US2454638A - Fractionation of fats - Google Patents

Description

Nov. 23, 1948. J. 'r. mc msoN ErAl. 2,454,638

' FBACTIONATION OP FATS Filed Jan. 20, 1945 2 sheets-sheet 1 FIG! ATTafK YEYF Patented Nov. 23, 1948 FRACTIONATION F FATS John T. Dickinson, Basking Ridge, N. J., and Oliver Moriit, Scarsdale, and Leo J. Van Orden, Olean, N. Y., assignors to The M. W. Kellogg Company, Jersey City, N. 1., a corporation of Delaware Application January 20, 1945, Serial No. 573,754 11. Claims. (Cl. 260-4285) This invention relates to improvements in the fractionation of natural fats. More particularly, the invention relates to an improved method for fractionating such fats in a continuously operated unitary fractionation zone to produce therefrom three or more fractions including at least a to fractionation in accordance with this invention after one or more preliminary treatments, such as neutralization, destearinization, saponiflcation, etc. The invention also includes the fractionation of fatty mixtures derived from the natural fats by chemical treatment and composed largely of fatty acids or glycerides. As examples of the fats which may be treated in accordance with this invention reference may be made tov tallow, fish oils, whale oil, soy bean oil, cottonseed oil, etc.

The fats are fractionated into at least three fractions in order to obtain therefrom products of differing characteristics which renders each of them more suitable for a certain use than was the original 011. For example, soy bean oil may be fractionated into at least three fractions, one of which contains the color bodies and compounds which it may be desired to recoverseparately, another of which may comprise a drying oil of substantially higher iodine number than the original oil, and another fraction of which may comprise a high quality salad oil. The proportions of the original oil which are recovered in each fraction depends upon the uses to which the oils recovered from the various fractions are to be put and the character and quality of the original oil. The fats tobe treated, in accord-' ance with this process, include normally liquid oils as well as solids which are liquid like oils under the conditlonsof the treatment. Regardless of the normal condition the fats which are treated are referred to in the following description as oil or oils.

In accordance with the improved process the oil is treated at moderate or low temperatures by means of a selective solvent under operating conditions effective to maintain the solvent in a liquid condition and dissolve only a portion of the oil in the solvent whereby there are formed two liquid phases between which the oil is distributed. The treatment is carried out at temperatures at which the solubility of the oil in the solvent decreases with rising temperature. This condition occurs generally inthe range of temperatures extending from 100 F. below the critical temperature of the solvent to a few degrees above the critical temperature of the solvent. Operating in this temperature range, and particularly at temperatures near the critical temperature, requires the use of solvents whose critical temperatures are substantially lower than the temperatures which would produce some thermal effect on the oil. The solvents which are employed, therefore, are those having critical temperatures not substantially higher than 450 F. and preferably lower than 325 F.

The solvents which are employed include relatively inert fluids of the desired boiling characteristics in which the oil is sufliciently soluble to effect extraction of a portion of the oil.

The low boiling hydrocarbons represent a desirable class of solvents because of their relative inertness and low cost. While the low boiling olefin hydrocarbons may be employed they are less desirable than the low boiling paraillns such as ethane, propane, the butanes, the pentanes and the hexanes, from the point of view of inertness. 0f the paramns, propane is preferred ordinarily because of the high degree of solubility of the oils in that solvent. However, ethane or the butanes can be employed to almost as great advantage. While relatively pure hydrocarbons are preferred mixtures of them may be employed. For example, mixtures of ethane and propane or mixtures of butane and methane may be employed in the proportions suitable to form solvents having the desired properties. While the low boiling hydrocarbons are particularly advantageous for use as solvents in the improved method other solvents having relatively low critical temperatures may be employed, such as ammonia, dichlordifluor methane, dimethyl ether, methyl fluoride and halogenated hydrocarbons in general.

In the further description of the invention propane will be referred to as the solvent. It will be understood, however, that propane merely exemplifies many solvents which may be employed under proper conditions of temperature and pressure and that the general principles of the invention, as exemplified by the use of propane, are applicable in'the use of such other solvents.

The improved process resides in carrying out the fractionation of the oils continuously in a unitary fractionation zone and withdrawing at least three different fractions from that zone. The oil and propane are contacted under conditions effective to dissolve at least a portion of the oil in the propane. This solution, or propane phase, is passed continuously through a rectification zone in which the solvent power of the propane phase for the less soluble constituents of the oil is lessened during the passage of the propane phase throughthe rectification zone and the precipitate is passed continuously in the reverse direction through the rectification zone in intimate contact with the oppositely flowing propane phase. This results in continuous precipitation, resolution and reprecipitation of the oil. The solvent power of the propane phase for the less soluble portions of the oil is lessened by changing the temperature of the propane phase, by changing the pressure, or by preferentially dissolving in the propane phase portions of the oil which are more soluble therein than some of the oil previously dissolved in the propane phase. The methods involving control of the temperature and the pressure may be employed independently, but each also involves the preferential resolution in the propane phase of portions of the oil which are more soluble therein than some of the oil previously dissolved when the oil phase formed by precipitation is flowed through a rectification zone in countercurrent contact with the propane phase. However, rectification of the propane phase can be effected without varying the temperature or pressure.

The rectified propane phase passes through the exit from the rectification zone and may be treated to recover an oil fraction therefrom.

