U.S. patent application number 09/984596 was filed with the patent office on 2002-06-13 for methods of preventing scaling involving inorganic compositions, and inorganic compositions therefor.
This patent application is currently assigned to HERCULES INCORPORATED. Invention is credited to Fader, Mitzi K., Ling, Tien-Feng, Nguyen, Duy T., Wang, Xiang Huai, Zhang, Fushan.
Application Number | 20020071783 09/984596 |
Document ID | / |
Family ID | 23304681 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020071783 |
Kind Code |
A1 |
Fader, Mitzi K. ; et
al. |
June 13, 2002 |
Methods of preventing scaling involving inorganic compositions, and
inorganic compositions therefor
Abstract
A composition including ground calcium carbonate and sodium
montmorillonite. A composition including magnesium aluminum
silicate and sodium montmorillonite. An aqueous pulp slurry,
including wood pulp, metal cations, anions, and about 50 to 500 ppm
of an anti-scalant comprised of at least one of magnesium aluminum
silicate, hydrated magnesium aluminum silicate, saponite,
sepiolite, calcium carbonate, magnesium carbonate, ferrous
carbonate, manganese carbonate, dolomite, hectorite, amorphous
magnesium silicate, and zinc carbonate.
Inventors: |
Fader, Mitzi K.;
(Jacksonville, FL) ; Nguyen, Duy T.;
(Jacksonville, FL) ; Wang, Xiang Huai;
(Alpharetta, GA) ; Zhang, Fushan; (Jacksonville,
FL) ; Ling, Tien-Feng; (Alpharetta, GA) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1941 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
HERCULES INCORPORATED
Wilmington
DE
|
Family ID: |
23304681 |
Appl. No.: |
09/984596 |
Filed: |
October 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09984596 |
Oct 30, 2001 |
|
|
|
09333891 |
Jun 16, 1999 |
|
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Current U.S.
Class: |
422/13 |
Current CPC
Class: |
C02F 2209/06 20130101;
C02F 5/105 20130101; C02F 5/00 20130101 |
Class at
Publication: |
422/13 |
International
Class: |
C23F 011/06 |
Claims
What is claimed is:
1. A composition, comprising: ground calcium carbonate; and sodium
montmorillonite.
2. The composition of claim 1, wherein a weight ratio of ground
calcium carbonate to sodium montmorillonite is about 0.1:1 to
20:1.
3. The composition of claim 1, comprising about 10 wt % to 95 wt %
of the ground calcium carbonate.
4. The composition of claim 1, comprising about 5 wt % to 90 wt %
of the sodium montmorillonite.
5. A composition, comprising: magnesium aluminum silicate; and
sodium montmorillonite.
6. The composition of claim 5, wherein a weight ratio of magnesium
aluminum silicate to sodium montmorillonite is about 0.1:1 to
20:1.
7. The composition of claim 5, comprising about 10 wt % to 95 wt %
of the magnesium aluminum silicate.
8. The composition of claim 5, comprising about 5 wt % to 90 wt %
of the sodium montmorillonite.
9. An aqueous pulp slurry, comprising: wood pulp; metal cations;
anions; and about 50 to 500 ppm of an anti-scalant comprised of at
least one of magnesium aluminum silicate, hydrated magnesium
aluminum silicate, saponite, sepiolite, calcium carbonate,
magnesium carbonate, ferrous carbonate, manganese carbonate,
dolomite, hectorite, amorphous magnesium silicate, and zinc
carbonate.
10. The aqueous pulp slurry of claim 9, wherein the anti-scalant
has a mean particle size less than about 10 microns.
11. The aqueous pulp slurry of claim 9, wherein the anti-scalant
has a specific surface area of about 10 to 1000 m.sup.2/g.
12. The aqueous pulp slurry of claim 9, wherein the aqueous
composition has a pH of about 9 to 14.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional application of U.S.
patent application Ser. No. 09/333,891, filed Jun. 16, 1999, the
disclosure of which is expressly incorporated by reference herein
in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to methods and inorganic
compositions, such as polyvalent metal silicates and polyvalent
metal carbonates, for inhibiting the formation, deposition, and/or
adherence of scale deposits on substrate surfaces in contact with a
scale-forming aqueous system. The scale deposits may be alkaline
earth metal scale deposits, such as alkaline earth metal carbonate
scale deposits, especially calcium carbonate scale deposits. The
present invention may be advantageously used to prevent scale in
kraft pulping processes.
[0004] 2. Discussion of Background
[0005] Scale build-up is a serious problem in many industrial water
systems, such as cooling towers, heat exchangers, evaporators,
pulping digesters, washers, and in the production and processing of
crude oil-water mixtures, etc. The build-up of scale deposits
reduces the efficiency of heat transfer systems, interferes with
fluid flow, facilitates corrosive processes and harbors bacteria.
Calcium carbonate, generated in various processes, is one of the
most commonly observed scale formers in industrial water systems.
This scale is an expensive problem in many industries, which causes
delays and shutdowns for cleaning and removal.
[0006] In particular, most industrial waters contain metal ions,
such as calcium, barium, magnesium, aluminium, strontium, iron,
etc. and several anions such as bicarbonate, carbonate, sulfate,
oxalate, phosphate, silicate, fluoride, etc. When combinations of
these anions and cations are present in concentrations which exceed
the solubility of their reaction products, precipitates form until
product solubility concentrations are no longer exceeded. For
example, when the concentrations of calcium ion and carbonate ion
exceed the solubility of the calcium carbonate reaction products, a
solid phase of calcium carbonate will form.
[0007] Solubility product concentrations are exceeded for various
reasons, such as partial evaporation of the water phase, change in
pH, temperature or pressure, and the introduction of additional
ions which form insoluble compounds with the ions already present
in the solution. As these reaction products precipitate on the
surfaces of the water carrying system, they form scale or
deposits.
[0008] For boiler systems and similar heat exchange systems, the
mechanism of scale formation is apparently one of crystallization
of scale-forming salts from a solution which is locally
supersaturated in the region adjacent the heating surface of the
system. The thin viscous film of water in this region tends to
become more concentrated than the remainder of the solution outside
this region. As a result, the solubility of the scale-forming salt
reaction product is first exceeded in this thin film, and
crystallization of scale results directly on the heating surface.
In addition to this, a common source of scale in boiler systems is
the breakdown of calcium bicarbonate to form calcium carbonate
water and carbon dioxide under the influence of heat.
[0009] For open recirculating cooling water systems, in which a
cooling tower, spray pond, evaporative condenser, and the like
serve to dissipate heat by evaporation of water, the chief factor
which promotes scale formation is concentration of solids dissolved
in the water by repeated evaporation of portions of the water
phase. Thus, even a water which is not scale forming on a
once-through basis usually will become scale forming when
concentrated a multiple number of times.
[0010] Also as disclosed in U.S. Pat. No. 3,518,204 to HANSEN et
al., the disclosure of which is herein incorporated by reference in
its entirety, water supplies employed as cooling media frequently
contain silts such as bentonitic or kaolinitic minerals. During use
of such silt containing waters in these systems, the silts react or
associate with other impurities which are present in the water such
as calcium and magnesium which are commonly referred to as
"hardness". As a consequence of such reaction or association, a
precipitate is formed and precipitated upon the surfaces of the
system containing the water. Such depositions may build up to the
extent that flow through the system is reduced or halted, and the
system must be shut down for costly cleaning. In addition, when
such deposition occurs on heat transfer surfaces, heat exchange is
reduced with a corresponding loss in process efficiency.
[0011] Scaling in kraft pulping processes occurs by a different
mechanism as a result of the presence of organic ligands. Black
liquor generated in the kraft pulping digester contains a very high
content of organics such as lignin, fatty/rosin soaps,
hemicelluloses, etc. Lignin fragments formed during pulping,
specifically those containing adjacent hydroxyl groups on an
aromatic ring, have a high tendency to interact with calcium
(originally from tree) to greatly increase its solubility in black
liquor. As the temperature increases (e.g., the temperature found
near the tube wall of an evaporator or cooking heater), the pH has
a tendency to decrease, especially if the residual active alkali is
low. As a consequence, calcium ions can be displaced from the
lignin by hydrogen ions, and react with carbonate ions thus
producing calcium carbonate scale. In addition to lignin, there are
many different organic species that complex calcium in the black
liquor. Any of these organic species, whose ability to complex with
calcium depends on the pH being in the normal pH range of black
liquor, will contribute to calcium carbonate scaling by releasing
ionic calcium as the temperature increases. Therefore, as long as
some of the aforementioned organic compounds are present and
sufficient calcium is available, a liquor will have the capacity to
deposit calcium carbonate scale. In addition to calcium and
carbonate, black liquor normally contains a number of other ions
such as sodium and sulfate which can precipitate and form
scale.
