Note: Descriptions are shown in the official language in which they were submitted.
--1--
STABILIZED AMORPHOUS CALCIUM CARBONATE
This invention relates to calcium carbonate which is
useful as a carbonating agent, to processes therefor and effer-
vescent compositions containing same.
The reaction of acidic compositions, hereinafter re-
ferred to as the "acid factor", with bicarbonate or carbonate-
containing compositions, hereinafter referred to as the "carbon-
ate factor", in an aqueous environment, such as a solution, to
produce or release carbon dioxide is well known in the art and
will hereinafter be referred to as the "effervescent reaction".
The effervescent reaction has heretofore been utilized in many
fields, such as the food and medicament industries, where a
rapid release of carbon dioxide at a controlled point in time
is desirable.
Products that undergo the efervescent reaction upon
use normally comprise a dry, solid mixture of an acid factor
and a carbonate factor, said mixture being hereinafter referred
to as an "effervescent composition". The acid factor and the
carbonate factor in the effervescènt compositions are normally
dry solids and are water soluble, at least in the presence of
each other. Additionally, the acid and carbonate factors uti
lized must be compatible with their intended use, i.e., if to
be consumed, they must be physiologically acceptable.
Many such effervescent compositions have been pro-
vided commercially. For instance, it is known that an efferves-
cent composition of citric acid, sodium bicarbonate (in less
than the stoichiometric equivalent of citric acid) and a flavor
will provide a carbonated beverage upon adding the composition
to the proper amount of water. Other examples of effervescent
compositions are the well-known effervescent medicament tab-
lets, baking sodas and the like. The major advantage of theseproducts is, of course, that the effervescent composition may
be easily and economically stored as a dry solid and may then
~,.B~t~
be used, as desired, by merely contacting it with water to pro-
duce a carbonated beverage, i.e., the release of carbon diox-
ide.
The food industry has long sought commercially feas-
ible products to provide a carbonated beverage from an efferves-
cent composition. Such a beverage must be highly palatable
and, as a practical matter, must afford a rapid rate of prepara-
tion by the consumer. Normally, the consumer expects to be
able to prepare the beverage in a short time, i.e., within
about one to three minutes at the most. It is essential, there-
fore that the effervescent composition rapidly undergo the
effervescent reaction upon contact with water providing a car-
bonated beverage that is highly palatable to the consumer.
Although many acid factors are available, such as
citric acid, fumaric acid, adipic acid, malic acid, tartaric
acid, etc., the primary carbonate factor heretoEore utilized in
effervescent compositions has been sodium bicarbonate. Sodium
bicarbonate is highly reactive with acid factors in aqueous
solutions, rapidly releasing carbon dioxide, and has become the
standard carbonate factor utilized by industry in effervescent
compositions. Other carbonate factors, such as calcium carbon-
ate and magnesium carbonate have been suggested as possible
alternatives, but to date only sodium bicarbonate has been able
to provide the desired rate of carbon dioxide release. Sodium
bicarbonate does, however, have a major drawback, particularly
in the food and medicament industries, in that it gives a dis-
tinctly disagreeable saline or soapy taste to the solutions con-
taining it, which is known to be due to the presence of the
sodium ion. Accordingly, many attempts have been made to sub-
stitute a more agreeable tasting cation in the carbonate fac-
tors utilized in effervescent compositions.
A cation that provides excellent taste characteris-
tics in aqueous solutions or compositions containing it is the
calcium ion. Although calcium carbonate and compositions con-
taining it have been heretofore suggested as carbonate factors
`' --`1 '
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for effervescent compositions, they have not been utilized in
commercial products due primarily to the slow rate of carbon
dioxide release they display in the effervescent reaction. For
instance, it takes the calcite state of calcium carbonate from
about ten to about fifteen times the length of time required
for an equivalent amount of sodium bicarbonate to release the
total available carbon dioxide in a given acidic aqueous solu-
tion. Although several crystalline states of calcium carbonate
are known such as the heretofore-mentioned calcite and others
such as aragonite and vaterite, none have been known-to possess
the requisite rate of carbon dioxide release for commercially
feasible use in effervescent compositions. It is obvious,
therefore, that a carbonate factor that contains calcium carbon-
ate and that will rapidly undergo the effervescent reaction
would be most welcome by those skilled in the art. Prior work-
ers in this field have been unable to provide such a carbonate
factor.
It is an object of the present invention to provide
such a carbonate factor.
It is also an object of the present invention to pro-
vide a process for producing calcium carbonate that can be read-
ily utilized as a carbonate factor in effervescent composi-
tions.
Furthermore, it is an object of the present invention
to provide effervescent compositions that contain such a carbon-
ate factor.
These and other objects and advantages will be appar-
ent from a consideration of the following description of the
inventlon .
Accordingly, this invention provides stabilized amor-
~hous calcium carbonate.
In accordance with one embodiment of the present
invention, there is provided a process for preparing stabilized
--4--
amorphous calcium carbonate which comprises (l) forming an alka-
line aqueous solution of calcium ions and a hydrogen-bonding ma-
terial, (2) contacting the solution with carbon dioxide while
maintaining the solution at a temperature below 15C to form a
precipitate containing chemically-bound water and continuing
said contacting until no more carbon dioxide is taken up, and
(3) reducing the amount of chemically-bound water contained in
the precipitate to below 15% by weight while retaining hydrogen-
-bonding material in the product and while maintaining the
resulting product in an environment that is essentially free of
unbound water, the said stabilized amorphous calcium carbonate
having a reactivity such that the time taken for a 0.18 g sam-
ple to react completely when added to a stirred solution pre-
pared by mixing 5 ml of O.lN citric acid with 200 ml of water
is less than one minute, and having a stability such that the
said time for complete reaction does not increase by more than
5~ when a 2 g sample of the stabilized amorphous calcium carbon-
ate is stored in a sealed 29.6 ml glass bottle at 20-25C for
one month~
In accordance with another embodiment of the present
invention, there is provided a stabilized amcrphous calcium car-
bonate that is the product of the above process.
In accordance with a further embodiment of the pre-
sent invention, there is provided a dry concentrate for prepar-
ing a carbonated beverage by admixture of the concentrate with
water, said concentrate comprising an acid factor and a carbon-
ate factor in less than the stoichiometric equivalent of the
acid factor, characterized in that the carbonate factor com-
prises the above stabilized amorphous calcium carbonate.
In accordance with a still further embodiment of the
present invention, there is provided a composition comprising a
dry carbonated beverage concentrate for preparing a carbonated
beverage by admixture with water, said concentrate comprising:
36~5~
--5--
a. stabilized amorphous calcium carbonate, substan-
tially devoid of calcium hydroxide, and
b. an anhydrous, nontoxic acid in an amount in ex-
cess of the amount theoretically required to completely evolve
the carbon dioxide from the amorphous calcium carbonate, and
c. a medicament.
Yet another embodiment of the present invention pro-
vides a process for preparing a dry concentrate for use in pre-
paring a carbonated beverage by admixture of the concentrate
with water, comprising
~1) forming an alkaline aqueous solution of calcium
ions and a hydrogen-bonding material,
(2) contacting the solution with carbon dioxicle
while maintaining the solution at a temperature below 15C to
form a precipitate containing chemically-bound water and con-
tinuing said contacting until no more carbon dioxide is taken
up, and
(3) reducing the amount of chemically-bound water
contained in the precipitate to below 15% by weight while re-
taining hydrogen-bonding material in the product and while main-
taining the resulting product in an environment that is essen-
tially free of unbound water,
the said stabilized amorphous calcium carbonate hav-
ing a reactivity such that the time taken for a 0.18 g sample
to react completely when added to a stirred solution prepared
by mixing 5 ml of O.lN citric acid with 200 ml of water is less
than one minute, and having a stability such that the said time
~or complete reaction does not increase by more than 5~ when a
2 g sample of the stabilized amorphous calcium carbonate is
stored in a sealed 29.6 ml glass bottle at 20-25C for one
month;
(4) and admixing said stabilized amorphous calcium
carbonate with an acid factor.
- ~8 86~i5g~
--6--
Still another embodiment of the present invention pro-
vides a process for preparing a dry, effervescent medicament
composition which comprises admixing:
a. stabilized amorphous calcium carbonate, substan-
tially devoid of calcium hydroxide, and
b. an anhydrous, nontoxic acid in an amount in
excess of the amount theoretically required to completely
evolve the carbon dioxide from the amorphous calcium carbonate,
and
c. a medicament.
STABILI ZED AMORPHOUS CALCIUM CARBONATE
For purposes of this discussion the term "amorphous"
shall mean that morphological state of a material that does not
show a crystalline state upon analysis by the known means of in-
vestigating a material's morphological state. For instance, a
material is considered to be amorphous if it does not show any
X-ray pattern upon X-ray analysis and shows only one refractive
index upon subjecting the material to refractive index analy-
sis .
For purposes of this discussion the term "stabilized"
means that the amorphous material under consideration will re-
main essentially in the amorphous state for significant periods
of time, i.e., for at least one month and longer when stored in
a closed container.
Amorphous calcium carbonate has been reported in sev-
eral sources [Louisfert, J. et al., Compt. rend. 235, 287
(1952) and Gillott, J.E., J. Appl. Chem. 17 185 tl967)].
Gillott states that carbonate of Ca~OH)2 may result in the
ormation of synthetic amorphous calcium carbonate which cry-
stallizes to calcite in the presence of moisture at room temper-
atu~e. Our experience with amorphous calcium carbonate agrees
with Gillott's findings. We have found, however, that stabi-
lized amorphous calcium carbonate is more resistant to calcite
crystal formation than previously known amorphous calcium car-
bonate.
It has been found that stabilized amorphous calcium
carbonate has an infra-red spectrum quite similar to that ob-
tained with the known crystalline states of calcium carbonate
but distinguishable in that stabilized amorphous calcium carbon-
ate gives a spectrum wherein the peaks obtained are significant-
ly broader than those obtained with the known crystalline
states of calcium carbonate.
Furthermore, examination under the electron micro-
scope reveals a significant difference between stabilized amor-
phous calcium carbonate and the known crystalline states of cal-
cium carbonate (calcite/ aragonite and vaterite). Calcite cry-
stals appear as well formed cubes unifcrm in size. Crystals of
vaterite occur as spheres of different size while those of
aragonite form fairly uniform neeales. In contrast, particles
of stabilized amorphous calcium carbonate have no distinct size
or shape at the same magnification. Further magnification
reveals that stabilized amorphous calcium carbonate has a rough
surface and non-uniform size suggesting an agglomerate of smal-
ler particles. Still further magnification shows extremely
small, substantially spherical particles with an average parti-
cle size of from about 10 A to about 340 A at the edge oflarger, irregularly-shaped agglomerates. Upon subjecting stabi-
lized amorphous calcium carbonate to X-ray analysis no X-ray
pattern is obtained. These results indicate that, in fact,
stabilized amorphous calcium carbonate is "amorphousl'.
