US2412251A - Purification of oil - Google Patents

Description

Dec. 10, 1946. B. CLAYTON 2,412,251

PURIFICATION OF 011. Filed April 21, 1945 Aer/yr I roars 0/1. 37

v I zlvwm'm beqjamin Waylon M mfltm 4W Patented Dec. 10, 1946 um'rau STAT as PATENT OFF-ICE PURIFICATION OF OIL Benjamin Clayton. Houston, Tex,

meme assignments, to Benjamin Houston. Ten, doing business as incorporated unis-nor, Clayton, Refining, Un-

, Application April :1, 1943, Serial No. 483,953

' 13 Claims. (01. zoo-42s) ties required to be removed may be coloring matter or materialswhich impart to the oil "a deleterious. taste or odor. Or it may be desired to treat an oil which has naturally occurring impurities in very limited quantities.

An example of a glycedle oil which requires color removal is a cottonseed oil which has been refined with non-s'aponifying alkalies such as soda ash or has been refined with insumcient caustic alkali to lower the color of the oil to the required extent. The employment of non-caustic alkali adequately removes the free fatty acid content and also removes substantially all of the gums but the resulting oil is usually of darker color than that desired. The losses resulting from the refining of vegetable oils in a continuous process using soda ash or other non-saponifying alkalies are much less than in processes in which sufilcient caustic alkali is employed in the first instance to not only remove fatty acids and gums from the oil but to produce a low colored oil.

It is, however, necessary to re-reflne the oil using a caustic alkali or similar color reducing material to produce a low colored oil.

continuous refining as strong caustic solutions cause the small amount of soap formed during the re-refining operation to be salted out of the caustic solution and to separate with the neutral oil in the centrifugal separator. By employing a strong caustic solution for color removal and then diluting the caustic immediately before or during separation of the oil from the decolorizing reagent, soap and precipitated impurities, it has been found that the beneficial effects of -.the strong caustic solution can be obtained while separation difficulties are obviated. Difliculties similar to those described above are encountered with various other oils which are low in free fatty acid and gum content and the employment of strong caustic solutions to precipitate or remove impurities from the oil, followed by dilution of the caustic solution during or just prior to separation, has also been found applicable in the treatment of such oils.

It is therefore an object of the present invention to provide an improved process for removing impurities from glyceride oils which are low in free fatty acid and gum content.

Another object of the invention is to provide an improved process of removing small amounts Cottonseed oils vary widely in their characteristics from year to year and in accordance with production areas. It has been found possible to re-reflne certain types of cottonseed 011. after they have been refined by a continuous soda ash process, by using small amounts ofrelatively dilute caustic alkali in a continuous process to 4 A still further object of the invention-is to obtain a properly decolorized oil with exceedingly small losses. However, it has alsov been found that many and perhaps most cottonseed oils, are not capable of being re-reflned with small amounts of relatively dilute caustic alkali. Such dilute alkali not only fails to reduce. the color of the oil but produces diflicultly separable emulsions which are not properly separated in a continuous centrifugal separator.-

In accordance with the present invention, it has been found that emulsion difliculties may be obviated and an adequate reduction of the color of the oil can be obtained by employing small amounts of relatively concentrated caustic soda, for example, concentrations between 20 and 50 Baum. The use of such concentrated solutions, however, has heretofore been found impossible in of impurities from glyceride oils having low free fatty acid and gum content in which process strong caustic alkali solutions are employed but are diluted prior to the separation operation.

v Another object of the invention is to provide a process of re-refining g1yceride.-oiis containing only a small amount of impurities in which refining losses are reduced.

A further object of the invention is to provide an improved process of eflectively removing impurities from glyceride oils which contain small amounts only of such impurities so as to overcome separation difficulties.

provide an improved process of reducing the color of refined glyceride oils by chemical treatment and with substantially no refining losses.

