US2752378A - Hydration method of refining glyceride oils - Google Patents

Description

United HYDRATION ll IETHOD OF REFINING GLYCERIDE OILS No Drawing. Application October 25, 1952, Serial No. 316,950

18 Claims. (Cl. 260-425) This invention relates to the refining of animal and vegetable oils with the main objectives of providing a neutral, refined oil as one product and a foots product which is higher in sterol content than the foots of methods heretofore known.

Processes for refining animal and vegetable oils to remove free fatty acids, color bodies, and unsaponifiable matter such as gums are well known and the losses incident upon the removal of such bodies are, of course, unavoidable. In most processes, however, the actual refining losses exceed those which can be accounted for by the components whose removal is desired, the excess thereover being usually due to entrainment of some refined oil in the foots, and/or to decomposition of the triglyceride molecules of the oil into products which enter the foots. It is desirable, of course, to use a refining process which minimizes losses of the latter kinds.

Inasmuch as numerous natural oils contain sterols which are of potential value as raw materials for the synthesis of many steroid derivatives, the refining process which is employed should permit the recovery of such sterols in a form which is as concentrated as possible, thereby to improve it for further economical processing. To the best of our knowledge, prior processes have not recovered the sterols in a concentrated form suitable for further efiicient processing. It should be recognized that 1 while oils contain a variety of sterols, only a portion of them can be recovered by the usual saponification refining methods. The method of the present invention efii ciently recovers that portion of the sterols which is recoverable. In order to have that portion account for a higher percentage of the foots product which contains them, it is necessary to keep the non-steroid materials in the foots product as low as possible. Thus it is necessary to minimize the non-steroid refining losses without decreasing the steroid refining losses. This is the broad objective of the invention.

We have now discovered that the refining of animal and vegetable oils can be advantageously carried out by treatments hereinafter described, said treatments entailing low non-steroid refining losses while also yielding a foots product which has a higher concentration of sterols than is secured by prior methods. The latter "foots product is eminently suited to further treatments permitting the efiicient and economical recovery of the sterols contained therein.

Accordingly, one object of our invention is to provide a refining process for animal and vegetable oils which minimizes non-steroid refining losses while yet recover ing as much of the sterols of the oils as possible.

A further object is to provide a process of the kind mentioned which yields a foots" product characterized by a relatively high concentration of sterols therein.

These and other objects will be apparent from the following description of the invention and of the best presently-known manner of practicing it.

Our process can in some instances consist of a single refining stage which is characterized by (1) the convertates atent sion of the oil to be refined into an emulsion containing certain identified refining agents, and (2) then breaking that emulsion in a centrifuge to yield a refined oil as one product and a sterol-containing foots as the other product. This single refining stage can be employed alone to best advantage when the oil has a titratable fatty acid content between about .15 and .35 Such an oil usually has a gum content below about 0.5%. When the gum content is above about 0.5% and/or when either the titratable or the free fatty acid content is greater than about .35 then the oil should be subjected to a conventional hot refining treatment modified to bring the oil within the foregoing limits while yet retaining an actual free fatty acid content of at least about 0.15%. However, non-steroid refining losses can be reduced appreciably over prior methods even when the titratable fatty acid content is as high as 1%. By a hot refining treatment, We mean one in which the latter is at a temperature of about 140 F. or above. Such a hot treatment is disclosed in the Clayton Reissue Patent No. 21,992, and such treatment, when modi fied to bring the fatty acid content within the preferred range stated above, is one which we prefer to use. According to that patent, the oil is refined by treating it with a non-saponifying agent such as soda ash, then is (at) either partially dehydrated to a controlled water content or (b) is fully dehydrated and then rehydrated to a predetermined extent, and lastly is centrifuged to separate the oil from the foots. When such a treatment precedes our single stage refining step, we modify it so that not all of the free fatty acid content is removed in the foots. This is accomplished by using only a small excess of the non-saponifying agent over the theoretical; for example, an amount corresponding to about 1.5 times the theoretical quantity needed to reduce the fatty acid content to about 0.25%, the said agent being introduced in the form of a 15% aqueous solution.

