US2598269A - Recovery of sterols - Google Patents

Description

Patented May 27, 1952 RECOVERY OF STEROLS Hans George Kirschenbauer, Allendale, N. .L, as-

signor to' Colgate-Palmolive-Peet Company, Jersey City, N. J a corporation of Delaware No Drawing.

Application May 27, 1949,

Serial No. 95,875

7 Claims.

This'invention relates to the recovery of high-- common technique has been the use of molecular distillation on the natural fats and oils andthe recovery of volatile unsaponifiables from the distillate. Such procedure is limited since the sterolsfor example occur in the triglycerides in relativelyminute quantities, only fair yields are obtained, and complex and costly operating techniques including short path high vacuum distillation are required.

Any means of recovery of the sterol content and: the like must" take into consideration the complex character of'the parent fatty material. The unsaponifiables represent only a small frac-- tion; of the total composition, a portion of the sterol content is combined in the form of esters with the higher fatty acids, and' in general the physical constants of various unsaponifiables maybe broadly of the same order as those of the main constituents of the fatty material.

A; simple and economical process has been developed however for the recovery of such high-boiling unsaponifi ables. Broadly, the pres-- ent invention comprises the recovery of the high-boiling alcohols, e. g. sterols, from still bottoms andthe like, derived from the hydrolysis and alcoholysis of a fatty material. By means ofthe application of conventional splitting proc esses,.the bulk of the higher fatty acids either in the form of free acidsor as relatively low boiling" fatty acid esters, glycerine, and any other relatively low-boiling volatile constituents, may be removed from the reaction mixture by conventional distillation practices. Simultaneously, there is formed" a still residue or still bottoms in which thehigh-boiling volatile alcohols are concentrated, and are partially combined as esters in significant amounts therein. These desired constituents are recoverable from the still residue by a combination of a saponification and a heat treatment, wherein the combined esters are sap'onified to liberate the high boiling alcohols and convert the residual fatty acid content to a non-volatiliza-ble form, and the free alcohols are vaporized from a substantially anhydrous molten saponifiedi mass at high temperatures in the presenceof an inert gas.

Accordingly, the present invention contemplates the hydrolysis of the fatty material in any suitable manner including the Twitchell and autoclave methods, and the removal by vaporization of at least the major portion of the fatty acids from the reaction products. The still bottoms resulting from continuous countercurrent high pressure fat-splitting operations with or without catalysts followed by distillation are preferred, such as the processes illustrated by Ittner, U. S. Patents Nos. 2,435,745 and 2,458,170. In such processes, the water" and fat or equivalent fatty material, are preheated to the operating temperature which is between 365 F. and 600 F., and generally about 450 to 500 F. Pressure onboth the water and the fat are raised to that corresponding to the pressure of saturated steam at the selected temperature, which pressure is within the range of 150 to 1,600 pounds and generally within about 250 to 750 pounds per square inch. The preheated water is pumped into the top of the splitting zone and the heated fatty material is introduced into the bottom of the splitting col' umn. Hydrolysis of the fat occurs as the water and fat are brought into intimate counter-current contact. Itis possible to attain over a 98% split of tallow at about 475 F; and about 600 pounds of pressure in a tower of suitable size. The fatty acids containing the sterols and other high boiling alcohols such as tocopher'ols are removed from the top of the tower, and the aqueous sweet water phase is recovered from the bottom.

The fatty acid stock is then distilled at about 450 to 500 F. maximum with reduced pressure, and with or without the aid of stripping steam. The maximum temperature depends principally upon the necessity of avoiding extensive polymerization of the acids. The distillation may occur either in batch stills or continuous techniques may be used. After the vaporization of bull: (e. g. about=-95%) of the fatty acids, the blackish gummy residue or still bottoms comprises free fatty acids, glycerides, a concentratcd unsaponifiable content including sterols, tocopherols, hydrocarbons, etc., and minor amounts of oxidized and polymerized fatty acids. A typical composition of still bottoms derived from tallow' after distillation of about of the fatty acids comprises. approximately 35% free fatty acids, 50% glycerides, 9%. unsaponifiables in free and combined form with a sterol content ofv about 2 to 3 generally, and about 6% oxidized acids. It is to be noted however that the proportions are variable and are dependent mainly upon the character of the fatty material and the amount of distillation.