Other objects and advantages of the invention will appear in the following description of preferred embodiments thereof given with reference to the attached drawing'in which:

Fig. l is a schematic diagram of an apparatus suitable for carrying out the present invention,

and Fig. 2 is a somewhat diagrammatic vertical sectional view through a centrifugal separator bowl,

portioning pump l2 and delivered through a heating coil I! of a heat exchange device M to a mixer l8. The tank ll may be provided with a heating coil ll or similar heating means for maintaining the oil in the tank H in fluid condition in case oils or fats solid at ordinary temperatures are being treated. The reagent for precipitating impurities may be withdrawn from a tank l8 and delivered by a proportioning pump I! through a heating coil 2| of the heat exchanger 22 to the mixer M. The mixer IB'may be of any suitable type such as a closed mechanical agitator but is preferably of the flow mixer type disclosed in the patent to Thurman 2,142,062 granted December 2'7, 1938.

A thorough mixture of the reagent and oil produced in the mixer i8 is then passed through a heating coil 23 of the heat exchanger 24 and dephase or heavy emuent and discharged through the spout 88 into a receiver 84 while the purifled oil is discharged through a spout 88 into a receiver 81. The proportioning pumps i2, i9

and 28 may be driven by a variable speed electric motor 88 connected directly to the oil pump l2 and through variable speed devices 39 and M between the motor 38 and the proportioning pumps is and 28, respectively. Other types of proportioning apparatus may, however, be employed, for example, that shown in patent to Thurman above referred.

Instead of delivering the diluting agent into the oil-reagent mixture as the mixture enters the v centrifugal separator, it is preferred to admix the diluting agent with the heavy effluent in the centrifugal after separation has been largely accomplished. This avoids substantially all contact between the oil and a dilute reagent so that emulsion difliculties are entirely overcome. A suitable type of centrifugal separator for accomplishing this operation is shownin Fig. 2. Such a separator may include a bowl 42 mounted upon,

a shaft 48 for rotation .at high speed and may also include an outlet port 44 for the light efliuent and anoutlet 48 for the heavy efliuent. The oil and reagent mixture containing precipitated impurities, as well as a small amount of soap, is delivered into the centrifugal through a stationary pipe 41 and then delivered into a tubular inner bowl member .8 by means of a distributor 49. The inner bowl member 48 divides the separation zone of the bowl from the inlet portion thereof and directs the incoming mixture downwardly and outwardly into the lower portion of the bowl. The separation zone of the bowl may be provided with a plurality of conical baiiie members 8| which are apertured at 82 adjacent the neutral zone of separation. Material to be separated flows upwardly through the apertures 82, the light effluent comprising the oil flowing inwardly in the bowl and being discharged through the outlet port 44. The heavier materials comprising the aqueous phase containing the precipitated impurities and'soap flow outwardly and then upwardly along the periphery of the bowl and are discharged through the port 48, the imperforate 88 preventing admixture of the heavy emuent with the oil being discharged through h port 44.

Water or other diluting agent is introduced into I the bowl by" the pipe :2 which extends downwardly through the pipe 28 so as to terminate within a circular bame member 84 which-maintains the water separate from the incoming oilreagent mixture and directs the diluting agent to the lower periphery of the bowl. The diluting agent admlxes with the heavy emuent'to' dilute the same and cause any soap present in the mix-- the reagent even before dilution with the dilutin agent. This aqueous solution contains excess reagent andsmall amounts of soap. 'Attempts to employ dilute precipitating agents result not only in lneflective removal of impurities from the oil but in the formation of tight emulsions which are not effectively separated in the centrifugal even though the mixture is separated atrela= 'tively high temperatures. In such cases, substantial amounts of reagent are carried out with the purified oil discharged from the port st, requiring extensive washing or other treatment to remove the included reagent from the oil. More importantly, a very substantial amount of the oil is entrained with and discharged with the heavy efiluent through the port 48, resulting in high refining losses. In many instances also the impurities are not adequately removed from the oil.

