A process for making acid-activated bleaching earth from certain
naturally occurring mixtures of calcium bentonite and attapulgite
clay. The process involves treating such clay with low levels of
activating acid which are mixed with the dried and ground clay,
or spray dried from slurries containing the clay-acid mixture. Advantages
include: lower acid costs/unit mass of clay treated, lower production
costs (no washing, filtering, or waste treatment steps) and environmental
soundness (no harmful environmental waste products are produced).
1. A method for producing bleaching earth from clay which comprises
selecting a naturally-occurring acidic mixture of palygorskite and
bentonite clays, mixing said selected clay mixture with an acid
solution in amount corresponding to an acid dosage in the range
of 1 to 10% by weight, reacting said clay with said acid and, without
washing the resulting reaction product with water, recovering it
for use as a bleaching earth.
2. The method of claim 1 wherein said selected clay has a slurry
pH in the range of 5 to 7.
3. The method of claim 1 wherein said clay has a pore volume in
the range 0.15-0.50 cc/gm.
4. The method of claim 1 wherein said selected clay contains no
more than about 5% CO.sub.2 by weight on a moisture free weight
5. The method of claim 1 wherein said selected clay is a naturally-occurring
mixture of the mineral attapulgite and bentonite.
6. The method of claim 5 wherein said selected clay contains from
about 10% to 90% attapulgite.
7. The method of claim 5 wherein said selected clay contains about
8. The method of claim 1 wherein the acid dosage is in the range
of 3 to 5%.
9. The method of claim 1 wherein said mixture is heated at a temperature
in the range of 77.degree. to 210 .degree. F. to react said clay
with said acid.
10. The method of claim 1 wherein said selected clay is dried and
ground before mixing with said acid.
11. The method of claim 1 wherein said mixture of clay and acid
is heated while it is spray dried.
12. The method of claim 1 wherein said mixture of clay and acid
is formed by spraying acid solution onto dried clay.
13. The method of claim 1 wherein said clay is dried and ground,
mixed with acid solution, filtered after heating, and filtrate is
14. The method of claim 1 wherein said acid is sulfuric.
15. The method of claim 1 wherein said acid is selected from the
group consisting of sulfuric, phosphoric, hydrochloric, formic and
16. A method for producing bleaching earth from naturally-occurring
mixture of attapulgite and bentonite clays in which the attapulgite
content is from 10% to 90% by weight, said clay mixture having a
slurry pH in the range of at least 5 and below 7 and a pore volume
in the range of 0.25-0.35 cc/gm, mixing said clay with a solution
of sulfuric acid in amount corresponding to an acid dosage in the
range of 1 to 10% by weight, heating said mixture to react said
clay with said acid and, without washing the resulting reaction
product, recovering it for use as a bleaching earth.
17. The method of claim 16 wherein said clay contains no more than
about 5% CO.sub.2 by weight on a moisture free weight basis.
18. The method of claim 16 wherein said selected clay contains
at from about 20% to 60% attapulgite.
19. The method of claim 16 wherein the acid dosage is in the range
of 3 to 5%.
20. The method of claim 16 wherein said mixture is heated at a
temperature in the range of 77.degree. to 210.degree. F.
21. The method of claim 16 wherein said clay is dried and ground
before mixing with said acid.
22. The method of claim 16 wherein said mixture of clay and acid
is heated while it is spray dried.
23. The method of claim 16 wherein said mixture of clay and acid
is formed by spraying acid solution onto dried clay.
24. The method of claim 16 wherein said clay is dried and ground,
mixed with acid solution, filtered after heating, and filtrate is
25. The bleaching earth product obtained by the method of claim
1 or 16.
This application is related to U.S. Ser. No. 352790 filed concurrently
FIELD OF THE INVENTION
The invention relates to a process for making acid-activated bleaching
earth from certain naturally occurring mixtures of palygorskite
clay (attapulgite or sepiolite ) and bentonite clay and to novel
acid-activated bleaching earth products obtained thereby.
