US2824885A - Refining triglyceride oils - Google Patents

Description

United State Patfiflf O REFINING TRIGLYCERIDE OILS George C. Cavanagh, Fresno, Calitl, assignor to Ranchers Cotton Gil, Fresno, Calif.

No Drawing. Application January 3, 1955 Serial No. 479,653

8 Claims. (Cl. 260-424) The present invention relates to fluid refining processes and more particularly to an improved water washing process for oils and other fluids immiscible with water.

The processing which crude oils of organic origin must receive in preparation for market is largely dependent upon the purposes for which the refined oil is intended and the character of the crude oil. Most animal, fish and vegetable oils require refining, especially when they are to be utilized as edible oils. For purposes of descriptive simplicity, preliminary reference is made to the refining of cottonseed oil and the application of the subject invention thereto, although it will later be understood that the invention is applicable to a wide range of oils and water immiscible fluids generally from which it is desired to remove soap, fatty acids, alkali metals and other impurities which are soluble in water, can be rendered soluble in water by the practice of the invention or can be precipitated from both the oil and the water by such practice.

Commercial refining of cottonseed oil frequently involves the treatment of the crude oil with caustic soda. The removal of free fatty acids of the crude oil is effected by their combination with caustic soda to form soap. This active ingredient may also be employedto extract coloring matter by selective solvent action and to coagulate, destroy or render non-objectionable other minor impurities such as the lipides and gossypols. These impurities generally are rendered insoluble in oil by the action of the caustic soda and with the soap are removed by settling, centrifugation, selective solvent action, or the like.

Known refining processes for cottonseed oil and similar materials may be briefly alluded to as the open kettle method which is now largely obsolete but which Was popular prior to 1930; the continuous method of caustic soda refining involving the vigorous mixing of caustic soda and oil and the subsequent rapid heating followed by separation of the impurities from the'refined oil by centrifugation; the modified continuous method in which soda ash solution is utilized to neutralize the free fatty acids, coagulate phosphatides and minor impurities after which the coagulated materials are removed by centrifugation; and refining in miscella comprising the subject matter of my copending United States patent application, Serial No. 366,458, entitled Extraction and Refining of Glyceride Oils and Fats From Source Materials Thereof.

. All such refining methods have as a prime objective, as does the present invention, the rendering of a maximum yield of refined oil which contains a minimum of free fatty acids, color bodies, non-fatty materials and other impurities.

It has previously been known in the various refining processes to Water-wash the refined oil as a final purifying step. This has been for the purpose of removing water soluble impurities, principally alkali metal soaps formed by the interaction of the alkali ions of caustic soda, soda ash, or the like with free fatty acids of the "ice oil. For more highly refined oils, it has become the practice to repeat the water washing process. In such instances, refined oil is washed with approximately 10% of water at about 180 F. in a first water-wash centrifuge maintained at a temperature of approximately F. In this first water-wash centrifuge, the oil is vigorously mixed with the hot water so that as much as possible of the water soluble impurities are dissolved in the water and the water and impurities held therein in solution are subsequently separated from the oil by centrifugation. The procedure is then repeated at approximately the same temperature in a second water-Wash centrifuge in which approximately 5% of hot water is utilized. The resultant oil usually contains approximately from 15 to 50 parts per million of soap which is an adequate reduction for some purposes but entirely inadequate for others.

Unfortunately, the vigorous agitation of the oils in the water-wash centrifuges frequently results in increased saponification and greater refining loss even though the resultant excessive soap may subsequently be removed.

To attain a lower soap content, it is the normal practice to pass the water-washed oil, after drying, through filter cloths impregnated with activated clays. This procedure is time consuming and expensive. Substantial portions of the oil are entrapped in the filter cloths and clays. Additional labor is required to control the filtering operation and the filter cloths and clays must be frequently cleaned, reactivated, and reinstalled for use. Unfortunately, odor and flavor reversion frequently occurs during the filtration. At best, the filtration can only be intermittently performed because of the down require-. ments for cleaning. In spite of these disadvantages, such additional purification is commercially practiced because it has heretofore been the only feasible method of reducing the soap content of the oil to levels required for certain uses. Although the efiicacy of this final filtering through activated clays is dependent upon many variables, it has frequently proved capable of reducing the soap content of the ultimate oil to as low as two parts per million. For this reason, it has heretofore been regarded as essential to perform the described filtration prior to hydrogenization. It should be noted that hydrogenization requires rior elimination of as much of the alkali metal ions as possible, particularly .sodium ions. During hydrogenization, various nickel compounds are employed as catalysts. If alkali metals are present, they interact with the nickel compounds to produce toxic products undesirable in edible oils. Further, the efficiency of the catalysts is impaired or destroyed by the presence of soap and/or alkali metal ions.

