US2520801A - Fractional separation of fatty oil substances - Google Patents

Description

Aug. 29, 1950 w. P. GEE

FRACTIONAL SEPARATION OF FATTY OIL SUBSTANCES Filed June 23, 1945 Patented Aug. 29, 1950 FBACTIONAL SEPARATION OF FATTY OIL l SUBSTANCES William P. Gee, Plainfield, N. J., assignor to Texaco Development Corporation, New lork, N. Y., a corporation of Delaware Application June 23, 1945, Serial No. 601,105

8 Claims. (Cl. 2260-4285) This invention relates to the fractional separation of fatty oil substances such as derived from vegetable, land and marine animal, or other sources. Such oils comprise saturated and unsaturated fatty acids having from about 12 to 18 carbon atoms per molecule and usually in the form of glycerides. In some instances. as, for example, in the case of sperm oil the acids are largely combined as esters of the higher aliphatic alcohols although they may be present as glycerides to the extent of 12 to 30% of the fatty oil.

The invention involves separation of fatty oil substances in the form of glycerides, esters, free fatty acids or mixtures thereof into fractions of different melting point or of different solidication point range by continuous filtration in the presence of a solvent liquid such as acetone. methylethyl ketone, acetonitrile, benzene. toluene. diand tri-chlorethylenes, low boiling petroleum hydrocarbons, namely propane, butane, pentane, etc. or mixtures of any of these solvents. The fatty substance to be treated may =be any particular portion of the oil, such as a mixture consisting essentially of free fatty acids obtained by acidulation of the saponifled acids separated from the oil.

Thus the fatty acid mixture may comprise essentially a mixture of stearic, palmitic, oleic, and linoleic acids. and from which mixture. in accordance with the inventionl may be separated a fraction consisting of the saturated acids stearic and palinitic. as well as separate fractions consisting essentially of oleic and linoleic acids, respectively.

The present application is a continuation-inpart of my abandoned application, S. N. 454.666, filed August 13, 1942, for Fractional Separation of Fatty Oil Substances.

The fatty oil substance to be filtered is mixed with the solvent liquid in an amount and under conditions of temperature such as to obtain a mixture composed of a liquid phase comprising fatty oil substance dissolved in solvent liquid and a solid phase consisting essentially of fatty constituents of predetermined and relatively narrow melting point or solidication point range. This phase mixture with the solid phase dispersed substantially uniformly throughout the liquid phase is passed in a continuous stream to a continuous filter advantageously of the rotating leaf or drum type wherein the filter surface passes through the mixture of liquid and solids. during which forming of filter cake upon the filter surface occurs, and then emerges from the filtering mixture for subsequent passage through zones of filter cake washing. drying and discharging. In other words, forming, washing, drying and discharging of filter cake occurs in 'a continuously recurring cycle of operations as will be described in more detail.

As disclosed in the aforementioned application, a portion of the total solvent liquid may be mixed initially with the fatty oil and this partially diluted mixture chilled to approximately the filtering temperature, the remainder of the solvent liquid, prechilled to the filtering temperature, being added to the partially diluted mixture prior to filtration.

The present application is particularly concerned with this chilling procedure since it has been found that more effective separation between components or component fractions of the fatty oil substance is obtained by effecting the chilling of the feed oil in the presence of a portion of the solvent liquid than is obtained when all of the solvent liquid required for the filtration is added prior to chilling the oil. This improved separation is obtained while realizing a high rate of filtration.

This amount of solvent to add initially should be sufficient to result in a balance between a good degree of separation and a good filtration rate. Too low an initial dilution will result in a low filtration rate while too high an initial dilution will result in a poor degree of separation between the fatty oil components. In other words, the proportion of solvent used in effecting the cooling and chilling of the feed oil is critical from the standpoint of crystallizing the solidiflable component in a form which permits obtaining a sharp separation between the solidified component and the liquid component or components and yet maintain a practical filtration rate. It has been found that this combination of good results can best be realized when the cooling or chilling of the feed oil is effected in the presence of a volume of solvent ranging from about 0.7 to 1.5 times the volume of the feed oil.

It is contemplated that the operation may involve a plurality of separate and successive filtrations wherein the -filtrate from a preceding stage is passed to a succeeding stage which may, for example, be operated at a lower temperature level. In this way the original fatty oil feed may be separated into a series of separate, substantially pure fractions.

