Note: Descriptions are shown in the official language in which they were submitted.
~6zg83
Background of the Invention ' ~
:, ,
Although the invention has general applicability to any given
system where the formation and deposition of scale and in particular cal- ;
cium phosphate is a potential problern, the invention will be discussed in
detail as it concerns boiler water systems.
As is well known and comprehensively described and dis-
. . . -:
cu~sed in the Betz Handbook of Industrial Water Conditioning, 6th Edition,
1968, Betz Laboratories, Inc., Trevose, Pennsylvania, pages 151-171, the
ormation of scale and sludge deposits on boiler heating surfaces is the
moet serious water problem encountered in steam generation. Although
current industrial steam producing systems make use of sophisticated
external treatments of the boiler feed water, e. g., coagulation, {iltration,
softening of water prior to its feed into the boiler system, those operations
are oiily moderately effective. In all cases, external treatment does not
in itself provide adequate treatment since muds, sludge, clay, silts, iron ~ ;
.oxides and hardness-imparting ions, 1. e., calcium, magnesium, and car-
~onate ions, escape the treatment and eventually are introduced into the
,
- steam generating system.
The problems which result from their introduction into the
.
;~ 20 steam generating system are apparent. Since the deposit forming materials
~- are present, they have a tendency to accumulate upon concentration of the `
water and to settle at points in the system where there is low flow and there-
~` ~ore restrict water circulation. The baking of mud and/or sludge on tubes
and sheets will result in overheating and failure, thereby requiring down
time for repair or replacement of the structural parts. In addition, mud,
- sludge, and silts may become incorporated in scale deposits adding to their
volume and heat insulating effect.
--2--
, ~ .
.~:
106Z9l33
Accordingly, internal treatments have been necessary to
maintain the mud and silts in a suspended state. These internal treatments
have been generally referred to in the industry as sludge conditioning agents.
In addition to the problems caused by mud, sludge or silts,
the industry has also had to contend with boiler scale. Although external
treatment is utilized specifically in an attempt to remove calcium and mag-
nesium from the feed water, scale formation due to residual hardness, i. e.,
calcium and magnesium salts, is always experienced. Accordingly, internal
treatment, i. e., treatment of the water fed to the system, i9 necessary to
prevent, reduce and/or retard formation of the scale-imparting compounds
and their deposition. The carbonates of magnesium and calcium are not the
only problem compounds as regards scale, but also waters having high con-
tenes of phosphate, sulfate and silicate ions elther occurring naturally or
added for other purposeF are problematic since calcium and magnesium, and
any iron or copper pre`sent, react with each, form the respective insoluble
8alt8 and deposit as boiler scale. The problem is compounded by the deposl-
~ion of iron oxides and clay with the other scale salts. Iron oxides enter the
Yy6tems by escaping the pretreatment procedures and/or are present due to
corrosion of the metal parts in contact with the aqueous medium. As is ob-
20 ' vious, the deposition of scale which by the present definition includes iron
oxide on the structural parts of a steam generating system causes poorer
eirculation and lower heat transfer capacity, resulting accordingly in an
overall loss in efficiency. ~-
Although the foregoing is directed to boiler water systems, or
more specifically steam generating systems, the same problems occur in pulp
and paper mill systems, cooling water systems, desalini~ation systems (cal- -
eium sulfate formation and deposition), scrubber systems and the like. The
'106;~9~3
problems encountered ;n these operations sometimes are more severe since
complete external treatments are not commonly utilized. Any aqueous system
having calcium and magnesium cations and the exemplified anions, in
particular phosphate and silicate, wiIl experience the formation and
deposition of the scaling salts.
Because of the foregoing, the water treatment industry is con-
stantly evaluating new processes, new products, new techniques in an effort
to permit the various process water systems to operate more effectively
for longer periods and at lower costs.
Many and different type materials have been used for internal
treatment of water systems, and in particular as sludge conditioning agents.
