US 2682551 A
Description (OCR text may contain errors)
Patented June 29, 1954 RECOVERY OF FATTY OILS Ralph Miller, Woodside, N. Y., assignor to The Chemical Foundation, Incorporated, a New York membership corporation No Drawing. Application March 9, 1948,
7 Serial No. 13,940
As is known, there are three methods in general use for the recovery of fatty oil from oleaginous materials, namely, hydraulic pressing, expelling and solvent extraction. In some cases materials are treated by mechanical expression followed by solvent extraction. Th oils recovered by each of these methods are described as crude fatty oils. They contain non-glyceridic objectionable components such as color bodies, gossypol, phosphatides, colloidally suspended proteinaceous materials, acidic substances, oxidized and polymerized components, unpleasant odoriferous and taste imparting constituents and the like. Before they can be used most advantageously, it is usually necessary to separate one ormore of the non-glyceridic substances present in the crude oil from the bulk of the triglycerides. The removal or separation of one or more objectionable, non-glyceridic substances from the bulk of the triglycerides is termed refining. Since most fatty oils are refined by treatment with alkaline reagents, a refined oil is one which is substantially free from all objectionable non-glyceridic components with the exception of certain types of color bodies that are removable by treatment with adsorptive reagents and volatile odor and taste imparting materials removable by stripping with steam at elevated temperatures. under vacuum. Hence, a refined oil is an oil which may be substantially freed from all of its objectionable, non-glyceridic components by bleaching and deodorization.
It is a primary object of this invention to recover substantially refined fatty oils from oil-com taining substances and to recover such substantially refined fatty oils from oil bearing substances at an operating cost below the operating cost of extracting crude oils from oil bearing materials by the methods now in use.
Fatty oils are of diverse origin. In most instances fatty til-containing substances must be conditioned prior to th oil separation opera tion. This conditioning treatment may consist of a cooking operation, a drying step, the destruction of tissue as by treatment with dilute alkali, and the like. vary with the type of oil-containing material. These preliminary operations form no part of the present invention.
The essence of the present invention is the solvent extraction of the oil-containing conditioned material with a specific type of solvent The conditioning treatment will under specific conditions. The oil recovered from the resulting oil-solvent solution is a substantially refined fatty oil. Certain types of oilcontaining materials have been more amenable to previously available solvent extraction technique than others. For example, soybeans have been successfully solvent extracted for many years. Cottonseeds have not been amenable to solvent extraction until but recently and the successful economical solvent extraction of cottonseeds is not proven to date. No mechanical method of separating fatty oils from oil-containing substances is able to recover as much of the oil content of an oleaginous material as can be recovered by a solvent extraction process. For this reason every oil-containing substance is a suitable raw material for a solvent extraction process after preliminary conditioning or after mechanical expression. Thus, this process may be applied to oilseeds, garbage, meat scraps, cracklings, dried fermentation residues, fish meals, etc.
There are a variety of reasons why some oilcontaining "materials have not been treated by solvent extraction to date. A principal difficulty is the tendency of some substances such as cottonseeds to break down into such fine particles that it is difiicult to separate the solid particles from the oil-solvent solution. The fines also tend to accumulate in certain parts of the equipment causing the process to operate inefficiently and eventually making it necessary to cease operations to remove the accumulated fines. In some cases the solvents extract undesirable constituents from the oil-containing material making the recovered oil either difiicult to refine or impossible to refine economically. In other instances the extracted oil is heated to such a high temperature in removing the last traces of solvent that undesirable chemical reactions take place and the recovered oil becomes difficult to refine.
The dimculties presented by the solvent extraction of cottonseeds are typical of many of the difficulties in this field. Cottonseeds are relatively fragile when the oil they contain is removed. This causes them to disintegrate readily when solvent extracted, resulting in the production of large quantities of fines. No process to date has been able to achieve the separation of these fines from the oil-so1vent solution without r ther elaborate equipment. and complicated processing steps.
The solvents usually suggested as suitable for the extraction of oil seeds and similar oil-containing substances are petroleum fractions such as hexane, or chlorinated hydrocarbons such as ethylene dichloride. These solvents extract large amounts of color bodies from the seed as well as the oil. In the case of cottonseeds, the heating of the miscella to an elevated temperature makes the crude oil difiioult to bleach. Solvents also extract gossypol from cottonseeds especially if the seed is not cooked prior to the extraction. The oil must 'be freed from gossypol before it can be used as a food. In addition to the solvents mentioned above, it has been suggested that alcohol and liquefied, normally gaseous hydrocarbons such as butane or propane as well as similar liquids be employed for the extraction of oil-bearing materials.
