US 2467906 A
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Description (OCR text may contain errors)
April 19, 1949.
l H. J. PAsslNo ErAL l 2,467,906
FRACTIONATION OF OLEAGINOUS MATERIALS Filed May 16, 1947 f'. 5. Jaaa- ATTORNEYS Patented Apr. 19, 1949 FRACTIONATION OF OLEAGINOUS MATERIALS Herbert'J. Passino, Englewood, N. J., and James M. Meyers, New York, N. Y., assignors to The M. W. Kellogg Company, Jersey City, N. J., a
corporation of Delaware Application May 16, 1947, serial No. 748,574
s claims. (o1. 26o-428.5)
This invention relates to the fractionation of fatty materials by solvent extraction with a lowboiling solvent, i. e. one having a critical temperature less than 450 F., in the para-critical range of temperatures between about 100 below the critical temperature of the solvent and a few degrees above said critical temperature, in which range solubility of the various components of fatty materials diminishes with increasing temperature. More particularly, the invention is an improved method for accomplishing a fractionation of this type with unusual precision and without excessive cost in the solvent use etc.; the improved method comprises rst fractionating the fatty material to obtain an extract phase containing at least two components, one of which is more soluble than the other; secondly, precipitating from said extract phase substantially all of said less soluble component and at least part of said more soluble component, leaving a solvent-rich phase; and finally, charging the precipitated oil components to the middle portion of a vertically extended fractionation zone, and charging the solvent-rich phase to the lower end of said fractionation zone, so that a counter-current contact takes place and the more soluble component is redissolved in the upwardly flowing solvent-rich phase. Preferably, the second step is' accomplished by heating the primary extract phase to the region of the critical temperature of the solvent, while avoiding vaporization, and then cooling both the solvent-rich phase and the oil-rich phase to substantially lower temperatures within the para-critical range before introducing them into the vertically extended fractionation zone.
The oils to be treated by the improved method of this invention include principally oils and fats of animal, vegetable and marine origin which may be designated generally as fatty materials. The term fatty materials is intended to include other naturally occurring high molecular weight compounds such as cashew nut shell liquid, even though such materials are not commonly considered as fatty materials. In carrying out the improved process, such oils are fractionated into a, plurality of fractions for a variety of purposes. These include the separation of the oil or fatty material into a plurality of fractions, at least one of which is superior in some respect to the original oil, and the treatment ofthe oil to remove minor impurities. For example, a fatty oil, such as a fish oil, may be treated to separate a fraction concentrated in fatty acids, to separate a fraction in which the color bodies are concentrated, or to separate a fraction in which desirable ingredients such as sterols and oil-soluble vitamins are obtained in high concentration. Also a soybean oil may be treated to separate a small fraction containing the color bodies, phosphatides and mucilaginous materials as well as a fraction rich in unsaturated glycerides and therefore suitable as a paint oil. Another fraction containing more saturated glycerides suitable for salad oils and a small fraction containing sterols and tocopherols ditions with the constituents of the crude oil.
Those solvents which have been found to be particularly useful in the present invention include low-boiling hydrocarbons such as methane, ethane, propane, the butanes, the pentanes and the corresponding olens, as well as mixtures thereof, such as a mixture of methane and normal butane. Other solvents include other organic compounds such as halogenated hydrocarbons including diehlordifluormethane and methyl fluoride. Still other solvents which may be used are carbon dioxide, ammonia, and dimethyl ether. In general, it may be said that inert and nonreactive compounds having critical temperatures not substantially higher than 450 F. and in which at least one component of the crude oil to be treated is soluble at temperatures above about F. below the critical temperature, may be employed satisfactorily and are to be included within the term low-boiling solvent. The preferred solvents are those having a critical temperature less than 325 F. such as normally gaseous compounds which have the desired solvent power when maintained in the liquefied state, for example propane. When treating Aan oil with a solvent extraction agent according to the present invention, an extract is obtained containing substantially all of the solvent and those constituents of the oil which .are4 soluble in the solvent under the conditions of temperature and pressure being employed. This extract phase is then treated to remove substantial quantities of the solvent so that the oil contained in said extract phase may be further treated to obtain additional fractions. 'Ihe removal of the solvent from the extract phase was previously carried out by heating the extract phase in order to evaporate the soivent. Another previous method for removing the solvent was to reduce the pressure on the extract phase so that the solvent would be vaporized. In both of these methods it was necessary to condense the solvent so that it could be used further in the system. This condensation could be carried out either by cooling the solvent vapors, if heat had been used for the vaporization thereof, or by compressing the solvent vapors, if reduction in pressure had been used for evaporation.