From the preceding brief description it will be understood that before carrying out our single stage refining step, we intentionally provide between about 0.15% and 0.35% of free fatty acids in the oil while also limiting or excluding gums. Preferably the titratable fatty acid content is not above about 0.35%. It should also be understood that since we desire to effect the recovery of sterols in our single stage treatment, any treatment antecedent thereto should have been designed and/ or adapted so as not to remove sterols. The hot refining practice of the Clayton Reissue Patent 21,992 minimizes the presence of sterols in the pre-refining foots, thereby retaining them in the oil for separation in our single stage treatment. Other known hot refining treatments which do not remove sterols can also be used, however.

In the foregoing discussion We have referred to titratable and free fatty acid contents of 0.15%-0.35%. The titratable values are intended to be those resulting from the usual and customary methods for measuring fatty acid content by titration in terms of oleic acid. Inasmuch as phosphatides are the main gums in animal and vegetable oils, and inasmuch as they contain a minor number of groups in their molecules which titrate as fatty acids when present, the titration methods customarily used for determining fatty acid content do not distinguish between actual fatty acids and acidity resulting from any phosphatides which may present. We, accordingly, intend that the stated titratable values should be so understood.

In accordance with the principles of our invention, our single stage refining treatment of an oil which has a limited content of gums and has a free fatty acid content between 0.15% and 0.35% involves, for example, the following sequence of steps:

1. Cooling the oil to between about 50 and 70 F 2. Agitating the cooled oil while adding the necessary small amount of an aqueous solution (all having a specific gravity between about 12 B. and 20 B., (1)) contain ing an alkali metal alkali refining agent in sufiicient quantity to yield a neutral refined oil, and containing one or more emulsion breaking agents selected from the group consisting of alkali metal borates, pyrophosphates, oxalates, silicates and acetates, and alkali metal salts of ethylene diamine tetra-acetic acid.

3. Continuouslyagitating the mixture of oil and aqueous solution to form anemulsionwhile keeping the temperature of the whole mass. between about 50 and 70 F., and

4. Within a few minutes (e. g. -l) after securing the aforementioned emulsion, centrifuging the emulsion to separate. it into a substantially anhydrous refined oil as the lighter effluent and an aducous"foots product as the heavier. effiuenuthe latter having a moderately high con centration of sterols therein.

The principles on which these steps are based are:

1. Sterols contained in an oil which has been hot prerefined, or sterols which are present in an unrefined, degurnmed oil are when hydrated, increasingly soluble in the oil as the temperature of the oil rises above about 50 F. By hydrating the sterols while keeping the temperature between about 50 and 70 F., the resulting hydrated sterols are brought approximately to the state of lowest solubility in the oil consistent with the retention of a free-flowing, centrifugeable emulsion.

2. The insoluble hydrated sterols by themselves do not settle well by gravity or by centrifugation, but can be separted effectively by centrifugation if a controlled amount of alkali metal soap of fatty acids naturally present in the oil is also precipitated concurrently with the hydrated sterols. The soap appears to entrain or otherwise become attached to the hydrated sterols and to carry them down into the fonts.

3. Hydration of the sterols is catalyzed by the presence of alkali and is also hastened greatly by emulsifying the hydrating water with the oil so as to bring the water and alkaline catalyst into intimate contact with the sterols dissolved in the oil.

4. Elfective separation of the hydrated sterols-soap precipitate depends critically on breakingthe emulsion in the centrifuge. This desired breaking of the emulsion in the centrifuge rather than elsewhere is accomplished through the use of borax and/or the other emulsion breaking agents named above.

