MASS TRANSFER EXTRACTION OF LIQUIDS FROM SOLIDS

Abstract: An extraction process comprises contacting a material to be extracted with an extracting fluid at an elevated pressure within a defined space, and separating the extracting fluid and extract, as a mass, from the extracted material while reducing the volume of the defined space. The extraction process is conducted in an apparatus as shown in Figure 1, for example. Basically, the extractor (10) comprises a thick-walled cylinder (20) within which is mounted a piston (40). The extractor (10) is operationally positioned within a hydraulic press (50). The piston (40) is adapted to move within the bore of the cylinder (20), thereby defining the variable volume cylinder (42) which serves as the extraction vessel.

Description: MASS TRANSFER EXTRACTION OF LIQUIDS FROM SOLIDS The present invention broadly relates to pro¬ cesses for extracting liquid materials from sol¬ ids, wherein the solids are contacted with an ex¬ tracting fluid at elevated pressure, and a mass transfer is effected to separate the liquid ex¬ tract and the extracting fluid from the solids while the elevated pressure is maintained. Pref¬ erably, the mass transfer is effected with physi¬ cal compaction of the solids. It is generally preferred that the extracting fluid be gaseous at the normal pressure and temperature. The present invention also relates to apparatus for carrying out such processes and specifically contemplates a variable volume extraction vessel and a screw press for use in such extractions. The present invention broadly provides a pro¬ cess and apparatus having maximum flexibility as to time, temperature and pressure conditions ap¬ plied to extract a wide variety of raw materials and, using a wide variety of extraction solvents, produce maximum yields of the product which may be either the extract or the extracted product, with¬ out the need to modify.the equipment. BACKGROUND OF INVENTION The use of liquified gases and supercritical fluids to carry out extractions at high elevated pressure has been described in the prior art. Such prior art processes involve the use of liqui¬ fied gases or supercritical fluids at pressures in excess of 3,000 to 5,000 psi, although in some cases the recommended pressures exceed 10,000 psi. Processes for extractions run at extremely high pressures are described in the following Uni¬ ted States patents: 4,156,688; 4,328,255; 4,466,923; 4,493,854; 4,495,207; and in Applicant's co-pending application Serial No. 732,362 filed May 8, 1985. Generally speaking, these prior art processes separate the extracted material from the residual solids by an elution or dilution process, wherein the supercritical fluids are pumped through the material to be extracted over a period of time, and as the extracting fluid is pumped through the solids, the level of extractable liquid in the so¬ lids is gradually reduced. SUMMARY OF THE INVENTION The present invention is based on the discov- ery that liquids may be advantageously extracted from solids by contacting the solid material to be extracted with selected extracting fluids at ele¬ vated pressure, and separating the fluids (i.e., the extracting fluid and the extracted liquid) in mass from the solids while maintaining the eleva¬ ted pressure, without the need to continuously pump additional extracting fluid through the ma¬ terial being extracted. Preferably, the mass transfer of the fluids from the solids is accom¬ plished while compacting the solids. In the first essential step, the extracting fluid is brought into contact with the material to 5 be extracted at an increased pressure level. The pressure and temperature are selected to provide the desired extraction and separation of the ma¬ terials involved. In the second essential step, the extracting fluid and the entrained or dis- 10 solved liquid extract are separated from the solid residue in mass while the pressure on the system is maintained at the selected level. Preferably, the extracted solid material is compacted, while maintaining the elevated pressure, in order to ex- 15 pel additional extracting fluid and extract. In the process of the present invention, the extracting fluid is preferably a gas at the opera¬ ting temperature and atmospheric pressure. Most preferably, the extracting fluid is a solvent for 20 the components of the material to be extracted. The process of the present invention differs from the prior art processes in effecting a mass transfer to separate the dissolved material from the solids, as distinguished from the prior art 25 processes, which are based on separation through dilution or elution. The present invention con¬ templates the separation of the fluids (i.e., the extracting fluid and the extracted liquids) in a single, continuous, brief operation without the 30 addition of further extracting fluid to the sys- C * * tern. The present invention provides advantages ov¬ er the prior art in the following particulars: 1. The present invention may be carried out in relatively simple apparatus which has few com¬ ponents which are easily maintained. The equip¬ ment cost is relatively low per unit volume of product processed therein. The process can be easily controlled and operated without large num¬ bers of skilled personnel. The process readily lends itself to automatic control. 2. The process is energy efficient in that it can be operated at maximum saturation of the extracting fluid throughout the full transfer cy¬ cle. The mass transfer (or discharge cycle) is relatively short in duration as compared to prior art elution or dilution processes. The present process may be operated with a reduced quantity of extracting fluid. The mass transfer rate may be maximized for the temperatures and pressures sel¬ ected for the extraction operation. The apparatus which forms a part of this in- vention, which is more fully described below, is mechanically efficient. The piston which closes the extraction chamber can be readily removed in and out of the cylinder with ut th * m- bersome manipulation of fasteners and complicated high pressure seals. Material to be processed is rapidly charged and readily removed after the ex¬ traction. The extraction process itself is rapid and can be readily automated to achieve large vol¬ ume production. In one embodiment of the process of the pre¬ sent invention, the material to be extracted is positioned within the extraction vessel where it is contacted with a suitable quantity of the ex- tracting fluid. The pressure on the extracting fluid in the presence of the material to be ex¬ tracted is thereafter increased to the desired el¬ evated pressure, which is selected to achieve the desired condition of extract solubility. When the variable volume cylinder type apparatus is used, the pressure may be increased by charging the cyl¬ inder with extracting fluid and moving the piston into the