It has been discovered that a small percentage of the high boiling unsaponifiables are distilled ofi with the fatty acids. However, the vast proportion or the sterols and similar unsaponifiables remains in the residue, apparently due to a number of factors including the necessity for avoiding non-polymerizing temperatures, the ready esterification of the high boiling alcohols with free fatty acids to form sterolic esters and the like, etc. From such still bottoms, the concentrated unsaponifiable alcohol content may be recovered in good yield. More particularly, it is desired to use the second still bottoms which are obtained-by recycling the original or first still bottoms through the splitting and distillation zones. There is then formed an enriched bottoms fraction which usually contains over 5% sterols by weight. A sterol concentration of at least about 2.5% to above 5% is efficacious since the percent losses during processing are thereby of a relatively small order.

Similarly, the original fatty material may be subjected to alcoholysis to form an unsapcnifiable concentrate. The processes disclosed by Allen et al., U. S. Patent No. 2,383,579; Dreger, U. S. Patent 2,383,596; and Trent, U. S. Patents 2,383,632 and 2,432,181 are fully applicable here- In such alcoholysis processes the fatty material is treated at low temperatures with a suitable monohydric alcohol generally in the presence of an alcoholysis catalyst whereby conversion of the triglycerides in the case of fats and oils to the more volatile fatty acid esters of the monohydric alcohols occurs rapidly. The monohydric alcohols are preferably the aliphatic ones of not more than about six carbon atoms, such as methyl, ethyl, propyl alcohols, etc.

The rate of the alcoholysis reaction is largely determined by the temperature and the presence or absence of catalysts. If a catalyst is used, an advantageous temperature range is from about to 150 C. The alcoholysis reaction proceeds quite rapidly even at room temperature in the presence of a catalyst but proceeds even more rapidly at elevated temperatures. Suitable catalysts include strong mineral acids such as sulphuric acid and alkaline materials such as sodium hydroxide, sodium alcoholate, etc. Where the reaction is carried out without catalysts,

higher temperatures are preferred within the range of about 100 to 300 C. The conversion to the volatile monoesters may be 98% complete at the end of an hour under suitable conditions.

The alcoholysis reaction products may be distilled or flash-distilled to separate unreacted alcohol, the alkyl esters, and glycerine, whereby a concentrated still residue is obtained containing the sterols and other unsaponifiables concentrated therein. Alternatively, the reaction mixture may be subjected to phase separation in order to recover separate ester and glycerine layers. The fatty acid esters and/or glycerine in each layer may be removed by either batch or continuous distillation. The still residues after separation of these and other readily volatile constituents, may be admixed if desired and consist of a relatively small volume of material containing generally some alkyl esters, acids, unreacted fatty acid glycerides, as well as the sterols and other unsaponiflables in a high concentration and unimpaired condition.

These still residues may now be saponiiled in any suitable manner, either by batch, semicontinuous or continuous operations. The saponification is accomplished by means of an alkaline saponfying agent or mixtures of such agents, preferably those having an alkali metal or an alkaline earth metal as the cation. For relatively low temperature saponification, e. g. kettle boiling, it is preferred to use the caustic alkalies such as sodium and potassium hydroxide. In high temperature saponification procedures, such agents as sodium carbonate, calcium oxide, and iron oxide may be used advantageously. The proportion of alkaline saponiiying agent should be sufiicient stoichiometrically to react with substantially all of the fatty acid material in the still bottoms. More specifically, in addition to reacting with free fatty acids, the saponifying agent should be suflicient to liberate substantially all of the combined fatty acids, whether combined in the form of sterolic or nonsterolic esters. It is important to decompose these sterolic esters in order to have a maximum free sterol content and maximum recovery of the sterols subsequently. Accordingly, approximately a molar equivalent and even an excess of saponifying agent may be utilized in order to effect complete saponification as much as possible. Any excess of saponifying agent should be generally up to about a 25% excess, and preferably a 10% excess, of the stoichiometric amount necessary for complete saponification. Large excesses of free alkali are deleterious and increase the yield of undesirable by-products, particularly during saponification at high temperatures. Amounts of saponifying agent not appreciably less than a molar equivalent may be utilized satisfactorily in high temperature saponification procedures since a small amount of free fatty acids may be removed from the reaction mixture by distillation.