5. Decomposition of the triglyceride molecules of the oil by the alkali metal alkali increases with increasing time of contact, and hence increased time of contact causes increased amounts of soap to enter the foots. By carefully controlling and limiting the time of contact in the emulsion phase of the treatment, a condition can be secured wherein the optimum quantity of hydrated sterols is precipitated along with the fatty acid soap while a minimum amount of soap resulting from cleavage of the triglyceride oil molecules is produced. Since the latter soap would simply dilute the sterol concentration in the foots, it is important where maximum sterol concentration is sought, as here, to minimizethe cleavage of the triglyceride molecules while. yet securing. optimum precipitation of the hydrated sterols. Thus, refining losses due to decomposition of the oil are minimizedby carefully limiting the timeof contact.

The following examplesillustratethe operation of the principles just enumerated.

F. Sodium carbonate in the form of a 15% aqueous soll was addedto the heated oil in an amount 1.5 times t heoretical eed d o re uc the aci i y of he oil to approximately 0.25%, and the resulting mixture was stirred vigorously for three minutes after which time the mixture was dehydrated and freed of carbon dioxide by heating to 200-212 F. under vacuum. The dehydrated mixture was then cooled to about F. and rehydrated by vigorously stirring into it about 4% of water. Stirring was continued for about 15 minutes while the temperature was maintained at 160 F. to ensure thorough wetting of the gums contained in the oil. At the end of this time the oil was centrifuged promptly. The lighter efiluent of the centrifuge was a partially rcfined, substantially anhydrous oil still containing about 0.19% free fatty acids and containing practically all of the sterols contained in the original crude oil. A portion of the partially-refined lighter efiluent was set aside for use in the tests described in subsequent examples. The remainder of said'p artially refined oil wasnext cooled to about-60 F. under agitation and 1.35% by weight onthe oil of a solution containing 5% borax and 11% caustic soda by weight was added; The mixture was stirred vigorously to produce a substantially homogeneous emulsion of water in' oil and stirring was continued for about 15 minutes thereafter. The temperature of the emulsion was maintained at about 60 F. throughout these operations. At the end of the 15 minutes of stirring, the emulsion was centrifuged. The emulsion broke in the centrifuge to yield a lighter effluent consisting of substantially neutral, refined soybean oil and a heavier effluent containing water, soapstock, sterols and some soybean oil. The sterol content of the heavier eiiluent was determined to be about 7% on wet basis. Other components thereof were found to be:

Per cent Soap 41 Oil 8.2 Moisture 40:0 Non-steroid unsaponifiablesfln 3.8

EXAMPLE II (Efiect of reagents in the 60 F. tr atment 0/? Example I) Various portions of the partially-refined oilwhich was setaside in Example I were treated at 60 F. with 1.35% by weight onthe oil in each portion with aqueous solutions containing the kinds and percentages of refining agents noted in the following table, the treatments being Sturols mfinmg Agom Cone. of sterols in Recovered heavy efflnrnt other from partially f acidificati n refined oil,

kind 1 Percent percent I 11 5.4% (dry basis) 0. 07s 10 5.6% (dry basis).. .047 i\ 011.. 11

10.83% (dry basis) .078 Borax 5 It will be seen from the results that while NaQH by itself brought down as great a quantity of sterols as the tration of sterols in the foots was only slightly higher than in the case of NaOH alone. The same applies to nonsteroid unsaponifiables.

EXAMPLE III (Efiect of temperature in the 60 F. treatment of Example I Samples of the partially refined oil of Example I were treated as in Example II with different reagents (1.35%

The data show that the sterols are not brought down in good yield at the higher temperatures (because of their increased solubility in the oil) and that the higher temperatures also induce higher refining losses as a result of cleavage of the oil molecules. Both of these adverse effects result in very low concentrations of sterols in the foots at the higher temperatures, and at 60 F. in the absence of the NaaPzOr.

EXAMPLE IV (Efiect of contact time in the 60 F. treatment of Ex. I)

Refining of different portions of the partially-refined oil set aside in Example I carried out with additions of 1.35% of an aqueous solution containing 11% NaOH and Na4P2O'z and was conducted as described in Example I except that the contact time was varied:

The data indicate that in the presence of sodium hydroxide, the sterols are hydrated to a substantial extent even in 3 minutes, but that the rate thereafter decreases progressively. In other words, a curve plotted to show sterol recovery as ordinates against time as abscissa would be rather steep in the first few minutes and then would gradually flatten off as the contact time extended beyond 15 or minutes.

