US 2721872 A
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Oct. 25, 1955 M. MATTIKOW ETAL REFINING 0F LOW-GRADE FATS Filed Feb. 19, 1952 BLACK GREASE MEI'HANOL, ACID REFL ux (Spurn/vs Mo EsTERIF/M no) METHYL ESTER-5 0F FATTY/1810.3,
COLOR/N6 MATTER, MEI'HANOL 140/0, 61. VCEROL, JTEROLS, TOCOPHEROLS.
COOL! NG AND FILTER/N6 (MAY CONTAIN STEROLS) METHYL ESTERS OF FHTTVAC/DS, COLORING MATTER, METHANOL, ACID,
GLYCEROL, srsRoLs, TOCOPHEROLS. /4
D/JT/LLAT/ON 0F METHANOL METHYL ESTERS 0F FA TTVAO/DS, COLOR/N6 MATTER, ACID, eLvcERoL, STEROLS TOCOPHEROLS.
v WATER, COLOR/N6 MA rrER, HEXANE ANDAOUEOUJ' Mag/1 WASHWG SALTS, NAOH, GLYCEROL.
Aqufous ALKALI k f7 METHYL ESTERS OF FArrYAc/as. are-Raw, TOCOPHEROLS, HEXANE, REMAINING COLORING MATTER. Y 16' BLEACMNG ABSORBANE BLEACIH/NG ABSORBANT COLOR/N6 MATTER- DECOLOR/Z/NG 30 2 METH w. ESTERS or F4 rrv ACIDS, STEROLS, TOCOPHEROLS, HEX/INA. 22
D/STlLLAT/ON HEX/W5 OF HEXA NE METHYL ESTERS OFFA rryAc/os,
STEROLS, r0 COPHEROL-S'. 24
VACUUM METHYL E8 TERS 0F mrrv ncros DIST/L LA r/0/v e5 STEROLJ, TOCOPHEROLS. /z6 METHANOL REFLUX/NG n IMS'OL UBLE [MPUR/T/ES Merl-mm AND H; TERI/V6 27 28 METHANOL ans/eons, TOCOPHEROLS. 9
COOL/N6 AND STEROLS PREC/P/TA TE) F/L TERING a0 INVENTORS rom /4512029 MET/4A NOL 31 l; lkzvui Perlman/ wMorris Mafia/cow ATTOR NEYS United States Patent REFHVING OF LOW-GRADE FATS Morris Mattikow and David Perlman, New York, N. Y., assignors to Benjamin Clayton, doing business under the fictitious name and style of Refining Unincorporated, a sole roprietorship of said Benjamin Clayton Application February 19, 1952, Serial No. 272,465
Claims. (Cl. 260-4125) This invention relates to the refining of low-grade fats and is particularly concerned with the upgrading of black grease although it is applicable to other low-grade fats.
Black grease is a low-grade product derived from the soapstock which is separated from glyceride oils in an alkali refining operation. Such soapstock contains fatty acid soaps, the gums originally present in the oil in partly decomposed form, excess alkali, entrained glyceride oil, a small amount of glycerine and a considerable portion of water. The most common commercial process of treating soapstock is to acidulate it with a large excess of concentrated sulfuric acid. This decomposes the fatty acid soaps to liberate fatty acids and furthermore chars and decomposes the gums. The acidulated material will separate upon standing into two layers, an upper layer of fatty material and a lower aqueous layer. The upper layer can be separated from the lower layer and constitutes the black grease of commerce.
This black grease is a dark colored material which contains a substantial proportion of free and combined fatty acids. That is to say, black grease is a complex mixture of pigments and other coloring matter, free fatty acids, glycerides, polymerized fats, products from the decomposition of phosphatides and other materials, including unsaponifiables such as sterols and tocopherols, and charred products resulting from the use of concentrated sulfuric acid. The free fatty acids may be directly distilled therefrom by vacuum distillation at high temperatures, but large losses and low-grade fatty acids result. Repeated distillation with further losses are necessary to obtain high-grade fatty acids. In general, the black grease is subjected to either an acid or an alkaline splitting operation to liberate the combined fatty acids prior to distillation. Thus, black grease is usually subjected to an aqueous acid splitting operation known as twitchellization. Alkaline splitting may be employed, in which case the resulting material is acidulated. In either case, an upper layer of fatty material may be separated from a lower aqueous layer and the separated fatty material is usually distilled in vacuum at high temperatures. The fatty acid which distilled over must in most instances be redistilled to obtain a sufficiently low colored product. Even when distilling the split black grease, the losses are high, as the still residue or pitch from the first distillation varies from to 25% of the weight of the fatty material. Either the black grease itself or the fatty material resulting from splitting the black grease resists decolorization with bleaching agents and bleaching earths.