[0012] In the paper industry, alkalinity from alkali digesting
solution and from dissolved solids from the wood chips, results in
an increased alkalinity of the black liquor, often reaching pH's of
12-13 and even higher. Under high pH conditions, the precipitation
of calcium carbonate is especially difficult to control. Acid is
often added to lower the pH to prevent calcium carbonate
scaling.
[0013] In the oil industry, the formation of insoluble calcium
salts is also a problem in the secondary recovery of oil from
subterranean formations by processes in which water is introduced
into injection wells and forced through the underground formations
to cause oil to be produced in a producing well. This type of
process is usually referred to as a waterflood system.
[0014] In view of the above, scale formation and deposition are
generated by the mechanisms of nucleation, crystal growth, and
aggregation of scale-forming particles. Various approaches to
reducing scale development include inhibition of nuclei/crystal
formation, modification of crystal growth, and dispersion of the
scale-forming particles.
[0015] Chelating or sequestering agents have been commonly used to
prevent deposition, precipitation and crystallization of calcium
carbonate in water-carrying systems. Other types of chemicals which
have been actively explored as calcium carbonate scale inhibiting
agents are threshold inhibitors.
[0016] Threshold inhibitors include water soluble polymers,
phosphonates, and polyphosphates (e.g., U.S. Pat. No. 5,182,028 to
BOFFARDI et al., the disclosure of which is herein incorporated by
reference in its entirety, discloses sodium hexametaphosphate and
monofluorophosphate). Such chemicals are effective as scale
inhibitors in amounts considerably less than that
stoichiometrically required.
[0017] Water soluble polymers, including groups derived from
acrylamide, maleic acid, vinyl acetate, vinyl alcohol, and acrylic
acid have been used to control calcium carbonate deposition. For
instance, such polymers are disclosed in U.S. Pat. No. 5,282,976 to
YEUNG; U.S. Pat. No. 5,496,914 to WOOD et al.; U.S. Pat. No.
4,008,164 to WATSON et al.; U.S. Pat. No. 3,518,204 to HANSEN et
al.; U.S. Pat. Nos. 3,928,196 and 4,936,987 to PERSINSKI et al.;
U.S. Pat. No. 3,965,027 to BOFFARDI et al.; U.S. Pat. No. 5,441,602
to HARRIS et al.; U.S. Pat. No. 5,580,462 to GILL; and U.S. Pat.
No. 5,409,571 to TOGO et al., the disclosures of which are herein
incorporated by reference in their entireties.
[0018] Polyallylamines having phosphonic, carboxylic, or sulfonic
groups are also used as scale control agents as disclosed in U.S.
Pat. No. 5,629,385 to KUO and U.S. Pat. No. 5,124,046 to SHERWOOD
et al., the disclosures of which are herein incorporated by
reference in their entireties.
[0019] Additionally, a number of anionic polyelectrolytes, such as
polyacrylates, polymaleic anhydrides, copolymers of acrylates and
sulfonates, and polymers of sulfonate styrenes, have been employed.
Examples of polyelectrolytes are disclosed in U.S. Pat. No.
4,640,793 to PERSINSKI et al.; U.S. Pat. No. 4,650,591 to BOOTHE et
al.; U.S. Pat. No. 4,457,847 to LORENC et al.; U.S. Pat. No.
5,407,583 to GILL et al.; and U.S. Pat. No. 4,671,888 to YORKE, the
disclosures of which are herein incorporated by reference in their
entireties.
[0020] Polyepoxysuccinic acid for inhibiting the formation and
deposition of scale in aqueous systems is disclosed in U.S. Pat.
Nos. 5,062,962 and 5,147,555 to BROWN et al., the disclosures of
which are herein incorporated by reference in their entireties.
[0021] Phosphonate based compounds are extensively used as calcium
carbonate scale control agents. Examples include ether
diphosphonate (U.S. Pat. No. 5,772,893 to REED et al., and U.S.
Pat. No. 5,647,995 to KNELLER et al., the disclosures of which are
herein incorporated by reference in their entireties),
hydroxyethylidene-1,1-diphosphonic acid, amino tri(methylene
phosphonic acid), aminomethylene phosphonates (U.S. Pat. No.
4,931,189 to DHAWAN et al., the disclosure of which is herein
incorporated by reference in its entirety),
N,N-bis(phosphonomethyl)-2-am- ino-1-propanol (U.S. Pat. No.
5,259,974 to CHEN et al., the disclosure of which is herein
incorporated by reference in its entirety), methylene phosphonates
of amino-terminated oxyalkylates (U.S. Pat. No. 4,080,375 to
QUINLAN, the disclosure of which is herein incorporated by
reference in its entirety), polyether polyamino methylene
phosphonates (EP 0 516 382 B1, the disclosure of which is herein
incorporated by reference in its entirety), and ethanolamine
N,N-dimethylene phosphonic acid (U.S. Pat. Nos. 2,917,528 and
2,964,549 to RAMSEY et al., the disclosures of which are herein
incorporated by reference in their entireties).
[0022] Additionally, it is known that certain inorganic
polyphosphonates would prevent precipitation when added in amounts
less than the concentrations needed for sequestering or chelating,
as disclosed in U.S. Pat. No. 2,358,222 to FINK et al. and U.S.
Pat. No. 2,539,305 to HATCH, the disclosures of which are herein
incorporated by reference in their entireties.
[0023] U.S. Pat. No. 3,960,576 to CARTER et al., the disclosure of
which is herein incorporated by reference in its entirety,
discloses that inorganic-silicate-based compositions also comprised
of an organic phosphonate and carboxy methyl cellulose are useful
for inhibiting corrosion of metal surfaces.
[0024] MANAHAN, Environmental Chemistry, pp. 183-213 (1991), the
disclosure of which is herein incorporated by reference in its
entirety, with particular attention directed to pp. 193-195,
discloses use in environmental chemistry of sodium aluminum
silicate minerals or zeolites as water softeners. The softening of
water by aluminum silicate minerals and zeolites is based on
ion-exchanging properties of the minerals. The divalent cations,
which are responsible for water hardness, are replaced by sodium
ions contained in the aluminum silicates, and then removed by
filtration. An example of a micaceous mineral which has been used
commercially in water softening is glauconite,
K.sub.2(MgFe).sub.2Al.sub.- 6(Si.sub.4O.sub.10).sub.3OH.sub.12.
[0025] Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.,
vol.24, pp.367-384 (1984), the disclosure of which is herein
incorporated by reference in its entirety, discloses that deposits
are usually controlled with dispersants and scale inhibitors in
cooling and process water. Among the dispersants mentioned are
polymers and copolymers, for example, poly(acrylic acid) and its
salts, acrylamideacrylic acid copolymers and poly(maleic acid).
[0026] Further, it is known to use clays such as talc and bentonite
in paper making for fillers, pitch control, and retention and
drainage control. In filler applications, talc or bentonite may be
added in an amount which is typically relatively high.
[0027] In pitch control applications, talc or bentonite may be
added before the washer and after the digester. At this position,
the temperature of the aqueous system is relatively low. The use of
talc and bentonite for pitch control is discussed in BOARDMAN, "The
Use of Organophilic Mineral Particulates in the Control of Anionic
Trash Like Pitch", TAPPI Proceedings (1996), the disclosure of
which is herein incorporated by reference in its entirety. In
particular, this article discloses using two pounds per ton of
montmorillonite.
[0028] In retention and drainage control, it is believed that
bentonite and a high molecular weight cationic polymer (e.g.,
molecular weight of about 1.times.10.sup.6 to 10.times.10.sup.6)
may be added just before the headbox. For instance, it is believed
that 3-10 lb of bentonite/ton of oven dried fibers may be added
near the headbox which would result in about 15-50 ppm of bentonite
in the aqueous system for a 1 wt % aqueous paper furnish. It is
believed that the aqueous system just before the headbox typically
has a pH of about 5 to 8.5 and a temperature of about 40.degree. C.
to 60.degree. C.
SUMMARY OF THE INVENTION
[0029] It is an object of the present invention to prevent scale
formation and/or deposition, such as alkaline earth metal scale
deposition, especially calcium carbonate scale deposition.
[0030] It is another object of the present invention to provide
inorganic compounds, such as polyvalent metal silicates and
polyvalent metal carbonates, that can effectively prevent scale
formation and/or deposition.