It thus will be seen that the currently accepted fluid cleansing practices of the character described are subject to major difficulties. The water washing steps, particularly if performed in two stages, require considerable volumes of water and are subject to waste water disposal problems. The best results attainable by current water washing procedures do not sufficiently effectively remove soap from the oils for many purposes. The additional filtration to attain desired purity is expensive, time consuming and frequently results in deterioration in the quality of the oil. Both the water washing and the fil tration are responsible for excessive losses in oil although such losses have heretofore been tolerated in order to gain adequate cleaning.

An object of the present invention is to provide an improved water washing process of the character described Which is far more eifective in its cleansing action than previously attainable.

Another object is to make possible a more complete removal of soaps, alkaline reagents and other water soluble materials from refined oils and the like.

Another object is to increase the efliciency ofthe water washingof refined oils to applicable in this manner.- a a V t i The broad essencef oftthe present invention resides in the discovery that by adjusting the acidity of the water.

' V The hydrogen viously available by two stagewashingfollowed by filtraj-tion through activated clays.

, Additional objects, are ito provide] a process of the character described which is economical'to perform, re-

quiresonly readily available apparatus, more rapidly attains effective soap removal than previously possible,'incurs less loss-in oil than conventionally incurred, and

V is fully. efiective in performing its intended functions with-t outfodor or flavor reversion. T

such an extent that a single stage washing operation can attain the best resultsprev Further objects and advan'tages 'will become'apparent "in the'subsequentdescription. t

=Aspre'viously alluded to, conventionalwater-wash cen- V 'trifuges receive therefined oiltto bewashed, vigorously intermixand agitatewater therewith to dissolve the water 7 soluble. constituents thereof; and subsequently separate the oil and water in the well known'centrifugal manner by takingadvantage of the difierences in their specific: t 'gravities. 'It has been known to water' wash other than pure oil,'such as miscellasof'oilsin' solvents therefor, and

other materials which are immiscible with oil, and it is 7 Moreprec isely defined, during the water Washingop'eration the hydrogen ion. concentration should substantially equal the alkali metal ion'concentration'. amount of ner described where greater purification, was required.

In employing the present invention, no filteringtis required.

Currently, by the practice of the presentinvention I' iwith the same equipment, the same type of oil andhexane: 1

miscella' is flowed through the water-wash centrifuge at f a rate of gallons of miscella perminute' One to five to be understood that the present invention is also broadly so thatt there is about'l gram equivalent of hydrogen ions tor'each 1 gram equivalentofthe aggregate alkaline metals" contained .thefoil and water mixture during "agitation, a vastlyv improvedfzcleansing action, soap removal, and minimizing of additional soap formation is attained; V V

ions replace the alkali metal ions of the soap during'agitation'to. convert the same. to the related fatty acids. The-fatty acidsfare'dissolved in oil but, are

present in such minute amounts that the oil is not deleteriously'efiected; Subsequent deodorization at temperatures above 350 E andvacuumi .of 5 to 15 mm. of mer cury remove the last'traces of fatty acids. The' released alkaliimetalgions combine with'the negative ions of the acidemploy'ed to form salts which are insoluble in oil.

Wherethe soap involved is a calcium soap, it' is also insoluble in water but, readily precipitates andthusiseasily removed. 5 In on refining processes the soap is rarely that i of calcium but: most frequently of sodium or occasionally potassium. The sodium and potassium salts are water soluble and thus readily removed in aqueous solution.

' Similarlyanyfree ions of; thejalkali rnetals are rendered readily removable by interaction withthe negative ions of the acid employed and are thus. not available for acl-' ditional-soap formation. i

The water used for oil washing purposes is acidulated by the addition thereto of any suitable acid-of mineralor organic origin. because they are cheaper and relatively stronger. Citric acid, however, has been particularlyuseful in this respect,

because of its sequesteringaction on metal ions; Inasmuch asiit is the practice in continuous refining processes,

