US3541122A - Separation of fatty materials - Google Patents

Description

United States Patent US. Cl. 260-419 14 Claims ABSTRACT OF THE DISCLOSURE A method is provided for separating mixtures of fatty materials. In the method the mixture of fatty material is formed at a temperature at which the mixture is substantially fluid. The mixture is thereafter cooled by placing the mixture under vacuum conditions and evaporating a lower boiling fluid in the presence of the fatty materials. The conditions are selected so as to establish a temperature in the mixture wherein at least a part of the mixture forms a solid phase. The liquid portion of the mixture is then emulsified with an aqueous solution of a surface active material by adding the solution to the mixture. The liquid portion of the fatty materials emulsified in the aqueous solution is thereafter separated with it from the solid phase by any suitable solid-liquid separation technique, such as filtration or centrifugation.

This invention relates generally to a method for separation of fatty materials, and more particularly it relates to the separation of mixtures of fatty materials or their derivatives.

Fatty materials, such as fatty acids and triglyceride oils, are usually obtained from natural or synthetic sources as a mixture of components which differ from one another by their melting points. It is sometimes desirable to separate these mixtures into components. For example, fatty acids derived from tallow may be separated into a stearic acid fraction and an oleic acid fraction.

One known process for separating fatty acids derived from tallow is by a pressing operation. In such process, the mixture of fatty acids obtained from tallow is subjected to successive pressing operations at temperature such that at least part of the mixture is solid. The saturated fatty acids, such as palmitic and stearic acids, solidifyfirst and are recovered as a solid fraction. The solid fraction obtained from pressing tallow is known as commercial stearic acid. The liquid fraction which is removed by the pressing contains primarily unsaturated fatty acids, principally oleic acid and is known as red oil. Separation of fatty acids by pressing is slow and gives poor recovery of the separate components of tallow.

To improve quality, the solids are sometimes given an additional pressing at higher temperatures to remove more of the liquid unsaturated fatty acid and produce a material known as double or triple pressed stearic acid. The above-described pressing method for separating fatty acids is subject to numerous disadvantages, including low quality of the components obtained, inetfic'ient operation, and slow and costly procedures.

Separation of fatty acids into solid and liquid components has also been effected by the use of solvents and by the formation of emulsions and subsequent centrifugation. These other known prior art methods for separating fatty acids are also subject to disadvantages in that a solvent recovery step must be elfected, or that costly centrifugal separation equipment must be utilized.

Centrifugal separation has been found to be essential in various prior art methods due to the type of solid phase crystals that is formed when a mixture of fatty ice acids is cooled rapidly. It would be desirable to provide an improved method for the separation of mixtures of fatty acids wherein cooling of a fluid mixture of fatty acids may be effected rapidly and still provide solid phase crystals that are readily separated from the liquid phase.

It would also be desirable to provide an improved process by which higher-melting glycerides can be removed from glyceride oils. A process for accomplishing this is generally referred to as winterization of the glyceride oil. Separation of such higher-melting glycerides was formerly carried out simply by allowing the glyceride oil to stand and settle out in outside tanks during the winter. The process is now carried out inside with mechanical refrigeration, but substantial improvement in the time required for separation of the higher-melting glycerides has not improved.

Winterized edible glyceride oils that will be substantially free of hard fat crystals at temperatures of 40 F. are required for use in products kept in household refrigerators. The problem in Winterizing oil is primarily a matter of providing crystals in a form that can be separated from the uncrystallized liquid oil. In normal practice, the oil must be cooled slowly over a period of several days to produce filterable crystals, and even under the most favorable circumstances, the final separation of solid, higher-melting glycerides and liquid oil is diflicult and incomplete. Because the operation of winterization is slow and better separations are desired, winterization is not a particularly satisfactory oil processing method. It would be desirable to provide an improved method for Winterizing liquid glyceride oils.

Accordingly, it is an object of the present invention to provide an improved method for separating fatty materials. Another object of the present invention is to pro vide a method for separating mixtures of fatty materials into components without the necessity of using organic solvents or centrifugal separation equipment. It is another object of the present invention to provide an improved method for the separation of fatty acid mixtures. It is a further object of the present invention to provide an improved method for the separation of high-melting glycerides from glyceride oils. It is a still further object of the present invention to provide an improved method for separating mixtures of fatty esters into components of different melting points. I

These and other objects of the present invention will become more apparent from the following detailed description and the drawing, which is a schematic diagram of a flow sheet embodying various of the features of the present invention.

