US2226211A - Process of refining oils - Google Patents

Description

Dw24,1940. B.H.THURMAN 2,226,211

FROCES S OF REFINING OILS Filed June 22 1938 Patented Dec; 24, 1940 PATENT OFFICE rnoonss or nnrmmo o ns Benjamin H. Thurman, Bronxville, N. Y., assignor to Refining, Inc., Reno, Nev., a corporation of Nevada Application June 22, 1938, Serial No. 215,251

4 8 Claims.

This invention relates toa process of refining animal and vegetable oils, and more particularly to a low temperature process in which relatively concentrated alkali refining solutions are employed.

An object of the present invention is to provide an improved process of alkali refining animal and vegetable oils by which the refining losses are reduced.

Another object of the invention is to provide a low temperature alkali refining process for the refining of animal and vegetable oils in which concentrated alkali refining solutions are employed in order to facilitate centrifugal-separa- 5 tion of soap stock from oil at relatively low temperatures.

A further object of the invention is -to provide a rapid process of refining animal and vegetable v oils in which relatively concentrated alkali refining reagents are employed and a clean separation of the resultant soap stock from the refined oil'efiected. 1

A still further object of the invention is to provide a continuous and rapid process of. refing5 ing animal and vegetable oils in which low temperatures and concentrated alkali refining solutions are employed in order to reduce refining lo'sses. W

Other objectsand advantages of the invention will appear in the following description of the preferred process, which will be described in conjunction with the attached drawin of whighz V Figure l is a schematic diagram Bfan apparatus capable of carrying out the process of the present invention; and

Figure 2 is a similar view of a modification of a portion of the apparatus.

Animal and vegetable oils are at present refined either inv batch or continuous processes by 0 adding an excess of an alkaline refining reagent, usually a caustic soda solution, in proportioned amounts, to the oil so as to form soap stock which is separated from the oil by difference in specific gravity. In these prior art processes, a relatively dilute refining reagent is employed. When such a refining solution is mixed with the oil, a difficulty separable emulsion, apparently of the water and oil type, tends to form and does form if the mixing is performed at relatively low temperature, for example, temperatures below F. This emulsion is broken by the employment of elevated temperatures, for example, tempera- .tures between 100 and 160 F., and usually between and F., so that soap stock can be separated from the oil. In batch operations this heating is performed subsequent to mixing and the soap stock allowed to settle from the oil. In continuous operations, which have largely superseded batch operations, the elevated temperature necessary for effective separation is obtained 5 either by heating the oil in flow prior to mixing or by heating the mixture in flow, and separation is eifected by continuously centrlfugally separating the soap stock from the oil. In these processes the concentration of the refining solution 1 ranges from approximately 12 B. to 20 B. The lower range is employed for high quality low free fatty acid oils, for example, hot pressed cottonseed oil having less than 1.5% free fatty acids, while the upper range is employed for low qual- 15 ity cold pressed oils having extremely large amounts of free fatty acids. The strength of refining solution for the usual run of oils seldom exceeds 20 B. For example, for cottonseed oils ordinarily encountered and containing 3% or less 20 free fatty acid, the strength of refining reagents ranges between aproximately 12 and 16 B.

In accordance with the present invention, I have found that a rapid process, and preferably a continuous process resulting in lowered refin- 25 ing losses, can be carried on at low temperatures, for example, 70 to 90 F., with refining solutions ranging between 20 and 50 B. In the present process with high quality low free fatty acid oils, for example, those having below 1.5% free fatty 3o acids, it is sometimes possible to employ refining solutions as low as 20 B., in contrast with 12 Brsolutions for prior processes, but more highly concentrated solutions are preferable, and the concentration will run as high as 50 B. for oils containing an excessive amount of free fatty acids, in contrast with a maximum of 20 B. for prior processes.

Adequate refining of neutral oil can be efiected by the known refining processes above discussed. 40 However, refining processes are always attended with substantial refining losses. These losses are made up of (1) loss due to neutralization of free fatty acids and precipitation and removal of gums, (2') losses due to saponification of neutral oil, and (3) losses .due to entrainment of neutral oil in the soap stock. The first of these refining losses is unavoidable. The known continuous processes result in lower losses due to saponification and entrainment of neutral oil than con- 50 ventional batch processes but the present process still further reduces these losses, thus resulting in savings in over-all refining losses.

Several factors affect the amount of neutral oil saponified. saponification of neutral oil goes short, time after mixing increases with decrease in concentration of the refining reagent. In accordance with the present invention, no emulsion is formed. during mixing, or, if formed, it is immediately broken; a low temperature is maintained throughout the process; the resultant soap stock along with excess reagent is promptly separated from the oil; and concentrated refining solutions are employed such that saponification of neutral oil is minimized.