According to the present invention the need for vaporizing and condensing the solvent is obviated. Furthermore, the fractionation is accomplished with substantially the same precision as if the oil were subjected to two successive treatments employing fresh solvent in each case. The present process involves the treatment of the extract phase obtained fram a fractionation step to obtain a solvent-rich liquid phase containing a higher proportion of the solvent than said extract phase and an oil-rich liquid phase containing a lower proportion of the solvent than said extract phase. This may be accomplished by heating the extract phase to a'. temperature above that employed in said extraction step, while at the same time maintaining pressure at such a level that the solvent will not be vaporized. Even though the extract phase and its constituents are maintained in the liquid phase when the temperature is increased to a point near the critical temperature, the solvent power of the solvent is decreased to such an extent that many or all of the oil components of the extract phase are separated as a separate phase. The solvent-rich phase may contain small quantities of those components which are. most soluble in the solvent but normally these components form only a very minor proportion of this phase, and the oil-rich phase may contain minor amounts of the solvent. It is also possible to effect a phase separation of the extract phase by reducing pressure While maintaining the temperature substantially the same. Of course, the pressure will not be reduced to or below the point at which the solvent will be vaporized but only sufficiently to lower the density of the solvent while maintaining it in the liquid state and thereby lower its solvent power for some of the components of the dissolved oil. Having separated the extract phase into a solvent-rich phase and an oil-rich phase in the manner described above, these components are contacted again under conditions which dier from the conditions employed during the first extraction step. When a counter-current extraction zone is used, the solvent-rich phase and the oil-rich phase are introduced at different points therein so as to obtain counter-current contact thereof. If desired, the temperature employed in the second extraction zone may be higher than that employed in the first extraction zone but must be lower than that employed during the phase separation. In this way the solvent-rich phase will redissolve only the more soluble components of the oil-rich phase. It has heretofore been the practice in similar processes to merely heat the extract phase from the first extraction to a temperature suitable for separating it as nearly as possible into the desired secondary extract phase and secondary raiiinate phase. The disadvantage of this is that the separation is not precise. Some of the raiiinate materials are more difficult to precipitate than others. The only way of fractionating them with precision is to precipitate -both the raiiinate and extract and redissolve the desired secondary extract. In the past this has entailed a second fractionation with fresh solvent. The present invention provides for precipitating all or at leastpart f the secondary extract, leaving a solvent-rich phase and then counter-currently contacting the precipitated oilrich phase with the solvent-rich phase in a vertically extended zone so that the desired secondary extract is redissolved, but no more; and the secondary ramnate is separated with precision because it is fully precipitated before entering the second extraction zone and is rejected there by control of the redissolving conditions in the various ways well known to those familiar with the are of solvent extraction. If desired, the second extraction may be carried out at the same temperature as in the first extraction zone but under different pressure conditions. On the other hand, the temperature and pressure may be the same as in the first extraction zone but the quantity of reflux introduced into said extraction zone for rectification purposes may be greater than that employed in said flrst extraction zone to eect a more selective fractionation. Any of these variations may be used separately or in combination in order to effectively fractionate the oil-rich phase.
The fractionation is carried out in two or more vertical fractionatingy towers suitably equipped with means for promoting the intimate contact of counter-flowing streams of solvent and oil. The oil to be fractionated is introduced into the first fractionating tower intermediate the ends thereof and the solvent such as propane is introduced at a point near the bottom of said tower. As the propane ascends the tower it mixes with the descending oil, and dissolves those components of the oil which under the conditions of temperature and pressure used, are soluble in the propane. Other components of the feed to the tower which are not dissolved by the upilowing propane are withdrawn from the bottom of' the tower. The propane extract containing dissolved portions of the oil is then treated to separate said extract into a solvent-rich phase and an oil-rich phase as described above. Accord-.- ing to the present invention the oil-rich phase thus recovered from the extract is introduced into a second fractionating tower at a point intermediate the ends thereof and the solvent-rich phase is introduced at a point near the bottom of said tower.