An important feature of the invention disclosed in the aforesaid pending application involves maintaining the proper relation between the solid the filter. A It is advantageous that the volume of such liquid phase be in the ratio of about 30 to 50 volumes per unit volume of solid phase. Expressed in terms of per cent solids it is desirable that the solids contained in the phase mixture passing to the filter be in the range about 3% by volume 'of the phase mixture and not substantially in excess of this value.

If the solid phase is present in the feed mixture to a larger extent than this, a filter cake is obtained which is too thick to permit effective displacement of liquid phase from the filter cake during the washing step and under such circumstances sharp separation between component fraction of the fatty oil feed is not realized.

'Ihe ratio of solid phase to liquid phase can be controlled by correlating the amount and character of the solvent liquid employed with the temperature at which the mixture is filtered and also by recycling either filtrate or solids to the mixture passing to the filter. Recycling of filtrate increases the ratio of liquid to solids and is advantageous from the standpoint of exerting a beneficial modifying action on the crystalline structure. of the solid phase whereby more efflcient ltration and more close-cut fractionation may be realized. n the other hand, solids may be recycled so as to maintain the aforesaid solid content of the feed mixture, particularly where the solvent content in the liquid phase cannot be reduced without an excessive increase in the viscosity of the liquid phase.

As already intimated liquid phase retained in the filter cake is displaced by washing prior to discharge from the filter. This washing is accomplished by applying a further quantity of the solvent liquid to the lter cake, in situ, in such manner as to displace the retained liquid phase as filtrate. Effective displacement is secured by applying the wash solvent liquid to the lter cake in the form of an unbroken lm or sheet of solvent liquid maintained over the cake for a period of time subsequent to its emergence from the filtering mixture. To facilitate realizing complete displacement of retained liquor, the filter cake should not exceed about one-quarter inch in thickness. On the other hand, the cake should be not less than about one-eighth inch in thickness; otherwise dimculty is encountered in discharging it from the filter surface.

An important advantage of the present invention is that it provides a, continuous method of effecting fractional separation of these fatty oils, such separation heretofore having been effected by pressing, usually involving a succession of pressing operations applied to the same fraction.

A further advantage is that the present invention permits realizing a sharper separation between individual fractions of the feed oil.

For example, when treating an oil derived from soya bean and consisting essentially of free fatty acids, in order to separate therefrom a. fraction consisting essentially of palmitic and stearic acids, in accordance with the process of this invention, a filter cake is obtained in a single iiltering operation which, after removal of the solvent, will have an iodine number of or less indicating the substantial absence of the unsaturated acids which are of lower melting point. By prior art methods involving pressing, about the best that can be expected is a product having an iodine number of about 15.

In order to describe the invention further, reference will now be made to the accompanying drawing.

As indicated in Figure 1, fatty oil from a source not shown is conducted through a pipe I to a.v

mixer 2 while solvent from a source not shown is conducted through a pipe 3 to the mixer. The solvent may be. for example. a low' molecular weight ketone such as acetone or methylethyl ketone or a, mixture of such ketoneswith benzol or other aromatic hydrocarbom. The solvent may be mixed with the fatty oil in the proportion of about 0.7 to 1.5 parts of solvent to 1 part by volume of fatty oil although the actual proportions used will depend upon the character of the fatty oil feed and also upon the degree of fractionation desired.

The resulting mixture may be conducted from the mixer 2 to a heater l wherein the mixture is warmed or heated sufficiently to effect 'complete solution of the fatty oil in the solvent liquid. If desired, the mixture may be raised to a temperature 25 to 50 F. above the temperature of complete solution in order. to condition the mixture. If desired, the heater 4 may be by-passed as indicated.

The solution is passed either from or around the heater 4 to a chiller or coole; 5 wherein the temperature of the solution is reduced to substantially the filtering temperature so as to effect crystallization of the constituent of the fraction desired to be separated. A solid phase is obtained containing fatty oil constitutents of predetermined melting point or solidification point range.

The temperature to which the mixture of fatty oil and solvent is chilled will depend upon the character of the feed oil and also upon the particular constituent which it is desired to crystallize therefrom. For example, when separating a. solid phase consisting of stearic and palmitic acid from a mixture of these acids with oleic and linoleic acid, the mixture may be chilled to a temperature of about |5 F. When separating a solid phase consisting of oleic acid from a mixture containing oleic and linoleic acid the ltering temperature is about 30 F. Y

The remainder of the solvent, after chilling in the chiller 5a to about the ltering temperature, is then mixed with the aforesaid chilled mixture in an amount suflicient to bring the total solvent in the fatty oil-solvent mixture up to an amount ranging from about 2 to 5 volumes per volume of feed oil.

