CA1162938A - Extraction of oil from vegetable material - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process is provided for the extraction of oil from undried, finely-divided vegetable material.
This process employs total immersion of moist solid in a solvent without production of emulsions or contamination of the miscella with finely-divided solids.

Description

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Case 3230 .

EXTRACTION OF OIL ~ROM
VEGETABLE MATERIALS

FIELD OF THE INVENTION
-This invention relates to the extraction of oil from vegetable materials - particularly those with relatively high moisture content.

BAC~GROUND OF THE INVENTION

~ There are numerous known methods for recovering oil from vegetable materials. One technique in commercial use involves continuously pressing the vegetable material at low moisture content to expel oil. A pretreatment steaming of the vegetable material is frequently employed to ~acilitate the pressing operation.

- Although mechanical pressing is a relatively simple procedure, it removes only part of the oil from such vegetable materials as corn germ obtained from the corn wet-milling process. The corn wet-milling process neèds no further description, because it is well known and has been extensively described in the literature.
See, for example, the chapter entitled "Sta~ch"~ by Stanley M. Parmerter, beginning on page 672 of ~olume 18 of Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, Interscience Publishers, a division of 1 1~29~

John l~Tiley & Sons, Inc., New York, London, Sydney, Toronto (1969). For this reason~ a combination of continuous screw pressing ~ollowed by solvent extraction of the pressed meal is frequently employed on high oil-content vegetable materials, i.e., those containing more than 25% oil.

One disadvantage o~ the prepressing~solvent extraction technique for processing hig~ oil-content materials is the high cost o~ the equipment. Not only must continuous screw presses be purchased and maintained but also a full-scale solvent extractor must be installed.

A second problem with the prepressing-solvent extraction technique relates to oil quality~ That oil which remains in the pressed cake has been ~exposed to the alr while at elevated temperatures. As a result, the oil extracted from the pressed cake is dark colored and difficult to refine to a light colored oil.
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One direct extraction method devised to overcome the drawbacks of the costly prepressing-solvent extraction operation is disclosed in Canadian Patent 763,968. In this process~ low~moisture content ~egetable material is comminuted to pass a 20-mesh screen and then slurried with hexane at 175-260F under pressure. The extract is separated an~ washed from the solids in a countercurrent manner in a series of hydrocyclones~ Although this treat-f' ~ ~829~

ment results in substantially complete removal of oil fromthe vegetable material, the exkraction must be carried out in pressure vessels and a "~ines" problem is encountered.
When the material is comminuted to pass a 20-mesh screen, some very ~ine particles are formed. ~lany of these are only 1-2 microns in diameter. On passage through the hydrocyclones, these fines remain with the extract and appear in the desol~entized crude oil. m e crude oil must then be filtered before it can be further processea.
This is an expensive step ~ecause of the lar~e amount of solids held in the oi~ and the difficulty of removing these finely-divided solids from the oil.

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- Another process for the direct extraction of oil from corn germ is disclosed in U.S. Patent 3,786,078.
The essential steps o~ this process are: (1) drying the corn germ to about 2% moisture, (2) finely grinding the dry material, (3) hydrating the ground material,l~
(4) ~laking the moist, ground material7 and (5) extl~acting the flakes with solvent in a conventional percolation extractor. In this case, as in the pre~ious one, the ~round germ undoubtedly contains much fine material but most of the fines are bound into the flakes on passage through the flaking rolls. The flaking step is critical and unless t.his is done correctly, poor extraction results.
If the moisture.content is too low or if the flakes are too thin, the flakes disintegrate ~iving fines which slow percolation Or the solvent and interfere with oil extraction ~ 16~93~

If the moisture content is too high or if the flakes are too thick, solvent penetration into the flakes is impeded resulting in poor extraction.

In U.S. patent no. 4,277~411 a process is disclosed which involves shredding the moist vegetable material by passing it between closely-set smooth rolls to rup ure the oil-containing cells without expelling the oil from them. The compressed material is dried and the oil is extracted with an oil solvent. While this procedure overcomes many of the problems associated with earlier processes, it gives material of very low bulk density which is hard to handle on a large scale and which requires bulky oil extracting equipment. An additional U.S. patent no. 4,246,184 describes an improved method for preparing oil-bearing vegetable materials for extraction. This method comprises comminuting the vegetable materiaI, forming agglomerates of the finely-divided material containing between about 20% and about 55% water by weight and drying the agglomerates to a moisture content of less than 15%
before they are extracted. Although this method is satisfactory in producing an extract that contains very few fines, it does requlre a drying and re-Eorming step before the extraction.