By employing strong precipitating reagents such as caustic soda solutions-ranging between 20 to 50 Baum, such emulsions are not encountered and in accordance with the present invention refining losses are reduced to a very low figure. However, small amounts of soap are formed by reaction of the caustic alkali with residual free fatty acids in the oil or by reaction with the oil itself and this soap is grained out of the heavy eflluent in the centrifugal. Three layersor strata tend to be built up in the centrifu'gal bowl: an inner oil layer, an intermediate soap layer, and an outer aqueous layer. These layers are not. definitely defined and any attempt to adjust the centrifugal to separate the soap with the aqueous layer causes high refining losses whereas failure to separate the soap with the aqueous layer produces an impure oil requiring extensive further purification treatment.

This difficulty can be overcome by diluting the mixture Just prior to centrifugal separation, for example, by introducing a diluting agent such as water into the mixture entering the centrifugal but a slight amount of difilcultly separable emulsion may be formed due to contact between the oil and diluted reagent and it is found thatv the precipitation of impurities such as coloring matter is not as effective 6.515 the case when separation is substantially complete prior to dilution of the mixture. In the centrifugal separator shown in Fig. 2, diluting of the heavy eiiluent after complete or substantially complete separation thereof from the oil causes the soap layer above referred to, to remain in solution or go into solution in the aqueous layer so that ittween these temperatures except in cases where the oil is delivered to the tank from a priorlrefining or similar process at a high temperature or the oil or fat requires heating to a higher temperature to render the same fluid. The heat exchanger I4 is therefore not employed when the oil is at the correct temperature for admixture with the precipitating reagent but may be employed to either cool or heat the oil in order to bring it to the desired temperature for mixing with the reagent. Similarly the heat exchanger 22 may be employed to either heat or cool the reagent to a desired mixing temperature. In general the temperature of the reagent will usually be adjusted to substantially that of the oil entering the mixer l8.

Properly proportioned amounts of the oil and reagent are thus delivered to the mixer l8 by means of proportioningpumps l2 and I8 and passed through the reaction coil 23 in the heat exchanger 24. Since the temperature giving most eflective separation is usually considerably above the most emcient reaction temperature, any desired heating medium may be circulated through the heat exchanger 24 to raise the temperature of the mixture to that required for effective centrifugal separation. These temperatures will usually range between 120 and 180 F., depending upon the type of oil being treated, the impurities desired to be removed and the melting temperature of the oil. The oils being treated will ordinarily contain not more than approximately 25% free fatty acid and only slight amounts or traces of gums. The preferred reagent is a concentrated aqueous solution of caustic soda, for example, solutions rang ing from 20 Baum up to Baum. A considerable excess of caustic soda over that required to neutralize any free fatty acids present is usually employed. Thus the amounts of caustic solution will usually range between approximately and 4%, the quantity most generally used being in the neighborhood of 2%.

As stated above, the temperature of mixing is preferably between '70 and F. although for removing certain types of impurities this temperature may be as high as to F. The

' temperature of separation will, however, usually range between 120 and F., although this temperature may at times be as low as 100 F.

Water is the preferred diluting agent and the amount of water will.ordinari1y range between approximately 2.5 and ten times the amount of as high as the temperature of' separation and preferably is somewhat higher. Thus the temperature of the diluting agent will range between approximately 100 and 200 F.

The material discharged from the centrifuge is in most cases largely water containing excess caustic soda anda small amount of soap. In general the amount of soap will not exceed 2% and is usuall between .2% and 1% of thematerial discharged. By employing strong caustic alkali solutions and diluting the same just prior to or during separation, the losses rarely exceed '.2% and usually do not exceed .15% whereas the losses when employing equivalent. amounts of dilute caustic soda in the first instance may run as high as 2% or higher. It has been found that even increasing the amount of caustic solution does not measurably increase the losses in the process provided suflicient diluting agent is introduced to carry the concentration of the reagent in the centrifugal below that at which soap tends to separate with the oil.