Of the vast number may be mentioned alginates, lignins, lignosulfonates,
tannins, carboxymethyl cellulose materials, synthetic polymers such as
polyacrylates and in particular polymethacrylates. U.S. Patents 2,723,956;
3,188,289; 3,519,538 are merëly representative of the type materials used
and the functions thereof. U.S. Patents 2,723,956 and 3,519,538 disclose
boiler treatments utilizing maleic anhydride and non-sulfonated styrene
copolymers wherein the mole ratio of anhydride to styrene has an excess of
anhydride and is at least 1:1 and preferably 2:1.
General-rbscription of the Invention - -
The inventors discovered that if an effective amount of a
particular type copolymer composed of essentially sulfonated styrene
moieties ànd those derived from maleic anhydride was added or introduced -
into the water of a process water system, the formation and deposition of
scale, particularly calcium and magnesium phosphates, silicate and -
iron oxide scale, on the metallic
: , .,
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~L062983 ~ -
.
structures of the equipment could be controlled to a degree necessary to
permit the continual and economical operation of the system.
The polymers which are the subject of the present invention
are those containing essentially sulfonated styrene moieties, i. e.,
~ ', . ' ' '
--~ C ----C ~
.
and moieties derived from maleic anhydride, i. e.,
H H
_ C - C - - .
L 1l= 1=
OM OM
where the sulfonated styrene moieties exceed the moieties derived from
the maleic anhydride.
Preferably the copolymers contain a mole ratio of styrene
moieties to maleic anhydride derived moieties of from about 2:1 to about
4:1 and preferably 3:1, and possess a molecular weight of from 500 to
100,000. The copolymers have been found to be effective and provide best
20 results when used at levels of from about 0.5 to 100 parts per million
of water and preferably from about 2, 5 to 25 parts per million parts of
water contained in the steam generating equipment.
The polymers of the present invention can be produced in
different ways, however, their manner of production does not affect in
; ,. .
^ :
1~629~33 :
. ,, ............. . .
any way their effectiveness as scale, calcium and magnesium phosphate
and silicate control agents.
One procedure for producing the polymers is to copolymerize
styrene with maleic anhydride in the specified ratios. After the polymer is
resolubilized by producing the various water- soluble salts (alkali metal),
the polymer is then sulfonated in accordance with well-known techniques
(note for example U. S. 2, 764, 576). The degree of sulfonation can vary but
substantially complete sulfonation of the styrene moieties i9 preferred.
Conversion of the polymers into the water soluble metal salts
such as the alkali metal salt forms is accomplished by normal methods. There-
fore M may represent any one of or a mixture of NH4, H, Na, K, etc.
As is apparent, the other manner of producing the polymers ~`
is to first sulfonate the styrene monomer utilizing a technique such as des-
cribed in the aforecited patent and then copolymerize the resulting sulfonatod
styrene with the maleic anhydride. .
.'
The methods and parameters of copolymerizing the two mono-
mers is well known and illustrated by U. S. Z, 723, 956. Generally the co-
polymerization may be affected at temperatures from about 80 to 120C
utilizing peroxide catalysts such as cumene hydroperoxide, benzyl peroxide,
etc. in an inert medium.
.
The copolymers of the instant invention,which are quite different
from the polymers of the cited patents, are very soluble in water which permits
the obtention of greater protcction against the potential depositions as des-
. . , -
cribed earlier.
Commercial polymers suitable for the instant purpose are
available from National Starch under the designation NSDP-2509-50 and 2727-
18.
-6-
~O~Z983
Specifi~ Embodiments - Steam Generation
. . .
The copolymers of the invention were subjected to steam generat-
ing conditions utilizing experimental boiler systems having an electrical heat
source. The boilers are equipped with a system permitting circulation of
water in a path via natural convection. Two probes are installed in the des-
cribed path positloned vertically one above the other. These probes permit
measurement of deposition, if any, at two different locations in the path -
through which the water clrculated,~ These probes are referred to in the
following Tables as the Upper and Lower probes.
~ - The tests conducted using the experimental boilers were
operated under the conditions specified in the Tables which follow. The re-
spective tests were designed to establish the effects, if any, of variations
found in the different steam generating operations.
During operation of the boilers, pressurè and heat probe amperage
were cont~nually monitored and the blowdown volumes and steam generation ~`
rate s were mea sured .
- ..