[0031] It is still another object of the present invention to
provide a family of compounds that can effectively prevent scale
formation and/or deposition on surfaces, such as metallic and
plastic surfaces, in contact with a scale-forming aqueous
system.
[0032] In accordance with one aspect, the present invention is
directed to a method for inhibiting scale deposits in an aqueous
system, comprising: adding anti-scalant to the aqueous system such
that an amount of anti-scalant in the aqueous system is up to about
500 ppm, wherein the anti-scalant comprises at least one of
polyvalent metal silicate and polyvalent metal carbonate, and
wherein the aqueous system has a pH of at least about 9.
[0033] In accordance with another aspect, the present invention is
directed to a method for inhibiting scale deposits in an aqueous
system, comprising: adding anti-scalant to the aqueous system such
that an amount of anti-scalant in the aqueous system is up to about
500 ppm, wherein the anti-scalant comprises at least one of
polyvalent metal silicate and polyvalent metal carbonate, and
wherein the aqueous system comprises up to about 0.4 ppm of
cationic polymer.
[0034] In accordance with still another aspect, the present
invention is directed to a method for inhibiting scale deposits in
an aqueous system of a paper mill, comprising: adding anti-scalant
to the aqueous system at at least one of before a pulping digester
and at a pulping digester, wherein the anti-scalant comprises at
least one of polyvalent metal silicate and polyvalent metal
carbonate.
[0035] In accordance with yet another aspect, the present invention
is directed to a method for inhibiting scale deposits in an aqueous
system, comprising: adding anti-scalant to the aqueous system such
that an amount of anti-scalant in the aqueous system is up to about
500 ppm, wherein the anti-scalant comprises at least one of
magnesium aluminum silicate, hydrated magnesium aluminum silicate,
calcium bentonite, saponite, sepiolite, calcium carbonate,
magnesium carbonate, ferrous carbonate, manganese carbonate,
dolomite, hectorite, amorphous magnesium silicate, and zinc
carbonate.
[0036] In accordance with another aspect, the present invention is
directed to a method for inhibiting scale deposits in an aqueous
system, comprising: adding a nucleation promoter/initiator to the
aqueous system to inhibit formation of scale deposits, such that an
amount of the nucleation promoter/initiator in the aqueous system
is up to about 500 ppm.
[0037] In accordance with a further aspect, the present invention
is directed to a method for inhibiting scale deposits in an aqueous
system, comprising: adding first cations to the aqueous system and
removing second cations which are distinct from the first cations
from the aqueous system, to inhibit the second cations from forming
scale deposits; and wherein the aqueous system is at a temperature
of about 70.degree. C. to 500.degree. C.
[0038] In accordance with another aspect, the present invention is
directed to a composition, comprising: ground calcium carbonate;
and sodium montmorillonite.
[0039] In accordance with yet another aspect, the present invention
is directed to a composition, comprising: magnesium aluminum
silicate; and sodium montmorillonite.
[0040] In accordance with another aspect, the present invention is
directed to an aqueous pulp slurry, comprising: wood pulp; metal
cations; anions; and about 50 to 500 ppm of an anti-scalant
comprised of at least one of magnesium aluminum silicate, hydrated
magnesium aluminum silicate, saponite, sepiolite, calcium
carbonate, magnesium carbonate, ferrous carbonate, manganese
carbonate, dolomite, hectorite, amorphous magnesium silicate, and
zinc carbonate.
[0041] In one aspect, the anti-scalant comprises an aluminosilicate
backbone.
[0042] In a further aspect, the anti-scalant comprises at least one
functional group which comprises at least one of carboxylic,
sulfonate, sulfate, and phosphate.
[0043] In another aspect, the anti-scalant comprises at least one
of sodium montmorillonite, magnesium aluminum silicate, talc,
hydrated magnesium aluminum silicate, calcium bentonite, saponite,
sepiolite, calcium carbonate, magnesium carbonate, ferrous
carbonate, manganese carbonate, and dolomite.
[0044] In yet another aspect, the anti-scalant comprises at least
one of sodium aluminosilicate, magnesium aluminosilicate,
hectorite, amorphous magnesium silicate, calcium carbonate,
magnesium carbonate, zinc carbonate, ferrous carbonate, and
manganese carbonate.
[0045] In still another aspect, the anti-scalant comprises
polyvalent metal silicate and comprises at least one of sodium
montmorillonite, magnesium aluminum silicate, talc, hydrated
magnesium aluminum silicate, calcium bentonite, saponite,
sepiolite, sodium aluminosilicate, hectorite, and amorphous
magnesium silicate.
[0046] In another aspect, the anti-scalant comprises polyvalent
metal carbonate and comprises at least one of calcium carbonate,
magnesium carbonate, ferrous carbonate, manganese carbonate,
dolomite, and zinc carbonate.
[0047] In yet another aspect, the anti-scalant comprises ground
calcium carbonate and sodium montmorillonite.
[0048] In still another aspect, the anti-scalant comprises
magnesium aluminum silicate and sodium montmorillonite.
[0049] In another aspect, the anti-scalant has a mean particle size
less than about 10 microns.
[0050] In yet another aspect, the anti-scalant has a specific
surface area of about 10 to 1000 m.sup.2/g.
[0051] In still another aspect, the aqueous system has a pH of
about 9 to 14.
[0052] In another aspect, the scale comprises alkaline earth metal
scale. The alkaline earth metal scale may comprise calcium
carbonate.
[0053] In still another aspect, the aqueous system comprises at
least one of calcium, barium, magnesium, aluminium, bicarbonate,
carbonate, sulfate, and phosphate.
[0054] In yet another aspect, the aqueous system has a [Ca.sup.+2]
of about 10 to 500 ppm and a [CO.sub.3.sup.-2] of about 100 to
30,000 ppm prior to addition of the anti-scalant.
[0055] In still another aspect, the aqueous system has a
temperature of about 25.degree. C. to 500.degree. C.
[0056] In a further aspect, the aqueous system is at a pressure of
about 80 to 1500 psi.
[0057] In another aspect, the anti-scalant is added to a cooling
tower, a heat exchanger, an evaporator, before a pulping digester,
to a pulping digester, or to a washer.
[0058] In still another aspect, the method further comprises
processing a crude oil-water mixture.
[0059] In yet another aspect, the scale comprises calcium
carbonate, the anti-sealant has a mean particle size of less than
about 10 microns, the anti-scalant has a specific surface area of
about 10 to 1000 m.sup.2/g, the aqueous system has a pH of about 9
to 14, the aqueous system has a [Ca.sup.+2] of about 10 to 500 ppm
and a [CO.sub.3.sup.-2] of about 100 to 30,000 ppm prior to
addition of the anti-scalant, and the aqueous system has a
temperature of about 25.degree. C. to 500.degree. C.
[0060] In still another aspect, the anti-scalant is added after a
chip bin.
[0061] In another aspect, the cationic polymer which is present in
the aqueous system has a molecular weight of greater than about
1.times.10.sup.6.
[0062] In a further aspect, a weight ratio of ground calcium
carbonate to sodium montmorillonite is about 0.1:1 to 20:1.
Accordingly, the anti-scalant may comprise about 10 wt % to 95 wt %
of the ground calcium carbonate. The anti-scalant may also comprise
about 5 wt % to 90 wt % of the sodium montmorillonite.
[0063] In yet another aspect, a weight ratio of magnesium aluminum
silicate to sodium montmorillonite is about 0.1:1 to 20:1. Thus,
the anti-scalant may comprise about 10 wt % to 95 wt % of the
magnesium aluminum silicate. The anti-scalant may comprise about 5
wt % to 90 wt % of the sodium montmorillonite.
DETAILED DESCRIPTION OF THE INVENTION
[0064] The particulars shown herein are by way of example and for
purposes of illustrative discussion of the various embodiments of
the present invention only and are presented in the cause of
providing what is believed to be the most useful and readily
understood description of the principles and conceptual aspects of
the invention. In this regard, no attempt is made to show details
of the invention in more detail than is necessary for a fundamental
understanding of the invention, the description making apparent to
those skilled in the art how the several forms of the invention may
be embodied in practice.
[0065] All percent measurements in this application, unless
otherwise stated, are measured by weight based upon 100% of a given
sample weight. Thus, for example, 30% represents 30 weight parts
out of every 100 weight parts of the sample.
[0066] Unless otherwise stated, a reference to a compound or
component, includes the compound or component by itself, as well as
in combination with other compounds or components, such as mixtures
of compounds.
[0067] Before further discussion, a definition of the following
terms will aid in the understanding of the present invention.
[0068] "Nucleation initiator/promoter": substance which initiates
and promotes nucleation and precipitation of polyvalent metal
silicate or polyvalent metal carbonate in the solution phase.
