated crystals of saturated acids is fed, again by gravity flow, through line 36 to a suitable mechanical filterA 38. Gravity iiow between the crystallizer and hold tank and the lhold tank and filter is important in preventing mechanical shear or heating of the crystal clusters, ,which normallyA occurs in pumps or othermcirculating devices.

In the filter 38, the saturated fatty acid granular agglomerates are separated from the unsaturated components remaining in solution. Although any suitable filtering apparatus may be employed, a continuous string discharge filter or other rotary drum type filter is preferred. The lter cake is washed with cold solvent, preferably entering the filter through line 40 from a second refrigerated hold tank 42 in communication with the condenser 28. The effect of the cold solvent wash is to remove any residual unsaturated fatty acid components occluded within the crystalline mass. The filter cake is then discharged and the washed crystals conveyed to a melt tank 44 maintained at a temperature of about 250 F. by steam coils or other suitable means. After melting, the solid fatty acids are concentrated to about 95% solids by ash evaporation at 280 F. to 320 F. in an evaporator 46, with residual amounts of solvent being removed by an inert gas such as nitrogen, in stripper 48. The saturated fatty acid product (essentially stearic and palmitic acids) is then ready for market or storage. The filtrate from filter 38 containing the dissolved unsaturated fatty acid components is likewise passed to a heater 50,

evaporator 52, and stripper 54, to produce the liquid un saturated acid products (oleic, linoleic, linolenic, etc.). Typical examples of the practice of this process are as follows:

Example I Employing the system substantially as shown in the drawing, 10,000 pounds of anhydrous acetone are charged each hour to the mixing tank and there mixed with 2,000 pounds per hour of a distilled fatty acid stock (prepared by splitting and distilling an inedible tallow) introduced through proportioning pump 18. The fatty acid stock may have a titre of 42 C. and an iodine value of 55. After being cooled to approximately F. the mixture of fatty acids and solvent is charged to a crystallizer and gradually subjected to a Vacuum of 20 mm. of Hg absolute. Evaporation of approximately 1;(5 of the total solvent present reduces the temperature of the solution to about 0 F. in approximately 25 minutes. Thereafter the chilled mixture is discharged by compressed air from the air compressor to the hold tank which is maintained at about 5 F. The chilled solution, now containing precipitated crystalline agglomerates of solid acids (in an amount approximating 10% by weight of the solution) is filtered continuously and washed with about 1,000 pounds per hour of cold acetone delivered from the solid recovery tank at a temperature of about 5 F. The solid acids removed from the filter are melted and liash evaporated at 300 F. to about 96% solids. After stripping, 800 pounds per hour of saturated acids (stearic and palmitic acids) are obtained having an iodine value of 3.7. The dissolved unsaturated acids are likewise evaporated and stripped to remove the solvent, providing 1,200 pounds per hour of unsaturated acids (predominantly oleic) of 5 C. titre.

Example II 2,000 pounds per hour of distilled fatty acid stock from soya oil is fed to the mixing tank simultaneously with 10,000 pounds per hour of substantially anhydrous methyl alcohol and thereafter chilled to a temperature of about 80 F. This solution is fed to a crystallizer and chilled at an absolute pressure of 15 mm. of Hg in about 30 minutes to a temperature of 14 F. 'I'he solid acidsv precipitated as crystalline agglomerates are removed by filtration and washed with cold methyl alcohol delivered to the filter at a temperature of about 14 F. The quantity of wash alcohol is approximately 1,000 pounds per hour. After further treatment of the filter cake and filtrate asin Example I, there is obtained 400 pounds per hour of solid acids (stearic and palmitic) havinglan iodine value of 25, and 1,600 pounds per hour of unsaturated acids (oleic, linoleic, and linolenic acids) of iodine value.

To those skilled in the art to which this invention relates, many variations in procedure and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

l. A method of separating fatty acids and unsaturated acids from a mixture of said acids, comprising the steps of: dissolving the mixture in a polar, substantially anhydrous, normally liquid organic solvent, the amount of mixture dissolved in the solvent being so controlled as to not exceed about 30% by weight of the solvent solution; gradually reducing the pressure of atmosphere adjacent said solution to below about 40 mm. of Hg absolute to cause evaporation of a substantial quantity of the solvent under essentially adiabatic conditions, and thereby to cause a rapid chilling of the solution in such manner that the normally solid fatty acids form interlocked agglomerations of crystals in easily lterable washable form; removing said interlocked crystalline agglomerates by ltration; and subsequently removingthe solvent from the remaining unsaturated acids.

2. The method of claim 1 wherein a maximum agglomeration or crystals occurs within 20 to 40 minutes after reducing the pressure of atmosphere adjacent.l the solution.. .y

3. The method of claim 1 wherein the temperature of the solution is lowered by the evaporative chilling step to between about F. and 14 F.

4. In the separation of, saturated fatty acids from a mixture of saturated and unsaturated fatt-y acids, the method comprising the steps of: rapidly chilling said fatty acid mixture in the presence of a normally liquid polar organic solvent to a iiltering temperature at whichy crystallization of desired solidiiiable constituents occurs; said chilling being induced to occur within a total elapsed'tirne of from y to 4-0 minutes as the result of a reduction in.

the pressure of atmosphere adjacent said solvent to below about 50 mm. of mercury to cause evaporation of a substantial portion thereof, said. rapid chilling forming at said filtering temperature interloeked agglomerates of fatty acid crystals in a readily ilterableV and washable form.