to direct a continuous stream of Water through the waterwash centrifuges, theacid is conveniently imparted tothe water 'by a regulated flow thereof into the stream ,prior to its passage'into the water-wash centrifuge. Manyjsuittion- Offlfl'lfi water must be at,-,least about .01 normal and the resultant acidic aqueous bath'is found to have a pH of approximatel-y 'l, There'is no'criticalprecise upper V limit to the amount of acid that may be employed but hydrogen ion concentrations in excess of .033' merely con-j stitute waste where the soap 'content is less than about I iO pat s per: million; and, te sors. ha 5 parts. per million ct -he acida e emnley d,. i caus s-a ka s s ndi color i lit-r sen o; dis olv ac n o the 93* a t ou h Mineral acids are normally preferred 7 gallonspof watertper minute are flowed throughthe water- Washcentn'fuge for the-washingtpurpo'seg' Thus, thewwater: makes up',.;from 5%"to20.% by volume, of themiscella i and watermixtureain. the centrifuge; This proportion is similar to that conventionally employed. From to 100, Y 7 drops sulfurioacidoffifi? Baum (98%) concentration, Y are; d livered t0 the'water 7 prior to its :introductio'ntto "the centrifuge. Sulfuric acid is economical to"employfis insoluble in both, the oil and, hexane and thus/excellently suited to theqpurposeti ,Anybtheracid'insoluble in oil Q and hexane could be" employedflin' equivalent; amounts; Reference has been previously made touthe desirable at sequestering action. of citric acid. Oxalic'acid is alsoa 1 a Y good sequestering agent but should not be usedin earner" The resultantacidulated water bath has a hydrogen" ion concentration of from .01 tov .033normal' and" is excellently suited to the purposeJAs. the bath'isvigor usIy mixed with the oil in the centrifuge,the conventional llh' re se. in: saponification incident to the vigorous agitation no longenoccurs; The hydrogenionsconvertlthe soap T P iQU Y formed, into. their. related fatty acids. T Theis'ulfate, ions of the acid interact with the'sodium ions released from the} soap toform sodiumsulfate: whicliiisreadily dissolved: in the water.v Any free-alkali metalions eon- V tained by the oil are similarly combined with. negative ions of the acid to form aisalt. In the'usualmannentha t water-washgcentrifuge then separates'the w'aterlwith the alkali metal saltsand other impurities therein fromfthe' miscella, In normal practice, soap is present'at-this;stage in the oil in at least about 15 to 50 parts'-per-million.- f Under the described practice of;:the-presentinvention,"

however,thesoaprcontent isjreducedqto approximately 2 7 parts per millionjhusobviating thev necessitylof asecond 7 I t willbe-apparentthatthe invention can be-performedasabatch' QpdlfltlQIlffilthQllgh: described in its-continuous, I embodiment-betterj'suitedto currentgcomrnercialpractices; It not only attains; superior cleansingresuks but requires; less;equipment,ilessivlahorrand avoids the eirpenses'and difficulties'incident toffiltrafion; The more'thorough re moval 1 of the; alkali-metal; 'ions' minimizes. formation of toxic niclgel: products, during [subsequent hydrogeniz'a j tion. Lesswa-ter is required for washing purposesand maller disposal problem for. the. water results; 2 Refininglosses: incident to increased.saponification injthe water-:- fwash centrifuges and 'incident'to entrapment inffilte'r s'is' E V avoidedit Thele rpe'nse of thefacid is obviously negligible; :While the inveriti'on has been illustrated and described f infwhat'is at present r'egarded as 'theinost practical and preferred embodiment, it is recognized that departures. a ba lad her m w h r m scope, oft ei ie h I whi ch is. not tobe. limited to the details disclosed'herein but tojb a qr edt e t llsmm of he so an. 1 1 enthtace anyandall equivalent rnethodsandprocesses, 1 1

. Hayingidesbfihedmy.'inveution,- what I .claimiasnjnew; 1

an sw mm rs! lark t stia eat s ass ses l. A continuous process for removing soapstock from a miscella of alkali refined cottonseed oil in a suitable solvent therefor comprising flowing the miscella in a stream through a water washing apparatus, flowing water in a stream through said washing apparatus wherein the water is intimately mixed with the miscella and subsequently separated therefrom, and adding acid to the water stream in advance of the washing apparatus in a quantity sutficient to attain a normal hydrogen ion concentration of from at least about .01 to .033 in the Water stream, said stream as it enters the water washing apparatus consisting substantially entirely of the acid and water.

2. A process for water washing a miscella of alkali refined cottonseed oil in hexane containing traces of alkali metal soap comprising forming an acidulated aqueous solution of .01 to .033 normal of an acid which is substantially insoluble in cottonseed oil and in hexane, the aqueous solution consisting substantially entirely of water in addition to the acid employed, and intimately mixing the aqueous solution in approximately to 20% by volume With the miscella.

3. A process for water washing a miscella of alkali refined cottonseed oil in hexane containing traces of alkali metal soap comprising forming an aqueous solution of sulfuric acid of a strength of .01 to .033 normal with the remainder of the solution consisting substantially entirely of water, intimately mixing the acid solution with the miscella whereby the hydrogen ions of the aqueous solution replace the alkali metal ions of the soap to form water soluble salts, dissolving said salts in the aqueous solution, and separating the aqueous solution with the salts dissolved therein from the miscella.

4. A process of further refining an alkali refined triglyceride oil in miscella containing traces of soapstock comprising converting the residual traces of soapstock in the miscella to free fatty acids and water soluble salts by intimately mixing an aqueous acid solution, containing an acid in a quantity suflicient to provide an hydrogen ion concentration of from about .01 to .033 normal with substantially all of the remainder of the solution being water, with the miscella whereby the free fatty acids dissolve in the miscella and the salts dissolve in the water of the aqueous solution; removing the aqueous solution containing the water soluble salts from the miscella containing the free fatty acids; and subsequently extracting the free fatty acids from the miscella.

