Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF T~IE INVENTION
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There are numerous known me-thods for extracting
oil from vegetable materials. One technique in commercial
use, for example, involves continuously pressing the vegetable
material at low moisture content to expel oil. A pretreat-
ment steaming of the vegetable material is frequently employed
to facilitate the pressing opera-tion. In addition, it is
common to employ a subsidiary step of solvent extracting
the pressed material to remove residual oil.
Unfortunately, these processes possess a number of
drawbacks. In particular, the expelling operation requires
heavy machinery and results in a substantial rise in tempera-
ture harmful to oil and vegetable protein qualities and
further tends to produce large quantities of vegetable fines
which must be separated from the expelled oil.
Other techniques designed to circumvent these
drawbacks have been found. These include the processes set
forth in Canadian Patent 763,968 and United States Patent
3,786,078. Both of these patented processes involve direct
extraction of the vegetable material with an oil solvent.
Because of their respective requirements of severe operating
conditions, extraction of finely divided material and/or
complex pretreatments of the oil-bearing vegetable material,
however, they have not proven altogether successful.
It is therefore an object of -this invention to
provide a simplified process for recovery of oil from vegetable
materials.
It is a further object to provide an oil extraction ~`
process which does not require subjection of the oil or
vegetable material to deleterious conditions of operation.
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It is a still further object to provide a process
which permits essentially complete recovery of oil from a
variety of vegetable materials.
Another object is to provide a-process which does
not release finely divided material into the oil solvent.
These and various other objectives, as are apparent
from the description which follows, are achieved through the
present invention.
DESCRIPTION OF THE INVENTION
_
The process of the present invention provides an
improved method for extracting oil from oil-bearing vegetable
materials. The method comprises forming a particulate
vegetable material containing between about 20% and about 55%
water by weight, drying the particulate vegetable material
to a moisture content of less than about 15% by weight and
then extracting the dried material with an oil solvent.
In a preferred embodiment of the invention, the
particulate vegetable material is formed by compressing the
oil-bearing vegetable material, containing between about 20%
and about 55% water by weight, by passing it between rolls
under pressure sufficient to rupture the oil-containing cells
without expelling the oil from caid vegetable material.
The process of this invention can be applied to all
oil-bearing vegetable materials. It is especially sui-table
for application to those materials of relatively high oil
content such as decorticated sunflower seed, decorticated
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cottonseed and the germ obtained by the wet milIing of corn.
This novel procedure is particularly well suited to the
extraction of oil from corn germ. Accordingly, the description
which follows is largely exemplary with respect to this
particular vegetable seed material.
The first step of the present process may be
accomplished by passing moist, oil-bearing vegetable material
between the rolls of a flaking machine. While smooth or
corrugated rolls may be used, the corrugated roll grooves
tend to become plugged with the wet material and so are less
satisfactory. The rolls may be of the same or different
diameters, and the rolls of the machine may rotate at the same
or at different speeds.
When dried corn germ is passed through flaking rolls
under pressure, large flakes are obtained and relatively large
amounts of energy are required to operate the rolls so as to
obtain flakes of the 0.15 to 0.5 mm thickness required for
nearly complete oil extraction. When wet corn germ is passed
through the flaking rolls, surprising differences are observed.
It requires much less energy to pass wet germ than it does to
pass dry germ through the rolls even when they are set closer
together to give a product of less than 0.05 mm thickness
which is required for this process. Further, the product is
obtained as small, stringy particles rather than flakes. The ;
pressure in this process must be sufficient to flatten the
particles and rupture the oil-containing cells so that the
oil can be easily extracted with an oil solvent. Surprisingly,
essentially no free oil is apparent in the shredded germ. An
additional unexpected result of this process is that the oil-
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containing particles are disrupted so that they release the
oil content without the production of fines which are so
difficult to separate from the oil obtained in the previously
known grinding and extraction processes. These fines have
been a particularly serious problem when corn germ has been
flaked or milled at low moisture content.
Although it is most economical to use undrie~ oil-
bearing material such as undried wet-milled corn germ in the
practice of this process, other starting materials may also
be used. A dried vegetable material may be converted to a
higher moisture product by mixing with a suitable amount of
water or other moistening agent. This mixture should contain
between about 20% to about 55%, preferably 25% to 50%, of
water by total weight.
The nature of the moistening agent employed to
rehydrate the vegetable material is not critical. Water
alone or other moistening agents may be used. In a preferred
embodiment, however, the moistening agent is light steepwater
(the unconcentrated liquor recovered from wet milling of corn).
In an alternative embodiment, one may use a mixture
of the dried and undried oil-bearing vegetable material, for
example, a mixture of undried and dried wet-milled corn germ.
This mixture may be blended and additional wetting agent added
as needed to obtain the desired moisture level before the
material is passed between the flaking rolls.
Suitable material for extraction can be obtained
using any conventional flaking apparatus with the rolls pre-
gapped to a distance suitable to obtain the desired pressure
on the material. We have found that in the case of the
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Ferrell-Ross flaking rolls, 12 x 12-inch, Serial No. 4798,
Ferrell-Ross Inc., Minneapolis, Minnesota, the rolls should
be pre-gapped at less than 0.05 mm to give a suitable product.
The Allis-Chalmers laboratory flaking rolls (6 x 6-inch, Serial
No. 1067), Allis-Chalmers, Milwaukee, Wisconsin, gave a
satisfactory product when the roll pressure was set at the
highest setting, 6Ø Samples may be passed through the rolls
two or more times as needed in a particular apparatus to
produce a product with the desired extractability.