cylinder until the desired pressure is achieved. Alternatively, the desired pressure level may be achieved by pumping sufficient ex¬ tracting fluid into the cylinder with an external pump to reach the desired pressure. Thereafter, the mass transfer separation of the extracting fluid and extract (which is soluble . or entrained in the extracting fluid) from the solid is effected by discharging the fluids from the cylinder at a controlled rate while the pres¬ sure within the extraction vessel is maintained. The piston is simultaneously moved into the cylin¬ der at a controlled rate, to compensate for the volume of the fluids which are bled off, thus maintaining the pressure within the extraction vessel relatively constant and maintaining the chosen extract solubility conditions. This per¬ mits a mass transfer separation of the extracting fluid and liquid extract from the remaining sol¬ ids, at high pressures, without the need to add more extracting fluid, under conditions in which the solubility of the extracted liquid in the ex¬ tracting fluid is highest, thus producing extrac¬ ted residue which has a greatly reduced level of extractable solubles. The most complete extrac- tion is achieved by physically compacting the ex¬ tracted solid material as the extracting fluid and extracted liquid are removed from the apparatus. The liquid mixture of extract and extracting fluid, which is removed from the cylinder at high pressure, can be effectively and completely separ¬ ated thereafter. The extracting fluid may be re¬ cycled for further extractions. Other objectives, advantages and capabilities of the present invention will become more apparent as the description proceeds, taken in conjunction with the accompanying drawings in which: DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic diagram of a variable volume cylinder extraction apparatus shown in cut¬ away side view; and FIGURE 2 is a schematic diagram of a screw press extraction apparatus, shown in cutaway, side view. APPARATUS - FIGURE 1 Referring to FIGURE 1 of the drawings, varia¬ ble volume cylinder extraction apparatus of the present invention is shown generally at 10. Bas¬ ically, the extractor 10 comprises thick-walled cylinder 20 within which is mounted piston 40. The extractor 10 is operationally positioned with¬ in hydraulic press 50. The cylinder 20 generally comprises a thick- walled stainless steel vessel with a closed bottom 21 having a cylindrical inner surface 22 adapted to mate with piston 40. Piston 40 is adapted to move within the bore of cylinder 20, thereby de¬ fining the variable volume cylinder 42 which serves as the extraction vessel. Piston 40 is re¬ movable from cylinder 20 in order to allow charg¬ ing of the material to be extracted 60. Preferab¬ ly the shape of the bottom 21 of the cylinder ap- proximates the shape of lower face 44 of piston 40, so that when the piston 40 is fully lowered, the effective volume of cylinder 42 is minimal and the material to be extracted 60 may be compacted under considerable force. The outer wall 24 of cylinder 20 defines wall 26 which is sufficiently strong to maintain the desired pressures, e.g., 15,000 psi., with an appropriate safety factor. It is preferred that the length of cylinder 20 be sufficient to maintain piston 40 in an axial alignment with the cylinder wall 26. Similarly, piston 40 must have sufficient length to maintain the axial relationship with the inner surface 22. Seal 46 on piston 40 provides a pressure seal ade¬ quate to avoid loss of pressure in the cylinder at the operating pressures, e.g., 15,000 psi or high¬ er. The seal may comprise an O-ring within a cup, but other forms of seals may also be used. Ex¬ tracting fluid charging port 32, within piston 40, is adapted to introduce the extracting fluid axi- ally into the cylinder 20 at the desired pres¬ sures. Extracting fluid charging port 32 is con¬ nected through valve 33 to an extracting fluid supply (not shown). At the cylinder bottom 21, liquid discharge port 34 connects the cylinder to a recovery vessel (not shown) through discharge valve 36. Perfora¬ ted plate 37 and gauze pad 38 are installed in the bottom of the cylinder above discharge port 34. The perforated plate 37 has a plurality of holes through its thickness and preferably has grooves in the bottom interconnecting the holes and dis¬ charge port 34. The perforated plate 37 and gauze pad 38 allows the extracting fluid-extract mix to be discharged over the whole area of the piston and to prevent the solid material being extracted 60 from being forced into discharge port 34. A pressure gauge 35 is connected to discharge line 34 in a manner to read on the pressure at the base 21 of cylinder 20. A similar gauze pad and per¬ forated plate (not shown) may be used above the material to be extracted 60 and below piston 40 to distribute the extracting fluid from charging port 32 over the whole area of the piston and to avoid any blockage of charging port 32. The hydraulic press 50 must be large enough to accommodate the variable volume cylinder 10, and strong enough to move piston 40 into the cyl- inder 20 to create or maintain the desired pres¬ sures and to maintain the desired pressures as the liquids are removed from the cylinder. Generally the variable volume cylinder 10 rests on and is supported by base 52 of hydraulic press 50. The piston 54 of the hydraulic press couples with the upper portion of piston 40 and is adapted to move piston 40 vertically. Gauge 56 is connected to the hydraulic system of the press and reads the force being exerted on cylinder 20 by the hydrau- lie press 50. It is preferred that inner surface of cylin¬ der 22 be smooth and free from surface blemishes, including inlet or outlet ports. Accordingly, it is preferred that the extracting fluid charging port 32 be arranged within the piston 40, and that the discharge port 34 be positioned axially, or below the piston. In this embodiment, the piston seal 46 will not encounter any discontinuous sur¬ faces in the face of the cylinder wall. In order to operate the apparatus of FIGURE 1, the piston 40 is removed from cylinder 20 and the material to be extracted 60 is charged into the cylinder 20. Piston 40 is then placed in cyl¬ inder 20 as shown in FIGURE 1 where it forms a gas-tight seal above charging port 32. It may be desirable to purge air from the cylinder using the extracting fluid in order to remove any oxygen or other gases not required or desired for the ex- . traction process. This may be done by charging the extracting fluid through port 32 while valve 36 is open. After any required purging has been acco - pushed, valve 36 is closed and the charging of the extracting fluid is continued until the de¬ sired level of extracting fluid has been charged to the cylinder through port 32. The amount of extracting fluid charged may vary over wide limits, depending upon the