One means of converting the still bottoms to the soap mass is by the usual type of kettle boil method, wherein the saponifiable material is boiled with strong aqueous alkali in order to effect saponification. After graining, washing, and settling with or without nigre removal, the resulting soap mass may have a concentration of total fatty acids (as soaps) and unsaponifiables of higher than by Weight. As indicated infra, it is desired to recover the sterols and like material from a substantially anhydrous mass. Accordingly, the kettle soap mass may be subjected to any suitable drying procedure, e. g. drum drying or spray drying, to remove substantially all of the water content. It is preferred to reduce the moisture content to less than about 10%, and preferably less than about 5%, of the weight of the saponified still bottoms. Roll drying of the saponified mass may be effected so as to remove all the water except for a few percent of the order of about 2 to about 5%. The substantial drying of the soap mass is of material consideration to achieve eflicient processing. Large amounts of water materially increase the time for attaining the desired temperature range to be used in the subsequent heat treatment and promote the possibility of hydrolysis of minor amounts of soap.

After saponification and drying, the reaction mixture is subjected to a severe heat treatment in the presence of an inert gas. At temperatures of at least about 225 C., the saponified still residue starts to liberate the high-boiling unsaponifiable in vapor form. While the temperature is being elevated and preferably between C. and 200 C., an inert gas such as steam, hydrocarbon vapor, carbon dioxide, or nitrogen is passed into the substantially anhydrous material. The inert gas avoids local overheating and polymerization, promotes thorough agitation, and prevents appreciable decomposition. The steam or other inert gas is requisite to the process since by its use the partial vapor pressures of the sterols and other high boiling volatile constituents are lowered and these materials are vaporized at temperatures below the range wherein substantial decomposition of such alcoholic materials occurs generally. Moreover, the inert gas blankets the distilling mass such that no undue oxidation appears to take place at'these high temperatures.

The temperatures employed for the heat treatment should range from at least about 225 C. to about 350 C., and preferably between at least about 250 C. to 300 C. at atmospheric pressure. Within this temperature range and with a current of inert gas passing through the molten mass, the high boiling volatiles such as the sterols are largely vaporized within a relatively short time. For substantially complete separation of these volatile unsaponifiable constituents, the amount of inert gas used should be substantial and reduced pressure of the order of 510 mm. and even to 0.5 mm. may be employed, in addition to increased time of treatment. The reaction mass during this heat treatment does not darken generally, and in fact often appears to be bleached by the inert gas.

The lowering of the partial pressures of the volatile constituents of the soap charge is preferably obtained by the use of open steam rather than by the other chemically inert gases. The

use of steam is more economical and results in less condensation and recovery problems in comparison to the employment of other inert gases such as carbon dioxide or nitrogen. superheated steam is advantageous and preferably a suflicient amount of superheat should be utilized to insure the use of practically dry steam (e. g. -12% moisture). For high vaporization efficiency, the steam should be introduced to the charge through a large number of small orifices and at an appreciable depth below the surface of the molten mass. Thus, the bubbles of steam rise through the molten charge and escape from the surface of the liquid with a concentration of the volatiles, governed by their partial vapor pressures.

A particular feature of the invention lies in the performance of the saponification and heat treatment steps in one unit operation. Thus, the still bottoms may be heated to a temperature of at least about 100 C. and generally about 150 C. to about 200 C. in order to turn the gummy mass into a fairly fluid. form. The alkaline saponifying agent, either as a finely ground solid or dissolved in a minimum amount of water or admixed with a low-boiling solvent, is added slowly either continuously or intermittently. The complete addition of the saponifying agent very rapidly is undesirable since the reaction mass may solidify and the saponification reaction be incomplete thereby. Either before, during, or after saponification, a strong current of steam or other inert gas is bubbled continuously into the reaction mixture. The saponificati'on reaction appears to take place instantaneously and equilibrium is attained within a relatively short time. At these temperatures, any low-boiling volatiles such as water, a. lowboiling solvent if used, etc., are vaporized and removed thereby. The resulting substantially anhydrous soap mass is generally molten at above 200 C. in the case of calcium soaps, 'suitable mixtures of potassium and sodium soaps, potassium. and calcium soaps, etc. Where sodium soaps only are present, it is generally necessary to attain a temperatureof at least about 250 C. to achieve a molten or fluid phase. t is thus evident that conversion has been effected from a molten normally solid still residue to a molten normally solid substantially anhydrous soap mass whereby the volatile fatty acids are converted to a non-volatile derivative, the free high-boiling alcoholic content is increased,the low-boiling volatiles vaporized, and the residue substantially dried, etc., Without the necessity of any intermediate treatment.

