US2268567A - Process of refining oils containing free fatty acids - Google Patents

Description

Jan. 6, 1942. B. CLAYTON ETAL v PROCESS OF REFINING OILS CONTAINING FREE FATTY ACIDS Filed Aug. 30, 1932 Caz/a r7 0 Pan P OOOQGOOOOQ a ye m r w o fl sw m M 5W6 77 5 IV 2 greeable color or odor to the oil.

novel prccessfor refining such oils.

Patented Jan. 6, 1942 UNITED" s T ATas PATEN PROCESS OF REFINING OILS CONTAINING FREE FATTY ACIDS 'r OFFICE Benjamin Clayton, Sugarland. Ten, and Walter B. Kerrick, Los Angeles, and Henry M. Stadt, Glendale, Calif., asslgnors, by direct and mesne assignments, to Refining, Inc., Reno, Nev., a

corporation of Nevada 1 Application August 30, 1932, Serial No. 631,002

4 Claims. (01. 260-425).

Theinvention relates to the treatment of oils, containing free fatty acids and other impurities tending to impart undesirable qualities to the oil, for the purpose of saponifying the acids and removing the impurities. It is applicable to suitable storage by meansnot shown to an oil tank I. A solution of caustic soda in water, herevarious animal or vegetable oils, including fish borhood of four hours.

It is a further object of the invention-to provide a process by which the oil can be continuous- 1y refined in a very much shorter time.

The caustic soda solution now used has a pref-- erential afiinity for the free fatty-acids, but also inafter called the reagent, of about 14? to 16 Baum gravity is delivered as required for the continuous operation of the process to a caustic tank 2. An oil pump 3 takes oil from the oil tank I through a pipe 4 and delivers it through a pipe 5 to a mixer 6. l -A reagent pump I takes reagent from the tank 2 through a pipe 8 and delivers it through a pipe 9 to the mixer 6. v

The operation of the process on this particular oil is improved if compressed air is delivered to the pipe 9 through a pipe it), .(having an automatic regulating valve- II and a manually operated valve l2). This compressed air is conveniently obtained from an air reservoir l3 which is supplied with air from a compressor l4 through tends to act on the oil itself, producing waste or low value reaction products and thereby causing substantial refining losses.

It is a further object of the invention to provide a process by which such'refining losses are greatly reduced. 1

While free fatty acid is the mostnoticeable impurity in such oils, they also contain other impurities which impart ag mdesirable' color to the oil. 1

It is a further object of the invention to provide a process by which these impurities are re moved.

. A specific example of one method of using 'theinvention in the refining of a high grade cottonfollows. The apparatus used is shown somewhat diagrammatically in the drawingin which, 2

Fig. 1 is an'isometric view of the apparatus employed. The various pieces of apparatus are diagrammatically indicated, and the drawing is not intended to indicate either the size or shape seed oil containing about 0.6% of fatty acid isas thereof, the selection of suitable units being wellwithin the power of anyone skilled in the art.

Fig. 2 is a section through-the upper portion of the air release tank.

The oil to be refined is delivered," as required a pipe l5. Suitable means, not shown, are provided for regulating the operation of the compressor It so that a'substantially uniform air pressure is maintained in the reservoir I3.

A convenient form of mixer is shown, in Fig. 3. The pipe 9 is connected to aninner p pe 6! which is provided with fine holes 62 and placed inside of and concentric with an outer pipe 63 leaving an annular space 64 between" the pipes 6i and 63. Oil to be'treated enters the left-hand end of the pipe 63 through the pipe 5. It then passes from left to right through the annular space as. During its passage through this space caustic solution is iniected'into the oil through the holes 62. These holes being small and the velocity of the oil in the space '64 being high, the

caustic solution is 'uniformly dispersed through the oil in the form of fine drops, this dispersion being assisted by a continuation of the annular space to-the right of the zone in which the initial inJection takes place. The oilthoroughly impregnated with the minute drops of caustic solution and containing many small air bubbles (if air isused) isthen delivered to the pipe 20.