nature of the fluid, the nature of the material to be ex¬ tracted and the type of process to be used. The examples which follow illustrate the use of carbon dioxide to extract wheat germ wherein equal weights of gas and material to be extracted are used, as well as processes wherein the weight of the gas is several times the weight of the materi¬ al to be extracted. As those skilled in the art might expect, the process employing greater a- mounts of gas provided greater yield of extract. The present invention also contemplates the use of less gas than solids, although it is generally be- 55 lieved the yield of extract will be diminished. As is explained above, the desired pressure within the extraction vessel may be achieved ei¬ ther by charging sufficient extracting fluid to achieve the pressure without movement of the pis- ID? ton or, alternatively, by charging a lesser amount of extracting fluid and achieving the desired pressure by moving the piston down into the cylin¬ der. The pressure used will be dependent upon the nature of the extracting fluid used and the mater- 15 ial to be extracted. Pressures of about 12,000 psi are useful for extracting wheat germ and soy¬ beans with CO2. The temperature at which the pro¬ cess takes place may vary over wide limits, de¬ pending upon the nature of the solids, the extrac- 20. ting fluid and the pressure used. The temperature is selected to achieve the desired level of solu¬ bility of the extract in the extracting fluid. In connection with the extraction of certain materials using certain extracting fluids, it may 25 be desirable to allow an induction period wherein the material to be extracted is allowed to remain in contact with the extracting fluid at selected temperatures and pressures for a limited period of time. 30/ After any required induction period has been completed, the extracted liquid and extracting fluid are then separated as a mass from the solids extracted. In the simplest case, pressure reduc- tion valve 36 is opened slightly to slowly bleed off the mixture of extracting gas and extracted liquid from cylinder 42 through outlet 34. The downward movement of the piston 40 into cylinder 20 is continued at a coordinated rate necessary to maintain the pressure in the extraction vessel at the desired level to maintain the solubility of the extract. The downward movement of the piston is continued until the charged solids become es- sentially a solid mass at which time the pressure generated by the hydraulic press, as shown by gauge 56, rises with little further downward move¬ ment of the piston 40. The discharge of the flu¬ ids through discharge valve 36 can be continued, but the pressure shown at gauge 35 does not in- . crease because at this point essentially all of the extracting fluid has been bled from the cylin¬ der along with the extracted liquid. The material to be extracted may be partially compacted before it is placed into the cylinder for extraction, but extensive compaction is pref¬ erably avoided. There is no general requirement for any pretreatment of the material to be extrac¬ ted. In other words, seed which are whole, flaked or steamed prior to treatment may be used, but the yields may differ depending upon the seed used and the particular pretreatment. Using the apparatus shown in FIGURE 1, the material to be extracted is charged by removing piston 40 from cylinder 20. The present invention contemplates a wide variety of charging mechan¬ isms. For instance, an open ended cylinder may be equipped with two opposed pistons which are timed to charge and discharge cakes of the material to be extracted. The use of a cylinder with two open ends provides advantages as to fabrication and maintenance. Alternatively, the cylinder may be equipped with an axial breach lock mechanism to permit the opening of the bottom of the cylinder to load the material to be extracted without the need to remove the piston from the cylinder. Breach lock mechanisms, such as are used in large guns which are secured by interrupted threads and suitable sealing mechanisms, may be used. If de¬ sired, the outlet port for the cylinder, including the necessary valving, may be built into the breach block mechanism. The present invention is not limited to any specific ratio of piston diameter to piston stroke. Generally speaking, it is contemplated that -increasing the ratio of the piston stroke to the piston diameter is advantageous for the ex- traction of materials containing a relatively high level of extractables. The apparatus of FIGURE 1 provides for great flexibility in carrying out the process of the present invention in that the time, temperature and pressure used to carry out the extraction for various raw materials can be readily selected and controlled without the need to modify the equip¬ ment. The type and amount of solvent may be var¬ ied and controlled, again without the need to mod- if the equipment. APPARATUS - FIGURE 2 The apparatus illustrated in FIGURE 2 is fun¬ damentally a screw press or screw mill or expeller type device 100 which comprises a screw 110 within barrel 120. Barrel 120 is closed at the input 122 end and at output end 124 is precision fitted with adjustable cone valve 126, which has a shape com- plimentary to tapered opening 128 in barrel 120. Screw 110 is driven by drive means 108. Screw mill 110 is divided into four different sections, namely sections 112, 114, 116 and 118, wherein the flights of the screw in these sections are con- structed to carry out different functions. At the input end of the press 100, the screw flights in section 112 are designed to form a plug of material to be extracted. The screw flights in section 114 are designed to masticate the compres- sed plug while extracting fluid is injected at el- . evated pressure into the barrel of 120 of mill 100. The mastication of the plug is essential to achieve intimate mixing of the extracting fluid with the material to be extracted. The mastica- tion may be achieved through the interrupted flights and/or fingers or dams or other flow re¬ stricting devices within the barrel. The objec¬ tive of section 114 is to masticate the material to be extracted in contact with the compressed ex- tracting fluid at the desired temperature and pressure. The screw flights in section 114 trans¬ port the mixture of the extracting fluid and ma¬ terial to be extracted to section 116, which pro¬ vides for a controlled release of the extracting fluid-extract mixture into manifold 160 through porous sieve 162. Finally, the solids move by the screw flights in section 118, to transport the so- lids to output end through adjustable precision fit cone valve 126. Material feed means 140 is designed to feed the material to be extracted to the screw press at the input end in section 112. The feed means may include feed hopper 142 and feed screw 144. The solvent gases may be injected into