In practice the chiller 5 Iusually comprises several stages of pipe coils and the remainder of solvent may be injected to the chilled fatty oil mixture prior to or during passage through the final stage of chilling or may be injected at a plurality of points throughout the chilling coils.

As referred to later, the precooled solvent added at this stage may comprise at least in part solvent contained in recycled filtrate.

In any case, the mixture brought to the desired filtering temperature is passed to a lter 6 advantageously comprising a hollow rotating cylinder or hollow rotating leaves covered with filter lcloth with means for creating vacuum within the interior of the lter element or for exerting positive pressure upon the exterior thereof.

The liquid phase is separated from the feed mixture as filtrate which is discharged through a pipe 1 to a receiver 8, while the solid phase is retained on the filter cloth as a filter cake and discharged from the filter through a conduit 9 to a receiver I 0.

The filter cake is washed, in situ, with additional solvent liquid which may be cooled in a chlller 8a and then introduced to the filter through the pipe II. 'I'he resulting wash nitrate is usually removed from the filter as a separate stream through a pipe I2 discharging into a receiver I3. This wash filtrate, lean in oil, ls advantageously used for mixing with fresh fatty oil feed to the system. In this case. since it is at about the filtration temperature, it is injected from a pipe I2a into the chilled partially diluted oil feed to provide the secondary prechilledsolvent liquid. It may be injected before, during, or after disf charge of the oil from the last stage of the chlller 5.

The interior of the filter 6 is maintained at approximately the same temperature as that of the entering feed mixture. This is accomplished by circulating gas through the filter. Thus, an inert gas such as flue gas is drawn from a storage tank Il by means of a blower I5 and passed through a heat exchanger I6 wherein the gas is brought to the desired temperature. From the heat exchanger IB the gas is passed through a pipe I'I into the hood of the filter 8 and is discharged from the interior of the filter through the filtrate discharge pipes 'I and I2. The discharged gas is removed from the receivers 8 and I3 and may be returned to the suction side of the blower i5 as indicated.

If necessary the circulating gas may be scrubbed with a suitable liquid medium to remove liquid components, water and solvent. Moreover, the scrubbing medium may also serve in the capacity of a cooling agent when it is desired to reduce the temperature of the gas.

The primary filtrate drawn off from the receiver 8 may be discharged through a pipe 20 leading to a solvent recovery unit 2I. This unit may comprise a distillation unit and other auxiliary apparatus adapted for removing the solvent iiquid from the fatty oil.

On the other hand, the filtrate may be conducted through a pipe 22 to a succeeding stage wherein it is subjected to filtration at a somewhat lower temperature or in the presence of a different solvent or in the presence of the same solvent but in different proportion so as to effect Bun l 2 3 4 Temperature of undiluted leeg? 1m 120 12D 137 Volume of solvent added for initial mixture basis one volume eed 3. 5 l. 0 l. Il l 0 Temperature of initial mix- 1m 1m im Temperature to which initial Filllixnuetghilled? gf-- +5 +5 +5 +5 er mpera ure +5 +6 5 5 Volume of solvent added to chilled initial mixture 0 2. 5 2. 0 2. l Total volume of solvent in llltering mixture e. 5 s. s 3.o 1 3.o Weight per cent cake basis feed--- 14 i3 13 14 Iodine number of cake 18 4 4. 5 l0 precipitation of another fraction consisting of constituents of the fatty oil feed.

As indicated, a portion of the primary filtrate may be recycled through a pipe 23 to the feed mixture. The recycled material which is already at a lowtemperature or at substantially the ltering temperature, may be mixed with the feed after passage of the feed through the chilling system, or may be mixed therewith at one or more intermediate points within the chiller 5. It may, however, be used in partial substitution of fresh solvent at preceding points or stages in the proc; ess.

The filter cake discharged into the receiver I0 may be drawn off through a, pipe 24 to a solvent irecovery unit 25 substantially similar to the unit 2I wherein solvent liquid is recovered from the fatty oil products.

The following examples provide acomparison of the eiliciency of separation realized by effecting the chilling of the fatty oil feed (1) in the presence of 3.5 volumes of solvent per volume of oil; (2) in the presence of l volume of solvent per volume of oil; and (3) in the substantial absence of solvent.

The'charge oil comprised a mixture of stearic, palmitic, oleic, linoleic and linolenic acids (the latter in small amount) split from soy-bean oil. The fatty acid mixture was characterized by havaudaci ing an iodine number of about 138, an acid value of about 190, and a titer of about 20.7 C.