Since the conditions of operation in the second fractionation tower differ from those in the rst tower, only a portion of the oil-rich phase will be dissolved in the solvent-rich phase as it ascends the tower. In this manner a second extract phase is obtained from the top of said tower and those components of the oil-rich phase which are insoluble in the solvent-rich phase can be withdrawn from the bottom of said tower and may, if desired, be subjected to further treatment.
In order to more clearly describe the present invention, reference will be made to the accompanying drawings which form a part of the present specification.
The figure represents a schematic representation of a system for fractionating an oil in accordance with the present invention in order to obtain at least four fractions.
A natural fatty material, such as, for example, soybean oil, may .be introduced -through line Il into a fractionating tower I2 at a point intermediate the ends thereof. A solvent, for example propane, is introduced at a point near the bottom of said tower through line I3. Those components of the soybean oil which are not soluble in propane are vwithdrawn from the bottom of tower i2 through line I4. These components, in the case of soybean oil, comprise the color bodies. phos- -are permitted to separate out.
top of fractionating tower I2 a stream is withdrawn through line I5 which comprises an extract phase containing substantially all .of the solvent and those components of the soybean oil which are solubletherein atthe conditions employed. Line I5 is provided with a heater 16 for raising the temperature of the extract phase so as to cause a phase separation in separator I1 as described hereinbefore. The upper phase or solvent-rich phase containing small, if any, quantities of oil is withdrawn from separator I1 through line I8. The lower phase or oil-rich phase is withdrawn from the separator I1 through line I9. A portion of the oil-rich phase may be transferred to the top of fractionating tower' I2 for refluxing through line which connects with line I9. This reflux material improves the rectication which takes place in the upper portion of the fractionating tower I2 so that a more emclent and sharper fractionation may be obtained. The remaining portion of the oil-rich Y phase ls passed through line 2I to a second fractionating tower 22 and is introduced at a mid-point thereof. Since the temperature of the oil-rich phase will be higher than that desired in fractionation tower 22, a cooler 23 is provided to reduce the temperature of the oil-rich phase to the desired point. Likewise, a cooler 24 is provided in-line I8 for cooling the solventrich phase to the desired temperature.. The
solvent-rich phase is introduced at a point near the bottom of fractionating tower 22. If the solvent-rich phase is substantially free from all oily components, it may be introduced at a point very near the bottom of said tower, but if this phase contains small, but nevertheless appreciable quantities of oil, it is preferable to introduce it at a point in the tower silghtly more elevated, for example, through line 25. Those components of the oil introduced through line 2| which are not dissolved in the solvent flow down through tower 22 and are withdrawn from the bottom thereof through line 26. In the case of soybean oil, this fraction consists largely of unsaturated materials constituted essentially of glycerides and it therefore serves as a suitable paint oil. The solvent which flows up through fractionation tower 22, carrying with it those components of the oil which are soluble therein, is withdrawn from the top of said tower through line 21. Since this second extract phase will contain whatever fatty acids are present, it might be desirable to remove said acids by neutralization before proceeding further with the fractionation of the oil. To accomplish this the oil is passed through line 28 where it is mixed with caustic supplied through line 29. This mixture is passed into the neutralizer 30 where the soaps The soaps can be withdrawn through line 3|. The neutralized oil 1s withdrawn from neutralizer 30 through line 32 and passed to a phase separator 33.v A heater 34 is provided in this line to increase the temperature of the neutralized extract phase so as to cause a phase separation in separator 33 as described hereinbefore. If it is unnecessary or undesirable to neutralize the extract phase recovered from fractionation tower 22, the entire.'