the screw press using a variety of mechanisms. In the preferred embodiment, barrel 120 includes extrac- ting fluid inlets 150, around periphery of barrel 120, which surrounds section 114 of the screw, in a manner which permits injection of the extracting fluid while maintaining the pressure at the de¬ sired levels, e.g., 12,000 psig. Fluid inlets 150 communicate with an extracting fluid supply (not shown) through manifold 152. Alternatively, the extracting fluid may be injected into the screw press 100 through an axial opening 154 in screw 110, which communicates with inlet openings 156 in section 114 of screw 110. Recovery zone 160 generally comprises an an¬ nular porous sieve 162, adapted to communicate fluid pressure in section 116 to pressure housing 164 through barrel 120. In this embodiment, the pressure within housing 164 is controlled to pro¬ vide a suitable pressure drop between the interior of the screw press at section 116 and the recovery system so that high pressure extracting fluid-ex¬ tract mixture emerges from the screw press to re- covery system 160. After passing through recovery zone 116, the extracted solids are transported through zone 118 to opening 124, at which time they are discharged from barrel 120 through adjustable precision fit cone valve 126, thus emerging as a compacted solid at atmospheric pressure. In operation, the material feed hopper 142 may be filled with soybean flakes or a similar ma¬ terial to be extracted. Feed screw 144 forces the soybean flakes under pressure into the screw press at section 112 where a plug of material to be ex¬ tracted is formed. In section 112, the flights of screw 110 are adjacent to the inner surface of barrel 120. The screw is turned at a rate which causes compaction of the input flakes sufficiently to withstand the desired operating pressures of the extraction, and prevent any blow back of high pressure extracting fluid. The compacted flakes . are then transported to section 114. At this point, the flights of screw 110 do not create any further compaction or any increase in pressure, • but permit the extracting fluid from inlets 150 and/or 156 to contact and mix with the compacted material to be extracted. The material to be ex¬ tracted is thus mixed with the extracting fluid while the mixture is transported from section 114 into section 116. Within section 116 the flights of screw 110 are separated from porous media 162 in order to build up a slight cake of solids which function as a filter which helps to avoid the extrusion of so¬ lids into the porous media 162. The porous media 162, however, permits the fluid materials to bleed through from the section 116 to recovery area 160. As this happens, the solids are progressive¬ ly transported from section 116 to section 118. No further compaction is required in section 118. The extracted material is transported to the ad¬ justable cone valve solids outlet 126 for dis¬ charge and recovery. The internal system pressure will assist the transport of solids to and through the precision cone valve 126. THE EXTRACTING FLUID In carrying out the invention, a wide variety of extracting fluids may be used. Although most of the examples herein below illustrate the use of carbon dioxide to extract lipid oils from seed vegetables, the present invention is not limited to any specific extracting fluid. Generally it is preferred to use an extrac- ting fluid which is normally gaseous. However, one may also use fluids which are liquid at normal conditions, but which are gaseous at the extrac¬ tion temperature and at atmospheric pressure. Ex¬ tracting fluids which are gaseous provide enhanced mass transfer separation of the extracted liquid from the extracted solids. Gaseous extracting fluids may be readily separated from extracted li¬ quids, which provides obvious advantages. It is most preferred to employ as the extrac- ting fluid a substance which is gaseous at operat¬ ing temperature and atmospheric presure and which under the conditions of the extraction, functions as a solvent for the extract or some portion of the extract. As is illustrated by the examples, at least under some conditions, extracting fluids having solvent properties provide higher extract yields. However, as is demonstrated by Example 4, below, non-solvent gases such a nitrogen are ef- fective and may be desirable in that they do not produce the pronounced refrigeration effect pro¬ duced by carbon dioxide and some other solvent type gases. Other useful gases include nitrogen, nitrous oxide, freons, low molecular weight hydro¬ carbons such as ethane or propane and mixtures thereof. The present invention contemplates the use of hexane, isopropanol, propylene glycol and other solvent-type materials as the extracting fluid. Liquid solvents may be employed for some purposes either alone or with gaseous extracting fluids. Mixtures of extracting fluids and multi¬ ple or sequential extractions using different ex¬ tracting fluids are also contemplated. In one embodiment, a supercritical fluid, . such as carbon dioxide, is used under conditions which cause liquefication. It is preferred to use the carbon dioxide at temperatures and pressures which provide for supercritical conditions, i.e., above 31.1°C. and above 73.8 bar. If gases other than carbon dioxide are used, the ranges with re¬ spect to the temperatures and pressures outlined hereinafter in the specification can be obtained from data described in handbooks of physical che - istry. The present invention also contemplates mix¬ ing the material to be extracted with the extrac¬ ting fluid before the material to be extracted is charged to the extraction vessel. For example, carbon dioxide, in the form of dry ice, may be premixed with the oil seeds and the mixture of dry ice with the oil seeds thereafter charged to the extraction vessel. It is contemplated that the addition of solid dry ice particles to oil seeds prior to passing the oil seeds through a conven¬ tional screw press in a deoiling process would en¬ hance the recovery of oil from such a process. EXTRACTING TEMPERATURE A wide variety of temperatures may be em¬ ployed in operating the equipment of the apparatus of the present invention. Although the examples which follow illustrate the use of temperatures in the 40-100°C range to extract oil seeds, higher temperatures may be preferable in that the ex¬ tracting fluids are more mobile even though they may be somewhat less effective as solvents at higher temperatures. Such factors as the moisture in the material to be extracted can vary the opti¬ mum conditions for carrying out the extraction. The present invention also contemplates the use of much higher temperatures, e.g., 500°C, wherein the apparatus functions as a chemical au- toclave. It is postulated that selected reactions could be carried out in a shorter reaction time, with less solvents and increased yield. EXTRACTING