' , 9 ~ 8 UOS. patent no. 4,277,~11 specifically shows that oil is incompletely extracted from undried corn germ by the process disclosed in that application unless the germ is dried before extraction. For other oil extraction processes in current use, it is necessary to dry the material to a comparatively low moisture content before the extraction~ Such drying processes are not entir~ly satisfactory because they cause hydrolysis of a portion of the oil to fxee fatty acids which must be removed from the oil in a subsequent refining step. In addition, the drying processes needed to remove the water tend to accelerate oxidation of the oil causing additional oil loss and requiring further refining operations.

U.S. patent no. 4,341,713 discloses an aqueous .. . . ..
extraction process for obtaining oil from finely~ground corn germ. This method gives oil of excellent quality which requires very little reflning. However, even this method suffers from the drawback that an apprecia~le amount of the oil remains in the ~et residues from the process.

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1 ~8~93 SUMMARY OF THE INV~NTION

It is an ob~ect of this invention to provide a new oil extraction process which does not require the use o~ expensive expelling equlpment.

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e It is another ob~ect Or th~s invention to provide an oil extraction process which does not require a flaking process with its a~tendant need for careful control of flaking conditions.

It is still another ob~ective of this invention to provide a direct oil extraction process which gi~es a miscella without the undesirable fines encountered in ~ , ~any previous direct extraction processes.

A ~urther object of thi9 invention is to provide an oil extraction process which can be used directly on moist vegetable material without the need for the expensive preliminary drying step with its attendant oil loss through hydrolysis and oxidation o~ the oil.
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These objec~s are~realized by the process of ..
this invention which is now described.

In one embodiment of the invention, finely~divided, undried corn germ obtained ~rom the corn wet-milling process~
containing at least about 40% water by weight, is dispersed in an oil solvent to give a s~lid-solvent dispersion. The _6-.

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oil is extracted from the solid-solvent dispersion with more oil solvent. Finally9 the oil-containing solyent is s~parated ~rom the insoluble material, and the oil is recovered fro~
the oil-containing solvent.

Wet decanter residues and sludge obtained from the aqueous extraction of oil from corn germ can be used as the ~inely-divided corn germ in this process.

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In a further embodiment of this invention, - -the process is applied to the extraction of oil from finely-divided, undried coconut meats.

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DESCRIPTION OF PRE:F~RRED E!'IBODIMENTS

The process o~ this ~nvention can be applied to various oil-bearing vegetable materials o~ relatively high oil content. This novel procedure is particularly well suited to the extraction of oil from undried corn germ obtained from the corn wet-milling process.
Accordingly, the description which follows is largely exemplary with respect to this particular vegetable seed material.

In the practice of this invention, undried vegetable matter of high moisture content is used. In the case of cor~ germ from the corn wet-milIing process, the pre~erred amount o~ water is from about 40% to about ~ ~62g~

60% by weight. The most preferred amount is from about 50% to about 55% water by weight. In the case of undried coconut meats, the moisture content is somewhat lower~ usually about 40% by weight.

One source of corn germ suitable for use in this process is the decanter residue and sludge obtained from the a~ueous extraction of oil from corn germ. The aqueous extraction process is disclosed in U.S. patent no. 4,341,713. This process gives a residue of finely-ground material which contains about 5% corn oil by weight on a dry solids basis. It also contains about 75% water by weight. There is also a sludge which contains additional oil. Oil can be extracted from the combined residue and sludge by the method of the present invention when it contains from about 50~ to about 80~ moisture by weight.

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Comminution is accomplished by any conventional means for reducing the size of particles, such as a hammer mill or other conventional mill. An Urschel COMITROL (trade mark) (Urschel Laboratories Company, Valparaiso, Indiana) fitted with a microcut head is particularly suited for this purpose. The particles should be of such a size that the oil can be readily extracted from ...........................

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1 ~6~938 them. It is desirable that the resldual meal after extraction contains less than about 5~ oil~ preferably less than 2% oil. In the case o~ corn germ, the particles should be so finely divided that more than about 50%, preferably more than about 80%, will pass throu~h a No. 100 U.S. Standard sieve.

The comminuted material is next mixed with an oil solvent. Typically, the oil solvent is a liquid .. . ..
hydrocarbon such as hexane. Mixing is accomplished by any means 'hat provides intimate contact between the solid and solvent. Circulation through a colloid mill, a homogenizer or e~en a centrif~al p~m~ may be used to per~orm this step The mixture of liquid and solid material can be separated at this stage. Optionally, the mixture is subjected to a second comminution step to promote more complete extraction of oil from the solid.