Other equipment may be used for compressing the
vegetable material. However, the pressure must be sufficient
to rupture the oil-bearing cells to give a product with the
desired extractability without expelling the oil from the
material.
The second essential step of the process is the
drying of the moist material which has passed through the
rolls. In order to obtain a product that gives good oil
extraction, the moisture content must be reduced to less
than about 15%, preferably less than about 5%, by weight.
This may be accomplished in any conventional drying equipment,
such as an air oven or belt dryer. The dried, pressed
material has a bulk density of less than 0.3, usually about
0.2 gram per cubic centimeter.
Extraction of the dry, oil-bearing vegetable material
may be performed with any of the conventional oil solvents.
Typically, however, the solvent is a liquid hydrocarbon such
as hexane.
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The mode and apparatus utilized for extraction may
likewise be selected from among those conventional in the art.
Counter-current, column or percolation extractors may be
operated in either batch or continuous manner as desired.
After extraction has been completed, the residual
meal will generally exhibit an oil content of less than 5%,
preferably less than about 2%, by weight. This material,
which has a high protein content, may be freed of solvent by
evaporation and used as animal feed or the like.
The oil is separated from the solvent, using con-
ventional equipment. The oil may be further treated as
desired using any one or a combination of the customary steps
of refining, bleaching and deodorizing to produce a high-grade,
edible vegetable oil.
Previous processes which have employed extraction
of oil from ~inely ground vegetable material have been costly.
The finely divided material has so impeded the flow of solvent
through the solids that extraction was very slow. In addition,
the extract has been contaminated by the accumulation of
very small protein bodies of about 1 micron in diameter.
It has been difficult and costly to remove the contaminants
from the extract.
The present process overcomes these difficulties
by producing a material through which the extraction solvent
flows readily. In addition, any particles that do pass into
the extract are large enough to permit easy removal by settling
or filtration.
Although the foregoing process has been described
chiefly in terms of a complete process for extracting the oil
from essentially naturally occurring forms of vegetable material,
it is not so limited. This process may be used in combina;tion
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with other conventional steps in oll extraction and by-product
recovery.
Throughout the present process and any preliminary
steps of treatment of the vegetable material, it is preferred
that conditions deleterious to the oil in the vegetable material
be minimized or avoided. of these conditions, elevated temper-
atures are the most serious. Such temperatures, unless for a
very brief time, can cause the quality of the oil to suffer.
In view of this, it is generally desirable to maintain moderate
temperatures to limit exposure to elevated temperatures to as
short a time as possible and to maintain an inert atmosphere
throughout the processing of the vegetable material and its
oil. This is particularly true during the drying step.
The following examples illustrate certain embodiments
of the present invention. Unless otherwise stated, all
proportions and percentages are provided on the basis of weight.
EXAMPLE I
Undried, full-fat corn germ (about 55% moisture~
obtained from the wet milling of corn was passed through the
smooth rolls of an Allis-Chalmers Laboratory Flaking Rolls,
6 x 6-inch rolls, Serial No. 1067, made by the Allis-Chalmers
Co., Milwaukee, Wisconsin. The rolls were operating at a
1:1 gear speed with pressure applied to the rolls. The
material was passed -through the rolls twice.
One portion of the material was dried to about 5%
moisture before extraction with hexane. A second portion was
extracted with hexane without drying.
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The hexane extraction was performed by the method
described in J. Am. Oil Chemists' Soc. 26, 422 (1949). A
Butt type extractor was used with a reflux rate of about
18 ml per minute. Residual oil was determined by the Spex
mill method. In this method 9 the sample is placed with
carbon tetrachloride in a small ball mill ~Spex mixer mill,
Catalog No. 8000) made by Spex Industries, Inc., Metuchen, N.J.,
and shaken thoroughly to disintegrate the meal. The ~round
slurry is heated for 30 minutes under reflux with carbon
t.etrachloride and filtered. The oil content of the filtrate
is determined after evaporation of the solvent.
Results, given in Table I, show that oil extraction
is more complete when the germ is dried before extraction.
In addition, a higher pressure setting on the rolls gives a
product from which the oil is more completely extracted.
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TABLE I
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Moisture (%)
Roll 1of Material ExtractionOil (%)
Pressure )Before ExtractionTime (Min)In Residue
5.3 52.8 50 19.2
5.3 4.8 50 8.4
5.6 52.0 50 12.7
5.6 52.0 90 9 7
5.6 6.5 50 4.7
)~rb~trary numbers on pressure scale - Allis-Chalmers
Laboratory Flak~ng Rolls.
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EXAMPLE II
Undried corn germ was treated ~enerally as set forth
in Example I. The compressed product was dried at various
temperatures before oil extraction.
Results, given in Table II, show that increased roll
pressure aids oil extraction and that drying the
product at temperatures up to 120C gives material from which
the oil is readily extracted.
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EXAMPLE III
Wet-milled corn germ (49% moisture) was passed through
the Ferrell-Ross ~lak~ng rolls two times. The rolls were run at
room temperature at a hydraulic pressure of 28 kg/cm2 (400 psi)
and with a pregap setting of 0.041 mm (0.0016 inch). One roll
ran at 1010 rpm, the other at 446 rpm.
A sample of the rolled germ was dried to 2.8% moisture
in a circulating air oven at 100C. The solid was extracted
with hexane ~or 60 minutes and the residual oil content was
determined according to the method given in Example I. The
oil content of the residue was 2.3%.
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