In each case a quantity of the fatty acid mixture was filtered in the presence of acetone at a temperature or about +5 F. so as to produce a filter cake of about la inch in thickness. The filter cake was then washed with solvent, which was prechilled to the filtering temperature, in the proportion of about 2 volumes of acetone per volume of fatty acid feed.

' l 0.9 volume of cool solvent added in increments during reduction of temperature from +70 to +5 F. in order to maintain fluidity.

As indicated by the foregoing data the best lresults from the standpoint of obtaining a filterv cake consisting essentially of the saturated acids stearic and palmitic were obtained in the two runs in which the chilling was elected in the presence of 1 volume of oil per volume of feed acid mixture. In these two runs the lter cake after removing of solvent was characterized by having an iodine number of 4 and 4.5 respectively indicating that the cakes were substantially free from the unsaturated acids. By contrast the filter cakes obtained in the other two experiments were characterized by a much higher iodine number and the yield of filter cake was larger in .each instance indicating the presence of unsaturated acids.

It is important to realize effective displacement washing of the filter cake prior to discharge from the filter and for this additional reason it is desirabie to form on the filter a lter cake which is susceptible to effective washing in situ. As mentioned earlier the forming of such cake is dependent upon controlling the ratio of solids to liquids in the liquid and solid phase mixture passing to the filter. One method of adjusting this ratio is by recycling of flltrate as previously disclosed. In some instances the recycled filtrate may amount to as much as 2 to 3 volumes per volume of fatty oil feed to the process.

Although soya bean oil has been referred to in the foregoing example, nevertheless the procedure of this invention is applicable to treatment of other vegetable and animal oils including corn oil. palm oil. cocoanut oil, linseed oil, rape oil, walnut oil, lard oil, sardine oil, etc. The process may be applied to the crude oil, distilled oil, or to any desired portion thereof. As previously intimated the crude oil or a fraction thereof may be saponified by treatment with caustic, the resulting saponied acid constituents separated, and thereafter treated with mineral acid so as to obtain a free fatty acid mixture. Fatty acids derived from other methods of splitting may be treated.

It may be applied to fatty acid mixtures prepared from any source such as by the oxidation of paraflln hydrocarbons, an example of which would be the products obtained by oxidizing petroleum wax.

pended claims.

I claim:

1. In the separation of a fraction of desiredhigher melting point range from fatty oil by filtration in the presence of a solvent liquid from which said fraction can be crystallized at a predetermined temperature below normal room temperature, the steps comprising partially diluting said fatty oil prior to cooling with a quantity of said solvent liquid in the range about 0.7 to 1.5 volumes of solvent per volume of fatty oil, cooling the resulting mixture to a temperature sufcien'tly low to crystallize said fraction thereby forming a mixture of a solid phase comprising said fraction and a liquid phase comprising liquid fatty oil and solvent at substantially filtering temperature. thereafter mixing additional cool solvent liquid with said mixed phases in an amount suiclent to provide a filterable mixture at said filtration temperature, passing resulting fillterable mixture to a zone of filtration, separating liquid phase as ltrate and forming a filter cake of solid phase, washing said filter cake in situ with solvent liquid to displace retained liquid phase, discharging filtrate from said zone, and separately discharging therefrom washed filter cake substantially free from fatty constituents having a melting point outside said desired range.

2. The method according to claim 1 in which the additional solvent liquid is separately cooled to substantially the temperature of the partially diluted fatty oil prior to mixing therewith.

3. The method according to claim 1 in which said additional cool lsolvent liquid consists, at least in part, of recycled filtrate.

l4. The method according to claim 1 in which said additional cool solvent consists, at least in part, of primary ltrate. y

5. The method according to claim i in which said additional cool solvent consists, at least in part, of wash filtrate.

6. In the separation of a fraction of desired higher melting point range from fatty oil by co-ntinuous vacuum filtration in the presence of a solvent liquid from which said fraction can be crystallized at a temperature below normal room temperature, said filtration involving forming, washing, drying, and discharging from a zone of filtration a filter cake of solids in a continuous recurring cycle, the steps comprising partially diluting said fatty oil prior to cooling with a quantity of said solvent liquid in the range about 0.7 to 1.5 volumes of solvent per volume of fatty oil, cooling the resulting mixture to a temperature sufficiently low to crystallize said fraction thereby forming a mixture of a solid phase comprising said crystallized fraction and a liquid phase comprising liquid fatty oil and solvent at substantially filtering temperature, thereafterl amount vwith said mixed phases to provide a illamasar mixing additional cool solvent in substantial.