Acid-activated clays of high activity are used to adsorb colored
pigments (carotenoids, chlorophyll) and colorless pigments (phospholipids)
from edible and inedible oils. This process is called "bleaching"
and serves both cosmetic and chemical purposes. Thus, bleaching
reduces color, whereby very clear, almost water white oils are produced
that meet with consumer expectations. Bleaching also stabilizes
the oil by removing colored and colorless pigments which tend to
"destabilize" the oil, resulting in oils that rancidify
more easily if they are not removed. The current, and expected long
term trend, favors the use of highest possible bleaching efficiency
clays with this process because: (i) the smaller amounts of the
high activity clays needed to produce desired refined oil properties
mean that lower inventories can be maintained by the oil refiner;
(ii) refined oil losses depend somewhat on the amount of clay used
because less of high activity clay needs to be used and therefore
oil losses are lower; and (iii) less spent clay is produced when
using high activity clay, and hence land-fill disposal costs are
The conventional process for producing acid-activated bleaching
clays utilizes calcium bentonite clays and requires relatively high
acid dosages to achieve maximum bleaching efficiencies. The calcium
bentonites used in the process are hydrated sodium calcium aluminosilicates
which typically are mildly basic. The manufacture of highest quality
commercial bleaching earths typically require 70-90 grams of 96%
H.sub.2 SO.sub.4 /100 grams of dry clay or 67.2-87.4% acid dosage
where: ##EQU1## Extensive leaching of the clay structure in the
form of solubilized salts takes place and these are removed in the
process. Because of these high acid dosages, and the extensive leaching
that takes place during the leaching process, the yield of bleaching
clay is low (typically in the range of 75-85 wt %). The acidic salts
formed during activation and residual acid must be washed off and
separated by filtration from the product clay. If high levels of
unused acid and acidic salts (iron and aluminum sulfates) are left
in the clay, the quality of the bleached oil is impaired. High residual
acid levels generate undesirable free fatty acids from the fatty
acid triglycerides in the oil. Finally, the leachate (acidic salts
and residual acid) is a waste stream that contains materials harmful
to aquatic life and therefore must be neutralized or otherwise disposed
of in an environmentally acceptable manner. This constitutes an
additional expense of producing bleaching clays from pure calcium
Clay sources used in the past to provide acid-activated bleaching
clay of high activities have been primarily restricted to calcium
bentonites, i.e., clays in which the principal exchangeable cation
is a calcium ion, and these are sometimes also referred to as sub-bentonites.
Another type of naturally-occurring clay simply requires heat to
impart bleaching activity. These are the clays rich in the minerals
attapulgite or sepiolite, now frequently classified as palygorskite
clays. Mineralogically, the palygorskite clays are readily distinguishable
from the bentonites (smectites or montmorillonites) and rarely are
palygorskites and bentonites used interchangeably.
It has been the general belief that palygorskite clays do not respond
to the conventional acid-activation treatment. The same is true
of certain bentonites, namely sodium (swelling) bentonites, such
as Wyoming bentonites.
The following publications pertain to the art of preparing bleaching
earths from naturally-occurring clays.
A. D. Rich, "Bleaching Clay", Industrial Rocks &
Minerals, 3rd. Ed., AIME, N.Y. pp 92-101 (1960).
R. Fahn, "Bleaching Earths-Preparation, Properties, Practical
Applications", Chapter 1 Internal Symposium, Brussels, April
L. L. Richardson, "Use of Bleaching Clays in Processing Edible
Oils", JAOCS, 55 777 (1978).
G. M. Clarke, "Special Clays", Ind. Minerals, Sept.,
D. R. Taylor, D. B. Jenkins, "Acid-Activated Clays",
Soc Mining Eng Of AIME, Transactions, 282 1901 (1988).
R. L. Grim, "Applied Clay Mineralogy", pp 320-326 (1962).
A. C. D. Newman, "Chemistry of Clays and Clay Minerals,"
pp 107-114 (1987).
The following patents relate to the production of acid-activated
U.S. Pat. No. 1397113 (1921); Prutzman
U.S. Pat. No. 1579326 (1924); Kauffman
U.S. Pat. No. 1642871 (1927); Chappell et. al.
U.S. Pat. No. 2470872 (1949); Secor
U.S. Pat. No. 2472489 (1949); Pierce
U.S. Pat. No. 2484828 (1949); Hickey
U.S. Pat. No. 2553239 (1946); Christianson
U.S. Pat. No. 2563977 (1949); Van Horn, Kahn
U.S. Pat. No. 2574895 (1951); Stecker
U.S. Pat. No. 2671058 (1952); Mickelson
U.S. Pat. No. 2872419 (1959); Farnand
U S. Pat. No. 2892800 (1959); Taipale
U.S. Pat. No. 2981697 (1961); Mickelson, et. al.
U.S. Pat. No. 3617215 (1971); Massaire, et. al.