2o Entrainment of oil in the soap stock depends primarily upon the effectiveness of the separation of the soap stock from the oil. Centrifugal separation of a properly conditioned mixture, 1. e. a well broken emulsion, results in much less entrainment of neutral oil than" batch settling operations. Also, entrainment increases with the amount of refining solution employed. The pres ent invention contemplates such centrifugal separation, and also the increased concentration of so the refining solutions decreases the amount of refining solution necessarily mixed with the oil to neutralize the free fatty acids and provide the proper excess found to be necessary for color reduction. Thus. the present invention also f markedly reduces the losses due to entrainment even over known continuous refining processes.

The concentration of the refining solution employed in accordance with the present invention should be sufilcient to produce almost immediate breaking of the emulsion at the low temperatures contemplated. If the refining solution is too concentrated, however, not only is the emulsion broken but the soap 'tends to separate from the water and excess refining reagent-by a salting but action. Thus, if too concentrated refining solutions are employed, the soap stock stratifies in the centrifugal separator into two layers, a soap layer,and a water or nigre layer,

and this effect increases with increase of concentration. The soap layer mixes with a large quantity of neutraloil, and the nigre with a small amount of soap is discharged as the heavy efiiu-' ent, while a large proportion of the' soap is discharged with the oil as the lighter eiiiuent, such that effective separation between soap and oil is not produced.

The amount of stratification in the centrifugal separator has also been found to increase with 'the time of treatment between mixing and separation. With certain oils, for example, cottonseed oil, which is a highly colored oil, it is desirable to provide a short period of time between the mixing and separation in order to cause the By employing Just sufilcient concentration of refining reagent to substantially immediately break any emulsion which tends to form at the low temperatures, it has been found that, with almost all oils, the mixture may be maintained 5 for a sufficient length of time to produce said color reduction without causing any substantial amount of stratification in the centrifugal separator. Separation operations involving settling of the soap stock from the oil are impractical. 10 since the time required for such settling causes stratification of the soap stock and admixture of a large quantity of neutral oil with soap; With certain oils, where difilculties with stratification are encountered, if sufiicient time of treatment 15 for satisfactory color removal is provided, it has been further found that the addition of a stream of water to the stream of mixture entering the centrifuge or to the soap stock-component of the mixture within the centrifuge will overcome-strat- 20' ification in the centrifuge, even though it would occur in the absence of added water. The water dilutes the nigre such that the concentration of excess refining reagent is reduced below that which produces stratification.- Water thus added 25 is not in contact with the mixture for sufiicient time to cause any appreciable amount of emulsion to form or increase in saponification of neutral oil as is the case where the refining reagent is relatively dilute when admixed with the oil. 30

This addition of water is not to be confused with a washing or flushing operation to wash the soap 1 stock out of the centrifugal, as insufilcient water is added for the latter-purpose.

Separation is preferably accomplished in the 85 heated centrifugal separator of the type disclosed in the patent to Clayton No. 2,100,277, granted Nov. 23, 1937. The soap stock at the temperature above mentioned will ordinarily not discharge continuously from a conventional centrifugal n separator, as it is a thick viscous material which adheres to the walls of the bowl. By employing the heated centrifugal referred to, the walls of the bowl may be heated sufilciently to cause the soap stock to slip continuously along the heated 5 surfaces of the bowl and thus be dischargedcontinuously therefrom. It is unnecessary to employ sufllcient heat to measurably increasethew temperature of the 011 being discharged from the centrifugal, although, in general, the average 50 temperature of the soap stock will be somewhat raised in the centrifugal bowl.

From the above discussion it will be observed that the present process is susceptible of being carried out with either continuous mixing of 55 streams of oil and reagent, or the oil and alkali may be mixed in such small batches that c'ontinuous centrifugal separation can be effected beforesubstantlal salting out with resultant stratification occurs. The continuous operation is so preferable, as the time of treatment of the mixture between mixing and separation can be made constant for all portions of the oil and more adcurately controlled and is desirably carried out in an apparatus similar to that shown in the 5 drawing above referred to.

Referring more particularly to the drawing, a source of supply for oil to be refined is indicated as a tank IO, and a source of supply for the alkaline refining reagent is indicated as a tank II.

The tanks Ill and II may be provided with heat exchange coils l2 and I3, respectively, through which a heating or cooling medium may be circuiated to bring the oil and alkali to the desired temperature. This temperature will range be- 15 tween 60 and 100 F., but usually between 70 and 90 F., and is preferably approximately 80 F. Thus no heating or cooling of the oil and alkali in the tanks ill and II will be necessary except under extreme weather conditions where the tanks are exposed to atmospheric temperatures.