In accordance with various of the features of the present invention, a mixture of fatty materials is formed at a temperature at which the mixture is substantially fluid. The mixture will include fatty materials having fatty acid residues with carbon chain lengths greater than 10 and may comprise glyceride materials, fatty acids or esters. The mixture is thereafter cooled by placing the mixture under vacuum conditions and evaporating a lower boiling fluid in the presence of the fatty materials. The lower boiling fluid may or may not be in admixture with the fatty materials. The cooling conditions are selected to establish a temperature in the mixture so that at least a part of the mixture forms a solid phase. The liquid portion of the mixture is then emulsified with an aqueous solution of a surface active material by adding the solution to the mixture. The liquid emulsion of fatty materials and the aqueous solution is thereafter separated from the solid phase by any suitable solid-liquid separation technique, such as filtration or centrifugation.

The method of the present invention is particularly suitable for separating mixtures of fatty acid esters or 3 fatty acids of both natural and synthetic origin and certain features of the invention will hereafter be described with reference to such mixtures.

Fatty acid esters, particularly glycerides, are usually obtained from the fat of vegetables and from land and marine animals. Examples of the various vegetable fats suitable for separation by the method of the present invention are coconut oil, rapeseed oil, soy bean oil, cottonseed oil, peanut oil, linseed oil, palm oil and olive oil. Animal fats include beef fat, particularly tallow, and hog fat. Marine fats include those obtained from whale oil, menhaden oil, codliver oil and herring oil. Fatty acid esters which contain alcohols other than glycerin as the alcohol component may also be processed by the method of the present invention.

Fatty acid mixtures are usually obtained from the naturally occurring fats mentioned above. The esters may be split with the aid of water or steam or may be saponifled with the aid of caustic after which the fatty acids are liberated from the resulting soaps with the aid of acids. Fatty acid mixtures may also be obtained by the oxidation of natural or synthetic paraffin or the oxidation of alcohol.

The invention is, however, not limited to any specific enumerated mixture of fatty acids or fatty acid esters, but is rather applicable to all similar mixtures regardless of the source or procedure for obtaining such mixtures.

The mixture of fatty materials to be separated is preferably heated to a temperature such that the higher melting of the components of the mixture substantially loses its crystal structure. However, it is not necessary to heat the mixture to a temperature wherein each of the components of the mixture is completely melted. For example, where a mixture of stearic acid and oleic acid is to be separated, the mixture of acids is preferably heated to a temperature of at least about 90 F., but does not have to be heated to a temperature in excess of 120 F. at which temperature the stearic acid is substantially melted.

After the mixture of fatty materials has been heated to the desired temperature, the mixture is transferred to a chamber which is equipped to draw vacuum therein. Vacuum equipment is provided for establishing a vacuum sufficient to effect desired cooling under the conditions of the system. It will be readily understood from the further detailed description of the cooling process of the invention that the rate of cooling is dependent on the level and capacity of vacuum, i.e., the lower the absolute pressure the more rapid the rate of cooling will be to the extent that the vacuum producing means is capable of withdrawing the evaporated fluid. The rate of cooling is also related to the rate of evaporation of the lower boiling fluid from the mixture of fatty materials and the latent heat of vaporization of the fluid. In general, it is desirable to provide an absolute pressure of less than about 50 mm. of mercury and preferably less than about 10 mm. of mercury.

Thereafter, a suitable fluid is evaporated in the presence of the mixture. The fluid may be introduced into the mixture of fatty materials prior to introduction of the mixture into the chamber or the fluid may be introduced separately into the chamber while the chamber is under vacuum. It is preferred that the fluid have a latent heat of vaporization of at least about 150 calories per gram at standard conditions of temperature and pressure and a boiling temperature at atmospheric pressure of less than about 200 C. A preferred fluid, for reasons of economy and availability, is water. However, other fluids having suitable evaporation and characteristics in terms of the latent heat of vaporization and atmospheric boiling temperature may be used so long as the fluid is substantially immiscible with and does not react with the fatty materials.

Preferably, a fluid is selected and vacuum conditions are established which permit the fluid to be evaporated at a rate sulficient to effect a temperature drop in the mixture of from about 25 F. to about 120 F. per hour. However, other rates of cooling are equally suitable. Evaporation of fluid is continued until the mixture is cooled to the desired temperature. The desired temperature is selected so that at least part of the mixture forms a solid phase. The mass or total weight of the mixture of fatty materials which is to be cooled is not important. The rate of cooling depends on the rate at which fluid is evaporated per pound of mixture. Consequently, large volumes of fatty materials may be rapidly cooled by the method of the invention. The described unique method of cooling fatty material provides a solid phase with a crystal form which is readily adaptable to separation by filtration. If desired, filtration or separation of the mixture of organic compounds now containing a solid phase and a liquid phase may be readily effected without further treatment.

