US2329889A - Process for refining fatty material - Google Patents

Description

Patented Sept. 21, 1943 2,329,889

UNITED STATES PATENT OFFICE PROCESS FOR REFINING FATTY MATERIAL Frederick J. Ewing, Los Angcles, Calif assignor 1t? Refining, Inc., Reno, Nev., a corporation of Application January 11, 1941, Serial No. 374,132

10 Claims. (01. 260-4285) This invention relates to the treatment and refining of fatty materials and glyceride oils, and which: relates more particularly to a method of solvent Figure 1 is a flow diagram with schematic refining such materials. representations of apparatus suitable for carrying Fats and oils are conventionally refined by 5 out my process; and treatment with chemical reagents. Objections to Figure 2 is a cross section of an extraction tower such treatment include the refining loss of good suitable for carrying out a modified form of my oil, the consumption of reagents, and the degprocess. radation oi the materials acted upon. For ex- Referring more particularly to Figure 1, I015 a ample, in the alkali refining of yceride oils, tank containing the crude stock, such as unrethere is both a saponiflcation and entrainment fined fatty oil, and H is a tank containing the loss of good oil, a conversion of the fatty acids diluent, preferably a pressure tank adapted to in the soapstock foots, and a substantial conhold liquefied propane. The crude stock is withsumption of reagents, including both the original drawn through a line I2 and brought to a suitalkali and the acid subsequently employed to able temperature in aheat exchanger l3, whence acidulate the soapstock. it is conducted by a pipe I to a Junction point It is possible to overcome these objections by IS. The diluent is withdrawn by means of a recourse to solvent refining, i. e., to extract the pipe 16, brought to a suitable temperature in a fatty material with solvent which is selective heat exchanger l1, and thence conducted by and which preferentially extracts the undesired means of a pipe l8 to the aforesaid juncture l5. constituents, or which forms with the fatty ma- The commingled streams formed at the juncture terial a system of conjugate phases, one of which, l5 are passed by means of a pipe l9 to a heat exthe extract phase, is relatively rich in undesired changer 20 in which the temperature of the comconstituents and the other of which, the raffinate bined streams may be further modified, and the phase, is relatively rich in the desired constituresulting solution or admixture is then passed by ents. I means of a pipe 2| to a separator, illustrated as a The solubility characteristics of the various decanter 22. The decanter comprises a closed normal constituents of fats do not differ greatly shell 23 having an interior partly divided by a apart from certain minor constituents, such as b fll 24 nd h vin a ower raw-oil line 25 gums and resins, and it is, accordingly, diflicult to through whi h, by means of opening a valve 2 find a solvent which will exercise the desired material separ t g and settling from the pro- Dreferential and selective action. pane-oil solution may e Withdrawn- Such ma- It is an object of the present invention to proterials are norm y omprised of gums, phosvide a method for the solvent refining of fatty Ph tides, resins, and the like. w i re commaterials which overcomes the stated difiiculties monly e m d or impurities? and which greatly increases the spread between The clarified p pan -oil solution is withdrawn desired and undesired constituent with regard from the upper P of the decanter 22 by means to their distribution in the extract and rafilnate Of draw-m line and if desired, be e phases directly to subsequent solvent extraction equip- The present invention is based, in part at least, 40 ment by opening a valve leading i a {leader on the discovery that, in the presence of suitable most instances' however it IS posslble to dnuents the degree of differential extraction of precip tate a substantial quantity of additional impurities from the propane-oil solution by furglyceride oils with a given extractive solvent may ther altefln it h i 1 t t b n be greatly increased particularly if the diluent g s p ys ca 8 a as y coo ng or 4 heating. For this purpose, the valve 3! may be employed is selected from the class of liquefied.-