[0069] "Water hardness": amount of magnesium and calcium ions in an
aqueous solution.
[0070] As an overview, the present invention relates to methods and
inorganic compositions for inhibiting the formation, deposition,
and adherence of scale deposits on substrate surfaces in contact
with a scale-forming aqueous system. The scale deposits may be
alkaline earth metal scale deposits, such as alkaline earth metal
carbonate scale deposits, especially calcium carbonate scale
deposits.
[0071] The preferred anti-scalants of the present invention include
polyvalent metal silicates and polyvalent metal carbonates. The
polyvalent metal silicate or polyvalent metal carbonate may be
crystalline or amorphous. The polyvalent metal silicates and
polyvalent metal carbonates may have functional groups such as
carboxylic, sulfonate, sulfate, and phosphate. For example, the
functional groups may be obtained by treating a polyvalent metal
silicate or polyvalent metal carbonate with an organic or inorganic
compound having a functional group such as carboxylic, sulfonate,
sulfate, and phosphate. Examples of these compounds include
polymers such as polyacrylate and polyacrylic acid, and surfactants
such as alkylbenzene sulfonate, alkylbenzene sulfate, and
alkylbenzene phosphate ester.
[0072] Polyvalent metal silicates include clays. Clays are
naturally occurring hydrous aluminosilicates with a 2- or 3-layer
crystal structure which has ion substitution for aluminium,
examples of such ion substitutes include magnesium, iron, and
sodium. Alkali and alkaline earth elements may also be constituents
of clays. Hydrogen is usually present as hydroxyl in the structure
and as water both within the structure and absorbed on the surface.
These substitutions create a wide diversity in chemical composition
within the broad general class of phyllosilicates or layer
silicates. It is well known that relatively small differences in
the chemical composition of clays can greatly influence their
chemical and physical properties.
[0073] All phyllosilicates contain silicate or aluminosilicate
layers in which sheets of tetrahedrally coordinated cations, Z,
such as ions of magnesium, aluminum, and iron, of composition
Z.sub.2O.sub.5, are linked through shared oxygens to sheets of
cations, which are octahedrally coordinated to oxygens and
hydroxyls. When one octahedral sheet is linked to one tetrahedral
sheet, a 1:1 layer is formed as in kaolinite; when one octahedral
sheet is linked to two tetrahedral sheets, one on each side, a 2:1
layer is produced as in talc and pyrophyllite. Structural units
that may be found between aluminosilicate layers are sheets of
cations octahedrally coordinated with hydroxyls, as in chlorites,
and individual cations which may or may not be hydrated, as in
smectites, bentonites, vermiculites, and micas. Some 2:1 layer
silicates swell in water, ethylene glycol, and a wide range of
similar compounds by intercalation of molecules between 2:1
layers.
[0074] Polyvalent metal carbonates include various combinations of
polyvalent metals and carbonates. Preferred examples of the
polyvalent metal include calcium, magnesium, iron, manganese, and
zinc. For instance, alkaline earth metal carbonates include calcium
carbonate mixed with magnesium carbonate. Depending on the milling
process and dispersants (e.g., polyacrylate) added to the
limestone, as discussed below, different particle sizes and
specific surface areas of ground calcium carbonate particles can be
generated.
[0075] The polyvalent metal silicates and polyvalent metal
carbonates may be synthetic or naturally occurring. Examples of
synthetic polyvalent metal silicates and polyvalent metal
carbonates include precipitated calcium carbonate and
silica-derived products such as magnesium silicate,
aluminosilicate, magnesium aluminum silicate, etc. As discussed in
more detail below, various particle sizes, surface areas, pore size
diameters, and ion exchange capacities of synthetic polyvalent
metal silicates and polyvalent metal carbonates can be made
commercially.
[0076] Preferred examples of the anti-scalants of the present
invention are listed in the following non-limiting list which is
not intended to be an exhaustive list:
NATURAL POLYVALENT METAL SILICATES AND METAL CARBONATES
[0077] POLYVALENT METAL SILICATES
[0078] sodium montmorillonite (bentonite)
[0079] magnesium aluminum silicate
[0080] smectite clay
[0081] colloidal attapulgite clay
[0082] talc (hydrous magnesium silicate)
[0083] hydrated magnesium aluminum silicate (e.g., smectite
clay)
[0084] calcium bentonite
[0085] saponite (magnesium bentonite)
[0086] sepiolite
[0087] POLYVALENT METAL CARBONATES
[0088] calcium carbonate
[0089] magnesium carbonate
[0090] ferrous carbonate
[0091] manganese carbonate
[0092] dolomite
SYNTHETIC POLYVALENT METAL SILICATES AND METAL CARBONATES
[0093] POLYVALENT METAL SILICATES
[0094] sodium aluminosilicate
[0095] hydrated Na-A type zeolite
[0096] mordenite zeolite
[0097] synthetic amorphous precipitated silicate
[0098] magnesium aluminum silicate
[0099] synthetic hectorite (synthetic magnesium silicate)
[0100] amorphous magnesium silicate
[0101] POLYVALENT METAL CARBONATES
[0102] calcium carbonate
[0103] magnesium carbonate
[0104] zinc carbonate
[0105] ferrous carbonate
[0106] manganese carbonate
[0107] In selecting other anti-scalants which may be useful in the
present invention, compounds with an aluminosilicate backbone tend
to function as anti-scalants.
[0108] Further, the selection of other anti-scalants may be based
upon how the anti-scalants of the present invention are
hypothesized to function. While not wishing to be bound by theory,
the present invention may involve one or more of the following
mechanisms, depending upon the type of anti-scalant.
[0109] For some anti-scalants, the mechanism of the present
invention may involve ion exchange similar to the ion exchange
involved in water softening. For instance, sodium ions could be
exchanged for calcium ions, so as to reduce the concentration of
calcium ions in the aqueous system to reduce precipitation of
calcium compounds. It is believed that reducing the calcium
concentration also slows the growth rate of calcium based crystals,
such that the crystals which are formed tend to be smaller and more
uniform. Smaller crystals are more stable in the aqueous phase and
are less likely to precipitate on the equipment.
[0110] According to another hypothesized mechanism, the
anti-scalant of the present invention may function as a nucleation
initiator/promoter. Thus, the anti-scalant of the present invention
may function as a seed. For instance, the scaling compound may
precipitate on the anti-scalant instead of precipitating on the
equipment. The nucleation initiator/promoter may be inorganic.
Although other compounds may function as nucleation
initiator/promoters, it is particularly believed that ground
calcium carbonate functions as a nucleation promoter/initiator.
[0111] According to still another hypothesized mechanism, the
anti-scalant of the present invention may function through surface
adsorption. Although surface adsorption may be involved in the ion
exchange and nucleation mechanisms described above, surface
adsorption may be an independent mechanism. For instance, in
surface adsorption it is not necessary for a separate solid phase
to be formed on the surface of the anti-scalant.
[0112] In view of the above, it is hypothesized that the
anti-scalant of the present invention may function as at least one
of an ion exchanger, a nucleation promoter/initiator, and a surface
adsorber, depending upon the anti-scalant.
[0113] The above listed anti-scalants may also be used in
combination with each other. It was surprisingly found that some
combinations of the above-listed anti-scalants resulted in
synergism. In particular, combinations of sodium montmorillonite
with either ground calcium carbonate or magnesium aluminum silicate
yield unexpected results.
[0114] Regarding the combination of calcium carbonate and sodium
montmorillonite, the weight ratio of calcium carbonate to sodium
montmorillonite is preferably about 0.1:1 to 20:1, more preferably
about 0.5:1 to 7:1, and most preferably about 1:1 to 4:1. Thus, the
amount of calcium carbonate in the combination of calcium carbonate
and sodium montmorillonite, with respect to a total amount of
anti-scalant, is preferably about 10 wt % to 95 wt %, more
preferably about 30 wt % to 90 wt %, and most preferably about 50
wt % to 80 wt %. Accordingly, the amount of sodium montmorillonite
in the combination of calcium carbonate and sodium montmorillonite,
with respect to a total amount of anti-scalant, is preferably about
5 wt % to 90 wt %, more preferably about 10 wt % to 70 wt %, and
most preferably about 20 wt % to 50 wt %.
