Note: Descriptions are shown in the official language in which they were submitted.
1 3 2 6 2 4 3
BACKGROUND OF THE INVENTION
This invention relates to a method for refining
glyceride oils by contacting the oils with adsorbents
capable of removing certain impurities. More
specifically, it has been found that glyceride oils can
be treated with a combination of materials which serves
to remove phospholipids, soaps and the like, facilitating
decolorization of the oil by filtration through a
packed bed of a pigment removal agent. This new
process can be used in physical refining or in caustic
refining operations. In the latter, it will be
lS particularly useful in the presence of high soap
levels, that is, even in the absence of the water wash
centrifuge treatment typically required following
caustic treatment. The disclosed method produces
commercially acceptable oil products having substan-
tially lowered concentrations of the indicated
impurities.
For purposes of this specification, the term
"impurities" refers to soaps, phospholipids and
chlorophyll. Gums or other mucillagenous materials, if
present, are also meant to be included. The
phospholipids are associated with metal ions and
together they will be referred to as "trace
contaminants." The term "glyceride oils" as used
herein is intended to encompass both vegetable and
animal oils. The term is primarily intended to
describe the so-called edible oils, i.e., oils derived
from animal fats or from fruits or seeds of plants and
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used chiefly in foodstuffs, but it is understood that
oils whose end use is as non-edibles (i.e., technical
grade oils) are to be included as well. The invention
is particularly applicable to oils which have been
subjected to caustic treatment, which is the refining
step in which soaps are formed in the oil. The invention
also will find utility in physical refining, where the
oil is not contaminated by soaps but where phospholipids
are present and where residual gums may be present even
following degumming steps.
- Refining of crude glyceride oil purifies the oil
of many undesirable substances, including gums,
pigments (such as green (chlorophyll A), red (carotene)
and yellow (xanthophyll) color bodies), phospholipids,
free fatty acids and other volatile species that impart
undesirable colors, flavors and odors to the oil.
Removal of these species results in oil having good
~ appearance, flavor, odor and stability. Many of these
! species are removed by contacting the oil with an
adsorbent (i.e., bleaching earths or amorphous silica).
Crude glyceride oils, particularly vegetable oils,
are refined by a multi-stage process, the first step of
which typically is "degumming" by treatment with water
or with a chemical such as phosphoric acid, citric acid
or acetic anhydride. This treatment removes some but
not all gums and certain other contaminants. Some of
the phosphorus content of the oil is removed with the
gums although significant levels of phospholipids still
may be present. Either crude or degummed oil may be
treated in either a physical or a chemical (caustic)
refining process. The physical refining process
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includes a pretreating and bleaching step, and a steam
refining and deodorizing step. No caustic refining
step is used. Alternatively, the oil may be refined by
a chemical process including neutralization ~caustic
treatment), bleaching and deodorization steps.
In chemical refining, the addition of an alkali
solution, caustic soda for example, to a crude or
degummed oil causes neutralization of free fatty acids
to form soaps. This step in the refining process will
be referred to herein as "caustic treatment" and oils
treated in this manner will be referred to as "caustic
treated oils." Soaps generated during caustic
treatment are an impurity which must be removed from
the oil because they have a detrimental effect on the
flavor and stability of the finished oil. Moreover,
the presence of soaps is harmful to the adsorbents used
in vacuum bleaching and to the catalysts used in the
oil hydrogenation process.
Current industrial practice is to first remove
soaps by centrifugal separation (referred to as
"primary centrifugation"). In this specification, oils
which have been subjected to caustic treatment and
primary centrifugation will be referred to as
"partially refined" oil. Conventionally, the caustic
refined oil, which still has significant soap content,
is subjected to a water wash, which dissolves the soaps
from the oil phase into the aqueous phase. The two
phases are separated by centrifugation, although
complete separation of the phases is not possible, even
under the best of conditions. The light phase
discharge is water-washed oil which now has reduced
soap content. The heavy phase is a dilute soapy water
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1 3 2 6 2 4 3
solution. Frequently, the water wash and centrifugation
steps must be repeated in order to reduce the soap content
of the oil below about 50 ppm. The water-washed oil (or
"refined" oil) is often dried to remove residual moisture
to between about 2500 and about 1000 parts per million.
The dried oil is then either transferred to the bleaching
process or is shipped or stored as refined oil.
A significant part of the waste discharge from the
caustic refining of vegetable oil results from the
water wash centrifuge step used to remove soaps. In
addition, in the caustic refining process, some oil is
lost in the water wash process. Moreover, the dilute
soapstock must be treated before disposal, tvpically
with an inorganic acid such as sulfuric acid in a
process termed acidulation. It can be seen that quite
a number of separate unit operations make up the soap
removal process, each of which results in some degree
of oil loss. The removal and disposal of soaps and
aqueous soapstock is one of the most considerable
problems associated with the caustic refining of
glyceride oils.
In addition, color bodies and phosphorus-containing
trace contaminants must be removed from the oil. The
presence of these trace cQntaminants can lend off colors,
odors and flavors to the finished oil product. These
compounds are phospholipids, with which are associated
ionic forms of the metals calcium, magnesium, iron and
copper. For purposes of this invention, references to
the removal or adsorption of phospholipids is intended
also to refer to removal or adsorption of the associated
metal ions. In the removal of color bodies, attention
is primarily given to the removal of chlorophyll.
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~ 1 3262~
Clays or bleaching earths commonly have been used
for removing phospholipids and color bodies from
glyceride oils by batch addition to the vacuum
bleacher. These adsorbents may be used in their
naturally occurring form or they may be acid-activated
prior to use (U.S. 4,443,379 (Taylor et al.)). It is
also known that amorphous silicas may be used in the
oil refining process. U.S. 4,629,588 (Welsh et al.)
teaches the utility of amorphous silica adsorbents for
the removal of trace contaminants, specifically
phospholipids and associated metal ions, from glyceride
oils.