The data also show that with prolonged contact time, the foots contain increasing amounts of non-sterol components which dilute the sterol concentration in the foots. Thus the achievement of high sterol concentrations involves limiting the contact time in a manner of compromise between the above effects, the time being controlled to yield approximately the optimum sterol concentration.

EXAMPLE V (Oil losses by various refining procedures) Dilferent portions of the crude soybean oil used in Example I were refined as in Example 1, except that the 60 F. treating step was modified as here noted. The samples were treated for 15 minutes with 1.35% of an aqueous solution of the following kinds and amounts of reagent and at the temperatures noted below, the ro-* cedures otherwise conforming to that described in Example I. The following table indicates the efiects of these variations on total oil loss occasioned by the treatments, expressed in percentage by weight of the crude soybean oil.

Refining Agent Temp, Oil Loss, F. percent Kind Percent NaOH 11 1.00 lllrlaggnn 60 1. 44

a N84P2OL- 5 60 70 NazCOa. 10 6O 0. 83

These data show that the use of electrolytes such' as Na4P2O7 in combination with sodium hydroxide markedly reduces the oil losses and makes the losses no greater and even somewhat less than the losses resulting from the use of non-saponifying agents such as sodium carbonate.

EXAMPLE VI (Effect of electrolytes used with NaOH) Sterols in Foots After Elecmlyte Acidification 10.70% (dry basis). 10.83% (dry basis). 7.39% (dry basis). 8.97% (dry basis). 9.57% (dry basis).

Sodium acetate. Tetra-sodium ethylene diamine tetra-acetic acid.

From the foregoing examples and description of the invention, it should be clear that the invention centers around the novel concepts of (1) separating hydrated sterols from an oil by means of low temperatures together with the use of about the smallest quantity of alkali metal soap of naturally-present fatty acids capable of effecting the recovery of the hydrated sterols in about optimum concentration, and (2) effecting hydration of the sterols and the in-situ formation of the said soap through the medium of an emulsion which does not break until it is admitted into a centrifuge.

Concept 1 above, in some instances, requires an antecedent refining of the oil to remove most of the gums, fatty acids, color bodies, etc. While leaving enough fatty acids (with or without small amounts of gums) to effect efiicient recovery of the sterols. Such antecedent refining treatment should not remove sterols except in such small quantities as are unavoidable with the selected antecedent refining treatment, and the treatment should be conducted at temperatures at least as high as about 140 F. Preferably the antecedent refining should also be one which minimizes refining losses. The latter preference is not a matter which in any way affects the sterol recovery in the later single refining stage, but is one which is of concern in the commercial refining of oil. Any of the known refining methods which exhibit 'the foregoing attributes can be employed in the antecedent refining treatment. In the broad sense such treatments per se form no part of this invention except toihe extent that they are involved in preparing the oil, when necessary, for treatment in accordance with concepts 1 and 2 above. 'f

Concept 1 involves a feature not heretofore dwelt on, but which is significant. We have discovered that the hydrated sterols are collected efiiciently and in good yield by alkali metal soaps of fatty acids which are naturally present in the oil, but are not collected in practicable quantities by comparable kinds and quantities of soaps which are either added as such or are formed in situ from fatty acids added to the oil. For this reason, the invention does not contemplate any adjustment of the fatty acid content of the oil to bring it within the limits of .15 to .35 other than by removing any naturallypresent fatty acids which may be in excess of that range.

Other attributes of concept 1 have already been explained hereinabove, and need not be repeated here.

Concept 2 involves attributes which also have been explained hereinabove, but there remain a few points which should be made clear.

The first point is that as far as the removal of the remaining fatty acids is concerned, our treatment of the oil with alkali metal alkalis conforms to known caustic alkali refining processes; that is, that the amount of alkali which is used is proportioned to the fatty acid content in accordance with known practices (e. g Ayres Patent Nos. 1,737,402 and 1,247,782, Rini Patent No. 2,507,184 and Bersworth Patent No. 2,463,015).

