Note: Descriptions are shown in the official language in which they were submitted.
.f~
ISOPROPENYL PHOSPHONIC ACID COPOLYMERS AND
METHODS OF USE THEREOF
Field of the Invention
The present invention pertains to a composition and method
of utilization of same to inhibit corrosion and control the formation
- and deposition of scale imparting compounds in water systems such as
cooling, boiler and gas scrubbing systems.
Background of ~he Xnvention
The problems of corrosion and scale fonmation and a~tendant
e~fects have troubled water systems for yearsO For instance, scale
tends to accumulate on internal walls of various water systems, such
as boiler and cooling systems, and thereby materially lessens the
operational efficiency of the sys~em.
Deposits in lines, heat exchange equipment, etc., may
originate from several causes. For example, precipitation of calcium
carbonate, calcium sulfate and calcium phosphate in the water system
leads to an agglomeration of these scale imparting compounds along
or around the metal surfaces which contact the flowing water circula-
ting through the system. In this manner, heat transfer functions of
the particular system are severely impeded.
3~'
~.,
Corrosion9 on the other hand, is a degradative electro-
chemical reaction of a metal with its environment. Simply stated, it
is the reversion of refined metals to their natural state~ For
example, iron ore is iron oxide. Iron oxide is refined into steel.
When the steel corrodes, it forms iron oxide which, if unattended,
may result in failure or des~ruc~ion of the metal, causing the par-
ticular water system to be shut down until the necessary repairs can
be made.
Typically, in cooling water systems, the formation of cal
cium sulfate, calcium phosphate and calcium carbonate, among others,
has proven deleterious to the overall efficacy of the cooling water
system. Recently, due to the popularity of cooling treatments using
high levels of orthophosphate to promote passivation of the me~al
surfaces in contact with the system water, it has become critically
important to control calcium phosphate crystallization so tha~ rela-
tively high levels of orthophosphate may be maintained in the sys-
tem, to achieve the desired passivation, without resulting in foul-
ing or impeded heat transfer functions which would normally be
caused by calcium phosphate crystallization.
Although steam generating systems are somewhat different
from cooling water systems, they share a common problem in regard to
deposit formation.
As detailed in the Betz Handbook of Industrial Water Con-
ditioning, 8th Edition, 1g80, Betz Laboratori~s, Inc., Trevose, PA
Pages 85-96, the formation of scale and sludge deposits on boiler
heating surfaces is a serious problem encountered in steam genera-
tion. Although current industrial steam producing systems make use
of sophisticated external treatments of the boiler feedwater9 e.g.,
coagulation, filtration, softening of water prior to its feed into
the boiler system, these operations are only moderately effective.
In all cases, external treatment does not in itself provide adequate
treatment since muds, sludge, silts and hardness-imparting ions
escape the treatment, and eventually are introduced into the stream
generating system.
In addition to the problems caused by mud, sludge or
silts, the industry has also had to contend with boiler scale. Al-
though external treatment is utilized specifically in an attempt toremove calcium and magnesium from the feedwater, 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, is necessary to prevent, reduce and/or
retard formation of the scale imparting compounds and their deposi-
tion. The carbonates of magnesium and calcium are not the only
problem compounds as regards scale, but also waters having high con-
tents of phosphate, sulfate and silicate ions either occurring
naturally or added for other purposes cause problems since calcium
and magnesium, and any iron or copper present, react with each and
deposit as boiler scale. As is obvious, the deposition of scale on
the structural parts of a steam generating system causes poorer cir-
culation and lower heat transfer capacity, resulting accordingly in
an overall loss in efficiency.
Detailed D_escription_of the Invention
In accordance with the invention, it has surprisingly been
discovered that a copolymer (I) having repeat unit moieties la) and
(b), as hereinbelow defined, is efficacious in controlling the for-
mation of mineral deposits and inhibiting corrosion in various watersystems. Repeat unit moiety (a) has the structure
CH3
l .
_--CH2 ~ C - _
X - P - X
O (a~
-
wherein X = OH, or OM wherein M is a cation.