EPA No. 0276954 (1988); Alexander
Generally, in the patents listed above, calcium bentonites are
the source clays and high acid dosages, typically above 40-50 gms
of 96% H.sub.2 SO.sub.4 /100 gms of dry clay, are required for maximum
improvement in bleaching efficiency. The acid treated clay is invariably
washed to remove soluble salts and entrained acid. See, for example,
U.S. Pat. No. 1397113 U.S. Pat. No. 1642871 and the recently
published EPA (0276954).
It is known to add citric acid to oils that are bleached with mixed
attapulgite/calcium bentonite bleaching earths in order to enhance
chlorophyll adsorption. Citric acid is not used to activate the
U.S. Pat. No. 3029783 (Sawyer, et al), directed to an improved
animal litter composition, describes an acid treatment, preferably
using an attapulgite clay, which employs relatively low acid dosages
without washing. The processing requires a calcination treatment
at 700.degree.-1000.degree. F. prior to the acid treatment and
a second calcination at 750.degree.-1100.degree. F. after acid
treatment. The patent is not directed to the manufacture of a bleaching
earth and we have found that the procedure does not lead to the
preparation of a high efficiency bleaching earth.
Surprisingly, it has been found that certain mildly acidic uncalcined
naturally-occurring mixtures of palygorskite clay and calcium bentonite
clay, hereinafter referred to as "high susceptibility source
clays" or "HSSC" require significantly lower acid
dosages (e.g., 5-10 grams of 96% H.sub.2 SO.sub.4 /100 grams clay)
to achieve their maximum bleaching levels. Because so little acid
needs to be used with these naturally-occurring clay mixtures, residual
acid levels left on these clays are quite low and subsequent washing,
filtration steps or post-calcination steps are unnecessary. In fact,
it has been found that the requisite acid can simply be sprayed
on dry powdered clay, or a clay-acid slurry can be mixed and then
spray dried, to produce a high activity bleaching clay.
Palygorskite clays include attapulgite clays also known as Attapulgus
clay, or Georgia-Florida fuller's earth. These clays are usually
frequently composed principally of the mineral attapulgite, a crystalline
hydrated magnesium aluminum silicate, but may also contain significant
amounts of other minerals such as bentonite (montmorillonite), calcium
carbonate, quartz and feldspar, and in some cases sepiolite. Those
attapulgite clay used in the practice of this invention contain
at least about 10% by weight and up to about 90% by weight, preferably
from 20% to 60% by weight, of the mineral attapulgite and are limited
to those clays which are low in their content of carbonate minerals.
This excludes most commercial deposits of primary and sedimentary
sources of attapulgite clay which are usually associated with limestone.
Similarly, naturally-occurring mixtures of sepiolite and bentonite
clays must be low in content of carbonates to be used in practice
of the invention.
The results of experiments conducted with high purity, low carbonate
attapulgite showed that it takes 10-30 wt % acid dosages to achieve
maximum activity with these materials. Even higher acid dosages
(i.e. 70-90 wt %) are required to achieve maximum adsorptive capacities
for bentonite clays. It was found that very low acid dosages (1-10%,
preferably 3-5 wt %) will work only with the particular naturally
occurring attapulgite/bentonite mixtures. I believe these particular
clays have features uniquely favorably for low acid dosage activations.
In the accompanying drawings:
FIG. 1 illustrates the convention process for producing bleaching
clay from conventional calcium bentonite source clays.
FIG. 2 outline the essential steps of the spray coating process
of the invention.
FIG. 3 illustrates the spray drier process of the invention.
FIG. 4 illustrates another embodiment of the invention.
FIGS. 5 and 6 are graphs showing the effect of increasing acid
(sulfuric) dosage on the chemical composition of a HSSC clay; FIG.
5 shows the change in SiO.sub.2 and Al.sub.2 O.sub.3 and FIG. 6
shows the change in iron, calcium, magnesium and phosphorus of the
same HSSC clay.
DESCRIPTION OF PREFERRED EMBODIMENTS
By high susceptibility clay, we mean those naturally occurring
attapulgite/bentonite mixtures which: (1) contain 10-90% attapulgite,
generally from 20% to 60% attapulgite, (2) possess a slurry pH less
than 7; and (3) have pore volume greater than about 0.20 cc/gm.
The especially preferred ranges are from about 37-78% attapulgite,
pH 5.4-6.5 and pore volume 0.25-0.35 cc/gm.
Mixed attapulgite/bentonite clays possessing the desired properties
for use in this invention are found in sedimentary beds located
in the state of Georgia near the town of Ochlocknee, in Thomas County.