In current refinery practice, chlorophyll is most
efficiently removed from glyceride oils by the use of
acid activated clays. Although commonly used in the
industry, clays and bleaching earths suffer from a
number of disadvantages. They typically do not filter
well and require the addition of costly filter aids.
Clays are associated with significant oil losses.
Moreover, the presence of soaps and phospholipids in
the oil is known to interfere with the clays' ability
to remove chlorophyll. It is for this reason that one
or more water wash centrifuge steps typically are
required in caustic refined oil operations, in order to
remove the soaps before the oil contacts the clay or
bleaching earth.
Due to the presence of soaps (in chemically
refined oil) or phospholipids (in physically refined
oil), it has not previously been possible to use
bleaching earths and clays in a packed bed format as
taught by this invention. Conventionally, the
~ 1 3262~3
hleaching material is added in a batch or slurry format
and is subsequently filtered from the oil. It is known
that chlorophyll removal capacity increases as the
filter becomes coated with clay, thus forming a packed
bed in s _ through which the oil is filtered. The
industry has attempted to take advantage of this packed
bed (or "press bleach") effect by partially pre-coating
the filter with a portion of the clay, perhaps up to
about 20~, with the remainder being added to the vacuum
bleacher in the usual (batch or continuous) fashion.
This mixed adaition format approach is the closest the
industry has been able to get to utilizing a packed bed
for decolorization of the oil. The mixed addition
format initially yields filtered oil with a high
chlorophyll content which drops over time as the packed
bed builds up. However, due to the relatively short
filter life achieved by this mixed approach, by the
time chlorophyll removal capacity is maximized by the
build-up of the bed, the filter must be changed.
Thus, although the advantages of a packed bed have
been recognized in terms of chlorophyll removal,
attempts to utilize a strictly packed bed operation in
practice have been frustrated. Even where caustic
treated oil is subjected to water wash centrifuge
steps, too much residual soap and phospholipid remains
to allow the use of a packed bed exclusively. A layer
of slime quickly builds up on the oil/clay interface,
causing severe pressure drop and preventing throughput
of the oil. Residual gums and phospholipids present in
physically refined oil cause similar sliming problems
and pressure drop. The filter life is extremely short.
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1 326243
,
Where no water wash centrifuge step is used, a packed
bed would be completely nonfunctional. Prior art use
of a packed bed in this process has therefore been
limited to only partially pre-coating the filter, while
still using continuous clay or bleaching earth addition
in the vacuum bleacher (i.e., a semi-batch process).
SUMMARY OF THE INVENTION
A simple dual phase adsorption and treatment
process has been found for removal of soaps, phospho-
lipids and chlorophyll from chemically or physically
refined glyceride oils. This unique process eliminates
impurities which poison decolorizing materials and
utilizes the latter materials-in a packed bed format.
The dual phase process described herein utilizes a
first phase in which the oil is contacted with
amorphous silica adsorbents to remove all or
substantially all soaps or gums or both from the oil -
and reduce the phospholipid content of the oil. In
conjunction with the use of silica to remove these
impurities, a second phase is utilized in which the oil
is filtered through a packed bed of a pigment removal
agent in order to decolorize the oil.
It is a primary object of this invention to
provide an adsorption and treatment process in which a
pigment removal agent can be employed in a packed bed
format for efficient oil decolorization. This dual
phase process allows adsorbent usage to be optimized.
A dramatically higher chlorophyll capacity, for example,
will be realized by the pigment removal agent when used
in the manner of this invention.
1 326243
It is an additional object to improve quality
control of the refined oil in terms of ensuring that
the composite oil (that is, the total volume of refined
oil out of bleaching at any particular point in time)
meets industry specifications for soaps, phospholipids
and color. A related object is to offer a process in
which the contact time between the oil and clay or
bleaching earth can be minimized, thereby reducing the
opportunity for side reactions which are deleterious to
the oil quality.
It is a further object to provide a process in
which the on-stream filter life can be more than
doubled by conserving the decolorizing capacity of the
pigment removal agent. It is thereby intended to make
more efficient use of the pigment removal agent than is
currently realized in the prior art vacuum bleaching
operations.
It is also intended that the process of this
invention provide tremendous advantage in chemical
refining of glyceride oils by eliminating the several
unit operations required when conventional water-washing,
centrifugation and drving are employed to remove soaps
from the oils. Over and above the cost savings realized
from this tremendous simplification of the oil processing,
the overall value of the product is increased since a
significant by-product of conventional caustic refining
is dilute aqueous soapstock, which is of very low value
and requires substantial treatment before disposal is
permitted by environmental authority.
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It is further intended, for embodiments utilizing
bleaching earth or clay as the pigment removal agent,
that reduction of the overall adsorbent usage will
result in substantial oil conservation as this step
typically results in significant oil loss. Moreover,
since spent bleaching earth has a tendency to undergo
spontaneous combustion, reduction of clay usage will
yield an occupationally and environmentally safer process.
DETAILED DESCRIPTION OF THE INVENTION
A dual phase adsorption and treatment process
allows for easy and efficient removal of soaps, gums,
phospholipids and pigments from glyceride oils in a
single unit operation. In the first phase, an
amorphous silica adsorbent is used to remove soaps or
gums or both, and phospholipids from the oil. In the
second phase, a pigment removing agent is used in a
packed bed to decolorize the oil. The process
essentially comprises the steps of selecting a
glyceride oil which contains impurities selected from
the group gums, soaps and phospholipids, and which also
contains pigments, contacting the oil with a sufficient
quantity of an amorphous silica adsorbent to reduce the
levels of the impurities (gums, soaps and
phospholipids) to levels which are noninhibitory to
operation of the packed bed of pigment removal agent,
and passing the silica adsorbent-treated oil through a -
packed bed comprising a pigment removal agent. At
least about 50% of the total quantity of the pigment
removal agent used in the adsorption and treatment
process is contained in the packed bed.