Oil is withdrawn from the tank i3 by means of speed motor I] with a speed exchange device i2 positioned between the pumps so that any desired amounts and proportions of the oil and alkali may be delivered to the mixer ii. The proportioning mechanism shown is merely by way of example, and any desired proportioning mechanism capable of delivering accurately proportioned streams of oil and refining reagent to the mixing device l 5 may be employed. 7

The mixing device i5 is preferably of the type disclosed in the copending application of BenjaminH. Thurman, Serial No. 190,673, filed Feb. 15, 1938, but any other type of eificient flow mixer such as a closed mechanical agitator may be employed in lieu thereof. In many instances, merely injecting a stream of alkali at right angles into a flowing stream of the oil is sumcient, as animal and vegetable oils containing free fatty acids mix readily with alkaline refining solutions. Neutralization of the free fatty acids occurs almost instantaneously in the mixer i5 and in the present process the alkaline refining reagent has sufficient concentration to prevent the formation of or almost immediately break any emulsion which tends to form at the temperature of mixing. Thus the mixture is almost immediately in condition for centrifugal separation, and, if no treating time for color reduction is necessary for the particular oil being treated, the mixture may be delivered through the pipe I 9 directly to the continuous centrifugal separator 20.

If a short time of treatment for color reduction is necessary or desirable, the mixture may be caused to flow through one or both of the coils 2| and 22. Thus by closing the valve 23 in the pipe i9 and opening the valve 24, while at the same time maintaining the valve 25 open and the valve 21 closed, the mixture may be caused to flow through the coil 2| Then, by closing the valve 25 and opening the valve 21, the mixture may be caused to also flow through the coil 22. Such coil-s. may provide conduits of substantial length, for example, 250 feet, such that an appreciable time may be required for passing the mixture therethrough. As a specific example, such a coil may be made of a inch pipe 250 feet in length, and the mixture pumped therethrough at a rate requiring 2 minutes for the mixture to pass through the coil. As many coils as necessary may be employed to produce the required treating time, which time rarely exceeds 5 minutes, and, at most, no more than 10 or 15 minutes.

' istead of employing coils such as 2i and 22 for providing time of treatment for color reduction, the mixture may be delivered into the chamber 34 of Figure 2, which chamber is-preferably closed from the atmosphere, and provided with an agitator 35 rotated from any suitable source of power through'a pulley 36. The

agitator- 35 is rotated at a rate which is sufilcient only to prevent settling of the soap stock and is insuflicient to cause beating the soap stock back into the oil. The amount of mixture maintained in the chamber 35 and, therefore, the time of treatment thereof between mixing and separation can be ,yaried by the valves 31, since the lowermost open valve 31 will determine the level of the mixture in the chamber 34.

In case it is found that appreciable quantities of 'soap are discharging with the neutral oil, from the centrifugal separator, a stream of water may be introduced into the pipe l9 through a pipe 28 in order to overcome the stratiflcation of the soap stock in the centrifugal. Only a .very small amount of water is required, as it is only necessary to slightlyreduce the concentration of the excess refining solution in the centrifugal in order to prevent stratification.

As disclosed in the copendi'ng application of Benjamin H. Thurman, above referred to, steam may be supplied to the centrifugal casing by means of the pipe 32 so as to surround the bowl and discharge passages thereof and cause the soap stock to continuously discharge from the centrifugal. Any condensate from the steam may be discharged through a pipe 33. A clean separation of the soap stock from the refined oil can thusbe-eifected, and refining losses reduced even with respect to modern continuous refining processes employing elevated temperatures for breaking the emulsion.

As specific examples of refining operations in the above apparatus, a Brazilian crude cottonseed oil containing 2.8% free fatty acidswas admixed with 5.9% of a 24 B. caustic soda solution in the mixer l5 at a temperature of 80 F. The mixture was passed through the two coils 2| and 22 and thus given a treating period for color removal of approximately 5 minutes. This mixture was then,, delivered directly to the centrifugal separator 2'; Separation was effected with suflicient stea'mjaround the bowl thereof to cause continuous discharge of the soap stock and neutral oil substantially free of soap stock discharged as the lighter efliuent.

As another example, acrude, cottonseed oil having a free fatty acid content of 3.5% was mixed with 4.25% of 30 B6. lye solution at 80 F. and sent through two coils at this temperature, then separated in the centrifuge with heat I lost in the process.

Thus the process of the present invention in volves the employment of low temperatures in order to decrease refining losses. The refining solution is employed in sufiicient concentration to substantially immediately break any emulsion which tends to form, which thereby decreases the refining loss both because the rate of reaction with neutral oil is decreased when the emulsion is broken and the concentrated refining solution saponifies neutral oil at a. lesser rate than more dilute solutions, if separation is effected shortly after mixing. The mixture is maintained for sufficient time only to reduce the color of the oil,'and this period of treatment is made as short as possible in order to decrease refining loss. The smalleramou'nt of refining solution which it is possible to use in'conjunction with efiicient centrifugal separation of the.

broken emulsion reduces loss due to'entrainment of neutral oil. separation of the resulting soap stock from the oil is effected before salting out, so as to avoid stratification in the centrifugal separator, and a heated .centrifugal separator is preferably em= ployed to insure continuous discharge of the soap stock from the centrifugal separator. As stated before, if the concentration of the refining reagent necessary to break the emulsion is sufficient to cause stratification in the centrifugal before the necessary color reduction has been effected, a small stream of water may be added to the mixture entering the centrifuge or to the soap stock layer in the centrifugal.