phase may be passed through line 35 to line 32 by passing the neutralization tower 30. The extract phase which is introduced into separator 33 settles out into two phases and the lower or oil-rich phase is withdrawn through line 36. A
- portion of this material may be recycled to fractionating tower 22 through line 31 where it is introduced at a point near the top thereof in order to improve'rectication in the upper portion ofsaid tower. The remaining portion of the oil-rich phase may be withdrawn from the system through line 38 or may -be introduced into a third fractlonating tower 39 through line 40. A cooler 4I may be provided to reduce the temperature of sai'd oil-rich phase. The upper phase in separator 33 is withdrawn through line 42 and may be introduced at a point near the bottom of. thethird fractionating tower 39 through lines 42 or 43. A cooler 44 is provided for reducing the temperature of said solventrich phase. 'I'he operation of fractionatlng tower 39 is similar to that described in connection with towers I2 and22. The undissolved material may be withdrawn from the bottom of said tower through line 45. This material may, for example,
comprise substantiallysaturated materials including the saturated glycerides. This material is lentirely suitable as an edible oil. The extract phase from the top of fractionating tower 39 is withdrawn'through line 46 provided with a heater 41 and is introduced into a phase separator 48. The lower or oil-rich phase is Withdrawn through line 49 and a portion thereof may be returned to the top of fractionating tower 39 through line 50. The remainder of said oilrich phasemay, if desired, be passed through line 49 to a chiller 5I for reducing the temperature so as to cause crystallization of various high melting point, high molecular weight compounds contained in said oil, such as stearin. The chilled mixture is passed to a filter 52 through line 53 for removal of the stearns through line 54. The destearinized or winterized oil is. withdrawn from filter 52 through lines 55, 56 and 51. The solvent-rich phase from separator 48 is passed through line 58 which is provided with a pressure reducing valve 59 into an evaporator 60 which may be provided with suitable means for heating said-solvent-rich phase to vaporize the solvent. The solvent vapors are wi-thdrawn through lines 6I and 62, the latter being provided with a cooler 63 for condensing said vapors and the condensed solvent is returned to propane inlet line I3. T he oil consisting substantially entirely of the unsaponifiable materials is withdrawn from evaporator through line 64. This oil may, if desired, be blended with the oil recovered from filter 52 by mixing through line 56.
As an alternative the oil-rich phase obtained from separator 33 through lines 36 and 38 may be passed directly to the chiller 5I through lines 65 and 49 and the solvent-rich phase may be passed directly to the evaporator 6I) through lines 42, 66
and 58. This arrangement may be used if it' is undesirable or unnecessary to separate the unsaponiiiable materials including the tocopherols and sterols from the edible oil. On the other hand, when such separation is desired, it is generally necessaryto further fractionate the oil-rich phasefrom separator 33 by passing it through the third fractionation tower 39.
It will be clear that various modifications of the system shown in the drawing may be employed without departing from the scope of the present invention. As stated above, the neutralization step may be eliminated altogether or it may be used at a different stage of the process, for example, either or both of the products in lines 64 or 49 may be neutralized. Also the destearinline 40.
izing or winterizing step may be omitted. Furthermore, if less than four fractions are desired, the third fractionation tower may be eliminated, or if more than four fractions are desired, additional towers may be employed.
According to this invention the subsequent fractionations are carried out on the oil obtained in the extract phase from a preceding fractionation. It is, therefore, generally desirable, at least in the first fractionation step, to employ conditions of temperature and pressure such that a substantial portion of the oil feed will be present in the extract phase, the remaining oil being withdrawn through line I4. In the case of soybean oil and when a color body fraction is to be removed in the first fractionation, a 1 per cent or 2 per cent cut is generally removed through line I4. If an unsaturated or paint oil fraction is desired, it is generally necessary to remove about 40 to 60 per cent of the oil through line 26, the 4remainder of the oil being treated to recover an edible oil from line 45 which may comprise about 60 to 40 per cent of the oil being fed through The unsaponifiables in lines 51 and 64 and the stearins from line 54 generally comprise only 1 per cent or 2 per cent of the original oil.
Sometimes it may not be desirable to pass the oil-rich phase from separator 33 to the third fractionation tower 39 and in this case separator 33 may be used as an evaporator so as to vaporize the solvent and recover it in substantially pure form for reuse. The recovered propane may be returned directly to line 62 via line 61 connecting with line 42. The residual oil of course may .be withdrawn from the system through line 38 or passed through lines 65 and 49 to chiller 5l for removal of stearin and the like components.
Having now described our invention and the method of practicing the same what we claim is:
1. In the fractionation of fatty materials with a solvent having a critical temperature less than upper and lower ends respectively of said vertically extended fractionation zone.