The amorphous state of stabilized amorphous calcium
carbonate was further confirmed by refractive index determina-
tions. It was found that not only is stabilized amorphous cal-
cium carbonate clearly isotropic but that it gives refractive
indices that are distinctly different from the refractive
indices found with other amorphous calcium carbonate and the
known crystalline states of calcium carbonate.
Stabilized amorphous calcium carbonate is useful wher-
ever small particle calcium carbonate has heretofore been found
useful. Furthermore, stabilized amorphous calcium carbonate is
~'
.~
i55~
8-
extremely useful as a carbonate factor in effervescent composi-
tions. Therefore, this invention also provides excellent effer-
vescent compositions comprising an acid factor and stabili~ed
amorphous calcium carbonate.
The term "hydrogen-bonding material" as utilized here-
in means a material or combination of two or more materials
that form hydrogen bonds in aqueous solutions. The hydrogen-
bonding material is preferably an organic material whose mole-
cule contains at least one oxygen or nitrogen atom that is cap-
able of bonding hydrogen in another part of the same moleculeor in some other molecule. ~urthermore, the hydrogen-bonding
material is preferably water-soluble at the temperatures contem-
plated for the precipitate-forming step of the process of the
present invention. It may occur that the hydrogen-bonding
material is not completely water-soluble per se in the forma-
tion of the aqueous solution but will go into solution as the
precipitate-forming step proceeds; these materials are also
within the scope of the present invention. Examples of
hydroyen-bonding materials include all the mono-, di-, tri- and
oligo- saccharides which are water-soluble such as sucrose, glu-
cose, fructose and mannose, or saccharide derivatives of the
hydrocolloid-type such as gum arabic, guar gum, propylene gly-
col, alginate, carrageen; the alcohols and polyhydric materials
which are water-soluble such as methanol, ethanol, propanol,
sorbitol and glycerine, the amino acids which are water-
soluble, including optically active and inactive materials and
polymeric amino acids (peptides), such as glycine and lysine,
aspartic acid, phenylalanine and the dipeptide esters thereof
such as the methyl ester of L-aspartyl-L-phenylalanine; the car-
boxylic and hydroxycarboxylic acids such as glycolic, acetic,tartaric and lactic acid. The preferred hydrogen-bonding
materials are the saccharides due to their ready availability
and usefulness in products to be consumed.
,.. . .
- 9 -
The concentration of the hydroyen-bonding material in
the aqueous solution to be utilized in the present invention
can generally be in the range of from about 2~ up to about 95%
by weight of the total solution. Although it is possible to
carry out the process at lower and higher levels of hydrogen-
bonding materials, it has been found that the range of from
about 10% up to about 45% by weight is the most practical from
a commercial operation point of view. However, it should be
understood that, depending on the particular hydrogen-bonding
materials selected, the concentration can be varied widely to
obtain the desired results. For instance, excellent results
have been obtained with a glycine concentration as low as about
10% whereas, with methanol, a concentration of about 90% has
been found to give excellent results.
In determining the proper amount of hydrogen-bonding
material to be utilized the physical effects of the hydrogen-
bonding material in the a~ueous solution should be considered.
For instance, the aqueous solution should not contain so high a
concentration o hydrogen-bonding material so as to form a solu-
tion that is so viscous as to present problems such as poorheat transfer, poor mixing~ etc. The preferred amount of
hydrogen-bonding material in the aqueous solution is in the
range of from about 10% to about 30% by weight of the total
solution. It has been found that when sucrose is utilized with-
in this range excellent results have been obtained with the pro-
cess of this invention.
The first step of the process of this invention com-
prises the formation of an aqueous solution of calcium ions and
the hydrogen-bonding material. The concentration of calcium
ions in the solution should be in the range of from about 0.01%
to about 23~ by weight of the solution and preferably from
about 1% to about 10%. Although, as a practical matter, this
latter range is preferred, the process can in fact be carried
out at lower levels of calcium ion concentration, dependent
only on the payload desired, whereas the higher levels are
~8~5~
-10-
dependent on the amount of calcium ion that can be placed in
solution which is, in turn, somewhat dependent upon the
hydrogen-bonding material utilized and the tempera-ture at which
the aqueous solution is formed.
Although there are a number of different ways to form
the aqueous solution containing calcium ions and hydrogen-
bonding material, this is not a critical aspect of the present
invention and many different methods may be utilized to form
this solution. For instance, the aqueous solution may be
formed by dissolving such calcium-containing materials as cal-
cium oxide, calcium hydroxide, calcium hydride, calcium per-
oxide or other water-soluble calcium salts such as calcium
chloride, etc. in either (a) water, and thereafter dispersing
the hydrogen-bonding material therein, or in (b) an aqueous
solution already containing the hydrogen-bonding material. It
is also possible to utilize calcium metal to provide the cal-
cium ions in the aqueous solution by contacting it with water,
although this is somewhat impractical.
It is, of course, also possible to form the aqueous
solution by admixing an aqueous solution of the calcium-
containing material with an aqueous solution of the hydrogen-
bonding material or any other such modifications thereof as
long as the resulting aqueous solution has the proper concentra-
tion of calcium ions and hydrogen-bonding material.
The water used for forming the aqueous solution can
be either distilled water or tap water as long as an undue
amount of hardness is avoided.
The temperature at which the solution is formed is
not critical to the process of this invention, but it is prefer-
ably below about 70C., so as to avoid any adverse conversionof the hydrogen-bonding material, such as, for instance, the
inversion of sucrose. In particular, it has been found that
excellent results can be obtained by forming the solution at
ambient temperatures. Moreover, it has been found that when
the hydrogen-bonding material is sucrose, the lower the tempera-
ture of the aqueous solution, the higher the level of calcium
ion concentration that can be provided in the solution which
is, of course, particularly advantageous to the process of the
present invention due to superior payloads per unit weight of
aqueous solution.
Although insoluble impurities sometimes found in the
aqueous solution of calcium ions and hydrogen-bonding material
do not significantly affect the process of this invention, they
can end up in the resulting prodwct as an impurity and result
in a decreased reactivity of the stabilized amorphous calcium
carbonate when it is utilized as a carbonate factor in an effer-
vescent composition. It is prefçrred, therefore, that the solu-
tion be filtered, centrifuged or otherwise treated so as to
remove most, if not all, of the insoluble impurities found in
the solution. Furthermore, it is preferred to form a solution
in the first step of the process of this invention that is
"clear", i.e., transparent, as opposed to an opaque solution.
This results in products that are substantially supe~ior in
their functionality in the effervescent reaction.
In regard to the removal of insoluble impurities,
there is a lower limitation on the temperature of the solution
when removing the insoluble impurities because it has been
found that the lower the temperature of the solution the slower
the rate of removal, such as by filtration, and therefore the
longer the time required for removing the insolubles. Because
it has been found that the calcium ion concentration in the
solution can be increased at lower temperatures with some
hydrogen-bonding agents, this lower limit on the temperature at
which removal of insolubles should take place will have to be
balanced against the desirability of improving or increasing
the calcium ion concentration. In general, it is preferred to
remove most of the insoluble impurities from the solution at
lower temperatures; that is, at as low a temperature as is pos-
s;ble wherein the insoluble impurities will be at a minimum,
s~
due to the higher solubillty of calcium-containing materials ak
lower temperatures, without requiring an undue amount of time
for removal. The insoluble impurities mentioned hereinabove
may be excess calcium oxide, other calcium-containing materials
such as calcium hydroxide, calcium carbonate and many of the
other insoluble salts that are found normal:Ly as an impurity in
calcium-containing materials.
Once the aqueous solution of calcium ions and hydro-
gen-bonding material has been formed, the second step, which
will herein be referred to as the "precipitate-forming step",
consists of contacting~the resulting solution with carbon diox-
ide in order to form a precipitate.
In general, it has been found that if the precipi-
tate-forming step is carried out at lower temperatures, the
stabilized amorphous calcium carbonate obtained has faster
rates of reactivity in effervescent reactions.
Therefore, it should be noted here that the tempera-
ture oE the aqueous solution during the precipitate-forming
step should, in general, be maintained below about 15C. down
to as low as about the freezing point of the aqueous solution
in order to obtain the more reactive products of this inven-
tion. Furthermore, it has been found that the temperature main-
tained in the aqueous solution during the precipitate-forming
step affects-the reproducibility of the desired products of
this invention. Although the reasons for such an effect are
not known, it has been found that the reproducibility of such
products is greatly improved at the lower temperatures. Accord-
ingly, it is preferred that the temperature of the aqueous solu-
tion in this precipitate-forming step be below about 10C.,
and further preferred that the temperature be from about -5C.
'o about +5C. and still further preferred that the tempera-
ture of the solution be from about -3C. to about 0C.
In regard to the temperature of the aqueous solution
while the precipitate-forming step is being carried out, it has
been observed that the presence of ice in the aqueous solution
-13-
will assist in the maintaining of the proper temperature of the
aqueous solution and also appears to assist in the formation of
an excellent procluct. Although a good prodllct is obtained with-
out the presence of ice, it should be noted that the presence
of ice in the aqueous solution will improve the product ob-
tained from the process of this invention.
The aqueous solution containing the hydrogen-bonding
material and calcium ions is brought to the proper temperature
and maintained at that temperature while contacting it with car-
bon dioxide. The carbon dioxide may be in the form of a gas ora solid or may be introduced on the surface of the solution,
sub-surface, or even contacted in a counter-current fashion.
The preferred method of contacting is subsurface to provide
both intimate contact and good agitation. Carbon dioxide may
also be introduced in conjunction with other gases, such as a
converter gas, as long as the other gases are inert.
Sufficient agitation of the aqueous solution should
be provided so that the temperature of the solution at any par-
ticular location in the aqueous solution does not rise above
about 15C. (i.e., to prevent localized "hot spots").
In carrying out the precipitate-forming step, the
aqueous solution must, at the outset, be in a basic or alkaline
state to form a precipitate. The pH will decrease as the preci-
pitation takes place. It has been found that this alkaline pH
condition is necessary to obtain stabilized amorphous calcium
carbonate. This alkaline state can ordinarily be obtained by
utilizing those forms of calcium that will form basic or alka-
line solutions upon contact with water but it can also be ob-
tained by incorporating alkaline materials in the aqueous solu-
tion.
The carbon dioxide should be introduced into theaqueous solution until no further carbon dioxide is taken up.
(The carbon dioxide can continue to be introduced but it has no
-14-
further effect on the aqueous solution.) If the aqueous solu-
tion evolves carbon dioxide (other than the normal carbon diox-
ide evolving from a carbon dioxide saturated aqueous solution)
then the aqueous solution should be allowed to equilibrate un-
til substantially all of the carbon dioxide has evolved.
The precipitate formed in the precipitate-forming
step is a form of calcium carbonate that contains a large pro-
portion by weight, based on the weight of the precipitate, of
chemically-bound water and also contains a hydrogen-bonding
material.