[0115] Concerning the combination of magnesium aluminum silicate
and sodium montmorillonite, the weight ratio of magnesium aluminum
silicate to sodium montmorillonite is preferably about 0.1:1 to
20:1, more preferably about 0.5:1 to 7:1, and most preferably about
1:1 to 4:1. Thus, the amount of magnesium aluminum silicate in the
combination of magnesium aluminum silicate and sodium
montmorillonite, with respect to a total amount of anti-scalant, is
preferably about 10 wt % to 95 wt %, more preferably about 30 wt %
to 90 wt %, and most preferably about 50 wt % to 80 wt %.
Accordingly, the amount of sodium montmorillonite in the
combination of magnesium aluminum silicate and sodium
montmorillonite, with respect to a total amount of anti-scalant, is
preferably about 5 wt % to 90 wt %, more preferably about 10 wt %
to 70 wt %, and most preferably about 20 wt % to 50 wt %.
[0116] The particle size of the anti-scalant is preferably small.
More specifically, depending upon the anti-scalant, the mean
particle size of the anti-scalant is preferably less than about 100
microns, more preferably less than about 10 microns, with ranges of
preferably about 0.01 to 10 microns, more preferably about 0.1 to
10 microns. Further, for alkaline earth metal carbonates the mean
particle size is preferably about 0.1 to 2 microns.
[0117] One reason that the particle size of the anti-scalant should
be small is to increase the specific surface area. Depending upon
the anti-scalant, the specific surface area of the anti-scalant is
preferably about 10 to 1500 m.sup.2/g, more preferably about 50 to
1000 m.sup.2/g. For example, zeolites available from Zeolyst
International, Delfziji, the Netherlands can be synthesized with a
specific surface area in the range of about 400 to 950
m.sup.2/g.
[0118] Depending upon the type of anti-scalant, the ion exchange
capacity of the anti-scalant may be an important variable. For
anti-scalants which may involve ion exchange for preventing
scaling, such as zeolites, the ion exchange capacity is preferably
at least about 0.1 Meq/g, more preferably at least about 0.5 Meq/g,
and most preferably about 1.0 Meq/g, with ranges typically of about
0.1 to 10 Meq/g, more typically about 0.5 to 8.0 Meq/g, and most
typically about 1.0 to 8.0 Meq/g. In contrast, the ion exchange
capacity of ground calcium carbonate is not important when the
ground calcium carbonate is used to seed out calcium carbonate.
[0119] The amount of anti-scalant added to the aqueous system
depends upon such variables as the temperature, the pH, and the
presence of other compounds. Regarding temperature, higher
temperatures usually require higher amounts of anti-scalant. The
effect of changes in pH on the amount of anti-scalant required
depends upon the type of anti-scalant. Similarly, the effect of the
presence of other compounds on the amount of anti-scalant depends
on the other compound. For instance, compounds containing magnesium
and iron may act as poisons such that more anti-scalant would be
necessary. In contrast, compounds such as lignin function as
enhancers such that less anti-scalant is necessary.
[0120] In view of the above, the anti-scalant is added to the
aqueous system at a concentration of preferably about 1 ppb to 10
ppm, more preferably about 10 ppb to 5 ppm, and most preferably
about 100 ppb to 5 ppm, per ppm of water hardness. Thus, the
anti-scalant is added to the system at a concentration of up to
about 50 ppm, more preferably up to about 75 ppm, even more
preferably up to about 95 ppm, even more preferably up to about 200
ppm, even more preferably up to about 500 ppm, a nd most preferably
up to about 1000 ppm, with ranges of preferably about 1 to 1000
ppm, more preferably about 2 to 500 ppm, and most preferably about
5 to 200 ppm. The anti-scalant may also be added to the system at a
concentration of about 5 to 100 ppm.
[0121] The aqueous system to which the anti-scalant is added may
contain metal ions, such as ions of calcium, barium, magnesium,
aluminum, strontium, iron, etc. and anions such as bicarbonate,
carbonate, sulfate, phosphate, silicate, fluoride, etc.
[0122] In aqueous systems having calcium ions and carbonate ions to
which the anti-scalant may be added, prior to the addition of the
anti-scalant the [Ca.sup.+2] is usually present at about 10 to 500
ppm, more usually about 20 to 300 ppm, and most usually about 50 to
200 ppm. Moreover, prior to addition of the anti-scalant, the
[CO.sub.3.sup.-2] in such systems is usually present at about 100
to 30,000 ppm, more usually about 500 to 25,000 ppm, and most
usually about 1000 to 20,000 ppm.
[0123] The aqueous system may also include other additives and
compounds. However, the anti-scalant of the present invention is
often used in the presence of up to about 0.4 ppm of cationic
polymer, more usually in the presence of up to about 0.1 ppm of
cationic polymer, and most usually in the presence of up to about
0.01 ppm of cationic polymer. The cationic polymer which is present
may have a molecular weight greater than about 1.times.10.sup.6,
with a usual range of about 1.times.10.sup.6 to
10.times.10.sup.6.
[0124] The aqueous system to which the anti-scalant is added may be
at an elevated temperature. For instance, the temperature of the
system may typically be about 25.degree. C. to 500.degree. C., more
typically about 70.degree. C. to 500.degree. C., even more
typically about 80.degree. C. to 200.degree. C. When the
anti-scalant is added to a digester, the temperature of the aqueous
system is usually about 150.degree. C. to 175.degree. C. When the
anti-scalant is added at a chip chute pump prior to the digester,
the temperature of the aqueous system is usually about 80.degree.
C. to 110.degree. C.
[0125] The anti-scalants of the present invention work under acidic
conditions against some forms of scale, but generally do not
function well against carbonate scales under acidic conditions.
Thus, the aqueous system to which the anti-scalant is added
generally has a basic pH, more usually a pH of at least about 9,
such as about 9 to 14, even more usually about 10 to 13. As noted
above, changes in pH may cause scaling.
[0126] The aqueous system to which the anti-scalant is added may be
under atmospheric conditions or under pressure. For instance, the
pressure is typically about 14 to 1500 psi, more typically about 80
to 1500 psi. When the aqueous system comprises a digester of a
paper mill, the pressure at the digester is typically about 125 to
150 psi. When the aqueous system comprises a boiler, the pressure
at the boiler is typically up to about 1500 psi.
[0127] To ensure that the anti-scalant is adequately dispersed in
the aqueous system, the anti-scalant is preferably added in the
form of a water-based slurry. Depending upon the anti-scalant, the
water-based slurry comprises preferably up to about 40 wt % of
anti-scalant, more preferably up to about 50 wt % of anti-scalant,
even more preferably up to about 60 wt % of anti-scalant, and most
preferably up to about 75 wt % of anti-scalant.
[0128] Examples of the systems to which the anti-scalant may be
added include industrial water systems, such as cooling towers,
heat exchangers, evaporators, pulping digesters, washers, and in
the production and processing of crude oil-water mixtures, etc.
[0129] In particular, scale deposition in a digester in kraft pulp
manufacturing can be controlled in accordance with the present
invention. It follows that the run length of the digester can be
extended to achieve improvements in productivity, uniform quality
of pulp, and a reduction in energy loss. Further, troubles arising
from scale deposit are greatly diminished, which makes a valuable
contribution to improvement of operating efficiency.
[0130] The addition point of the anti-scalant may be at or before
where scale may be formed. For example, the anti-scalant may be
added before a pulping digester or at the pulping digester. When
the anti-scalant is added before the pulping digester, it is often
added after or during mechanical treatment of the wood chips. For
instance, the anti-scalant may be added after a chip bin, at a wood
chip chute pump, at a cooking liquor heater pump, or at an in-line
drainer. When the anti-scalant is added directly to the digester or
other systems, the addition point may be targeted to where the
anti-scaling is needed most. For instance, the anti-scalant may be
added in the cooking zone of the digester.
[0131] The anti-scalants of the present invention perform better
than known anti-scaling polymers under many conditions. In addition
to adequate or improved performance, the raw material cost of the
polyvalent metal silicates and polyvalent metal carbonates is
significantly lower than that of the known anti-scalants.
Therefore, an advantage of the present invention is
cost-effectiveness.
[0132] Once the anti-scalant has been used, it may be preferred
that the anti-scalant be removed from the system. The removal of
the anti-scalant depends upon the system. For instance, removal may
be by filtration or centrifugation. Another removal technique
involves cationic fixation with a high molecular weight cationic
polymer. The molecular weight of the cationic polymer is preferably
about 1.times.10.sup.6 to 10.times.10.sup.6. Examples of preferred
cationic polymers which may be used in cationic fixation include
polyamine and polyDADMAC (diallyldimethylammonium chloride).
[0133] The present invention will be further illustrated by way of
the following Examples. These examples are non-limiting and do not
restrict the scope of the invention.
[0134] Unless stated otherwise, all percentages, parts, etc.
presented in the examples are by weight.