PRESSURE Although the examples which follow illustrate the use of 12,000 pounds per square inch pressure within the extraction vessel on oil seeds, the present invention is not so limited. A wide vari¬ ety of pressures, extracting fluids and operating temperatures and pressures may be used. The pre- sent invention further contemplates the extraction using variable pressures during the extraction process. It is considered essential to maintain the pressure in the extraction vessel, while the ex¬ tracting fluid-extract mixture is separated from the extracted solids and discharged from the ex- traction vessel. The pressure in the extraction vessel, however, need not be the maximum pressure of the extraction, nor is it necessary to maintain a uniform pressure in the extraction vessel throughout the separation. For certain materials, it may be desirable to permit a dwell time wherein the extracting fluid is maintained under pressure in contact with the material to be extracted. COMPACTION A preferred embodiment of the present inven- tion contemplates the compaction or physical crushing of the material to be extracted in order to expel the maximum amount of extract. The com¬ paction functions to enhance the mass transfer se¬ paration of the extracting fluid and the extracted liquid from the solid residue. In the case of seed vegetables, it is postulated that the compac¬ tion will rupture cells and thus enhance the availability of the oil in the cells. Tests have shown that using the apparatus of FIGURE 1 that an extraction without compaction will produce a cake with as much as 3% retained oil, while an extrac¬ tion run under generally the same conditions, but with compaction, will produce a cake with less than 1% of retained oil. It has been found that using the variable volume cylinder described above and shown in FIG¬ URE 1, that better yields of the extracted liquids are achieved by charging sufficient material to be extracted into the cylinder to form a cake of some depth, e.g., one inch thick, after compaction. It is postulated that a thick cake is less prone to channeling of the extracting fluid than a rela- 5 tively thin cake. RECOVERY OF EXTRACT The oil which is bled off through the dis¬ charge valve along with the liquefied carbon diox¬ ide may be recovered simply by allowing the carbon ID: dioxide to volitalize. Alternatively, the carbon dioxide-oil mix¬ tures removed from the variable volume cylinder may be retained under reduced, but substantial pressures, e.g., 1,500 psi. Under such condi- 15. tions, the solubility of the oil in the carbon di- . oxide is significantly reduced and the recovery of the oil from the gas may be accomplished without volatilizing the gas. The carbon dioxide may be retained at elevated pressure, e.g., 1,500 psi, 2D? for recycling through the extraction vessel. MATERIALS EXTRACTED The process and apparatus of the present in¬ vention may be applied to extract of a wide vari¬ ety of liquids from a wide variety of solid mater- 25 ials. Although the word "liquid" has been and hereinto define the "extract" of the extraction process, the process of the present invention may be used to separate solid extracts, such as waxy materials, or solids which are soluble in the ex- 0 tracting fluid from the solid material being ex¬ tracted. The present invention also contemplates the extraction of liquids from other liquids or semi-solid materials. As is illustrated by the examples, the pre¬ sent invention may be adapted to extract a wide variety of liquids from organic matter, including the extraction of oils from wheat germ and soy- beans. The present invention also contemplates extracting caffine from coffee or tea, hops ex¬ traction, the extraction of residual oils from various substances including petroleum products from oil shale or tar sands. It is further con- templated that the processes and products of the present invention may be used to recover diluted solvents from water, diesel oil from drilling muds and other compounds, to regenerated activated car¬ bon and other adsorbants which are contaminated with organics, coal liquefication or extraction, removal of impurities from polymer melts, separat¬ ing waxes and resins from residual oil, delignifi- cation and pulping of wood, oxidation of hazardous wastes and deashing synthetic fuels. The process and apparatus of the present in¬ vention may be used to extract colors, flavors, essences and medicinal products, such as drugs, from such natural products as roots, bark, leaves, flowers and seeds. For example, colors may be ex- tracted from annato, turmeric and cochineal; oleo- resins may be extracted from roots and the like. Similarly, animal based products, such as glands, liver, pancreas and spinal cord may be extracted. The present invention also may be used to produce marine source products, such as separation and concentration of selected fatty acids from marine lipids. The process and apparatus of the present in¬ vention is particularly useful in carrying out the extraction of oil from seed vegetables as is de¬ scribed in U.S. Patent No. 4,493,854 to Friedrich and Eldridge, the extraction of lipids from lipid containing materials as described in U.S. Patent No. 4,466,923 to Friedrich, and the production of food grain corn germ as described in U.S. Patent No. 4,495,03 to Christianson and Friedrich, in ex- tracting coffee oil from roasted coffee as de¬ scribed in U.S. Patent No. 4,328,255 to Roselius, Vitzthum and Hurbert, and in fractionating butter- fat as described in U.S. Patent No. 4,504,503 to Biernoth et al. The following examples will serve to illus¬ trate the process of the present invention and the apparatus thereof in extracting several oil seeds, but it is understood that these examples are set forth for illustration and many other products may be extracted using suitable variations. Examples 1, 6 and 12 do not illustrate the present inven¬ tion, but are set forth for comparative purposes. All examples were conducted in an apparatus similar to that depicted by FIGURE 1. EXAMPLE 1 The cylinder had an outside diameter of 5 inches and was 11-3/4 inches high with a central bore 2-1/4 inches in diameter and 9-3/8 inches long. The piston was 10 inches in length and 2- 1/4 inches in diameter, which gave it an effective area of 3.96 square inches. The effective stroke of the piston was about 5 inches. A wad of gauze 38 was placed at the bottom of the cylinder above perforated plate 37. The cyl¬ inder was charged with 100 grams of full-fat wheat germ meal containing about 10.5% fat. A wad of gauze was placed over the charge of wheat germ meal and a perforated plate was placed on top of the gauze. Valve 36 was opened to permit the es¬ cape of any gases in the system. Valve 33 was closed throughout the experiment. The piston was inserted in the cylinder and hand closed. The uncompressed cake was about 4 