According to Grim (Clay Mineralogy, 2nd Ed., McGraw-Hill Book Co.,
New York), such clay deposits are often formed when detrital materials
are laid down and transformed in magnesium rich lacustrine environments.
At any rate, clays of the desired type obtained from the Ochlocknee
area have properties as shown below.
Physicochemical Properties of High Susceptibility Attapulgite/Bentonite
Source Clay (Typical) Chemical Analysis (Wt %, Vf basis) Physical
SiO.sub.2 71-75% CaO 0.70-2.3% pH (10% slurry) 5.0-5.8 Al.sub.2
O.sub.3 11-16% Na.sub.2 O 0.20-0.40% Surface area (m.sup.2 /gm)
100-150 Fe.sub.2 O.sub.3 3.8-6.7% K.sub.2 O 1.1-1.5% Pore Volume
(cc/gm) 0.20-0.31 MgO 2.8-5.8% P.sub.2 O.sub.5 0.30-1.2% __________________________________________________________________________
The invention is not limited, however, to the use of such clay.
In defining clays the terms "volatile matter" (V.M.)
and "Loss on Ignition" (L.O.I.) must frequently be used.
Volatile material is classified according to three levels of thermal
treatment: loosely-held water of hydration known as free-moisture
(F.M.) which is measured by heating to constant weight at 220.degree.
F., structural water that is held chemically in the molecular structure
of the clay and is measured by heating from 220.degree. F. to constant
weight at 1200.degree. F., and other volatile matter such as inorganic
carbonates, principally calcium carbonate, which release CO.sub.2
at 1800.degree. F.
Various methods related to water content or thermal treatment may
be used to express percentages of components in the clay. A moisture-free
weight, or dry weight, is the weight of the clay after heating to
constant weight at 220.degree. F. A volatile-free basis weight is
the weight of the clay after heating to constant weight at 1200.degree.
F., and a loss-on-ignition or L.O.I. basis weight is determined
by heating to constant weight at 1800.degree. F. Also, volatiles
content may be expressed on an as received basis.
The difference between loss on ignition weight and volatile-free
weight is a fairly accurate representation of carbonate content,
since carbonates generally account for virtually all of the non-aqueous
volatile matter in the clay. An alternative method for measuring
the carbonate content (as % CO.sub.2) is to finely pulverize the
clay and heat in the presence of a strong mineral acid such as hydrochloric
acid to release carbon dioxide. The gas can then be collected and
its volume measured, from which the weight percent of CO.sub.2 can
be calculated. This former method was employed to determine the
carbonate content of clays used in the examples described hereinafter.
XRD METHOD OF DETERMINING ATTAPULGITE CONTENT
X-ray diffraction is used to determine the attapulgite content
of the attapulgite/montmorillonite clays described in this patent
application (referred to as high susceptibility source clays). To
do this, a comparison is made between the peak areas of the 110
peak of attapulgite and the 001 peak of the montmorillonite in the
region 3.degree.-20.degree. 2.theta. when XRD machine conditions
are as follows:
Cu K--.alpha./Ni filter
beam current--31 mA
chart speed--1 cm/min.
range--1K or 10K CPS
time constant--1 sec.
In order to calibrate the intensity of these two peaks, a series
of mixtures of pure crude attapulgite (Emcor.RTM. 66 low-carbonate
attapulgite clay supplied by Engelhard Corporation) and pure crude
bentonite (Filtrol Gr 2) were prepared by mixing known quantities
of the finely ground powders (100% T-325 mesh) whose moisture contents
were also known. With this information (i.e.--weight and moisture
content of the clays used) and the resultant XRD patterns for each
of the mixtures, it is possible to calibrate the relative response
of these two peaks to the x-ray beam. The assumption is made that
the response of these peaks in a physical mixture is the same as
it will be in the naturally occurring mixture of these two clays.
Using this method, it was determined that the intensity correspondence
between the 110 peak of attapulgite and the 001 peak of montmorillonite
X-ray patterns of suitable HSSC was found to be essentially the
same as would be expected from X-ray patterns of mechanical mixtures
of attapulgite and calcium bentonite, although a low intensity peak
at 7.2 Angstrom units was observed from a HSSC that was not observed
in X-ray patterns of either pure attapulgite or calcium bentonite
or their mechanical mixtures.
Mineral acids (hydrochloric, phosphoric and sulfuric), a strong
organic acid (formic) and a complexing acid (citric) have been utilized
in practice of the invention. Sulfuric acid is preferred.