This precipitate must then be treated to reduce the
amount of chemically-bound water contained in the resulting pre-
cipitate to below about 15%, or in other words, to cause a
"dehydration" of the precipitate. It is critical that -the dehy-
dration be carried out in a manner such that the resulting com-
position is maintained in an environment that is essentially
free of unbound water. By this statement it is meant that r to
provide the products of the present invention by proper dehydra-
tion, means must be provided to substantially avoid contacting
the resulting composition with water that is in a free state;
either water from the aqueous solution or water that has been
released from the precipitate. It has been found that the
novel products of this invention can only be provided in this
manner.
Several methods have been developed to carry out the
dehydration. One of these methods comprises isolating the pre-
cipitate from the aqueous solution by recovering the precipi-
tate from the solution and washing it with a volatile organic
solvent and subsequently dehydrating the precipitate in an
environment that facilitates a substantially instantaneous
removal of a portion of the chemically-bound water from the
remaining composition once the water has been released from its
chemically-bound form in the precipitate. This method is des-
cribed in greater detail as follows.
i5i~3
-15-
Once the precipitate-forming step of the process of
this invention has been completed, the precipitate can be recov-
ered from the aqueous solution. Recovery can be carried out by
any of the usual means of recovering a solid from a li~uid con-
taining it, such as, by filtration, centrifugation or sedimenta-
tion, etc., resulting in a cake of the precipitate with some of
the aqueous solution adhering to it.
The recovered cake can then be washed free of the
aqueous solution by solvent displacement with a water-miscible
organic solvent so as to remove the last traces of any remain-
ing aqueous solution that may be adhering to the particles of
the precipitate. The preferred water-miscible organic solvents
to be utilized in washing the cake are the lower alkyl alco-
hols, such as methanol, ethanol or isopropanol; or the ketones,
such as acetone that can be readily removed from the precipi-
tate by drying at low temperatures. This results in a material
that is free of any of the aqueous solution from which it was
ormed.
It has been ~ound that some organic solvents will not
only remove the aqueous solution adhering to the precipitate
cake but will also cause some portion of the chemically-bound
water to be removed. This is not only not detrimental but is
desirable as it requires less dehydration of the resulting iso-
lated precipitate without adversely affecting the resulting end
product.
During recovery and washing it is preferred to main-
tain the precipitate at low temperatures until the cake i5 sub-
stantially free of the aqueous solution. It is preferred to
conduct the isolation, including the solvent displacement or
washing portion, at temperatures below about 15C. and prefer-
ably at temperatures below about 10C. and particularly pre-
ferred at temperatures of from about -5C. to about +5C.
This provides excellent products of this invention.
The temperatures utilized in removing the water-
miscible solvent from the precipitate may vary somewhat depend-
ing on the particular organic solvent utilized for washing the
Stj~
--16-
precipitate without adverse effects in the resulting products.
For instance it has been found that, when utilizing me-thanol, a
temperature up to about 40C. can be used whereas with acetone
and ethanol a temperature higher than about 5C. can cause
adverse effects in the resulting produc-ts.
After washing with the organic so]vent, it has been
found that the water now remaini~g in the precipitate is chemi-
cally-bound rather than merely adhering to the precipitate par-
ticles and is a large part by weight of the precipitate.
The precipitate must then be treated to reduce the
amount of chemically-bound water contained therein to below
about 15~ so as to provide stabilized amorphous calcium carbon-
ate. The reduction of the amount of chemically-bound water in
the resulting precipitate is accomplished by treating the preci-
pitate in a particular manner for removal of the chemically-
bound water and should be clearly distinguished from the isola-
tion of recovery of the precipitate from the aqueous solution
as previously described. In particular, the precipitate as
isolated above must now be treated in an environment that faci-
litates the substantially instantaneous removal of a portion of
the chemically-bound water from the remaining composition once
the water has been released from its chemically-bound form in
the precipitate. In other words, there is a two-fold effect
required that co~prises (a) causing a portion of the
chemically-bound water to be released from the combination in
which it is bound, while (b) substantially instantaneously
removing the water so released from the resulting composition.
The dehydration can be carried out by va~ious means
and in many types of equipment. For instance, it has been
found that excellent dehydration results are obtained by treat-
ing the solvent washed and dried precipitate in vacuum ovens,
fluid bed dryers, and, although the length of time required is
increased, even dehydration ~y air drying in low humidity condi-
tions. In each of these procedures the solvent washed and
. ~
,
-17-
dried precipitate is treated so as to cause a portion of the
chemically-bound water to be released while substantially
instantaneously removing the water from the surrounding composi-
tion as it is released. Dehydration should be continued until
the amount of chemically-bound water remaining in the resulting
composition is less than 15~ by weight. While the chemically-
bound water content can be reduced to as low as about 0.1% of
the resulting composition the dehydration is preferably stopped
when the chemically-bound water content is from about 2~ to
about 5~ by weight of the composition.
The undehydrated precipitate, after isolation from
the solution in which it was formed and whether solvent washed
or not, is a soft, friable semi-solid. When properly dehy-
drated it retains this friable condition but becomes harder and
more solid.~ If not properly dehydrated, i.e., the water is not
removed rapidly enough, the soft, friable semi-solid loses its
shape and becomes a slurry. Drying the slurry results in a
hard, brittle, chalk-like solid which is apparently the calcite
crystalline state of calcium carbonate which does not have the
desired rate of reactivity in the effervescent reaction. This
undesirable effect will be hereinafter referred to as ~Idecompo-
sition".
In another illustrative embodiment of the dehydration
portion of the process of the present invention, it has been
found that dehydration can be carried out in the following man-
ner. This embodiment consists of forming a cold aqueous slurry
of the precipitate formed in the precipitate-forming step of
the process of this invention and spray drying the slurry.
One way of preparing the cold aqueous slurry is by
separating the major portion of the aqueous solution, in which
the precipitate was formed, by such means as filtration, centri-
fugation, sedimentation, etc., leaving a wet cake which has
adhering to it a small amount of aqueous solution and subse-
quently slurrying the wet cake in cold water.
5'i~
-18-
Alternatively~ less of the aqueous solution can be
separated from the precipitate leaving a cold aqueous slurry of
the precipitate in the aqueous solution. The degree of separa-
tion of the aqueous solution from the precipitate will depend
on the desirability of recycling the aqueous solution back
through the first step of the process of this invention so as
to avoid undue use of the hydrogen-bonding material balanced
against the economics of providing cold make-up water to reslur-
ry the cake. The cold aqueous slurry formed may even be a com-
promise between the two above illustrations wherein the aqueous
solution is not separated enough to form a cake of the precipi- ;
tate but cold water is added, nevertheless, to provide the slur-
ry desired. In any case, the resulting slurry should be main-
tained at all times during formation and until drying below
about 15C. so as to avoid adverse effects on the resulting
product.
The cold aqueous slurry is then spray dried while
maintaining the spray dryer at conditions sufficient to rapidly
dry and dehydrate the slurry and precipitate that is being
introduced into the spray dryer at below about 15C.
It has been found that this embodiment of the process
of the present invention will result in a combination of com-
pleting the isolation of the precipitate from the aqueous solu-
tion in which it was formed and at the same time causing the
release of chemically-bound water while substantially instan-
taneously removing the water so released. This portion of the
process of this invention is thereby simplified and improved
resulting in less preparation time. Furthermore, this proce-
dure eliminates the necessity of washing the precipitate with a
30 water-miscible solvent.
It is to be noted that the effect on the precipitate
using spray drying is essentially the same as previously dis-
closed. That is, the action of the spra~ dryer removes the
remaining aqueous solution from the precipitate which, in
essence, completes the isolation as previously described and~
,
5~
--19--
concurrently, the spray drying causes a release of most of the
chemically-bound water from the precipitate while causing the
substantially instantaneous removal of the water so freed from
the surrounding composition. It has been found that the result-
ing chemically~bound water in the product is within the pre-
ferred range of chemically-bound water content.
It should be understood that the products of this
invention while having the desirable characteristics previously
described can also have some of the undesirable properties of
materials of the prior art due to partial decomposition appar-
entiy due to conditions maintained during the dehydration step.
A test was developed to measure the reactivity of
various calcium carbonates which is as follows: 200 milli-
liters of distilled water is mixed with 5.0 milliliters of 1.0
normal citric acid solution to form a solution that contains 5
milli-equivalents of citric acid. The pH of this citric acid
solution is 2.6 as measured on a Leeds and Northrup pH meter
with expandable scale (the full scale deflection is 2 pH
units). The pH meter is connected to a Leeds and Northrup
recorder with a 6.5 inch width chart and a speed equivalent to
8 inches per minute and adjusted so that full scale deflection
is 2 pH units. The electrodes of the pH meter are immersed in
the citric acid solution and the beaker containing the solution
is placed on a magnetic stirrer. The stirrer is adjusted to
approximately 125 rpm. The pH meter is ad~usted to 0 deflec-
tion (the recorder is therefore also at 0 deflection). The
recorder chart is activated. A 0.18 gram sample of the calcium
carbonate to be tested is then added to the beaker. The pH of
the solution, as recorded on the recorder, will increase until
all of the calcium carbonate has reacted and the reaction is
considered to be complete when the pH of the solution no longer
increases. By determining the point at which the pH no longer
increases, the length of time required for a particular sample
of calcium carbonate to react can be observed.
~;
S~ f
-20-
Utili~ing this reactivity test, the "reactivity" of
various calcium carbonates can be determined. It has been
found that those calcium carbonates that have a reactivity time
of less than one minute, when measured by the above test, will
provide carbonate factors for effervescent compositions that
are extremely useful in that they are capable of supporting
extremely rapid effervescent reactions upon use. The process
of the present invention will provide such calcium carbonates.
During the investigations which resulted in the
lCf present invention it was found that some calcium carbonates
prepared, although initially possessing this desirable
characteristic of rapid reactivity, would lose their rapid
reactivity after periods of storage. It was found that, in
contact with saturated air, many such rapidly reactive calcium
carbonates quickly lose their rapid reactivity. A lower degree
of saturation or relative humidity resulted in a slower loss in
the rapid reactivity. Those samples that were stored under low
humidity conditions retained their rapid reactivity for longer
periods of time.
2Q It was found that the most severe conditions of
storage for such calcium carbonates is storage in a small
sealed container (i.e. with very little air space~. This is
apparently due to the fact that the sample has only to give up
a very small amount of water to saturate the air in the
container. (Saturated air at 22.2C. contains 0.0002 grams
water vapor/cc.)
s~
-21-
In order to determine the "storability" of various
rapidly reactive calcium carbonates including those of the pre-
sent invention the following test was developed. Weiyh 2.0 g.
of a sample into a 1 oz. glass bottle and seal with a cap.
Store the bottle and contents at room temperature (20-25C.).
At the end of one month storage measure reactivity by the
above-described test. If the "reactivity" increases more than
5% in this test the sample tested does not have an acceptable
storability.
In generall we have found that a chemically-bound
water content in stabilized amorphous calcium carbonate of
below about 5% is desired for good storability. However~ it
has been found that the storability of the materials of this
invention is not solely dependent on the chemically-bound water
content. Materials have been prepared containing as much as
15~ chemically-bound water which have been found storable for
greater than 3 months and other materials containing only 2
water were found to be nonstorable in less than one month.