Separation of the liquid extract from suspended solid material may be achieved by filtration 3r centri-fugation. If a centrifuge is used, it is desirable to choose operating conditions so that the water present is retained in the solid and is not squeezed out to form a separate liquid layer. The solid is mlxed with fresh solvent and the separation step is repeated as many times as necessary for oil extraction~ Economical large-scale extr2ctions o~ the mlxture may be acco~plished by pass'ng the slurry through hydrocyclones. The oil solvent ls passed countercurrently through the same system. A
typical arrangement for a hydrocyclone countercurrent washing system is-disclosed in U.S. Patent 2,840,524 .. . . _ . .... . .. ..... _ _ Afte;r extractiOn has bee~ completed, the residual vegetable mater~al will generally exhibit an oil content of less than 5%, preferabl~ less than about 2%, by weight.
This material~ which has a high protein ontent, may be ~reed o~ solvent by evaporation and used as animal reed or the li~e. Since the vegetable material has not been dried, the protein is not denatured and is of high quality.

The oil is separated from the solvent using conventional equipment. The oil may be further treated as desired us~ng any one J or a combination~ of the customary steps of refining, bleaching and deodorizi~g to produce a high grade vegetable oil.

Although the foregoinæ process has been described .
chiefly in terms o~ a complete process for extracting the oil from essentially naturally occurr~ng forms Qf ve~etable material~ it is not so limited. This process may be used in combination with other conventional steps in oil ex-traction and by-product recovery.

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( g~8 Throughout the present process and any prelim~nary steps Or treatment o~ the vegetable maberial, it is preferred that condltions deleterious to the oil in the vegetable material be minimized or avoided. Of these cond1tions, elevated temperatures are the most serious. Such te~per-atures, unless for a very brie~ timel can cause the qualit~
of the oil to suf~er. In view of khis, it is generally desirahle to maintain moderate temperatur~s~ to limlt exposure to elevated temperakures ~o as s~Drt a time as possi~le and to maintain an inert atmosphere throughout the processing of the vegetable material and its oil.

The following examples illustrate certain embodlments of the present invention. Unless otherwise staked, all proportions and percentages are provided on the basis of weighk.

EXAMPLE I

Undried, full-fat corn ~erm (about 55% moisture) obtained from the wet millin~ o~ corn was ground in a 12.7-cm`diameter micropulverizer kype SH s~ainless steel hammer mill made by Pulverizing Nachinery Company, Summit, New Jersey. The mill was operated at 8800 rpm. The germ was ~round in two passes, first through a 3. 2-mm screen, t~en through a 1.6-mm screen. The ground wet germ was slurried ~ n an equal weight o~ hexane. The slurry was passed twice throu~h a Manton-Gaulin homo~enizer, kype ~ ~ 6~g3~

15M 8T~, made by the Manton-Gaulln Manu~acturing Company, Inc , Everett, Massachusetts, operating at 422 kg/cm2.
The homogenized slurry W2S extr2cted 7 times with hexane.
Separation was made in an International No. 2 centri~uge manufactured by the International Equipment Co~any, Boston, Massachusetts~ ~he centri~uge was brought to 1500 rpm before the motor was turned o~f. The extract was then ~ecanted ~rom the solid. The volume Or hexane added for each extractlon was èqual to the volume of extract separated in the pre~ious extracti~n. A brilliant clear extract was obtained. Residual oil content of the solid was 1.2~.

Residual oil was determlned by the Spex mill method. In this method, the sample is placed with carbon tetrachloride in a small ball mill tspex mixer mill, Catalog No. 8000) made by Spex ~ndus~ries, Inc., Metuchen, N.J., and shaken thoroughly to disintegrate the meal.
The ~round slurry is heated for 30 minutes under ref~ux with carbon tetrachloride and ~iltered. The oil content o~ the ~iltrate is determined a~ter evaporation of the solvent.

Separation between the wet ~erm and hexane is so rapid that gravity separation is ~easlble in dilute systems. An 8% (dry substance) slurry could be separated in a separatory ~unnel.

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The process of Example 1 was repeated except that the wet corn germ was ground through an Urschel Laboratories Model 1700 COMITROL mill made by the Urschel Laboratories Company~ Valparaiso, Indianag using an 180084-2 microcut head with the impellor rotating at 12,000 rpm. The residual oil content of the solid was 1% . ' . _..

The process of Example 2 was repeated with - other corn germ samples using various microcut heads in the COMITROL mill. Extraction results and extraction cond7tions are reported in Table I.
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Good oil extraction w~s achie~ed pro~ided that the ground corn germ is further mllled in hexan,e slurry ~note Runs 2 and 3). These results also indicate that the more finely-ground material is more completely extracted by this process.

