Method for purifying vegetable oil obtained by mechanical extraction

This invention relates to a method of refining a crude vegetable oil by removing insoluble material from the oil to provide a substantially clarified oil. The process comprises cooling the vegetable oil and maintaining the vegetable oil at the desired low temperature. The vegetable oil is then heated to provide an amount of a substantially clarified oil that can be separated from the insoluble material. The process is useful for a wide variety of oils including soybean oil, sunflower oil, safflower oil, corn oil, sesame oil, rapeseed oil, linseed oil, cottonseed oil, rice bran oil, perilla oil, castor oil, olive oil, tsubaki oil, coconut oil, palm oil, hemp seed oil, tung oil, kapok oil, tea seed oil.

FIELD OF THE INVENTION
 This invention generally relates to a method of purifying oils. More
 specifically this invention is directed to a method of purifying a
 vegetable oil to provide a clarified vegetable oil.
 BACKGROUND OF THE INVENTION
 Vegetable oils find a wide variety of uses in consumer products including
 use as food additives, lubricants, solvents and coating additives. Most
 applications require refined vegetable oil that is essentially colorless
 to light yellow and free from insoluble material. Generally, vegetable oil
 is obtained by dry extruding vegetables, for example, vegetable seeds, in
 a friction extruder-usually at a temperature of greater than 130.degree.
 C. to provide a semi-fluid extrudate. Then the semi-fluid extrudate is
 processed in a screw press to yield a crude vegetable oil and a solid or
 semi-solid vegetable meal, which is separated from the crude vegetable
 oil. Despite this initial separation, the crude vegetable oil still
 contains a variety of suspended insoluble solids. The suspended insoluble
 solids include semi-solid or gummy material that can be particularly
 difficult to remove by typical mechanical separation means. The insoluble
 solids do not readily precipitate from the crude oil. Attempts to filter
 out the insoluble solids present problems because the semi-solid and/or
 gummy material clogs the filter medium.
 In an effort to address these problem, in the past crude oil has been
 refined using a solvent extraction process. In a solvent extraction
 process the crude oil is extracted with an organic solvent, for example, a
 mixture of hexanes. The organic solvent absorbs greater than 90% of the
 seed oils. The extract can be filtered, if necessary, to remove any
 particulate and/or insoluble matter. After filtering, the solvent is
 removed, typically by evaporation, to provide a partially refined
 vegetable oil, which can be used in many commercial products or further
 processed if desired.
 While solvent extraction provides a process for refining vegetable oil,
 this process presents some significant problems. Along with the insoluble
 material, many of the beneficial, natural nutrients such as antioxidants
 and vitamins are removed from the vegetable oil. Both the extracted oil
 and solid material inevitably contain residual hexanes. Hexanes are toxic
 to humans and other animals and must be removed before the resulting oil
 and solid material are suitable for consumption by humans and other
 animals. While the hexanes are recycled for reuse, inevitably a
 significant amount of hexanes escape into the atmosphere and contribute to
 environmental pollution. In addition, hexane is an extremely flammable
 solvent and, therefore, presents a significant risk to fire and
 explosions. It is desirable to provide an alternative process for
 purifying vegetable oil.
 Thus, there is a need to provide a process for purifying vegetable oils
 that avoids the problems described above. The present invention addresses
 this need in a novel and nonobvious way.
