Note: Descriptions are shown in the official language in which they were submitted.
INTRODUCTION
The present invention relates to using acrylic acid
polymers which contain amidoalkylphosphonate groups for
preventing the formation of scale and corrosion on metal
surfaces in contac~ with corrosive and/or scale forming
industrial process waters.
BACKGROUND OF THE: IPJVENTION
The utilization of water which contains certain inorganic
impurities, and the production and processing of crude oil-
water mixtures containing such impurities, is plagued by the
precipitat,ion of these impurities with subsequent scale
formation. In the case of water which contains these
contaminants the harm~ul effects of scale formation are
generally confined to the reduction of the capacity or bore of
receptacles and conduits employed to store and convey the
contaminated water. In ~he case of conduits, the impedance of
flow is an obvious consequence. However, a number of equally
consequential problems are realized in specific utilizations of
contaminated water. For example, scale formed upon the
surfaces of storage vessels and conveying lines for process
water may break loose and these large masses of deposit are
entrained in and conveyed by the process water to damage and
clog equipment through which the water is passed, e.g., tubes,
valves, filters and screens. In addltion, these crystalline
deposits may appear in, and detract from, the final product
which is derived from the process, e.g., paper formed from an
aqueous suspension of pulp. Furthermore, when the contaminated
water i5 involved in a heat exchange process, as either the
"hot" or "cold" medium, scale will be formed upon the heat
exchange surfaces which are contacted by the water. Such scale
formation forms an insulating or thenmal opacifying barrier
which impairs heat trans~er e~iciency as well as impeding flow
through the system.
While calcium sulfate and calcium carbonate are primary
contributors to scale formation, other salts of alkaline-earth
metals and the aluminum silicates are also offenders, e.g.,
magnesium carbonate, barium sulfate, the aluminum silicates
provided by silts of the ben~onitic, illitic, kaolinitic, etc.,
types.
Many other industrial waters, while not being scale
forming, tend to be corrosive. Such watars, when in contact
with a variety of metal surfaces such as ferrous metals,
aluminum, copper and its alloys, tend to corrode one or more of
such me~als, or alloys. A variety of compounds have been
suggested to alleviate these problems. Such materials are lew
molecular weight polyacrylic acid polymers. Corrosive waters
o~ thi~ type are usually acidic in pH and are commonly found in
closed recirculating systems.
Numerous compounds have been added to these industrial
waters in an at~empt to prevent or reduce scale and corrosion.
One such class of materials are the well known
organophosphonates which are illustrated by the compounds
hydroxyethylidene diphosphonic acid (HEDP) and phosphonobutane
tr.icaxboxylic acid (PBTC). Another group of active scale and
corrosion inhibitors are the monosodium phosphinicobis
(succinic acids) which are described in U.S. 4,08~,678.
Prior Art
U.S. 4,678,~40 teaches polymers of ~he type described in
this invention and broadly suggests that they may be useful as
dispersants and as scale inhibitors. In U.S. 4,675,359, it is
suggested that polymers of the type used in this inventicn hav~
a variety of uses. It is broadly suggested that they would be
usaful as water ~reating agen~s. U.S. 4,526,728 shows that co-
polymers of acrylic acid or acrylamide with 2-(meth)acrylamide-
2-methylpropanephosphonic acids are useful as scale
inhibitors. This proper~y of these polymers is illustrated in
Examples 4 and 6 of this patent.
Summary_of the Invention
The present invention relates to preventing scale and
corrosion of metal surfaces in contac~ with scale ~orming or
corrosive industrial process waters by using as the inhibitor a
small, y~t effective, amount of an acrylamide pol~mer which
contains from 1 to 30 mole percent of an
amido(Cl-C6)alkylphosphonate groups. These polymers also
contain amounts of acrylic acid which make up the halance of
the composition thereof.
THE INVENTION
The invention comprises a method of inhibiting scale and
corrosion of metal surfaces in con~act with scale forming
and/or corrosive industrial process waters which comprises
treating such waters with at least one part per million of an
acrylic acid polymer which contains from 0-95 mole percent of
acrylamide groups and from 1-30 mole percent of
amido(Cl-C6)alkylphosphonate groups from the group consisting
of:
a. amidom thylphosphonate groups,
b. alpha-hydroxy-beta-amidoethylphosphonate groups
c. alpha-hydroxy-beta-amidoisopropylphosphonate groups,
and;
d. amidopropylphosphonate groups
with said polymer having a molecular weight range between 1-
100,000.