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This invention may be employed with physically
refined oil for the removal of gums, phospholipids and
pigments. The invention also may be employed with
` chemically refined oils for the removal of gums, soaps,
phospholipids and pigments. The presence of increasing
soaps in the oil actually enhances the capacity of
amorphous silica to adsorb phospholipids. The use of
~ silica adsorbents to remove phospholipids and soaps or
! gums or both, in conjunction with a packed bed of a
pigment removal agent very clearly protects the
capacity of that agent to decolorize the oil.
i
The Oils
The process described herein can be used for the
removal of impurities from any glyceride oil, for
example, oils of soybean, peanut, rapeseed (canola),
corn, sunflower, palm, coconut, olive, cottonseed, etc.
or animal fats. The following description will focus
on the treatment of caustic treated oils for the
removal of soaps, phospholipids and chlorophyll.
However, this invention also may be used with
physically refined oil to remove gums, phospholipids
and chlorophyll. Additionally, the invention may be
used to treat oil in which chlorophyll levels are not
problematic, in order to remove other pigments or
impurities. For example, it may be desired to remove
phospholipids and reduce red colors in palm oil by the
method of this invention. Any of these other oils may
be substituted for the caustic treated oils of the
following disclosure.
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The caustic refining process involves the
neutralization of the free fatty acid content of crude
or degummed oil by treatment with bases, such as sodium
hydroxide or sodium carbonate, which typically are used
in aqueous solution. The neutralized free fatty acid
present as the alkali or alkaline earth salt is defined
as soap. The soap content of caustic treated oil will vary
depending on the free fatty content of the unrefined oil.
Values disclosed as typical in the industry are
stated as about 300 ppm soap for partially refined
(caustic treated, primary centrifuged) oil (Erickson,
Ed., Handbook of Soy Oil Processing and Utilization,
Chapter 7, "Refining," p. 91 (1980)), but in practice,
soap levels at this stage may range up to 500 to
1000 ppm. Conventional separation and water wash
centrifuge processes remove about 90% of the soap
content generated by the caustic treatment step.
Levels of 10-50 ppm soap are taught for refined oil
(that is, caustic treated oil that has been primarv
centrifuged and fully water washed) (Christenson, Short
Course, Processing and Quality Control of Fats and
Oils, Fig. 1, presented at Amer. Oil Chemists' Soc.
(May 5-7, 1983) and Erickson, p. 92). These values are
summarized in Table I.
Fully refined oils must have soap values
approaching zero. The process disclosed herein will
reduce soaps to levels acceptable to the industry, even
where incoming oil contains up to 600 ppm soap
following caustic treatment and primary centrifuge, or
even higher in the absence of primary centrifugation.
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Of course, the dual phase process is not restrieted to
use only at these very high soap values. It also will
be advantageously used to treat refined oil having soap
levels of 10-50 ppm. The dual phase process of this
invention will reduce soap levels to less than about
10 ppm, preferably less than about 5 ppm, most preferably
about zero ppm. However, the process is not limited to
use in the presence of soaps, but can be used to treat
soap-free oils also.
Removal of trace contaminants (phospholipids and
associated metal ions) from edible oils is required in
the oil refining process because they can cause off
colors, odors and flavors in the finished oil. Typically,
the acceptable concentration of phosphorus in the
finished oil product should be less than about 15.0
ppm, preferably less than about 5.0 ppm, aceording to
general industry practice. As an illustration of the
refining goals with respect to trace contaminants,
typical phosphorus levels in soybean oil at various
stages of ehemical refining are shown in Table I.
, . . .
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~ 1 326243
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-- 14 --
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P 1 326243
In addition to phospholipid removal, the process
of this invention also removes from edible oils ionic
forms of the metals calcium, magnesium, iron and
copper, which are believed to be chemically associated
with phospholipids, and which are removed in
con~unction with the phospholipids. These metal ions
themselves have a deleterious effect on the refined oil
products. Calcium and magnesium ions can result in the
formation of precipitates, particularly with free fatty
acids, resulting in undesired soaps in the finished
oil. The presence of iron and copper ions promote
oxidative instability. Moreover, each of these metal
ions is associated with catalyst poisoning where the
refined oil is catalytically hydrogenated. Typical
concentrations of these metals in soybean oil at
various stages of chemical refining are shown in Table
I. Throughout the description of this invention,
unless otherwise indicated, reference to the removal of
phospholipids is meant to encompass the removal of
associated metal ions as well.
Residual gums and other mucillagenous materials
may be present in the oil, even after conventional
degumming procedures. While low levels of gums are not
deleterious to the oil itself, their presence would
make the use of packed bed filtration difficult or
impossible due to slime formation on the packed bed
materials at the oil/adsorbent interface.
The dual phase process described herein very
effectively and efficiently removes pigments (or color
bodies) from glyceride oil. The pigments of interest
in oil refining are green (chlorophyll), red (carotene)
and yellow (xanthophyll). It is chlorophyll A which is
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~ 1 326243
of greatest concern here, but references herein to
chlorophyll will be understood to refer to all relevant
forms of chlorophyll, or their degradation products,
such as pheophytin. In addition, reference to removal
or reduction of chlorophyll also shall refer to
decolorization of the oil in general, that is, it shall
also be intended to encompass removal or reduction of
red and yellow color bodies, whether or not in the
presence of chlorophyll, unless otherwise noted.
Chlorophyll is produced only in plants and this
invention is therefore intended primarily for use with
vegetable oils. However, it may be desired to treat
animal fats and tallows, or other oils which contain
little or no chlorophyll, in order to remove dietary
chlorophyll or for removal of other color bodies.