 SUMMARY OF THE INVENTION
 Accordingly, there is provided in accordance with the present invention a
 novel process for purifying a vegetable oil. In one form, the process
 removes insoluble material from crude vegetable oil. The process comprises
 the steps of maintaining the crude oil at a temperature below about
 10.degree. C.; heating the crude oil to a temperature sufficient to
 provide an amount of substantially clarified oil; and drawing off the
 substantially clarified oil. In preferred embodiments the vegetable oil is
 cooled to a temperature to induce the insoluble material to agglomerate
 and to form larger masses of insoluble material. More preferably, the
 crude oil is cooled to a temperature between about 5.degree. C. and about
 0.degree. C. The vegetable oil may be maintained at this cold temperature
 for a selected amount of time, preferably between about 1 hour and about 8
 hours. After the vegetable oil has been cooled, typically the oil is
 rapidly heated to induce the insoluble material to precipitate. In
 preferred embodiments, the vegetable oil is heated to a temperature
 between about 50.degree. C. and about 80.degree. C. A wide variety of
 crude vegetable oils can be processed according to this invention. For
 example, the vegetable oil can be selected from soybean oil, sunflower
 oil, safflower oil, corn oil, sesame oil, rapeseed oil, linseed oil,
 cottonseed oil, rice bran oil, perilla oil, castor oil, olive oil, tsubaki
 oil, coconut oil, palm oil, perilla oil, hemp seed oil, tung oil, kapok
 oil, tea seed oil and mixtures thereof This invention provides a clarified
 vegetable oil, which can be readily separated from the solid particles.
 In yet another embodiment of the present invention, there is provided a
 process for purifying a vegetable oil composition containing insoluble
 matter. The process comprises cooling the vegetable oil to a temperature
 below about 10.degree. C.; maintaining for a time to obtain agglomeration;
 heating to a temperature above about 50.degree. C. to provide a clarified
 vegetable oil capable of being separated from the insoluble material; and
 drawing off the substantially clarified vegetable oil.
 Further objects, features, aspects, forms, advantages and benefits shall
 become apparent from the description contained herein.
 DETAILED DESCRIPTION OF THE INVENTION
 For the purposes of promoting an understanding of the principles of the
 invention, reference will now be made to the embodiments illustrated
 herein and specific language will be used to describe the same. It will
 nevertheless be understood that no limitation of the scope of the
 invention is thereby intended. Any alterations and further modifications
 in the described processes, systems or devices, and any further
 applications of the principles of the invention as described herein, are
 contemplated as would normally occur to one skilled in the art to which
 the invention relates.
 In general the present invention provides an improved process for purifying
 vegetable oil. The process provides clarified oil that is substantially
 free of insoluble material. The resulting clarified oil is useful for a
 variety of applications and can be included in a food additive, a solvent,
 a lubricant, a diluent, a coating additive or further purified in a
 subsequent downstream process. In one form, the process provides the
 clarified oil without requiring solvent extraction of the crude oil. In
 another form, the present invention refines the oil by removing insoluble
 material. This process uses minimal mechanical manipulations, and
 decreases production time, cost, and harm to the environment, while still
 providing a refined oil that is substantially free of insoluble material.
 The process is useful to purify a wide variety of oils, including oils
 obtained from vegetables, preferably seed vegetables. Typically, but not
 required, the crude oil processed using the present invention is received
 directly from an extractor and/or extruding process. The vegetable oil can
 be crude oil or it can be partially processed oil in need of further
 refining. It is to be understood that oil from any source is potentially
 useful with the present invention.
 As has been mentioned, the vegetable oil for use in the present invention
 can be derived from a wide variety of vegetables, primarily, but not
 exclusively vegetable seeds. Typical examples of vegetable oils for use
 with this invention include soybean oil, sunflower oil, safflower oil,
 corn oil, sesame oil, rapeseed oil, linseed oil, cottonseed oil, rice bran
 oil, perilla oil, castor oil, olive oil, tsubaki oil, coconut oil, palm
 oil, hemp seed oil, tung oil, kapok oil, tea seed oil and mixtures of
 these oils.
 The insoluble material in the crude oil may be of any form such is commonly
 found in vegetable oil and may appear as particulate, flocculent, or waxy
 material. The insoluble material can cause the crude oil to appear turbid,
 cloudy or discolored. The crude vegetable oil can include seed debris,
 lecithins, phospholipids (phosphatides), free fatty acids, sterols, and
 unsaponified matter as well as a variety of other insoluble material. The
 insoluble material can originate from a variety of sources including the
 vegetable, vegetable debris, by-products from prior processing procedures
 or other sources.