Repeat unit ~b) is characterized by the formula
_
IR2
_--CH2~ C _
C = O
_ R1 _ (b~
wherein R1 is chosen from the group consis~ing of hydroxy, hydroxy-
lated alkoxy, and amide, and water soluble salts thereof. Prefera-
bly, R1 is hydroxylated lower alkyl o-f from abou~ 2-6 carbon atoms.
R2 in the above formula may equal alkyl of From 1-3 carbon atoms,
or H, moieties. Based upon experimental data, the preferred repeat
unit (b) is 2-hydroxypropylacrylate.
It is to be noted that terpolymers comprising two or more
different members selected from the repeat unit (b) grouping and a
member from the repeat unit (a) grouping are also within the purview
of the invention.
In addition to the above two noted essential repeat units,
(a) and (b), an optional third repeat unit (c) may be incorporated
into the polymer backbone. Preferably, this third unit (c) is a
maleic acid or maleic anhydride moiety.
The phosphonic acid monomer corresponding to repeat unit
(a) above, which is to be co-polymerized with a monomer or monomers
corresponding to repeat unit (b), may be prepared by a reaction
mechanism involving the nucleophilic addition of PC13 to the
carbonyl group of acetone. For instance, the reaction may proceed
in accordance with the following equations:
H3C ~ 3
(1) /C=O + PC13 ~ /C \
H3C H3C P+Cl3
H3C O~ H3C Cl
\ / ~ HOAc \ /
(2) C > C
~ \ (HCl) / \
H3 P+Cl3 H3C PO(OH)2
H3C\ /Cl
10 (3) /C > CH2 = C - PO(OH)2
H3C PO(OH)z CH3
In this manner, the isopropenylphosphonic acid monomer (a) may be
produced in a most cost efFective manner due to the relativity low
economic cost of the precursor acetone.
It is also possible to produce the desired monomer ~a)
via dehydration, by heating.2-hydroxy-2-propane phosphonic acid
at a temperature of about 125-250C, as is detailed in U. S. Patent
2,365,466.
As to monomer (b), hydroxylated alkyl acrylates are pre-
ferred, with the 2-hydroxypropylacrylate being most preferred.
These moieties can be readily prepared via an addition reaction be-
tween acrylic acid or its derivatives or water soluble salts and the
o~ide of the alkyl derivative desired. For example, to prepare 2-
hydroxypropylacrylate, acrylic acid may be reacted with propylene
oxide.
With respect to other monomeric possibili-ties correspond-
ing to repeat unit (b), they are well known in the art. For in-
stance, acrylic acid may be prepared directly from ethylene cyano-
hydrin. Methacrylic acid may be prepared from acetone cyanohydrin,
and acrylamide monomers may be prepared from acrylonitrile via treat-
ment wi~h H2S04 or HCl.
If desired, it is possible to prepare a terpolymer utili-
zing a third monomer (c) such as maleic acid or its anhydride.
After the desired monomers are obtained, copolymerizationmay proceed under step~reaction techniques in bulk, suspension, emul-
sion, solution, or thermal polymerization conditions. For instance,
an aqueous solution system may be used with ammonium persulfate
serving as the initiator. Other standard copolymerization systems
utilizing initiators such as benzoyl peroxide, azobisisobutyronitrile
or ferrous sulfate may also ~e employed. The molecular weights of
the copolymers may be controlled utilizing standard chain control
agents such as secondary alcohols (isopropanol), mercaptans, halo-
carbons, etc.
3~
The resulting copolymers (I) most advantageously have amolar ratio of moieties (a:b) of from about 3:1 to about 0.5:1,
and most preferably from about 1:1, to 2:1.
Based upon presently available experimental data the pre-
ferred copolymer (I) is isopropenylphosphonic acid/2-hydroxypropyl-
acrylate (molar ratio a:b = 1:1).
The fact that polymers were formed, in accordance with
inYention, was substantiated by 31PMR spectroscopy where broad
absorptions between about -2G and -40 ppm (vs. o-H3P04) are known
to indicate significant polymer formation.