EXAMPLES 1-39 AND COMPARATIVE EXAMPLES 1 AND 2
[0135] A bottle test was conducted to determine the effect of
polyvalent metal silicates and polyvalent metal carbonates on
calcium carbonate scale inhibition and to compare their performance
to known scale inhibitors. As discussed in more detail below, the
test conditions were 70.degree. C., pH 12.4, and a one-hour
incubation time with mild agitation.
[0136] An aqueous hardness solution of 2.205 wt % calcium chloride
was prepared. An aqueous alkaline solution of 0.18 wt % sodium
carbonate and 0.2125 wt % sodium hydroxide was prepared. Both
solutions were simultaneously added to 100 ml glass bottles
followed by anti-scalants, as listed in Table 1, in proportions to
achieve 100 g of final solution having the compositions listed in
Tables 2 and 3, below. The solution pH was adjusted to 12.4 by
adding sodium hydroxide. As shown in Tables 2 and 3, the final
solution involved either a "mild" scaling condition of 60 ppm
Ca.sup.+2 (150 ppm as CaCO.sub.3) and 1000 ppm CO.sub.3.sup.-2, or
a "harsh" scaling condition of 100 ppm Ca.sup.+2 (250 ppm as
CaCO.sub.3) and 10,000 ppm CO.sub.3.sup.-2.
[0137] After being agitated for 1 hour at 70.degree. C., the
solution was removed from the test bottle and subjected to vacuum
filtration using a #4 Whatman filter (pore size <20-25 .mu.m).
For these Examples and Comparative Examples, it is approximated
that CaCO.sub.3 crystals having a particle size less than about
20-25 microns have less tendency to precipitate on a substrate, and
that crystals having a particle size greater than about 20-25
microns would be more likely to precipitate on a substrate and,
therefore, would likely precipitate as scale. For instance, the
relationship between particle size, crystallization rate, and
precipitation is discussed in column 3 of U.S. Pat. No. 3,518,204
to HANSEN et al., the disclosure of which is herein incorporated by
reference in its entirety. The filtrate sample was added to 2 grams
of 30 wt % hydrochloric acid to prevent further crystal
formation/growth.
[0138] After removal of the test solution from the test bottle, an
"adherent" sample was generated for each test bottle, which
involved rinsing the glass bottle with 50 grams of 14 wt % nitric
acid. The adherent sample indicates the amount of calcium carbonate
that deposits onto the bottle surface during the test period.
[0139] All liquid samples were analyzed by Inductively Coupled
Plasma (ICP) for calcium ion concentrations. ICP was conducted by
using an "IRIS-AP Duo" inductively coupled plasma spectrometer
available from Thermo Jarrell Ash Corporation, Franklin, Mass. The
operating conditions of the "IRIS-AP Duo" inductively coupled
plasma spectrometer were as follows. The exhaust was turned on and
the pressure gauge indicated a pressure drop of 0.8 to 1.2 psi. The
CID (charge injection device) temperature was below -70.degree. C.
and the FPA (Focal Plane Array) temperature was above 5.degree. C.
The purge time was set to 90 seconds. The ignition parameters were:
RF (Radio Frequency) Power: 1150 watts, Auxiliary Flow: medium,
Nebulizer Flow: 0.55 L/min, and Pump Rate 110 rpm. The purge gas
valves for tank and main were set to 4 L/min and 6 L/min,
respectively. The camera valve setting was 2 L/min. After the
spectrometer was set as discussed above, the spectrometer was
allowed to warm up for at least 15 minutes before running the
auto-sampler.
[0140] As noted above, Table 1 lists the anti-scalants which were
used in these Examples and Comparative Examples.
1TABLE 1 Anti- Chemical Trade Physical/Chemical Scalant Name Name
Mfg. Properties A sodium Valfor The PQ Silica-to-alumina molar
alumino- 100 Corp., ratio = 2:1 silicate Valley median particle
size 3 to (hydrated Forge, 6 .mu.m Na-A type PA normal pore size
zeolite) diameter = 4.2 Angstroms pH of 1 wt % dispersion = 10 to
11 ion exchange capacity = 5.6 Meq/g hydrated zeolite calcium
exchange capacity = 270-300 mg CaCO.sub.3/g anhydrous zeolite
Na.sub.2O(17 wt %), Al.sub.2O.sub.3(28 wt %), SiO.sub.2(33 wt %),
H.sub.2O(22 wt %) B sodium Valfor The PQ SiO.sub.2/Al.sub.2O.sub.3
mole alumino- CBV Corp., ratio = 20 silicate 20A Valley Surface
Area = 500 m.sup.2/g (mordenite Forge, type PA zeolite) C magnesium
Min- Floridin, median particle aluminum U-Gel Tallahassee, size
3.22 .mu.m silicate 400 FL (range 3.02 to 3.47 .mu.m) (colloidal pH
= 9.7 sp. gr. = 2.4 attapulgite Al.sub.2O.sub.3(10.37 wt %), clay)
SiO.sub.2(58.66 wt %), MgO(8.59 wt %), Fe.sub.2O.sub.3(3.56 wt %),
CaO(2.59 wt %), H.sub.2O(11.4 wt %) D ground Hydro- OMYA, mean
particle diameter = calcium carb 60 Inc., 1.9 .mu.m carbonate
Proctor, VT specific surface area = 6 m.sup.2/g pH slurry = 8.5 sp.
gr. = 2.71 E ground Hydro- OMYA, mean particle diameter = calcium
carb 65 Inc., 0.7 .mu.m carbonate Proctor, VT specific surface area
= 14 m.sup.2/g pH slurry = 8.5 sp. gr. = 2.71 F ground Hydro- OMYA,
mean particle diameter = calcium carb Inc., 0.3 .mu.m carbonate HG
Proctor, VT pH slurry = 8.5 sp. gr. = 2.71 G sodium Bento- Southern
particle size range = montmor- lite HS Clay 0.1 to 5 microns
illonite Products, pH = 10.3 (bentonite) Inc., moisture = 6 wt %
Gonzales, TX H synthetic Lapon- Southern surface area = 370
m.sup.2/g hectorite ite RD Clay pH of 2 wt % (synthetic Products,
suspension = 9.8 magnesium Inc., SiO.sub.2(59.5 wt %), silicate)
Gonzales, MgO(27.5 wt %), TX Na.sub.2O(2.8 wt %), Li.sub.2O(0.8 wt
%), ignition loss (8.2 wt %) I talc Vantalc R.T. mean particle
diameter = (hydrous F2003 Vanderbilt 2.8 .mu.m magnesium Co.,
specific surface area = silicate) Norwalk, CT 10 m.sup.2/g pH
slurry = 9.5 sp. gr. = 2.75 SiO.sub.2(59.5 wt %), MgO(30 4 wt %),
Al.sub.2O.sub.3(0.4 wt %), Fe.sub.2O.sub.3(3.2 wt %), CaO(0.3 wt
%), ignition loss (6.3 wt %) J magnesium Veegum R.T. SiO.sub.2(63
wt %), aluminum Vanderbilt MgO(10.5 wt %), silicate Co.,
Al.sub.2O.sub.3(10.5 wt %), (smectite Norwalk, Fe.sub.2O.sub.3(0.9
wt %), clay) CT CaO(2.3 wt %), Na.sub.2O(2.4 wt %), K.sub.2O(1.3 wt
%), ignition loss (7.5 wt %) sp. gr. = 2.6 pH slurry = 9.5 K
hydrated Veegum R.T. SiO.sub.2(62 wt %), magnesium HV Vanderbilt
MgO(11.9 wt %), aluminum Co., Al.sub.2O.sub.3(10.7 wt %), silicate
Norwalk, Fe.sub.2O.sub.3(0.7 wt %), (smectite CT CaO(2.4 wt %),
clay) Na.sub.2O(2.6 wt %), K.sub.2O(1.7 wt %), ignition loss (9 wt
%) L sodium Zeolex Kraft avg. particle size = alumino- 23A Chemical
6 .mu.m silicate Co., Melrose pH of 20 wt % (synthetic Park, IL
dispersion = 10.2 amorphous surface area = 75 m.sup.2/g
precipitated silicate) M amorphous DAC III Delta Chem., sp. gr. =
2.5 magnesium Inc., silicate Searsport, ME N a blend of GEL IMV 97%
minimum < magnesium Nevada, 200 mesh bentonite Amardosa
SiO.sub.2(47.2 wt %), and calcium Valley, NV Al.sub.2O.sub.3(14.1
wt %), bentonite MgO(12.4 wt %), Fe.sub.2O.sub.3(2 wt %), CaO(4.2
wt %) O sepiolite Ther- IMV finely-ground powder mogel Nevada,
SiO.sub.2(56 wt %), Armdosa Al.sub.2O.sub.3(4 wt %), Valley, NV
MgO(20 wt %), Fe.sub.2O.sub.3(1 wt %), CaO(0.5 wt %) P hydrated
Veegum R.T. 2 to 4 wt % cristobalite magnesium F Vanderbilt
aluminum Co., silicate Norwalk, CT Q hydrated VanGel R.T. 4 to 6 wt
% cristobalite magnesium B Vanderbilt aluminum Co., silicate
Norwalk, CT R sepiolite Sepio- IMV 90% minimum < gel F Nevada,
325 mesh Armdosa moisture = 14 wt % Valley, NV S calcium IGB IMV
98% minimum < bentonite Nevada, 200 mesh Armdosa moisture = 13
wt % Valley, NV SiO.sub.2(50.9 wt %), Al.sub.2O.sub.3(20.8 wt %),
Fe.sub.2O.sub.3(1.5 wt %), MgO(2.4 wt %), CaO(4 wt %) T saponite
Imvite IMV finely-ground powder (magnesium 1016 Nevada, moisture =
10 wt % bentonite) Armdosa SiO.sub.2(44.6 wt %), Valley, NV
Al.sub.2O.sub.3(7.8 wt %), Fe.sub.2O.sub.3(2.5 wt %), MgO(22.8 wt
%), CaO(4.5 wt %) U magnesium Magna- American soft white flakes
aluminum brite T Colloid Co., sp. gr. = 2.6 silicate Arlington
Heights, IL
[0141] The conditions and results of these tests are shown in
Tables 2 and 3 below. For Table 2 the test conditions were at a
temperature of 70.degree. C., pH of 12.5, [Ca.sup.+2]=60 ppm, and
[CO.sub.3.sup.-2]=1000 ppm. In Table 2, "% inhibition" is a
relative measure of how much scale formation is prevented, such
that higher values reflect better prevention of scale formation.