Instead of being acidulated with concentrated sulfuric acid to first produce black grease, the soapstock is sometimes boiled with added caustic alkali to saponify the entrained glyceride oil and the remaining mass then grained with salt and washed with water. The resulting soap is of very low grade as to color, odor and stability. This soap is sometimes acidulated to yield an upper layer of fatty material containing fatty acids. Such fatty acids 'are dark in color and must be distilled to be acceptable as commercial fatty acids. Again the losses during distilla- 2,121,872 Patented Oct. 25, 1955 tion are high. The temperatures of distillation in any of the fatty acid distillation steps above discussed are high, for example, 490 F. and a high vacuum must be maintained. Under these conditions sterol esters of fatty acids are formed and remain as part of the residue in the still, i. e., part of the pitch. The only upgraded products recovered in the above processes are a part of the fatty acids and it is apparent that the prior processes of treating soapstock are expensive and unsatisfactory and result in the destruction or loss of valuable products such as sterols and tocopherols and a substantial portion of the fatty acids.
In accordance with the preferred process of the present invention, the black grease is first subjected to a combined splitting and esterification step employing a lower monohydric aliphatic alcohol and a strong mineral acid. This step is preferably carried out under reflux conditions and the water content of the mixture is maintained as low as practicable. Thus the amount of water should preferably not exceed 2.5% by weight of the reaction mixture although amounts of water up to about 6.5% can be tolerated if the longer splitting times are employed. The time of treatment should be suflicient to split substantially all of the glycerides and to esterify substantially all of the fatty acids with the lower aliphatic alcohol. That is to say, the splitting operation is continued until all of the fatty material goes into solution or only a very small amount of undissolved material remains.
The resulting mixture is cooled and preferably filtered to remove any insoluble matter. This insoluble matter may include a small amount of sterols if the sterol concentration in the mixture is relatively high. These sterols can be recovered from the insoluble matter. The excess alcohol in the filtrate is then distilled and recovered in concentrated form for reuse in the splitting and esterification step. The resulting residue is predominantly fatty acid esters of the lower aliphatic alcohol but contains a substantial amount of coloring matter, the acid employed in the splitting step, glycerol, sterols and in some cases tocopherols.
It has been found that the greater part of the coloring matter may be removed from this mixture by washing the same with an aqueous solution of caustic alkali. This treatment also conditions the mixture for subsequent substantially complete decolorization with bleaching adsorbents. Best results are obtained when the mixture referred to is first dissolved in a volatile organic solvent therefor, for example, a light petroleum solvent such as commercial hexane or petroleum ether. The mixture resulting from the washing operation readily separates into an aqueous material and a solvent layer containing fatty material in solution. The aqueous layer or spent washing liquor contains most of the coloring matter, water soluble inorganic salts, excess alkali, glycerol and other water soluble materials. Valuable materials such as gycerol or choline or inositol compounds, if present, may be recovered from the spent washing liquor.
The purified and partially decolorized fatty material from the washing step is preferably treated with a bleaching adsorbent while still containing the hexane or equivalent solvent and upon being removed from contact with the adsorbent, a solvent solution of light colored fatty material is obtained. The solvent may be readily distilled from the solution leaving a material which is predominantly the fatty acid esters of the lower aliphatic alcohol employed. This material is a high grade light colored product and can be employed or sold Without further treatment for various purposes.