During the passage of the propane phase through the rectification zone the character of the oil in solution therein continuously changes. Therefore a portion of the propane phase may be withdrawn from the rectification zone as a side stream to recover therefrom a difierent oil fraction. A plurality of such side streams may be withdrawn to obtain a plurality of difierent oil fractions.

The oil phase, which flows in intimate countercurrent contact with the propane phase in the rectification zone, also changes continuously. Therefore at least one side stream may be taken from this phase for recovery of a still different oil fraction. If, as is usually the case, the charge oil is not dissolved entirely in the propane the undissolved portion furnishes a separate oil fraction. Consequently the oil phase may be recovered separately near its exit from the rectification zone to produce a different intermediate fraction.

Preferably the concentration is carried out in a vertical tower, to take advantage of the difference in gravity of the propane and the oil in effecting counter-current contact of the phases. However, the process is not limited in application to the use of a vertical tower but may be carried out by pumpin the propane and the oil countercurrently through a series of separate contact zones which may or may not be maintained under the same conditions of temperature and pressure. The invention will be described in detail by reference to the accompanying drawings which show a vertical tower but it will be understood that the operation described in connection with such a tower is applicable also to an extraction process carried out in a series of separate zones.

In the drawings Fig. 1 is a diagrammatic view in elevation, partly in cross section, of apparatus suitable for carrying out the improved process propane occurs at l2.

whereby three or more different oil fractions are obtained from the charge oil. Fig. 2 is a similar view of similar apparatus but provided with means for carrying out certain difierent modifications of the improvedlprocess. Fig. 3 is a diagrammatic view in elevation of an alternative form of apparatus in which the fractionation zone comprises the interiors of two different vessels. 4

Referring to Fig. 1 the charge oil is introduced through line It) into an elongated fractionating tower II at an intermediate point l2. The interior of tower H is thus divided into two zones. The upper, or rectification, zone occupies the space above I2 and the lower, or stripping, zone lies below 12. This designation of these zones distinguishes between their functions, although the stripping zone necessarily involves some rectification and this may be intensified by imposing a temperature gradient on that zone.

The propane is introduced through line l3 into the bottom of tower H and passes upwardly through tower II, as a substantially continuous phase, to the top of the tower. Conditions of temperature and pressure which will mantain liquid conditions in the tower are imposed therein.

The initial contact of the charge oil with the Under normal conditions of operation a portion, at most, of the oil goes into solution in the propane at l2. The undissolved portion flows downwardly in the tower, as a result of the substantial difference in gravity between the phases. The prolonged and intimate contact between the phases may be promoted by providing tower II with bafiies, packing, or similar contact means, which are indicated diagrammatically in Fig, l. The character of such contact means and the upward linear velocity of the propane stream are chosen to .permit the down flow of the oil phase at an effective rate.

Undissolved oil flows downwardly in tower H and a substantial proportion of this oil is dissolved in the propane stream during the passage of the oil down the tower. A smaller proportion of the propane is absorbed by the undissolved oil stream. These separate liquid phases are designated with reasonable accuracy as the propane phase and the oil phase since the propane principally comprises propane and the oil phase contains a much larger proportion of oil than does the propanephase.

The temperature and time of contact of the phases in the strippin zone in tower II are regulated to absorb in the propane phase all portions of the charge oil except that fraction desired as the bottom product. Because of the relatively large bulk of the propane charge its temperature substantially controls the temperature existing in the bottoinof tower I I. However, other means may be provided for maintaining the desired temperature at that point.

The rate of withdrawal of the oil phase from the bottom of tower H through'line I4 is regulated to maintain any desired level of the oil phase in the bottom of the towerl The interface between the reservoir thus maintained and the continuous propane phase may be maintained above or below the propane charge point, but it is desired ordinarily to intensify the stripping effect of the propane stream by bubbling it through the oil phase tothe interface.

As the propane phase flows upwardly in tower II it takes into solution a substantial amount of oil from the downwardly flowing oil phase. This amount may be reduced by increasing the temperature of the propane phase as it flows up the tower, for example, by the provision of heating coils It in tower ll below l2. Alternatively such temperature increase may be effected by the introduction at intermediate points in the tower of additional propane heated to a higher temperature than the propane in the bottom of the tower. For this purpose line It may be provided to connect line It, by means of branch lines l1, l8 and I9, with intermediate points along the length of tower Ii. Such additional propane may be introduced without regard to temperature control to alter the solvent power of the propane phase as it flows up the tower. In any case, however, such additional propane is introduced through lines l1, l8 and I! at a temperature at least as high as the temperature of the propane phase at the point of introduction. Heating elements 20 may be provided in line It for such control of the temperature of the propane. As the propane phase flows past the oil charge point at l2 it has its final contact with the residue of the charge 011. Above that point the propane phase is rectified by decreasing the solvent power of the propane phase, as it flows upwardly, for the less soluble constituents of the oil. This may be effected by raising the temperature of the propane phase above the oil charge point or by preferentially dissolving in the propane phase above the oil charge point portions of the oil which are more soluble in the propane phase than some of the oil which is carried by the propane phase into the rectification zone. Rectification could be accomplished also by pressure adjustment, as by dividing the rectification zone of tower ll into a series of separate compartments, by means not shown. The propane phase would be passed through such separate compartments at progressively lower pressure to effect precipitation of part of the oil in each compartment. The precipitate in each compartment would be pumped into the next lower compartment into contact with the propane phase therein. This method of operation, however, is less desirable than the other methods as it requires more elaborate equipment and is less efllcient.