The temperature of the molten substantially anhydrous soap mass may now be rapidly elevated in the presence oft-he inert gas at atmospheric pressure or ordinary reduced pressure (as distinguished from short path high vacuum molecular distillation) as previously setforth in order to volatilize the high-boiling unsaponifiablessuch as the sterois and tocopherols.

Alternatively, molten still bottoms may be admixed with the saponifying agent either in batch or continuous operations and slowly fed into a reaction vessel heated to any temperature from above the melting point of the substantially anhydrous soap mass to be formed and up to the ultimate temperature desired for the recovery of the high-boiling unsaponifiables. The inert. gas is brought into intimate contact with the reacting mass and simultaneous saponification and steam distillation of the high-boiling unsaponifiables occur thereby. The combined chemical and physical treatments are complete and the desired volatile unsaponifiables are vaporized and removed by the steam distillation within a rela=- tively short time.

These unsaponifiables which are co-distilled with the steam or other inert gas may be fractionated or the entire distillate may be condensed and the components isolated and purified subsequently in any suitable manner. It is preferred to condense the aqueous content of the overhead separately from the desired constituents by suitable fractionation means since this is a simple, efiicient and economical procedure in view of the Widedifference in condensation temperatures between the steam and the sterols and the like in the overhead. Thus, the distillate would be passed into a vapor condenser wherein the temperature is so regulated that substantially all of the desired unsaponifiab'le's are liquefied and the steam is maintained in the vapor state. Any unsaponifiables entrained in the steam may be removed by the use of suitable baiiies, centrifugal separators, etc. The steam, freed from the unsaponifiables, may be condensed subsequently or passed into a preheater for recycling through the system.

From the condensed unsaponifiables derived from animal fatty materials, cholesterol may be recovered in good yields and a high degree of purity. Phytcsterols, e. g. stigmasterol and si-tosterol, are recoverable from the vegetable materials by practice of the present invention. Where mixtures of animal and vegetable mate-- rials; e. g. tallow and coconut oil, are utilized for the initial hydrolysis or alcoh'olysis reaction, both cholesterol and phytosterols will be present in the distillate. In the use of wool fat and the like, large amounts of long-chain alcohols such as ceryl alcohol. are vaporized along with the cholesterol. Where present, it will generally be found. that minor amounts; of. hydrocarbons, vitamin A and E type compounds and other highboiling unsaponifiables will be found in the distillate also.

These condensed organic constituents may be further purified or isolated in any suitable manner including crystallization or liquid-liquid phase separation from solvents, high temperature distillation, molecular distillation, chromatographic adsorption, etc.

The non-volatile residue resulting from the steam distillation may be treated in any suitable manner to recover the soaps, or the fatty acids therefrom. Thus the anhydrous soap mass may be hydrated and used as such or in admixture with other soaps. Alternatively, the soaps may be split by acidification, and the fatty acids separated from the acidified mixture, e. g. by distillation. The separated fatty acids may be used for preparing high grade soaps, monoglycerides, lubricants or other desired products.

The following are additional specific examples designed to be illustrative of the natur of the invention:

Example I Tallow is split by continuous counter-current bottoms and 160 parts of soda ash are mixed and fed slowly into a closed vessel having a stirrer, thermometer, a steam inlet and an outlet to a condenser for a period of one hour. A vessel temperature of 280 C. and a vacuum of 16 mm.

absolute pressure are maintained continuously.

A current of steam is run through an orifice into the bottom of the vessel at a pressure of four lbs. per square inch gauge before the orifice. Steaming is continued for two hours at 270-280 C. and 560 parts of aqueous overhead are recovered by condensation. The water is removed from the condensate by settling and subsequent heating under vacuum. Analysis of the residue discloses the presence of 21.2 parts of cholesterol.