It is preferred, however, that stabilized amorphous
calcium carbonate have a water content of no more than about 5
to have a reasonably predictable and acceptable storability.
The process of the present invention will be more rea-
dily understood by reference to the following examples, of
which Example 1 is a general procedure, which are understood
not to limit the present invention, but to be construed broadly
5~
-22-
and be restricted solely by the appended claims. In these exam-
ples the water content of the dehydrated precipitate refers to
chemically-bound water content. Unless otherwise noted in
these examples, analyses of the products resulting from the
following procedures show the presence therein of the hydrogen-
bonding material utilized.
EXAMPLE 1
In a suitable vessel, an aqueous solution of calcium
ions and sucrose is prepared. The preferred amount of sucrose
in the aqueous solution is from about 10% to about 30% by
weight of the solution. The concentration of calcium ions in
the solution can be from about .~1~ to about 23% by weight
calcium per weight of the total solution. This solution may be
formed by dispersing such calcium-containing materials as a
calcium oxide, calcium hydroxide, calcium hydride, calcium
peroxide or other water soluble salts such as calcium
chlorides, etc., in either water and subsequently adding
sucrose, or in an aqueous sucrose solution. It is preferred to
add the calcium-containing material before the sucrose, and it
has been found tha~ the calcium ion solubility is increased as
the sucrose concentration in the aqueous solution is increased.
It is preferred to form the calcium ions and sucrose
aqueous solution by adding calcium oxide to water to form a
slaked lime slurry adding sucrose to the resulting slurry. For
illustrative purposes calcium oxide will be utrilized in this
example. The purity of the sucrose material is not critical as
long as excessive amounts of impurities are avoided.
The purity of the calcium oxide utilized is also not
critical, but it is undesirable to have much more than a trace
amount of magnesium ions associated with the aqueous solution~
It is also particularly helpful in forming the solution to
. ~
~ i
5S~3
-23-
select the materials that have uniformly small particle sizes
so as to afford a fairly rapid rate of dissolving the material.
It is preferred to obtain an aqueous solution that
has both sucrose and calcium at the higher levels oE the
above-noted ranges due to superior yields in product per unit
weight of solution.
The temperature utilized in forming the solution is
not critical to the process of this invent:ion, but it is
preferably below about 70C. so as to avoid any adverse
conversion of the sucrose such as by inversion. Furthermore,
it has been found that the lower the temperature of the
sucrose-containing aqueous solution when adding the calcium
oxide thereto, the higher the concentration of calcium ions
that can be placed in the solution. It is preferred to remove
any insolubles remaining in the solution.
The resulting aqueous solution of sucrose and calcium
ions is then contacted with carbon dioxide. The solution is at
a temperature preferably of from about -3C. to about -~3C.,
and maintained at that temperature while contacting it with
carbon dioxide. The carbon dioxide is in the form of a gas and
is introduced into the solution subsurface. This provides both
; intimate contact and good agitation. A precipitate begins to
form after about 1.4 to about 1.5 moles carbon dioxide/moles
calcium in the solution has been consumed and continues to form
until about 1.7 to about 2.2 moles of carbon dioxide per mole
of calcium has been consumed; the formation of a precipitate in
this phase is exothermic. At this point, it is preferred to
stop the feeding of the carbon dioxide to the solution,
although the processs of this invention can be carried out by
continuing to feed carbon dioxide into the solution.
it~
-24-
When the exothermic phase of the precipitate-forming
step has been concluded, the solution begins to evolve carbon
dioxide in an endothermic phase. If the carbon dioxide feed
stream is continuously being fed to the aqueous solution, it
can be observed that the amount being released from the
solution is greater than the amount being added thereto. If
the carbon dioxide feed stream to the aqueous solution has been
stopped at the end of the exothermic phase as above-described
the solution containing the precipitate will evolve carbon
dioxide. In either case, this endothermic carbon
dioxide-releasing phase continues until the mole ratio of
consumed carbon dioxide to calcium in the solution is about 1.0
moles of carbon dioxide per mole of calcium. It is critical in
the formation of the precipitate that the phases as described
above be completed and, further, that the second phase be
continued until the point where carbon dioxide release has
essentially ceased.
The precipitate is then isolated from the solution,
such as by centrifugation, followed by washing with
water-miscible solvent and evaporating the solvent. This
procedure results in a washed precipitate that is free of any
of the solution from which it was formed. Any water remaining
in the precipitate is chemically-bound rather than merely
adhering to the precipitate particles. The amount of this
chemically-bound water must be reduced below about 15% so as to
provide stabilized amorphous calcium carbonate.
The washed precipitate is then dehydrated. For
instance, this can be carried out most readily in a vacuum oven
at high vacuum that continuously removes the water as it is
released from its chemically-bound condition.
The resulting products are finely divided white
powders that, upon subjection to the above described reactivity
~.~
- 25 -
test, react within one minute and maintain this reactivity
for at least one month storage.
EXAMPLE 2
In a suitable vessel, a mixture of 75.0 g. of calcium
oxide and 225.0 g. of water ~as stirred at ambient temperature
for 15 minutes to form a slaked lime slurry. A solution of
337.5 g. of sucrose and 937.5 g. of water was added to the
slaked lime slurry and the resulting mixture was stirred 15
minutes at ambient temperature and then cooled to 5C. Twenty
grams of the product marketed under the trade mark "Dicalite
Speed-Plus" (filter-aid) was added and the mixture was filtered
through 20 g. of Dicalite Speed-Plus. The filtrate was then
cooled to 0C. and 1000 g. of ice was added, resulting in a
mixture containing 2.0% calcium and 1~.1% sucrose. To this
mixture was added 40 liters of C02, fed into the mixture
subsurface with rapid stirring with a precipi-tate being formed.
The resulting mixture was stirred for one hour at -2 &., then
warmed to ~2C. and the precipitate was removed in a basket
centrifuge. The precipitate cake was slurred in 700 ml. of
0C. water (13% solids) and the slurry was spray dried at
500 F. inlet temperature (outlet temperature 300F.).
Ninety grams of product were recovered. Analysis indicated
the presence of 4.9% H20. The reactivity of the product was
45 sec. and remained so over extended periods of storage
-26-
EXAMPLE 3
In a suitable vessel, a mixture of 1300 g. of water,
300 g. of sucrose and 30 g. of calcium oxicle was stirred for
one hour at ambient temperature, then cooled to 5C. Twenty
grams of Dicalite Speed-Plus was added and the mixture was
vacuum filtered through 20g. of Dicalite Speed-Plus. The
filtrate was then cooled to 0C., 300 g. of crushed ice was
added resulting in a mixture containing 1.1~ calcium and 15.5%
sucrose and 0.85 cu. ft. of C02 was fed into this mixture
subsurface with rapid stirring with a precipitate being formed.
The resulting mixture was stirred at -2C. for one hour and
then warmed to +1C. The precip~jtate was removed by
centrifugation and slurried 4 times with 550 ml. quantities of
5C. acetone. After each wash the solvent was removed by
vacuum filtration. The washed precipitate was dehydrated for
18 hours at 44C. in a vacuum oven (0.45 mm). The product
obtained contained 9.1~ H20, had a reactivity of 45 seconds
and retained this reactivity for extended periods of storage.
~,_~,1
5S~
--27--
EXAMPLE ~
Following the procedure of Example 2 a precipitate
was prepared and centrifuged. The resulting cake (250 g.) was
washed 4 times with 475 ml. quantities of 2C. acetone. The
acetone was removed after each wash by vacuum filtration. The
washed precipitate was dried in a fluid bed dryer at 40C.
with 5-5.5 ft.3/min. air flow for 60 minutes. The resulting
product contained 7.5% H20, had a reactivity of 45 seconds
and retained this reactivity for extended periods of storage.
EXAMPLE 5
A precipitate is prepared by the following procedure.
In a suitable vessel, a mixture of 75.0 g. of calcium oxide
and 225 . O g. of water was stirred at ambient temperature for 15
minutes to- form a slaked lime slurry. A solution of 337.5 g.
of sucrose and 937.5 g. of water was added to the slaked lime
slurry and the resulting mixture was stirred 15 minutes at
am~ient temperature and then cooled to 5C~ Twenty grams oE
Dicalite Speed-Plus (filter aid) was added and the mixture was
filtered through 20 g. of Dicalite Speed-Plus. The filtrate
was then cooled to 0C., 750 g. of ice was added resulting in
a mixture containing 2.2% calcium and 14.5% sucrose. Forty
liters of C02 was fed subsurface with rapid stirring with a
precipitate being formed. The resulting mixture was stirred
for one hour at -2C., then warmed to +2C. and the
precipitate was removed in a basket centrifuge. Samples of the
precipitate cake prepared by the above procedure were dried
and/or dehydrated as follows:
A. The precipitate cake is dried "as is" --
(without solvent wash).
;cj~
~28-
~1) Ten grams of cake dried in vacuum oven
tNational Appliance Co., inside dimensions
12"x8"x8") at 25~C. and less than 1.0
mm. for 4 hours followed by drying at 67C.
and less than 1.0 mm. for 18 hours.
Water Content - 4.6~
Reactivity - 45 seconds
Storability - excellent
(2) Forty grams of cake dried in vacuum oven
0 at 25C. and less than 1.0 mm. for 2 hours
followed by drying at 84C and less than
1.00 mm. for 18 hour~
Water content - 0.8
Reactivity - 102 seconds
(3) Twenty-five grams of cake dried in a forced
draft oven IBlue M Electric Co., Blue Island,
Illinois) at 45C. for 20 hours.
Wa-ter content = 1.0~
Reactivity - 102 seconds
0 (4) Twenty-five grams of cake dried in oven
(National Appliance Co.) at 70C. for 20
hours.
Water content - 0.8%
Reactivity - 150 seconds
(5) Twenty-five grams of cake allowed to dry
on bench at 30% relative humidity and
24C. for 20 hours.
Water content - 1.1%
Reactivity - 120 seconds
5~
-2~-
(6) Forty grams of cake dried in oven ~National
Appliance Co.) at 200C. for 18 hours.
Water content - 0.2~
Reactivity - 165 seconds
The dehydration carried out in A. (2) through (6) illustrates
the decomposition of the precipitate due to improper
dehydration as compared to the proper dehydration carried out
in A. (1). In A. (1) a small amount of precipitate was
dehydrated in a high vacuum and the resultant material had
excellent reactivity and storability. In A. (2) through (6)
the precipitate formed a slurry during the dehydration and
resulted in a hard, brittle chalk-like solid that had a low
water content and poor reactivity apparently due to not
removlng the free water from the precipitate being dried
rapidly enough.
B. The precipitate cake (250-300 g.) is washed
twice with 353 g. quantities of 0-5C.
anhydrous acetone. Acetone removed after each
wash by suction filtration. The washed
20 precipitate was dehydrated as Eollows:
(1) Two hundred grams of cake dried in vacuum
oven at 25C. and less than 1 mm. for 4
hours followed by drying at 86C. and
less than 1 mm. for 18 hours.