Removal of chlorophyll from vegetable oils is a
significant step in refining vegetable oils because the
chlorophyll imparts an unacceptably high level of green
coloring to the oil. In addition, chlorophyll has been
implicated as a factor in the instability of oils on
exposure to light. Chlorophyll levels vary
dramatically from oil to oil, as well as from crop to
crop, depending on growing and harvesting conditions.
Although target chlorophyll values vary from refiner to
refiner, the target values for bleached oils and for
deodorized oils typically are in the range of about
0.05 to about 0.20 ppm or less, as shown in Table I.
In referring to caustic treated, partially refined
and refined glyceride oils, it is intended to refer
only to oils in the form in which they normally would
result from those well-established refining processes.
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1 326243
It is not intended, for example, to include treatment
of oil miscella, in which the oil is dissolved in
quantities of a solvent such as hexane. In the
refining process in which this invention will be
employed, solvents used in extracting the glyceride oil
from seeds will have been removed at a step prior to
the dual phase process described here.
The Adsorption and Treatment Materials
Two different types of adsorption and treatment
materials are used in this dual phase process. In the
first phase, a material is used which is uniquely able
to remove both soaps and phospholipids, especially in
the presence of high soap levels. Gums, if present,
are also removed in this first phase. The material of
choice here is amorphous silica. In the second phase,
a pigment removal agent is used which will decolorize
the oil. Clay or bleaching earth is preferred.
Silica Adsorbents - The term "amorphous silica" as
used herein is intended to embrace silica gels,
precipitated silicas, dialytic silicas and fumed
silicas in their various prepared or activated forms.
The specific manufacturing process used to prepare the
amorphous silica is not expected to affect its utility
in this method.
In the preferred embodiment of this invention,
the silica adsorbent will have a high proportion of its
surface area in pores which are large enough to permit
access to soap and phospholipid molecules, while being
capable of maintaining good structural integrity upon
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1 326243
contact with the oil. The requirement of structural
integrity is particularly important where the silica
adsorbents are used in continuous flow systems, which
are susceptible to disruption and plugging. Amorphous
5 silicas suitable for use in this process have surface
areas of up to about 1200 square meters per gram,
preferably between 100 and 1200 square meters per gram.
It is preferred for as much as possible of the surface
area to be contained in pores with diameters greater
than 50 to 60 Angstroms, although amorphous silicas
with smaller pore diameters may be used in the process.
In particular, partially dried amorphous silica hydrogels
having an average pore diameter ("APD") less than 60A
(i.e., down to about 20A) and having a moisture content
of at least about 25 weight percent will be suitable.
The practical upper APD limit is about 5000A.
The preferred porosity for soap and phospholipid
adsorption may be achieved by the creation of an
artificial pore network of interparticle voids in the
50 to 5000A range. For example, non-porous silicas
(i.e., fumed silica) can be used as aggregated
particles. Silicas of any porosity may be used under
conditions which create this artificial pore network.
Thus it is preferred to select amorphous silicas for
use in this process which have an "effective average
pore diameter" greater than 50A. This term includes
both measured intraparticle APD and interparticle APD,
designating the pores created by aggregation or packing
of silica particles.
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,
1 3 2 6 2
-
The purity of the amorphous silica used in this
invention is not believed to be critical in terms of
the adsorption of impurities. However, where the
finished products are intended to be food grade oils,
care should be taken to ensure that the silica used
does not contain leachable impurities which could
compromise the desired purity of the product(s). It is
preferred, therefore, to use a substantially pure
amorphous silica, although minor amounts, i.e., less
than about 10%, of other inorganic constituents may be
present. For example, suitable silicas may comprise
iron as Fe203, aluminum as Al203, titanium as TiO2,
calcium as CaO, sodium as Na2O, zirconium as Zr02,
sulfur as SO4, and/or trace elements.
Especially preferred are organic acid-treated
amorphous silicas. U.S. 4,734,226 (Parker et al.)
teaches that amorphous silicas treated with citric
acid, acetic acid, ascorbic acid or tartaric acid to a
total volatiles content of at least about 10~ are
useful for removal of trace contaminants, specifically
phospholipids and associated metal ions, from oils.
Citric acid-treated amorphous silicas are particularly
preferred.
Pigment Removal Agents - The pigment removal agent
used in the second phase of this process may comprise
any material known to remove pigments from glyceride
oil by chemical reaction, physical adsorption or both.
This includes but is not limited to activated carbon,
acid-treated amorphous silica, and natural or synthetic
silica-alumina materials. The silica-aluminas may be
acid-activated or non-activated, and may be amorphous
or crystalline.
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The natural silica-alumina materials comprise
clays and bleaching earths. The term "clay" as used
herein is intended to embrace natural (i.e., non-acid-
activated) and acid-activated clays, bleaching clays
and bleaching earths, as these products are variously
termed. Clay products are widely known and used in the
glyceride oil refining industry. The clays most
typically used are sub- or metal-bentonites and
fuller's earths. Montmorillonite is the major
component of the sub-bentonite clays, which also may
contain non-clay components. The fuller's earths are
predominantly montmorillonite and attapulgite with
small amounts of kaolinite, halloysite, and illite, as
well as some non-clay materials. Acid-activation
procedures are well known to the industry and are
described in U.S. 4,443,379 (Taylor et al.).
Where clay or primarily clay is used, it may be
necessary to mix in a filter aid to facilitate
processing of the oil through the packed bed. Filter
aids such as diatomaceous earth, perlite, sand, or the
like may be used. Although it may be desirable or
necessary to use a filter aid, the present process
minimizes the need for filter aids.
Synthetic silica-alumina materials also have the
ability to remove pigments from glyceride oils. These
synthetic materials can be amorphous, including for
example M-S microspherical silica alumina powders
(Davison Div., W. R. Grace & Co.), or the like.