Percent inhibition is calculated as follows: 1 % inhibition = ( Ca
conc . of treated sample ) - ( Ca conc . of untreated sample ) ( Ca
conc . total ) - ( Ca conc . of untreated sample )
[0142] Taking into consideration that the Ca concentration (as
CaCO.sub.3) of the untreated sample is the Ca concentration (as
CaCO.sub.3) of Comparative Example 1 which is 5.9 ppm, and taking
into consideration that the Ca concentration (as CaCO.sub.3) total
is 150 ppm, the percent inhibition for Example 1 is 11%
=(21-5.9)/(150-5.9). Also, in Table 2, "% deposition" is the weight
percent of Ca (as CaCO.sub.3) which deposited on the surface.
2 TABLE 2 Soluble Calcium Conc. (CaCO.sub.3 crystal size < Scale
Deposition 20 microns) on Surface Ca Conc. Ca Conc. (as % (as %
Anti- Conc. CaCO.sub.3) Inhibi- CaCO.sub.3) deposi- Example scalant
(ppm) (ppm) tion (ppm) tion Comp. 1 None -- 5.9 -- 22 15% 1 A 50 21
11% 2.8 2% 2 A 100 96 63% 7.6 5% 3 B 25 17 8% 13 9% 4 B 50 16 7% 9
6% 5 B 100 19 9% 9.7 7% 6 C 25 54 33% 2.8 2% 7 C 50 63 40% 2.3 2% 8
C 100 76 49% 1.8 1% 9 G 25 56 35% 2.8 2% 10 G 50 54 33% 1.6 1% 11 G
100 139 92% 1.1 1% 12 H 100 96 62% 7 5% 13 I 25 38 22% 2.1 1% 14 I
50 41 25% 2.1 1% 15 I 100 33 19% 1.9 1% 16 L 100 23 12% 17 11% 17 M
100 55 34% 7.4 5% 18 N 50 128 85% 1.8 1% 19 N 100 138 92% 2.7 2% 20
O 50 88 57% 2.7 2% 21 O 100 96 63% 2.7 2% 22 P 50 102 67% 1.4 1% 23
P 100 92 60% 2.4 2% 24 Q 50 73 47% 2.5 2% 25 Q 100 93 60% 5.1 3% 26
R 50 108 71% 1.5 1% 27 R 100 110 72% 1.8 1% 28 S 50 97 63% 2.2 2%
29 S 100 117 77% 2.9 2% 30 T 50 127 84% 1.9 1% 31 T 100 127 84% 2.1
1% 32 U 50 118 78% 1.5 1% 33 U 100 122 81% 1.2 1%
[0143] Table 2 shows that under the "mild" scaling condition (i.e.,
60 ppm Ca.sup.+2 and 1000 ppm CO.sub.3.sup.-2), all tested
anti-scalants, except anti-scalants B and L, were effective at
either inhibiting crystal formation or reducing scale deposition on
surface. The percent scale deposition was significantly reduced
when calcium carbonate was treated with these polyvalent metal
silicates and polyvalent metal carbonates, especially anti-scalants
C, G, I, and N-U.
[0144] In Table 3 below, the test conditions were at a temperature
of 70.degree. C., pH 12.5, [Ca.sup.+2]=100 ppm, and
[CO.sub.3.sup.-2]=10,000 ppm.
3 TABLE 3 Soluble Calcium Conc. (CaCO.sub.3 crystal size < Scale
Deposition 20 microns) on Surface Ca Conc. Ca Conc. Anti- Conc. (as
% Inhi- (as % depo- Example scalant (ppm) CaCO.sub.3) bition
CaCO.sub.3) sition Comp. 2 None -- 15 -- 27.0 11% 34 G 50 54 17%
4.5 2% 35 N 50 161 62% 3.7 2% 36 O 50 87 31% 4.5 2% 37 R 50 95 34%
4.2 2% 38 T 50 181 71% 3.1 1% 39 U 50 154 59% 2.9 1%
[0145] Table 3 indicates that anti-scalants G, N, O, R, T, and U
were also effective at reducing scale formation and deposition
under the "harsh" condition (i.e., 100 ppm Ca.sup.+2 and 10,000 ppm
CO.sub.3.sup.-2).
[0146] In looking at the data of Tables 2 and 3, it should be noted
that polyvalent metal silicates and polyvalent metal carbonates,
such as magnesium aluminum silicate, magnesium silicate, magnesium
bentonite, calcium bentonite, and sepiolite, are not normally used
as water softeners, due to the lack of ion-exchanging properties.
However, these polyvalent metal silicates and polyvalent metal
carbonates perform effectively for CaCO.sub.3 scale control.
Surprisingly, sodium aluminosilicates (e.g., anti-scalant B and L),
which supposedly function as water softeners, do not perform as
well in terms of inhibiting CaCO.sub.3 crystal formation and
reducing scale deposition.
EXAMPLES 40-43 AND COMPARATIVE EXAMPLES 3-7
[0147] A "Parr.RTM." bomb test was conducted to compare the
performance of sodium montmorillonite (bentonite), i.e.,
anti-scalant G, with a known anti-scaling polymer. The experiments
were conducted at a temperature which simulates the temperature of
kraft pulping processes.
[0148] The test conditions were 170.degree. C., pH 12.4, 60 ppm
Ca.sup.+2, 1000 ppm CO.sub.3.sup.-2, and a one-hour incubation time
without agitation. The carbonate solution was preheated to
70.degree. C. before mixing to obtain solutions having the
concentrations listed in Tables 4 and 5, using the procedure
described in Examples 1-39 and Comparative Examples 1 and 2.
[0149] After adding the solution to a Parr.RTM. bomb, Model 4751
available from Parr Instrument Company, Moline, Ill., having a
capacity of 125 ml, the bombs were placed in an oven at 170.degree.
C. for one hour at a typical pressure of between 120 and 150 psi.
After treatment, the bombs were removed from the oven and allowed
to cool for one hour. The resulting fluids were removed from the
bombs and subjected to a vacuum filtration as described in Examples
1-39 and Comparative Examples 1 and 2. After the fluid was removed
from the bomb, an "adherent" sample was also generated from each
Parr.RTM. bomb by dissolving the deposited calcium carbonate on the
substrate surface with 50 grams of 14 wt % nitric acid. All fluid
samples were analyzed by Inductively Coupled Plasma (ICP) for
calcium ion concentrations using the procedure described in
Examples 1-39 and Comparative Examples 1 and 2.