The decolorized fatty acid esters still contain substantially all of the unsaponifiables such as sterols and tocopherols. The fatty acid esters may be separated from the unsaponifiables by a vacuum distillation step at a much lower temperature than is necessary for distilling fatty acids themselves. Under these conditions sterol esters of fatty acids do not form. The distillate is substantially pure fatty acid esters of the lower aliphatic alcohol and is a high-grade product of light color. Again, it may be employed or sold in the form it is recovered from the distillation step or it may be split to recover high-grade fatty acids in either an alkaline or acid splitting step. The residue in the still is largely unsaponifiables and may be fractionated into sterols and tocopherols with a lower aliphatic alcohol such as methanol in which the tocopherols are very soluble and the sterols substantially insoluble at room temperature and below.
While the invention is particularly applicable to the direct treatment of black grease, other low-grade fatty materials may be similarly treated. Thus the fatty material resulting from alkaline splitting of soapstock followed by acidulation and separation as discussed above can be employed as the starting material in the present process. The same is true of the fatty material resulting from the acid splitting of black grease or the alkaline splitting of such material followed by acidulation. Also, the gums from the degumming of glyceride oils or the soapstock from refining operations employing volatile neutralizing agents, particularly in the case when such gums or soapstock are highly colored, may be advantageously treated in accordance with the present invention. They may be first dried and then introduced into the splitting and esterification step of the present invention or the wet materials may be first subjected to an acid splitting operation in order to obtain a fatty phase which may be treated in the present process. Alternatively, such gums or soapstock may be split with a caustic alkali and the resulting product acidulated and separated to recover a fatty phase suitable for introduction into the present process. Even if the fatty acids have been substantially all. liberated from chemical combination by previous steps such as discussed immediately above, the present process enables high-grade fatty materials to be more easily recovered from low-grade fatty materials. Thus, substantially any low-grade fatty material of low water content can be advantageously subjected to the process of the present invention.
It is, therefore, an object of the present invention to provide an improved process of upgrading low-grade fatty materials.
It is another object of the invention to provide a process of upgrading low-grade fatty materials in which the fatty acids are liberated and converted into esters of a lower monohydric aliphatic alcohol and the esters then refined with a caustic alkali.
A further object of the invention is to provide an improved process of recovering high-grade low colored products from low-grade fatty material in which process the free or combined fatty acids of the low-grade material are first converted into fatty acid esters of lower monohydric aliphatic alcohols and the esters refined to recover high quality esters and other valuable byproducts.
Other objects and advantages of the invention will appear in the following detailed description of the process illustrated in the attached drawing which is a flow sheet of the process.
Since black grease, particularly cottonseed black grease, is one of the most diliicult low-grade fatty materials to upgrade, the invention will first be described with reference thereto. Referring more particularly to the drawing, black grease may be introduced into a combined splitting and esterification step as indicated by the arrow 11, and a lower monohydric aliphatic alcohol and a strong mineral acid also introduced in this step as indicated by the arrow 12. The preferred alcohol is methanol and the process will be described with reference thereto, although other lower monohydric aliphatic alcohols, such as ethyl, normal propyl, and isopropyl alcohols may be employed. The amount of alcohol employed will ordinarily be just suificient to retain the methyl esters of the fatty acids in solution after estification has been effected and the resulting solution cooled. This amount of alcohol will usually range from 2.5 to 12 times the weight of the black grease introduced. The amount of acid employed is sufiicient to make the reaction mixture strongly acid and will usually range from 25 to parts by weight per 100 parts by weight of the black grease. The reaction in the splitting and esterification step 10 is ordinarily carried on at the reflux temperature of the alcohol and the treatment is continued until the material becomes homogeneous or only a small amount of oily material remains. This step may, however, be carried out under pressure and at higher temperatures. That is to say, temperatures between approximately 64 C. and C. may be employed. This time will usually range between 3 and 24 hours, depending upon the nature and concentration of the acid and the temperature employed as Well as the water content of the reaction mixture.
The products discharged from the splitting and esterification step 10 are essentially a methanol solution of methyl esters of fatty acids containing coloring matter, the strong acid, glycerol, sterols and tocopherols. This material may be delivered into a cooling and filtering step 13 in which the materials are cooled to approximately room temperature or below, i. e., zero to 20 C. and filtered to remove any insoluble material. The insolubles, which may contain sterols, may be discharged from the process as indicated by the arrow 14. The materials delivered from the cooling and filtering step to the next step of the process are substantially the same as those delivered into the cooling and filtering step, except that materials insoluble in the methanol solution have been removed. This material may be delivered into a distillation step 14 in which the excess methanol is distilled. This distillation may be at atmospheric pressure and the methanol may be condensed and recovered in concentrated form for return to the splitting and esterification step 10. The residue discharged from the distillation step 14 is essentially methyl esters of fatty acids containing coloring matter, acid, glycerol, sterols and tocopherols.