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The process of Example 2 was repeated except that the wet corn germ was tw~ce ground through the ~rschel mill equipped with a 20084-1 head with an impellor speed of 9500 rpm. The twice-ground germ, ~5 kg, was mixed with 198 kg hexane by twice passing the slurry through a Tri-Homo Disperser Homogenizer, Model 2LA, -manufactured by Patterson Industries, Inc., East Liverpool, Ohio. The liquld exkract was separated from the solid by passing the mixture through a hydrocyclone, DorrClone , . ..
P-50-A, made by Dorr-Oliver, Inc., Stam~ord, Connecticut.
The supply pressure was 0.84 kg/cm . Extraction of the solid was repeated 7 times. In each case, the amount of fresh hexane used was equal to the weight of the extract separated in the previous extraction. The underflow from the final extraction was d1luted with 0.63 parts o~ hexane and centri~uged in a solid-bowl,scroll-discharge centri~uge (P-660 Continuous Superdecanter, made by Sharples Corp., Philadelphia, Pennsylvania) at 6000 rpm before residual oil was determined. Residual oil content o~ the solid was 3.2~ (average cf 2 runs).

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~ 9 Fresh coconut meats (50 grams) containing 41.6~ moisture ~ere shredded and then ground with 75 ml of hexane in a l-quart Waring Blendor at high speed for 60 seconds. The solvent, containing oil, was separated from the solid by centrifùging at 1500 rpm for l second in a Model PRl International centrifuge.
This gives an average centrifugal force of about - ~
500 x g. Seven such extractions using ~resh hexane each time'reduced the residual oil content of the coconut meat to 2.5% by weight on a dry solids basis.
The crude coconut oil was nearly water white and contained only 0.1% free fatty acids expressed'as lauric acid. This contrasts with crude co~mercial coconut oil which normally contains about 5% free fatty acids. ' - ' , Extractions were much less e~ficient, leaving 6.5% residual oil, whén separations were made by gravity - rather than using a centri~uge. Extracti~ns were also .
less efricient when the residue after the ~irst extraction was further extracted by shaking with hexane rather than by stirring at high speed in a Waring Blendor.

, This example illustrates that the pr~cess is suitable for extracting oil ~rom undried coconut meats, as well as from undried corn germ.

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A sample of decanter residue from the aqueous extraction process described in U.S. patent no. 4,341,713 was found to contain 74.3% moisture. Analysis showed that 5.9% of the dry material was oil. This residue without further grinding was extracted with seven portions of hexane as described for the extraction of the homogenized slurry of corn germ in Example l. A
clear miscella was obtained. The extracted residue contained only 0.5% oil by weight on a dry solids basis.

The extraction process was repèated using a combination of decanter residue and sludge obtained from the aqueous extraction of oil from corn germ.
This mixture before extraction analyzed for 74.4 moisture and 15.6% oil by weight on a dry solids basis.
Seven extractions with hexane again gave a clear miscella and left a residue containing only 0.4~ oil by weight on a dry solids basis. The extractions in this example show that the process of this invention gives efficient removal of the oil from the combined residue and slud~e obtained from the aqueous extraction of oil from corn germ.

Thus, it is apparent that there has been provided, in accordance with the invention, a process for the total immersion e~traction of oil from high oil-bearing seeds that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is ëvident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the fore~oing description. Accordingly, it is intended to include all such alternatives, modifications, and variations as set forth within the spirit and scope of the appended claims.

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the extraction of oil from vegetable material comprising the steps of:

a) dispersing a member selected from the group consisting of finely-divided, undried corn germ and finely-divided, undried coconut meats containing at least about 40% water by weight, in an oil solvent to give a solid-solvent dispersion;

b) extracting oil from the solid-solvent dispersion with additional oil solvent;

c) separating the oil solvent with oil from insoluble material; and d) recovering the oil from the oil solvent with oil.

2. The process of claim 1 wherein the solid-solvent dispersion is subjected to a further comminuting step before the oil is extracted.

3. The process of claims 1 or 2 wherein the oil-bearing solvent is separated from the insoluble material by means of hydrocyclones.

4. The process of claims 1 or 2 wherein the finely-divided solid is dispersed in the oil solvent by means of a homogenizer.

5. The process of claims 1 or 2 wherein the oil solvent is hexane.

6. The process of claims 1 or 2 wherein the finely-divided corn germ is obtained from the corn wet-milling process and contains from about 40% to about 60% water by weight.

7. The process of claims 1 or 2 wherein the finely-divided corn germ is comprised of at least one member selected from the group consisting of decanter residue and sludge obtained from the aqueous extraction of oil from corn germ.