[0150] In Table 4 below, the test conditions were at a temperature
of 170.degree. C., pH 12.5, [Ca.sup.+2]=60 ppm, and
[CO.sub.3.sup.-2]=1000 ppm. Comparative Examples 4 and 5 involve
"DRAWFAX342" copolymer of maleic acid and acrylic acid (2:1 molar
ratio) having a molecular weight of about 2700, available from Draw
Chemical Company.
4 TABLE 4 Soluble Calcium Conc. (crystal Scale Deposition size <
20 microns) on Surface Ca Conc. Ca Conc. Anti- Conc. (as % Inhi-
(as % De- Example scalant (ppm) CaCO.sub.3) bition CaCO.sub.3)
position Comp. 3 None -- 11 -- 77 51% 40 G 25 44 24% 62 41% 41 G 50
56 32% 43 29% 42 G 100 128 84% 21 14% Comp. 4 DF342 20 34 16% 58
39% Comp. 5 DF342 30 22 7% 47 31%
[0151] Table 4 shows that anti-scalant G, i.e., sodium
montmorillonite, is more effective than the known polymer, i.e.,
"DRAWFAX342" copolymer of maleic acid and acrylic acid, with
respect to the inhibition of crystal growth and reduction in scale
deposition.
[0152] In Table 5 below, the test conditions were at a temperature
of 170.degree. C., pH 12.5, [Ca.sup.+2]=100 ppm, and
[CO.sub.3.sup.-2]=10,00- 0 ppm.
5 TABLE 5 Soluble Calcium Conc. (crystal Scale Deposition size <
20 microns) on Surface Ca Conc. Ca Conc. Anti- Conc. (as % Inhi-
(as % De- Example scalant (ppm) CaCO.sub.3) bition CaCO.sub.3)
position Comp. 6 None -- 7.4 -- 88 35% 43 G 100 125 48% 8 3% Comp.
7 DF342 100 106 41% 98 39%
[0153] Table 5 shows that anti-scalant G, i.e., sodium
montmorillonite, performed even better when subjected to the
"harsh" condition.
EXAMPLES 44-66 AND COMPARATIVE EXAMPLES 8-18
[0154] These Examples and Comparative Examples involve using a
dynamic tube blocking test to study the effectiveness of various
scale inhibitors. A basic solution containing carbonate and
anti-scalant was mixed with a calcium solution in a capillary to
test the effectiveness of the anti-scalants in preventing scaling
as measured by pressure build-up in the capillary.
[0155] In view of the above, except for Examples 54 and 55 which
involved 73.78 g/l Na.sub.2CO.sub.3, the basic solution
included:
[0156] 37.09 g/l Na.sub.2CO.sub.3;
[0157] 6 g/l NaOH (50 wt %); and
[0158] anti-scalant in an amount to obtain the concentrations of
Tables 6 and 7. The basic solution was fed through a first
capillary at a flow rate of 12.5 ml/min. The calcium solution
involved 0.74 g/l CaCl.sub.2.2H.sub.2O and was fed at a rate of
12.5 ml/min through a second capillary which joined the first
capillary to form a 2 meter-long capillary tube (internal diameter
0.127 cm).
[0159] As a result, the basic solution and calcium solution were
mixed to form a supersaturated solution. The composition of the
supersaturated aqueous solution was as follows, except for Examples
54 and 55 which involved 20,000 ppm of carbonate:
6 Calcium ions 96 ppm Carbonate ions 10,054 ppm NaOH 0.15 wt % (pH
= 12.5) Temperature 170.degree. C.
[0160] The supersaturated solution was pumped through the 2
meter-long capillary at a flow rate of 25 ml/min at a temperature
of 170.degree. C. and pressure of 55 psi.
[0161] Calcium carbonate crystals formed and precipitated as soon
as the two solutions were mixed in the capillary tube. The degree
of precipitation was dependent on the effectiveness and
concentration of the scale inhibitor, and was indicated by the back
pressure across the capillary, which was measured by a pressure
transducer. A low differential pressure was indicative of an
effective treatment. The test was run for 30 minutes or until an
increase of 1 psi was obtained. The longer the time (i.e., induced
time) elapsed to reach 1 psi, the more effective the chemical
treatment.
[0162] As listed in Tables 6 and 7, a number of polyvalent metal
silicates and polyvalent metal carbonates were tested using the
dynamic tube blocking test and the results were compared to the
performance of known anti-scalants, such as PESA (polyepoxysuccinic
acid), AMP (amino tri-(methylene phosphonic acid)), PBTC
(2-phosphonobutane-1,2,4-tricarbox- ylic acid), "DRAWFAX342"
copolymer (described above), and "SB 37105" polyacrylic acid having
a molecular weight of 3300, available from Performance Process
Incorporated, Mundelein, Ill.
7TABLE 6 Anti- Conc. Induction Time to Example sealant (ppm)
[CO.sub.3.sup.-2] 1 psi (minutes) Comp. 8 None -- 10,054 2 Comp. 9
PESA 25 10,054 2 Comp. 10 PESA 50 10,054 2 Comp. 11 DF342 50 10,054
11 Comp. 12 DF342 70 10,054 14 Comp. 13 DF342 150 10,054 20 Comp.
14 SB 37105 45 10,054 6 Comp. 15 SB 37105 150 10,054 26 Comp. 16
AMP 60 10,054 24 Comp. 17 PBTC 50 10,054 14 44 E 30 10,054 29 45 F
10 10,054 29 46 F 15 10,054 >30 (0.7 psi @ 30 min) 47 F 30
10,054 26 48 G 15 10,054 10 49 G 30 10,054 31 (0.9 psi @ 30 min) 50
G 50 10,054 >30 (0.8 psi @ 30 min) 51 G 70 10,054 >30 (0.3
psi @ 30 min) 52 G 150 10,054 >30 (0.3 psi @ 30 min) 53 K 150
10,054 20 54 K 500 20,000 4 55 G 200 20,000 >30 (0.5 psi @ 30
min)
[0163] The results in Table 6 indicate that PESA and maleic acid
copolymer were not effective at inhibiting crystal growth and
reducing scale deposition on the tube surface, as reflected by the
very short induction time (2-6 minutes) to reach a differential
pressure of 1 psi. In comparison, the untreated calcium carbonate
solution reached this differential pressure in approximately 2
minutes.
[0164] Table 6 also indicates that the performance of anti-scalants
E, F, and G was superior to the known anti-scalants. For instance,
the performance of anti-scalant G at 30 ppm was more efficient than
that of AMP at 60 ppm. It was expected that sodium aluminosilicate
zeolite (i.e., anti-scalant A) would not perform well under the
conditions of 96 ppm calcium and 20,000 ppm carbonate
concentration, while Example 55 shows that under these conditions
anti-scalant G still effectively controlled CaCO.sub.3 scale
formation and deposition.
[0165] Table 7 involves scale inhibitio n of so dium
montmorillonite blended with either another polyvalent metal
silicate or a polyvalent metal carbonate.
8TABLE 7 Anti- Conc. Induction Time to Ex. Sealant (ppm) 1 psi
(minutes) Comp. 18 None 2 56 G 30 ppm 31 (0.9 psi @ 30 min) 57 G 50
ppm >30 (0.8 psi @ 30 min) 58 G 70 ppm >30 (0.3 psi @ 30 min)
59 G/J (1:1) 40 ppm >30 (0.4 psi @ 30 min) 60 J 70 ppm 6 61 J
150 ppm 20 62 G/E (1:1) 30 ppm >30 (0.9 psi @ 30 min) 63 G/E
(1:3) 30 ppm 26 (0.6 psi @ 30 min) 64 G/F (2:1) 10 ppm >30 (0.3
psi @ 30 min) 65 G/F (2:1) 20 ppm >30 (0.3 psi @ 30 min) 66 G/F
(2:1) 200 ppm >30 (0.2 psi @ 30 min)
[0166] Table 7 shows that a strong synergism was observed when
anti-scalant F was blended with anti-scalant G at a weight ratio of
1:2. For instance, at 30 minutes the blend still exhibited a very
low differential pressure (0.3 psi), at a very low dosage of 10
ppm. In comparison, a differential pressure of 1 psi was reached
for anti-scalant G (15 ppm) at 10 minutes and 29 minutes for
anti-scalant F (10 ppm) at the same pressure. Table 7 also shows
that a blend of anti-scalant J and anti-scalant G appeared to show
a synergy.
[0167] While the invention has been described in connection with
certain preferred embodiments so that aspects thereof may be more
fully understood and appreciated, it is not intended to limit the
invention to these particular embodiments. On the contrary, it is
intended to cover all alternatives, modifications and equivalents
as may be included within the scope of the invention as defined by
the appended claims.
* * * * *