A fundamental lack of all processes either in use 01' suggested for the recovery of fatty oils from oil-bearing materials is that the separated oil requires refining prior to use.
The present invention as stated above is concerned with the recovery of substantially refined fatty oil directly from the source material.
The present invention is conveniently described in terms of processing cottonseeds although it is equally applicable to other oil-bearing materials such as soybeans, flaxseeds, peanuts, corn germ and the like, making such obvious changes in procedure as are required by the material being treated.
As mentioned above, it has been proposed before to extract oil-bearing seeds with liquefied, normally gaseous hydrocarbons such as propane and butane. This was suggested as long ago as 1928 by E. E. Reid in U. S. Patent No. 1,802,533. Additional innovations have been suggested by Rosenthal in U. S. Patent No. 2,254,245. It is apparent from this prior art that the principal advantage found by previous investigators of this type of solvent is the low temperature at which the solvent could be separated from the oil and meal compared with hexane, chlorinated hydrocarbons and alcohol. By maintaining the temperature below 80 F. while the solvent is in contact with the seed and not permitting the temperature to exceed 210 F. during the separation of the solvent from the oil, Rosenthal is able to produce a crude cottonseed oil which upon subsequent alkali refining and bleaching meets the specifications of a white oil. The present invention employs liquefied, normally gaseous hydrocarbons to extract the oil from oil-bearing materials such as cottonseeds, under novel conditions not described before with results that have not been achieved hitherto.
In order to extract the oil from materials such i as oilseeds, the cellular structure in which the oil is contained must be broken down to permit access of the solvent to the oil. When cottonseeds are extracted by conventional processes, they require delinting, dehulling, cracking and flaking prior to being contacted with the solvent. In some processes the meats are also cooked prior to flaking. The present process may utilize these conventional conditioning operations or may substitute any other procedure which will permit easy access of the solvent to the oil. One novel procedure which can be employed prepares the oil-bearing material for the extraction operation using liquefied, normally gaseous hydrocarbons as a process aid. While this procedure is not es sential to the achieving of the results described below, in some circumstances it permits substantial economies to be made.
This novel method of preparing the oil-bearing material such as cottonseeds, employs the latent energy of liquefied, normally gaseous hydrocarbons to disintegrate the material. For example, cottonseed is preferably delinted and dehulled. The seed is then mixed with the liquefied solvent in a container or gun under pressure and preferably at a pressure greater than the pressure required to maintain the solvent in the liquid phase. By imposing the additional pressure on the solvent-seed mixture, the solvent penetrates the seed more rapidly and causes it to permeate the seed more thoroughly. The temperature can be maintained at any convenient level although it is preferred to have the seed-solvent mixture above room temperature. The seed-solvent mixture is then permitted to flow through a nozzle into a chamber maintained at a pressure substantially lower than the pressure prevailing at the inlet'of the nozzle. This causes the solvent to expand precipitously, thereby shattering the seed particles. The extent to which the seeds are shattered is controlled by varying the ratio of seed to expandible fluid and the ratio of pressure prior to the expansion and pressure after the mixture has passed through the nozzle. Although it is advantageous to comminute the seeds in this fashion, other methods of breaking down the cellular structure of the seeds can be used.
A unique feature of the present invention is that the extraction step of the process may readily be carried out irrespective of how finely divided the meal may be. If desired, and it usually is desirable, no solid particles will accompany the oil-solvent solution when it leaves the extraction step of the process. A major problem of all previous processes for the extraction of oils from oilseeds was keeping the production of fines to a minimum and devising means to handle those that formed. In the present process the handling of fines in the extraction step requires no additional equipment. Any fines produced irrespective of quantity or particle size will automatically accompany the meal.
The separation of the oil from the meal is carried out by introducing the conditioned meats into a vertical extraction .tower adapted for continuously contacting finely divided solids with a liquefied, normally gaseous hydrocarbon solvent preferably in a counter-current manner.