, While the present process is particularly adaptable to the re-refining of cottonseed oil previously refined by a continuous soda ash process, such as oil refined by the processes disclosed in my Patents Nd. 2,249,701 and No. 2,249,702, granted July 15, 1941, certain vegetable or animal oils in the form they are recovered from the raw material are naturally low in free fatty acids and gumsand the present process may be advantageously employed for removal of small amounts of impurities therefrom. Also substantially completely refined oils intended for edible purposes are frequently processed under conditions which somewhat increase their free fatty acid content and impart deleterious tastes or odors thereto. Such oils or fats are advantageously subjected to the process of the present invention for removal of the small amounts of impurities contained therein. Furthermore, certain light colored oils, such as corn oil, requiring no treatment for color reduction after refining in continuous soda ash processes, are benefited by, treatment in accordance with the present invention as in some instances such oils are extremely difficult to wash without excessive refining losses. It has been found that treatment in accordance with the present invention in conjunction with a subreagent employed. In general, it has been found desirable to reduce the concentration of the excess reagent in the centrifugal to at least 8 Baum although in some instances higher concentrations up to 10 or 12 Baum have been found operable and lower concentrations ranging down to approximately 4 Baum may'sometimes be found advantageous in the centrifugal separator. or other diluting agent employed in the centrifugal separator should be sufficient to cause the soap to separate in solution or in dispersed form in the aqueous phase. Also the temperature of the diluting agent should in general, be at least In any event, the amount of water sequent water washing operation produces much lower losses than direct washing of the oil from the primary refining operation. Thus the present process conditions the oil for a washing operation with low losses.

While caustic soda is a preferred reagent in the present invention, it is also possible to employ sodium peroxide which liberates caustic soda while admixed with water and should be used in sufficient amounts to produce the concentration of caustic soda contemplated in the present invention. The sodium peroxide additionally liberates oxygen which materially assists in removing coloring matter and other impurities from the oil. An advantageous operation is to employ a reagent consisting predominantly of caustic soda but containing a small amount of sodium peroxide or other oxygen liberating material. Other equivalent alkali metal compounds such as potassium compounds are also suitable. I

This application is a continuation-in-part of my copending application Serial N0..398,489, filed June 17, 1941, which is in turn a division of Serial No. 296,685, filed September 26, 1939, now Patent No. 2,249,701, granted July 15, 1941.

While I have disclosed the preferred embodicontains small amounts of other impurities, which 1 process comprises, mixing with saidoil a caustic soda solution having a concentration between approximately 20 and 50 B., said reagent being added in sufficient amount to precipitate said impurities and prevent'the formation of an emul-' sion in said oil and said reagent, whereby the resulting mixture will separate into an oil layer,

a' soap layer, and an aqueous layer containing said impurities when subjected to centrifugal separation, subjecting the resulting mixture to centrifugal separation and diluting said mixture prior to complete separation in the centrifugal to lower the concentration of the aqueous layer to between approximately 4 and 10 B., whereby said soap discharges with said aqueous layer from said centrifugal.

2. The process of purifying a glyceride oil which is low in free fatty acid and gum content and contains small amounts of other impurities, which process comprises, mixing with said all a caustic soda solution having a concentration between approximately 20 and 50 B., said reagent being added in sufiicient amount to precipitate said impurities and prevent the formation of anemulsion of said oil and said reagent, whereby the resulting mixture will separate into an oil layer,

a soap layer, and an aqueous layer containing said impurities when subjected to centrifugal separation, subjecting the resulting mixture to centrifugal separation and diluting said reagent prior to complete separation in the centrifugal so as to produce a concentration in said aqueous layer not substantially greater than 8 B., whereby said soap discharges with said aqueous layer from said centrifugal.