Water content - 8.3~
Reactivity - 45 seconds
Storability - excellent
(2) Two hundred grams of cake dried in vacuum
oven at 25C. and 10 mm. for 4 hours
~ollowed by drying at 74C. and 10-15 mm.
for 18 hours.
~, .
5S~
~30-
Water Content - 0.5%
Reactivity - 135 seconds
~3) Twenty-five grams of cake dried in a
forced draft oven at 47C. for 20
hours.
Water content 2.15~
Reactivity - 150 seconds
(4) Twenty-five grams of cake dried in oven
at 72 DC . for 20 hours.
Water content 1~0%
Reactivity - 150 seconds
(5) Twenty-five grams of cake dried on bench
at relative humidity and 24C.
Water content - 1.0%
Reactivity - 150 seconds.
As in Part A. the samples dehydrated in B. l2) through ~5) are
examples of improper dehydration causing decomposition of the
precipitate In B. (2) through (5) a slurry was formed during
the dehydration step and a hard, brittle, chalk-like material
resulted which had low water content and poor reactiyity. On
the other hand, B. (1) illustrates the proper manner of
carrying out the dehydration step as no decomposition occurred
and the product resulting therefrom was excellent.
~,
C. The precipita-te cake is washed twice wikh a
5:1 ratio (ml. solvent: g. cake) oE 25C.
methanol. The solvent was removed after each
wash by vacuum filtration. The washed preci-
pitate was dehydrated as follows:
(1) Two hundred grams of cake dried in a
vacuum oven at 25C. and c2 mm. for 4
hours followed by drying at 76C. and
~2 mm. for 18 hours.
Water content - 3.9%
Reactivity - 45 seconds
Storability - excellent
(2) Two hundred grams of cake dried in a
vacuum oven at 25C. and 7.8 mm. for
4 hours and at 63C. and 7.8 mm. for
18 hours.
Water content - 16.1%
Reactivity - 45 seconds
Storability - poor
(3) Twenty-five grams of cake dried in a
forced draft oven at 48C. for 20 hours
Water content - 12,7~
Reactivity - 45 seconds
Storability - poor
(4) Twenty-five grams of cake dried in an
oven at 40C. for 20 hours.
Water content - 2.7~
Reactivity - 45 seconds
Storability - excellent
s~
-32-
(5) Fifteen grams sample of cake dried on
the bench at 39~ relat:ive humidity and
24C. for 20 hours.
Water content - 15.0%
Reactivity - 45 seconds
Storability - excel:lent
The samples dehydrated in Part C. (2) and (3) are
illustrative of a manner of carrying out the dehydration step
under the proper conditions but not for a sufficient length of
time, thereby resulting in products that have excellent
reactivity initially but that have poor storabilit~. C. (1),
(4) and (5) are illustrative of the proper manner of carrying
out the de~hydration step and the product resulting therefrom.
EXAMPLE 6
In a suitable vessel, a mixture of 20.0 g. of calcium
o~ide and 60.0 g. of water was stirred at ambient temperature
for 15 minutes to form a slaked lime slurry~ A solution of
90.0 g. of sucrose and 250.0 g. of water was added to the
slaked lime slurry and the resulting mixture was stirred 15
minutes at ambient temperature and then coole'd 5C. Ten grams
of Dicalite Speed-Plus was added and the mixture was
filtered through 10 g. of Dicalite Speed-Plus. The
filtrate was then cooled to 0C., 240 g of ice was added
resulting in a mixture containing 2.1~ calcium and 13.6
sucrose and 24 liters of C02 was fed into the mixture
subsurface with rapid stirring to form a precipitate. The
resulting mixture was stirred for one hour at -2C., then
warmed to +0.5C. and the precipitate recovered b~ vacuum
filtration. The resulting cake
was slurried twice with 400 g. quantities of 25C.
, I
5~i~
water. The water was removed by vacuum filtration and the cake
was then washed with 400 ml. of 25C. methanol. The washed
precipitate was allowed to air dry at a relative humidity of
45% and a temperature of about 24C. for 18 hours.
The resulting white solid powder had an unacceptable reactivity
of 79 seconds. The product apparently changed during the water
washing step and upon analysis it was determined that no
sucrose was present in the precipitate.
EXAMPLE 7
In a suitable vessel, a mixture of 20.0 g. of calcium
oxide and 60.0 g. of water was stirred at ambient temperature
Eor 15 minutes to form a slaked lime slurry. A solution of
90.0 g. of sucrose and 490.0 g. of water was added to the
slaked lime slurry and the resulting mixture was stirred 15
minutes at ambient temperature and then cooled to 12C. Ten
grams of Dicalite Speed-Plus was added and the mixture was
filtered through 10 g. of Dicalite Speed-Plus. The filtrate
containing 2.1% calcium and 13.6~ sucrose was then cooled to
13C. and 27 1. of C02 was fed subsurface with rapid
stirring to Eorm a precipitate. During this time the
temperature rose to 17C. The resulting mixture was stirred
for an hour at about 15C. and the precipitate recovered by
vacuum filtration. The resulting cake was slurried twice with
400 ml. quantities of 25C. methanol. The methanol was
removed by vacuum filtration and the washed precipitate was
air-dried at a relative humidity of 43% and a temperature of
about 24C. for 18 hours.
The resulting fine, white powder had a reactivity of
45 seconds and retained this reactivity during storage.
i5'~`9~
- 34 -
EXAMPLE 8
In a suitable vessel, a mixture of 10.0 g. of
calcium oxide and 30.0 g. of water was stirred at ambient
temperature for 15 minutes to form a slaked lime slurry.
A solution of 50.0 g. of glucose and 300.0 g. of water was
added to the slaked lime slurry and the resulting mixture
was stirred and cooled to 5C. The mixture was filtered
through 10 g. of "Dicalite Speed-Plus". I'he filtrate was
then cooled to 0C and 200 g. of ice was added resulting in
a mixture containing 1.1~ calcium and 8.5% glucose. Ten
liters of C02 was fed subsur-face into the mixture with rapid
stirring to foxm a precipitate. The resulting mixture was
stirred for 45 minutes at - 2C, then warmed to ~2C., and
the precipitate recovered by vacuum filtration. The resulting
cake was slurred twice with 150 ml. quantities of 25C.
methanol. The methanol was removed by vacuum iltration and
the washed precipitate was air dried for 24 hours at a
relative humidity of 20% and a temperature of 24C.
The resulting fine white powder contained about
15.0% water, had a reactivity of 30 seconds and retained this
reactivity for extended periods of storage.
EXAMPLE 9
In a suitable vessel, a mixture of 1162.5 g. of
water, 337.5 g. of glucose and 75.0 g. of calcium oxide was
stirred for 1 hour at ambient temperature and then cooled
to 5C. Twenty grams of the product marketed under the trade
mark "Hyflo Supercel" tfilter-aid) was added and the resulting
mixture was vacuum filtered through 20 g. of "Hyflo Supercel".
The filtrate was then cooled to 0C., 900 g. of crushed ice
was added resulting in a mixture containing 2.1~ calcium and
13.6% glucose and 40 liters of C02 was fed subsurface
into the mixture with rapid stirring
:~,
~ "i
s~
-35-
to form a precipitate. The resulting mixture was stirred at
-l~C. for one hour, then warmed to +1C. and the precipitate
was recovered in a basket centrifuge. The resulting cake was
slurried in 700 ml. of 0C. water (13 wt. % solids) and the
slurry was spray dried at 500F. inlet temperature ~300F.
outlet temperature). The resulting fine white powder contained
4.7% water, had a reactivity of 30 seconds and had excellent
storability over extended periods of storage.
EXAMPLE 10
'10
In a suitable vessel, a mixture of 20.0 g. of calcium
oxide and 60.0 g. of water was stirred at ambient temperature
for 15 minutes to form a slaked lime slurry. A solution of
90.0 g. sorbitol and 250.0 g. of water was added to the slaked
lime slurry and the resulting mixtùre was stirred and cooled to
3C. The mixture was filtered through lO g. of Dicalite
Speed-Plus. The filtrate was then cooled to 0C. and 240 g.
of ice was added resulting in a mixture containing 2.1~ calcium
and i3.1% sorbitol and 27 liters of C02 was fed into the
mixture subsurface with rapid stirring to form a precipitate~
The resulting mixture was stirred for 70 minutes at -2C, then
warmed to +1C. and the precipitate recovered by vacuum
filtration. The precipitate cake was slurried twice with 400
ml. quantities of 25C. methanol and twice with 400 ml.
quantities of acetone. The solvents were removed by vacuum
filtration and the washed precipitate was air dried 24 hours at
a relative humidity of 40~ and a temperature of 25C.
The water content of the resulting product was about
17.6~ and its reactivity was 45 seconds. However, the product
3~ did not retain this reactivity during storage.
~,~
5~
-36-
EXAMPLE 11
In a suitable vessel, a mixture of ~0 g. of calcium
oxide and 180 g. of water was stirred at ambient temperature
for 15 minutes to form a slaked lime slurry. A solution of 270
g. of sorbitol and 750 g. of water was added to the slaked lime
slurry and the resulting mixture was stirrled 15 minutes at
ambient temperature and then cooled to 5C. Twenty grarns of
Hyflo Supercel ~filter-aid) was added and the mixture was
filtered through 20 g. of Hyflo Supercel. The filtrate was
cooled to ODC., 720 g. of ice was charged resulting in a
mixture containing 2.1% calcium and 13.6~ sorbitol and 41
liters of C02 was fed into the mixture subsurface with rapid
stirring to form a precipitate. The resulting mixture was
stirred for one hour at -1C., then warmed to +1C. and the
precipitate was recovered in a basket centrifuge. The
resulting cake was slurried in 700 ml. of 0C. water (11
solids) and the slurry was spray dried at 500F. inlet
temperature, 300F. outlet temperature.
The resulting product contained 4.4% water, had a
reactivity of 50 seconds and retained its reactivity for
extended periods of storage.
EXAMPLE 12
In suitable vessel, a mixture of lO.0 g. of calcium
oxide and 30.0 g. of water was stirred at ambient temperature
for 15 minutes to form a slaked lime slurry. 500.0 g. of
methanol was added to the slaked lime slurry and the resulting
mixture containing 92.5% methanol and 1.3~ calcium was then
cooled to -12C. 24 liters of C02 were fed into the mixture
subsurface with rapid stirring during which the temperature
rose to -5.5C. and then decreased again to -12C. with a
precipitate being formed. The precipitate was
recovered by filtration and washed twice with 250 ml. of
cold methanol. The methanol was removed by vacuum Eiltration.
The washed precipitate was air dried for 72 hours at a relative
humidity of 15% and a temperature of 24C.
The resulting product contained 11.7% water, had a
reactivity of 60 seconds and was unable to retain this
reactivity upon storage.