Alternatively, crystalline aluminosilicates, such as
zeolites, etc., may be used as pigment removal agents
in this process.
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It also has been found that amorphous silicas,
such as those described in the preceeding section, can
be effective chlorophyll removal agents if they first
are pre-treated with an acid. Use of amorphous silica
treated in this manner for the removal of phospholipids
and color bodies from glyceride oil is taught in USSN
50,594 (Pryor et al.), "Process for the Removal of
Chlorophyll, Color Bodies and Phospholipids from
Glyceride Oils Using Acid-Treated Silica Adsorbents."
Acids suitable for preparation of the acid-treated
silica adsorbent can be of any type -- inorganic,
organic or acidic salt -- but must have a PKa Of about
3.5 or lower. Inorganic acids are preferred. In the
preferred embodiment, the acid will be a mineral acid,
with the stronger acids being the most effective.
Sulfuric acid is the most preferred, both for its
effectiveness and for its ability to remain supported
on the silica. Phosphoric acid is effective for
adsorption, but has a tendency to come off the silica
into the oil, which may make it less desirable in
certain applications. Alternatively, hydrochloric acid
may be used. The acids may be used singly or in
combination.
Strong organic acids also may be supported on the
silica for use in this invention. Typically, these
will be modified organic acids such as toluene sulfonic
acid, trifluoroacetic acid and the like. Alternatively,
acidic salts, such as magnesium sulfate, aluminum
chloride, aluminum sulfate and the like, may be used in
this invention.
- 21 -
:
..
1 326243
The possible acid-base interaction of the acid
with the support should be considered when selecting
the two materials. The pH of the acid-treated adsorbent
should be less than or equal to about 3.0 when measured
as the pH of a 5.0 wt% (dry basis) slurry of the
adsorbent in de-ionized water. In other words, there
should be sufficient free acid available in the acid-
treated adsorbent beyond any amounts of acid which may
interact with the support material. The acid content
of the acid-treated adsorbent should be at least about
1.0 wt%, preferably about 3.0 to about 10.0 wt%, and
most preferably about 5.0 wt%, based on the dry weight
of the amorphous silica. Persons of ordinary skill in
the art will be capable of selecting appropriate acids
for support on the amorphous silica in order to achieve
this overall product pH.
Treatment of the silica may be with neat acid or
with an aqueous acid solution. The acid strength and
concentration on the support should be such that:
Acidity Factor = Ka x Moles of Acid
Grams of Support
> 2.0 x 10
where Ka is the dissociation constant of the acid. It
will be appreciated that the acid strength and concen-
tration may be easily adjusted to achieve an acidity
factor in this range.
It is desired to support a sufficient amount of
acid on the silica such that the total volatiles
content of the acid-treated silica is about 10 wt% to
about 80 wt~, preferably at least about 30 wt%, and
most preferably about 40 to 80 wt%.
- 22 -
.--~
1 326243
The amorphous silica can be treated with the acid
or acidic solution in several ways. First, the silica
may be slurried in the acidic solution for long enough
, for the acid to enter the pores of the silica,
typically a period of at least about one half hour, up
to about twenty hours. The slurry preferably will be
agitated during this period to increase entry of the
acid into the pore structure of the amorphous silica.
;, The acid-treated silica is then conveniently separated
from the solution by filtration and may be dried to the
desired total volatiles content.
Alternatively, the acid solution can be introduced
to the amorphous silica in a fixed bed configuration,
for a similar period of contact. This would be
particularly advantageous for treating unsized, washed
silica hydrogel, since it would eliminate the standard
i dewatering/filtration step in processing the hydrogel.
, A third method is by introducing a fine spray or jet of
the organic solution into the amorphous silica as it is
fed to a milling/sizing operation or at any other
convenient step. These latter two methods will be
preferred for treating silica in a commercial scale
operation.
Any of the pigment removal agents described above
may be used alone in the packed bed of this invention,
with or without a filter aid. Alternatively, two or
more agents may be used together in the packed bed,
either mixed or serially, and again, either with or
without filter aid.
- ~3 -
1 326243
The Adsorption Process
The process of this invention presents a dual
phase adsorption and treatment operation. In the first
phase, soaps and phospholipids ~or gums and
phospholipids) are removed from the oil by contact with
amorphous silica. In the second phase, the oil is put
through a packed bed comprising a pigment removal agent
for removal of pigments.
' As discussed above, amorphous silicas are to be
used as the adsorbent in the first phase of this
process. They are particularly well suited for
removing both soaps and phospholipids from caustic
treated or partially refined glyceride oils. The
capacity of the silica for adsorbing phospholipids is
actually improved with increasing soap levels in the
starting oil, provided that sufficient silica is used
, to obtain adsorbent-treated oil with soap levels of
approximately 30 ppm or less. It is when the residual
soap levels ~in the adsorbent-treated oil) are reduced
to below about 30 ppm that the increased capacity of
the silica for phospholipid adsorption is seen. It is
believed that the total available adsorption capacity
of amorphous silica is about 50 to 150 wt.~ on a dry
basis.
~ 25 The silica usage should be adjusted so that the
`~ total soap and phospholipid content of the caustic
- treated or partially refined oil does not exceed about
S0 to 150 wt.% of the silica added on a dry basis. The
- maximum adsorption capacity observed in a particular
application is expected to be a function of the
't specific properties of the silica used, the oil type
,;
-- 24 --
?
.
.
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~ ' ' . ' .
~ ^
~ 1 326243
.
and stage of refinement, and processing conditions such
as temperature, degree of mixing and silica-oil contact
time. Calculations for a specific application are well
within the knowledge of a person of ordinary skill as
, 5 guided by this specification.