It has been found, however, that a higher degree of separation of the liquid phase of the mixture from the solid phase may be effected by first forming an emulsion with an aqueous solution of a surface active material. It is generally preferred to use levels of aqueous solution of from about 50 to about 500 percent by weight of the mixture of fatty materials. The emulsion may be effected by shaking, stirring or any other manner assuring intimate contact between the mixture and the aqueous solution of a surface active material. During formation of the emulsion, the solid phase crystals are dispersed throughout the emulsion.

The surface active material reduces the interfacial tension between the solid phase crystals and the aqueous medium. Surface active materials are organic compounds which contain hydrophobic and hydrophilic groups in the same molecule, usually separated by a long carbon chain. The formation of an emulsion of the liquid phase of the mixture with the aqueous solution of the surface active material appears to tend to maintain the liquid phase separate from the solid phase. Since the interfacial tension between the solid phase and the aqueous emulsion has been reduced, the solid phase is more easily separated therefrom. In this connection, however, the physical characteristics of the crystals of the solid phase are important to effect a desirable separation, and it is important to effect cooling of the mixture of fatty materials to provide solid phase crystals suitable for separation by the described method.

Any known or conventional surface acting materials which are chemically inert with respect to the other components of the mixture of fatty materials and which are water dispersible may be used. See, for example, those described in the publication Encyclopedia of Surface Active Agents, 1. P. Sisley and P. I. Wood, New York, 1952. Examples of suitable surface active materials include alkylphenolpolyglycol ether, alkylsulfonate, fatty alcohol sulfate and alkylbenzyl sulfonate.

The amount and concentration of the surface active material to be used depends upon the properties of the surface active material and upon the level of aqueous phase used in forming the emulsion. Generally, concentrations of from about 0.05 percent to about 1.0 percent by weight of the mixture of fatty materials provides suitable results.

As previously described, the aqueous solution of the surface active material provides a wetting action which enables the aqueous phase to wet the surface of the crystals of the solid phase and displace the liquid phase adhering thereto. In addition, the aqueous solution of a surface active material has an emulsifying property with respect to the liquid phase. It is desirable to limit the emulsifying action of the aqueous solution of a surface active material so as to provide an emulsification effect that is not so strong as to cause difficulty in the subsequent separation of the liquid phase from the aqueous solution. The emulsifying properties of the solution of surface active material can be influenced by the addition of electrolytes which are inert to the fatty materials of the mixture. Electrolytes in the form of magnesium, calcium, aluminum or other soluble metal salts are suitable for this purpose. A preferred electrolyte is magnesium sulfate. The concentration of the electrolyte is dependent upon the property of the surface active material which is used. Generally, concentrations of electrolyte of from about 1.0 percent to about 7.0 percent by weight provides the desired result of limiting the emulsifying power of the surface active material.

As previously described, the cooling method of the described invention provides a solid phase of the higher melting components of the mixture of fatty materials that are suitable for separation by conventional solidliquid techniques such as vacuum filtration or filter presses.

It will be appreciated by one skilled in the art that the conditions of separation, such as temperature, level of aqueous solution of surface active material used, method of separation used, and other variables will affect the properties of the liquid and the solid fatty material that are obtained.

When the temperature at which the separation is to be effected is below about 60 F., it is sometimes desirable to effect at least part of the cooling of the mixture of fatty materials by chilling the aqueous solution of surface active material prior to introduction of the aqueous solution into the mixture. Thus, after the mixture of fatty material is cooled by vacuum evaporation, as previously described, to a particular temperature, the aqueous solution at a temperature below that to which the organic materials have been cooled is added and an equilibrium temperature intermediate that of the mix ture of fatty materials and the aqueous solution is obtained. This method for further cooling of the organic mixture may be desirable where refrigeration capabilities are available for effecting cooling of the aqueous solution of surface active material.

Also, it may sometimes be desirable to effect at least part of the cooling of the mixture of fatty materials by circulating a cooling fluid in a jacket surrounding the chamber in which the fatty materials are contained. This additional cooling may be desirable when the proportion of solid fatty materials is small in relation to the liquid fatty materials.