3.- The process of purifying a glyceride oil which is low in free fatty acid and gum content and contains small amounts of other impurities, which process comprises, mixing with said oil a caustic alkali solution having a concentration between approximately 20 and 50 B. to precipitate said impurities and form a small amount of soap, whereby the resulting mixture stratifles into an oil phase, a soap phase and an aqueous phase when the same is subjected to centrifugal separation, subjecting the resulting mixture to centrifugal separation, and adding sufficient water to said aqueous phase in said centrifugal after said aqueous phase and soap have been at least partially separated from said oil to reduce the concentration of said aqueous phase to between approximately 4 and 10 B. whereby said soap discharges from said centrifugal with said aqueous phase.

4.. The process of purifying a glyceride oil which is low in free fatty acid and gum content and contains small amounts of other impurities, which process comprises, mixing with said oil a caustic alkali solution having a concentration between approximately 20 and 50 36. to precipitate said impurities and form a, small amount of soap,

whereby the resulting mixture stratifies into an,

oil phase, a soap phase and an aqueous phase when the same is subjected to centrifugal separation,

subjecting the resulting mixture to centrifugal separation,'and adding sumcient water to said aqueous phase in said centrifugal after said:

aqueou phase and said soap have been at least partially separated from said oil, to reduce the concentration of said aqueous. phase to at-least 8 B. whereby said soap discharges from said centrifugal with said aqueous phase.

5. The process of purifying a glyceride oil which is low in free fatty acids and gum content, which process comprises mixing with said oil a caustic alkali solution having a concentration between approximately 20 and 50 B. to precipitate saidimpurities and to form a small amount of soap, and of suiiicient concentration to stratify the mixture into an oil phase, a soap phase and an aqueous phase when the same is subjected to centrifugal separation, thus interfering with such separation, subjecting the resulting mixture to centrifugal separation and conditioning such stratified mixture for centrifugal separation by adding suflicient water to said aqueous phase in said centrifugal to reduce the concentration thereof to such an extent that said stratiflcation is overcome and said soap is discharged with the said aqueous phase.

6. The process as defined in claim 5 in which the concentration of said aqueous phase is reduced to between approximately 4 and 10 B. I 7. The process of purifying vegetable and animal oils containing impurities, including free fatty acids, which comprises, mixing therewith an alkaline refining reageant capable of reacting with said impurities to precipitate the same and produce soap, said reagent being added in sufficiently high concentration to produce a stratifled mixture including an oil phase, a soap phase,

5 and an aqueou phase when the mixture is subjected to centrifugal separation, thus interfering with said separation, reducing concentration by adding an aqueous diluent to said mixture in sumcient quantity to overcome such stratification,

whereby to permit said soap to bedischarged with said aqueous layer, and centrifugally separating the thus conditioned mixture.

8. The process as defined in claim 7 in which the dilution produces a separation of the heavier eifluenthaving a Baum between approximately 4 and 10.

9. The process as defined in claim 7 in which the dilution is effected after the soap has been at least partially separated from the oil in the centrifugai apparatus.

10. The process as defined in claim 7 in which the dilution occurs prior to complete separation in the centrifugal.

11. The process as defined in claim '7 in which 5 the impurities separatedfrom the oil in the centrifugal are diluted in the centrifugal after substantial separation from the oil.

12. A re-refining process for oils of low impurity content which process comprises the treatment of said oils with a caustic solution in a concentration su'mciently high to cause stratiflcation into an oil phase, a soap phase and an aqueous phase'when the'mixture is subjected to centrifugal separation, introducing water to said mixture in suflicient quantity to convert the mixture from its thus stratifled condition to a sufficiently nonstratifled condition to permit the soapstocl-r to be discharged with the aqueous phase, and centrifugally separating the thus conditioned mixture.

13. The process as defined in claim 12 in'which' the water is introduced at the point of separation inthe centrifugal. i

I BENJAMIN CLAYTON.

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