After test completion, the heat transfer probes were re-
moved and visual observations were recorded as to deposit color, quantity,
and quality. Chemical analyses were employed to determine total deposit I -
quantiy. In certain instances, the deposit was dissolved in hydrochloric ¦~
acid and hydrofluoric acid and the solution was analyzed for insolubles
calcium, magnesium, phosphate and silica. Deposit weight waa calculated
from the solution composition and these results have been reported in the
Tables which follow.
In order to establish the ccope of the invention, polymers
ha~ing a 1:1 mole ratio of sulfonated styrene to maleic anhydride were
also tested It was felt that the comparative results provided the necessary
evidence to establish the true parameters of the invention.
.
` 1062983
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~062983
It is evident from the data recorded in the foregoing Table
that the copolymers containing less than 2 moles of sulfonated styrene
moieties per mole of maleic anhydride moieties were less effective while
those having 2 or more were quite effective.
Additional comparisons were conducted utiliæing various
specific tests, the reqults of which are recorded in Table I.
In Table IA which follows are recorded specific data derived
from a comparison of Copolymer A used at l0 ppm (Item 5 under Table I,
Section B) ~rith a Control, i. e., no treatment. The test conditions and boiler
balances were those as specified in Table I, Section B, Item 5. The scale
was analyzed to establish the effect that treatment had on scala composition.
` . ' ' ~ . ',~. .
TABLE IA
Scale Deposit (g/ft~) Deposit (g/ft2) % Scale Reduction
ComponentControlCopolymer A on High Heat Transfer
~?pm Area
t~a 3. 69 0. 06 98
P04 5.33 0.10 9B
MgO 1. 49 0. 08 9S
SiO2 0. 26 0. 06 77
Insolubles * 4. 08 0. 61 ~5
Total 14. 85 0. 91 94
* In~olubles are composed of magnesium silicate and iron oxide
In Table IB which follows, the results of a deposit comparison
are recorded utilizing a Control, the Commercial Polymethacrylate (Item 6,
Table I, Section B) and Copolymer A (Item 3, Table 1, Section B). The con-
ditions were those as specified in Table I in the réspective Section under
boiler balances with the Control being conducted at comparable boiler balances.
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~629~33
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Table IC records data relative to a comparison of Copoly-
mer B (2:1 ratio) and Copolymer A (3:1 ratio) with each other in the con-
ditions specified (Items 5 and 6 respectively in Table I, Section B) and
with a Control. The results not only establish the effectiveness of the.
polymer of the invention but also the relative superiority of the 3:1 ratio
polymer to the 2:1 polymer.
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1~6Z983
It is apparent from the testing and the data recorded in the
foregoing Tables that the prescribed copolymers which are the subject of
this invention performed quite impressively. This is particularly evident
from the comparative results obtained with respect to the commercial
product which has been and in some instances is currently being used for
deposit control in steam generating systems.
A~ in Tables IA through IC, Table IIA contains data recorded
relative to specific comparisons of the copolymer of the present invention ;
with the Control and PMA commercial grade. The conditions for the
respective tests were those set forth in Table II, Section B, Items 1 and 4,
with the Control being conducted at comparable conditions. Even at in-
creased pressures, the instant polymers are significantly more effective
than the PMA.
.
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iS;pe_ific Embodimcnts - General Aqueous Systems
,,, . ' , . ~ ' '
In order to establish that the present in~rention provided overall
~effectiveness, two different evaluations were conducted which assimilated
water conditions found in cooling water systems where the concentration of
calciumions and phosphate îons are such as to provide a calcium phosphate
~cale prone system.
Th~ evaluations were conducted utilizing solutions respectively
cbntaining calcium ion and ortho-phosphate ion. After mixing the two solu-
tions and the specified equilibration time, residual phosphate ion measure-
ments were made after the mixture had been filtered. High residual phos-
phate ion concentration indicated good inhibition.
The specifics of the test procedure are as follows:
Conditions of Test: Static; T = 70C; pH = 8~ 5; equilibration time - 17 hours;
Concentration of Ca++ as CaCO3 = 250 ppm; concentration of PO4 3 = 6. 0 ppm.
Treatment dosage = 10 ppm.
. ~ . .