The pumps '3 andl are connected by a shaft so that they run at the same speed and, operating on the all above described,- are so proportioned and adjusted that from 2% to 3% of reagent solution is delivered to the mixer 6 for each 100% of Oil so delivered. The pumps 3 and Tare then run at the proper speed to deliver about 1.85

v gallons of oil per minute to the mixer 6.

. Fig.3is an enlarged view partly in section showing'. the mixer.

The regulating valve .llis set at a pressure which will deliver.- about five cubic feet of air per minute to thefiowing stream of reagent in the 1 pipe 9, this air being carried into the mixer 6,

which maybe ofany convenienttype suited to tor the continuous operation of theprocess, from .inject the stream of air and reagentintothe oil.

The roughly mixed air, reagent, and oil are delivered through a pipe 20 having a gauge It to a helical pipe coil 2| carried in a water bath in a tank 22. The pipe coil 2| in the apparatus actually used consists of 500 linear feet of pipe of inside diameter through which the mixture first passes, and 250 linear feet of pipe of inside diameter into which the mixture is delivered from the /2" pipe. All of this pipe is arranged in roughly circular coils which are surrounded by the water bath.

The water bath is heated by means of a fuel burner 23 suitably controlled by a thermostat (not shown), the thermostat being set to maintain a temperature on the fluid leaving the coil 22 through a pipe 24 of between 100 and 120 F., this temperature being indicated on a thermometer 25.

The average time required for the fluid to pass through the coil 22 under the conditions above described will be about four minutes and the pressure required to force the fluid through the coil will be between 150 and 1'75 pounds per square inch above atmospheric pressure, as indicated on the gauge l6 connected to the pipe 20. This pressure is due to the frictional resistance of the fiuid passing through the coil 22, the pressure at the outlet pipe 24 being practically atmospheric pressure. Fluid is delivered from the pipe 24 into the central portion of an air release tank 30. During the passage of the fluid through the coil 22 practically complete saponification of the free fatty acid takes place, producing reaction products commonly termed foots which may be greenish black or brown in color, and which have a considerably lower specific gravity thanthe oil so that they tend to rise in the air release tank 30, the free air also rising in this tank, thus assisting in lifting the foots and escaping from the surface of the liquid.

The rim 3| of the tank 30 is surrounded by a launder 32 which catches any liquid which overflows from over the rim 3|. This liquid, consisting of foots containing some free oil, may be delivered through a pipe 33 to a centrifuge 34 in which the foots are separated from the oil and delivered through a pipe 36 to storage (not shown), the separated oil being delivered through a pipe 35 to storage (not shown).

Oil and water, not being mutually soluble, will not form a solution, each liquid tending to retain its original state and if there is some difference in the specific gravity of the liquids if allowed to stand quiescent, they will stratify. If, however, a quantity of one liquid is placed in a vessel containing the other liouid and a violent agitation is produced which affects both liquids, a mixture is produced consisting of small drops or particles of one liquid suspended in the other. Such mixtures are commonly termed emulsions. Water and oil form two distinct types of emulsion. In one form drops of water are suspended in oil, the water then being the dispersed liquid and the oil being in continuous liquid, the emulsion being said to be of the water in oil type. It is also possible to suspend drops of oil in water, the oil being the dispersed liquid, and the water being the continuous liquid. Such an emulsion is said to be the oil in water type.

One of these .two types of emulsion occurs whenever oil and water are agitated together, and, of course, these emulsions also occur when aqueous solutions are substituted for pure water.

aqueous solution and when mixed with oil one type of emulsion or the other is produced.

The two types of emulsion are mutually convertible. In other words, one may be changed into the other under certain conditions, in which case the liquids are reversed, the continuous liquid becoming dispersed, and the dispersed liquid becoming continuous.

When we add from 2% to 3% of aqueous caustic solution to the oil, we first produce a water in oil emulsion; that is, the solution is dispersed in the form of small particles in the continuous body of oil, The foots, however, at the conclusion of our process are themselves of the oil in water type; that is to say, any oil carried over by the foots through the pipe 33 into the centrifuge 34 is in the form of purified or refined oil suspended in the form of small drops in the aqueous mass of foots which form the continuous phase of the liquid. In other words, the liquid as it enters the coil 2| is a water in oil emulsion, but the foots in the pipe 33 are an oil in water emulsion. To this extent we may say that in our process we reverse the phase of the emulsion.