Thé copolymers (I) should be added to the aqueous system,
for which corrosion inhibiting, and/or deposit control activity is
desired, in an amount effective for the purpose. This amount will
vary depending upon the particular system for which treatment is
desired and will be influenced by factors such as9 the area subject
to co~rosion, pH, temperature, water quantity and the respective
concentrations in the water of the potential scale and deposit form-
ing species. For the most part, the copolymers will be effective
when used at levels of about 0.1-500 parts per million parts of
water, and preferably from about 10 to 20 parts per million of
water contained in the aqueous system to be treated. The co-
polymers may be added directly into the desired water system in a
fixed quantity and in the state of an aqueous solution, either
continuously or intermittently.
The copolymers of the present invention are not limited to
use in any specific category of water system. For instance, in
addition to boiler and cooling water systems, the polymers may also
be effectively utilized in scrubber systems and the like wherein
corrosion and/or the formation and deposition oF scale forming salts
is a problem. Other possible environments in which the inventive
polymers may be used include heat distribution type sea water de-
salting apparatus and dust collection systems in iron and steelmanufacturing indus~ries.
The copolymers of the present invention can also be used
with other components in order to enhance the corrosion inhibition
and scale controlling properties thereof. For instance the co-
polymers may be used in combination ~ith one or more kinds of
- compounds selected from the group consisting o~ inorganic phosphoric
acids, phosphonic acid salts, organic phosphoric acid esters, and
polyvalent metal salts.
Examples of such inorganic phosphoric acids include con
densed phosphoric acids and ~ater soluble salts thereof. The
phosphoric acids include an orthophosphoric acid, a primary phos-
phoric acid and a secondary phosphoric acid. Inorganic condensed
phosphoric acids include polyphosphoric acids such as pyrophosphoric
acid, tripolyphosphoric acid and the like, metaphosphoric acids such
as trimetaphosphoric acid, and tetrametaphosphoric acid.
As to the other phosphonic acid derivatives which are to
be added in addition to the copolymers of the present invention,
there may be mentioned aminopolyphosphonic acids such as aminotri-
methylene phosphonic acid, ethylene diamine tetramethylene phos-
phonic acid and the like, methylene diphosphonic acid, hydroxyethylidene~ diphosphonic acid, 2-phosphonobu~ane-1,2,4-tri-
carboxylic acid, etc.
~3~6
-10-
Exemplary organic phosphoric acid esters which may be com-
bined with the polymers of the present invention include phosphoric
acid esters of alkyl alcohols such as methyl phosphoric acid ester,
ethyl phosphoric acid ester, etc., phosphoric acid esters of methyl
cellosolve and ethyl cellosolve, and phosphoric acid esters of poly-
oxyalkyla~ed polyhydroxy compounds obtained by adding ethylene oxide
to polyhydroxy compounds such as glycerol, mannitol, sorbitol, etc.
Other suitable organic phosphoric esters are the phosphoric acid
esters of amino alcohols such as mono, di, and tri-ethanol amines.
-
Inorganic phosphoric acid, phosphonic acid, and organic
phosphoric acid esters may be salts, pre~erably salts of alkali metal,
ammonia, amine and so forth.
Exemplary polyvalent metal salts with may be combined withthe polymers of Formula (I) above include those capable of dissociat-
ing polyvalent metal cations in water such as Zn~+, Ni++, e~c,which include zinc chloride, zinc sulfate, nickel sulfate, nickel
chloride and so Forth.
'~hen the copolymer (I) is added to the aqueous system in
combination with an additional component selected from the group
consisting o-F inorganic phosphoric acids, phosphonic acids, organic
phosphoric acids esters, or their water-soluble salts (all being re-
ferred to hereinafter as phosphoric compounds), and polyvalent metal
salts, a fixed quantity of said copolymer (I) may be added
separately and in the state of aqueous solution into the system.
The copolymers (I) may be added either continuously or inter-
mittently. Alternatively, the copolymers (I) may be blended witn
the above noted phosphoric compounds or polyvalent metal salts and
then added in the state oF aqueous solution into the water system
either continuously or intennittently. The phosphoric compounds or
polyvalent metal salts are utilized in the usual manner for corro-
sion and scale preventing purposes. For instance, the phosphoric
compounds or polyvalent metal salts may be added to a water sys~m
continuously or intermittently to maintain their necessary
concentrations.