The preferred solvent is propane. A suitable extraction tower is a vertical tower equipped with simple baffles that will not permit solids to accumulate on them. Mixing devices, preferably hydraulic, are built into the tower to insure intimate contact of the solvent and solid. The solid particles preferably enter the tower as a slurry mixed with some of the solvent at a point below the top outlet of the tower. A suitable distance is 10 or more feet although a lesser distance can be employed. Propane, in the liquid phase, is pumped into the tower close to the base but above the bottom outlet of the tower. If desired, the propane may be introduced into the tower at a multiplicity of points at strategic locations through nozzles to aid the mixing of meal and solvent. The meal is denser than the solvent and tends to sink. The tower dimensions as well as the other controllable variables are chosen so that the meal falls through the rising solvent. As the meal moves counter-currently to the rising solvent, the oil dissolves so that by the time the meal reaches the bottom outlet of the tower substantially all of the oil originally contained in the meal is in the propane solution. The temperature of the oil-solvent solution within the tower is controlled so that the temperature of the solution above the top inlet of the tower is higher than the maximum temperature atwhich the oil and solvent in the ratio existing within the tower are completely miscible. In addition, at some point lower in the tower the temperature of the solution is controlled so that it is below that prevailing above the top inlet. By controlling the temperature of the solution within the tower so that these two conditions are met, two separable, liquid phases are formed.
One liquid phase is composed of most of the solvent and most of the oil originally present in the meats. It is the less dense phase. The'more dense phase contains the remainder of the solvent, a small amount of the oil, many of the color bodies which dissolve in the solvent at the lowest temperature existing within the tower and other objectionable, non-glyceridic substances that dissolve in the solvent at the maximum temperature at which the oil and solvent, in the ratio existing within the tower, are completely miscible. Among the objectionable non-glyceridic constituents that tend to dissolve in the solvent at lower temperatures are phosphatides, ashforming constituents, oxidized fats and fatty acids, polymers of triglycerides, nitrogen-containing substances and the like.
The solvents employed in this process, liquefied, normally gaseous hydrocarbons, not only possess a negative temperature-solubility coefficient towards triglycerides but they also possess selective solubility characteristics with respect to the difiicultly-removable objectionable non-glyceridic constituents that will dissolve in these solvents at temperatures at and below the maximum temperature at which the solvent and oil in the particular ratio employed are completely miscible. As a result of the selective solubility of these solvents with respect to these difficultly-removable, objectionable, non-glyceridic materials,
these substances come out of solution along with the first small quantity of triglycerides that come out of solution when the maximum temperature, at which the oil and solvent in the particular ratio employed are completely miscible, is exceeded. Because of the unique selectivity of these solvents when employed in the manner described, the above mentioned difficultly-removable, objectionable, non-glyceridic components are concentrated in the more dense liquid phase.
The ratio of solvent to oil charged to the tower is usually about 7 or more to 1. It is preferable but not essential that a uniform temperature gradient be employed within the tower with the maximum temperature existing close to the top of the tower and the minimum temperature prevailing at the base of the tower. The rates at which the meats and propane are charged to the tower are controlled so that the upward velocity of the lighter phase does not prevent the more dense phase from settling through it.
When the ratio of propane to oil is about 8 to l by volume, a suitable maximum temperature is about 160 F. The temperature in the bottom portion of the tower is somewhat lower. The relatively high temperature in the top section of the extraction tower insures the formation of a second liquid phase. This, in turn, means that the oil dissolved in the solvent that leaves the top outlet of the tower will contain only that type of objectionable, non-glyceridic components that are readily removed by absorption or vaporization. In addition, the formation and settling of the second liquid phase performs another func" tion which Will be pointed out below.
The oil-bearing meats are denser than the sol vent and hence tend to fall through the upfiowing propane. Ihe propane charged to the tower contains substantially no oil. As it contacts the oil-containing meats, the oil adhering to the meats diffuses into the solvent flowing past it. As the propane flows upward, it comes in contact with solid particles associated with more and more oil until it reaches the top inlet of the tower. The solvent thus leaves the extraction step of the process after contacting the solid par ticles which are associated with the maximum amount of oil. Similarly, as the meats move down the tower they contact propane solutions which are progressively more dilute with respect to dissolved oil. This increases the rate at which the oil diffuses from the solid into the solution. By the time the meats reach the bottom inlet of the tower, they are being washed by substantially pure propane and leave the final contacting with the solvent phase substantially free from triglycerides.