I The soap and phospholipid reduction is accomplished
by contacting the amorphous silica and the oil in a
manner which facilitates the adsorption. This
t adsorption step may be by any convenient batch or
'' 10 continuous process. Agitation or other mixing will
enhance the adsorption efficiency of the silica. It is
- preferred that the silica be added in a continuous or
semi-continuous manner. It is also preferred to
contact the oil and silica in the substantial absence
15 of pigment removal agent, although some quantities of
~, the latter may be present in alternative embodiments.
The caustic refined oil and amorphous silica are
, contacted as described above for a period sufficient to
substantially remove the soaps and phospholipids from
20 the oil. Residual quantities may remain but these must
~j be sufficiently minor so as not to create sliming and
`~ blockage of the packed bed in the second phase of this
process. The specific contact time will vary somewhat
with the adsorbent usage, that is, the relative quantity
of amorphous silica adsorbent and the pigment removal
~ agent which are brought into contact with the oil. The
,.,'5. adsorbent usage is quantified as the weight percent of
the materials (on a dry weight basis after ignition at
.
, .
- 25 -
.
,, .
,
".
~ 326243
:;
1750F), calculated on the basis of the weight of the
oil processed. The preferred amorphous silica usage is
at least about 0.01 to about 1.0 wt.%, dry basis, most
preferably at least about 0.03 to about 0.30 wt.~, dry
basis.
Where this process is used to treat physically
refined oil, the procedures will be the same. The
~j adsorbent usage will be calculated on the basis of
; phospholipid content, however, instead of soap content.10 Here again, it is intended that the impurities be
substantially removed. The preferred adsorbent usage
will be about 0.01 to about 1.0 wt.% (dry basis). For
treatment of oils whose phosphorus levels are reduced
to about 5.0 ppm phosphorus or less, the dry basis
15 capacity of amorphous silicas is about 12.0 to about
45.0 wt~.
In the pigment removal phase of the invention, the
. oil is filtered through a packed bed of a pigment
removal agent. The first and second phases of the
20 process may be separated, with the silica being
filtered from the oil prior to the oil contacting the
packed bed. Alternatively, the spent amorphous silica
from the first phase of the process is removed
4 simultaneously as the oil is passed through the packed
25 bed of pigment removal agent in the second phase.
Selection of one of these alternative embodiments will
depend on the particular plant set-up. In either case,
it is preferred that the silica adsorbent of the first
phase and the pigment removal agent of the second phase
30 remain substantially completely unmixed.
,
,
- 26 -
.,
~ - , ' '
: , ,
~ 1 326243
,
In the preferred embodiment of this invention, a
filter is pre-coated with a pigment removal agent and
the pre-coated filter is used to decolorize the oil.
sy pre-coating the filter in the manner of this
5 invention, it is preferred that the full loading of
pigment removal agent is presented to the oil in a
packed bed. This protects the pigment removal agent
from contamination by soaps and phospholipids, thus
~;~ maintaining the agent's capacity and effectiveness for
10 removing chlorophyll and other color bodies from the
oil. More efficient chlorophyll A reduction is consis-
tently obtained by this method than by batch or continuous
co-addition or sequenti~al addition of silica and clay.
As stated, in the preferred embodiment, all of the
15 pigment removal agent used in the adsorption and
treatment process will be contained in the packed bed
as described. The silica adsorbent and the pigment
removal agent preferably will remain substantially
unmixed, although some incidental mixing may occur at
x 20 the front end of the packed bed. Although not
preferred, less than 100% of the pigment removal agent
can be used in the packed bed, with the remainder being
;~Jj added to the oil in the first phase of the process. To
the extent that this is done, however, the full benefit
25 of pigment removal capacity is compromised. However,
, up to about 50% of the pigment removal agent may be
added in this manner. That is, for the present
invention, at least about 50% of the pigment removal
~ agent should be used in the packed bed, preferably at
i 30 least about 75%, most preferably 90 to 100%. A filter
aid may be used in addition to the pigment removal
agent, as described above.
- ~7 -
.,
.,
,,
1 326243
:'
n general, the longer the length of the packed
bed in the second phase of this process, the better the
- utilizaton of the decolorization capacity of the
pigment removal agent will be. However, improved
capacity must be balanced against the greater pressure
drop associated with a longer bed. This type of
~; adjustment is common in industrial processes and will
be within the skill of the refiner. The preferred
pigment removal agent usage is at least about 0.01 to
about 1.0 wt~, dry basis, preferably 0.05 to 0.5 wt%,
dry basis. In terms of filter pre-coat, the usage
should be in the range of about 0.3 to about 6.0 pounds
per square foot of filter, preferably about 1.0 to
about 4.0 pounds.
The process of this invention can be conducted at
any convenient temperature at which the oil is a liquid.
The preferred temperature will depend on which pigment
removal agent is selected, and the optimum temperature
can be expected to vary somewhat. In addition, the
optimum temperature for each of the two phases of the
~.
-, process is different. If the two process phases are
separated, it may be desired to adjust the oil
temperature to approximate the optimum for each phase.
In general, higher temperatures result in better
decolorization, and it is preferred that the oil be at
about 90 to about 120C for this stage. Oil temperatures
may be as high as 150C, or even higher in some cases.
' For the first phase of the invention (that is, for
adsorption of gums or soaps and phospholipids), lower
s 30 oil temperatures are preferred. The oil temperature
preferably is about 25 to about 100C, more preferably
about 60 to about 80C.
- 28 -
-
.. . .
., ,
,. .
,
1 326243
It can be seen, then, that some balancing must be
- done in targeting the oil temperature for this process.
Alternatively, the oil may be heated between the first
and second phase of the process. Constraints based on
the overall refining operation may also be present.
For example, where oil is sent to bleaching directly
from the previous processing stage, temperatures
typically will be at least about 70 to 80C, which is
satisfactory for use here. However, where oil has been
stored prior to bleaching, it may be cooler and may
require heating before or while being treated by the
i~ present process.