In one embodiment of the invention, 3-5% by weight of concentrated
acid (based on the dry free weight of clay being activated) is added
to enough water and clay so that the dry free solids content of
the resultant clay/acid/water slurry is in the range 20-25 wt %.
Thereafter, the slurry can be heated for 1-5 hours with gentle stirring,
filtered (washing is not necessary, but can be practiced), dried,
and ground to yield a finished product suitable for use as described
below. Although higher acid dosages may be employed, no significant
advantages are imparted by this effort, and since acid is a costly
reagent, lower acid dosages are preferred. (See Table 1).
In general, the process of the invention comprises selecting an
acidic naturally-occurring mixture of bentonite/palygorskite clays,
crushing, preferably subjecting the clay to a preliminary drying
step; typically to 15 to 30 wt % VM, grinding the dry clay, mixing
the clay with a diluted acid, drying and thereafter pulverizing
unless the acid treated clay is already in desired particulate form.
Preliminary drying is carried out under conditions such as to render
the clay amenable to the grinding method used, e.g., heating at
200.degree.-300.degree. F. to reduce 15 to 25 wt % VM. Optionally,
the source clay is extruded before drying and grinding. In some
instances, grinding can take place before drying.
Reference to FIGS. 1-4 serves to illustrate advantages and essential
differences between the processes made possible by the use of high
susceptibility source clays in accordance with this invention (FIGS.
2-4) and conventional calcium bentonite source clays (FIG. 1).
As shown in FIG. 1 conventional processing entails crushing, predrying
(necessary so the clay particles will break apart or "slake"
properly when added to water to give a uniform, colloidal dispersion
suitable for activation), a mixing step (where clay, acid and water
are combined), a treater or "leach" step (where the clay/acid/water
slurry is heated to near boiling with gentle agitation for about
5 to 51/2 hours), and a washing/filtration step (where entrained
unused acid and acidic salts are extracted from the filter cake).
Some of the liquid waste stream from this step can be recycled back
to the mixer, but the greater majority must be disposed of by other
means. Since aluminum containing salts formed from the reaction
between the acid and bentonite clay during the leaching process
are highly toxic to aquatic life, the waste stream from this process
cannot be discharged to surface waters or to the subsurface water
table. In some cases, an expensive deep well injection facility
must be maintained to dispose of these wastes, and in other cases,
the acidic wastes are precipitated with lime or caustic, and the
neutral solids produced are placed in land-fill. In any case, some
method of waste disposal is required for an environmentally sound
operation. The extracted filter cake from this operation is then
dried ground, and bagged or placed in bulk storage.
In contrast to the process just described, processes of the invention
utilizing high susceptibility source clays are simpler, more economical
and do not generate waste products which are difficult to dispose
of and add to production costs.
FIG. 2 outlines the essential steps of the spray coating process
for producing acid-activated bleaching clay from high susceptibility
source clays. In accordance with one embodiment of the invention,
the coarse feed from the crusher (nominal 1/4" diameter particles)
is feed directly to a drying and grinding operation where it is
dried to a level somewhat drier. than desired for the finished product,
and ground to the desired average particle size. Typically, the
production has 10-15 wt % VM and 80-85 wt % is finer than 200 mesh.
An acid/water mixture is then sprayed directly onto the dried and
ground powder using such proportions of acid and water that optimized
bleaching performance of the finished product is attained. Preferably,
the acid/water spray is added directly to the powder while it is
still warm and before it takes up moisture from the surrounding
atmosphere. Intimate mixing of the raw clay powder and the acid/water
spray can be achieved by any number of methods, including, for example,
spraying the acid/water into the clay as it is mixed in a glass-lined
Pfaudler mixing vessel, by spraying acid solution into the tumbled
clay powder in a rotating rotary pan spray-coating machine, by spraying
onto the clay as it travels along a moving belt conveying system,
or by spraying onto the clay as it is moved by a screw conveyor.
The dried, ground powder, now impregnated with the acid/water mixture,
is bagged or placed in bulk storage as finished product.
FIG. 3 outlines the essential steps of the spray drying process
to produce acid-activated bleaching clay from high susceptibility
source clays. In this case, raw clay is first crushed, then dried,
typically to 20-30 wt % VM at 200 .degree.-300.degree. F., and pulverized
to produce a finely ground powder (e.g., 99%-200 mesh) suitable
for spray drying using either high pressure nozzles or a spinning
disk as commonly used in these apparatus. The finely ground clay
is mixed with sufficient water and requisite sulfuric acid to form
a slurry which can be spray dried. The high susceptibility source
clay used in this process will be activated instantaneously during
the spray drying operation; therefore, heating of the slurry before
the spraying operation need not be practiced although such heating
will not be deleterious to the final product. The spraying conditions
are set to produce spray-dried particles whose average diameter
falls in the range 15-30 microns. These particles of acid-activated
high susceptibility source clay can be bagged or placed in bulk
storage as finished product.