closed and a valve 33 opened leading into the normally gaseous hydrocarbons, typically and suction of a pump 34, which may be operated preferably liquefied propane. to maintain the desired pressure conditions dur- It is an obJect of the present invention to proing subsequent t vide a method for treating fatty materials with The discharge from t pump 34 1 passeda p r y of solvents, 0116 i g P ri y a through a heat interchanger 35, where it is diluent and the other a selective solvent adapted brought to the desired temperature, and it is to extract certain selected constituents. then passed by means of a pipe 36 into a second Further objects and aspects of the invention separator, illustrated as a decanter 40. Addiwill become apparent in the following discussion, tional impurities separating from the propanemade with special reference to the drawing, in

oil solution at this point may be withdrawn by means of a valved withdrawal line 4| at the bottom of the decanter, and the clarified (and at least partially purified) propane-oil solution removed through a draw-off line 42 through a heat exchanger 43, which may serve as a cooler in case high temperature precipitation is employed in the second decanter, and thence through a back-pressure valve 44 which is adjusted to maintain the desired pressure on the decanter 40. Diluent vapors may also be withdrawn from the decanter 40, if desired, by means of a vapor withdrawal line 45.

The clarified propane-oil solution from either the first or second decanter is gathered in the header 32 and thence passed to a solvent extraction plant. The solvent extraction plant typified in the drawing is a three-stage countercurrent plant comprising mixers 5|, 52, and 53 and settling vessels 54, 55, and 56. A selective solvent contained in a tank 60 is withdrawn by means of a pipe 6|, passed through a heat exchanger 62, and thence passed into a mixer 53. The propane-oil solution in the header 32 is passed through the heat exchanger 63 and thence into the mixer 5|.

Each mixer receives a commingled stream of propane-oil or raflinate phase largely constituted by the propane-oil, and a, selective solvent or an extract phase largely constituted by a selective solvent. These streams are thoroughly admixed in the mixer to form a set of conjugate phases which are in substantial equilibrium, and this mixture then passes to the settling vessel where it layers out into an upper raiiinate phase and a lower extract phase.

Accordingly, the path of the oil-diluent, or the rafiinate phase resulting therefrom, is from the heat exchanger 63 to the mixer 5|, thence to the settling vessel 54 to form a raflinate phase which is withdrawn by means of a pipe 65 leading to a heat exchanger 66, thence to the mixer 52 and into the settling vessel 55 to form a raffinate phase which is withdrawn by means of a pipe 61 conducting same to a heat exchanger 68, thence to the mixer 53, and thence to the settling vessel 56 to form a rafflnate phase which is withdrawn by means of a pipe 69.

The path of the selective solvent, or the extract phase rich in the selective solvent, isvirtually countercurrent to the above and is from the heat exchanger 62 to the mixer 56, to the settling vessel 56 to form an extract phase which is withdrawn by means of a pipe I and conducted to a heat exchanger II, thence to the mixer 52 and settling vessel 55 to form an extract phase which is withdrawn by means of a pipe I2 and conducted to a heat exchanger 13. and thence to the mixer I' and settling vessel 54 to form a final extract phase which is withdrawn through a pipe 14.

The rafflnate phase withdrawn through the pipe 69 comprises the desired constituents of the crude stock and most of the diluent employed, and may, under certain circumstances, contain some small amount of selective solvent. In case it is desirable to exercise some further chemical refining of the oil, this chemical refining is best practiced on the diluted rafllnate phase as obtained at this point. Thus, for example, the raflinate phase may be chemically or physically treated by direct admixture with a refining reagent (such as a solution of caustic alkali or soda ash) or with a slurry of clay, or the like.

For this purpose, a valve 80 in the pipe 69 is closed and a valve 8| is opened leading to a pipe 82. A valved inlet pipe 83 permits the introduction of clay slurry, caustic alkali, or other reagent into the stream flowing through the pipe 82. The resulting admixture may be passed through a heat exchanger 84 to bring it to opti-- mum refining temperature, and thence to a decanting or other separating vessel 85 having a lower draw-01f line 86 through which soapstock foots, spent clay, or the like may be withdrawn. The purified raifinate phase is withdrawn from the top of the decanter 85 through a pipe 81 and this material may then be returned to the pipe 69 by means of a valve 88. If desired, the chemical refining equipment may be by-passed by closing the valves iii and 88 and opening the valve 80.