The second point is that except for sodium acetate the salts which we have discovered to be effective in breaking the emulsion in the centrifuge are sparingly soluble in aqueous solutions of alkali metal alkalis. All of the salts are dissolved in the solutions in amounts up to saturation levels. Lesser amounts of the salt(s), including sodium acetate, make the emulsion increasingly stable in the centrifuge. Accordingly, the amount of agent used can be varied widely, but cleanest separation of the heavy and light effluents is promoted by using as much of the sa1t(s) as can be dissolved in an aqueous alkali metal alkali solution having a specific gravity between about 12 B. and 20 B. These gravity limitations are also of significance in that they limit the amount of water which is introduced and emulsified. Specific gravities below about 12 B. introduce too much water while gravities above about 20 B. introduce too little water. We prefer a specific gravity of about 16 B. for most oils.

The principles of our invention can be applied to any of the crude or partially refined animal and/or vegetable oils which contain sterols and concurrently contain at least 0.15 of free fatty acids. Although we prefer to use a degummed oil, i. e. one containing from about 0.15% to 0.35% titratable fatty acids and less than about 0.5% gum, as indicated above all oils (degumrned, partially degummed and non-degummed) are amenable to our treatment. treated, the oil can be tailored by any of the known hot refining methods to fall within our expressed preferences and specifications. Further, the non-degummed crude oils can be refined by the herein-described hydration" treatment to secure lower non-steroid oil loss than would result from a hot refining of the same oils. Such oils as soya, cottonseed, corn, peanut, linseed, and various fish oils are especially contemplated.

It will be apparent that the principles of our invention can be effectuated either in a batch refining treatment or in a semi-continuous treatment.

Having now described our invention, what we claim is:

1. In the process of refining animal and vegetable oils which contain sterols, the improvement which comprises: providing a mass of said glyceride oil containing natural free fatty acids in an amount between about 0.15% and 1%, and having a gum content below about 0.5% bringing said oil to a temperature between about 50 and 70 F. and while maintaining the oil within said range of temperature emulsifying it with a small quantity of an aqueous solution which: (a) has a specific gravity between about 12 B. and 20 B.; (b) contains at least one alkali metal alkali dissolved therein Thus when a non-degummed oil is in an amount at least sufiicient to neutralize the free fatty acid content of the oil; and (c) which contains dissolved therein an emulsion breaking amount of at least one emulsion breaking agent from the group, consisting of alkali metal borates, pyrophosphates, silicates, acetates, and oxalates, and alkali metal salts of ethylene diamine tetraacetic acid; maintaining said emulsion at temperatures between about F. and 70 F. for a time period between about 3 and 20 minutes, while subjecting it to vigorous agitation; at the end of said time period promptly passing the emulsion to a centrifuge wherein the emulsion is broken as a result of the presence of said emulsion breaking amount of emulsion breaking agent and is separated into a substantially neutral refined oil as the light efiiuent, and a heavier foots fraction characterized by having a higher concentration of sterols therein than is present in a comparable foots fraction secured when the said provided mass of oil is similarly treated, but without any emulsion-breaking agent.

2. The process as claimed in claim 1 wherein the provided mass of oil has a free fatty acid between about 0.15% and 0.35%.

3. The process as claimed in claim 2 wherein the emulsion breakingagent is borax.

4. The process as defined in claim 3 wherein the aqueous solution employed in treating the oil is substantially saturated with borax.

5. The process as claimed in claim 4 where said aqueous solution has a specific gravity of about 16 B.

6. The process as claimed in claim 2 wherein the emulsion breaking agent is tetrasodium pyrophosphate.

7. The process as claimed in claim 6 wherein the aqueous solution employed in treating the oil is substantially saturated with tetrasodium pyrophosphate.

8. The process as claimed in claim 7 wherein said aqueous solution has a specific gravity of about 16 Be.

9. The process as claimed in claim 2 wherein the emulsion breaking agent is a sodium salt of ethylene diamine in tetra-acetic acid.