FIG. 4 outlines the essential steps of the modified conventional
process to produce acid-activated bleaching clay from high susceptibility
source clays. This process uses the same equipment and process train
as that previously described for a conventional acid-activation
process (FIG. 1), but with the following essential differences:
(i) much lower acid dosages are employed (i.e., 3-10 grams of 98%
H.sub.2 SO.sub.4 /100 grams of dry clay); (ii) shorter reaction
times can be employed (1-3 hours); (iii) 100% of the "sour
" water which is recovered from the filtration step can be
recycled back to the mixing step where only enough additional water
plus fresh mineral acid is added to achieve the desired levels of
bleaching activity; and (iv) since all of the sour water is recycled,
there is no waste stream of acidic salts and unused acid requiring
When edible (and inedible) animal or vegetable oils are treated
with bleaching clays, the objective is to reduce the levels of certain
trace constituents (including carotenoids such as B-carotene, pheophytins
and chlorophyll, and peroxides, among others). Color pigments, such
as B-carotene (reddish-orange pigment) and chlorophyll (green pigment)
must be removed if the oils is to be of suitably light color to
meet with consumer acceptance; peroxides (highly reactive molecules)
must be removed in order to obtain an oil exhibiting good photolytic
and chemical stability (i.e.,--one which will not rancidify easily).
Additionally, it is desired that levels of free fatty acids produced
when contacting vegetable oils with acid-activated bleaching clays
should not be excessively high since they constitute a refining
Those familiar with the art of bleaching are aware of these and
other quality control tests to monitor oil quality during bleaching.
Red and yellow color is commonly monitored using an automatic tintometer
according to the procedures listed in the American Oil Chemists'
Society Official and Tentative Methods (AOCS Official Method Cc
13b-45); chlorophyll (AOCS Official Method Cc 13d-44); peroxides
(AOCS Official Method Cd 8-53; rev. Ja 8-87); and free fatty acids
(AOCS Official Method Ca 51-40). In all cases, the lower the values
obtained, the better the quality of the resultant oil. Typically,
for instance, when bleaching a caustic refined soybean oil, refiners
find that chlorophyll reduction is the most important quality parameter,
and over time, it has been found that adequate bleaching has occurred
if this constituent can be reduced to the 50-90 ppb range. When
this level is obtained, other oil constituents are usually well
below the levels of which they would cause problems with regard
to achieving satisfactory finished oil quality.
The following examples are presented in order to more fully explain
and illustrate the invention. The examples are not be construed
as limiting the invention.
Three different source clays (A--high purity attapulgite clay;
B--high purity bentonite clay; and C--high susceptibility clay)
were subjected to acid-activation with sulfuric acid at varying
acid dosages for 51/2 hours, and then washed, filtered, dried and
ground to finished products.
These materials were then used at constant dosage (0.5 wt % clay,
as is, based on amount of oil) to treat a typical caustic refined
soybean oil. The oil quality parameters previously discussed were
then measured as a function of activating acid dosage as shown in
TABLE 1 and compared to those obtained when using two commercial
bleaching clays, high activity Filtrol Gr 105 and very high activity
Filtrol Gr 160.
Data in TABLE 1 show that all of the clay samples tested benefited
from the acid-activation process. For example, compare the results
obtained at 0% acid dosage (raw clay) versus those obtained at higher
acid dosages. Nevertheless, the high purity attapulgite which contained
3% carbonate required at least 20% acid dosage to produce a product
capable of achieving an oil quality where the most important quality
parameter, chlorophyll, falls in the desired range (50 to 90 ppb).
The high purity bentonite required even higher dosages (in the range
45-90%) to achieve comparable bleaching activity. In contrast, the
high susceptibility source clay which contains both attapulgite
and calcium bentonite achieved a comparable chlorophyll bleaching
efficiency with as little as 10% acid dosage.
A sample of high susceptibility source clay (C) was dried at 110.degree.