Generally, the phosphoric compounds should be present in
the aqueous system in an amount of about 1-100 ppm (as P04) or the
polyvalent metal salts should be present in an amount of about I to
50 ppm (as metal cation).
As is conventional in the art, the phosphoric compounds or
polyvalent me~al salts may be added, as pretreabment dosages, to the
water system in an amount of about 20 to about 500 ppm, and thereafter
a small quantity of chemicals may be added, as maintenance dosages.
The copolymers (I) may be used in combination with conven-
tional corrosion inhibitors for iron, steel 9 copper, copper alloys
or other metals, conventional scale and contamination inhibitors,
metal ion seques~ering agents, and other conventional water treating
agents. Exemplary corrosion inhibitors comprise chromates, bichro-
mates, tungstate, molybdates, nitrites, borates, silicates, oxycar-
boxylic acids, amino acids, catechols, aliphatic amino surface active
agents, benzotriazole, and mercaptobenzothia~ole. Other scale and
contamination inhibitors include lignin deriva~ives, tannic acids,
starch, po1yacrylic soda, polyacrylic amide, etc. Metal ion seques-
tering agents include ethylene diamine, diethylene triamine and thelike and polyamino carboxylic acids including nitrilo triacetic
acid, ethylene diamine tetraacetic acid, and diethylene triamine
pentaacetic acid.
~L~B~
-12-
Examples
The invention will now be further described with reference
to a number of specific examples which are to be regarded solely as
illustrative, and not as restricting the scope of the inve~tion.
Preparation of Isopropenyl/Phosphonic Acid Monomer
To a 3 liter 3 neck flask equipped with a magnetic stirrer,
thermometer, and pressure compensated addition funnel, was added 300 9
(5.2 mole) of acetone. Phosphorus trichloride (730 9; ~.3 mole) was
added rapidly through the addition funnel. The addition ~as only
slightly exothermic. The mixture was stirred for 4 1/2 hours.
Acetic acid (1500 ml) was then added and a reflux condenser was
added to the flask. The mixture became cloudy and refluxed as a
copius quantity of hydrogen chloride was evolved. After the
refluxing had subsided, hydrogen chloride gas was bubbled through
the solution for 1/2 hour. The reaction mixture was then allowed
to stir at room temperature overnigh~. The flask was equipped for
distillation and volatiles were removed at atmospheric pressure
until a head temperature of 118C was reached. A water aspirator
was attached and the distillation continued until the pot tempera-
ture reached 175C. The remainder of the Yolatiles were removed
at ~ 1 mm and a pot temperature of 180-190C. The product was a
viscous golden-yellow liquid and weighed 571 9 (91%). After the
mixture was cooled sufficient water was added to give a 50% aqueous
solution. The l3CMR spec~rum of aqueous product showed three
doubiets at ~ = 140.4, 132.7 ppm (J = 172.1 Hz~; 129.9, 129.5 ppm
(J= 9.8 Hz); 19.4, 18.9 ppm (J = 13.4 Hz). The 31PMR spectrum
showed a single peak at ~ = -19.0 ppm. There was a trace of an
inorganic pnosphorus impurity.
-13-
Example 1
Preparation of_Isopropenyl Phosphonic Acid/
Hy_roxypropylacrylate Copolymer (1:1 molar ratlo)
To a 500 ml resin kettle equipped wi-th a mechanical stir-
rer, thermometer, pressure compensated addition funnel, and re-Flux
condenser, was added hydroxypropylacrylate (26.6 9; 0.2 mole). Iso-
propenyl phosphonic acid (25.4 g; 0.2 mole) was dissolved in 154.2 9
water and added rapidly to the kettle. -The reaction mixture was
then sparged with nitrogen for 1/2 hour. Ammonium persulfate (6 9)
- 10 was added and the nitrogen sparge continued for an additional 1/2
hour. The mixture was heated to reflux for 2 hours. An additional
6 9 of ammonium persulfate was added. The mixture was then refluxed
for an additional 2 hours. There was a definite increase in vis- -
cosity after the second addition of ammonium persulfate. The yellow
product had a pH of 1.00 and was tested without further purifica-
tion. A 31PMR spectrum showed broad polymer absorptions centered
at ~ = 32.9 and -34.7 ppm and a small amount of monomer at ~ =
-19.0 ppm. There was also a trace of inorganic phosphate.
