Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Case 3230
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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
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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.
...... .. .. . .
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-
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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.
.
- 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
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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.
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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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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.
.
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
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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.
. .
In a further embodiment of this invention,
- -the process is applied to the extraction of oil from
finely-divided, undried coconut meats.
.
.
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
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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.
.
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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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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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
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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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EXAMPLE 2
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% . ' . _..
EXAMPLE 3
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.
.
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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EXAMPLE 4
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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EXAMPLE 5
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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EXAMPLE 6
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.
3 8
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.
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