As seen in the Examples, significant reduction in
soap and phospholipid content can be achieved by the
method of this invention. The initial soap content and
the phosphorus content of the oil will depend primarily
on the oil itself, as well as on the silica, usage,
process, etc. For example, by reference to Table I, it
will be appreciated that the initial soap content will
vary significantly depending whether the oil is treated
~, by this adsorption method following caustic treatment
~ alone, or following primary centrifuge or water wash
.,~ centrifuge. Similarly, the phosphorus content will be
somewhat reduced following degumming, caustic
"
treatment, primary centrifuge and/or water wash
' centrifuge. The first phase of this process will
reduce the levels of impurities (i.e., gums, phospho-
lipids, soaps) to levels which are noninhibitory to
operation of the packed bed. However, phosphorus
levels of less than about 2.0 ppm, preferably
,,
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- 29 -
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~ '
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~ ~ 3~43
substantially zero, and soap levels of less than about
10 ppm and most preferably substantially zero, are
achieved by this adsorption method. Gum levels
preferably are reduced to less than about 2.0 ppm,
preferably substantially zero.
Similarly, chlorophyll levels are reduced in
accordance with industry standards, that is, to less
` than about 0.2, preferably to between about 0.05 and
0.2 ppm, or less. The loading of the pigment removal
agent can be adjusted according to the chlorophyll
levels of the incoming oil, which are subject to large
fluctuation as discussed above. It is already within
the skill of refinery operators to vary the quantity of
bleaching material relative to the incoming chlorophyll
levels in conventional vacuum bleaching processes.
Although similar adjustments will be necessary in the
process of this invention, significantly less pigment
removal agent will be used per volume of treated oil
than has been possible in the prior art processes.
The present invention makes it possible to use a
fully formed packed bed (i.e., with the entire loading
~ of pigment removal agent) throughout the entire period
- the filter is on-stream. In addition, filter on-stream
` times are at least doubled, as compared with the
conventional use of clay alone or the co-addition or
sequential addition of clay and silica to the oil,
- followed by filtration. The dual phase treatment of
7 this invention gives the refiner the advantage of
- optimum materials and filter usage, as well as better
quality control.
,
~ - 30 -
^- .
.
,
,
, ~ ,
-` 1 326243
Quality control of the oil in terms of the
impurities addressed by this process is significantly
improved. Contrary to the prior art processes, the
first oil coming out of the packed bed of this
invention contains no chlorophyll at all. As the
"
chlorophyll-removing capacity of the packed bed is
filled, the chlorophyll level of the oil leaving the
filter begins to rise, as does that of the composite
, oil (i.e., the full volume of treated oil). Therefore,
it is an easy matter to monitor chlorophyll in the
composite oil, and to cut off the oil stream before the
oil goes out of specification. The composite oil,
ii however, is always within the targeted chlorophyll
levels.
This contrasts with prior art processes in which
the initially treated oil has high chlorophyll levels,
perhaps above specification. In that case, the
~ composite oil may not come within specification for
,J, chlorophyll until the filter has been on-stream for
several hours and the chlorophyll levels of the oil
leaving the filter are low enough to balance the high
initial levels. System upsets or shut-downs prior to
that time may result in out-of-spec composite oil.
The dual phase process described here results in
greatly enhanced removal of key glyceride oil
impurities -- soaps, phospholipids and pigments. The
~; capacities of pigment removal agents for decolorizing
oil are dramatically increased by the ability to use
the agents in a packed bed format. At the same time,
- 30 this is accomplished at greatly reduced adsorbent
' usages, or, conversely, with greatly extended filter
~,
, .
.,
~ 1 --
~, .
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~` ~ 1 326~43
lifetimes. Moreover, this dual phase process allows
the water wash step(s) to be entirely eliminated from
chemical refining operations, if desired, thereby
reducing wastewater processing and costs as well as
; 5 environmental hazards.
The examples which follow are given for
illustrative purposes and are not meant to limit the
invention described herein. The following abbreviations
have been used throughout in describing the invention:
~; lO A _ Angstrom(s)
APD - average pore diameter
C - capacity
Ca - calcium
ChlA - chlorophyll A
Cu - copper
C - degrees Centigrade
, db - dry basis
Fe - iron
;~i ft2 - square foot
gm - gram(s)
hr - hour(s)
lb - pound(s)
Mg - magnesium
min - minutes
ml - milliliter(s)
P - phosphorus
, PL - phospholipids
i ppm - parts per million (by weight)
~ PRA - pigment removal agent
- 30 ~ - percent
S - soaps
wt - weight
- 32 -
:'
,
, ;, ~ ~ .
:, ~ , . "
~ ~ 326~43
EXAMPLE I
Chemically refined soybean oil was treated by the
dual phase adsorption and treatment process of this
invention. By "refined" is meant oil which has been
i 5 caustic treated, primary centrifuged and water
centrifuged.
A high pressure column reactor system with a sand
bath heater was used in this experiment. The refined
oil was treated with 1.0 wt~ (dry basis) TriSylTM
; lO amorphous silica hydrogel (Davison Div., W. R. Grace &
Co.) and filtered to remove the spent silica. Analysis
for soap and phospholipid content was done at this
point. Soap was reduced from 24.0 ppm to zero and
phosphorus from l.0 to below 0.1 ppm, the limit of
detection for the analytical test used.
The oil then was passed through the column
containing the pigment removal agent ~PRA). As shown
in Table II, three different agents were tested.
; M-S M13 silica-alumina powder, Grade 135 (Davison Div.,
W. R. Grace & Co.) is a synthetic product which was
,~ acid alum treated for one hour at 538C and screened on
230 Mesh. NevergreenTM clay (Harshaw/Filtrol
Partnership) is an acid-activated montmorillonite
bleaching clay, which was mixed with diatomaceous earth
filter aid in a 5:1 ratio of clay-to-earth. TriSylTM
amorphous silica hydrogel was treated with aluminum
sulfate. Table II shows the results of using these
3, pigment removal agents in the present dual phase
process at different loadings and temperatures.