~8~
-14-
Example 2
Isopropenyl Phosphonic Acid/
. . .
Hydroxypropylacrylate Copolymer _1.1 molar ratio)
The polymer was formed as in Example 1 except that the
aqueous solution of isopropenylphosphonic acid was neutralized to
pH 2.5 before addition to the reaction kettle. The amount of ammo-
nium persulfate was reduced to 2 x 2.5 9. The yellowish brown solu-
tion had a pH of 2.55. The 31PMR spectrum showed polymer absorp-
tions centered at S = -33.1, -31.0, -27.5 and -24.7 ppm. There was
no evidence of phosphorus monomer.
-15-
Exa_ple 3
Isopropenyl Phosphonic Acid/
_ _
Hydroxypropylacrylate Copolymer (1:1 molar ratio)
__.
The polymer was formed as described in Example 2 except
that the pH of the isopropenylphosphonic acid solution was adjusted
to 4.0 before polymerization. The yellow aqueous product had a
final pH of 3.67. The 31PMR spectrum showed polymer absorptions
centered at -28~9 and -22.9 ppm. There were also trace quantities
of inorganic phosphates.
Example_4
Isopropenyl Phosphonic Ac d/
Hydroxypropylacrylate-copolymer (3:1 molar ratio)
Using the same polymerization apparatus as described in
Example 1, 17.1 9 (0.13 mole) of hydroxypropylacrylate and 49.8 9
(0.41 mole3 of isopropenylphosphonic acid in 202.5 9 water
(neutralized to pH 2.5) was heated to reflux with 6 9 of ammonium
persulfate. After 2 hours of reflux an additional 6 9 of initiator
was added followed by 2 hours of reflux. The final pH of the brown
solution was 2.7. The 31PMR spectrum of the product had polymer
absorptions at -30 to -33 ppm and -2~ ppm.
Example 5
Isopropenyl Phosphonic Acid/
Hydroxypropylacrylate Copolymer (2:1 molar ratio)
Using the apparatus and methodology as described in Exam-
ple 1, isopropenyl phosphonic acid (61.6 9, 54%, 0.27 mole), hydroxy-
propylacrylate ~16.6 9, 0.13 mole) and water (121.8 9) were charged
in the reactor. Ammonium persulfate (6 9) was added. After 1-1/2
hours of reflux, 6 9 additional persulfate was added followed by an
equivalent reflux period. The final pH of the yellow solu~ion was
0.72.
Example 6
Isopropenylphosphonic Acid/
Hydroxypropylacrylate Copolymer (0.5:1 molar ratio)
Used the method of Example 5, isopropenyl phosphonic acid
(30.7 g, 54%, 0.14 mole), hydroxypropylacrylate (36.4 g, 0.28 mole)
and water (144.9 g) were charged in the reactor . The bulk of the
polymer crystallized during the first period of reflux and was found
to be insoluble in water. -
-19-
Example 7
Isopropenyl Phosphonic Acid/
Acrylamide Copo ymer (1:1 molar ratio)
. . _
Aqueous isopropenyl phosphonic acid (47 9; 54%9 0.2 mole)
5 and aqueous acrylamide (28 9, 50%, 0.2 mole) were mixed in a resin
kettle as previously described. Ammonium persulfate (6 9) and an
additional 84 9 oF water were then added. The solution was sparged
with nitrogen for 1/2 hour and heated to reflux. After 1-1/2 hours,
an additional 6 9 of initiator was added followed by an additional
- 10 1-1/2 hours of reflux. The aqueous product was yellow with a finalpH of 1.3. The 31PMR showed polymeric absorptions at ~ = -30.2
to -33.7 ppm and -25 to -29 ppm.
-20-
Example_8
Isopropenyl Phosphonic Acid/
. . . _
Hydroxyethylmethacrylate ~3:1 molar ratio)
Aqueous isopropenyl phosphonic acid (71 9, 54%, 0.3 mole)
S and hydroxyethylme~hacrylate (13 9, 0.1 mole) were mixed with 121.6
g water in a resin kettle. Ammonium persulfate (6 9) was added.