The raffinate, with or without additional chemical refining, is subjected to a step of distillation to recover the diluent and such of the selective solvent as may be dissolved in or mechanically admixed with the rafiinate phase, whereby a refined oil free from diluent or associated solvents is ultimately obtained.

A suitable distillation method is shown in the drawing and comprises passing the raffinatc phase from the pipe 69 through a, heater 90 where it is brought to a temperature sufilcient for the flash distillation of the diluents, such as propane, and thence through a valve 9| into a flash rectifying column 92, wherein the propane vapors are sent overhead through a vapor line 93 to the intake of a compressor 94.

The compressed vapors or liquids issuing from the compressor 94 are cooled or condensed in a condenser 95 to form a liquefied diluent which is returned to the dilent tank II by means of a return line 96.

The residual fraction or bottoms from the rectifying tower 92 are withdrawn by means of a line I00. This material is virtually free of diluents at this stage but may still contain some selective solvent due to mechanical entrainment or partial miscibility in the solvent refining stage. The bottoms are accordingly further heated in a heat exchanger IM and sent to a stripping tower I02 wherein all trances of solvent or other low boiling materials are removed as a vaporous overhead. The overhead vapors are withdrawn through a vapor line I03 and passed to the suction of a pump I04, which is preferably arranged to maintain subatmospheric pressure on the stripping column I02. The discharge of the pump I04 is passed through a condenser I05 and the condensed solvent is returned by means of a pipe I06 to the selective solvent tank 60.

If desired, the stripping action in the column I02 may be aided by the injection of steam through a steam pipe I01. The bottom fraction from the tower I02 is withdrawn through a valve I08 into a discharge line I09. These bottoms constitute the refined stock and, as such, are the principal product of my process.

The extract phase withdrawn through the line 14 consists preponderantly of selective solvent and the undesired constituents of the crude stock. There may be present in this phase some quantity of diluent due to effects of mechanical entrainment or partial miscibility. This extract phase is subjected to distillation steps similar in principle to those described in connection with the raiiinate phase and illustrated, for purposes of simplicity, as being conducted in the same type of apparatus. It will be understood, however, that, with the raflinate phase, the chief overhead product is diluent, whereas, with the extract phase, the chief overhead product is solvent, and that, in practice, these distinctions will make for the use of different sized towers, different levels of temperature, and the like, in handling the two phases. schematically, however, the extract phase is passed through a heat exchanger H and into a flash tower III where any diluent is vaporized and sent overhead to the suction of the compressor 94. The bottoms of the tower III are passed by means of a pipe H2 to a heat exchanger H3, and thence into a solvent recovery tower H4 in which the solvent is taken overhead through a line II to the suction of the pump I04. The bottom from the tower 4, which may be subjected to stripping with steam, if desired, by injecting steam-through a pipe IIG, are withdrawn from the tower H4 by means of a valve II'I leading into a pipe H8.

These bottoms in the pipe I I8 are completely free from diluent and selective solvent and comprise the fractions which it was desired to remove from the refined stock. It will be noted that this extract material is obtained substantially unmodified by any chemical action, which is very advantageous in many instances.

In some instances, it is preferable to subject the stock to the simultaneous action of countercurrent streams of diluent and selective solvent. An extraction tower adapted to carry out this type of treatment is shown in Figure 2 and comprises an extraction tower I30 partially filled with inert contact masses I3I. The diluent, having a low specific gravity, is introduced near the bottom of the tower through a line I 32, the injected diluent being preferably distributed by use ofan upwardly directed spray rlng I33.

The selective solvent, having a relatively high density, is introduced into the column I30 near the top thereof by means of a pipe I35 in communication with a downwardly directed spray ring I 36. The crude stock is injected near the middle of the column by means of a pipe I31 terminating in a spray head I38.

The selective solvent descends through the column, extracting the undesired constituents and forming an extract phase which is removable from the bottom of the column by means of an extract draw-off line I40. The diluent rises through the column and dissolves the desired fractions of the oil to form a rafi'inate phase which is withdrawable from the upper end of the column througha draw-ofi line I. These phases may be distilled or otherwise handled, as exemplified in the discussion of Figure 1.