inches high. The cylinder was maintained at a temperature of about 90-95°C throughout the exper¬ iment. The hydraulic press was engaged and the piston moved downwardly 2.75, at which time gauge 56 showed a reading of 30 tons, which is approxi¬ mately 15,000 psi pressing on the cake in the cyl¬ inder. The cake was about 1.25 inches thick and had a specific gravity of 1.1. No oil was dis- charged from the apparatus during this experiment, although traces of oil could be seen on the gauze. EXAMPLE 2 Using the apparatus described in Example 1, 100 grams of full-fat wheat germ meal were placed in the cylinder. Cotton gauze and a perforated plate were placed on top, according to the proce¬ dure of Example 1. The cylinder was maintained at 90-93°C. Valve 36 was closed and carbon dioxide was charged to the system through valve 33 to a pressure in the cylinder of 1,100 psi. This charged about 100 grams of CO2 into the cylinder. When the charging had been accomplished, gauge 56 read about 2 tons which is equivalent to 1,000 psi in the cylinder. Valve 33 was closed and piston 40 was lowered until gauge 35 showed the gas pres¬ sure within the cylinder was 12,000 psi. At this point, valve 36 was opened to permit the discharge of a mixture of CO2 gas and wheat germ oil, while the piston was lowered to hold the pressure at 12,000 psi. About 7 grams of a very cold, thick oil emerged from valve 36 during a 30-40 second inter- val. The operation of the hydraulic press was continued until the force shown by gauge 56 began to rise above 24 tons, which was equivalent to 12,000 psi within the extraction cylinder, without any increase in the gas pressure shown by gauge 35. The resulting compressed cake was smaller than the cake produced in Example 1 and had a lighter color. The cake had about 4% retained oil which indicates about 60% of the original oil was removed. EXAMPLE 3 Using the equipment and procedure of Example 1, 100 grams of wheat germ was placed in the cyl¬ inder and CO2 gas was charged continuously until about 12,000 psi was reached. This provided a ra¬ tio of 3 parts of gas by weight for each part of meal. A few seconds after the operating pressure of 12,000 psi was reached, the carbon dioxide-wheat germ oil was bled off through valve 36 while main¬ taining the pressure with a hydraulic press. Again, the pressure was maintained on the cake un¬ til all of the CO2 and dissolved wheat germ oil had been discharged. The resulting cake contained 1.1% oil (based on an ether extract). Similar to Example 2, continued pressure on the cake with the hydraulic press did not dis- charge any additional oil. EXAMPLE 4 Using an apparatus described in Example 2, the cylinder was charged with 100 grams of full- fat wheat germ meal and pressurized with nitrogen gas to 2,500 psi. The piston was lowered using the hydraulic press to achieve 12,000 psi whereup¬ on valve 36 was opened to discharge the nitrogen gas and entrained oil. As the nitrogen was re¬ moved, a quantity of oil was recovered. The piston was raised and the cylinder was again charged with 2,500 psi of nitrogen (at 92° C) . Again, the piston was lowered to achieve 12,000 psi and the nitrogen-entrained gas was dis¬ charged through valve 36. An additional quantity of oil was recovered leaving a residual fat of about 5% in the cake (based on ether extract). The cake had a similar appearance to the cake in Example 2. The use of nitrogen gas, as illus¬ trated in Example 4, was found advantageous in that nitrogen does not demonstrate a pronounced refrigeration effect. Thus, problems with freeze up of valves and plugging of lines are largely avoided through the use of nitrogen. EXAMPLE 5 A variable volume cylinder similar to that shown in FIGURE 1 was used, but the cylinder had a gas injection port through the sidewall of the cylinder near the top of the cylinder. The cylinder was charged with 40 grams of full-fat, raw soybean flakes. The piston was put in place to form a gas tight seal above the gas * injection port. The cylinder was flushed with carbon dioxide to thoroughly purge any air. Valve 36 was then closed. The temperature of the cylinder was heated to 52°. The heaters were turned off and CO2 at 1,300 psi was applied to the cylinder until the flow stopped. Approximately 2 parts by weight of CO2 were used for each part by weight of soy flakes. The gas charging valve 33 was closed and the pis¬ ton was gradually lowered using the hydraulic press. At the beginning of the downstroke, the piston was 5 inches from the bottom of the cylin¬ der. When the piston was 1.75 inches from the bottom, the pressure in the cylinder was 12,000 psi. At this point the pressure release valve was opened to bleed the Cθ2~soybean oil off at a rate sufficient to maintain the pressure at 12,000 psi, while the piston was continuously lowered. When the piston was to 0.75 inches above the bottom, essentially all of the gas had been removed from the cylinder and the pressure on the hydraulic press rose to 30 tons without any further increase of extraction fluid pressure within the extraction vessel. The piston was removed and the soybean flake residue recovered. The process, which con- sumed approximately 5 minutes, reduced the oil content of the soybean flakes from 17.6% to 3.7%, as determined by ether extraction. The approximate dynamics of Example 5 are shown in Table I below. TABLE I Press Trial Piston-Inches Pressure Cylinder Minutes From Bottom Tons Pressure 0 5 3 1,300 0.2 4 4 1,400 0.4 3 5 1,500 0.6 2.5 10 1,700 0.8 2 18 4,000 1.0 1.75 24 12,000 3.0 1.25 24 12,000 5.0 0.75 30 12,000 EXAMPLE 6 The apparatus of Example 5 was charged with 100 grams of full fat, soy flakes, which included the hulls of the beans. The soy contained approx¬ imately 17% fat and 12% moisture. The soy flakes filled occupied the lower 3 inches of the cylin¬ der. The piston was inserted and the cylinder was purged with carbon dioxide. After purging, valve 36 was closed and the cylinder charged to 1,500 psi with C02« Using an external pump, additional CO2 was pumped into the cylinder until the pres¬ sure reached 12,000 psi. This provided 3 parts by weight of CO2 for every one part by weight of soy¬ bean meal. The flakes were permitted to soak in the pressurized CO2 for 20 minutes. The temperature of the cylinder was heated to 51°C. and the pressure release valve was opened to bleed off the Cθ2~soybean oil at the bottom of the cylinder while additional CO2 was pumped into the top of the cylinder at a rate sufficient to main¬ tain the pressure at 12,000 psi. The pumping of 5 the CO2 at 12,000 psi was continued until 30 parts by weight of gas for each part by weight of soy¬ bean flakes had been passed through the soybean flakes. The CO2 initially emerging from the cyl¬ inder was saturated with soybean oil, but as the ITT * process continued the amount of soybean oil in the gas declined. The piston was not lowered