Since cottonseeds tend to be fragile when stripped of their oil content and since no special effort need be made in carrying out this process to minimize the quantity of fines which are pro duced either in the extraction operation or in conditioning the meats, the automatic way in which the fines are handled requires explaining. In the conditioning operation prior to the actual contacting of the meats with the solvent some of the solid is reduced in size to substantially colloidal dimensions. As the meats enter the extraction column these very minute particles tend to move upward with the rising propane stream. As the particles tend to rise along with the upward flowing propane they are contacted by the second liquid phase which is settling against the rising propane. The more dense second liquid phase collects most of these fine particles. As the propane rises in the tower, its temperature is also raised. The temperature, as explained previously, is raised to the point where some of the dissolved oil plussubstantially all of the objectionable, non-glyceridic impurities come out of solution as a second liquid phase. As this second liquid phase comes out of solution it is in direct intimate contact with any solid particles irrespective of minuteness of size which have reached that position in the tower. As the droplets of the second, more dense liquid phase aggregate to form larger droplets. they encompass these solid particles. The solid particles become a part of the second liquid phase and hence settle against the rising solvent phase. The more dense second liquid phase thus acts as a liquid filter moving counter-currently against the solvent phase in which the solid particles are suspended. Finally, the liquid filter is actually formed around any solid particles which escape the filtering action of the previously formed liquid filter. In this way no solid particles even in extremely divided form leave the tower through the top outlet.
The more dense second liquid phase composed of minute solid particles, triglycerides, objectionable, non-glyceridic substances and the like, settles through the up flowing propane along with the larger solid particles. As the two liquid phases contact each other, the triglycerides in the more dense liquid phase tend to dissolve in the upfiowing propane phase, since the tempera ture of the solvent with which it is coming in contact is progressively lower as the more dense second liquid phase settles in the tower. As the oil in the more dense liquid phase is removed, the minute solid particles aggregate among themselves and also adhere to the larger sized meats with which they are intimately mixed. The nonglyceridic components of the oil that come out of solution as a result of the formation of the second liquid phase act as a cementing agency between the agglomerating fines and the fines and larger sized particles. The non-glyceridic, objectionable constituents of the oil are not only separated from the oil by this procedure but they actually are made to perform a positive function in the handling of the fines.
The pressure within the tower is equal to the vapor pressure of the solvent at the maximum temperature within the tower plus a small superimposed pressure of about 30 pounds per square inch. The meal substantially free from oil plus the fines and the non-glyceridic components not soluble in propane at the temperature prevailing close to the top outlet of the tower leave the extraction tower through a bottom outlet. The pressure within the tower is used to force the settled meal through a valve-controlled outlet into a chamber maintained at a pressure substantially lower than the pressure within the tower and connected with the solvent recovery system. A small amount of propane accompanies the meal. Most of the propane vaporizes at the lower pressure. The meal may be heated indirectly to drive off any remaining propane or may be heated directly with steam to strip off any propane that tends to remain with the meal. In either event the flashing of the propane causes some of the fines to be suspended in the gas stream. These fines must be removed from the gas before it reaches the solvent recovery system since they tend to clog valves and interfere with the operation of the compressor.
The conventional method of recovering propane or a similar solvent mixed with a fatty oil is to distill the solvent under sufficient pressure to that it condenses when cooled to a temperature easily attained by means of the available cooling water. In excess of 90% of the solvent contained in the solution is recovered under these conditions. The remaining solvent is recovered by distilling the fatty oil rich solution at a lower pressure concomitantly with steam stripping. The steam is condensed and the gaseous solvent is fed to the suction side of the compressor. The recovered solvent is purified each time it completes a cycle. The evaporation of the solvent and its condensation requires the consumption of steam and cooling water. In addition suitable equipment is required to evaporate the solvent and to condense it. The cost of recovering the solvent is usually the largest single item of operating expense in a solvent extraction plant.
I have found that by recycling a solvent which is not pure but contains a small amount of fatty oil it is possible to carry out the solvent extraction of fatty oil-bearing material at a lower cost than when all the solvent is purified prior to recycling.
Instead of distilling the fatty oil-solvent solution in the conventional manner, the solution is heated to about the critical temperature of the solvent and under a sufficient pressure to maintain the solvent substantially in the liquid condition. Heating the solution under these conditions causes most of the fatty oil dissolved in the solvent to come out of solution and to form a second liquid phase which is denser than the solvent phase. The solvent under these conditions is able to dissolve but a few percent of its own weight of fatty oil. The fatty oil is able to dissolve a little more than half of its own weight of solvent. The mixture of two immiscible phases are separated. The simplest Way is to pipe the mixture to a pressure vessel sufficiently large to permit the two phases to segregate. The more dense phase is removed from the bottom outlet of the pressure vessel. The less dense phase is removed from the top outlet of the pressure vessel. The solvent contained in the more dense or oil-rich phase is recovered by distillation. The solvent contained in the less dense or solventrich phase is not separated from the fatty oil with which it is admixed. The solvent rich phase is returned to the extraction step of the process. It is preferable to cool the solvent rich phase before returning it to the extractor by putting it in heat exchange relationship with the solvent-oil solution flowing from the extractor to the pressure vessel. By operating in this fashion most of the solvent is recirculated without the necessity of evaporation. The remainder of the'solvent must be evaporated and is substantially pure solvent.