The separation of the solid phase from the aqueous emulsion may be effected in certain cases by allowing the mixture to stand and thereafter decantingthe layers of materials which form. In accordance with a preferred embodiment of the invention, however, the aqueous emulsion is separated from the solid phase by vacuum or pressure filtration. For this purpose, any suitable type of vacuum or pressure filtering apparatus which is commercially available may be used. Centrifugal separation may also be used where the costs are not prohibitive.

The following examples are provided to further illustrate various features of the present invention, but are intended to in no way limit the scope of the invention, which is defined in the appended claims.

EXAMPLE I One thousand grams of tallow fatty acids were heated to a temperature of 115 F. to provide a liquefied mixture of fatty acids. The tallow fatty acids contained 49 percent saturated fatty acids and 51 percent unsaturated fatty acids. The liquefied fatty acids at a temperature of 115 F. were introduced into a glass container equipped with ports to permit drawing vacuum therein and to introduce a liquid while vacuum was maintained in the container. A vacuum of 6 mm. mercury pressure was drawn in the chamber. Water was then introduced into the container through a port in the bottom of the container. The water was added at a level of 0.3 gram per gram of fatty acid over a period of 1.5 hours. During this time period the temperature of the fatty acids was reduced to 43 F.

One thousand grams of an aqueous solution containing 50 grams of magnesium sulfate and one gram of sodium lauryl sulfate was then added to the container after the vacuum had been broken. The aqueous solution had been chilled to the same temperature as the fatty acids, i.e., 43 F. prior to introduction into the container. The Water was added slowly with constant stirring to provide an emulsion. After the aqueous solution had been added, the mixture was stirred for five minutes to complete wetting of the solid crystals of saturated fatty acids. The emulsion, containing a dispersion of the solid crystals, was then transferred to a Buchner funnel lined with coarse filter paper. The aqueous emulsion containing the liquid unsaturated fatty acids was then separated from the solid crystals over a period of minutes, using a vacuum of 15 inches. The aqueous emulsion broke immediately after filtration. The liquid phases obtained from the filtration step were then allowed to set,.overnight in a steam bath. A liquid phase which Was rich in oleic acid was then removed from the aqueous phase by means of a separatory funnel.

The titer of the liquid oleic acid rich phase was then determined by the procedure described in A.O.C.S. Method Tr-Ia-64. Titer is an arbitrary designation for the solidification temperature of a fatty material. The titer of the liquid oleic acid rich phase obtained by the method of the invention was 2.5 C. The titer of commercially available oleic acid is not usually lower than about 15 20 C.

EXAMPLE II One thousand grams of tallow fatty acids were heated to a temperature of 115 F. to provide a liquefied mixture of fatty acids. The tallow fatty acids contained 49 percent saturated fatty acids and 51 percent unsaturated fatty acids. The liquefied fatty acids at a temperature of 115 F. were introduced into a glass container equipped with ports to permit drawing vacuum therein and to introduce a liquid while vacuum was maintained in the container. A vacuum of 6 mm. mercury pressure was drawn in the chamber. Water was then introduced into the container through a port in the bottom of the container. The water was added at a level of 0.3 gram per gram of fatty acid over a period of 1.5 hours. During this time period the temperature of the fatty acids was reduced to 52 F.

One thousand grams of an aqueous solution containing 50 grams of magnesium sulfate and one gram of sodium lauryl sulfate was then added to the container after the vacuum had been broken. The aqueous solution had been chilled to a temperature of 30 -F. prior to introduction into the container. The equilibrium temperature of the mixture of fatty acids and the water was 42 F. The water was added slowly with constant stirring to' provide an emulsion. After the aqueous solution had been added, the mixture was stirred for five minutes to complete wetting of the solid crystals of saturated fatty acids. The emulsion, containing a dispersion of the solid crystals, was then transferred to a Buchner funnel lined with coarse filter paper. The aqueous emulsion containing the liquid unsaturated fatty acids was then separated from the solid crystals over a period of minutes, using a vacuum of 15 inches. The aqueous emulsion broke immediately after tfiltration. The liquid phases obtained from the filtration step were then allowed to set overnight in a steam bath. A liquid organic phase which was rich in oleic acid was then removed from the aqueous phase by means of a separatory funnel. The liquid organic phase obtained had a titer of 2.5 C.