It seems probable that oil in water emulsions are easier to separate into their constituent parts (oil and water) than water in oil emulsions. In any event, the separation in the centrifuge 34 of any entrained oil from the foots is very easy and quite complete.

We are of the opinion that the air plays an important part in this reversal of the emulsion. in addition to reducing the specific gravity of the foots so that the foots readily float out of the oil. This reduction in specific gravity is probably due to the entrainment of small air bubbles in the foots.

In the operation of the plan as described above the foots produced are of lower specific gravity than the oil and readily separate from the oil by rising in the tank 30 and overflowing into the launder 32 so that oil, substantially free from foots, may be withdrawn from the bottom of the tank 30 through a pipe 31 and passed directly to suitable storage. If any heavy foots or other impurities are produced which tend to sink in the oil, they are separated from the oil in a centrifuge 4| from which refined oil is discharged through a pipe 43 and foots are discharged through a pipe 42. We have found that the foots produced when air is used have a tenacious hold on the entrained air, this air very slowly escaping if the foots are allowed to stand,

From the above description it will be evident that the process operates as follows:

The raw oil, containing about 0.6% of free fatty acid, is roughly mixed in the mixer 6 with about 2% to 3% of a 14 to 16 Baum solution of caustic soda from the tank 2 and with compressed air, and the mixture is passed into the coil 22, the oil being delivered by the pump 3 at the rate of 1.85 gallons a minute and the air being delivered through the pipe W at the rate The caustic solution used by us is, of course, an each other.

Due to the repeated contacting of the different fluids in the coil 22, the reagent is able to act very rapidly on the free fatty acids of the oil.

and the mixture leaving the coil 22 through the .pipe 24 contains practically no free fatty acid,

The small drops of soap solution produced by the reactionof the small particles of caustic solution (injected into the oil in the mixer 6) with the free fatty acids of the oil, are agglomerated into larger masses of foots which, if air is used, contain considerable entrained air.

greenish black. The proportion of air introduced 1 does not seem to be very critical andltis probable that the action of the air is largely mechanical rather than chemical, and will vary with the viscosity and other characteristics of the 011 being treated. Since the amount of air introduced can be readily regulated by the valves and II, the

In the tank 30 practically all the saponifled foots are floated off the oil. The production of low specific gravity foots is an important advanarated from the oil.

The limitations of the process seem to be about as follows:

(a) The process is probably only applicable to oils containing free fatty acids; that is, to animal, vegetable, or fish oils.

(b) The process requires the use of a reaction chamber, such as the coil 2|, through which the mixture of oil and reagent is driven at relatively high velocity. It will be noted that although the mixture is driven through the coil 2| at a high velocity and intimate contacting between the'constituents of the mixture is produced by this high velocity and the constant changes in the direction produced by the curvature of the coil, nevertheless the coil is free from constrictions or obstructions, the inner surface of the pipe used being smooth and free from projections tending to produce violent eddies in the stream of fluid and all constrictions of the stream being avoided. "High velocity is intended to indicate velocities sufliciently high to produce intimate contacting. We have found that a velocity of 375 feet a minute is proper on certain oils. In some cases velocities as low as 100 feet a minute are effective. It is apparently quite important that the velocities be regulated between limits. If the velocity is too high, emulsification occurs,

- and if too low, the contacting is not emcient. In

operation the velocity is regulated by regulating the speed of the pumps 3 and l.

proper proportion of air to produce a complete flotation of the foots can be easily determined by,

trial.

scribed a pressure of from 150 to 1'75 pounds per square inch is indicated on the gauge IS, the pressure at the outlet end of the coil 2| being substantially atmospheric, this pressure is wholly due to fluid friction of the mixture with the intage in our process since foots can be readily sep- (c) It is necessary for the successful operation of the process, if the oil is heated, that the maximum temperature of the oil shall not exceed that at which thermal decomposition of the oil occurs in material amounts during the time the oilis passing through the coil and at which the reagent is still effective in removing free fatty acids and impurities tending to impart a commercially undesirable color to the oil. On cottonseed oils 9. temperature below 120 F. seems to be quite effective. The temperature should be kept high enough to lower the viscosity of the oil to a point where the centrifuge works efllciently.