In a preferred em~odlment of the invention the acrylamide
poly~mer contains from 5-50 mole percent of acrylamide groups.
Th~ molecular weigh~ o~ the po:Lymers may be between 1,000-
100,000. P-eferably i~ is within the range of 1,000-20,000
and most preferably within the range of 1,000-10,000.
The amount of polymers required to reduce scale and
corrosion will vary depending upon the severity of the system
in which they are employed, and whether the condition prevalent
i5 scale and/or corrosion. Dosage~ range from between as
little as one part per million up to as much as 400 ppm.
Typical dosages, however, are within the range of 3-20 ppm.
Routine experiment~tion can determine the exact amount of
polymer that is necessary to achieve optimum results. These
dosages relate to the dosages of the active polymer which are
oftentimes supplied commercially in ~he form of aqueous
solutions or as water-in-oil emuls1on.
PREPARATION OF THE POLYMER5
The polymers used in the practice of the invention, are
described in prior publications. Their method of preparation
is described in U.S. 4,678,840 and U.S. 4,675,359. The
disclosures of these patents are incorporated herein by
reference.
In U.S. 4,678,840 there is shown a transamidation reaction
whereby the amide groups of an acrylamide polymer are
substituted by reacting them with an aminoalkylpho~phonate.
Another method of producing the pol~mers resides in the
reaction of an amino(Cl-C6 alkyl)phosphonate directly with an
acrylic acid polymer under conditions whereby the amino radical
is amidated with the carboxylic acid groups of the acrylic acid
polymer. ~his technique which has been used ~o amidate
aminoalkylsulfonic acld is the subject of U.S. 4,604,431, the
disclosure o which is incorporated harein by reference.
Yet another method of producing the pol~mers of the
invention is to oxidi~e phosphinate polymers, e.g., polymers
corresponding exactly to those used in the invention, to the
corresponding phosphinate polymers. These polymers are readily
oxidized using peroxides and other well known oxidizing agents
used to oxidize the phosphinate groups to the phosphonate
groups.
It is to be understood that in the practice of the
invention the term "phosphonate groups" or the term
"phosphona~e" is intended to include, both in the specification
and in the claims, not only the water soluble salts of the
phosphonic acid groups, e.g. the alkali metal such as sodium or
potassium, but also the ammonium or amine salts. Also included
is the free acid form of the phosphonic acid.
EVALUATION OF T~E INVENTION
A series of laboratory screening tests were undertaken to
evaluate a number of phosphonate containing polymers.
Table 1 (Backbone Polymers) lists a number of acrylic
acid, acrylamide and acrylamide-acrylic acid co-polymers that
were modified with aminoalkylphosphonates. It should be noted
that certain of these backbone polymers contain minor amounts
of diluent monomers such as acrylonitrile (AN), methacrylic
acid (~AA) and vinyl acetate (vAc); when used such diluent
monomers may be present in amounts ranging between 1-15 mole
percent. The amount used should not be such so as to diminish
water solubility of ~he polymer. In Table 1 AA is acrylic acid
and AAm is acrylamide.
Tables 2-5 shows several of the backbone polymers modified
with various phosphonate groups evaluated as scale and
corrosion inhibitors.