After 1-1/2 hours of reflux, an additional 6 9 of initiator was added
followed by another 1-1/2 hours of reflux. The final product was a
yellow solution with a pH of 0.68. The 31PMR showed polymeric
absoprtions centered at ~ = -29.5 and -24.3 ppm.
-21-
Example 9
Isopropenyl Phosphonic Acid/Hydroxypropylacrylate/
Acrylic Acid Terpolymer 4:4:1 (molar ratio)
Aqueous isopropenyl phosphonic acid (47 9, 54%, 0.2 mole),
hydroxypropylacrylate (26 9, 0.2 mole) and maleic anhydride (5 g,
0.05 mole, neutralized to pH 5 in 50 ml water) were mixed with 82.6
g waker in a resin kettle under nitrogen. Ammonium persulfate (6 g)
was added followed by 1-1/2 hours of reflux. An equivalent amount
of initiator was added and the reflux period repeated. The final
product was yellow with a pH of 0.99. The 31PMR showed polymer
absorptions centered at ~ = -34, -32.3 and -28.8 ppm.
Example 10
Isopropenyl Phosphonic Acid/Hydroxypropylacrylate/
_
Methyl Acrylate Terpolymer (15:5:3 molar ratio)
. . . ~
Aqueous isopropenyl phosphonic acid (71 9, 54%, 0.3 mole),
hydroxypropylacrylate (13 9, 0.1 mole) and methyl acrylate (5 9,
0.06 mole) were mixed with 121.6 9 water containing 6 9 of ammonium
pursulfate. After sparging with nitrogen for 1/2 hour, the mixture
was heated to reflux for 1-1/2 hours. An additional 6 9 of initia-
tor was added followed by an equivalent period of reflux. The final
product had a pH of 0.65. The 31PMR showed significant polymeric
absorptions at -32.4 and -24~3 ppm.
-23-
Example 11
Isopropenyl Phosphonic Acid/Hydroxyeropylacrylate/
Acrylic Ac~d Terpolymer ( 3.3:1 molar ratio)
In a manner described in Example 8, aqueous isopropenyl
phosphonic acid (47 9, 54%, 0.2 mole)~ hydroxypropylacrylate (26 9,
0.2 mole) and acrylic acid (5 9, 0.07 mole, neutralized to pH 5 in
50 ml wa~er) were mîxed wi~h 82.6 9 of water and polymerized. The
final product had a pH of 1.08.
-24-
Example 12
In ~rder to evaluate the efficacy of isopropenylphosphonic
acid/2-hydroxypropylacrylate copolymer (produced in accordance with
Example 1) as a corrosion inhibitor and deposit control agent for
cooling water systems, this copolymer was tested utili~ing a pro-
cedure commonly referred to as the "Recirculator Test." According
to this test, mild steel corrosion test coupons, and admiralty cor-
rosion test coupons are cleaned, weighed and disposed on a rotating
holder in a simulated cooling water bath which is contained within a
17 liter glass. The temperature of the system was maintained at
about 120F and the rotational speed of the coupon holder was ad-
justed so as to give a water velocity of about 1.3 feet per second
past the coupons. Certain of the coupons were pretreated with zinc
polyphosphate whereas the remaining coupons were not so pretreated.-
The system has a constant makeup of new water and chemicals andblowdown. A heat transfer tube is also present in the system allow-
ing a study of the effect of corrosion and scaling on a heat trans-
fer surface. One end of the heat transfer tube is pretreated in
similar fashion to coupon pretreatment.
Corrosion rate measurement was determined by weight loss
measurement. At the end of one day, one mild steel coupon, one
pretreated mild steel coupon, and one admiralty coupon were removed
from the bath and a second weight measurement taken for each. At
the termination of the test run, the remaining coupons were removed,
cleaned and weighed.
Corrosion rates for the coupons were computed by differen-
tial weight loss according to the following equation:
Corrosion Rate = Nth Day Weight LOSTS - lSt Day ~lght_Loss
wherein N = 6 or 7.