 According to this invention the greater than about 75% by volume of the
 insoluble material is removed from the crude vegetable oil. More
 preferably greater than about 85% by volume of the insoluble material is
 removed, and yet still more preferably greater than about 95% by volume of
 the insoluble material is removed from the crude vegetable oil. Thus, the
 clarified oil prepared according to this invention comprises less than
 about 25% by volume insoluble material. More preferably clarified oil
 comprises less than 15% by volume insoluble material; yet still more
 preferably, the clarified oil comprises less than about 10% by volume or
 less of the insoluble material. The resulting clarified oil is
 substantially a clear liquid having exhibiting an amber color.
 In one form of the invention process, the crude vegetable oil received from
 mechanically extraction is cooled. Preferably the crude vegetable oil is
 cooled sufficiently to induce agglomeration or to cause the insoluble
 matter to mass together. In preferred embodiments, the vegetable oil is
 cooled to a temperature below about 10.degree. C., more preferably,
 between about 5.degree. and 0.degree. C. It is understood that lower
 temperatures can be used if necessary or desired. For example, lower
 temperatures can be employed to induce semi-solid or gummy insoluble
 material to become hardened and even solidify in some circumstances. Those
 skilled in the art will appreciate that typically the lower temperatures
 decrease the solubility of other material, which may be contained in the
 crude vegetable oil, and thus, cooling the vegetable oil can also induce
 separation of additional solid or semi-solid material from the crude oil.
 The additional insoluble material may also be removed using this process.
 The vegetable oil can be maintained at the desired low temperature for a
 time selected to induce the insoluble material to form larger masses of
 insoluble material and/or enhance separation of the insoluble material
 from the vegetable oil. In preferred embodiments, the vegetable oil is
 maintained at the desired low temperature for about 1 hour to about 8
 hours; more preferably, about 2 hours to about 4 hours. While it is
 understood that longer times can be employed to allow the insoluble
 material to form larger masses, it has been discovered that the majority
 of the insoluble material separates from the oil within about 8 hours.
 During the period the vegetable oil is maintained cold, it is desirable
 that the cold oil remain undisturbed to avoid stirring up any material
 that has begun to precipitate from the crude oil. However, it has been
 observed that the insoluble material does not always precipitate from the
 cold, crude oil. It will be appreciated that the cooled oil exhibits
 increased viscosity, and, generally, the lower the temperature, the more
 viscous the oil becomes. At sufficiently low temperatures the crude oil
 can obtain a "gel-like" consistency. While not intending to be bound by
 any theory, it is thought that the insoluble material exhibits an
 increased tendency to remain suspended in the cold, viscous oil. Thus,
 while the colder temperatures can induce the insoluble material to
 agglomerate and/or form larger masses this material often remains
 suspended in the cold oil.
 After the vegetable oil has been maintained at the desired temperature for
 the selected amount of time, the oil is heated to provide a clarified oil
 that is capable of being separated from the insoluble material. In
 preferred embodiments, the vegetable oil is heated to a temperature above
 50.degree. C., but not to exceed the temperature at which a substantial
 portion of the oil thermally degrades. Preferably, the oil is heated to a
 temperature between about 50.degree. C. and about 80.degree. C.; still
 more preferably, between about 60.degree. C. and about 70.degree. C. The
 heating can be accomplished by a variety of methods including any method
 commonly used or known in the art.
 In an alternate form of the present invention it is desirable to rapidly
 heat the oil to the desired temperature. Preferably the oil is heated at a
 rate of about 50.degree. C./hour to about 80.degree. C./hour; more
 preferably, about 60.degree. C./hour to about 70.degree. C./hour. Most
 preferably, the oil is heated in a manner to maintain the insoluble
 material in a semi-solid or solid state that does not dissolve in the
 heated vegetable oil.