As Fig. 1 is provided to illustrate the modification of the invention wherein rectification of the propane phase is effected by heating it to a higher temperature a series of heating coils 2|, 22,:23, 24 and 25 is provided along the length of the rectification zone. Such heating may be replaced or amplified as has been indicated below, by the injection of heated propane at intervals along the length of the rectification zone. The spacing of the heating means along the length of the rec-'-' tification zone, as shown, is the preferred arrangement as it permits a relatively uniform increase in the temperature of the-propane phase as it flows upwardly. While all the heat necessary could be imposed at one point in the rectification zone this is less satisfactory and less advisable than the arrangement shown.

In the modification of Fig. 1 the lowest temperature in tower I i is maintained in the bottom. This low temperature may extend from the bottom to point l2 or if desired a temperature gradient may be imposed in the stripping zone as has been described. As the propane phase flows upwardly in the rectification zone, that is above I! in tower II, it is heated gradually to the maximum temperature of the tower which ordinarily is not reached until the propane is passind through the top-most portion of the tower. This heating eilect causes continuous precipitation of a separate oil phase which contains propane in a substantially lower proportion than in the propane phase. The oil phase thus separated has a higher specific gravity than the propane phase and it flows downwardly in counter-current contact with the rising propane phase, the linear velocity of the latter being regulated to permit this counter-current flow.

As the oil phase passes downwardly from one point to another in the rectification zone it contacts propane phase which is at a lower temperature and which contains some oil which is less soluble than some of the oil precipitated at the higher point. As a result oi. these two factors some of the oil precipitated at the higher point goes back into the solution at the lower point. There is a corresponding precipitation of oil at the lower point in the rectification zone as the result of selective absorption of more soluble oil and heating of the propane phase which occurs at that point.

As the oil phase flows downwardly in the rectification zone of tower I I it is thus subjected constantly to the stripping action of the propane phase whereby the more soluble portions of the precipitated oil phase are redissolved. This is balanced, however, by constant accretions to the oil phase in the form of additional precipitate. As a result of this treatment the character of the oil which is dissolved in the propane phase changes continuously as the propane phase passes through the length of the rectification zone.

Likewise the character of the oil in the separate oil phase changes continuously as that phase flows downwardly through the rectification zone.

The maximum temperature employed in the fractionating tower is maintained ordinarily at the top of the tower. This temperature may be higher than the critical temperature of the propane but ordinarily is at or below the critical temperature. Ordinarily the top temperature in the fractionating tower will be between the critical temperature of the propane and 40 F. below that temperature. Relatively low top temperatures are employed when the tower is operated to carry out of the tower in the propane phase a relatively large fraction of the oil charge. Conversely, relatively high top temperatures are employed to produce a relatively small overhead fraction. As the proportion the oil absorbed in the propane phase is greater-when relatively high ratios of propane to oil arelemployed it is evident that higher top temperatures are permissible when employing relatively high ratios of propane to oil.

The bottom temperature in the fractionating tower is maintained suiliciently low to permit stripping from the oil phase at that point substantially all constituents which it is desired to exclude from the bottom product. However, this temperature must be maintained above any tem perature at which there occurs complete solubility of the oil in the propane. The preferred bottom temperatures ordinarily are 40 F. or more below the critical temperature 015 the solvent.

In the stripping zone of tower l I, that is below II, a uniform temperature may be maintained to promote the stripping action of the propane stream. However, a temperature gradient may be maintained also in the stripping zone although this temperature gradient ordinarily is not as great as the gradient above the oil charge point. Ordinarily a temperature gradient of at least F. is necessary between the oil charge point, at l2, and the top of tower II to produce sufllcient rectification.

When using a propane solvent the top temperature ordinarily falls within the range of 170 to 210 F. and the bottom temperature ordinarily is substantially lower and below 170 F. The temperature at the oil charge point may be the same as the bottom temperature, or slightly higher.

The pressure on fractionating tower II is maintained sufliciently higher than the temperature necessary to keep the content of the tower liquid to permit some adjustment of the pressure during the operation. Ordinarily a pressure of 50 pounds per square inch higher than vapor pressure of the propane at the highest contemplated operating temperature is satisfactory.

The propane and oil are charged to tower II at a relatively high volumetric ratio of propane to oil. High ratios of propane to oil permit greater rectification and fractionation but naturally involve greater expense. Ordinarily the ratio of propane to oil should be at least 10:1 and ratios of :1 to 100:1 or higher are preferred.

The propane phase is withdrawn from the top of tower ll through line 26 which connects with means, not shown, for separately recovering the propane and the oil fraction contained therein. A portion of the propane phase flowing through line 26 may be diverted through line 21 which passes through heating means 28 and connects with a separator 29. At 28 the propane phase is heated to a temperature higher than the maximum temperature in tower H to precipitate at least a portion of the oil content thereof. The oil whichis thus separated collects as a lower phase in separator 29. The upper, or propane, phase in separator 29 is withdrawn overhead through line 30. This phase may be substantially denuded of oil or may still contain a substantial proportion of oil. The propane phase passing through line 30 may be separately treated for the recovery of the propane and oil fraction or it may be returned to line 26. The oil phase separated in 29 is withdrawn through line 3| for recovery of the oil fraction contained therein.