The simulated cooling water was manufactured to give the
following conditions:
~00 ppm Ca+2 as CaC03
300 ppm Mg+2 as CaC03
30 ppm total phosphates
18 ppm total inorganic phosphates
12 ppm orthophosphates
pH = 7.0
A system pretreatmen~ step at a 25 ppm level (actives) of
the copolymer was carried out over the first day of testing. After
one day of this system pretreabment, the copolymer concentration was
maintained at 10 ppm tactives) for the remainder of the test.
Results
A~erage corrosion rates for the mild steel and admiralty
coupons, respectively, were a highly acceptable 1.5 mpy and 0.3 mpy.
A blue black film of unknown composition formed on the mild steel
coupons and on the non-pretreated end of the heat transfer tube.
At the 25 ppm level of copolymer, the system water was
clear and an analytical test indicated no loss of orthophosphate
in the water. The heat transfer surface was free of scale.
-26-
At a 10 ppm level of copolymer, the precipitation of ortho-
phosphate was completely inhibited. This observation was supported
by both physical and chemical analyses. The system water filtered
easily through 0.2 um, and the chemical analyses for phosphate
showed no loss of orthophosphate. At this copolymer treatment
level, a black tightly adherent film formed on the heat transfer
surface. It is not believed that this film would significantly re-
duce heat transfer.
~3~
-27-
Example 14
Another method of evaluating deposit control activity of a
material consists of measuring its abilit~ to prevent bulk phase
precipitation of a salt at conditions for which the salt would
S usually precipitate. It is additionally important to recognize that
the material being evaluated is tested at l'substoichiometric" con-
centrations. That is, typical molar ratios of precipitating cation
to the material being evaluated are on the order of 20:1 and much
greater. Consequently, stoichiometric sequestration is not the
route through which bulk phase precipitation is prevented. The well
known phenomenon is also called "threshold" treatment and is widely
practiced in water treatment technology for the prevention of scale
(salt~ deposits from forming on various surfaces. In the results
that follo~l calcium phosphate, commonly found in industrial water
systems under various conditions, was selected as a precipitant.
The copolymers of the present invention have been evaluated for
their ability to prevent precipitation (i.e., inhibit crystalli-
7ation) of this salt. The results are expressed as "percent inhi-
bition", positive values indicate the stated percentage of the
precipitate was prevented from being formed. Except as where noted
to the contrary, the following conditions, solutions, and testing
procedure were utilized to perform the calcium phosphate and
inhibition tests, the results of which are reported herein in the
following table:
$
-2~-
CALÇIUM PHOSPHATE INHIBITION PROCEDURE
~ ~ . . .
Conditions Solutions
T = 70C 36.76 CaCl2 2H20/liter DIH20
pH 8.5 0.4482g NazHP04/liter DIH20
17 hour equilibration
Ca+2 = 250 ppm as CaC03
P04~3 = 6 ppm
Procedure
1) To about 1800 ml DIH20 in a 2 liter volumetric flask, add 20 ml
of CaCl2 2H~0 solution followed by 2 drops of conc. HCl.
2) Add 40 ml of Na2HP04 solution.
3) Bring volume to 2 liters with DI water.
4~ Place 100 ml aliquots of solution in 4 oz glass bottles.
5) Add treatment.
6) Adjust pH as desired.
7) Place in 70~C water ba~h and equilibrate for 17 hours.
8) Remove samples and filter while hot through 0.2 u filters.
9) Cool to room temperature and ~ake Absorbance measurements using
Leitz photometer (640 nm).
Preparation for Leitz
a. 5 mls filtrate
b. 10 mls Molybdate Reagent
c. 1 dipper Stannous Reagent
d. Swirl 1 minute, pour into Leitz cuvette;
wait 1 minute before reading.
10) Using current calibration curve (Absorbance vs ppm P04~3) find
ppm Po4-3 of each sample.
Calculation:
% Inhibition = pPpPmm PPo4-3 (sttoecakt)ed) pPpm Po4-3 (Cconntrol) X 100
-29 - -
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-30-
While certain features of this invention have been
described in detail with respect to various embodiments thereof~ it
w;ll, of course, be apparent that other modifications can be made
within the spirit and scope of this invention and it is not in-
tended to limit the invention to the exact details shown above ex-
cept insofar as they are defined in the appended claims.