Ewamplc II The first still bottoms of No. 4 tallow acids, derived from the splitting of tallow and distillation of the acids fraction, and having a saponification value of 178.6 (17.86% KOH) and an unsaponifiable content of 7.9% are utilized herein. The still residue (1000 parts) is heated in a closed vessel provided with a steam inlet near the bottom and below the surface of the still bottoms and an outlet leading to condensers and receiv ing vessels. It is not necessary to use an agitator. The still residue is heated above 100 C. and a current of superheated steam (270 C.) is bubbled into the bottoms. The steam forms an inert atmosphere above the soap mass and agitates the same in its passage therethrough. All the soda ash (180 parts) is slowly fed into the reaction vessel during elevation of the temperature from above 100 C. to above 250 C. whereby a molten mass of anhydrous soaps is obtained. The resulting soap mass is rapidly heated then to about 270-275 C., and extensive amounts of volatile unsaponifiable material are co-distilled with the steam for about 30 minutes. The steam and the vaporized unsaponifiables are fractionally'condensed to separate the aqueous fraction. Cholesterol (20.4 parts) is recovered from the condensed unsaponifiables by molecular distillation.

Example III 1000 parts of cottonseed oil are converted at room temperature to the methyl esters and free glycerine by alcoholysis with 241 parts of methanol containing 8.1 parts of sodium hydroxide as a catalyst. The reaction product is flash distilled to separate excess methanol, the alkyl esters and glycerine, leaving a still bottoms residue of about 100 parts.

This residue is heated to 150 C. at atmospheric pressure, and the calculated amount of ground caustic soda is introduced into the molten still bottoms. The superheated steam is introduced into the bottom of the closed reaction vessel, and the temperature is thereafter elevated to 300 to 310 C. whereupon large amounts of steam and vaporized unsaponifiables are removed as distillate. The vapors are condensed in fractional condensers to remove the water content. The condensed unsaponifiables are subjected to molecular distillation whereby 10.3 parts of sterols and 1.25 parts of tocopherols are recovered in purified form.

Example IV Alcoholysis is performed on preheated wool grease with methyl alcohol in the presence of an alkaline catalyst, and the reaction mass is neutralized until it has a pH value of 5.5. The reaction products are flash distilled at 230C. and 2-3 mm.'of mercury to remove about 85% of the alkyl esters.

The still bottoms are reacted with the calculated amount of sodium hydroxide during elevation of the temperature from 150 C. to 250 C. to prepare a molten mixture of the substantially anhydrous soap mass. A current of nitrogen is injected into the soap mass immediately before addition of the alkali to form an inert atmosphere and to agitate the molten mass. The temperature is rapidly elevated to 275-280 C. at a vacuum of 6 mm. mercury, whereupon the cholesterol and long chain aliphatic alcohols including ceryl and lanyl alcohols are vaporized and subsequently condensed to the liquid state. The aliphatic alcohols and the cholesterol are separated from each other by molecular distillation.

Example V Per cent Free cholesterol 6.5 Total cholesterol (free and combined) 6.6

Total unsaponifiables (including cholesterol) 12.2 Total fatty acids and unsap 85.0 Moisture 2.5

The original bottoms had possessed an acid value (KOH) of 9.5% and a saponification value of 15.2% with an unsaponifiable content of The roll dried saponified still bottoms are heated to 100 C. in a closed vessel. A current of superheated steam is bubbled through the contents of the vessel and forms a blanket over the reaction mass. The temperature of the reaction mass is rapidly elevated to 300 C. for 45 minutes, and the vaporized material is condensed fractionally to recover the unsaponiflables comprising largely cholesterol with minor amounts of tocopherols and hydrocarbons.