EXAMPLE 13
In a suitable vessel, a mixture of 10.0 g. of calcium
oxide and 30.0 g. of water was stirred at ambient temperature
1~ for 15 minutes to form a slaked lime slurry. A mixture of
250.0 g. of methanol and 250.0 g. of water was added to the
slaked lime slurry and the resulting mixture containing 46.3%
methanol and 1.3% calcium was then cooled to -12.5C. 52
liters of C02 was fed into the mixture subsurface with rapid
stirring during whi~h the temperature rose to -8C. and
dropped again to -12.5C. with a precipitate being formed.
The precipitate was recovered by vacuum filtration and washed
twice with 150 ml. of cold methanol. The methanol was removed
by vacuum filtration and the washed precipitate was air dried
2~ for 72 hours at a relative humidity of 4~ and a temperature of
24C.
The resulting product contained 2.7% water, had a
reactivity of 50 seconds and retained this reactivity during
extended periods of storage.
EXAMPLE 14
In a suitable vessel, a mixture of 20.0 g. of calcium
oxide and 60.0 g. of water was stirred at ambient temperature
for 15 minutes to form a slaked lime slurry. A solution of
90.0 g. of glycerine and 25n.0 g. of water was added to the
slaked lime slurry. The resulting mixture was stirred
~and cooled to 5C. and was then filtered through
t~
-38~
10 g. of Dicalite Speed-Plus. The filtrate was then cooled to
0C. and 240 g. of ice was added resulting in a mixture
containing 2.3% calcium and 15.0~ glycerine and 17 liters of
C2 was fed into the mixture subsurEace with rapid stirring
at -4C. with a precipita-te being formed. The resulting
mixture was warmed to 1C. and the precipitate was recovered
by vacuum filtration. The precipitate cake was slurried twice
with 250 ml. quantities of 25C. methanol and the methanol was
removed by vacuum filtration. The washed precipitate was
air-dried for 24 hours at a relative humiclity of 25% and a
temperature of 24C.
The resulting fine white powder contained 1.3% water
and had a reac~ivity of 45 seconds. The product retained this
reactivity during extended periods of storage.
EXAMPLE 15
In a suitable vessel, a mixture of 20.0 g. of calcium
oxide and 60.0 g. of water was stirred at ambient temperature
for 15 minutes to form a s`laked lime slurry. A solution of 45
g. glycine and 250.0 g. of water was added to -the s:Laked lime
slurry and the resulting mixture was stirred and cooled to
5C. The mixture was filtered through 10 g. of Dicalite
Speed-Plus. The filtrate was then cooled to 0 and 240 g. of
ice was added resulting in a mixture containing 1.9% calcium
and 7.3~ glycine and 52 liters of C02 was fed into the
mixture subsurface with rapid stirring with a precipitate being
formed. The mixture was then stirred for 30 minutes at -2C.,
then warmed to +1C. and the precipitate was recovered by
vacuum filtration. The precipitate cake was slurried twice
with 450 ml. quantities of 25C. methanol. The methanol was
~0 removed by vacuum filtration and the washed
precipitate was air dried for 24 hours at a relative
~r~
.
5~
-39-
humidity of 35% and a temperature of 24C.
The resulting product contains 1707% water and has
a reactivity of 55 seconds but did not retain this reactivity
during storage.
EXAMPLE 16
In a suitable vessel, a mixture of 60 g. of calcium
oxide and 1~0 g. of water was stirred at ambient te~perature
for 15 minutes to form a slaked lime slurry. A solution of
67.5 g. of glycine and 750 g. of water was added to the slaked
lime slurry and the resulting mixture was stirred 15 minutes at
ambient temperature and then cooled to 5C. Twenty grams of
Hyflo Supercel ~filter-aid) was added and the mixture was
filtered through 20 g. of Hyflo Supercel. The filtrate was
then cooled to 0C., 720 g of ice was added resulting in a
mixture containing 1.0% calcium and 3.8% glycine and 35 liters
f C2 was fed into the mixture subsurface with rapid
stirring with precipitate being formed. The resulting mixture
was stirred for one hour at -1C., then warmed to +1C. and
the precipitate was recovered in a basket centrifuge. The
resulting cake was slurried in 500 ml. of 0C. water and the
slurry was spray dried at 50QF inlet, 300F outlet
temperature.
The resulting product contained 3.7~ water had a
reactivity of 45 seconds and retained this reactivity for
extended periods of storage.
EXAMPLE 17
In a suitable vessel, a mixture of 10 g. CaO and 30
g. water was stirred at ambient temperature for 15 minutes to
form a slaked lime slurry. A solution of 25 g. lysine and 250
g. water was added to the slaked lime slurry and the
resulting mixture was stirred 15 minutes at ambient temperature
~ . ,
s~ ~
-40-
and then cooled to 5C. Ten grams of filter-aid was added to
the mixture which was then filtered through 10 g. of
filter-aid. The filtrate was then cooled to 0C., 240 g. of
ice was added resulting in a mixture containing 0.6% calcium
and 4.5% lysine and 22.5 liters of C02 was fed into the
mixture subsurface with rapid stirring with a precipitate being
formed. The resulting mixture was stirred for one hour at
-1.5C., warmed to 0C. and the precipitate was recovered by
. vacuum filtration. The precipitate cake was slurried twice
with 200 ml. of 25C. methanol and then twice with 200 ml. of
25C. acetone. The precipitate was removed from the solvents
each time by vacuum filtration. The washed precipitate was
allowed to air dry on the laboratory bench for 18 hours at a
relative humidity of 35~ and a temperature of 24C.
The resulting product contained 11.7~ water and had a
reactivity of 33 seconds but did not retain this reactivity
during storage.
EXAMPLE 18
In a suitable vessel, a mixture of 70 g. of calcium
oxide and 210 g. of water was stirred at ambient temperature
for 15 minutes to form a slaked lime slurry. A solution of 175
g. of lysine and 1750 g. of water was added to the slaked lime
slurry and the resulting mixture was stirred 15 minutes at
ambient temperature and then cooled to 5C. Twenty grams of
Hyflo Supercel (filter-aid) was added and the mixture was
filtered through 20 g. of Hyflo Supercel. The filtrate was
then cooled to 0C., 1680 g. of ice was added resulting in a
mixture containing 0.6~ calcium and 4.5% lysine and
P5~3
-41-
37 liters of C02 was fed into the mixture subsurface with
rapid stirring with a precipitate being formed. The resulting
mixture was stirred for one hour at -1C., then warmed to
+1C and the precipitate was recovered in a basket centrifuge.
The resulting cake was slurried in 700 ml. of 0C. water (12%
solids) and the slurry was spray dried at 500F. inlet
temperature, 300F. outlet.
The resulting product contained 4.5% water, had a
reactivity of 55 seconds and retained this reactivity during
extended periods of storage.
EXAMPLE 19
In a suitable vessel, a mixture of 75.0 g~ of calcium
oxide and 225.0 g. of water was stirred at ambient temperature
for 15 minutes to form a slaked lime slurry. A solution of
337.5 g. oE sucrose and 937.5 g. of water was added to the
slaked lime slurry and the resulting mixture was stirred 15
minutes at ambient temperature and then cooled to 5C. Twenty
grams of Dicalite Speed-Plus (filter-aid) was added and the
mixture was filtered through 20 g. of Dicalite Speed-Plus. The
filtrate containing 3.2% calcium and 21.4% sucrose was then
cooled to -2C. and, with external cooling, 40 liters of C02
was fed into the mixture subsurface with rapid stirring at such
a rate that the temperature did not exceed 0C. with a
precipi~ate being formed. The resulting mixture was stirred
for one hour at 0C. and the precipitate was recovered in a
basket centrifuge. The cake was slurried twice with 1000 ml.
quantities of methanol. The solvent was removed aEter each
wash by vacuum filtration. The washed precipitate was air
dried for 18 hours at a relative humidity of 15% and a
temperature of 24C.
:~ 18~i5~i~
-~2-
The resulting product contained about 15.0~ water and
had a reactivity of 55 seconds which it retained for extended
periods of storage.
EXAMPLE 20
In a suitable vessel, a mixture of 382 g. of water,
9.6 g. of CaO and 39.2 g. of sucrose was stirred at 25C. for
45 minutes, then with ice bath cooling until the temperature of
the mixture was 5C. Five grams of Hyflo Supercel
(filter-aid) was added and the mixture was stirred for an
additional 5 minutes. The mixture was suction filtered through
a filter precoated with Hyflo Supercel. The filtrate was then
cooled with stirring at 0C., 100 g. of ice was added
resulting in a mixture containing 1.2% calcium and 7.3% sucrose
and 5.5 liters of C02 was fed into the mixture subsurface
with rapid stirring with a precipitate being formed. The
resulting mixture was stirred at -1C. for one hour, then
warmed to +1C.. The precipitate was recovered by vacuum
iltration and slurried 2 times with 50 g. quantities of 2C
acetone. The solvent was removed after each wash by vacuum
filtration; The washed precipitate was dried in a vacuum oven
at less than one mm. for 2 hours at 25C and for 18 hours at
70C.
The resulting product contained 7.5% water and had a
reactivity of 50 seconds which it retained during extended
periods ~f storage.
EXA~PLE 21
In a suitable vessel, a mixture of 20 g. CaO and 60
g. water was stirred at ambient temperature for 15 minutes to
form a slaked lime slurry. A solution of 22.5 g. glycine and
250 g. water was added to the slaked lime slurry and the
resulting mixture was stirred 15 minutes at ambient temperature
and then cooled to 5~. Ten grams of fiIter-aid was added
, . . .
1,
cj~
-43-
to the mixture which was then filtered through 10 g.
filter-aid. The filtrate was then cooled to 0C., 240 g. of
ice were added resulting in a mixture containing 1.0% calcium
and 3.8% glycine and 36 liters of C02 was fed into the
mixture subsurface with rapid stirring with a precipitate being
formed. The resulting mixture was stirred for half an hour at
-1.5C., warmed to 0C. and the precipitate was recovered by
vacuum filtration. The precipitate cake was slurried twice
with methanol (5 ml./g.) and twice with acetone (5 ml./g.).
The precipitate was removed from the solvents each time by
vacuum filtration. The washed precipitate was allowed to air
dry on the laboratory bench for 18 hours at a relative humidity
of 40~ and a temperature of 24C.
The resulting product contained 15.3% water and had a
reactivity of 33 seconds but did not retain this reactivity in
storage.
EXAMPLE_22
In a suitable vessel, a solution of 34 g. CaC12, 90
g. sucrose and 310 g~ water was cooled to 0C. and 240 g. of
ice was added resulting in a mixture containing 0.18% calcium
and 13.4% sucrose. The mixture was stirred rapidly while C02
was fed subsurface. The pH of the mixture was 7.0 at the
beginning of the introduction of C02 and decreased to 3.5
during the C02 addition.
No precipitate resulted after 25 minutes of feeding
CO2 .