While I have disclosed the preferred embodiments of my invention, it is to be understood that the details thereof may be varied within the scope of the following claims.

I claim:

1. The process of refining animal and vegetable oils containing free fatty acids, which comprises, mixing with said oil at a temperature below F. a proportioned amount of an alkaline refining solution having a concentration between 20 and 50 B. and of sufiicient concentration to prevent the formation of a stable emulsion at said temperature, whereby said fatty acids are neutralized and a mixture of oil and soap stock conditioned for centrifugal separation is formed, and thereafter promptly delivering said mixture while at a temperature below 100 F. to a centrifugal separator and centrifugally separating said soap stock from said oil prior to the time at which stratification of said soap stock into a soap layer and nigre layer takes place during said separation. a

2. The process of refining animal and vegetable oils containing free fatty acids, which comprises, mixing with said oil at'a temperature below 100 F. an alkaline refining solution having a concentration 'between 20 and 50 B. and of sufficient concentration to prevent the formation of a stable emulsion at said temperature, whereby said fatty acids are neutralized and a mixture of oil and soap stock conditioned for centrifugal separation is formed, and thereafterpromptly continuously centrifugally separating said soap stock from said oil at substantially the temperature of mixing and while said all is below a tempera ture of 100 F., said separation being carried out before sufficient time has elapsed to cause stratification of said soap stock into soap and a liquid fraction in said centrifugal, whereby said soap is substantially cleanly separated from said oil, without substantial entrainment of oil in said soap stock.

3. In the art of refining-animal and vegetable oils in which an alkaline refining reagent is mixed with the oil to neutralize said fatty acids and form soap stock and said soap stock is continuously centrifugally separated from said oil, the

Continuous centrifugal improvement which comprises, performing said mixing at a temperature below approximately 100 F., employing a refining reagent having a concentration between 20 and 50 B. of sufficient concentration to condition said mixture for ration.

oil while said oil is below a temperature of 100 F.

prior to the time at which stratificationof said soap stock into a soap layer and a nigre layer takes place during said separation.

5. The process of refining animal and vegetable oils containing free fatty acids, which'comprises,

mixing with said oil at a temperature below 100 F. a proportioned amount of an alkaline refining solution having a concentration between 20 and 50 B. and of sufficient concentration to condition the resulting mixture of oil and soap stockfor continuous centrifugal separation at said temperature, thereafter promptly continuously centrifugally separating said soap stock from said oil in a centrifugal separator while said oil is at a temperature below 100' F., and simultaneously continuously introducing water into said centrifugal to prevent stratification of said soap stock into a soap layer and a nigre layer due to the concentration of the refining solution.

6. The process of refining animal and vegetable oils containing free fatty acids and coloring materials, which comprises, mixing with said oil at a temperature below 100 F. an excess of a caustic soda solution having a concentration between 20 and 50 B, and of suincientconcentratlon to condition the resulting mixture of oil and soap stock for continuous centrifugal separation, maintaining said mixture in a state of movement at said temperature for suflicient time to substantially reduce the color of said oil, thereafter tion the resulting mixture of oil and soap stock for continuous centrifugal separation at said temperature, advancing said mixture for sufiicient time to effect substantial color reduction of said oil under sufficient conditions of movement to prevent settling of said soap stock from said 01],

thereafter promptly continuously centrifugally separating said soap stock from said oil while said oil is at a temperature below 100 F., and simultaneously introducing a stream of water into the zone of centrifugal separation to prevent stratiflcation of said soap stock into a soap layer and a nigre layer during said separation, whereby said oil is eflectively separated from said soap stock with minimum entrainment of oil in said soap stock. a

8. A continuous process of refining animal and vegetable oils, which comprises, mixing at a temperature between approximately 70 and 90 F. proportioned streams of said oil and a caustic soda solution having a concentration between 20 and 50' B6. and or sumcient concentration to condition the resulting mixture or oil and soap stock for continuous centrifugal separation at said temperature, advancing a stream of the resulting mixture of oil and soap stock toward a centrifugal separator with sufficient movement to prevent settling of said soap stock from said oil while substantial reduction oi! the color of said oil is eflected, and thereafter promptly continuously centritugally separating said soap stock from said oiljin said centrifugal separator at sub- -BENJAMIN H. THURMAN.

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