Where the term fatty material or its equivalent is specified in the description and claims, it is intended to mean the fats, fatty oils and waxes of animal, vegetable or marine origin. Suitable examples of fatty materials which may be used as an original reactant are tallow, lard, wool fat, shark oil, whale oil, sperm oil, spermaceti, palm oil, coconut oil, olive oil, cottonseed oil, linseed oil, soya bean oil, or mixtures thereof, etc. By the wording still residue, still bottoms or the equivalent is meant the crude mixtures containing concentrated unsaponifiables and saponifiable fatty acid material which remain after distillation or evaporation of the products derived from the hydrolysis and alcoholysis of a fatty material. All percentages and proportions illustrated are by weight unless otherwise specified.

Since certain changes may be made in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all the generic and specific features of the invention herein described, and all statements of the scope of the invention, which as a matter of language might be said to fall therebetween.

Having described the invention what is desired to be secured by Letters Patent is:

l. A process of recovering sterols from fatty materials containing the same comprising treating said fatty material with water at a temperature between about 365 F. and 600 F., and at a pressure within the range of about 150 to 1600 lbs. per square inch to hydrolyze said fatty material and produce a fatty acid stock containing said sterols and an aqueous glycerine phase, separating said fatty acid fraction, vaporizing the major portion of the fatty acids present therein and recovering a gummy still bottoms residue comprising saponiflable matter and concentrated sterols, heating said still bottoms and maintaining the same in a molten fluid condition, adding alkaline saponifying agent thereto and saponifying said still bottoms in the molten phase at said elevated temperature to convert said saponifiable material to soaps and liberate additional free sterols, the resulting saponified still bottoms residue being maintained at a temperature above its melting point to maintain a molten fluidized mass, vaporizing said sterols therefrom in the presence of an inert gas at a temperature at least about 225 C. and below the temperature at which substantial polymerization and decomposition occurs and recovering said sterols.

2. The process of claim 1 wherein the still bottoms residue is resubmitted to the hydrolysis and fatty acid vaporization treatments to form a second 'still bottoms having an enriched sterol content.

3. The process of claim 1 wherein the fatty material is of animal origin and cholesterol is recovered thereby.

4. A unitary process of recovering cholesterol from gummy still bottoms containing fatty acid material and concentrated cholesterol in free and combined form, which comprises heating said still bottoms and maintaining the same in a molten fluid condition, adding alkaline saponifying agent thereto at a temperature above about C. and saponifying fatty acid material in the molten phase at said elevated temperature to form soaps of fatty acid material and liberate additional free cholesterol, the final temperature being sufliciently high to maintain the resulting soap-containing mass in a molten fluid condition, heating the resultant molten saponified still bottoms at a temperature from about 225 C. to about 350 C. in the presence of an inert gas and vaporizing cholesterol, and recovering said cholesterol.

5. A unitary process of recovering cholesterol from gummy still bottoms containing fatty material and concentrated cholesterol in free and combined form, which comprises heating said still bottoms and maintaining the same in a molten fluid condition, adding alkaline saponifying agent thereto, saponifying said bottoms in the molten phase at said elevated temperature to form soaps of said fatty material and liberate additional free cholesterol, the final temperature being sufliciently high to maintain the resulting soap-containing mass in a molten fluid condition substantially free of low-boiling volatile liquids, heating the resultant molten saponified still bottoms at a temperature from about 225 C. to about 350 C. in the presence of an inert gas and vaporizing cholesterol, and recovering said cholesterol.

6. A unitary process of recovering sterol from gummy still bottoms containing fatty material and concentrated sterol in free and combined form, which comprises heating said still bottoms and maintaining the same in a molten fluid condition, adding alkaline saponifying agent thereto, saponifying said bottoms in the molten phase at said elevated temperature to form soaps of said fatty material and liberate additional free sterol, the final temperature being sufliciently high to maintain the resulting soap-containing mass in a molten fluid condition substantially free of lowboiling volatile liquids, heating the resultant molten saponified still bottoms at a temperature from about 225 C. to about 350 C. in the presence of an inert gas and vaporizing sterol, and recovering said sterol.

7. The process of claim 6 wherein the inert as is steam.

HANS GEORGE KIRSCHENBAUER.

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

UNITED STATES PATENTS Number Name Date 1,610,854 Fowler Dec. 14, 1926 2,056,984 Schellmann Oct. 13, 1936 2,262,950 Lorenz Nov. 18, 1941 2,280,815 Fernholz Apr. 28, 1942 2,316,068 Hickman et al. Apr. 6, 1943