EXAMPLE 23
In a suitable vessel, a solution of 34 g. CaC12, 90
g. sucrose, 210 g. water and 100 g. lN NaOH was cooled to 0C.
and 240 g. of ice was added. The resulting mixture containing
0.18% calcium and 13.4% sucrose was stirred rapidly while C02
was fed subsurface which caused a precipitate to form. The
resulting mixture was stirred for one hour at
~8~
-44-
-1.5C., warmed to 0C. and the precipitate was recovered by
vacuum filtration. The precipitate cake was washed twice with
methanol ( 5 ml.g.) and twice with acetone (5 ml./g.) The
precipitate was removed from the solvents each time by ~acuum
filtration. The washed precipitate was allowed to air dry on
the laboratory bench for 18 hours at a relative humidity of 49%
and a temperature oE 24C.
The resulting product contained 15.5% water and had a
reactivity of 33 seconds but did not retain this reactivity
durin~g storage.
EXAMPLE 24
In a suitable vessel, a mixture of 7.5gO of CaO and
225 g. of water was slurried for 15 minutes at ambient
temperature, 1275 g. of water was added and the mixture was
cooled to 0C. To this cold mixture was added 900 ~. of ice
resulting in a mixture containing 2.2~ calcium. With vigorous
stirring C02 was fed into the mixture subsurface until no`
more was absorbed causing the formation of precipitate. The
resulting mixture was stirred for one hour at 0C. then warmed
to ~1C. The precipitate was recovered by centrifugation.
The cake was slurried with 500 ml. of 0C. water and the
slurry was spray dried at 500F. inlet and 300F. outlet.
The reactivity time of the product was 180 seconds and the
product contained 5.6% H20.
This example illustrates the need for the presence of
a hydrogen-bonding material in the precipitated calcium
carbonate.
EXAMPLE 25
In a suitable vessel, a mixture of 75.0 g. of
3 calcium oxide and 225.0 g. of water was stirred at ambient
b~ ~
-45-
temperature for 15 minutes to form a slaked lime slurry. A
solution of 337.5 g. of sucrose and 1937.5 g. H20 was added
to the slaked lime slurry and the resulting mixture was stirred
15 minutes at ambient temperature and then cooled to 6C.
Twenty grams of filter-aid was added and the mixture was
filtered through 20 g. of filter-aid. The filtrate containing
2.0% calcium and 13.2~ sucrose was then cooled to 2C. and
C2 was fed into the mixture subsurface with rapid stirring
causing a precipitate to form. The temperature range during
C02 addition was 2-8C. The resulting mixture was stirred
for one hour at 1C. and the precipitate was recovered in a
basket centrifuge. Much of the precipitate was lost through
the filter paper. 100 g. of wet precipitate cake was slurried
with about 300 ml. of ice water and spray dried.
The resulting product contained 1.99% water and had a
reactivity of 112 seconds.
EXAMPLE 26
In a suitable vessel, a mixture of 75.0 g. of calcium
oxide and 225.0 g. of water was stirred at ambient temperature
for 15 minutes to Eorm a slaked lime slurry. A solution of
337.5 g. of sucrose and 1937.5 g. H20 was added to the slaked
`'ime slurry and the resulting mixture was stirred 15 minutes at
ambient temperature and then cooled to 11C. Twenty grams of
filter-aid was added and the mixture was filtered through 20 g.
of filter-aid. The filtrate containing 2.0% calcium and 13.2%
sucrose was then cooled to 8C and C02 was fed into the
mixture subsurface with rapid stirring causing a precipitate to
form. The temperature range during C02 addition was
8-12C. The resulting mixture was stirred for one hour at
7-9C. and
~.86~
-~6-
the precipitate was recovered in a basket centriEuge. 150 g.
of wet precipitate cake was slurried with 300 ml. o ice water
and spray aried.
The resulting product contained 1.7~ water and had a
reactivity of 112 seconds.
EXAMPLE 27
In a suitable vessel, a mixture of 75.0 g. o calcium
oxide and 225.0 g. of water was stirred at ambient temperature
for 15 minutes to form a slaked lime slurry. A solution of
337.5 g. of sucrose and 1937.5 g. of water'was added to the
slaked lime slurry and the resulting mixture was stlrred 15
minutes at ambient temperature and then cooled to 15C.
Twenty grams of filter-aid was added and the mixture was
filtered through 20 g. of filter-aid. The filtrate containing
2.0~ calcium and 13.2~ sucrose was then cooled to 12C. and
C2 was fed into the mixture subsurface with rapid stirring
causing a precipitate to form. The temperature range during
C2 addition was 12-17C. The resulting mixture was
stirred for one hour at 14-16C. and the precipitate was
recovered in a basket centrifuge. The 140 g. of wet
precipitate cake was slurried with 300 ml. of ice water and
then spray dried.
The resulting product contained 1.7% water and had a
reactivity of 78.5 seconds.
EXAMPLE 28
In a suitable vessel, a mixture of 75.0 g. of calcium
oxide and 225.0 g. of water was stirred at ambient temperature
for 15 minutes to form a slaked lime slurry. A solution of
3375 g. of sucrose and 1937.5 g. of water was added to the
slaked lime slurry and the resulting mixture was stirred 15
minutes at ambient temperature. Twenty grams of filter-aid was
added and the mixture was filtered through 20 g. of
filter-aid. The filtrate containing 2.0% calcium and
s~
-47-
13.2% sucrose was then cooled to 18C. and C02 was fed into
the mixture subsurface with rapid stirring causing a
precipitate to form. The temperature during C02 addition was
18-23DC. The resulting mixture was stirred for one hour at
21-23C. and the precipitate was recoverecl by vacuum
filtration. 140 g. of wet precipitate cake was slurried with
200 ml. of ice water and spray dried.
The resulting product contained U.89% water and had a
reactivity of 90 seconds.
lQ Examples 25-28 illustrate the generally lower
reactivities obtained with precipitates formed at increasingly
higher temperatures~
Heretofore, amorphous calcium carbonate has been
obtained by some investigators. However, the heretofore
obtained amorphous calcium carbonate has rapidly changed ~rom
the amorphous state to a crystalline state. In other words, no
prior investigator has been able to obtain amorphous calcium
carbonate that will remain stable in the amorphous state for
significant periods oE time (i.e., for periods exceeding about
one month). It has now been Eound that the calcium carbonate
provided by this invention is amorphous calcium carbonate that
is stabilized in the amorphous state.
It has been found that the stabilized amorphous
calcium carbonate prepared by the above described process
comprises stabilized amorphous calcium carbonate that contains
from about 0.1~ to 15% by weight chemically-bound water and a
hydrogen-bonding material. Stabilized amorphous calcium
carbonate is a fine, white powder. Analyses show that
stabilized amorphous calcium carbonate consists of agglomerates
of extremely small particles of calcium carbonate that
5~
-48-
are substantia]ly amorphous. Comparative analysis of
stabilized amorphous calcium carbonate show that the particles
of calcium carbonate are apparently stabilized in this
amorphous state by the presence therein of the proper amount of
chemically-bound water and a hydrogen-bonding material.
The analyses of stabilized amorphous calcium
carbonate that will be described for illustrative purposes is
that material prepared by the procedure of Example 2. For
purposes of brevity and for this description this material will
be hereinafter referred to as "stabilized amorphous calcium
carbonate-2. n
Stabilized amorphous calcium carbonate-2 was examined
under the electron microscope and was studied by X-ray and
infrared analyses.
Examination under the electron microscope reveals the
significant difference between stabilized amorphous calcium
carbonate-2 and the known crystalline states of calcium
carbonate (calcite, aragonite and vaterite). Calcite crystals
appear as well-formed cubes uniform in size at a magnification
of 4000X. Crystals oE vaterite seem to occur as spheres of
differing size, while those of aragonite form fairly uniform
needles. In contrast, particles of stabilized amorphous
calcium carbonate-2 have no distinct size or shape at a
magnification of 4000X. ~agnified by 20,000X, stabilized
amorphous calcium carbonate-2 appears to have a rough surface
and non-uniform size suggesting an agglomerate of smaller
particles. Photomicrographs were taken at magnifications of
57,000X and 147,000X that show spherical particles with an
average particle size of from about lOA to about ~40A at
the edge of larger, irrregularly-shaped agglomerates.
After determining that the particles of stabilized
amor~hous calcium carbonate-2 appear different from the known
s~
-49-
crystalline states of calcium carbonate under an electron
microscope, further examination was made by X-ray analysis.
Unlike the known crystalline states of calcium carbonate,
stabilized amorphous calcium carbonate-2 gives no X-ray pattern
at all, that is, stabilized amorphous calc:ium carbonate-2 is
"amorphous" to X-ray analysis. Being "amorphous 1l -to X-ray
analysis is due to one of two reasons: either (1) stabilized
amorphous calcium carbonate-2 is not a simple carbonate, but a
polymeric or hydrogen-bonaed species whose repeating units are
irregular or too long to be measured by the X-ray analysis, or
(2) the particles of stabilized amorphous calcium carbonate-2
are too small to be detected by X-ray analysis.
Infrared analysis supports the second reason for
stabilized amorphous calcium carbonate-2 being X-ray amorphous.
Infrared spectra were run on two samples of stabilized
amorphous calcium carbonate-2 using the ~sI pellet technique
giving spectra from 4000 cm 1 to 200 cm 1. One of these
samples was combined with an e~tra 10~ ground sucrose so as to
intensify the peaks caused by sucrose. Upon comparison of
these two spectra the peaks due to sucrose become evident
allowing the peaks due to the carbonate group to be isolated.
Table I shows the result of this comparison.
That the remaining isolated peaks are due to the
carbonate group is confirmed by comparison of those remaining
peaks to the spectra obtained using the Nujol mull technique
with calcium carbonate prepared without a hydrogen-bonding
agent by the procedure of Example 24. Table II shows the
results of this comparison.
The remaining isolated peaks were compared to spectra
for calcite, aragonite and vaterite obtained in our laboratory
-50-
on the same instrument. This comparison is shown in Table III
which clearly shows that stabilized amorphous calcium
carbonate-2 does, in fact, contain a carbonate group but that
it does not resemble any one particular morphological state.
The basic difference in the spectra of stabilized amorphous
calcium carbonate-2 and the other known calcium carbonates is
that the peaks of stabilized amorphous calcium carbonate-2 are
much broader than those obtained with the other crystalline
states of calcium carbonate. Additionally, these spectra show
that stabilized amorphous calcium carbonate-2 does, in fact,
contain sucrose.
This conclusion as to a carbonate group is further
confirmed by comparison of the peaks obtained with stabilized
amorphous calcium carbonate-2 with the values for calcium
carbonate shown in the literature. These comparisons are shown
in Table IV with calcite, Table V with vaterite and Table VI
with aragonite.
., .
~`
-51-
TABLE I
Stabilized ~morphous Stab.ilized Amorphous
Calcium Carbonate-2 Calcium Carbonate-2
(0% Extra Sugar) (10% Extra Suqar)
(CsI Pellet) (CsI Pellet)
Wave Numbers (cm ) Wave Numbers (cm
***3440 ***- 3440
*2940 *- 2940
2510 (weak) 2510
1770 (shoulder)1770 (shoulder)
**1650 (shoulder)**1650 (shoulder)
1470 1470
**1285
*1245
*1210
*1165 (shoulder)
*1130 *~1130
*1070 *`1070
* 995 *. 995
* 942
* 925
* 920
* 910
3 ~split peak)~ (split Deak)
* 700 ~broad) *'700 (broad)
* 570 (broad) *'570 (broad)
320 320
* sucrose, ** water, *** sucrose and water,
~ bands with increased intensity
1070 Cm 1 and 700 cm 1 bands are due to both sucrose and
the carbonate group.