Instead of, or in addition to, the method of separating a side stream illustrated at 29 means may be provided for obtaining such a side stream from the propane phase as it flows through the rectification zone. For this purpose a partition plate 32 may be provided in tower |l, preferably at a point somewhat above l2. The oil which precipitates from the propane phase passing upwardly in the tower above plate 32 is permitted to collect thereon and maintain a desired level of the-oil phase at that point, the rate of flow of the oil phase downwardly through plate 32 being controlled by valve 33 which is regulated in response to variations in the oil level on plate 32. Upwardly rising propane phase which is trapped under plate 32 is withdrawn as a side stream through line 34 which connects with a side stream fractionator 35. Fractionator 35 may be operated to effect any desired degree of separation between the oil and the propane. For example, the propane phase introduced through line 35 may be substantially completely separated into propane and oil portions by suitable reduction of pressure. Preferably, however, fractionator 35 is maintained at the same or higher pressure than tower H and recovery of an oil fraction is efiected by heating fractionator 35 to a higher temperature than the temperature of tower ll just below plate 32. For this purpose a pump 36 is provided in line 34 and a heating coil 31 is provided in fractionator 35. By this means there is precipitated in fractionator 35 a separate oil phase. Depending upon the extent of the heating applied to the propane phase in fractionator 35 the oil phase separated therein may include a part or substantially all of the oil content thereof. The oil phase thus separated is withdrawn from fractionator 35 through line 38 for further treatment for recovery of propane and oil fractions. The propane phase is withdrawn from the top of fractionator 35 through line 39. This phase may be treated separately for the recovery of any oil fraction contained therein or may be recycled directly for reuse in tower I if it is substantially denuded of oil. Preferably, however, the material flowing through line 39 is diverted wholly or in part through line 40 which connects with tower H at a point above plate 32, This method of operation is necessary when operating in the manner shown whereby all the propane phase flowing up the tower is passed through fractionator 35. Instead of the latter method of operation a simple baffle may be substituted for plate 32 whereby a portion only of the upwardly flowing propane phase is diverted through line 34 and whereby there is no accumulation of oil phase above the baffle. This method of operation is necessary if it is desired to recover as one or more side stream fractions substantially all of the oil diverted through line 34.

In the preferred method of operation of tower oil fraction products would be recovered at I4, 26 and 38. In addition, however, separate, and cliflerent oil fractions may be obtained at 30, 3| and 39.

Fig. 2 illustrates a diflerent method of obtaining rectification of the fractionating tower. In Fig. 2 tower 4| is generally similar in construction to tower (XCQDt for certain diflerences which are discussed in detail below. The charge oil is introduced through line 42 and the propane is charged through line 43 in the same manner as illustrated in Fig. 1. The bottoms product is withdrawn through line 44 and the final propane phase is passed overhead through line 45. Heating coils 46 may be provided below the oil charge point at 41 and other heating coils 48, 49, 50 and 5| may be provided above 41. However, means are provided, in connection with tower 4| for inducing rectification regardless of the maintenance of a temperature gradient in the tower. In accordance with this modification the solvent power of the propane phase for the less soluble constituents of the oil is decreased during its passage through the rectification zone by introducing into the rectification zone at a point near the top thereof a portion of the .oil which is more soluble in the propane phase than some of the oil already dissolved therein. This preferentially soluble oil is introduced directly into the rectification zone at the point at which it is desired to change the propane phase, or is introduced into the rectification zone at a point at which the propane phase is substantially saturated whereby the oil thus introduced flows downwardly to a point in the rectification zone at which it is more soluble in the propane stream. When employing this method of operation the fractionating tower may be operated at a uniform temvaporization of a substantial proportion or all of the propane contained therein. This gaseous propane passes overhead from separator 53 through line 55 for recovery for reuse in tower 4|. Evaporation of the propane may be assisted by heating means at 56 and by further heating means, not shown, in separator 53. Alternatively, separator 53 may be maintained substantially at the pressure of tower 4| and evaporation ofthe propane eflected entirely by the application of heat.

While substantially all the propane may be separated from the oil in 53 ordinarily to eflect only a partial evaporation of the propane whereby some propane is left in the oil residue in separator 53.

When the operation in this manner is stabilized that portion of the propane phase passing through line 45 which is not diverted through line 52 is passed to separating means, not shown, for the recovery of the oil fraction contained therein. Alternatively all of the propane phase passing through line 45 may be subjected to the separation step in 53 and a portion of the liquid residue from separator 53 may be withdrawn separately, by means not shown, for the recovery of the oil fraction contained therein.

The liquid phase which accumulates in separator 53 may be withdrawn for use as reflux by means of line 51 which connects with tower 4| at the top thereof. Line 51 'is provided with a pump 58 and a cooler 59. 'Under stabilized conditions of operation that portion of the liquid conta ned in separator 53 which is not to be withdrawn as product is passed continuously through line 51 to the upper portion of tower II at the temperature desired at that point.

When initiating the operation of tower 4| with external refluxing the stabil zed condition of oneration is reached more quickly by returning all of the overhead product to the tower through line 51. After the equilibrium condition of o eration is reached, as is shown by obtaining at 53 an oil fraction of desired characteristics. a portion of the liquid cooled in fractionator 53 may be withdrawn as product. tions of operations the ratio of the quantity of oil returned to tower ll through line 51 to the quantity of charge oil introduced through line 42 is controlled to regulate or vary the conditions in the rectification zone.