 It has been discovered that heating the crude oil facilitates separation of
 the insoluble material from the crude oil to provide a substantially
 clarified oil. While not to be bound by any theory, it is thought that
 heating the oil increases the fluidity (or decreases the viscosity) of the
 crude oil sufficiently to allow the insoluble material to readily separate
 from the oil. Thus, it is desirable to heat the oil in a manner to
 decrease the viscosity of the oil while maintaining the insoluble material
 as an agglomerated mass. In addition, it is thought that the vegetable oil
 exhibits a greater thermal conductivity than the insoluble material. Thus,
 the oil absorbs sufficient energy from the applied heat to exhibit a less
 viscous behavior. The insoluble material remains as an agglomerated
 material in a hardened or semi-hardened state, which precipitates from the
 heated vegetable oil.
 The clarified oil is separated from the insoluble material using any of the
 methods commonly used in the art including decanting, pouring, siphoning,
 and pumping the clarified oil from the settling tank. The most preferable
 method for withdrawing the clarified oil includes decanting the clarified
 oil from the settling tank. As with any separation process, complete
 separation may not always achieved. In practice it may be desirable to
 remove the bulk of the clarified oil and leave a residual portion of the
 vegetable oil in the settling tank with the precipitated material. This
 residual portion of vegetable oil and any entrained solid material can be
 recycled in a subsequent refining procedure.
 In an alternative form, the clarified oil can be separated from the
 insoluble material by removing the insoluble material from the bottom of
 the settling tank leaving the clarified oil in the settling tank. This
 method also provides an effective separation of the insoluble material
 from the clarified oil. The insoluble material and any residual oil
 contained therein can be collected for use in other applications, such as
 in animal feed, or the insoluble material and the residual oil can be
 collected and further refined in a subsequent refining procedure.
 This process provides a substantially clarified oil that is suitable for
 many commercial applications. Further, this novel process can be used in
 conjunction with a variety of subsequent processing procedures including
 filtering, chemical extraction, bleaching, and decolorizing. Thus, this
 inventive process provides particular advantages by reducing the cost and
 efforts needed in subsequent refinement processes.
 The present invention contemplates modifications as would occur to those
 skilled in the art. It is also contemplated that processes embodied in the
 present invention can be altered, rearranged, substituted, deleted,
 duplicated, combined, or added to other processes as would occur to those
 skilled in the art without departing from the spirit of the present
 invention. In addition, the various stages, steps, procedures, techniques,
 phases, and operations within these processes may be altered, rearranged,
 substituted, deleted, duplicated, or combined as would occur to those
 skilled in the art. Further, any theory of operation, proof, or finding
 stated herein is meant to further enhance understanding of the present
 invention and is not intended to make the scope of the present invention
 dependent upon such theory, proof, or finding.

For the purpose of promoting further understanding and appreciation of the
 present invention and its advantages, the following Examples are provided.
 It will be understood, however, that these Examples are illustrative and
 not limiting in any fashion.
 Example 1
 Approximately 500 gallons (1890 liters) of a crude soybean oil obtained
 from an extruding-expelling process commonly used in the art was charged
 to a 500 gallon settling tank that included a chilling unit. (M-500 model,
 manufactured by Mueller) The crude soybean oil was chilled to about
 36.degree.-38.degree. F. (2-3.degree. C.). The crude soybean oil was
 maintained between 36.degree. and 38.degree. F. for an additional 2 hours.
 The chilled soybean oil was then rapidly heated to 150.degree. F.
 (65.degree. C.) by inserting 6 electric heating units (742 G manufactured
 by Allied Precision) into the chilled soybean oil. As the oil heated up,
 the insoluble material settled to the bottom of the settling tank. The hot
 clarified soybean oil was then decanted from the settling tank to provide
 495 gallons (1735 liters) of a clarified soybean oil.
 The above-described process can be repeated up to 4 or 5 times with
 different batches of crude oil before the total accumulated insoluble
 material is collected and removed from the settling tank. The soybean oil
 thus processed exhibited a clear liquid having an amber color.
 While the invention has been illustrated and described in detail in the
 drawings and foregoing description, the same is considered to be
 illustrative and not restrictive in character, it is understood that only
 the preferred embodiments have been shown and described and that all
 changes and modifications that come within the spirit of the invention are
 desired to be protected.