2 Q ~ ~ r~ ~ ~
TABLE 1
Backbone Polymers
NO COMPOSITION ~W ~ POLYMER
1 100~ AA 4500 32.5
2 100% AA 7100 35
3 100~ A~ 5000 35
4 50/50 AA-AAm 6000 35
50/50 AA-A~m 4750 35
6 50/50 AA-AAm 6450 35
7 50/50 AA-AAm 15700 32.5
50/30/20 AA/AAm/MAA 11200 35
9 4S/50/5 AA/~Am/AN 6500 35
45/50/5 AA/AAm/VAc 7050 35
11 100% A~ 5400 3~
12 50/50 AA/AAm 2500 35
2 ~ ~
T~3LE 2
POLYMERS MODIFIED WITH AMINOMETHANE PHOSPHONIC ACID
SAMPLE BACKBONEPRODUCT COMPOSITION
NUMBER POLYMER(PO3/CO2H)a %POLYMER
1 4/96 31.0
094 1 2.5/97.5 31.9
23 2 2.2/97.8 3~.2
34 2 2.1/97.9 32.4
107 3 2/98 34.1
7A 4 12/66 29.5
095 5 8/75 34.~3
24 6 3.1/61 34.6
6 5.3/47 33.8
6A 7 18/69 29.1
076 4 4.3/69 34.7
078 4 11.1/56 34.9
8 ~.3/53 34.3
37 8 5.5/53 33.2
27 9 3.7/58 34.8
42 9 4.9/56 33.6
26 ~ 10 3.8/63 34.9
04~ 10 4.7/60 33.6
a. mole percen~ ba~ed on~ total mer uni~5~ as de~ennined by
colloid titration
2 ~
TA~LE 2 (CONTINUED)
POLYMERS MODIFIED WITH ALPHA-HYDROXY-BETA-AMINOETHYLPHOSPHINIC
ACID AND THEN OXIDIZED
~ ( C -- C )--
O-C-NH-CH2-C(OH)-P(O) (OH)(H or OH)
H
S~MPLE 8ACK~ONE PHOSPHINATE CHARGE
NUMBER POLYMER (MOLE ~) ~POLYMER
027 11 10 33 . 7
031-A (Oxidized 027 ) 32 . 3
031-13 11 25 33 . O
033 (Oxldized 031~ 30.4
0~8 12 10 34 . 1
032 A (Oxidized 02~) 32.7
032 B 12 25 33.1
034 ( Oxidized 032 ) 30 . 5
POL~MERS MODIFIED WITH ALPHA-HYDROXY-BETA-
-
AMINOISOPROPYLPXOSPHINIC ACID AND THEN OXIDIZED
__ _
'- (C -- C)--
O=C-NH-CH2-C(OH)-P(O) (OH)(H or OH)
CH3
% ~
SAMPLEBACKBONE PHOSP:HINATE CHARGE %
NIJMBERPOLYMhR ( MOLE ~ )POLYMER
039 11 10 33 . 9
035 (Oxidized 039) 32.6
045 11 25 33 . 4
036 (Oxidized 045 ) 30 . 8
040 12 10 34 . 3
037 (Oxidized 040) 32 . 9
046 12 25 33 . 5
038 (Oxidized 046) 30.9
POLYMEE~ MODI~IED WIT~ ALLYL AMINE , THEN NaH2 PO2, AI13N ,
AND THEN OXIDIZED
--( C -- C )--
O-C-NH-CH2-CH2-CH2-P(O) (OH) (H or OH)
SAMP~EBACKBONE AMINE CH~RGE %
NIJ~IBERPOLYMER _ (MOLE % ~ _POLYMER
014 11 10 ~1 . 9
027 (Oxidized 014) 21. 3
025 11 25 21 . 7
029 (Oxidized 025 ) 20 . 3
015 12 10 21 . 9
028 ( Oxidized 015 ) 21. 3
026 12 25 21 . 6
030 ( Oxidized 026 ) 20 . 2
11
~ $ `~ 3 ~
TABLE 3
Benchtop Screening Test for Calcium Carbonate Scale Inhibitlon
of Several Aminoalkylphosphonic Acid Modified Polymers
Water Chemistry / Conditions:
360 ppm Ca/200~ppm ~g/500 ppm ~C03 (as CaCO3)
Temperature: 60C, Stir rate: 300 rpm
Titrant: 0.10 Normal NaOH
Dosage: 5,10 and 15 ppm actives
Standard Deviation of Saturation Ratio: +/- 6.6
Saturation ratio of blank: 3.0
Poly_~rs modified with aminomethanephosphonic acid
Saturation Ratio
Inhibitor 5 ppm 10 p~ 15
-
l(b.b) 74.8 91.1 113.7-125.9131.9-140.5
97.1 113.7143.2
94 69.9 118.6136.5
2(b.b.) --- --- 142.1
23 --- --- 144.3
34 --- --- 145.9
3(b.b.) --- --- ~~~
107 97.1 116.8131.9
4~b.b.) 31.9 48.9 48.9
7A 97.1 119.9137.7
76 53.9 121.7112.3
78 66.9 112.3136.9
5(b.b.) 21.7 28.630.9
70.0 116.8131.9
6(b.b~ --- --- 35.1
24 --- --- 131.9
--- 128.9
7(b.b.) 42.1 47.548.9
6A 65.2 97.1110.6
8(b.b.) --- --- 127.4
--- --- 109.1
37 ~ -- 107.9
Inhibitor ~ _p~ 15 ppm
-
9(b.b) --- -- 30 9
27 ~~ 137.7
4~ 133.1
10(b.b) --- --- 35.1
26 --- --- 131.9
43 --- --- 143.2
Backbone Inhibitor 5 ppm ~_ee~15 ppm
Oxidized Samples of alpha-hydroxy-beta-aminoe~hylphosphinic
aci modified ~ymers:
11 031A 76. a 124.8 142.6
11 033 7~.~ 112.3 136.3
12 032A 24.6 71.8 93.9
12 034 4~.9 71.8 11~.6
Oxidized Samples of alpha~y~roxY-beta-aminoisoe~py~lphosphinic
aci mo i ied polYmers:
11 035 65.2 122.9 137.7
11 036 57.9 106.0 124.~
12 037 34.0 82.3 g9.5
12 038 36.8 71.8 106.0
Oxidized Samples of ~oly~ers modified with allyl amine, then
NaH2PO2, AIBN: *
11 027 62.3 121.8 130.9
11 029 34.0 46.4 30.9
12 028 39.1 39.1 30.g
12 030 16.1 30.9 22.