This method of operation of tower 4| is initiated preferably by filling the tower with liquid propane and introducing propane and oil at the desired rates. However, during the period in which the operation of the tower is being brought to a stabilized condition the temperature, pressure and propane to oil ratio may be adjusted as necessary to facilitate reaching the desired condition of operation. The temperature which is employed may be such that all the oil is dissolved in the propane initially. However, the return of all of the oil to tower ll through line 51 soon reduces the solvent power of the propane it is more convenient Under stabilized condi phase whereby an oil phase appears at the bottom of the tower. Thus the stabilized condition of operation may involve an operating temperature at which the oil would be completely soluble in the propane at the ratio of which these are charged to the tower. However, the accumulation of refluxed oil in the propane phase in the tower reduces the solvent power of the propane phase to the point where it has the desired selectivity as a solvent.

The temperature may vary within the range of 110 F. to 210 F. when propane is employed as the solvent. The tower temperature and the reflux ratio are adjusted to produce overhead and bottom products of the desired character. Necessarily when solvents other than propane are employed different temperatures may be necessary.

The reflux ratio (that is theratio of the quantity of oil returned to tower 4| from separator 53 to the quantity of oil withdrawn from separator 53 as product) varies from infinity at the beginning of the operation to an equilibrium ratio which may be in the range of 0.5:1 to :1 or higher.

As in the operation of tower l I the pressure on tower 4| is maintained sufficiently high to maintain liquid conditions in the tower and permit some variation in the pressure during the operation. A pressure which is 50 pounds per square inch higher than the vapor pressure of the solvent at the highest contemplated operating temperature is satisfactory.

Under stabilized conditions of operation the oil which is introduced into tower 4| through line 51 contacts propane phase which is substantially saturated with oil. However, since some of the refluxed oil is more soluble than some of the oil already dissolved in the propane phase there is some exchange of oil between the phases. The undissolved reflux oil and oil which is precipitated from the propane phase forms the separate oil phase which flows downwardly in tower it through the rectification zone in the manner in which the oil phase flows downwardly through the rectification zone of tower H. Since the oil phase always contains some components which are more soluble than some of the components in the propane phase with which the oil phase is in contact there is a continuous exchange of oil components between the phases. Consequently the character of theoil phase changes continuously as it flows through the rectification zone as does the character of the oil component of the propane phase. This makes possible the withdrawal of a portion of either of the phases from an intermediate point in the rectification zone as a side stream. Such a side stream may be treated to recover therefrom an oil fraction different from the oil fractions recovered from the top and bottom products of the tower operation. In connection with the operation of Fig. 1 such a side stream was obtained by withdrawing a part of the propane phase from an intermediate point in the rectification zone. This method of obtaining a side stream product could be applied also with equal facility to tower 4|. However, an alternative method of obtaining a side stream is illustrated in connection with Fig. 2 in which a por- 1 1 For diverting such a side stream a suitable trap-out tray 60 is provided in tower 4|, preferably above 41. A portion of the downwardly flowing oil phase accumulates on tray 60 and is with-' drawn as a side stream through line 6|. This material may be passed to any suitable separator for the recovery of an oil product fraction. It may be desired, however, to subject this oil fraction to further fractionating treatment. For this purpose oil phase flowing through line 6| is diverted through line 62 which connects with a separate fractionator 63. In fractionator 63 the oil phase introduced through line 62 is contacted with additional propane which is introduced through line 64. In fractionator 83 the oil is stripped by means of the propane stream whereby the more soluble components thereof are dissolved in the propane. The remaining undissolved portion collects in the bottom of fractionator 63 as a separate oil phase and is withdrawn through line 65. This material is then subjected to further treatment for recovery of an oil fraction therefrom. If desired heating means 66 may be provided in fractionator 63 to impose a temperature gradient and intensify the degree of fractionation. The propane stream containing dissolved light components of the oil passes overhead from fractionator 63 through line 66 which connects with tower 4i at a point above trap-out tray 60. This propane stream combines with the propane stream moving upwardly in tower 4| for further rectification in the manner described.

The ordinary operation of the apparatus of Fig. 2 provides separate oil fraction products at 45, 6i and 44. An additional and different fraction also may be obtained by treatment of a part of the side stream in line Si in fractionator 63.

Fig. 3 illustrates a modification of the improved process which employs two separate vessels in the fractionating zone. In Fig. 3 the oil charge is introduced into a first tower 61 at an intermediate point 68. The propane is introduced into tower 61 at a point near the bottom thereof through line 69. Therefore, that part of tower 61 between 68 and line 69 constitutes the stripping section. The stripped oil phase containing the desired bottoms product is withdrawn through line 10. The propane phase passes overhead from tower 61 through line H which connects with a second tower 12 at a point 13 somewhat above the bottom thereof. The propane phase passes upwardly from 13 in tower 12 to the top thereof and is withdrawn through line 14. Line 14 connects with a separator 15 and is provided with a valve 16 to permit release of pressure on the propane phase to effect evaporation of all or part of the propane in the manner described in connection with Fig. 2. The propane vapors are withdrawn from separator 15 through line 11 which connects with a propane accumulator 18. Line TI is provided with cooling means, not shown, for effecting condensation of the propane. Line 69 connects accumulator 18 with the bottom of tower 61 for recirculation of the liquid propane. A pump 19 and heating means 80 are provided in line 69 in order to supply the propane to tower 61 at the desired temperature and pressure.

The oil residue separated in separator 15, which may contain some propane, is withdrawn thereillustrated by Fig. 3.