terable mixture at said filtration temperature, forming at said filtration temperature a mixture in which said solid phase amounts to about 3% by volume of the liquid phase, passing said mixed phases to a zone of continuous rotary lvacuum filtration, separating liquid phase as filtrate and forming a filter cake of solid phase, washing said lter cake in situ to displace retained liquid phase, continuously discharging filtrate from said zone, and separately discharging from said zone washed filter cake substantially free from fatty constituents having a melting Point outside saidl desired range;

7. In the separation,of a fraction of desired higher melting point range from a fatty oil substance by filtration in the presence of a solvent liquid from which said fraction can be crystallized by chilling to a filtration temperature in the range of normal roo-m temperature to minus 30 F., involving chilling to said filtration temperature with only partial dilution of the fatty oil substance, the steps comprising effecting said crystallization during said chilling in the presence of an amount of solvent liquid ranging from about 0.7 to about 1.5 volumes per volume of fatty oil substance thereby forming a mixture of a solid phase comprising said crystallized fraction and a liquid phase comprising partially diluted liquid fatty oil substance, thereafter mixing additional cooled solvent liquid with said mixed phases in an amount sumcient to provide a illterable mixture at said filtration temperature, passing resulting lterable mixture to a zone of ltration, separating liquid phase as filtrate and forming a filter cake of solid phase, washing said filter cake in situ with solvent liquid to displace retained liquid phase, discharging filtrate from said zone and separately discharging from said zone washed filter cake substantially free from fatty constituents having a melting point outside said desired range.

8. The steps according to claim 7 wherein the fatty oil substance consists essentially of a mixture of stearic, palmitic. oleic, linoleic and linolenic acids.

WILLIAM P. GEE.

REFERENCES CITED The following references areof record in the f'lle of this patent:

l UNITED STATES PATENTS Number Name Date 1,974,542 Parkhurst Sept. 25, 1934 2,107,664 Gee Feb. 8, 1938 2,166,891 Gee July 18, 1939 2,228,040 Voogt Jan. 7, 1941 2,248,668 Gee July 8, 1941 2,288,441 Ewing June 30, 1942 2,293,676 Myers Aug. 18, 1942 2,350,944 Thornton June 6, 1944 2,356,346 Packie et al Aug. 22, 1944

Claims (1)

1. IN THE SEPARATION OF A FRACTION OF DESIRED HIGHER MELTING POINT RANGE FROM FATTY OIL BY FILTRATION IN THE PRESENCE OF A SOLVENT LIQUID FROM WHICH SAID FRACTION CAN BE CRYSTALLIZED AT A PREDETERMINED TEMPERATURE BELOW NORMAL ROOM TEMPERATURE, THE STEPS COMPRISING PARTIALLY DILUTING SAID FATTY OIL PRIOR TO COOLING WITH A QUANTITY OF SAID SOLVENT LIQUID IN THE RANGE ABOUT 0.7 TO 1.5 VOLUMES OF SOLVENT PER VOLUME OF FATTY OIL, COOLING THE RESULTING MIXTURE TO A TEMPERATURE SUFFICIENTLY LOW TO CRYSTALLIZE SAID FRACTION THEREBY FORMING A MIXTURE OF A SOLID PHASE COMPRISING SAID FRACTION AND A LIQUID PHASE COMPRISING LIQUID FATTY OIL AND SOLVENT AT SUBSTANTIALLY FILTERING TEMPERATURE, THEREAFTER MIXING ADDITIONAL COOL SOLVENT LIQUID WITH SAID MIXED PHASES IN AN AMOUNT SUFFICIENT TO PROVIDE A FILTERABLE MIXTURE AT SAID FILTRATION TEMPERATURE, PASSING RESULTING FILTERABLE MIXTURE TO A ZONE OF FILTRATION, SEPARATING LIQUID PHASE AS FILTRATE AND FORMING A FILTER CAKE OF SOLID PHASE, WASHING SAID FILTER CAKE IN SITU WITH SOLVENT LIQUID TO DISPLACE RETAINED LIQUID PHASE, DISCHARGING FILTRATE FROM SAID ZONE, AND SEPARATELY DISCHARGING THEREFROM WASHED FILTER CAKE SUBSTANTIALLY FREE FROM FATTY CONSTITUENTS HAVING A MELTING POINT OUTSIDE SAID DESIRED RANGE.

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