5. The method of claim 4 wherein the amount of or-V ganic solvent' present prior to chilling-is from about- 3 to about 10 volumes of the fatty acidv mixture and the amount of solvent evaporated is from about 1/2 to about 2 volumes of. the fatty acid mixture.

6. The method of claim 4 whereinl said filtering` temperature-isbelow about 14 F.

7. The method of separating saturated. components from mixtures of saturated and unsaturated fatty acids comprising: diluting the mixture with 3, to. 10 volumes. ofl a polar normally liquid organic solvent selected from the class consisting of acetone and methyl alcohol; reducing the pressure on the solution to below about mm. of Hg absolute to cause evaporation of a portion of the lsolvent under essentially adiabatic conditions, thereby lowering the temperature of the solution to a pointV between about 0 F. and 14 F. with suiiicient rapidity to cause easily washable, filterable, crystalline agglomerates of.'

the solvent from the liltrate to recover unsaturated com-V ponents; and expelling the final traces of solvent'rfrom such components by stripping with an inert gas.

8. The method of claim 7 wherein the proportion of separated saturated components, prior to iiltering, comprises from about 8% to 12% by volume of the Asolventv being retained.

9. The method ofV claim 8 whereinsaid. crystalline agglomerates are caused toV form within'a period of fromabout 20 minutes to about 40 minutes after the pressure on the solution isreduced.

10. The method of' claim 7 wherein the portion? of solvent evaporated amounts to about 15% to 25% of the solvent employed to dil-nte the Yfatty acid mixture.

11. A method of obtaining granular agglomerates of fatty acid crystals in readily iiltrable form-from a mixture of saturated and unsaturated fatty acids which comprises: dissolving a volume of mixedv saturated and unsaturated fatty acids in from 3 to 1`0 volumes of a normally liquid, polar, organic solvent; and reducing the pressure ambient said solution to below about 50 mm. of mercury to evaporate from about one-half to about two volumes of solvent from said solution andi rapidly chill the same under substantially adiabatic conditionsl to a temperature below about 14 F., whereby granular,

readily fltrable agglornerates of fatty acidV crystals are.

formed in said solution.

12. The method as statedin claim 111 wherein the polar solvent issubstantially anhydrous andthe solution does not contain more than 5% of Water.

13. The method as stated' in claim'll wherein the polar solvent is substantially anhydrous` an'd the solution does not contain more than 5%` of water and wherein saidv solution is chilled rapidly' to. below about 14 F. in less than minutes.

14. In the separation of saturated fatty acids from a mixturel of saturated and unsaturated: fatty acids, the steps of: rapidly chilling a solutionv of mixed saturated and unsaturated fatty acids in a normally liquid, polar organic solvent by reducing the; pressure ambient said solution to below aboutx50'mm. of mercury to evaporate aportion of. said solvent and to form granular agglomerates of fatty acid crystals in readily tiltrable form within a period of between 1.0 to 60 minutes.

1`5. 'Ihe method as stated in claim 14 wherein thel solution, prior to chilling, comprises betweenv about 3 toV 10 volumes of polar. solvent to one volume of mixed 17. The method as stated inclaim 14 wherein the polarv solvent is substantially anhydrous andthe solution does not contain more than 5% of water.

References Cited in the le of this patent UNITED STATES PAIEISYS 1,974,542 Parkhurst et al'. Sept.- 25, 193'4 `2,257,616 Miller Sept."30, 1941i 2,576,841 Leaders et al. U Nov. k27, 195.1

FOREIGN PATENTS '555,570

Great Britain Ang. so, 1943v

Claims (1)

1. A METHOD OF SEPARATING FATTY ACIDS AND UNSATURATED ACIDS FROM A MIXTURE OF SAID ACIDS, COMPRISING THE STEPS OF: DISSOLVING THE MIXTURE OF POLAR, SUBSTANTIALLY ANHYDROUS, NORMALLY LIQUID ORGANIC SOLVENT, THE AMOUNT OF MIXTURE DISSOLVED IN THE SOLVENT BEING SO CONTROLLED AS TO NOT EXCEED ABOUT 30% BY WEIGHT OF THE SOLVENT SOLUTION, GRADUALLY REDUCING THE PRESSURE OF ATMOSPHERE ADJACENT SAID SOLUTION TO BELOW ABOUT 40 MM. OF HG ABSOLUTE TO CAUSE EVAPORATION OF A SUBSTANTIAL QUANTITY OF THE SOLVENT UNDER ESSENTIALLY ADIABATIC CONDITIONS, AND TTHEREBY TO CAUSE A RAPID CHILLING OF THE SOLUTION IN SUCH MANNER THAT THE NORMALLY SOLID FATTY ACIDS FROM INTERLOCKED AGGLOMERATIONS OF CRYSTALS IN EASILY FILTERABLE WASHABLE FORM, REMOVING SAID INTERLOCKED CRYSTALLINE AGGLOMERATES BY FILTRATION, AND SUBSEQUENTTLY REMOVING THE SOLVENT FROM THE REMAINING UNSATURATED ACIDS.

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