12 provides means for effecting rectification in towers 61 and 12 in the manner illustrated in Fig. 2. In addition, however, heating elements may be supplied in towers 61 and 12, as illustrated in Figs; 1 and 2, for imposing a temperature gradient in each tower.

The separate oil phase which is formed by such refluxing and rectifying means flows downwardly through tower l2 and collects in the bottom thereof. This material is withdrawn through line 83 and a part thereof is passed to separating means, not shown, for the recovery of that intermediate liquid product fraction. The remainder of this material is transferred to the top of tower 61 by means of line 84 which connects line 83 with tower 61 and is'provided with a pump 85. If desired the oil phase-which collects in the bottom of tower 12 may be subjected to further stripping by means of additional propane which is introduced into the bottom of tower 12 through line 86 which connects with line 69. Cooling or heating means may be provided in connection with line 86 for delivering the propane to the bottom of tower 12 at the desired temperature. This additional propane strips a part of the oil from the oil phase in the bottom of tower I2 and the resulting propane solution passes upwardly in that tower in admixture with the propane phase introduced through line H.

In the apparatus of Fig. 3 the main stripping zone is in tower 61 between point 68 and the propane charge point. The rectification zone includes the portion of tower 61 above point 68 and the portion of tower 12 above point 13. That portion of tower 12 below point 13 constitutes a secondary stripping zone for the intermediate fraction. The transfer of oil phase from tower 12 to tower 61 through line 84 merely extends to tower 61 the refluxing which is provided in tower 12 by a. return of oil through line 82. In addition a temperature gradient may be imposed on either or both of towers 6'1 and 12. For example, a uniform temperature gradient may be maintained between a maximum temperature in the top of tower I2 and a minimum temperature in tower 61 somewhere below point 68.

The invention will be described further by reference to specific examples of operations carried out in apparatus of the general character of that The apparatus employed in the operations which are referred to in the examples did not, however, provide for introducing propane into the bottom of tower 12 as is provided for in Fig. 3. The propane phase from tower 61 was introduced by means of line H at a point near the bottom of tower 12 instead of at a point somewhat above the bottom as is shown in Fig. 3. In the apparatus employed in the operations of the following examples each of towers 61 and 12 was 18 ft. high and had an inside diameter of 2 in. The oil was charged at point 68 in tower 61 10 ft. from the top of the tower. The propane was introduced into tower 61 through line 69 at a point 2 ft. from the bottom of the tower. The propane phase from tower 61 was passed through line H to a point 2 ft. from the bottom of tower 12. Reflux was returned through line 82 to tower 12 at a point 4 ft. from the top of that tower. Oil phase was transferred from tower 12 to tower 61 through line 84 to a point 1 ft. from the top of tower 61. Each tower was provided with suflicient internal heating means to impose a temperature gradient in the tower,

13 Exmru I In this operation a sardine body oil was charged to tower 61 at the rate of 3,000 ccs. per hour. Propane was charged to tower 81 at the rate of 89,700 ccs. per hour. A uniform temperature of 158 F. was maintained in tower 01 between the of oil withdrawn as product through line ll. Oil

phase from the bottom of tower 12 was returned to tower 61 through line 84 at the rate of 0.97 volume of oil per volume of oil withdrawn as intermediate product through line 03. The resuits of this operation are given below in Table I which includes the percentages of oil recovered in the overhead, intermediate and bottoms products as well as various inspections on these product fractions and the charge oil.

The inspections given in Table I indicate that the intermediate product obtained in accordance with this invention differed considerably in its properties from the overhead product and the bottoms product. The intermediate product had a high iodine number as compared with the overhead product but was considerably lighter in color than the bottoms product which had a still higher iodine number. The overhead oil represented a suitable base material for the manufacture of salad oil and also represented a high quality soap stock. The intermediate oil was a high quality drying oil because of its low iodine number, its low content of free fatty acids and its good color. The bottoms product represented an even more superior drying oil because of its extremely high iodine number and was satisfactory for use in blending with drying oils of low iodine number for uses in which the dark color could be tolerated.

Exams: II

This operation differed from Example I in the employment of a lower temperature gradient and a higher reflux ratio. A uniform temperature of 166 F. was maintained in tower 61 below point B9 and a temperature gradient of 4 F. was maintained between point 08 and approximately the mid point of tower 12. A uniform temperature of about 170 F. was maintained in the upper half of tower l2. Reflux liquid was returned to tower 12 through line 82 at the rate of 11.0 volumes of oil per volume of oil withdrawn as product through line 8|. Oil phase was returned from tower 12 to tower 81 through line 84 at the rate of 1.63 volumes of oil per volume of oil withdrawn as intermediate product fraction through line 83. In this operation the sardine body oil was charged at the rate of 3,000 ccs. per

. 14 hour and propane was charged at the rate of 101,200 ccs. per hour. The results of this operation are summarized below in Table II.

The data of Table 11 show that this operation produced substantially diflerentoverhead, intermediate and bottoms product fractions. The relatively small overhead fraction represented a substantial concentration of the vitamin A potency of the oil and this fact combined with its low iodine number and good color recommend it for use as a vitamin oil, particularly in the preparation of poultry feed. The intermediate product fraction had an extremely good color and a fairly high iodine number. For this reason it could be used either as a medium grade drying oil or as soap stock. The bottoms fraction had a high iodine number and low content of free fatty acids. These characteristics recommend it for use as a high quality drying oil. As indicated by the results of Example I this 011 could be further improved for that use by the separation of a small bottoms fractionin which the color bodies would be concentrated.