As the diluent, I prefer to employ low molecular weight water-immiscible material, such as liquefied normally gaseous hydrocarbon, including ethane, propane, and butane. Liquefied propane or commercially available mixtures which are largely propane but which maycontain some ethane, butane, and the like, constitute a particularly advantageous diluent.

The relative proportions of diluents and crude stock may be varied over a wide range. For example, with one volume of crude stock, a fraction of a volume up to eight or ten volumes of diluent may be employed.

The liquefied normally gaseous hydrocarbons, and, in particular, propane, exercise a precipitating action on minor impurities such as gums, resins, phosphatides, and the like. Provision is made for the preliminary segregation of such materials in Figure 1 in the decanters 22 and 40.

When operating in accordance with Figure 2, the

minor impurities are, for the most part, dissolved in the extract phase.

Temperature is frequently an important factor in the precipitation of the minor impurities. When using several volumes of propane for the volume of crude stock, minor impurities may be substantially precipitated at room temperature, and, by chilling, further quantities may be precipitated. If desired, this additional precipita-g tion by f ther chilling may constitute a second stage, for example, as effected in the decante r 40. However, it is frequently advisable to carry out a second stage of precipitation at substantially elevated temperatures, for example, F or higher. At these temperatures, the liquid propane undergoes a substantial reduction in solvent power due to the fact that it is approaching its critical temperature, and additional quantities of impurities or undesired fractions may accordingly be precipitated by conducting the second stage at substantially elevated temperature.

The choice of a selective solvent depends, in large part, on the character of the crude stock and the constituents which it is desired to remove. As a typical instance, in treating certain crude glyceride oils, the undesired constituents will normally be regarded as consisting largely of free fatty acids. Various sol ents may be used to extract the free fatty acid of the propane-oil solution, such solvents including, but not being limited to, alcohols, ketones, aldehydes, low mo lecular weight organic acids, etc. These solvents may be anhydrous, e. g., glacial acetic acid or anhydrous ethyl alcohol, but in many instances they may be advantageously associated with sufflcient water to reduce or prevent their miscibility with the liquefied normally gaseous hydrocarbon diluent. Isopropyl alcohol containing from 5% to 20% of water is a good selective solvent for fatty acids.

Various other selective solvents may also be employed in the present process, these solvents in general being characterized by their relatively polar character, high internal pressure, and relatively restricted miscibility with liquefied propane or other liquefied normally gaseous hydrocarbon. In this connection, there may be mentioned phenol, cresylic acids, nitrobenzene, sulphur dioxide, dichlorethyl ether, and the like.

The character and quantity of selective solvent will be varied according to the material worked upon and the separation which is desired. Thus, for example, in solvent refining a crude glyceride oil to remove a few per cent of free fatty acids, a relatively small amount of selective solvent having a relatively low solvent power, for example, aqueous isopropyl alcohol, may be employed. If it is desired to solvent fractionate the glyceride constituents themselves according to molecular weight, unsaturation, and general chemical character of the fatty acids combined with the glycerine, then substantially larger quantities of a more powerful solvent, such as sulphur dioxide, phenol, or the like, may be employed. Or, again, the crude stock may consist largely of a complex mixture of free fatty acids which it is desired to segregate on the basis of their solubility characteristics, in which case solvents such as phenols, alcohols, etc., may be advantageously employed.

Modifying agents may be employed to modify the solvent power of the selective solvent. Thus, the selective solvent, which, in the majority of instances, will be partially-miscible with water, may be associated with more or less water to modify its solvent power. In some instances, an alkaline agent, preferably a volatile alkali, such as ammonia, may be incorporated in the selective solvent, particularly where the extraction of acidic constituents is desired. The volatile alkali may be largely recovered in distillation of the extract since the dissociation temperatures of ammonia soaps are relatively low.

In some instances, the solvent may be modified subsequent to phase separation, as by the addition of water to an extract phase formed by the action of a water-soluble selective solvent to precipitate the fatty acids or other extracted oleaginous constituent.