450 F. by contacting said fatty material with said solvent under a liquefying pressure and at temperatures in the paracritical range between about 100 F. below critical temperature and approximately critical temperature, an improved method for fractionating said fatty material into three fractions of different solubilities, which includes the steps of: contacting said material with said solvent in said paracritical range in a first fractionation zone to obtain a primary rainate phase, containing the least soluble fraction, and a primary extract phase containing the two most soluble fractions; withdrawing said primary extract phase and adjusting the physical condition thereof to decrease the .solvent power of said solvent, while substantially preventing vaporization, to precipitate all of the least soluble remaining fraction and at least a part of the most soluble fraction into an oil-rich phase, leaving a solventrich phase; separately withdrawing said solventrich and oil-rich phases and introducing said phases into a vertically extended fractionation zone, said solvent-rich phase at the lower end thereof and said oil-rich phase at a substantially higher point therein; readjusting the physical condition of said'phases to increase the solvent power of said solvent, and counter-currently contacting said phases in said vertically extended fractionation zone to redissolve all of said most soluble fraction in a secondary extract phase and reject said fraction of lesser solubility into a secondary rafiinate phase and withdrawing said secondary extract and raflinate phases from the 2. A process as claimed in claim 1 wherein the solvent is a' liquefied normally gaseous hydrocarbon.
3. A process as claimed in claim 1, wherein the solvent is propane.
4. A process as claimed in claim 1 wherein the temperature of said counter-current extraction zone is maintained above that employed in said first contacting step.
5. In the fractionation of fatty materials with a solvent having a critical temperature less than 450 F. by contacting said fatty material with said solvent under a liquefying pressure and at temperatures in the paracritical range between about F. below critical temperature and approximately critical temperature, an improved method for fractionating said fatty material into three fractions of different solubilities, which includes the steps of: contacting said material with a fractionating liquid comprised primarily of said solvent in said paracritical range in a first vertically extended fractionation zone to obtain a primary rafllnate phase, containing the least soluble fraction, and a primary extract phase. containing the two most soluble fractions; withdrawing said primary extractphase and adjusting the physical condition thereof to decrease the solvent power of said solvent, while substantially preventing vaporization, to precipitate all of the least soluble remaining fraction and at least a part of the most soluble fraction into an oil-rich phase, leaving a solvent-rich phase; separately withdrawing the remainder of said solvent-rich and oil-rich phases and introducing said withdrawn phases into a second vertically extended fractionation zone, said solvent-rich phase at the lower end thereof and said oil-rich phase at a substantially higher point therein; recycling part of said solvent-rich phase to the lower portion of said first fractionation zone to provide at least part of the fractionation liquid therein; recycling part of said oil-rich phase to the upper portion of said first fractionation zone to serve as reflux therein; readjusting the physical condition of said withdrawn phases to increase the solvent power of said solvent, and counter-currently contacting said phases in said vertically extended fractionation zone to redissolve all of said most soluble fraction in a secondary extract phase and reject said fraction of lesser solubility into a secondary raffinate phase; and withdrawing said secondary extract and raflinate phases from the upper and lower ends respectively of said vertically extended fractionation zone.
6. In the fractionation of a fatty material with a solvent having a critical temperature less than 450 F. by contacting said fatty material with said solvent under liquefying pressure and at temperatures in the paracritical range between about 100 F. below critical temperature and approximately critical temperature, the improved method for obtaining a desired extract which includes the steps of contacting said material with said solvent in said paracritical range in a first fractionation zone to obtain a primary rafllinate phase and a primary extract phase containing said desired extract and a relatively less soluble component; withdrawing said primary extract phase and heating it, while substantially preventing vaporization, to precipitate substantially all of said less soluble component and at least part of said desired extract into an oil-rich and raiilnate phases from the upper and lower ends respectively of said vertically extended fractionation zone.
HERBERT J. PASSINO. JAMES M. MEYERS.
REFERENCES CITED The following references are of record in the flle of this patent:
UNITED STATES PATENTS Number Name Date 2,139,392 Tijmstra Dec. 6, 1938 2,247,496 Hixson et a1. July 1, 1941 2,329,889 Ewing Sept. 21, 1943 2,346,491 Kirsted Apr. 11, 1944