~/C/~/ (bb: polymer backbone)yQ
* - 2,2' azobis(2-met~apropanenitrile) catalyst
13
? ~
TABLE 4
~enchtop Screening Test for Calcium Carbonate Scale Inhibition
of Several ~minoalkylphosphonic Acid ~odified Poly~ers
Stir and S~ttle Test
Water_Chemistry / Conditions:
360 ppm Ca / 200 ppm Mg / 500 ~C03 (a5 CaC03 )
Temperature: 60OC, Stir Rate: 250 rpm
Titrant: 0.10 ~ormal NaOH, pH: 9.0 for two hours
Blank: 0.6 % inhibition, 1.3 ~ dispersancy
Inhibitor 5 ppm ~ 15 ppm
Aminomethane~hosphonic acid modified polymers
% inhibition: 55.3% 65.9% 99.5%
% dispersancy: 54.5% 77.3% 99.3%
094 % inhibition: 46.4% 47.1~ 68.4%
% dispersancy: 50.1% 53.9% 82.5%
09S ~ inhibition: 44.8% 62.3% 100%
% dispersancy: 44.8% 76.7% 93.3~
076 % inhibition: 49.5% 66.8% 74.0%
~ dispersancy: 47.5% 79.4~ 80.0%
107 % inhibition: 45.4% 65.3% 74.4%
% dispersancy: 45.8% 69.6% 85.7%
078 % inhibition: 49.6% 72.4% 79.7%
% dispersancy: 49.4% 71.4~ 88.3
043 % inhibition: 44.8% 57.5% 75.0%
% dispersancy: 44.8% 59.4% 81.3~
Ox dized Sample of alpha-hydroxy-beta-aminoethylphosphinic acid
mo i ie po ymer
033 % inhibition: 42.4% 46.3% 52.3%
% dispersancy: 35.6~ 46.7% 57.7%
$ :~
TABLE 5
Electrochemical Screening Test for Mild Steel Corrosion
Inhibition of Several Aminoalkylphosphonic Acid Modified
PolYmers.
.
Water Chemistry / Conditions:
360 ppm Ca / 200 ppm Mg / 440 HC03 (as CaC03)
Temperature: 120 F, pH: uncontrolled, air agitation,
Pre-polished Mild Steel specimen, 30 minute delay time, 500 rpm
Standard deviation of corrosion rate: t-/- 0.345 mpy
Inhibitor_Combination:
(A). 20 ppm inhibitor, 0 ppm PBTCl, 15 ppm of a sulfonated
solution polymer
(B). 10 ppm inhibitor, 10 ppm PBTC, 15 ppm of a sulfonated
solution polymer
(C). 10 ppm inhibitor, 10 ppm PBTC, 15 ppm substituted
acrylamide, acrylate polymer
Corrosion Rate (mpy)
Inhibitor (A) (B) (C)
Blank 8.63 .975 1.92
Aminomethanephosphonic acid modified polymers:
094 .650 2.09 2.07
095 1.03 1.57 1.05
023 1.44 .81~ xxx
034 1.85 1.28 xxx
024 1.16 1.45 xx~
035 4.29 .997 xxx
02~ 1.52 .828 xxx
037 1.18 5.75 x~x
026 5.16 2.94 xxx
~43 .978 4.22 1.38
Phosphonobutane tricarboxylic acid
T~BLE 5 CONTINUED:
027 2.11 1.24 xxx
042 1.47 4.46 xxx
Corrosion Rate (mpy)
Inhi (A) (B) (C)
Oxidized Samples of alpha-hydroxy-beta-aminoethyl~hosphinic
acid modified polymers:
031 xxx .715 xxx
032 xx~ .453 xxx
Oxidized Samples of alpha-h~droxy-beta-aminoisopropylphosphinic
acid modifie polymers:
035 xxx 2.05 xxx
037 xxx .67g xxx
Oxidized Sam~le of ~olym~r modified with allyl amine, then
NaH2PO2 AIBN*:
_ !