. ~ ... .
....
TABLE II
Stabilized
Amorphous CalciumCalcium Carbonate
carbonate-2of Example 24
(CsI Pellet)_1(Nujol mull)
Wave Numbers (cm )Wave Numbers (cm
***3440
***3400
*2940
2510 (weak)
1770 (shoulder)
1750
**165 (shoulder)
1470
1460
*1130
*1070 1070
* 995
* 925
8 ~
\(split peak) 867
8~_/
* 700 (broad)
* 570 (broad)
320
-53-
TABLE III
tabilized Amorphous ! _
~Calcium Carbonate-2 Calcite ¦Aragonite__ ~ rite
(CsI Pellet)(CsI Pellet)l(Nujol Mull),(CsI Pellet)
~ave Numbers (cm )Wave Numbers (cm
11 I
***3440
*2940 2520 1 1
2510 (weak) 2500 2510
~ 1775
1770 (shoulder)
17460
**1650 (shoulder)
1445
*1130 . 1090
1085 1078
*107905 .
* 925 . 878
(split peak~ 875 877
847
710 715 744
* 700 (broad) 700
320
-54-
TABLE IV
Stabili~ed Amorphous ¦
Calcium Carbonate-2 ¦ Calcite _ _
~CsI Pellet) 1 ~ (2) ¦(3) ¦ (4) ¦(5)1 (6)
Wave Numbers (cm ) ! Wave Num ers (cm ?
***3440 l l
*2940 I i
2510 (weak) ¦
1792
1770 (shoulder)
**1650 (shoulder)
1470
~1130 ~144~ I ~ 1 432
r 107 0 I ~ I
* 999255
881
877 J 877
87~(split) 874 873
(peak ) 847 847
713 713 713
710 712
* 700 (broad)
* 570 (broad)
320 (broad)
315 shoulder)
(1) Miller, F.A. and Wilkins, C.H.,228 (shouldert
Anal. Chem. 22(12), 1253 (1950)190 (should~r)
(2) Louisfert, J. and Pobeguin, T.,106 (shoulaer
Compt. rend. 235, 287 (1952)
(3) Angino, E.E., Am. Mineral~ 52, 137-48 (1967)
(4) Weir, C.E. and Lippincot~, E.R., Journal of
Research of the National Bureau of Standards
A Physics and Chemistry,-Vol. 65A,No.3,May-June 1961,p.173.
(5) Angino,E.E.,Am. Mineral.52,137-48(1967)
(6) Bertin, E.P.,Penland,R.B.,Mizushima,S.,Curran C., and
Quagliano, J.V., JACS 81,3818 (1959)
.
~ r
-55-
TABLE V
.
Stabilized Amorphous
Calcium Carbonate-2 Va-terite
(CsI Pellet) -1 (1) (2) 1 (3) _1 (4)
Wave Numbers (cm ) Wave Numbers (Cm
. _ _ .
***3440
*2940
2510 (weak)
1829
1770 (shoulder)
**1650 (shoulder) 1761
1488
1470
. 1450 1450
i 14417
*1130 1 1090
l 1088 1089
*1070 1070
* 999255
878 1877
(split) 874 !
~peak) ~ 88756
747 l 850
745 741 1 744
!
*700 (broad) i
*570 (broad)
320 (broad)
(1) Louisfert, J. and Poberguin, T., Compt. rend. 235,287 (1952)
(2) Baron,G. and Pesneau, M., Compt. rend. 243, 1217 (1956)
(3) Weir, C.E. and Lippincott,E.R.,Journal of Research of the
the National Bureau of Standards A Physics and Chemistry,
Vol. 65A, No. 3 May-June 1961,p.173.
(4) Sterzel, W. and Charinsky, E., Spectrochim. Acta 24A.
353 (1967).
-56-
TABLE VI
Stabilized Amorphous
Calclum Carbonate-2 Aragonite
(CsI Pellet) -1 (1) (2) 1 ~3) ~ (5)
Wave Numbers (cm ) Wave Numbersl(cm ) j
1,
**3440
*2940
2510 (weak) 1774
1770 (shoulder)
**1650 (shoulder)
1550
1475~1489
1470 1440
1430
*1130
1087 '1083
1080 1080
*19795
* 925
877
(split) 866
/(peak) l i
865l 858 857 1857
856
7845
'I 713 713 715 1713
* 700 (broad) ! 710 703 ¦
698 696
* 570 (broad) I
320 (broad) j. ¦
L i I 1 ;
(1) Murphy, C.B.,Anal. Chem. 38¦5), 443R-45IR (1966).
(2) Louisfert, J. and Pobeguin, T., Compt. rend.235,287(1952).
(3) Baron, G. and Pesneau, M. Compt. rend. 243, 1217 (1956).
(4) Weir, C.E. and Lippincott, E.R., Journal of Research of the
National Bureau of Standards A Physics and Chemistry, Vol.
65A, No. 3, May-June 1961, p. 173.
(5) Sterzel, W. and Charinsky, E., Spectrochim. Acta 24A,
353 (1967).
~ '
55~3
Examination by these different analytical methods
indicates that stabilized amorphous calcium carbonate-2
comprises extremely smal] particles of amorphous calcium
carbonate. In this sense, stabilized amorphous calcium
carbonate is "amorphous" in that it has no crystal lattice
that can be identified by available analytical means.
The amorphous state of stabilized amorphous calcium
carbonate was further confirmed by refractive index
determinations utilizing a Light-Two-Beam, '~Mach-~ellnde~
(Trade Name~ Interference Microscope for transmitted
light (Manuf.: Ernt~ Leitz, Wetzlar, W. Germany). This
instrument enables one to determine the refractive
indices of solids by the interferometer method.
With this instrument it was found that not only was
stabilized amorphous calcium carbonate clearly isotropic
but it gave refractive indices that are distinctly
different from the refractive indices found with heretofore
known amorphous calcium carbonate and known crystalline
states of calcium carbonate. For comparative purposes
Table VII gives refractive indices for calcium carbonate
materials found in the literature together with the -
refractive indices found with products made by the procedures
of Examples 2, 11 and 16 (mounted in Dow 710 silicone
oil with a refractive index of 1.52~5).
s~
-58-
TABLE VII
Literature
Material Refractive Indices Reference
-
n~ n ~ n~
calcite 1.648~ 1.4820 --- (1)
aragonite 1.5296 1.6804 1.6849 (2)
vaterite 1.5460 1.6470 --- (3)
calcium
carbonate
hexahydrate 1~460 1.535 1.545 (4)
calcium
carbonate
monohydrate 1.590 1.543 --- (5)
prior art
amorphous
calcium
carbonate 1.51-1.53 --- --- (6)
Ex. 2 1.5791 --- ---
Ex. 2
(replicate) 1.5806 --- ---
Ex. 11 1.5850 --- ---
Ex. lG 1.5830 --- ---
(1) Bailly, Am. Mineralogist, 33,519 (1948).
(2) Yamaguchi, J. Geol. Soc. Tokyo ~, 159 (1927
(3) Yoshimura, J. Geol. Soc. Tokyo 36, 7 t1929).
Gibson, Wyckoff, Merwin, Am. J. of Sci. (5)10, 325 (1925)
~4) J. Johnsto~, H.E. Merwin, E.D. Williamson, Am. J. Sci.
(4) 41,473 (1916)
(5) Lippmann, Naturwiss. 46,553 (1959).
(6) Johnston, Merwin, Williamson, Am.J. Sci.~4)41,491(1916)
From Table VII it can be concluded that no
significant difference can be attributed to the products
prepared with the hydrogen-bonding materials sorbitol, sucrose
or glycine.
As noted before, amorphous calcium carbonate has been
reported in several sources ~Louisfert, J. et al, Compt. rend.
235 287 (1952) and Gillott, J.E., J. Appl. Chem. 17, 185
(1967)]. Gillott states that carbonation of Ca(OH)2 may
result in the formation of snythetic amorphous calcium
carbonate which crystallizes to calcite in the presence of
moisture at room temperature. Our experience with amorphous
.....
s~
-59-
calcium carbonate agrees with Gillott's findings. We have
found, however, that stabilized amorphous calcium carbonate is
more resistant to calcite crystal formation than previously
known amorphous calcium carbonate.
Utilizing stabi7ized amorphous calcium carbonate as a
carbonate factor enables one to prepare effervescent
compositions that will rapidly undergo the effervescent
reaction upon contact with water and will provide a carbonated
beverage that is highly palatable to the consumer. For
instance, a typical dry beverage base effervescent composition
may comprise a flavor, a sweetener, a color, an acid factor,
such as citric acid, and a carbonate factor (in less than the
stoichiometric equivalent of the acid factor). When stabilized
amorphous calcium carbonate is utilized as the carbonate
factor, excellent carbonated beverages result.
Typical effervescent compositions are the well-known
effervescent medicament compositions which comprise an acid
factor, such as citric acid, medicaments and a carbonate
factor. Utilizing stabilized amorphous calcium carbonate as a
carbonate factor in the proper proportions, i.e., sufficient to
provide the desired C02 release, in such a composition will
provide medicated beverages with improved taste.
Other effervescent compositions illustrating the use
of stabilized amorphous calcium carbonate as the carbonate
factor (termed "SACC") are shown in Table VIII. Table VIII
also shows the volumes of C02 developed with these
effervescent compositions upon contacting them with 178 ml. of
water at 40F.
~`
J ,,~.~
5~
-60-
_BLE VII
Ingredient Co osition (wt. grams)
(1) (2) ~3) (4)
Flavor 0.08 0.08 - -
Color
Sweetener(Synthetic) 0.09 0.09
Acid Factor (Citric) 2.60 2.70 1.74 3.30
10 SACC 1.70 1.45 1.30 2.40
Sodium bicarbonate 0.15 b. 28
Vol. CO2 developed 2.3 2.3 2.4 3.0
It has been Eound that excellent sweetened carbonated
beverages can be obtained with effervescent compositions
containing stabilized amorphous calcium carbonate and the
synthetic sweeteners such as, for instance, saccharin,
cyclamates, perilla-adehyde-aldoxin, dihydrochalcone
derivatives, dulcin, steriosid, 5-t3-hydroxyphenyl)-lH-
tetrazole and the newly discovered dipeptides as exemplified in
U.S. Patent 3, 492rl31, Belgian Patent 739 r543 and West German
Patent lr936,159 and the like.
While the invention has been described herein with
regard to certain specific embodiments r it is not so limited.
It is to be unde~stood that variations and modifications thereof
may be made by those skilled in the art without departing from
the spirit and scope of the invention.
, ~ . .