Solutions: (1) prepare solution of 0.4482g. of Na2HPO4 per liter DI water
- (2j prepare solutior OI 36. 76g. CaCl2 2Ei2O per liter DI water (3) to 1800
mi DI water, add 20 ml solution (2), followed by Z drop~ conc. HCl. Then add
40 ml solution (1) and bring volume to 2000 ml with DI water,
Mcthod: Place 100 ml aliquot of solution (3) in clean 4 oz. glass bottle. Add
1 ml of .1% treatment solution and adjust pH to R. 5 using NaOH. Place bottle
in water bath set to 70C and allow to equilibrate 17 hours.
Anatysis: Filtration - remove sample from water bath, filter through 0. 2 ,~L .
millipore filter. Allow filtrate to cool to room temperature and analyze for
PO4 3 using Leitz Photometer.
Treatment waq added to phosphate solution before mixing~
- 1 6-
1(1 629i33
,
TABI.E III
Ratio sulfonated Dosage Residual phos-
Treatment styrene-maleic ppm phate concentr3-
anhvdride moieites _ tion (ppm PO~~ )
. ' ' . ' ' ' ~ ' .
Control _ o o
Copolymer A 3:1 5 4.0
.
Copolymer A 3:1 10 5. ~
. . .
The effectiveness of the polymer of the invention was apparent.
Without treatment all phosphate precipitated while almost 100% inhibition was
~0 obtained when 10 ppm of treatment was utilized.
A 6econd evaluation was conducted utilizing the aforedescribed
procedure. In this evaluation comparisons were made again:t commercial
gsade sulfonated polyst~renes and certain Inaleic aIYhydride polym:rs. In
this test the percentage inhibition was determined from the measuren~ent of
the residual phosphate ion. ~ -
, .
'' ' ;~
-17_
: 1~6;~983 ~:
T.ABLE rv
Sulfonated Maleic % Calcium Phosphate
Treatment PolystyreneAnhydride Inhibition
__. Moieties Moieties
Copolymer A 75 25 100
Copolymer B 66.6 33.3 90.2
Copolymer C 50 50 75.4
SPS (MW 34, 000) 100 . _ . 62.3
SPS (MW 70, 000) 100 - - 47.6
~ SPS (MW 400, 000) 100 _ 14. 6
SPS (MW 700, 000) 100 - . 4.1 .
Ethylene maleic - .100 < 5
anhydride polymer
~lalcic anhydride - 100 < 5 `~
telemer
'' ~
.
: ~ The data clearly established that the homopolymers of sul-
fonated polystyrene, maleic anhydride and ethylene maleic anhydride poly-
.mer~ do not control calcium phosphate as well as the polymers of the in- !1 . ,. ..
- stant inventlon. In addition, the data confirmed the importance of having at
20 - least a mole ratio of 2 or greater of sulfonated styrene to 1 of maleiF an- :`
hydride. . ' , ~ - .
The invention is applicable to any aqueous system where cal- .
dum phosphate formation and precipitation is a potential problem. For
example, the inventive process would be effective in gas scrubbing systems .
where scrubbing mediums such as primary sewage effluents, which contain . .
' . ' ' ""
~L06Z9~33
high phosphate levels are used as the scrubbing or washing medium. These
systems would have the prerequisite for the formation and deposition of
calcium phosphate which is to be avoided. The additional areas of
application will be apparent to those operating in the areas of process
water systems.
Ef~icacy in Related Areas
In order to determine the efficacy of the polymers of the
invention in related areas, certain tests were conducted to
(i) establish the dispersive effect of the polymers on sus-
pended matter, more specifically clay and iron oxide, and
(ii) establish the capability of the polymers to inhibit the
formation and thereby the deposition of calcium carbonate ~
in an aqueous system where the effect was likely to occur. ~ -
The protocols followed and the results of the tests were as follows:
A. Deflocculation and Dispersion of Suspended Matter
A 0.1% iron oxide or clay suspension in deioni~ed water was
prepared. The hardness of the slurry was adjusted to 200 ppm CaC03 and the
resultant medium was mixed for a time required to obtain a uniform sus-
pension. The pH was then adjusted to the testing level.