Since two solvent streams of different degrees of purity are returned to the extractor, it is better to keep them separate and to permit them to enter the extractor at different locations. The pure solvent is pumped into the extractor so that it contacts the fatty oil bearing material just prior to its exit from the extractor. The oilcontaining solvent is pumped into the extractor at a point somewhat closer to the outlet of the oil-solvent solution. Thus, the-pure solvent contacts fatty oil bearing material which has already been extracted by the less ure solvent. Operating in this manner permits practically as much oil to be recovered from the fatty oil bearing material as may be recovered by employing a volume of pure solvent equal to the sum of the volume of pure solvent and volume of oil-containing solvent.
As mentioned previously, the preferred solvent is propane although solvents composed of other liquefied, normally gaseous solvents can be used. When propane is employed, a suitable temperature to which the fatty oil-solvent solution may be heated is about 216 F. The mixture is maintained at about this temperature in the ressure vessel prior to the segregation of the two phases.
The modification in which the preponderant amount of solvent that is recirculated contains a small amount of dissolved fatty oils is the preferred method of operation and constitutes an integral part of this invention. While cottonseeds have been selected as an example of a fatty oil bearing material and propane is the preferred solvent, other fatty oil bearing substances can be treated with equal facility and other liquefiable, normally gaseous hydrocarbons or solvents with similar selective properties can be employed without departing from the teachings imparted herein.
1. The process of treating a fatty-oil bearing material containing a substantial quantity of non-oleaginous solids which comprises i .roducing said material into one end of a liquid-solid extraction system, passing the non-cleaginous solids through the extraction system countercurrent to a solvent solution and then out of the other end of the system, said solids after leaving the system, being substantially separated from the oleaginous constituents which dissolve in the solvent solution, introducing into said sys- .bearing material inlet to an outlet, thereby increasing the fatty oil concentration of the solution as it flows through the system; introducing into said system a second solvent solution composed of a liquefied, normally gaseous hydrocarbon substantially free from fatty oil at'a'point between the inlet of the first mentioned recycled solvent solution and the non-oleaginous solids outlet, flowing said second solvent solution counter-current to the solids towards the first mentioned recycled solvent solution inlet to form a solution composed of a liquefied, normally gaseous hydrocarbon and dissolved fatty oil, which solution becomes part of the total solution flowing towards the fatty oil-bearing material inlet to the solution outlet; heating the solution leaving the liquid-solid extraction system to about the critical temperature of the liquefied, normally gaseous hydrocarbon under sufiicient pressure to maintain the hydrocarbon in substantially the liquid phase to thereby form two immiscible liquid phases of difierent density, the less dense phase being composed substantially of most of the hydrocarbon and a minor percentage of oleaginous material and the more dense phase being composed of a mixture of the remainder of the hydrocarbon and the balance 01 the oleaginous material; separating the less dense phase from the more dense phase the separated less dense phase forming the said recycled solvent solution and recycling the same to the said extraction system at a temperature below the temperature at which the two immiscible liquid phases were separated.
2. A process in accordance with claim 1 in which the liquefied, normally gaseously hydrocarbon contained in the separated more dense liquid phase is separated as oil-free solventand is returned to the extraction system as the said sec ond solvent solution.
3. A process in accordance with claim 1 in which the liquefied, normally gaseous hydrocarbon is propane.
4. A process in accordance with claim 2 in which the normally gaseous liquefied hydrocarbon is propane.
5. A process in accordance with claim 1 in which the separated less dense phase constituting the recycled solvent solution is cooled prior to recycling to the extraction system.
6. A process in accordance with claim 1 in which the separated less dense phase is passed in heat exchange relationship with the said solution leaving the liquid-solid extraction system to thereby cool the said separated less dense phase and passing such cooled recycled solvent solution to the said extraction system.
7. A process in accordance with claim 6 in which the liquefied normally gaseous hydrocarbons contained in the separated more dense liquid phase is separated as oil-free solvent and is returned to the extraction system as the said second solvent solution.
8. A process in accordance with claim 6 in which the normally gaseous liquefied hydrocarbon is propane.
9. A process in accordance with claim 7 in which the normally gaseous liquefied hydrocarbon is propane.
OTHER REFERENCES Hixson et al.: Trans. of Am. Inst. of Chem. Engrs., vol. 39, pages 906-908.
Drew et al.: Trans. of Am. Inst. of Chem;
Engrs, vol. 40, page 682.