during this test. The CO2 emerging at the end of the process contained essentially no oil. Analysis of the cake showed that it contained 2.62 retained 15 oil (based on an ether extraction). EXAMPLE 7 Using the apparatus described in Example 1, the cylinder was again loaded with 100 grams of full-fat soy flakes described in Example 6. The 20 cylinder was purged using Cθ2f after which the cylinder was charged to 1,500 lbs. using CO2. An external pump was used to increase the CO2 pres¬ sure to 12,000 psi which gave a weight ratio of 3 to 1 gas to meal. This again was allowed to soak 25 for 20 minutes at 65°C. After the soaking, the pressure release valve was opened to start to bleed out the Cθ2~soybean oil mixture while the piston was lowered to main¬ tain the pressure at 12,000 psi. The process con- 30 " tinued until the cake was compressed from the ini¬ tial 3 inches to 1 inch. The resulting cake contained 2.39% retained fat (based on an ether extract) and a moisture of about 13.42. This indicates little, if any, mois¬ ture was extracted, but only one-tenth the amount of gas was used as compared to Example 6. EXAMPLE 8 Using the apparatus described in Example 1, 100 grams of soybean flakes, as described in Exam¬ ple 6, were charged into the cylinder. The cylinder was purged with nitrogen at 2,800 psi and then the purge valve was closed and the nitrogen was charged to 2,800 psi. An extern¬ al pump was used to pump additional nitrogen into the cylinder until the pressure reached 12,000 psi. This was allowed to soak for 20 minutes at a temperature of 55-63°C. The pressure release . valve was OD t a w the nitrogen-soybean oil to bleed out of the cylinder while the piston was lowered to maintain the pressure at 12,000 psi. No refrigeration affects were noticed by the re- lease of the nitrogen. No oil was noted in the initial discharge of the nitrogen, while the ram was closed from 5 inches to about 2 inches. How¬ ever, during the last 1 inch stroke of the piston, a great volume of oil was released with the nitro- gen. Analysis of the soybean flake cake retained in the cylinder showed 2.36% retained oil with a moisture content of 13.07. The soybean meal recovered from the cylinder has a specific gravity of about 1.1 which is ap¬ proximately the same as the specific gravity of CO2 at 12,000 psi. EXAMPLE 9 An extraction procedure was carried out in the same manner as in Example 8, except that Argon gas was used in place of nitrogen. The retained soybean cake contained 9.61% retained fat and a moisture of 13.37%. This indicates Argon did not have the same affect as nitrogen with respect to the extraction of oil from soybean flakes. EXAMPLE 10 The apparatus of Example 1 was charged with 33 grams of raw wheat germ meal. The meal con¬ tained approximately 9% by weight of fat and about 13% by weight of moisture. Using the procedure of Example 7, the cylin- der was purged with 1,500 psi CO2. The purge valve was closed and the CO2 was admitted until 1,500 psi was reached. CO2 was then continuously added by an external pump until 12,000 psi was reached. This provided 11 parts by weight of gas to each part by weight of meal. The temperature was maintained at 66°C. After a dwell time of about 1.5 minutes, the discharge valve was opened and the piston was low¬ ered to hold the pressure at 12,000 psi. The discharge of the CO2-0U required about 3-1/2. minutes to complete. The wheat germ cake was recovered and analyzed to show it retained about 0.74% of the fat (based on ether extract). EXAMPLE 11 The apparatus of Example 1 was charged with 100 grams of wheat germ meal in the manner of Ex¬ ample 10. The cylinder was pressurized with CO2 to 12,000 psi. The pressure release valve was opened and the CO2 gas with the entrained wheat germ oil was allowed to bleed off until the pres¬ sure in the cylinder reached 4,000 psi. This re¬ quired about 24 seconds. The piston was then low- ered, maintaining the pressure at 4,000 psi. The wheat germ cake was recovered and ana¬ lyzed. It contained 1.94% of retained fat. EXAMPLE 12 Another extraction was run in the manner of Example 10, wherein 33 grams of wheat germ were charged into the cylinder which was then charged to 12,000 psi with carbon dioxide. This gave a ratio of 11 parts of gas by weight to 1 part of wheat germ by weight. After soaking for 5 min- utes, the CO2 was allowed to bleed off while main- . taining the temperature at 46°C. The bleeding was allowed to reduce the cylinder to 1,500 psi. Thereafter, the cake was flushed with CO2 for 5 minutes using 1,500 psi CO2. The cake was recovered. Analysis indicated the cake had 6.19% retained fat. EXAMPLES 13 - 16 Examples 13 through 16 were carried out in apparatus illustrated by FIGURE 1 and described in Example 1. In each case, 100 grams of wheat germ containing 10.5% fat was placed in the cylinder and moistened with the co-solvent shown in Table II below. In Examples 13 through 15, carbon diox¬ ide was then charged to 950 psi and the piston was lowered to achieve a pressure of 4,000 psi. Mass transfer separation of the CO2, co-solvent, and dissolved oil from the solids was carried out at 4,000 psi. The retained fat of the solids cake is also shown. In Example 16 no carbon dioxide was used, but the cake was compacted to 12,000 psi in the pres¬ ence of the isopropanol. It is estimated that the extraction of wheat germ using the above amounts of isopropanol or hexane without carbon dioxide and without high pressure would produce a cake having 6-8% retained fat. The results of Examples 13 through 17 are shown in Table II. TABLE II Wheat 11 1__ 11 11 Germ - g 100 100 100 100 Co-Solvent Isopro¬ Hexane Isopro¬ Isopro panol panol panol Co-Solvent Amount 50 ml 50 ml 25 ml 50 ml CO2 Charge 950 950 950 psi psi psi None CO2 Pressure 4,000 4,000 4,000 psi psi psi None Compaction 4,000 4,000 4,000 12,000 psi psi psi psi Retained Fat % 1.26 1.76 2.56 2.98 EXAMPLE 17 The apparatus described in Example 1 was charged with 100 grams of crushed, whole rapeseed, including some hull fragments. The charged solids contained 42.6% oil, by weight. Carbon dioxide was charged to the system to 11,000 psi at a temperature of 55°C. This gave a ratio of 3 parts by weight of carbon dioxide for each part by weight of seed. Following the proce- dure of Example 3, the piston was lowered and the carbon dioxide-rapeseed oil mixture was dis¬ charged. The rapeseed oil was recovered. The resulting cake, in two similar experi¬ ments, contained 7.57% and 9.86% retained oil by weight, based on ether extract. This indicates that about 85% to 90% of the oil was extracted from the seed. The scope of the invention herein shown and described is to be considered only as illustra- tive. It will be apparent to those skilled in the . art numerous modifications may be made therein without departure from the spirit of the invention or the scope of the appended claims.