Aliquots of the suspension were drawn off, placed in glass `
bottles and the appropriate amount of treatment added. The samples were
then shaken to insure good mixing of treatment and suspension. Using a
turbidimeter or an instrument which measures light transmission, the
effect of the treatment compared to a control (suspension to which no treat-
ment was added) was measured. Treatments causing an increase in turbidity
: : .
or a decrease in light transmitted are considered dispersants.
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As apparent from the results of the studies, the polymers
of the invention and even the SS/MA polymer having a 1:1 ratio were quite
effective in dispersing the suspended matter after an 18 hour duration. The
1/2 hour duration results,although not overwhelming,were acceptable for
all practical purposes since the 18 hour test is felt to be the more important
re sult .
- '` :~ '
B. Calcium Carbonate Studies
.
A synthetic environmental was produced containing known
quantities of water soluble calciurxl chloride and sodium carbonate under
Dpecific pH and temperature conditions. Treatments were added to various
samples of the solution and the amount of calcium remaining in solution
after à period of time was measured and compared to a Control.~ The test
measured quite accurately the capacity of the polyIners to inhibit the forma-
.
tion and ultlmate deposition of calcium carbonate.
The treatment utilized consisted of 10 ppm of A. a 3:1 SS/
:. : ...
MA polymer; B. a 2:1 SS/MA polymer; and C. a l:l SSlMA polymer. The
result~ expressed as % CaC03 Inhibition respectively were 29. 6~o; 29. 3~10;
and 36. 6%. The polymers were considered to be significant since they did
establish efficacy. Although the degree of efficacy was perhaps lower than
those polymers currently commercially available for calcium carbonate con-
trol, this capacity of the polymers when considered together with the results
achievable against calcium and magnesium phosphates, magnesium silicates,
iron oxides, mud, and claSr make the use of these polymers clearly an im-
portant advancement in the art.
- -21-
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~L~6291~3
Sulonation Study
The contribution of sulfonation sn the efficacy of the copolymers
of the instant invention, i. e., sodium salt of sulfonated styrene-maleic an-
hydride copolymers (SS/MA) was investigated to a certain degree and was
only partially resolved. The data determined indicated that sulfonation con-
tributes quite beneficially. The drawback to complete resolution of the question
was due to the difficulty in obtaining a 100% solution of the 3:1 mole ratio
fftyrene-maleic anhydride polymer so that a '~truly" representative sample
could be evaluated.
The following is a synopsis of the work performed in this
area:
Styrene-maleic anhydride polymers (SMA) are available in
the 1:1, 2:1, and 3:1 styrene to maleic anhydride mole ratios and are reported
to have a 1600 molecular weight. However, conversion to a useable eoluble
~orm (i. e., ammonium or sodium salts) becon~es more difficult as the styrene ~ ~ -
content increases. En~phasis was directed toward the 3:1 mole ratio because
.
this mole ratio was found to be the most effective copolymer of the present
invention. Although the manu~acturer's literature recommended conversiop
to the ammonium salt, attempts were made to convert the 3:1 SMA polymer
to both the ammonium salt and the sodium salt. This manufacturer's pro-
; ~ ~ cedure was not effective for the 3~1 SMA since some copolymer remained
insoluble. Boiler test results indicated the material to be quite ineffective.
Therefore attention was directed toward neutralization as the
sodium salt. The SMA (3:1 ratio) was at least partially converted to the
sodium salt by a procedure outlined by the manufacturer except the proper
amount of sodium hydroxide, rather than ammonium hydroxide, was employed
based on the acid numbers provided and higher temperatures were used. The
-22-
. .
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1~629~3 : `
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solution which resulted from the 3:1 solubilization still contained some in-
soluble material and it is not known whether the resultant solution was repre-
sentative of the dry material although it is estimated that 90 to 95% of the . ;:
copolymer went into solution.
However, the 3:1 copolymer (SMA) solutions (one the ammonium
salt and the other the sodium salt) were evaluated and the results and the :
testing conditions are set forth in the following tahle. The comparative ~: :
teet results established quite conclusively that the sulfonated polymers of the .;
invention performed quite superiorly, ;
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