5. A process for further refining an alkali refined triglyceride oil in a miscella of a suitable solvent for the oil, which miscella contains traces of soapstock formed by the interaction of alkali with free fatty acids of the oil comprising washing the miscella with an aqueous solution of an acid which is substantially insoluble in the miscella to reconvert the traces of soapstock into free fatty acids which dissolve in the miscella and into water soluble salts which dissolve in the water of the aqueous solution, the aqueous solution containing the acid in a quantity sufficient to provide an hydrogen ion concentration of from about .01 to .033 normal with substantially all of the remainder of the solution being water, removing the aqueous solution and dissolved salts from the miscella, and subsequently subjecting the miscella to a vacuum to extract the solvent and fatty acids from the oil.

6. In the alkali miscella refining of triglyceride oil in a suitable solvent therefor in which free fatty acids of the oil are converted into soapstock and the soapstock is subsequently extracted from the miscella to an extent leaving from approximately 15 to 50 parts per million of soapstock dissolved in the miscella and making available alkali metal ions of the soapstock, the steps of reacting an acid which is substantially insoluble in the oil and in the solvent with the soapstock while in aqueous solution to form free fatty acids which dissolve in the miscella and water soluble salts which dissolve in the water, said aqueous solution consisting of acid in a quantity suflicient to provide an hydrogen ion concentration substantially equal to the alkali metal ion concentration of the soapstock in the miscella and the remainder of the solution being substantially entirely water, removing the water containing the soluble salts from the miscella containing free fatty acids, and subsequently extracting the free fatty acids from the miscella at a temperature of approximately 350 F. and under a vacuum of from substantially 5 to 15 millimeters of mercury.

7. A process for water Washing a miscella of alkali refined cottonseed oil in hexane containing traces of sodium soap of the fatty acids of the oil but from which substantial portions of said soap and color bodies have already been removed comprising intimately mixing an aqueous solution of sulphuric acid of a strength of approximately .01 to .033 normal with the miscella whereby hydrogen ions of the acid solution replace the sodium ions of the soap to form a resultant water soluble salt which dissolves in the aqueous solution and whereby the soap is converted into fatty acid which dissolves in the miscella, said aqueous solution in addition to the sulphuric acid being substantially entirely water, and subsequently extracting the fatty acids from the miscella.

8. In a process of further refining an alkali refined triglyceride oil in miscella containing approximately 15 to 50 parts per million of soapstock in the miscella, the steps of flowing the miscella and soapstock through a water wash centrifuge, and flowing an aqueous acid solution through the centrifuge with the miscella in a quantity of from about to /5 of the quantity of the miscella, the

aqueous solution consisting substantially entirely of water i and an acid in a quantity sufiicient to provide from about .01 to .033 normal hydrogen ion concentration in the solution whereby the soapstock in the miscella is reconverted to free fatty acids which dissolve in the miscella and into water soluble salts which dissolve in the aqueous solution.

References Cited in the tile of this patent UNITED STATES PATENTS 1,147,392 Hagemann July 20, 1915 2,374,924 Clayton May 1, 1945 2,510,379 Christenson June 6, 1950 2,654,766 Taussky Oct. 6, 1953 2,739,164 Weber Mar. 20, 1956 FOREIGN PATENTS 886,365 France Oct. 13, 1943

Claims (1)

1. 4. A PROCESS OF FURTHER REFINING AN ALKALI REFINED TRIGLYCERIDE OIL IN MISCELLA CONTAINING TRACES OF SOAPSTOCK COMPRISING CONVERTING THE RESIDUAL TRACES OF SOAPSTOCK IN THE MISCELLA TO FREE FATTY ACIDS AND WATER SOLUBLE SALTS BY INTIMATELY MIXING AN AQUEOUS ACID SOLUTION, CONTAINING AN ACID IN A QUANTITY SUFFICIENT TO PROVIDE AN HYDROGEN ION CONCENTRATION OF FROM ABOUT .01 TO .033 NORMAL WITH SUBSTANTIALLY ALL OF THE REMINDER OF THE SOLUTION BEING WATER, WITH THE MISCELLA WHEREBY THE FREE FATTY ACIDS DISSOLVE IN THE MISCELLA AND THE SALTS DISSOLVE IN THE WATER OF THE AQUEOUS SOLUTION, REMOVING THE AQUEOUS SOLUTION CONTAINING THE WATER SOLUBLE SALTS FROM THE MISCELLA CONTAINING THE FREE FATTY ACIDS, AND SUBSEQUENTLY EXTRACTING THE FREE FATTY ACIDS FROM THE MISCELLA.