The foregoing examples indicate the possibilities of the process in the treatment of fish oils for the recovery of a multiplicity of fractions. Reference also has been made above to the separation of soy oil by this method into a plurality of fractions. The process also is applicable to the process of many oils for that purpose. For example, linseed oil may be separated into a bottoms fraction representing a concentration of the color bodies, a high quality drying oli intermediate fraction, and an overhead fraction suitable for use as a soap stock or as a medium quality drying oil.

We claim:

1. In the fractionation of fatty oils the method which comprises contacting a fatty oil with a .low boiling solvent whose critical temperature is not substantially higher than 450 F. under conditions of temperature and pressure effective to maintain said solvent in a liquid condition and dissolve at least a portion of said oil in said solvent, continuously introducing the solution thus obtained into'one end of an elongated rectification zone maintained under pressure effective to keep the solution liquefied and in the temperature range in which the solubility of the dissolved oil in the solvent decreases with rising temperature, flowing said solution through said rectification zone to the opposite end thereof in intimate contact with an oppositely flowing separate oil phase comprising a mixture of the oil and solvent in a substantially lower ratio of solvent to oil than exists in said first-mentioned solution or solvent phase, continuously withdrawing said solvent phase from said rectification zone at said opposite end thereof, treating said solvent phase in said rectification zone to separate therefrom a portion of the oil component thereof as a component of said separate oil phase, flowing said oil phase in intimate contact with said solution toward the end of said zone at which the first-mentioned solution is introduced, withdrawing said oil phase from said zone at a point adjacent the end at which said first-mentioned solution is introduced, and continuously withdrawing as a side stream a portion of one of said counterflowing phases from said rectification zone at a point intermediate the ends thereof to obtain a fraction of said fatty oil of intermediate characteristics.

2. In the fractionation of fatty oils the method which comprises contacting a fatty oil with a low boiling solvent whose critical temperature is not substantially higher than 450 F. under conditions of temperature and pressure effective to maintain said solvent in a liquid condition and dissolve at least a portion of said oil in said solvent, continuously introducing the solution thus obtained into one end of an elongated rectification zone maintained under pressure effective to keep the solution liquefied and in the temperature range in which the solubility of the dissolved oil in the solvent decreases with rising temperature, flowing said solution through said rectification zone to the opposite end thereof in intimate contact with an oppositely flowing separate oil phase comprising a mixture of the oil and solvent in a substantially lower ratio of solvent to oil than exists in said first-mentioned solution or solvent phase, continuously withdrawing said solvent phase from said rectification zone at said opposite end thereof, treating said solvent phase in said rectification zone to separate therefrom a portion of the oil component thereof as a component of said separate oil phase, flowing said oil phase in intimate contact with said solution toward the end of said zone at which the firstmentioned solution is introduced, withdrawing said oil phase from said zone at a point adjacent the end at which said first-mentioned solution is introduced, continuously withdrawing a portion of said solvent phase free from oil phase material from said rectification zone as aside stream from an intermediate point thereof, and recovering from said withdrawn side stream a fraction of said fatty oil of intermediate characteristics.

3. In the fractionation of fatty oils the method which comprises contacting a fatty oil with a low boiling solvent whose critical temperature is not substantially higher than 450 F. under conditions of temperature and pressure effective to maintain said solvent in a liquid condition and dissolve at least a portion of said oil in said solvent, continuously introducing the solution thus obtained into one end of an elongated rectification zone maintained under pressure effective to keep the solution liquefied and in the temperature range in which the solubility of the dissolved oil in the solvent decreases with rising temperature, flowing said solution through said rectification zone to the opposite end thereof in intimate contact with an oppositely flowing separate oil phase comprising 'a mixture of the oil and solvent in a substantially lower ratio of solvent to oil than exists in said first-mentioned solution or solvent phase, continuously withdrawing said solvent phase from said rectification zone at said opposite end thereof, treating said solvent phase in said rectification zone to separate therefrom a por tion of the oil component thereof as a component of said separate oil phase, flowing said oil phase in intimate contact with said solution toward the end of said zone at which the first mentioned solution is introduced, withdrawing said oil phase from said zone at a point adjacent the end at which said first-mentioned solution is introduced, and continuously withdrawing from said rectification zone at an intermediate point thereof a side stream comprising a portion of said separate oil phase free from solvent phase material to obtain a fraction of said fatty oil of intermediate characteristics.

4. A method in accordance with claim 1 in which the solvent is one whose critical temperature is lower than 325 F.

5. A method in accordance with claim 1 in which propane is employed as the solvent.

6. A method in accordance with claim 1 in which the solvent phase is heated to a higher temperature as it flows through the rectification zone to effect separation of a portion of the oil component thereof.

7. A method in accordance with claim 1 in which at least a portion of the solvent phase withdrawn at said opposite end of said rectification zone is treated to remove at least a part of the solvent therefrom, and the residue of said separation treatment is continuously reintroduced into the rectification zone near said opposite end thereof to initiate the formation of said oppositely flowing oil phase.