,
,.
; .
- 33 -
;
~ ~ 326243
The data from these trials is tabulated in Table
- II in a way which compares the performance of the
various runs of this Example as might be encountered in
i a commercial process. This Table quantifies the amount
of oil which could be processed over a given quantity
of pigment removal agent while meeting a specification
of 0.05 ppm chlorophyll A for the processed oil as a
- composite. That is, the processed oil is pooled to
reach the 0.05 ppm level, combining the initial process
j 10 stream in which the chlorophyll levels will be below
i 0.05 ppm with the final process stream in which
~' chlorophyll levels will be above 0.05 ppm.
.,. /
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- 34 -
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-- 35 -
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~ 3~6243
EXAMPLE II
Samples of chemically refined soybean oil as in
Example I were treated with 1.0 wt% (dry basis)
TriSylTM amorphous silica hydrogel (Davison Div., W. R.
,~ 5 Grace ~ Co.) and filtered to remove the spent silica.Next, the oil was treated with several pigment removal
agents at 85, 100 or 120C. This example was done in
a batch process, and does not demonstrate the packed
, bed process of this invention. Rather, it is offeredlO to demonstrate the effect of temperature on oil
decolorization.
The three pigment removal agents tested were:
, M-S 13 silica-alumina powder, Grade 135 (Davison Div.,
- W. R. Grace & Co.), NevergreenTM clay (Harshaw/Filtrol
15 Partnership), and Filtrol 160TM acid-activated
montmorillonite bleaching clay (Harshaw/Filtrol
Partnership). The usage of each pigment removal agent
is given in Table III in wt~ (as is). Chlorophyll removal
Y capacity is calculated as (gm ChlA/gm PRA) x 106. The
j 20 results shown in Table III demonstrate increasing
,~ chlorophyll removal capacity with increasing
temperature for each of the pigment removal agents
tested.
'`~, ~
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1 326243
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- 37 -
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EXAMPLE III
Chemically refined soybean oil as in Example I was
subjected to the dual phase method of this invention.
A 2000.0 ml quantity of oil was treated with
16.3 gm (as is) TriSylTM amorphous silica hydrogel
(Davison Div., W. R. Grace & Co.) and then separated
from the spent silica. The oil had a measured
chlorophyll A content of 0.46 ppm. The oil was then
passed through a 3.0 gm packed bed of M-STM13
silica-alumina powder, Grade 135 (Davison Div.,
W. R. Grace & Co.) that had been acid alum activated as
in Example I. The oil eluted during the early stages
of this experiment (~100/ml) had no measurable
chlorophyll A content. When 500 ml had been treated,
the outlet ChlA was about 0.1 ppm. At 1000 ml, the
outlet ChlA was about 0.2 ppm. At 2000 ml, the outlet
ChlA was about 0.3 ppm.
The adsorbent saturation capacity for ChlA using
' the packed bed format of this invention was roughly
; 20 seven times greater than that expected based on batch
isotherm data. From a simple theoretical viewpoint,
~ assuming negligible co-adsorption effects, the
- saturation capacity of the fixed bed should equal the
extrapolated equilibrium isotherm determined from batch
-' 25 contacting of the adsorbent and oil at various
, loadings. The expected saturation capacity is
determined by extrapolating the isotherm data to the
initial ChlA concentration. The packed bed format
~,' allows one to approach this capacity in commercial
practice while maintaining low contaminant levels in
the outlet process stream. However, the seven-fold
- 38 -
' ~ . ' ~ .
',
~ ~ 3~6~43
greater than expected saturation capacity indicates
that the complex oil mixture contains as yet
unidentified poisons that are effectively removed at
the front end of the packed bed. As a result, there is
a performance benefit observed in the packed bed that
would not be expected from a standard adsorption
isotherm analysis. This phenomenon is another reason
that the p~cked bed format is desirable.
.. ,
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- 39 -
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~ 326~43
EXAMPLE IV
Chemically refined soybean oil, as in Example I,
was treated by the dual phase process of this invention
in a plant scale operation. The levels of soap,
phospholipids and chlorophyll A for the incoming oil
are indicated in Table IV, for each of four different
runs, one control and three runs which embodied the
present invention. In each run, a filter leaf filter
- was pre-coated with 1.5 pounds Filtrol 160 M clay
(~arshaw/Filtrol Partnership) per square foot of
filter. Oil was put through the filter at a rate of
75.0 lb/ft2-hr. Oil temperature was about 82C on
contacting the silica adsorbent, and about 100C on
contacting the packed bed of pigment removal agent
~ . .
(clay).
In the control run, no amorphous silica adsorbent
was used, in order to demonstrate the poor results
obtained in attempting to simply use a packed bed of
bleaching clay. Each of the other runs demonstrated
the dual phase process of this invention. TriSylTM
~i
amorphous silica hydrogel (Davision Div., W. R. Grace &
Co.) was used in Runs 1 and 2. The citric acid-treated
4 silica hydrogel (Davison Div., W. R. Grace ~ Co.), used
in Run 3 was an amorphous silica hydrogel treated with
citric acid as taught in U.S. 4,734,226 (Parker et
al.). Table IV summarizes the results.
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- 40 -
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1 326~43
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,
- 1 326243
The principles, preferred embodiments and modes of
operation of the present invention have been described
in the foregoing specification. The invention which is
intended to be protected herein, however, is not to be
construed as limited to the particular ~orms disclosed,
since these are to be regarded as illustrative rather
than restrictive. Variations and changes may be made
-, by those skilled in the art without departing from the
spirit of the invention.
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