10. The process as claimed in claim 9 wherein the cmul sion breaking agent is the tetrasodium salt.

11. The process as claimed in claim 10 wherein the aqueous solution employed in treating the oil is substantially saturated with the tetrasodium salt.

12. The process as claimed in claim 11 wherein the said aqueous solution has a specific gravity of about 16 B.

13. The process as claimed in claim 2 wherein the emulsion breaking agent is sodium acetate.

14. The process as claimed in claim 13 wherein the aqueous solution employed in treating the oil contains sodium acetate in an amount of about 5%.

15. The process as claimed in claim 14 wherein, said aqueous solution has a specific gravity of about 16 B6.

16. The process as claimed in claim 2 wherein the aqueous solution has a specific gravity of about 16 B.

17. The process as claimed in claim 16 wherein the temperature of the oil is maintained at about F., and said aqueous solution amounts to about 1.35% by weight of the oil.

18. The process as claimed in claim 17 wherein the amount of emulsion-breaking agent is about 5% by weight of said aqueous solution, and wherein the alkali-metal alkali is sodium hydroxide.

References Cited in the file of, this patent UNITED STATES PATENTS 2,225,575 Thurman Dec. 17, 1940 2,463,015 Bersworth ,Mar. 1, 1949 2,507,184 Rini May 9, 1950 2,638,476 James May 12', 1953

Claims (1)

1. IN THE PROCESS OF REFINING ANIMAL AND VEGETABLE OILS WHICH CONTAIN STEROLS, THE IMPROVEMENT WHICH COMPRISES: PROVIDING A MASS OF SAID GLYCERIDE OIL CONTAINING NATURAL FREE FATTY ACIDS IN AN AMOUNT BETWEEN ABOUT 0.15% AND 1%, AND HAVING A GUM CONTENT BELOW ABOUT 0.5% BRINGING SAID OIL TO A TEMPERATURE BETWEEN ABOUT 50* AND 70* F. AND WHILE MAINTAINING THE OIL WITHIN SAID RANGE OF TEMPERATURE EMULSIFYING IT WITH A SMALL QUANTITY OF AN AQUEOUS SOLUTION WHICH: (A) HAS A SPECIFIC GRAVITY BETWEEN ABOUT 12* BE. AND 20* BE.; (B) CONTAINS AT LEAST ONE ALKALI METAL ALKALI DISSOLVED THEREIN IN AN AMOUNT AT LEAST SUFFICIENT TO NEUTRALIZE THE FREE FATTY ACID CONTENT OF THE OIL; AND (C) WHICH CONTAINS DISSOLVED THEREIN AN EMULSION BREAKING AMOUNT OF AT LEAST ONE EMULSION BREAKING AGENT FROM THE GROUP CONSISTING OF ALKALI METAL BORATES, PYROPHOSPHATES, SILICATES, ACETATES, AND OXALATES, AND ALKALI METAL SALTS OF ETHYLENE DIAMINE TETRAACETIC ACID; MAINTAINING SAID EMULSION AT TEMPERATURES BETWEEN ABOUT 50* F. AND 70* F. FOR A TIME PERIOD BETWEEN ABOUT 3 TO 20 MINUTES, WHILE SUBJECTING IT TO VIGOROUS AGITATION; AT THE END OF SAID TIME PERIOD PROMPTLY PASSING THE EMULSION TO A CENTRIFUGE WHEREIN THE EMULSION IS BROKEN AS A RESULT OF THE PRESENCE OF SAID EMULSION BREAKING AMOUNT OF EMULSION BREAKING AGENT AND IS SEPARATED AND A HEAVIER "FOOTS" FRACTION CHARACTERIZED BY HAVING A HIGHER CONCENTRATION OF STEROLS THEREIN THAN IS PRESENT IN A COMPARABLE "FOOTS" FRACTION SECURED WHEN THE SAID PROVIDED MASS OF OIL IS SIMILARLY TREATED, BUT WITHOUT ANY EMULSION-BREAKING AGENT.