8. In the fractionation of fatty oils the method which comprises flowing upwardly through a vertically elongated fractionating zone a solvent whose critical temperature is not substantially higher than 450 F., maintaining said zone under temperature and pressure conditions effective to maintain said solvent in a liquid condition and capable of dissolving at least a portion of said fatty oil, continuously introducing said fatty oil into said zone at an intermediate point to form a solvent phase comprising said solvent stream and oil dissolved therein and an undissolved oil phase, flowing said oil phase downwardly in said zone from the oil charge point to effect stripping thereof by said solvent stream, withdrawing undissolved oil from the bottom of said zone as a product fraction, flowing said solvent phase upwardly through a rectification zone in said fractionating zone above said oil charge point to the upper end of said fractionating zone in intimate contact with a downwardly flowing separate oil phase comprising a mixture of the solvent and oil in a substantially lower ratio of solvent to oil than exists in said solvent phase, treating said solvent phase in said rectification zone to separate therefrom a portion of the oil dissolved therein as a component of said separate oil phase, continu-- ously withdrawing said solvent phase from the upper end of said fractionation zone, and continuously withdrawing as a side stream a portion of one of said counterflowing phases from said fractionating zone at a point within the rectification zone to obtain a fraction of said fatty oil of intermediate characteristics.

I 9. In fractionation of fatty oils the method which comprises: contacting a fatty oil with a low-boiling solvent whose critical temperature is not substantially higher than 450 F. under conditions of temperature and pressure effective to maintain said solvent in a liquid condition and dissolve a portion of said oil in said solvent; continuously introducing the solution thus obtained into the lower or charging end of an elongated rectification zone maintained under pressure effective to keep the solution liquefied and in the temperature range in which the solubility of the success 17 dissolved oil in the solvent decreases with rising temperature; flowing said solution upwardly through said rectification zone to the upper or extract end thereof in intimate contact with an solvent phase from said rectification zone at said extract end thereof; treating said solvent phase in said rectification zone to separate therefrom a portion of the oil component thereof as a component of said separate oil phase; flowing said oil phase in intimate contact with said solution toward said charging end of said zone; withdrawing from said rectification zone an oil or primary rafllnate phase from a point near said charging end; withdrawing an intermediate rafiinate portion of said oil phase from said rectification zone at a point between said charging end and said extract end; subjecting said intermediate raftinate phase to stripping with solvent to effect a separation into a secondary extract phase and a secondary rafiinate phase, said extract phase containing a greater proportion of solvent than said rafflnate phate; and reintroducing said secondary extract phase into said rectification zone.

10. In the fractionation of fatty oils the method which comprises: contacting a fatty oil with a low-boiling solvent whose critical temperature is not substantially higher than 450 F. under conditions of temperature and pressure effective to maintain said solvent in a liquid condition and dissolve a portion of said oil in said solvent; continuously introducing the solution thus obtained into the lower or charging end of an elongated rectification zone maintained under pressure effective to keep the solution liquefied and in the temperature range at which the solubility of the dissolved oil from the solvent decreases with rise in temperature; flowing said solution upwardly through said rectification zone to the upper or extract end thereof in intimate contact with an oppositely and downwardly flowing oil phase comprising a mixture of oil and solvent in a substantially lower ratio of solvent to oil than exists in said first-mentioned solution of solvent phase; treating said solvent phase in said rectification zone to separate therefrom a portion of the oil component thereof as a component of said separate oil phase; flowing said oil phase in intimate contact with said solution toward said charging end of said zone; withdrawing from said rectification zone an oil or primary raiflnate phase from a point near said charging end and a solvent or extract phase from a point near said extract end; introducing said solvent phase withdrawn from said extract end of said first rectification zone into a second rectification zone having a second upwardly flowing stream of said low-boiling solvent and treating said counter-currently flowing streams of oil and solvent to produce a downwardly flowing oil phase and an upwardly flowing solvent phase; withdrawing a second -oil phase at the lower end of said second rectification zone and a second extract phase at the upper end of said second rectification zone; withdrawing at least a portion of the downwardly flowing phase in said second rectification zone and introducing it-into said first rectification zone at a point near said extract end of said first rectification zone to form at least a portion of the downwardly flowing oil phase therein.

11. In the fractionation of fatty oils the method which comprises flowing upwardly through a vertically elongated fractionating zone a solvent whose critical temperature is not substantially higher than 450 F., maintaining said zone under temperature and pressure conditions effective to maintain said solvent in a liquid condition and capable of dissolving at least a portion of said fatty oil, continuously introducing said fatty oil into said zone at an intermediate point to form a solvent phase comprising said solvent stream and oil dissolved therein and an undissolved oil phase, flowing said oil phase downwardly in said zone from the oil charge point to effect stripping thereof by said solvent stream, withdrawing undissolved oil from the bottom of said zone as a product fraction, flowing said solvent phase upwardly through a rectification zone in said fractionating zone above said oil chargepoint to the upper end of said fractionating zone in intimate contact with a downwardly flowing separate oil phase comprising a mixture of the solvent and oil in a substantially lower ratio of solvent to oil than exists in said solvent phase, treating said solvent phase in said rectification zone to separate therefrom a portion of the oil dissolved therein as a component of said separate oil phase, continuously withdrawing said solve t phase from the upper end of said fractionation zone, and continuously withdrawing as a-side stream a portion of said downwardly flowing oil phase from said fractionating zone at a point within the rectification zone to obtain a fraction of said fatty oil of intermediate characteristics.

JOHN T. DICKINSON.

OLIVER MORFIT.

LEO J. VAN ORDEN.

Romances crrnn The following references are of record inthe flle of this patent:

UNITED STATES PAW Batchelder June 9, 1942

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