C. to 10.5 wt % LOI (loss on drying, 300.degree. C./1 hour), ground
(90% <200 mesh) and then samples were spray-coated with dilute
(10%-25%) sulfuric acid solutions to yield samples which were subjected
to acid dosages between 1-8 wt %. The spray-coating was accomplished
by spraying a mist of the dilute sulfuric acid solution into a rotating
vessel containing the dried, powdered samples of high susceptibility
clay. After allowing the samples to equilibrate at room temperature
for three days in closed containers, they were redried (at 110.degree.
C.) to 10.5 wt % LOI, and any agglomerates broken up so that the
final sample was at least 90%-200 mesh.
As shown in TABLE 2 dosages as low as 1 wt % sulfuric acid were
sufficient to produce good activity bleaching clays. In this case,
all of the acid added to the clay remained associated with that
sample, although conversion to calcium and magnesium salts via reaction
with the high susceptibility clay is highly likely. At any rate,
adsorptive activities of these materials as well as their tendency
to generate free fatty acids were quite acceptable even through
none of the samples received any subsequent washing (a salient feature
of being able to use this process with high susceptibility source
clays.) Using this procedure, optimum bleaching activities appeared
to be realized when acid dosages were 3-5 wt %.
More specifically, data in TABLE 2 show better reduction of red
color and peroxide value (in the oil) was obtained with the high
susceptibility source clay when activated with 3-5 wt % sulfuric
acid than was realized with premium quality Filtrol Gr 160 bleaching
clay. Increased production of free fatty acids was nil with the
spray-coated high susceptibility source clay, whereas increased
production of free fatty acids was clearly evident with the commercial
Filtrol Gr 160 bleaching clay. Although the spray-coated high susceptibility
source clay was not as efficient as Gr 160 bleaching clay for removing
green color (chlorophyll) on an equal weight basis, it would still
be considered adequate, particularly in view of its other superior
A sample of high susceptibility source clay (C) was sized to an
average of 1/4" and dried to a moisture content of about 20
wt % (LOI @1000.degree. C.). The clay sample was then slurried
(24 wt % VF clay weight) with water/sulfuric acid at either 5% or
10% acid dosage for three hours at 210.degree. F. After the reaction
period was over, the samples were filtered, and in some cases washed
with additional volumes of water, and then dried and ground as previously
described in Example 2.
Table 3 give the results of the activity testing (as described
above) for these samples versus the degree of washing they received.
One measure of the degree of washing was the residual acidity exhibited
by these materials. Residual acidity was determined by boiling 5
grams (as is basis) of clay with 100 ml of distilled water or 3
minutes, filtering, adding 100 ml of hot distilled water to the
filter cake just before it dried, and repeating one more time. The
filtrate (plus one drop of phenolphthalein indicator solution) was
then titrated with 0.0893 N KOH solution to the pink end point.
The residual acidity is reported as mg of KOH/gram of clay (and
can be obtained as a direct reading of the buret in milliliters
when using 0.0893 N KOH solution). As can be seen from data in Table
3 washing, or the lack of washing (as measured by residual acidity)
has no effect on the performance of the activated bleaching clay
when prepared at 5% acid dosage level. At the 10% acid dosage level,
the unwashed sample shows some loss of efficiency for removing chlorophyll,
and a slight tendency to increase free fatty acids; however, the
values obtained are well with the acceptable range. Also, even lower
peroxide values were obtained with the materials prepared at the
A series of no-wash acid activations was carried out using HSSC,
an acidic sedimented naturally occurring mixture of attapulgite
and calcium bentonite mined near Ochlocknee. A description of the
chemical and physical properties of this clay appears in Example
Acid-activated samples of HSSC Hole #1 (composite) clay were prepared
at the 1 3 and 5% acid dosage levels by adding the clay to water
and sulfuric acid so that the volatile free solids content at the
resultant clay/acid/water slurry was 25 wt %. The slurries were
then heated for 1 3 and 5.5 hours at temperatures of 77 110 140
175 and 210.degree. F. The acid treated samples were ground and
dried as in Example 1. The 1 and 3 hour samples were obtained by
extracting portions (40 cc) of the clay-acid slurry from the reaction
flask using a wide-mouthed baster. The 5.5 hour sample was composed
of the material remaining in the flask at the end of the run. Following
the treatment period, the samples were filtered, and the resulting
cakes dried at 30.degree. C.. The samples were then ground to 100%-200
The acid-activated HSSC, the unactivated HSSC, and Gr 105 and Gr
160 standards (sized to 100%-200 mesh) were contacted with refined
soybean oil at 0.5 wt % dosage. The bleaching results (TABLES 4-8)
show that the activity of the acid-activated products was primarily
affected by acid dosage level, rather than time or temperature.