027 xx~ 1.59 xxx
2 ~
* AI~N: 2,2' azobis(2-methylpropananitrile) catalyst
2 ~
The test methods used to generate the above data are set forth
below.
Saturation Ratio Test
A test solution was prepared by adding calcium, magnesium,
inhibitor and bicarbonate to deionized water. Initial
concentrations of the salts should be: 360 ppm Ca+2, 200 ppm
Mg+2, 500 ppm HC03-. ~as CaCO3) and 5, 10, or 15 ppm of
inhibitor as actives/solids. The temperature was maintained at
140F (60OC), the solution was stirred at all times, and the pH
was continuously monitored. The solution was titrated with
dilute NaOH at a constant rate. With the addition of NaOH, the
p~ of the test solution slowly increased, then decreased
slightly, and increased again. The maximum pH prior to the
slight decrease at supersaturation was the breaXpoint pH. A
mineral solubiLity computer program was then used to calculate
the calcium carbonate supersaturatic)n ratio based on test
conditions at the breakpoint pH. T~lis supersaturation ratio is
related to the calcium carbonate inhibi~ion performance. The
test procedure was repeated for difi-`erent inhibitor solutions
and dosages. All precipitated calcium carbona~e must be
removed from the test apparatus with dilute HCl prior to the
next test run.
Benchtop Screening_Test or Calcium Carbonate Inhibition
Calcium, magnesium, inhibitor and bicarbonate were added
to deionized water to prepare a test solution with 360 ppm
la
Ca+2, 200 ppm Mg+2, 500 ppm HC03- ~as CaC03) and 5, 10 or lS
ppm inhibitor as actives/solids. An initial sample of the test
water was collected for calcium analysis by atomic absorption.
The test temperature was malntained at 140F (600C). Using
dilute NaOH, the p~ of the solution was slowly increased to
9.0, and maintained during ~he two hour dura~ion of the test.
At the conclusion of the test, a small sample of the solution
was filtered (0.45 um) and the calcium concentration was
/ determin~ by atomic absorption. The remainder of the
6l~/~J unfiltered sample was allowed to settle, undisturbed for 24
hours, at room temperature. Water was th~n collected from the
top of the flask after 24 hours and analyzed for calcium. The
% inhibition and % dispersancy are calculated in the following
manner:
% inhibition = ppm Ca+ 2 filtered
X 100
ppm Ca~ 2 initial
dispe~sancy = ppm Ca+2 unfiltered, settled
X 100
ppm Ca+ 2 initial
Electrochemical Test
Both the Ta~el plo~s and linear polarization resistance
te~ts ware conducted in the same water chemistry and
conditions. The test solution ~or the electrochemical
corrosion cell was prepared by adding calcium, magnesium,
2 ~ n3 ~
various inhibitors and bicarbonate to deionized water to obtain
360 ppm Ca+2, Z00 ppm Mg+2, 440 ppm HC03- (as CaC03).
Temperature was maintained at 120F and the solution was
aerated throughout the test period. pH wa~ uncontrolled. A
standard three elec~rode cell was assembled for the
polarization studies. Pre-polished mild steel specimens were
used as the rotating working electrode, at a speed of 500 rpm.
All potential measurements were made against a saturated
calomel reference electrode. Two graphite rods were used as
the counter electrode. Polarization resistance measurements
were conducted within +~- 20 mV of the corrosion potential at a
scan rate of 0.1 mV/sec. Tafel plots were performed by
polarizins the mild steel specimen at 250 mV cathodically and
anodically from the corrosion potential.