This material may be delivered into a washing step 15. Hexane or similar solvent is preferably first added in the step 15 so as to dissolve the fatty material therein. The amount of hexane will ordinarily be approximately equal to the weight of the fatty materials introduced into the process but may range from 50 to 200 parts by weight per 100 parts by weight of such fatty materials. The hexane reduces the viscosity of the materials in this step and assists in the alkali washing step although it is entirely possible to perform this step without the presence of a solvent. An aqueous solution of a caustic alkali, such as sodium hydroxide is added in the washing step 15 and stirred with the fatty material. The amount of alkali on a dry basis employed will usually range from approximately 12 to 50 parts by weight per 100 parts by weight of the fatty material introduced into the process and the concentration of the aqueous solution will usually range between approximately 6% and 25%. After stirring for a short period of time, for example 5 to 20 minutes, the mixture may be settled and separates cleanly into two phases, an upper fatty phase and a lower aqueous phase. The aqueous phase may be discharged from the process as indicated by the arrow 17 and is essentially an aqueous solution of the excess alkali, glycerol and the salts resulting from neutralization of the acid employed in the splitting and esterification step 10. It contains a substantial amount of the coloring matter present in the fatty material. If any other water soluble material, such as choline or inositol compounds are present, they are also removed with the aqueous phase and may be recovered therefrom. Any lower aliphatic alcohol which might remain is also removed in the washing step and except for the fact that such alcohol is difiicult to recover from the separated aqueous alkaline solution, all of the alcohol distillation step can be omitted and all of the excess lower aliphatic alcohol removed in the washing step 15.
The fatty phase may be discharged from the washing step 15 and delivered into decolorizing step 18. This fatty material is essentially a hexane solution of methyl esters of fatty acids containing sterols, tocopherols and the remaining coloring matter. A bleaching adsorbent, such as activated carbon, acid treated clay, fullers earth, etc., may be introduced into the decolorizing step as indicated by the arrow 20. Although the methyl esters of fatty acids, even in the absence of hexane or similar solvent, are liquid materials and the solvent may also be omitted in the decolorizing step, the solvent is advantageously employed in this step in order to decrease the viscosity of the fatty material and minimize adherence thereof to the bleaching adsorbent. The amount of bleaching adsorbent will usually range approximately between 1 and 3% by weight of the fatty material introduced into the process. The bleaching adsorbent may be stirred with the esters or solvent solution thereof for a short period of time, for example 10 to 30 minutes, and the resulting mixture filtered. The bleaching adsorbent may be discharged from the process as indicated by the arrow 21 and carries with it substantially all of the remaining coloring material.
The filtered fatty material may be delivered into a distillation step 22 and is essentially a hexane solution of light colored methanol esters of fatty acids containing sterols and tocopherols. The hexane may be easily distilled from this solution at atmospheric temperature and may be condensed and recovered, for reuse in the washing step 15. The fatty material constituting the residue in the distillation step 22 may be delivered into a vacuum distillation step 24. This material is essentially methyl esters of fatty acids containing sterols and tocopherols. The methyl esters of fatty acids may be distilled under vacuum conditions from the fatty material and condensed and discharged from the process as indicated by the arrow 25. These are high-grade light colored esters of fatty acids and have a variety of uses.
The residue from the vacuum distillation step 24 is essentially high-grade sterols and tocopherols as distinguished from the pitch resulting from prior fatty acid distillation steps as applied to black grease. This material may be delivered to a methanol treating step 26. Sufficient methanol to dissolve the tocophcrols but not the sterols, when the solution is cold, is introduced into the step 26 as indicated by the arrow 27. The mixture is preferably heated to the boiling point of the alcohol in the step 26 and filtered hot. Both the sterols and tocopherols dissolve in the heated solution. Thus, the methanol solution may be refluxed for a short period of time, for example, to minutes, and then filtered at the reflux temperature so as to remove insoluble impurities. A small amount of insoluble material is usually present. These insolubles may be discharged from the process, as indicated by the arrow 28.