The products treated at 1% acid dosage were clearly less active
than those treated at 3 and 5% dosages. However, treatment at the
3% level was sufficient to obtain maximum activity.
Effects on bleaching activity due to time and temperature (TABLES
4-6) were associated mainly with the removal of red color and, to
a lesser extent, the peroxides. In fact, only for the 1% acid-activated
case did the beneficial effects of increasing temperature cause
consistent and significant reductions in the levels of these components.
The effects of time in this case, and both time and temperature
for the 3 and 5% acid dosage levels, appear less significant.
Under optimum conditions, the acid-activated HSSC clay prepared
in this study showed an activity for red removal which comes between
Gr 105 and Gr 160 (compare Table 5 with Table 7). Regarding the
removal of chlorophyll and peroxides, acid-activated HSSC clay was
comparable to Gr 160. These results differed from those previously
observed in that activated HSSC was comparable to or better than
Gr 160 in the removal of red color and peroxides, but slightly less
so in the removal of chlorophyll. It is believed that the difference
arises from the different soybean oil feedstocks used in the tests.
An evaluation of the relative bleaching efficiencies of the 3%/3
hours 110.degree. F. sample and the unactivated source clay vs.
Gr 105 Std. are given in TABLE 8.
A series of (no wash) acid-activated products, using HSSC Hole
#1 as source material, were prepared at 4% acid dosage under variable
time and temperature conditions. The run conditions, bleaching efficiencies
(in refined soybean oil), filtration times and selected phsyiochemical
properties for the products are summarized in TABLE 9. The results
shows that the more finely ground products (Runs 1-4 and 5 [fine])
exhibited bleaching activities comparable to or slightly greater
than Gr 105 while maintaining much improved filtration rates (lower
times). In particular, samples from runs 34 and 5 (fine) show rates
which are almost as fast as Gr 105 SF (which is a fast filtering
version of GR 105).
Mineral acids hydrochloric, phosphoric and sulfuric, a strong organic
acid (formic) and a complexing acid (citric) were used with HSSC
in practice of the invention. Conditions used in the acid treatments
are described in TABLE 10 and TABLE 11.
Using slurry activation conditions, some selective differences
in removing pigments and other trace constituents from soya oil
were noted as a function of the type of acid used; however, overall
adsorptive capacity relative to the unactivated clay was always
improved except for free fatty acids rise where the raw clay acts
as a net adsorber of free free fatty acids (see TABLE 10).
Data in TABLE 11 show that different acids can be simply spray
coated onto the HSSC to yield improved products, but it is clear
that Lovibond red color and peroxides in the oil were most reduced
when sulfuric acid was utilized. For chlorophyll reduction, phosphoric
or citric treated products showed a slight advantage. In all cases,
the sulfuric acid treated HSSC was equivalent or superior to the
use of Oil Dri PureFlow B80 when the oil was treated with 4% citric
acid before bleaching. As is also clear from this table, neither
pure attapulgite nor pure bentonite clays respond to these low acid-dosage
activations as well as HSSC.
As can be seen from tabulated chemical analyses in Example 1 and
accompanying FIGS. 5 and 6 treatment with acid tends to reduce
Fe.sub.2 O.sub.3 CaO, MgO, and P.sub.2 O.sub.5 content at all dosage
levels (accompanied by an apparent increased in SiO.sub.2 content).
Only at the higher acid dosages is Al.sub.2 O.sub.3 significantly
removed from the clay. This suggests that exchange of Ca.sup.++
and Mg.sup.++ for protons is the primary role of the acid at lower
dosages, but that actual leaching of the clay structure (i.e.--removal
of structural ions) does begin to occur at the higher acid dosages.
The processes just described have numerous economic and procedural
advantages over the process normally employed: (1) lower acid costs
per unit mass of clay treated; (2) lower production costs (no washing,
filtering, or waste treatments steps); and (3) environmental soundness
(i.e.--no harmful environmental waste products are produced). Considering
the fact that attapulgite clays are not normally used as the source
of acid activated clay and almost a century of effort has been directed
to manufacturing and improving acid-activated bleaching earths,
the results were unexpected. It is believed that the vast number
of prior art investigators overlooked the effect of carbonate (limestone)
impurities on the activation process, thereby failing to note that
certain palygorskite/bentonite clays (those naturally acidic, hence
low in free carbonate) would be amendable to a simple, cost effective