(d) The use of compressed air in the process seems to increase its efliciency. Some of this readily floats out of the oil in the tank 30. The foots so produced from cottonseed oil maybe 75 and thereaftd ner surface of-the coil 2! and internal friction in the liquid itself. and will vary with the, size of the coil, the characteristics of the oil being treated, and the amount 'of oil pumped.

(f) The time of treatment, which is less than four minutes in the typical case cited, seems to be important, since the longer the oil is in contact with the reagent. the greater the losses due to reactions between the oil and reagent.

(g) The reagent used in the above typical ex-' ample is a caustic soda solution of 14 to 16 Baum gravity. This solution is quite effective on cottonseed or other oils. Many other reagents have been used in the refining of such oils and it is not considered that the use of this particular solution is absolutely essential to the successful operation of the process, since other well known reagents may be employed.

(h) While we have shown a centrifuge 4| for removing any particles of caustic solution not floated out of the oil, practice shows that operating on some oils the centrifuge M is not necessary ifthe tank 30 is made large enough to effect complete gravitational separation. If necessary, two or more tanks like tank 30 may be used, one or more being used as settling tanks, while another is being filled. A complete gravitational separation will then be effected in the quiescent tanks and the supernatant foots can be pumped or drawn off from above the oil, leaving a very clear and pure oil which does not need to be centrifuged. We have found a very real advantage in decanting off the foots without centrifuging the oil, since while the centrifuge 4| readily removes the larger waterpartlcles from the oil, it alsdtends, due to the high velocity of. the fluid therein, to break up the water solution particles into fine droplets and to disperse them in the oil in such a manner as to produce some cloudiness in the finished product.

(i) The use of the exact amount of caustic solution necessary to react with the known amount of free acid in the 'oil is made possible by the exact proportioning produced by the pumps 3 and I and the eflicient, rapid, and uniform dispersion (by the mixer 6) of the caustic solution in the 'oil.

- We claim' as our invention:

1. A process of refining oils containing free fatty acids; that is, animal, vegetable, and fish oils, which comprises: mixing the oil with a reagent capable of saponifying said acids; injecting compressed air into said mixture; forcingthe mixture to flow at a highvelocity in a thin stream through a reaction chamber in which the fatty acids are intimately contacted with the reagent due \to the turbulence of said stream; separating said air andthe re- (e) While in the typical operation above del action products produced by the action of said reagent on said acids from the oil.

2. A process of refining oils containing free fatty acids; that is, animal, vegetable, and fish oils, which comprises: mixing the oil with a reagent capable of saponifying said acids; injecting compressed air into said mixture; forcing the mixture to flow at a high velocity in a thin stream through a reaction chamber in which the fatty acids are intimately contacted with the reagent due to the turbulence of said stream; progressively heating the mixture: as it flows through said reaction chamber; and thereafter separating said air and the reaction products produced by the action of said reagent on said acids from the oil.

3. A process of refining oils containing free fatty acids; that is, animal, vegetable, and fish oils, which comprises: mixing the oil with anagent capable of saponifying said acids; injecting compressed air into said mixture; forcing the mixture to flow at a high velocity in a thin stream through a reaction chamber in which the fatty acids are intimately contacted with the reagent due to the turbulence of said stream; and thereafter separating said air and the reaction products produced by the action of said reagent on said acids from the oil, the reaction chamber being so constructed that no tight emulsion is formed therein but high fluid friction losses occur therein.

4. A process of refining oils containing free fatty acids; that is, animal, vegetable, and fish oils, which comprises: mixing the oil with a reagent capable of saponifying said acids; injecting compressed air into said mixture; forcing the mixture to flow at a high velocity in a thin stream through a reaction chamber in which the fatty acids are intimately contacted. with the reagent due to the turbulence of said stream; progressively heating the mixture as it flows through said reaction chamber; and thereafter separating said air and the reaction products produced by the action of said reagent on said acids from the oil, the reaction chamber'being so constructed that no tight emulsion is formed therein but high fluid friction losses: occur therein.

BENJAMIN CLAYTON. WALTER B. KERRICK. HENRY M. STADTL.

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