EXAMPLJE III Cottonseed oil was treated by the method of the invention to effect winterization thereof. 900 grams of refined and bleached cottonseed oil was heated to a temperature of F. and was held at that temperature for a period of 30 minutes to insure the melting of the solid saturated triglycerides. Thereafter, the cottonseed oil was transferred to a chamber adapted for drawing vacuum and introducing a liquid thereto while the vacuum was being held. The chamber was also provided with a jacket through which a cooling fluid could be circulated. The cottonseed oil was then cooled to a temperature of 45 F. over a period of 30 minutes while being slowly stirred by circulating chilled water through the jacket. At this temperature a slight haze was observed in the cottonseed oil. A vacuum of 10 millimeters of mercury was then drawn. Water was then bubbled into the chamber from the bottom over a period of 7 hours at a rate of 0.3 gram of water per gram of cottonseed oil. The temperature of the cottonseed oil was reduced to 40 F. 30 inches of vacuum was maintained at a temperature of 40 F. by the continued vacuum evaporation of the water. The vacuum was then broken and an aqueous solution was slowly introduced into the chamber while the cottonseed oil was continuously stirred. The aqueous solution contained 900 grams of water, 1.8 grams of sodium lauryl sulfate and 45 grams of magnesium sulfate. The water had been previously chilled to a temperature of 40 F. and the temperature of the mixture was maintained at 40 F.

After the water had been added, the mixture was stirred for two minutes to form a loose emulsion of the water with the liquid phase of the oil and containing a dispersion of the solid crystals therein. The emulsion was then transferred to a Bnchner funnel located in a room maintained at a temperature of 45 F. and the solid phase was separated therefrom.

The liquid cottonseed oil was then recovered from the emulsion by the method described in Example I. The yield was 83 percent by weight of the starting oil and the liquid. cottonseed oil obtained had a cold test of 132 hours. This compares with a yield of about 65 percent and a cold test of about hours obtained when winterization is effected by conventional vat cooling.

Various of the features of the invention are defined in the appended claims.

It is claimed that:

1. A method for the separation of a mixture of fatty materials into fractions wherein the components of the mixture have different melting points which method comprises, providing a mixture of fatty materials in at least a partially melted state, treating the mixture so as to lower the temperature to a level wherein at least part of the mixture is solid, said temperature also being such that at least part of the mixture remains liquid, said lowering of temperature being effected by providing a lower boiling fluid in said mixture and subjecting the mixture and fluid to vacuum conditions so as to evaporate said fluid from said mixture thereby cooling said mixture, adding to said cooled mixture an aqueous solution containing a surface active material, forming an emulsion of said aqueous solution with said liquid portion of said cooled mixture, and thereafter separating said emulsion into a liquid phase and a solid phase.

2. A method in accordance with claim 1 wherein said fluid which is to be evaporated is added to said mixture of fatty materials prior to subjecting said mixture to vacuum.

3. A method in accordance with claim 11 wherein said fluid which is to be evaporated is added incrementally to said mixture of fatty materials after said mixture is subjected to vacuum conditions.

4. A method in accordance with claim 1 wherein said surface active material has at least one hydrophilic group and at least one hydrophobic group.

5. A method in accordance with claim 1 wherein said surface active material is present at a level of at least 0.05 percent by weight of said fatty materials and wherein said aqueous solution is present at a level of from about percent to about 500 percent by weight of said fatty materials.

6. A method in accordance with claim 1 wherein said aqueous solution of a surface active material also contains an electrolyte.

7. A method in acordance with claim 6 wherein said electrolyte is present at a level of from about 1.0 to about 7.0 percent by weight of said aqueous solution.

8. A method in accordance with claim 1 wherein said vacuum condition is established at an absolute pressure of 50 millimeters of mercury or less and wherein said fluid is evaporated from said container at a level sufficient to cool said mixture of fatty material at a rate of from about 25 F. to about F. per hour.

9. A method in accordance with claim 1 wherein said mixture of fatty materials is selected from saturated and unsaturated fatty acids.

10. A method in accordance with claim 1 wherein said fluid which is to be evaporated has a latent heat of vaporization of at least about calories per gram at standard conditions of temperature and pressure.

11. A method in accordance with claim 1 wherein said fluid which is to be evaporated has a boiling temperature at atmospheric pressure of less than about 200 C.

12. A method in accordance with claim 1 wherein said fluid which is to be evaporated is water.

13. A method in accordance with claim 1 wherein said aqueous solution is cooled prior to adding to said cooled mixture.

14. A method in accordance with claim 1 wherein said mixture of fatty materials is at least partially cooled by heat transfer between said mixture of fatty materials and a cooler fluid material.

References Cited FOREIGN PATENTS 165,094 3/1954 Australia. 658,967 10/1951 Great Britain.

LEWIS GOTTS, Primary Examiner.

E. G. LOVE, Assitant Examiner.

U.S. Cl. X.R. 260428