The hot filtered methanol solution of sterols and tocopherols may be delivered into a cooling and separating step 29 in which the solution is cooled to room temperature or below, i. e., 0 to C. The sterols precipitate and may be removed from the cooled solution by filtration and may be discharged from the process as indicated by the arrow 30. A methanol solution of tocopherols may be discharged from the cooling and filtering step 29 as the filtrate, as indicated by the arrow 31, and this material may then be subjected to a methanol distillation step similar to the step 14 to recover concentrated methanol for return to the splitting and esterification step 10 and a tocopherol concentrate.
The lower layer, i. e., the aqueous material discharged from the washing step 15 can be acidified to produce a precipitate of coloring material. Upon adding hydrochloric acid or other strong mineral acid to this material, a green-black precipitate is produced. This precipitate may be filtered from the aqueous solution and washed with water until free of acid, salts and glyeerine. Upon being dried, the precipitate is crystalline and dark green in color. It is insoluble in water and petroleum ether but soluble in methanol, acetone and chloroform. The material is a pigment having high tinctorial powers and can be used as a dye in systems which require dyes resistant to acids but not to alkalies.
The fatty acid esters discharged from the distillation step 24 may be hydrolyzed with aqueous acid solutions to yield light colored high-grade free fatty acids. They also may be hydrogenated to produce hydrogenated methyl esters useful for various purposes. They may also be converted either in the form discharged or, after being hydrogenated, to high-grade monoor diglycerides or even triglycerides by heating them with the calculated quantities of glycerol in the presence of a catalyst such as sodium methoxide or alkaline soaps of fatty acids in vacuo. In such a step concentrated lower aliphatic alcohol may be condensed and recovered for return to the splitting and esterification step of the present invention.
As a specific example of a process in accordance with the present invention, the following treatment of cottonseed black grease is illustrative.
parts by weight of cottonseed black grease were refluxed with 950 parts by weight of methanol and 46.7 parts by weight of concentrated hydrochloric acid for 12 hours. The resulting liquid material was cooled to 20 C. and filtered. The filtrate was transferred to distilling apparatus fitted with a condenser and the methanol distilled at atmospheric pressure, condensed and recovered. The residue was cooled to approximately 20 C., and 96 parts by weight of petroleum ether was added thereto. The fatty material of the residue dissolved in the petroleum ether to form an upper layer, a small lower layer containing the acid and minor amounts of other materials also forming. This lower layer was withdrawn and a solution of 24 parts by weight of sodium hydroxide in 200 parts by weight of water was added to the remaining upper layer while stirring. After 10 minutes stirring the agitation was stopped and the reaction mass allowed to settle. Settling was rapid, the upper fatty layer being reddish in color and the lower aqueous layer being jet black. The upper layer was withdrawn and 2 parts by weight of activated carbon added thereto. The mixture was stirred for 15 minutes and then filtered, the filtrate being a light colored material. The petroleum ether was distilled from this filtrate at atmospheric pressure and was condensed and recovered. The residue was a light colored material which was essentially the methyl esters of the fatty acids containing a small amount of sterols and tocopherols. The color was 20 Y-ll. R (5%" column) Lovibon-d. The yield was 78.3 parts by weight, the material having a saponification equivalent of 296 (saponification value 189). Vacuum distillation is effective to separate high-grade esters from the sterols and tocopherols which may in turn be separated by precipitating the sterols from methanol.
The lower layer, i. e., the aqueous liquor from the caustic wash, was acidified with enough hydrochloric acid to make it strongly acid. A green-black precipitate was produced and was filtered and washed. The precipitate was dried and was dark green in color and the yield of the precipitate was 3.2 parts by weight.
In the above specific example, hydrochloric acid was employed as the catalyst in the splitting and esterification step 10. However, substantially any other strong acid or mixtures thereof which are non-oxidizing, i. e., which do not have greater oxidizing properties than sulfuric acid, may be employed. Examples of such other acids are sulfuric, phosphoric, benzene sulfonic acid, aromatic or aryl sulfonic acids, aryl sulfuric acids, trichloracetic acid, trifluoracetic acid, other alpha-polyhalocarboxylic acids and even strong cationic exchange resins of the sulfonic acid type; hydrochloric or sulfuric acid being preferred. Although methanol is the preferred alcohol, other monohydric aliphatic alcohols, for example, those containing up to three carbon atoms, can be employed. Mixtures of such alcohols can also be employed. Also substantially any volatile organic solvent for the fatty material, which is inert to the fatty material at the boiling point of the solvent, can be employed instead of hexane or petroleum ether.