The temperature of solvent extraction should, in general, be sufliciently below the critical solution temperature for the system concerned to insure the formation of conjugate phases. Depending upon the character of the stock, the selective solvent employed, and various other factors, subatmospheric, atmospheric, or superatmospheric temperatures may be indicated as optimum for the process of solvent extraction. In many instances, it is desirable to maintain a temperature gradient throughout the countercurrent extraction such that the highest temperature is maintained in the zone from which the final rafiinate is taken. A plurality of intermediate heat exchangers are shown in Figure l for the purpose of establishing any desired temperature gradient in the extraction zone.

In the present specification and claims, the term fatty materials is to be understood as generic to glyceride oils, fats, fatty acids, and like educts or products of animal or vegetable fats and oils.

It will be understood that the details of the above examples are not limiting, and that various modifications of the described process may be practiced without departing from the scope of the appended claims.

I claim as my invention:

1. The process of refining glyceride oils containing free fatty acids to separate free fatty acids from said oil, which comprises, commingling the oil with a liquefied normally gaseous hydrocarbon and a selective solvent for said fatty acids which is substantially immiscible with said oil in the presence of said liquefied hydrocarbon, maintaining the materials under sufiicient pressure to retain said hydrocarbon in liquid form so as to produce a liquid extract phase containing said selective solvent and free fatty acids and a rafiinate phase containing substantially all of the glycerides of said oils and separating said phases by difference in specific gravity.

. 2. The process defined in claim 1 in which the selective solvent is iso-propyl alcohol.

3. The process defined in claim 1 in which the selective solvent is miscible with water and is employed in admixture with water.

4. The process defined in claim 1 in which the selective solvent comprises iso-propyl alcohol in admixture with water.

5. The process defined in claim 1 in which the selective solvent contains an alkaline reagent.

6. The process of refining crude glyceride oils containing gummy materials and free fatty acids, which comprises the steps of, mixing said glyceride oil with a liquefied normally gaseous hydrocarbon to dissolve the fatty material of said oils and precipitate gummy material, separating the precipitated gummy material from said fatty material, thereafter treating the fatty material with a selective solvent for fatty acids which is substantially immiscible with said oil in the presence of said liquefied hydrocarbon,

maintaining the materials in said process under sufiicient pressure to retain said hydrocarbon in liquid form so as to produce a liquid extract phase containing said selective solvent and free fatty acids and a rafiinate phase containing substantially all of the glycerides of said oils and separating said phases by difference in specific gravity.

'7. The process defined in claim 6 in which the liquefied normally gaseous hydrocarbon is propane and the selective solvent is iso-propyl alcohol in admixture with water.

8. The process defined in claim 6 in which said rafiinate phase containing said liquefied hydrocarbon is further treated with a neutralizing agent to neutralize residual free fatty acids and form soap stock and in which said soap stock is separated from said phase.

9. The process defined in claim 6 in which said raffinate phase containin said liquefied hydrocarbon is further treated with a decolorizing agent and the decolorizing agent separated from said phase.

10. The process of refining glyceride oils containing free fatty acids to separate free acids from said il, which comprises, continuously introducing a stream of said oil into a body of oil at an intermediate level in an extraction zone containing said body of oil, continuously introducing a stream of a liquefied normally gaseous hydrocarbon into said body of oil at a lower level in said zone below said intermediate level, whereby said hydrocarbon is commingled with said oil and moves upwardly therethrough, continuously introducing a stream of a selective solvent of fatty acids which is substantially immiscible with said oil in the presence of said hydrocarbon into said body of oil at an upper level in said zone above said intermediate level, said selective solvent having a greater specific gravity than said oil, whereby said solvent commingles with said oil and moves downwardly therethrough in the presence of said hydrocarbon, continuously withdrawing a raflinate phase containing said hydrocarbon and substantially all of the glycerides of said oil from said zone at a level above said upper level and continuously withdrawing a solvent phase containing solvent and free fatty acids from said zone at a level below said lower level.

FREDERICK J. EWING.

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