Claims: I CLAIM: 1. A method of extracting liquids from so¬ lids which comprises: contacting a solid material to be extrac¬ ted with an extracting fluid at a selected elevated pressure within a defined space; and separating said extracting fluid and ex¬ tracted liquids as a mass from said solid ma¬ terial while reducing the volume of said de¬ fined space and while maintaining elevated pressure within said space. 2. A method as described in Claim 1, wherein said solid material is compacted as the volume of said space is reduced. 3. A method as described in Claim 1, wherein said extracting fluids and extracted liquid are separated without added extracting fluid. 4. A method as described in Claim 1, wherein the pressure in the separation step is at least as high as the pressure in the contacting step. 5. A method as described in Claim 1, wherein said extracting fluid is gaseous at the tempera¬ ture of the separating step and atmospheric pres¬ sure. 6. A method as described in Claim 1, wherein said extracting fluid comprises a solvent for said extracted liquids at the temperature and pressure of the contacting step. 7. A method as described in Claim 1, wherein the extracting fluid and extracted liquid are se¬ parated from said solid material by discharging said extracting fluid and extracted liquid to an environment of lower pressure. 8. A method as described in Claim 7, wherein the space occupied by the solid material and the extracting fluid is reduced at a rate adapted to maintain said elevated pressure within said space as said extracting fluid and extracted liquids are discharged. 9. A method as described in Claim 1, wherein said solid material is physically compacted as the extracting fluid and extracted liquids are separa¬ ted from said solid material. 10. A method as described in Claim 1, com¬ prising the additional steps of separating extrac¬ ting fluid from the extracted liquid, recovering said extracted liquid and recycling the separated extracting fluid. 11. A method as described in Claim 1, wherein the material to be extracted is a lipid bearing vegetable seed. 12. A method as described in Claim 11, where¬ in the seed is soybean. 13. A method as described in Claim 11, where¬ in the seed is wheat germ. 14. A method as described in Claim 11, where¬ in the seed is rapeseed. 15. A method as described in Claim 5, wherein the extraction fluid is Cθ2« 16. A method as described in Claim 5, wherein the extraction fluid is nitrogen. 17. A method as described in Claim 5, wherein the extraction fluid is argon. 18. A method as described in Claim 5, wherein the extracting fluid is a mixture of a gas and a liquid solvent. 19. An apparatus for extracting liquids from solids at high pressures which comprises: an extraction vessel adopted to confine a solid material to be extracted; means to contact said confined solid ma¬ terial with an extracting fluid; means to increase the pressure within said extraction vessel; and means to effect a mass transfer separa- tion of said extracting fluid and extracted liquids from said confined solid material while increased pressure is maintained within said extraction vessel. 20. An apparatus as described in Claim 19, which includes means to charge said solid material before said extracting fluid is charged into said extraction vessel. 21. An apparatus as described in Claim 19, which includes means to physically compact said solid material as extracting fluids and extracted liquid are separated. 22. An apparatus as described in Claim 19, which includes means to separate said extracting fluid and extracted liquid from confined solids by discharging said extracting fluid and extracted liquid from said extraction vessel into an envi¬ ronment of lower pressure. 23. An apparatus as described in Claim 22, which includes means to reduce the volume of said extraction vessel at a rate adapted to maintain said elevated pressure within said vessel as said extracting fluid and extracted liquids are dis¬ charged. 24. An apparatus as described in Claim 23, which includes means to physically compact said solid material as the extracting fluid and extrac¬ ted liquids are discharged. 25. An apparatus as described in Claim 22, comprising means to separate discharged extracting fluid from the extracted liquid and recycle the separated extracting fluid. 26. An apparatus for carrying out a high pressure extraction which comprises: a thick-walled cylinder having one closed end; a piston reciprocally disposed in said cylinder to provide a variable volume cham¬ ber; means to charge said chamber with a ma¬ terial to be extracted; means to charge said chamber with extrac¬ ting fluid; means to elevate the pressure in said chamber whereby said extracting fluid con¬ tacts said material to be extracted at said elevated pressure; means to mass transfer discharge mixed extracting fluid and extracted liquid from said chamber; and means to controlably move the piston into said cylinder to reduce the volume in said chamber and thereby maintain said elevated pressure in said chamber as said mixed sol¬ vent fluid and extracted liquids are dis¬ charged. 27. An apparatus as described in Claim 26, comprising: means to move said piston into said cyl¬ inder to compress said extracting fluid while in contact with said material to be extracted and to thereby increase the pressure within said chamber. 28. An apparatus as described in Claim 26, wherein the means to charge the material to be ex¬ tracted is axially disposed. 29. An apparatus as described in Claim 26, wherein the means to charge the extracting fluid is axially disposed. 30. An apparatus as described in Claim 26, wherein the means to discharge the extracting flu¬ id and extracted liquid is axially disposed. 31. An apparatus for continuous extraction of liquids from solids at high pressures which com¬ prises: a screw press, said screw press compris- ing: an input section, said input section adapted to form a plug of material to be ex¬ tracted, said plug having sufficient struc¬ ture to sustain the extraction pressures; an extracting fluid injection section adapted to inject effective quantities of ex¬ tracting fluid at elevated pressure; an extract discharge section provided with means to discharge mixtures of extrac- ting fluid and extracted liquid from said screw press at the periphery of said screw, said extract discharge section adapted to maintain elevated pressure within the screw press; and a solid discharge section adapted to form a plug of extracted solid material sufficient to withstand extraction pressures and adapted to discharge extracted solids at a controlled rate. 32. An apparatus as described in Claim 31, wherein said extract discharge section physically compacts the material to be extracted as fluids are discharged. 33. An apparatus as described in Claim 31, wherein the extracting fluid is injected axially . from the screw hub. 34. An apparatus as described in Claim 31, . wherein the extracting fluid is injected peripher- ially from the barrel of the screw press. 35. An apparatus as described in Claim 31, wherein the extracting fluid is mixed with the ma¬ terial to be extracted prior to input into the screw press. 36. An apparatus as described in Claim 31, wherein the extracting fluid injection section is adapted to compact the extracting fluid to the se¬ lected operating pressure in the presence of the material to be extracted.

Inventors: RICE WAYNE K, RICE, WAYNE, K.
Applicants: VITAMINS INC, VITAMINS, INC.
Application year: 1986
Main classification: C09F5
IPC codes: B01D11, C11B1