From the above, it should be apparent that an improved process of upgrading fatty materials has been provided. This process gives high yields of high-grade, low colored stable fatty acid esters of lower monohydric aliphatic alcohols, which esters may be readily converted into fatty acids or otherwise employed. Such esters containing small amounts of unsaponifiables are obtained from low-grade fats without necessity of distillation although distillation of the esters may be carried out to further purify the esters by separating them from contained unsaponifiables. The bulk of the coloring matters which are the most difficult impurities to remove from low-grade fatty materials are separated from the esters of the fatty acids in an easily carried out alkali washing step. This enables the subsequent removal of residual color with bleaching or decolorizing agents. The lower aliphatic alcohol esters of fatty acids are much less viscous than triglycerides or fatty acids and are more easily handled. In general, they are liquid at room temperature and can be mixed with bleaching earth and readily filtered, even in the absence of a solvent, although the presence of a solvent in the alkali washing and bleaching step is advantageous.
1. In a process for refining low grade fatty material containing substantial amounts of fatty acids and coloring matter wherein said fatty material is treated to convert said fatty acids into fatty acid esters of a low aliphatic, monohydric alcohol and said esters are removed by distillation, the step of washing said fatty material containing said esters prior to distillation of said esters with an aqueous solution of caustic alkali in an amount sufiicient to remove the major portion of said coloring matter to insure a permanently light-colored fatty material after distillation of said esters.
2. In a process for refining low grade fatty material containing substantial amounts of fatty acids and coloring matter wherein said fatty material is treated to convert said fatty acids into fatty acid esters of a lower aliphatic, monohydric alcohol and said esters are removed by distillation, the step of washing said fatty material containing said esters prior to distillation of said esters with an 8 aqueous solution of 12 to 50 parts by weight of caustic alkali for each parts by weight of said low grade fatty material to remove the major portion of said coloring matter to insure a permanently light-colored fatty material after distillation of said esters.
3. In a process for refining low grade fatty material containing substantial amounts of fatty acids and coloring matter wherein said fatty material is treated to convert said fatty acids into fatty acid esters of a lower aliphatic, monohydric alcohol and said esters are removed by distillation, the step of washing said fatty material containing said esters prior to distillation of said esters with an aqueous solution of 12 to 50 parts by weight of caustic alkali for each 100 parts by weight of said low grade fatty material, said aqueous solution having a concentration of said caustic alkali of from 6% to 25%, to remove the major portion of said coloring matter to insure a permanently light-colored fatty material after distillation of said esters.
4. In a process for refining low grade fatty material containing substantial amounts of fatty acids and coloring matter wherein said fatty material is treated to convert said fatty acids into fatty acid esters of a lower aliphatic, monohydric alcohol and said esters are removed by distillation, the step of washing said fatty material containing said esters prior to distillation of said esters with an aqueous solution of caustic alkali in an amount sufficient to remove the major portion of said coloring matter to insure a permanently light-colored fatty material after distillation of said esters, said fatty material containing said esters being dissolved in a water-immiscible volatile organic solvent to reduce the viscosity thereof during said washing step.
5. The process of claim 4 wherein said solvent is hexane.
References Cited in the file of this patent UNITED STATES PATENTS 1,701,703 Starrels Feb. 12, 1929 2,223,398 Bennett Dec. 3, 1940 2,280,815 Fernholz Apr. 28, 1942 2,432,181 Trent Dec. 9, 1947 2,516,834 Bohm Aug. 1, 1950 2,585,954 Mattikow et al Feb. 19, 1952 FOREIGN PATENTS 612,667 Great Britain Nov. 16, 1948 OTHER REFERENCES Chem. Abstracts, vols. 31-40, pages 5358-9 (1937- 1946).
Ser. No. 414,980, Grandel et al. (A. P. C.), published May 11, 1943.